{ÉÉ´É®ú ]ÅõÉƺɡòÉǨɮúºÉ B´ÉÆ Ê®úBC]õºÉÇ POWER TRANSFORMERS & REACTORS +xÉÖnäù¶É {ÉÖκiÉEòÉ INSTRUCTION MANUAL ºlÉÉ{ÉxÉ, Eò¨ÉÒ¶ÉËxÉMÉ {ÉÊ®úSÉɱÉxÉ B´ÉÆ +xÉÖ®úIÉhÉ Eäò ʱɪÉä +xÉÖnäù¶É (JÉÆb÷ - 2) INSTRUCTIONS FOR INSTALLATION, COMMISSIONING, OPERATION AND MAINTENANCE (VOLUME - II) ¦ÉÉ®úiÉ ½äþ´ÉÒ <±ÉäÎC]ÅõEò±ºÉ ʱÉʨÉ]äõb÷, ¦ÉÉä{ÉÉ±É BHART HEAVY ELECTRICALS LIMITED, BHOPAL {ÉÉ´É®ú ]ÅõÉƺɡòɨÉÇ®úºÉÇ B´ÉÆ Ê®úBC]õºÉÇ Eäò ºlÉÉ{ÉxÉ, Eò¨ÉÒ¶ÉËxÉMÉ {ÉÊ®úSÉɱÉxÉ B´ÉÆ +xÉÖ®úIÉhÉ Eäò ʱɪÉä +xÉÖnäù¶É INSTRUCTIONS FOR INSTALLATION, COMMISSIONING, OPERATION AND MAINTENANCE OF POWER TRANSFORMERS & REACTORS ¦ÉÉ®úiÉ ½äþ´ÉÒ <±ÉäÎC]ÅõEò±ºÉ ʱÉʨÉ]äõb÷, ¦ÉÉä{ÉÉ±É BHART HEAVY ELECTRICALS LIMITED, BHOPAL Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ºlÉÉ{ÉxÉ, Eò¨ÉÒ¶ÉËxÉMÉ, {ÉÊ®úSÉɱÉxÉ B´ÉÆ +xÉÖ®úIÉhÉ Eäò +xÉÖnäù¶É JÉÆb÷ - II (EÖò±É JÉÆb÷ - 2) INSTALLATION, COMMISSIONING, OPERATION AND MAINTENANCE INSTRUCTIONS VOL-II of II Prepared By Samvet Lahari, Bhopal. Phone- 5277412 PREFACE BHEL Transformers and Reactors are designed, manufactured and tested with care. With proper attention during installation and use, the user should receive from it the maximum expected service. Before installing the transformers/ reactor read these instructions carefully. These instructions have been prepared to provide information on assembly, installation, commissioning and regular maintenance of the transformers/reactors and shall form part of Instruction Manual. These instructions do not intend to cover operation and maintenance of the transformer under abnormal conditions. Should further information be needed or any problem arises which is not covered by these instructions, please ask BHEL for further information. In operating the Transformer/Reactor, Care should be taken that loading limits as specified are strictly followed. For instructions regarding, general information on accessories such as OLTC, WTI, OTI, Buchholz relay, fan, pump, etc. Vol. I may please be referred. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 CONTENTS Page No. SECTION SECTION SECTION SECTION 1 GENERAL INFORMATION 1.1 INTRODUCTION 11 1.2 TRANSPORT OF TRANSFORMER / REACTOR 13 2 INSTALLATION 2.1 RECEPTION AND ASSEMBLING OF TRANSFORMERS / REACTORS DESPATCHED PARTLY DISMANTLED AND FILLED WITH NITROGEN 21 2.2 STORING OF TRANSFORMER / REACTOR DESPATCHED FILLED WITH NITROGEN 33 2.3 ASSEMBLING OF EXTERNAL PIPES 35 2.4 INSULATING OIL, QUALITY AND TREATMENT 37 2.5 OIL FILLING UNDER VACUUM 41 2.6 OIL FILLING INSTRUCTIONS FOR CONSERVATORS WITH AIR CELL 47 2.7 UNTANKING OF ACTIVE PART 53 2.8 MOUNTING OF GASKETS 55 2.9 WELDED COVER (IF APPLICABLE) 57 2.10 EARTHING OF ACTIVE PART AND CORE INSULATION TEST 59 2.11 TOUCH-UP PAINTING 69 3 COMMISSIONING 3.1 TESTING AFTER ASSEMBLY OF THE TRANSFORMER / REACTOR AT SITE 77 3.2 COMMISSIONING CHECKS - TRANSFORMER 79 3.3 COMMISSIONING CHECKS - REACTOR 93 4 MAINTENANCE AND OPERATION 4.1 SUPERVISION OF TRANSFORMER / REACTOR 101 4.2 SUPERVISION AND CONTROL OF OIL 109 4.3 TROUBLE SHOUTING 109 4.4 PARALLEL OPERATION 119 4.5 DO'S AND DON'TS 137 4.6 DISPOSAL 145 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ¦ÉÉMÉ-1 ºÉɨÉÉxªÉ VÉÉxÉEòÉ®úÒ SECTION-1 GENERAL INFORMATION Prepared By Samvet Lahari, Bhopal. Phone- 5277412 SECTION 1 GENERAL INFORMATION 1.1 INTRODUCTION 1.1.1 POWER TRANSFORMERS Unlike shunt reactor and Neutral Grounding Reactors where standard specification is generally followed by utilities, requirements of power transformers vary depending upon the system design. Hence a tailor made product becomes the answer. Depending upon the requirements two winding/ three winding/ auto connection/ split winding arrangement with ON LOAD or OFF CIRCUIT tap changer, five limbs/ three limbs core construction, welded or bolted tank construction are adopted. Variation in capacity, impedance and transport profile result in different sizes of transformer. Refer VoI I for specific requirements of the equipment. 1.1.2 SHUNT REACTORS Shunt Reactors are used in high voltage systems to compensate capacitive generation from long lightly loaded overhead lines or extended cable systems and also for control of dynamic over voltages. Gapped core construction is preferred for high system voltages over coreless construction due to the high energy density that can be achieved in gapped core construction. The core sections between consecutive air gaps are moulded in epoxy resin to prevent movement between individual laminations. The spacers forming the air gaps are blocks of ceramics with a high modules of elasticity and the whole stacking of core modules is cemented together during the assembly to form a solid column without possibility of rocking , or rubbing between individual parts. The core segments are of radial laminated configuration. The radial laminations prevent fringing flux from entering flat surfaces of core steel which would result in eddy current overheating and hot spots. Five limbed core construction is adopted to achieve high zero sequence impedance. In addition to the three gapped core limbs with windings, there are two continuous outer return limbs. The two unwound side limbs help in achieving zero sequence impedance approximately equal to the positive sequence impedance. Other construction type can be a three limbed construction. For single phase reactors e.g. 800 KV class middle leg wound with two return legs type of construction is adopted. Interleaved disc winding has been used for rated voltages 220 KV and above. This type of winding configuration provides better impulse voltage distribution. For lower voltage classes a continuous disc winding or a multi layer helical winding are used. The tank is rectangular in construction with flat cover welded to the tank rim at top. The associated cooling control equipment is housed in a tank mounted weather proof marshalling box. The reactors are equipped with all standard measuring and controlling fittings and accessories as described in Volume I. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Reactors have been designed for resting on concrete foundation as shown in the foundation plan drawing. Rollers have been provided only for movement of the reactor at site. 1.1.3 NEUTRAL GROUNDING REACTOR When single pole reclosing is used on lines, the Neutral Grounding Reactor is used. The Neutral Grounding Reactors are connected between neutral point of 400 kV/800 KV reactors and earth, where the neutral of shunt Reactor is suitable for 145 kV class insulation. The reactors are oil immersed type ONAN cooled (oil immersed with natural air cooling) with continuous rating of 10/15 Amps and a 10 sec. rating as indicated in the Rating Data sheet. As continuous losses of the reactors are negligible, reactor tank surface is adequate for dissipation of these losses. Hence radiators are not provided. Considering linear impedance characteristic requirement upto rated short time current a core less design with magnetic shielding of CRGO sheet has been made. The magnetic circuit, therefore consists of rectangular frame of CRGO steel lamination packets of adequate area. Area of magnetic circuit is selected such that saturation does not take place under short time current. A rigid clamping structure is provided for clamping of magnetic frame and a very low flux density is used to minimize the vibration and achieve linear impedance characteristic. The graded disc type concentric winding suitable for a rated voltage of 145 kV and basic insulation level of 550 kVp has been provided without core inside. Winding is held in position by way of special insulation structure inside winding and finally kept under pressure between top and bottom yokes of magnetic frame. Return path of flux is provided by way of two return limbs. The line terminal is taken out through the tank cover via 145 kV, 800 Amps OIP condenser bushing provided with suitable terminal connector. The neutral lead is taken out through the tank cover via a 36kV, 630 Amps porcelain bushing. The tank is of welded mild steel plate construction shot blasted on the inside and outside to remove scales before painting. The tank is painted on the inside with yellow paint and its outside surface is painted with two coats of primer paint and finishing coat, of light grey paint to shade 631 of IS:5. This is a standard painting scheme followed for all equipment . The fittings include a conservator with a magnetic oil gauge, pressure relief device, drain and filter valves, sampling valves, thermometer pockets, Buchholz relay, temperature indicator for oil and silicagel breather . These reactors are designed for mounting directly on plinth. 1.2 TRANSPORT OF TRANSFORMER/REACTOR Power Transformers and Reactors hereinafter referred as "Transformers," depending upon the restriction imposed by transport weight and/or other considerations, have to be transported either filled with oil or nitrogen as per the description given below. The transformer is loaded on wagon as per loading gauge drawing prepared in each case. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 1.2.1 WITH OIL The Transformer is filled with oil such that about 10% of the tank volume is left clear for expansion to limit the excess internal air pressure to 0.35 kg/cm2. Fittings dismantled before transport are packed in packing cases in line with shipping list. All openings resulting from removal of fittings for shipment are sealed with suitable gasketted blanking plates during transport. The balance oil quantity required for the complete filling of the reactor is supplied separately. A transformer despatched according to this method can be stored at site or elsewhere for one year provided, that all insulating materials are covered with oil and silicagel breather is mounted and quality of oil is maintained as per IS: 1866. Measures to be taken on reception at site are given clause 2.1 1.2.2 WITH NITROGEN Large oil filled transformers/reactors are not normally oil filled during shipping due to weight limitations. To protect the active parts against moisture the transformer tank is filled with dry Nitrogen at a positive pressure of 0.175 kg/cm2 (2.5 psi) at BHEL works before despatch. The internal pressure at the time of shipment is painted on the tank. All openings resulting from the removal of fittings for shipment are sealed with suitable gasketted blanking plates during transport. A Transformer despatched according to this method should normally be stored upto 3 months after arrival at site or elsewhere. For control of gas pressure and maintaining the pressure during transport and possible storage before assembling, the transformer is equipped with an automatic device. This device is called two stage N2 regulator and is kept in a steel box and mounted on the frame provided on tank side for keeping two back up Nitrogen cylinders. Nitrogen regulator is connected to two cylinders by copper tubes and to tank by a rubber hose as shown in the Fig. 1.1. N2 regulator reduces cylinder high pressure of 120 to 140 kg/cm2 to required low pressure of 0.175 kg/cm2 in two stages. One gauge provided on the first stage indicates the cylinder pressure, whereas other gauge provided on second stage indicates the tank pressure. Regulator is fixed at factory. When tank pressure falls below 0.15 kg/cm2, due to leakage/fall of ambient temperature, regulator automatically feeds the gas from cylinders, to build up required pressure in the tank. The gas consumption during transport and possible storage is difficult to estimate as it depends on ambient temperature variation, possible leakages as well as on the duration of transport and storage. However, two back up cylinders are provided to meet the gas requirement. Normally one cylinder is kept open and the other shut. When the pressure of first cylinder falls to 10 kg/cm2 this should be considered as empty and immediately its valve should be closed and the valve of second cylinder should be opened. When cylinder is required to be removed for refilling, disconnect copper tubing from cylinder valve. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Use only dry Nitrogen gas to IS:1747 with 50 ppm moisture and 1% oxygen by volume. If the storage time exceeds 3 months, the transformer is filled with oil according to directions given in clause 2.5. If for some reason oil filling is not possible, then nitrogen must be continuously maintained at a positive pressure. Measures to be taken on receipt at site are given in clause 2.1. 1.2.3 INSTRUCTIONS FOR FILLING DRY PURE NITROGEN GAS WITH BACK UP CYLINDERS (AT WORKS) Lower the oil level to the minimum necessary to dismantle the items (such as bushing and turrets) which must be removed for shipping. Pull 500 mm mercury vacuum after blanking off all openings. Break the vacuum by admitting dry nitrogen through a convenient valve at the top of the tank and drain the oil completely. Continue to supply nitrogen until it maintains a steady pressure of 0.17 ± 0.02 kg/cm2 above the atmosphere. Pressure of nitrogen gas shall be maintained at 0.17 ± 0.02 kg/cm2 at same reference temperature. Pressure would be monitored by taking three readings within 24 hours to ensure that there is no leakage of gas. Shut off the gas supply valve and fit dry nitrogen back up cylinders through nitrogen regulator valve. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ¦ÉÉMÉ-2 ºlÉÉ{ÉxÉ SECTION-2 INSTALLATION Prepared By Samvet Lahari, Bhopal. Phone- 5277412 SECTION 2 2. INSTALLATION 2.1 RECEPTION AND ASSEMBLING OF TRANSFORMER/REACTOR DESPATCHED PARTLY DISMANTLED AND FILLED WITH NITROGEN. To ensure that a Transformer will function satisfactorily it is important that handling, lifting, storing and assembling are carried out with great care and cleanliness by experienced personnel who know the various working operations very well. This section gives instructions how handling, lifting, storing and assembling should be carried out. For large Transformers it is recommended that the work is done by BHEL or is under supervision by experts from BHEL. 2.1.1 INSPECTION In connection with receiving and unloading at site, and at the final storing place before assembling, the transformers shall be inspected carefully. External visible damages as dents, paint damages etc. may imply that the transformer has been subjected to careless handling during transport and/or re-loadings, and a careful investigation is therefore justified. After the arrival of the material at receiving points, the customer should, in case of possible damage/loss of any component, make the necessary claims with the contractors representatives under intimation to supplier so that such claims can be registered with the transport agents. Before unloading, the condition of packing and of the visible parts should be checked and possible traces of leaks verified (condenser bushings). If necessary, appropriate statements and claims should be made. Drums containing oil which have been despatched separately should be examined carefully for leaks or any sign of tampering. All drums are despatched filled up to their capacity and any shortage should be reported. In order to protect the active part against moisture, the transformer tank is filled with nitrogen during transport at an over pressure of 0.17 kg/ sq.cm (2.5 psi) approximately at room temperature. Check immediately the gas pressure at the arrival. A positive pressure indicates that the tank and the transformer components respectively are tight, and that the active part including the insulation materials is dry. If there is no positive gas-pressure, transformer should be immediately filled with dry Nitrogen gas at a pressure of 0.17 kg/cm2 (2.5 psi) without loss of time as per instructions given para 1.2.3 Otherwise, it should be checked if the core isolation is satisfactory and that accessories packed separately have not been damaged during the transport. Instructions for checking of the core isolation are given in clause 2.10 2.1.2 UNLOADING Typical unloading arrangement of the transformer is shown in fig 2.1. Whenever rollers/trolleys are supplied with transformer, movement of transformer at site is carried out by mounting these rollers/trolleys. For mounting of rollers refer roller mounting drawing included in Vol.I. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Alternatively for movement of transformer from loading bay to actual site of the equipment, skidding on greased rails etc. can also be resorted to. 2.1.3 STORING Dismantled equipment and components are packed to be protected against normal handling and transport stresses. The instructions for lifting given on the packages, must be complied with to avoid damages. Goods stored outdoors must not be placed directly on the ground, and should be covered carefully with tarpaulin or similar material. Oil drums should be stored in horizontal (lying) position with both the bungs also in horizontal position. 2.1.4 LIFTING Lifting devices on the transformer tank are dimensioned for lifting of the complete transformer filled with oil. The positioning of the lifting devices, permissible lifting angles, minimum height to crane hook and transformer weight, appear from the OGA drawings. Check at lifting of complete transformer that the lifting wires/ropes are not in contact with bushing or other components on the cover. For lifting with hydraulic jacks, the transformer is provided with jacking pads dimensioned for lifting of complete transformer filled with oil. The position of the pads appear on the OGA drawings. If active part is to be lifted refer instructions given in clause 2.7. 2.1.5 LOCATION AND SITE PREPARATION a) Reactor shall always be placed on concrete plinth without rollers as per foundation plan drawing whereas transformer may be even placed with rollers. Therefore it is very important to refer foundation drawing before placing the transformer/reactor on final location. b) Transformer/reactor should be placed on the foundation so that easy access is available all around and diagram plates, thermometers, valves, oil gauges, etc. can be easily reached or read. Adequate electrical clearances are also to be provided from various live points of the transformer to earthed parts. c) ONAN type transformers/reactors depend entirely upon the surrounding air for carrying away the heat generated due to losses. For indoor installation, therefore, the room must be well ventilated so that the heated air can escape readily and be replaced by cool air . Air inlets and outlets should be of sufficient size and number to pass adequate air to cool the transformer. The inlets should be as near the floor as possible and outlets as high as the building will allow. Where necessary, exhaust fans can be installed for the purpose. d) The transformers should always be separated from one another and from all walls and partitions to permit free circulation of air. In this connection reference is also drawn to IS: 10028 (Part II). Prepared By Samvet Lahari, Bhopal. Phone- 5277412 e) Where rollers are not fitted, level concrete plinth with bearing plates of sufficient size and strength can be adopted for outdoor transformers. To prevent the formation of rust, it is essential to avoid presence of air and water in the space between the plinth and the base of the transformer by use of cretex or similar bituminous compound. f) Where rollers are fitted, suitable rails or tracks should be used and the wheels locked to prevent accidental movement of the transformer. Where walls are provided, it should be ensured that the transformer gets a good ventilation as mentioned above for indoor transformers. Provision should be made for the emergency drainage of the oil from the transformers (e.g. in case of fire in neighbouring apparatus or bushing or the transformer tank), by surrounding the transformer plinth with sump filled with small pebbles. 2.1.6 INTERNAL INSPECTION AND CHECK POINTS FOR ASSEMBLING THE TRANSFORMER/REACTOR (a) Check-points before starting assembly: 1. Conditions of leads. 2. Bracing, clamping of leads. 3. Connections. 4. Tapchanger checks. 5. General conditions of insulation. 6. Core check that it has not moved in transit. 7. Core-ground; this is checked with the megger after removing earth connection. 8. CTs, including the secondary leads and their passage through metal parts. 9. Check that shipping frame for bushings have been removed. 10. Check that coil position has not moved in transit. 11. Check for dirt, metal swarf, moisture. 12. Check that the bushing leads set without being too close to ground or other points of different potential. (b) Check-points during Assembly By means of the Part list and the transformer/reactor OGA, the assembling of a fully completed transformer is carried out according to the following instructions. The following precautions are to be taken: (i) Fire-fighting equipment shall be available at the oil-treatment equipment as well as at work on and adjacent to the transformer . (ii) Welding work on or adjacent to the transformer shall be avoided, but if this is not possible, the work shall be supervised by fire-protection personnel. (iii) Smoking on or near the transformer shall not be allowed. (iv) Transformer tank, control cabinet etc. as well as assembling and oiltreatment equipment shall be connected with the permanent earthing system of the station. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) (xiii) (xiv) (xv) (xvi) (xvii) Check that there is no overpressure in the transformer when blanking plates or connection lids are to be opened. All loose objects, tools, screws, nuts etc., shall be removed from the transformer cover before opening the connection and blanking lids. All loose objects (tools, pencils, spectacles etc.,) shall be removed from the boiler-suit pockets etc. before starting the work through man holes. Tools to be used inside the transformer/reactor -e.g. for tightening of screw-joints- shall be fastened to the wrist or another fixed point by means of cotton tape or string. Tools with loose sleeves and tools with catches must not be used at work inside the transformer. Greatest possible cleanliness shall be observed at work inside the transformer/reactor, and at handling of parts to be mounted inside the transformer. Fibrous cleaning material should not be used as it can deterioate oil when mixed with it. All components despatched separately should be cleaned inside and outside before being fitted. A transformer/reactor is best protected from damp hazard by circulating warm, dry, deaerated oil through it until it temperature is 5° C to 100 C above ambient. This should be done before allowing external excess to the interior of the tank. The warm oil should be circulated all the time transformer is open to atmosphere, Oil pump & all joints in the oil pipe work should be airtight to avoid entrance of air through leakage joints. The active part (core and winding) should be exposed to the surrounding air as short time as possible. Open therefore only one blanking plate or connection lid at a time for remounting of bushings, valves etc. Objects which-despite all precaution are dropped inside transformer/ reactor, must absolutely be brought up from the equipment. Check that the oxygen content inside the transformer tank is minimum 20% if a person is to enter the tank. 2.1.7 ASSEMBLY OF WHEELS Mounting of wheels under reactor/transformer is to be done as per roller arrangement drawing. The reactor however in service, is to be placed on plinth with anti-earthquake fastening without rollers. Transformer placement can be with or without rollers as per applicable OGA/foundation drawing. 2.1.8 ASSEMBLY OF BUSHINGS In case the bushings are mounted on turrets on the transformer/reactor cover, they are either delivered mounted on their turret or -incase of large bushings dismantled from the turrets. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 The turrets are often individually adapted; check therefore that they are re-mounted in correct places, which appear from the OGA drawing and ,part list. Assembling of bushings is carried out according to the detailed information documents available. 2.1.9 ASSEMBLY OF VALVES Valves which may affect the loading gauge, or will be subjected to damages, should be dismounted before delivery. Re-mount the valves -the positionings appear from the OGA drawing and part list. The gasketting surfaces shall be cleaned well and new gaskets fitted. Check that all valves are closed. 2.1.10 ASSEMBLY OF COOLING DEVICES Valves which are not dismantled like shut-off valves for radiators, coolers and possible headers shall be provided with blanking plates during the transport. Remove the blanking plates when the assembling of the coolers is to be started. Check first that the valves are closed. Check that each radiator and possible header are assembled in the correct positions according to OGA drawing. In case of OFAF or OFWF cooler mounting shall be done as per the relevant leaflet given in Vol.I The shut-off valves against the transformer tank shall be closed until the oil-filling is started. 2.1.11 ASSEMBLY OF OIL CONSERVATOR The conservator, which may be with or without aircell is assembled either on the transformer, or on a separate frame. Before the conservator is assembled it shall be checked that belonging equipment -e.g. Oil-level indicator -functions satisfactorily. The breather is connected to the oil conservator, and it is very important that joints and couplings in the pipe between breather and conservator are air tight. Refer Clause 2.6 for detailed instruction for oil filling. 2.1.12 ASSEMBLY OF PIPE WORK Pipes with flanges for connection of conservator, radiators, as well as pipes for equalising of turrets etc. are mostly delivered completely ready for assembling according to OGA & part list. In certain cases -e.g. at a separately assembled oil conservator -certain fitting and welding of pipes and flanges on site is however required. Instruction for such assembly of external pipes is given in Clause 2.3 2.1.13 FLANGES, BLANKING PLATES When re-mounting blanking plates, connection flanges etc., the gasketting surface shall be cleaned well and new gaskets fitted. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.1.14 ACCESSORIES Accessories like cooling fans, pumps, OLTC and components for supervision and control, oil-level indicator, flow indicators, gauges, Buchnolz relay, PRV, thermometers etc. are assembled according to leaflet/description valid for the components (refer Vol. I). 2.1.15 CONTROL CABLING Re-assemble the control cables according to the drawing of wiring system and connect the cable ends to terminal blocks in instruments, terminal boxes, junction boxes and control cabinets according to valid connection diagram. 2.1.16 GASKETS The sealing system normally used against oil and gas in BHEL's transformers and belonging components has rubber gaskets in grooves and nitrile rubber bonded cork gaskets at other places. Refer clause 2.8 for general information and assembly instructions for gasket mounting. 2.1.17 OIL FILLING The completely mounted Transformer is oil-filled according to directions in Clause 2.5 & 2.6. The oil shall be treated according to Clause 2.4. The lower and upper shut-off valves for radiators/coolers and possible headers shall be open during evacuation and oil-filling. If coolers are placed on suspension beams, which are mounted at right angle to the tank, the suspension beams shall be supported against the ground during the evacuation. Also radiators mounted on the tank wall shall be supported in a similar way. The hose for filling of oil is connected to the bottom valve of the transformer which must not be opened until the hose has been deaerated and completely filled with oil. 2.1.18 CLEANING & PAINTING The transformer and its equipment are cleaned carefully from dirt, oil, lubricating grease, and damaged surfaces are touch-up painted with the primer paints and finish paints delivered as per clause 2.11. 2.1.19 EXCHANGE OF BUSHING When exchanging a damaged bushing or other component on the cover of a fully oil- filled transformer, we should proceed according to the following: Close the valve in the pipe between the transformer and the oil conservator. Pump oil from the transformer tank into the oil conservator so that the oil quantity which need be drained off to lower the oil-level enough below the transformer cover is pushed to the conservator. As the oil is being transferred from tank to conservator, fill up the tank with dry nitrogen via a suitable valve on the cover or in turrets. Exchange the faulty bushing and transfer then the oil from the conservator to the tank by opening the valve in the pipe between conservator and main tank. De-air the bushings and turrets. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.2 STORING OF TRANSFORMER/REACTOR DESPATCHED FILLED WITH NITROGEN 2.2.1 STORING BEFORE COMPLETE ASSEMBLING The storing place should be easily accessible for inspection and maintenance of the transformer. The bedding for the equipment should be larger than its bottom surface and dimensioned for the load. The transformer is placed on boardings or beams so that good ventilation is obtained underneath the transformer bottom. Before storing, the transformer is inspected according to directions in Clause 2.1 "Reception and assembling of transformer/reactors despatched partly dismantled and filled with nitrogen". A transformer without remarks may be stored up to 3 months after arrival at the site without oil-filling. During the storing time, the inert gas (nitrogen) filling shall be maintained and pressure regulated, so that exposure of active part to atmosphere is avoided. If the storage time is judged to exceed 3 months, the transformer should be provided with oil conservator including oil-level indicator and breather, and oil-filled according to Clause 2.5. "Oil filling under vacuum". Certain valves must be re-mounted to enable the oil-filling being carried out. Furthermore, at the time at oil-filling of a completely assembled transformer, certain rules in Clause 2.5 & 2.6 must be complied with absolutely. Wherever possible it would be most desirable to keep the transformer energized even at a low voltage so that its temperature is higher than the ambient temperature. The low voltage may be applied under open circuit or short circuit conditions. It may be ascertained whether partial cooling is required in such a case. The oil quality should also be periodically monitored. If for some reason, oil filling cannot be carried out after a storage period longer than 3 months, the nitrogen pressure shall be maintained and supervised carefully. If the storage time without oil exceeds 18 months BHEL should be consulted about measures to be taken. 2.2.2 STORING OF COMPONENTS AND ACCESSORIES BEFORE COMPLETE ASSEMBLING Independent of the duration of the storing time, the directions below apply for dismounted components and accessories, as well as for material to be used in connection with the assembling work. (a) Storing indoors In such a room, the following articles should be stored: (i) Insulation material as paper, pressboard, bakelite, wood, cotton tape etc. (ii) Insulated details as paper-insulated conductors, pressboard insulated shielding bodies etc. (iii) Chemicals as solvents, glues, varnishes, hardeners etc. (iv) Breathers, drying agents. (v) Terminal boxes, connection boxes, control cabinets. (vi) Gas relays, oil-level indicators, thermometers, pressure valves etc. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (vii) MBox, OLTC motor drive, Fans, Pumps, Instruments & fittings. (Heating elements provided shall be connected to supply) (b) Storing outdoors The below components may be stored outdoors. They should be placed above ground and covered with tarpaulin etc. (i) Oil-conservator with blanking plates for all openings. (ii) Radiators and coolers with blanking plates for all openings. (iii) Structures, A frames, Pipe supports, Supports for oil-conservators, radiators, control cabinets etc. 2.2.3 SUPERVISION During the storing time, the storing place, transformer/reactor components and accessories are inspected regularly. Tap changer if provided should be operated at 6 monthly intervals. Two or three runs from one end of the range to the other and back are sufficient. Observations, readings, measures and dates should be noted and BHEL should be contacted for directions about possible measures. Check at even intervals -and further more at weather changes as rain, storm, frost or thawing the foundation material (boardings, beams etc.) and the condition of the ground. Inspect the transformer/reactor periodically with regard to possible external faults and/or rust-damage. Check also that screws and nuts in sealing joints (covers, lids etc.) are tightened. Check every second week that the connected-in heating elements in control cabinets function. If the Transformer is inert gas filled, one shall check every second week the overpressure or inert gas consumption. If the reactor is oil-filled, one shall take oil-samples after 6 months, and then min. once a year. The oil is investigated with regard to Electric Strength (BDV) and moisture content. Inspect periodically stored components and accessories with regard to possible , external damages and/or rust damages. If any touching up of paint is required it should be carried out as per clause 2.11. Check at the same time that insulation material and insulated details are not damaged or have become dirty. 2.3 ASSEMBLING OF EXTERNAL PIPES 2.3.1 This technical description shall be applied at assembling of transformers, when external pipes, for some reasons, are not fully completed at delivery but require some kind of machining or fitting at site. At the design occasion it is judged which details that can be made fully completed in the workshop and which details that must be fitted into position at site. Fully completed details are delivered with complete surface treatment. Details of the pipe work despatched can be seen at shipping list. 2.3.2 BREATHER PIPE The pipe is normally made of 15 NB painted steel pipe. The pipe shall be cleaned carefully after machining. Supplementary surface treatment is, not required normally. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 It is very important that the pipe is tight. Possible leakage will cause moisture on the transformer with the service disturbances. Mounting of the breather pipe shall be as per OGA drawing. 2.3.3. OIL CONSERVATOR For position of conservator along with necessary supports, refer OGA drawing. 2.3.4 OIL CONSERVATOR PIPE The pipe has dimension 80 mm usually and has welded flanges. The pipe shall be painted internally with a yellow, oil-resistant paint, and externally with a paint specified on the drawing. The pipes shall always incline upwards minimum 2/3 degrees from the transformer. 2.3.5 EQUALISING PIPES The pipe system in connection with the transformer cover is as a rule manufactured in workshop. The pipe between transformer and conservator may be pre-assembled. The pipe is provided with weld-flanges. No pipe part is allowed to be so long that internal inspection and cleaning is difficult to carry out. Besides straight extensions, each pipe part may contain one bend. The pipes shall always be placed with minimum 2/3 degrees inclining upwards from the transformer. Internal surface treatment is with yellow oil resistant paint. External surface treatment is made as specified on the drawing as per specification. Cleanliness is extremely important. 2.3.6 COOLERS The positioning of the radiators/coolers is indicated on OGA drawing. These are positioned so that the highest point of the oil-pipe system is always positioned below the bottom level of the conservator. The pipe system is provided with filter valves at the start and finish to enable pumping the oil through the system. All places where air may be collected are provided with air release plugs/ valves. 2.3.7 COOLER PIPES The pipe having dimensions as per OGA drawing and may be provided with weld- flanges, expansion joints. No pipe part is allowed to be so long that internal inspection and cleaning will be difficult. The pipes shall be placed so that air release plugs will be positioned at the highest point of the pipe part. The pipes shall be painted internally with a yellow, oil-resistant paint and externally according to the paint as per specification. 2.4 INSULATING OIL, QUALITY AND TREATMENT 2.4.1 QUALITY The oil to be filled in transformer generally complies with the requirements of the customer's specification. The characteristics of fresh oil as per IS: 335 "Specification for New Insulating Oil" are given below: Prepared By Samvet Lahari, Bhopal. Phone- 5277412 CHARACTERISTICS AND PARAMETERS OF NEW INSULATING OIL Sr.No. Characteristics 1. Appearance 2. 3. Density at 29.5°C Kinematic Viscosity at 27° C (max.) Interfacial tension at 27oC (Min) Flash Point (Min) Pour Point (Max) Neutralisation value (Total acidity), (Max) Corrosive sulphur : Electric strength (breakdown voltage) (Min) New untreated oil, 4. 5. 6. 7. 8. 9. (a) (b) 10. 11. 12. 13. a) b) 14. a) b) c) d) 15 After filtration Dielectric dissipation factor (tan δ) at 90°C (Max) Water content (Max) Specific resistance (Min) at900C at27OC Oxidation stability Neutralisation value (Max) Total sludge after oxidation (Max) Ageing characteristics after accelerated ageing (open beaker method with copper catalyst). Resistivity (Min) at 900C at 270C Tan δ at 90°C (Max) Total acidity (Max) Sludge content by weight (Max) Presence of oxidation Unit Requirement gm/cc The oil shall be clear, transparent & free from suspended matter or sediments. 0.89 Cst 27 N/m o C o C 0.04 140 -6 mg/KOH/g 0.03 Non-corrosive kV (rms) kV (rms) 30 (If the above value is not obtained the oil shall be filtered in laboratory). 60 ppm 0.002 50 ohm-cm ohm-cm 35x1012 1500 x 1012 mg/KOH/g 0.4 mg/KOH/g 0.10% ohm-cm ohm-cm 0.2x 1012 2.5 x 1012 0.2 0.05 0.05% Oil shall not contain inhibitor oxidation inhibitor mg/KOH/g Note: Methods of test shall be as per IS: 335 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.4.2 SUPPLY AND TESTING The transformer oil is despatched directly to site from oil refinery. The oil is thoroughly inspected and tested at oil supplier's works in presence of BHEL and/or customer's representative or their authorised representatives. Test certificate giving values obtained for all characteristics is issued. 2.4.3 HANDLING The oil drums should be carefully handled at site, details of which are given in Clause 9.1of IS:1866. 2.4.4 RECONDITIONING Transformer oil is usually contaminated during handling, transport and storage due to ingress of moisture and solid impurities. Hence, oil shall be vacuum filtered separately at 50 0C to 60 °C using a suitable filtration machine and a spare clean tank before filling in the transformer. Details of filtration are given in Clause 9.2 of IS:1866. Oil treatment shall be terminated when the following parameters are attained. TABLE 2.1 kV Class of transformer Recommended Permissible limit Electric Strength (BDV) in kV (Min) Upto 145 245 420 60 65 70 Moisture Content ppm (Max) 20 15 15 Storage tank shall be as per typical arrangement shown in Fig 2.2 Electric strength and moisture content shall be determined following the test procedure of IS: 335. 2.5 OIL FILLING UNDER VACUUM 2.5.1 APPLICATION Transformers and Reactors with vacuum-proof tanks shall be filled with oil according to this method. 2.5.2 STORING TIME Generally it applies that Transformers and reactors which during transport are filled with dry nitrogen on arrival at the site shall be evacuated and oil filled. Before storing, the equipment shall be inspected according to the directions given in Clause 2.1 "Reception and assembling of transformer/reactor despatched partly dissembled and filled with nitrogen". During the storing time, overpressure shall be maintained, and nitrogen consumption checked according Clause 2.2. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.5.3 FLOW CHART FOR HANDLING In Annexure 2.1 is given a flow chart of handling procedures. The pressure should be measured at different times. The pressure is OK if it is maintained according to instructions given in Clause 2.2. Reference is also drawn to para 9.0 of IS: 1866 regarding handling and filling of oil. 2.5.4 UNITS Annexure 2.1 gives the relation between different units. 2.5.5 EVACUATION The transformer tank (excluding cooler bank & conservator) shall be evacuated to a pressure of 1.00 torr. max. The pressure shall be maintained for the time given in Table 2.2. TABLE 2.2 VACUUM TREATMENT System Voltage Evacuate and hold vacuum for Standing time after oil circulation before application of voltage kV hours hours Upto 145 12 12 145 & upto 420 24 48 Above 420 36 120 The equipment required for vacuum treatment and oil-filling under vacuum should generally be as per Annexure 2.2. The transformer tank and electrical terminals shall be earthed for safety reasons. No electrical test on the Transformer is permitted during the evacuation. Fig. 2.3 shows a typical example of pipe work and valve positioning. Oil conservators are not evacuated. Valve 7 shall be closed. Valve 6 shall be open unless a breather is fitted. 2.5.6 OIL FILLING 2.5.6.1 OIL QUALITY The transformer/reactor shall be filled under vacuum with oil which has been purified and degassed according to Clause 2.4 2.5.6.2 OIL FILLING IN MAIN TANK The oil shall be heated to a temperature of 500- 60°C measured at the filter outlet valve. The pressure during the filling shall be max. 1 torr. During the oil-filling, a transparent plastic tube (5) can be used as an oil-level gauge. The tube which should be a wall thickness of 5-8 mm, may be connected to a top and a bottom valve on the transformer. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Oil-filling of the tank is done through valve (12) at a low level on the transformer and at a maximum rate of 4-5 kL/hour. The pressure in the oil pipes shall be kept positive and shall be checked by a manometer 13 (if provided). When the oil-level has reached about 50 mm below the cover/the vacuum pump is stopped it is preferred that dry nitrogen is introduced in the tank by opening valve (8). Valve (7) is then opened .and valve (6) closed and the filling is continued in tank and conservator until the correct oil- level has been reached in the conservator. Conservator supplied with rubber air cell shall be filled according Clause 2.6. For oil filling in diverter switch assembly of a OLTC refer leaflet (Vol.1). Separate vacuum-proof cooler system/radiators can be evacuated for about 1-2 hours and filled separately with purified and degassed oil. The oil is then circulated through the vacuum filter at least twice via drain valves as near as possible to the transformer. When the oil circulation has been completed the valves between coolers and main tank shall be opened. Care should be taken to keep all air release plugs and valves open to allow escape of trapped air during oil filling operation. These valves/plugs should be closed after completion of oil filling. 2.5.7 HOT OIL CIRCULATION To facilitate oil-penetration and absorption of possible gas bubbles, the temperature of transformer shall-after completed oil-filling-be increased by circulating the oil through the vacuum filter and with circulation direction according to Fig. 2.4. The oil will be circulated through a vacuum filtration machine till the parameters are attained as per table 2.3 below. TABLE 2.3 kV Class of Transformer Recommended Permissible Limits Electric Strength (BDV) in kV (min) Moisture Content ppm (Max) Resistivity * at 90oC (Ohm-cm) Tan delta* at 90oC Upto 72.5 145 40 50 25 20 1x1012 1x1012 0.05 0.05 245 and 420 60 15 1x1012 0.05 * Subject to availability of testing facility at site. Method of test for Electric Strength and moisture content shall be as per IS:335. CAUTION: The temperature during oil circulation should not increase beyond 70oC otherwise this may cause oxidation of oil. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.5.7.1 SAMPLING Oil sampling at various stages shall be done in accordance with IS: 6855. when samples are taken from transformer tank, oil will be drawn from bottom of the tank. When it is desired to know gas content and composition of dissolved gases in transformer oil before commissioning for reference purposes (required for interpretation of Dissolved Gas Analysis results during service), sampling shall be done as per IS 9434. 2.5.8 STANDING TIME Standing time is the time between 'finished oil circulation' and 'energisation'. The time appears form table 2.2. 2.5.9 FINAL OIL FILLING OF TRANSFORMERS/REACTORS DESPACTCHED OIL FILLED. Smaller transformers/reactors are often factory-filled with degassed oil up to about 10% below the cover and transported in this condition. The final filling up to the correct level in the conservator is made at site. 2.5.9.1 TRANSFORMERS/REACTORS WITH SYSTEM VOL TAGE < 36 KV Previously degassed oil (e.g., at the factory) stored in tight drums may be used for the filling. Check the dielectric strength of the oil which should be as per Cluase 2.4.4. If accepted, the oil is pumped into the conservator and in this way fed into the tansformer. To prevent any free water in the drums from entering the reactor the opening of the suction tube must lie 0.1 m above the lowest point in the drum. A suitable valve on the cover and/or valves or upper tightening nuts at the bushings have to be opened for complete removal of air below the cover and in the bushings. When the oil is seeping out at these points, shut the valves and tighten the nuts at the bushings. 2.5.9.2 TRANSFORMERS/REACTORS WITH SYSTEM VOLTAGE > 36 KV The filling is performed as described above, but at least a paper filter must be used for drying the oil. 2.6 OIL FILLING INSTRUCTIONS FOR CONSERVATORS WITH AIR CELL 2.6.1 INTRODUCTION In all transformers specially in high voltage class, maintenance of insulating oil notably its dielectric property forms one of the determining factors of reliability of equipment in service. Oxidation and contamination of transformers/reactor oil can be avoided in a simple and effective way by use of above oil preservation system. The complete system is known as "Conservator with Air Cell". In this oil preservation system a flexible air cell made of oil resistant nitrile rubber is placed inside the conservator and floats on the oil surface. The air cell inflates or deflates as the oil level in the conservator falls or rises depending on the ambient temperature and load on the reactor. The inside of the rubber bag (Air Cell) is put into communication with atmosphere by means of a silica gel breather which ensures dry atmosphere inside the air cell. In addition to the above this system provides following advantages. (i) It avoids saturation of absorbed gases. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (ii) As no gas is used in this system, which operates at constant pressure, this formation of gas bubbles at low ambient temperature and load is eliminated. The system thus preserves the oil quality particularly its dielectric properties. The conservator with air cell is provided with a magnetic oil gauge having one electrical contact. The indication shown on the dial physically corresponds to the oil level in the conservator which is due to balance of static pressure between the oil of the conservator and the atmospheric air inside the air cell. This system is also provided sometimes with a set of pressure and vacuum valves. These valves operate to pass either oil or air in the event of over filling or under filling the conservator during installation. 2.6.2 DESCRIPTION OF OPERATION Figure 2.5 indicates the general arrangement of oil preservation system, The oil connection between conservator and transformer tank is made through Buchbolz relay and valves are provided in between. The flexible air cell is connected to the top of the conservator through gasket ted joint. Under normal condition air cell is completely surrounded by oil and floats in the conservator. The air cell inflates/deflates as the oil volume changes. The float of the MOG which is always in contact with under side of the air cell moves up and down and indicates the oil level. The cell will sink in the remote event if it is damaged and MOG alarm will operate. The conservator then functions as a conventional conservator without effecting the performance of the transformers/reactor. 2.6.3 INSTALLATION This system is shipped separately from main tank. The air cell is shipped fitted in the conservator. A low positive pressure of less than .07 kg/sq.cm (1 psi) is maintained to avoid excessive movement of air cell in the conservator during transit. MOG is also shipped fitted on the conservator. Install the conservator and associate parts except breather as per transformers/reactor outline drawings and assemble oil pipe work. 2.6.4 OIL FILLING The following procedure is recommended. (i) Close and blank the valve (14) to isolate the conservator from main tank. Fill the oil in transformer under vacuum upto Buchholz level as per instructions given else where. ' (ii) After filling the oil in transformer and breaking the vacuum, oil can be filled in the conservator either through reactor or by drain valve (4). (iii) Remove the inspection cover (11) provided on the side of the conservator and check the air cell assuring that it is inflated. The air cell must remain in fully inflated condition during oil filling operation. If the air cell is found deflated fit the inspection cover and inflate the air cell with dry air/nitrogen gas to 0.035 kg/sq.cm max. through connection (8). A gauge may be put by removing plug (10). After filling close these connections. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (iv) Remove air release plugs (5) (6) and (7) provided on top of the conservator. (v) Slowly pump the oil through the main reactor/drain valve (4). Temporarily stop filling operation when oil starts coming from opening (5) and (6) after ensuring that no air bubbles come out through these air release holes. Fit the two air release plugs. (vi) Continue oil filling till oil start coming from air release plug (7) stop oil after ensuring that no air bubbles come out. Fit the plug (7). (vii) Now release the air pressure held inside the air cell from point (8) and continue oil filling until magnetic oil gauge (3) indicates 35°Clevel. (viii) Remove oil pump and connect air cell to breather (9) from point (8). Also remove pressure gauge and put plug (10). (ix) The system is now properly filled. Air release plugs (5), (6) and (7) are fitted in normal operation. 2.6.5 (i) PRECAUTIONS Oil filling in the conservator and also draining whenever required must be done very slowly. During oil filling, pressure in the air ce]l should not exceed 0.1kg/sq.cm (1.5 psi). (ii) If a pressure or vacuum is ever applied to the main reactor tank the conservator must be disconnected and a blanking plate fitted on shut off valve. (iii) Do not weld on conservator to avoid damage to the air cell. (iv) Once all the air has been driven out during oil filling in the conservator do not remove air release plugs (5), (6) and (7). Otherwise air will be sucked inside the conservator. 2.6.6 MAINTENANCE Little maintenance work will normally be required except routine visual inspection. However, it is desirable to check the breather opening to ensure it is not blocked. Further silicagel should be regenerated/replaced when its colour changes from blue to pink. 2.6.7 AIR CELL Air cell is made from Nylon fabric coated with Nitrile rubber, In the event it becomes necessary to replace or test the air cell for leaks the following method is recommended. (i) De-energise the transformers/reactor. (ii) Isolate the conservator by closing the valves (14). (iii) Drain the oil from the conservator through the valve (4) by removing air release plugs (5) and (6). Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (iv) Remove inspection cover (11) if necessary, Install the pressure gauge on point (10). (v) Pressurise the air cell (2) by dry air/nitrogen to a max. pressure of 1.5 psi and seal. Check the pressure for 6 hours. (vi) If leaks are found, air cell to be repaired by patching or replaced by a new air cell. (vii) For taking out the air cell from conservator, remove the air cell flange and loops from hooks provided on inside of the conservator top. Collapse the air cell slowly and fold, remove it from conservator very carefully. (viii) In the event air cell is not available immediately, conservator may be used as a conventional conservator. 2.6.8 OIL PRESSURE TEST Oil pressure test on fully erected Transformer/Reactor to be conducted as per annexure 2.3 before hot oil circulation. 2.7 UNTANKING OF ACTIVE PART 2.7.1 GENERAL If for some reason it becomes necessary to untank the active part (core and windings) of a large reactor/transformer, it ought to be done under supervision by BHEL erectors. Universal instruction for the untanking procedure cannot be given, as the design practices of large equipment vary. The following general directions are, however, applicable in most cases. The untanking must be done indoors. If there is no suitable hall available, lifting can be done in the temporarily arranged room. e.g. a tent. The oil & the internal parts of the transformer must not in any case be exposed to rain or humidity. In case of bell shaped transformer, only bell cover is lifted for access to active part. 2.7.2 OIL DRAINAGE Drain off the oil from the transformers/reactor either partly or completely. 2.7.3 DISCONNECTING Disconnect leads to bushings, current transformers, winding temperature devices and earthing leads between active part and cover or tank side. Disconnections mentioned above can usually be made through handholes in cover or tank side. 2.7.4 REMOVAL Remove all large bushings, cover mounted conservator and lightning arrestors (if provided). Break all connections between cover and tank-piping to oil conservator and cooler thermometers etc. Remove the cover bolts. If the cover is welded to the tank flange, free the cover according to directions given in Clause 2.9. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.7.4.1 COVER When lifting the cover use the cover-lifting eyes which are designed for a minimum angle of 60 degrees between sling branches and the horizontal plane. The length of the sling should therefore be sufficient for at least this angle. Place the cover on suitable wooden supports and in such a way that thermometer pockets, small bushing etc. underneath the cover are not damaged. No grinding or cleaning up of the tank flange is to be carried out before the active part is lifted out of the tank. 2.7.4.2 UNTANKING Loosen locking devices, if any, between top core clamps and tank side. Lift the active part by means of lifting eyes or lifting lugs provided on the top core clamps. The untanking height is shown on the outline drawing. To avoid damages on the active part it is important that it is centered carefully in the tank during lifting procedure. After untanking, place the active part on a horizontal foundation. 2.7.5 RETANKING Grinding or/and cleaning up of the tank flange has to be done before the active part is lowered into the tank. Check that the tank inside is free from contaminations. Retanking is then done in the reverse order that is outlined above. Note that guiding pins or blocks are welded to the tank bottom to prevent the active part from moving in the tank. When lowering the active part, check that it fits exactly the guiding pins or blocks. 2.7.6 REASSEMBLING Wipe the underside of the cover free from any dirt or foreign matter before lifting it into correct position above the reactor tank. Lower the cover the last few inches exactly into position without sliding on the gaskets. Reassemble bolts nuts of supporting devices. Weld the cover when the welded construction is used. Reassemble Bushings, conservator etc., and reconnect pipings, leads to bushings, current transformers, etc. Reassemble inspection covers. After the transformer is completely assembled, it may be necessary to dry it before oil fining- see clause 2.5. 2.8 MOUNTING OF GASKETS 2.8.1 The gaskets have a circular/flat cross-section and are made of oil and heat- resistant synthetic nitrile rubber/nitrile rubber bonded cork. For small gaskets, O-rings are used with diameter 3,5.0 or 8.0 mm, while round rubber cords with diameters 8,12 or 19 mm are used for large gaskets. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 The groove is normally milled or turned, but for large flanges the groove is created by means of steel bars welded on top of the flange. The width of the groove is slightly smaller than the cross-section diameter of the gasket in order to keep the gasket in position during the assembling work. Opened sealing joints may be sealed again using the same gasket provided that the same has not been damaged. If the gasket has become hard or got small cracks on the surface, it is recommended to change the gasket by a new one. When handling and lifting flange, cover etc. with gasket grooves, care should be taken when using tools and lifting devices to avoid that the grooves getting damaged or deformed. Before assembling of groove gaskets, it is checked that the grooves and contact-surface in the joint are free from foreign particles and that the paint is free from thick coatings, trickles and drops. When assembling the rubber cord in the groove, the cord length shall be continuous . The gasket is given a small surplus length to compensate for shrinkage. The gasket is pressed down into the groove without stretching or slackening. To prevent the gasket from falling from the groove on vertical surfaces, the gasket may be spot-glued to the bottom of the groove. The screws in the sealing joint shall be tightened so that an even pressure is obtained on the gasket. This is obtained preferably by means of a moment spanner. Rubber gaskets in grooves need not normally be re-tightened. Above description is followed generally for turrets, inspection cover etc. For main tank rim joint, LV turrets of Generator Transformers where metallic stops are provided, nitrile rubber bonded cork is used, for which following instructions shall apply. 2.8.2 (i) Gaskets when supplied loose, have no bolt holes in them. They are usually cut to the size and shape required, although they may be supplied as straight, angled pieces from which complete gaskets can be built up. (ii) Scarfed joints should be used. A 40 mm scarf in 5 mm thick material is recommended. Joints should be located away from comers and bolt holes, and should be well bonded, smooth and free from local thickening. Neoprene solution is used as an adhesive for joints. (iii) Gaskets are best stored in hermetically sealed containers in a cool place. They must be protected from damp, oil and grease(iv) To make a gasket joint, first clean the metal surfaces ensuring that they are free from oil, rust, scale etc. Using one of the flanges as a template, punch the necessary bolt holes. Insert the bolts and tighten the bolts sequentially, a little every time so that uniform pressure is exerted on the gasket until the gasket is compressed to about 2/3 of its original thickness. Joints should not be subjected to pressure until tightening is complete. If care is taken in making joints, and in handling the gasket, it is possible to break and remake a joint several times, using the same gasket. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (v) For making leak proof and good gasket joints, it is necessary that uniform pressure is achieved all over the gasket after matching rims/ flanges have been clamped with bolts/studs. Following instructions be followed for proper tightening of bolts/studs. a) Tighten lightly the bolts/studs diagonally in the sequence as shown in the fig. 2.6. b) Tighten again bolts/studs in the same sequence with the torque given below : Bolt/Stud Max. Torque Size (Kg-M) M 10 1 M 12 2 M 16 6 M 20 12 M 24 20 M 30 30 In case of metallic stoppers tighten until metal to metal contact is achieved. c) Do not overtighten, otherwise gasket will get crushed. 2.9 WELDED COVER (IF APPLICABLE) In order to obtain a good sealing between the transformer tank and the cover a welded joint is recommended. The welding is performed in a certain way to permit opening and new welding repeated a number of times. The chiselling up and re-welding will take about the same time as dismantling and reassembling of bolted cover . If the welded cover for any reason has to be removed proceed as follows: 2.9.1 OPENING THE COVER When opening the cover the welding joint should be removed by a suitable grinding wheel. The cover should be clamped to the frame by means of Gclamps to prevent iron chips from penetrating into the tank. Any parts of the weld which may possibly remain on the tank flange should be removed by a chisel to enable a good result of the re-welding. 2.9.2 REASSEMBLY When fitting the cover again cork-rubber gaskets, 25 x 5 or as specified are fitted on the tank flange, see fig. 2.7. The gaskets are kept in the correct position with glue base on rubber base. The cover should be clamped to the tank flange by means of G-clamps evenly distributed along the flange with about 600 mm spacing. Tack welding is carried out with about 100 mm spacing. An extra G-clamp is used during the tack welding and is moved along the flange during the progress of the work. The continuous weld is then applied. Finally the weld should be cleaned and painted. WARNING When welding, a fire-extinguishing equipment should be available, and the work supervised by fire-protection personnel. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.10 EARTHING OF ACTIVE PART AND CORE INSULATION TEST 2.10.1 REACTORS The ground-connection terminals for the reactor active part are located in a box at the tank end, close to the bottom. Please see fig. 2.8. The terminal are protected by a cover. The cover can be removed with the tank oil- filled. The terminal box contains a terminal block with three terminals. -The terminal marked CL is connected to the core laminations. -The terminal marked CC is connected to the core clamps. -The terminal marked G is connected to ground (the tank). For the core-insulation test, remove the cover. Disconnect the closing link that connects the two terminals CL-G. Use perferably 3500 V direct voltage between CL and CC + G. The tank shall be grounded during the test. The insulation value after 1 min. test- time shall be minimum 1000 kohms. There is no general requirement on the insulation level CC-G . 2.10.2 TRANSFORMERS For checking core insulation incase of transformers refer Fig. 2.9 for connection details. 2.11 TOUCH-UP PAINTING 2.11.1 PURPOSE A basic principle at touch-up painting should be to restore a damaged paint coat on a surface to the same quality and finish as of the surrounding surface. The touch-up painting should be limited to a surface as small as possible. 2.11.2 CLEANING Both damaged and surrounding surface should be cleaned so that all grease, dust and other impurities will be removed. 2.11.3 GRINDING OF DAMAGES Large damages and defects are ground by means of a coarse abrasive paper, e.g. No.100. The surface is then ground with a finer paper in connection with the damage, e.g. 150 or 180. Damages that are limited to the paint coat only, should be ground off completely at which glazing can be avoided. 2.11.4 PRIMER PAINTING Damages on the primer paint and grinding down to the steel surface should be painted with two coats of anti-corrosive priming paint. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 2.11.5 FINISHING PAINT Two coats of finishing paint should be applied as per specification which is generally light grey shade No.631 of lS: 5. Please refer Table 2.4 for suppliers reference. TABLE 2.4 SI Suppliers No. Name Suppliers Reference Anti corrosive High Quality full priming paint for gloss outdoor outside painting finishing paint 1. Addison IS 2907 Shade 631 of IS 5 jasmine yellow shade no.397 of IS 5 for inside painting 2. Asian 32/F 3257 Apcolite synthetic - 3. Berger BPL Red oxide Zinc Chromate Luxol 3H1 Glass synthetic enamel - 4. Alkali Chemicals 32-781 Dulux synthetic enamel - 5. Garware PR-4460 - - 6. Shalimar Sample No. 5999/1 Superlac synthetic 7377/1 7. Goodlass 205/023 500 Series 548/101 Oil resistant air drying synthetic enamel Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 2.1 FLOW CHART FOR HANDLING ARRIVAL AT SITE MEASUREMENT OF PRESSURE ASSEMBLY EVACUATION AND OIL FILLING OIL-CIRCULATION THROUGH FILTER STANDING TIME ACCORDING TO TABLE 2.2. VOLTAGE APPLICATION Relationship between different units 1 bar = 105 Pa = 750 Torr = 14.5 psi = 1.02 kg/sq.cm 1 Torr = 1.33 mbar = 0.133 kPa 1 kPa = 103 Pa = 10 mbar = 7.501 Torr 1 MPa = 106 Pa Force 1 kp = 9.807 N Volume 11itre = 0.26 US gallons 1 US gallon = 3.781itres 11itre = 0.22 Imp gallons 1 Imp = 4.551itres gallon Temperature C = 5 x (F-32)/9 F = 9 x (C+32)/5 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 2.2 EQUIPMENT FOR OIL-FILLING UNDER VACUUM (i) High-vacuum 2 stage oil filtration plant provided with thermostatcontrolled oil heaters and vacuum-proof hoses with independant vacuum pumping system for tank evacuation. Capacity: 6000 lph. (ii) Oil-storage tanks provided with silica-gel breathers and inlet/outlet valves for oil circulation. Recommended capacity 20 kL -30 kL (Clause 2.4) (iii) Vacuum gauges provided in filtration plant. (iv) Equipment for measurement of electric strength (BDV) of oil- 100 kV set. (v) Equipment for moisture content of oil. (vi) Equipment for measurement of Resistivity and Tan delta at 90o C. (vii) Oil-sampling cans or bottles. (viii) Transparent vacuum-proof tubes for checking of oil-level during oil filling. (ix) Valves, fittings, gaskets etc. (x) Dry nitrogen cylinders. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (1) (2) HAULAGE HOLE- JÉÓSÉxÉä Eäò ʱɪÉä ÊUôpù (3) JACK- VÉäEò (4) (5) (6) (7) (8) RLY. WELL WAGON- ®äú±É´Éä ´Éä±É ´ÉäMÉxÉ JACKING LUG- VÉäËEòMÉ ±ÉMÉ 90 LB. RAIL - 90 B±É ¤ÉÒ ®äú±É SUPPORTS TO PREVENT SLIPPING- Ê¡òºÉ±ÉxÉ ºÉä ¤ÉSÉxÉä Eäò ʱɪÉä +ÉvÉÉ®ú GROUND LEVEL- ¦ÉÚ欃 ºÉiɽþ THESE SLEEPERS WILL BE PUT AT SITE AT THE TIME OF UNLOADING- <xÉ º±ÉÒ{É®úÉå EòÉä =iÉÉ®úxÉä Eäò ºÉ¨ÉªÉ ºÉÉ<]õ {É®ú ®úJÉå Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Fig. 2.1 Typical Unloading Arrangement of the Transformer ÊSÉjÉ 2.1 ]ÅõÉƺɡòɨÉÇ®ú EòÉä =iÉÉ®úxÉä EòÒ ´ªÉ´ÉºlÉÉ EòÉ xɨÉÚxÉÉ Prepared By Samvet Lahari, Bhopal. Phone- 5277412 1. 2. 3. 4. 5. 6. OIL SAMPLING VALVE 15 mm 2 Nos. iÉä±É ºÉä¨{É˱ÉMÉ ´Éɱ´É 15 ʨɨÉÒ. 2 xÉÆ. FILLTER VALVE 50 mm 2 Nos. Ê¡ò±]õ®ú ´Éɱ´É 50 ʨɨÉÒ. 2 xÉÆ. DRAIN VALVE 80 mm 1 No. bÅä÷xÉ ´Éɱ´É 80 ʨɨÉÒ. 1 xÉÆ. DRAIN PLUG 15 mm 1 No. bÅä÷xÉ {±ÉMÉ 15 ʨɨÉÒ. 1 xÉÆ. MAN HOLE 1 No. ¨ÉèxÉ ½þÉä±É 1 xÉÆ. VACUUM APPLICATION VALVE 25 mm 1 No. ´ÉäCªÉÚ¨É ´Éɱ´É 25 ʨɨÉÒ. 1 xÉÆ. 7. BUSHING MOUNTING HOLES WITH BLANKING FLANGE 3 Nos. ¤ÉÖ˶ÉMÉ ±ÉMÉÉxÉä Eäò ʱɪÉä ÊUôpù ¤±ÉåËEòMÉ }±ÉéVÉ ºÉʽþiÉ 3 xÉÆ. Fig. 2.2 Typical Arrangement of oil Storage tank ÊSÉjÉ 2.2 iÉä±É ºÉÆOɽþ Eò®úxÉä EòÒ ]ÆõEòÒ EòÉ xɨÉÚxÉÉ 1. Oil-filtering plant with heater (1) ½þÒ]õ®ú Eäò ºÉÉlÉ iÉä±É Ê¡ò±]õË®úMÉ {±ÉÉÆ]õ 2. Oil-storage tank (2) iÉä±É ºÉÆOɽþ Eò®úxÉä Eäò ʱɪÉä ]åõEò 3. High-vacuum pump (3) =SSÉ ÊxÉ´ÉÉÇiÉ {ɨ{É 4. Conservator (4) EòxVÉ®ú´Éä]õ®ú 5. Oil-level indicator (5) iÉä±É-ºiÉ®ú ºÉÚSÉEò 6. Valve (6) ´Éɱ´É 7. Valve (7) ´Éɱ´É 8. Valve (8) ´Éɱ´É 9. Valve (9) ´Éɱ´É 10. Valve (10) ´Éɱ´É 11. Dry-N2 container (11) ¶ÉÖ¹Eò xÉÉ<]ÅõÉäVÉxÉ ºÉÆOɽþEò 12. Valve 13. Manometer Fig. 2.3 ÊSÉjÉ 2.3 (12) ´Éɱ´É (13) ¨ÉäxÉÉä¨ÉÒ]õ®ú Prepared By Samvet Lahari, Bhopal. Phone- 5277412 TRANSFORMER REACTOR VACUUM FILTER ]ÅõÉƺɡòɨÉÇ®ú/Ê®úBC]õ®ú ]ÆõEòÒ ´ÉèCªÉÚ¨É Ê¡ò±]õ®ú Fig. 2.4 ÊSÉjÉ 2.4 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 OIL PRESERVATION SYSTEM WITH AIR CELL +É<±É Ê|ÉVÉ´Éæ¶ÉxÉ ÊºÉº]õ¨É BªÉ®ú ºÉä±É Eäò ºÉÉlÉ GENERAL ARRANGEMENT ºÉɨÉÉxªÉ ´ªÉ´ÉºlÉÉ SL.No. Gò. ºÉÆ. DESCRIPTION Ê´É´É®úhÉ 1. AIR CELL BªÉ®ú ºÉä±É 2. MAGNETIC OIL GAUGE ¨ÉäMÉxÉäÊ]õEò 3. BREATHER ¥ÉÒnù®ú 4. DRAIN VALVE bÅä÷xÉ ´Éɱ´É 5. AIR RELEASE PLUGS +É<±É MÉäVÉ BªÉ®ú Ê®ú±ÉÒVÉ {±ÉMÉ 6. FLANGE FOR TRANSFORMER CONNECTION ]ÅõÉƺɡòɨÉÇ®ú 7. AIR CELL SUPPORTING LUGS BªÉ®ú 8. OIL 9. PRESSURE GAUGE CONNECTION (WITH PLUG) |Éä¶É®ú ºÉä VÉÉäc÷xÉä Eäò ʱɪÉä }±ÉåVÉ ºÉä±É Eäò +ÉvÉÉ®ú ±ÉMÉ iÉä±É 10. PRESSURE GAUGE |Éä¶É®ú MÉäVÉ EòÉ EòxÉäC¶ÉxÉ ({±ÉMÉ Eäò ºÉÉlÉ) MÉäVÉ 11. BREATHER CONNECTING FLANGE ¥ÉÒnù®ú VÉÉäc÷xÉä ´ÉɱÉÒ }±ÉåVÉ 12. CONSERVATOR END COVER EòxVÉ®ú´Éä]õ®ú Bxb÷ Eò´É®ú 13. INSPECTION COVER <xºÉ{ÉäC¶ÉxÉ Eò´É®ú Fig. 2.5 ÊSÉjÉ 2.5 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Fig. 2.6 ÊSÉjÉ 2.6 Fig. 2.7 ÊSÉjÉ 2.7 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Fig. 2.8 ÊSÉjÉ 2.8 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Fig. 2.9 ÊSÉjÉ 2.9 NOTE: 1. WHILE DISCONNECTING/EARTHING CONNECTION BETWEEN CORE/YOKE CLAMP & TANK, REMOVE THE LINK. 1. EòÉä®ú/ªÉÉäEò C±Éä¨{É B´ÉÆ ]ÆõEòÒ EòÉ ¦ÉÚºÉÆ{ÉEÇò ʴɪÉÖHò Eò®úxÉä Eäò ʱÉB ªÉ½þ Eòb÷Ò ½þ]õÉ nåù* 2. WHILE PUTTING IN SERVICE PLACE LINKS IN POSITION. 2. {ÉÊ®úSÉɱÉxÉ Eäò ºÉ¨ÉªÉ ªÉ½þ Eòb÷Ò VÉMɽþ {É®ú ±ÉMÉÉ nåù* Earthing Connections from core and top yoke clamp. EòÉä®ú B´ÉÆ ]õÉì{É ªÉÉäEò C±Éä¨{É ºÉä ¦ÉÚºÉÆ{ÉEÇò ªÉÖÊHò Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 2.3 PRESSURE TESTING OF TRANSFORMER / REACTORS AT SITE 1. After completion of oil filling, lock PRV and pressurise the air cell by filling nitrogen/ dry air to 5.0 p.s.i. (0.35 Kg/cm.sq.). 2. Maintain above pressure for at least 12 hours. 3. Inspect all joints for leakage, if any. 4. Record pressure testing as given below. 5. After pressure testing unlock PRV and release the nitrogen/ dry air pressure of air cell. NOTE: In case of conventional oil preservation system (without air cell) pressurise conservator by filling nitrogen/dry air in conservator . RECORD OF PRESSURE TESTING AT SITE 1. Date & Time of testing DATE TIME (a) Started on ......... ......... (b) Finished on ......... ......... 2. Initial pressure .................................... 3. Pressure after 12 hours .................................... 4. Leakages observed if any location of leakages YES /NO .................................... 5. If leakages are observed. Same to be arrested and pressure testing is to be repeated. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ¦ÉÉMÉ-3 Eò¨ÉÒ¶ÉËxÉMÉ SECTION-3 COMMISSIONING Prepared By Samvet Lahari, Bhopal. Phone- 5277412 SECTION 3 3 COMMISSIONING 3.1 TESTING AFTER ASSEMBLY OF THE TRANSFORMER/ REACTOR AT SITE. After the transformer/reactor has been assembled at site, it shall be tested in order to check that it has not been damaged during transport and assembly to such an extent that its future operation will be at risk. Regarding the performance of the test, refer to the testing method as per standards. The results of the test shall be documented as detailed in Clause 3.2 "commissioning checks -Transformers" and Clause 3.3 commissioning checks - Reactors. 3.1.1 APPLICATION OF VOLTAGE If possible, the voltage should be increased step by step up to rated voltage. This may be done by connecting the transformer/reactor to a generator whose voltage is raised slowly. The higher the rated voltage of transformer/ reactor the more important it becomes that the application of the voltage is done as described. If it is not possible to use a generator, the transformer/ reactor may be connected directly to a live line. After the first application of voltage, the transformer/reactor shall be checked carefully (gas relay, temperatures, leakages). When the transformer/reactor has been is service for some weeks with normal working temperature, all sealing joints shall be re-tightened. 3.1.2 ENERGISING The initial magnetising current at the time of switching will be very high. This depends on the particular moment in the cycle. The transformer should always be soaked for few hours under constant care i.e. keep it energized. If the breaker trips on differential, Buchholz or any other device, the cause must be investigated before re-energising the transformer or reactor. After successful charging, performance of the transformer/reactor , OTI, WTI readings should be monitored for 24 hours and ensured that they are as per loading. 3.1.3 ANALYSIS OF GAS The gas conected in the relay will help to identify the nature of the fault. It is suggested that the following checks are made at convenient intervals or following the indication of accumulation of gas through alarm signal. 1. Rate of gas collection- The greater the rate of gas collection, the more severe is the nature of the developing fault. 2. Colour of the gas helps in finding the affected material as follows. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Colour Identification White Gas of decomposed paper and cloth insulation. Yellow Gas of decomposed wood insulation. Grey Gas of overheated oil due to burning of iron portion Black Gas of decomposed oil due to electric arc. 3. Combustibility of Gas- A small amount of gas drawn through the top pet cock if brightens the test flame, then the gas is combustible. Incombustible gas indicates air. 4. Chemical Analysis of the Gas -The principles of working gas analyzing equipment is illustrated in the figure 3.1. Two solutions are prepared as detailed below and best results are obtained with freshly prepared solution. Solution 1: 5 gms of silver nitrate (AgNO3) dissolved in 100 ml distilled water. Solution 2: A week solution of ammonia in water is slowly added to 100 ml of solution 1, until a white curdled precipitate which forms first disappears in the mixture. The gas analyser loaded with these solution is then connected to the top pet cock. Small quantities of gas collected in the relay is allowed to pass through the two solutions as illustrated. The results are identified as follows: 1. Both solutions are clear : Gas is air . 2. Solution 1 -White precipitate turning brown on exposure to sunlight : Gas of oil decomposition. 3. Solution 2 -turning to Dark brown precipitate : Gas of decomposed paper, cotton or wood insulation. Note: THE ABOVE INFORMATION ON GAS ANALYSIS ARE AS DETAILED IN IS:3638-1966. PLEASE REFER IS:3638-1966 FOR ALTERNATIVE METHOD OF CHEMICAL ANALYSIS. 3.2 COMMISSIONING CHECKS -TRANSFORMER 3.2.0 SCOPE This schedule covers the tests to be done at site after transformer has been installed and dried out. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.1 GENERAL Check the following: Sl.No. Description 1. 2. 3. 4. 5. 6. 7. 8. Breather Silicagel (Blue when dry) Oil in the Breather housing cup. All valves for their correct opening and closing sequence. Oil level in conservator tank. Oil in cooling system. Oil level in bushings. Release air, wherever necessary. Cooling accessories (Pump motors, Fan motors etc.) for direction and O/L setting. Buchholz, oil level indicator, pressure gauges, thermometer,Temp. indicators etc. for operation. Earthing of main tank M.Box T/C driving gear, diverter, Pump Fan motor etc. Neutral earthing. Earth Resistance of Electrodes. Earthing of bushing test tap. Check oil leakage for 24 hrs. Check Auxiliary circuit voltage (415 V). Calibration of OTI/WTI with hot oil. Check Working of WTI/RTD repeaters at control room. IR of core to earth. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 3.2.2 INSULATION RESISTANCE TEST Sl. Description No. 1. 2. 3. 4. Control wiring Tap Changer a) Motor b) Control Cooling system a) Motor Fan b) Motor pump c) Control wiring Main winding a) HV/E+LV b) IV/E+HV c) LV/E+HV+IV d) HV/IV e) IV/LV f) HV/LV Date Time in Hrs Megger used IR Temp. Value oC Remarks (Not less than 500 V megger) (Not less than 1000V megger) NOTE : (1) While checking these values no external line, lightning arrestors etc. should be in circuit. (2) Special care should always be taken while meggering the transformer winding to ensure that there is no leakage in the leads. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.3 OIL CHARACTERISTICS Take necessary precaution (regarding rinsing the bottle, cleaning hand, air bubble etc.) while withdrawing the samples (Please refer IS:6855). Each sample should be free of air bubbles and should not be tested when it is hot The sample should satisfy IS:1866. Sl. Oil Sample No. From Time & Condition Moisture Break Date Time Weather in PPM down Voltage in kV Resisti Tan- Rem vity at 90oC arks at 90oC (in ohm -cm) 1. Tank Top Sample Bottom Sample 2. Cooling system Top Sample Bottom Sample 3. OLTC Diverter (each phase) 3.2.4 1. 2. 3. 4. 3.2.5 TESTS ON CT Ratio Polarity Magnetising current IR value. ON LOAD TAP CHANGER Sl. Description No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Date Observation Remarks Visual Inspection of equipment. Hand operation on all taps. Complete wiring of the circuits. Limit Switch Over running device. Remote Panel wiring. Over load Device of Driving Motor. Local Operation (Electrical). Remote Operation (Electrical). Tap Position Indicator. Step by step contractor. Out of Step Relay. Note : While operating the mechanism on Electrical Control, check once again limit switches, step by step contractor, over running device etc. for their actual operation and ensure that they are functioning properly. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.6 OFF CIRCUIT TAP SWITCH Tap switch handle should not be left halfway and/or unlocked. 3.2.7 CONTINUITY TEST Continuity between line and neutral (for neutral end TC) or line to line (for line end TC) with multimeter on all taps and phases to be confirmed. 3.2.8 Winding MEASUREMENT OF WINDING RESISTANCE: Tap No. HV 1 Winding 2 Phase U Phase V Phase W Temp Remarks 3 4 5 6 7 8 9(a) 9(b) 9(c) 10 11 12 13 14 15 16 17 IV Winding LV Winding Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.9 VOLTAGE RATIO TEST Ratio on all taps is to be checked by hand operation only. This can be done any time, once the tap changer is completely erected. Start the tap changer from lowest tap and then go on increasing tap by tap while checking the value instead of starting from normal tap. Tap Nos. Voltage applied Voltage Measured Ratio obtained Remarks 1. 2. 3. 4. 5. 6. 7. 8. 9. (a) 9. (b) 9. (c) 10. 11. 12. 13. 14. 15. 16. 17. 3.2.10 a) Note: Voltage Applied Current measured U-V V-W U-W U phase V phase W phase Volts Volts Volts Remarks m Amps m Amps m Amps In case of single phase transformer, apply 230 V, 1 phase supply between line terminal and earth. b) Apply 3 phase 415 V on LV terminals and keep HV open. u-v v-w u-w Note: MAGNETISATION CURRENT Apply 3 phase 415 V on HV Terminals and keep LV open. volts volts volts u phase v phase w phase m Amps m Amps m Amps In case of single phase transformer apply 230 V, 1 phase between line and earth terminal. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.11 VECTOR GROUP Check the vector group of the transformer by connecting in a suitable manner. Vector group Diagram of connection Diagram as connected for test CONDITIONS TO BE PROVED 1. 2. 3. Remarks VOLTAGE MEASURED 1. 2. 3. 3.2.12 FINAL IR CHECKS The megger readings finally after the transformer is connected to the system Date ......................... Time ........................Temp ....................... Windings Megger used Value obtained in Mega ohms Remarks HV/E+LV IV/E+HV+LV LV/E+HV+IV HV/IV IV/LV HV/LV 3.2.13 OTHER TEST WTI Setting Alarm Trip Fan Start Fan Stop Pump Start Pump Stop Set for Proved OTI Setting Set for Proved Alarm Trip Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.2.14 PROTECTION AND ALARMS Prove the tripping of associated breakers by actual operation of the various devices and relays. UNDER NO CIRCUMSTANCES SHORTING OF ELECTRICAL CONNECTIONS SHOULD BE DONE. Sl.No. Device 1. 2. Set for Alarm Trip Proved Alarm Trip Remarks Buchholz Excessive Winding temperature Excessive Oil Temp. Oil flow failure Water flow failure Differential pressure (OFWF cooling system) Fan failure Low oil level (conservator tank) Pressure relief valve Differential relay Over current relay Earth fault (REF) Instt. Earth fault Inter trip, if any Trip free check. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 3.2.15 a) RECORD THE FOLLOWING AFTER CHARGING No load current at relay terminal U phase A V phase A CT Ratio W phase A b) Temperature (at the time of charging) o O.T.I. C o W.T.I. C o C Ambient c) Maximum temperature after 24 hours. C o Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.3 COMMISSIONING CHECKS REACTOR Customer W.O. No. Site Sl.No. Rating Voltage class Scope This schedule covers the tests to be done at site after reactor has been installed and dried out. 3.3.1 GENERAL Check the following : Sl.No. Description 1. 2. 3. 4. 5. 6. 7. 8. Breather Silicagel (Blue When Dry) Oil in the Breather Cup. All valves for their correct opening and closing sequence. Oil level in conservator tank. Oil in cooling system. Oil level in bushings. Release air, wherever necessary. Buchholz, oil level indicator, thermometer, temp. indicators etc. for operation. Earthing of main tank, M. Box. Neutral earthing. Earth Resistance of Electrodes. Earthing of bushing test tap. Check oil leakage for 24 hours. Check auxiliary circuit voltage (415 V). Calibration of OTI/WTI with hot oil. Check Working of WTI/RTD repeaters at control room. IR of core to earth., 9. 10. 11. 12. 13. 14. 15. 16. 17. 3.3.2 INSULATION RESISTANCE TEST Sl. Description No. 1. 2. a) Remarks Control Wiring Main Winding HV/E Date Time in hrs. Megger used IR Value Temp. Remarks 500 V >1000V Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Note: (i) While checking these values no external lines, lightning arresstors etc. should be in circuit. Special care should always be taken while meggering the reactor winding to ensure that there is no leakage in the leads. (ii) 3.3.3 OIL CHARACTERISTICS Take necessary precaution (regarding rinsing the bottle, cleaning hand, air bubble etc.) while-withdrawing the samples. Each sample should be free of air bubbles and should be tested when it is hot. The sample should satisfy IS:1866. SI. Oil Sample No. From 1. 2. Time & Condition Moisture Date Time Weather in PPM Break Resisti Tandown vity at at Voltage 90oC 90oC in kV (in ohmcm) Rem arks Tank Top Sample Bottom Sample Cooling system Top Sample Bottom Sample 3.3.4 1. 2. 3. 4. 3.3.5 TESTS ON CT Ratio Polarity Magnetising current IR value MEASUREMENT OF WINDING RESISTANCE Phase U Phase V Phase W Temp. Remarks Winding 3.3.6 a) CURRENT MEASUREMENT Apply 3 phase 415 volts on HV Terminals. Voltage Applied Current measured U-V Volts U Phase mA V-W Volts V Phase mA W-U Volts W Phase mA Remarks Note: In case of single phase reactors apply 230 V, 1 phase between line terminal and earth. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 3.3.7 FINAL CHECKS The megger readings finally after the reactor is connected to the system. Date Winding Time Megger used Temperature Value Obtained in megaohms Remarks HV/E 3.3.8 OTHER TEST WTI Setting Set for Proved OTI Setting Set for Proved Alarm Trip 3.3.9 PROTECTION AND ALARMS Prove the tripping of associated breakers by actual operation of the various devices and relays. Note: Under no circumstances shorting of electrical connections be done. Sl.No. Device 1. 2. Set for Alarm Trip Proved Alarm Trip Remarks Buchholz Excessive Winding Temperature Excessive Oil Temp. Oil Level (Low & Max.) Pressure Relief Valve. 3. 4. 5. 3.3.10 RECORD THE FOLLOWING AFTER CHARGING a) No load current at relay terminal U phase mA V phase mA W phase mA CT Ratio b) Temperature (at the time of charging) o O.T.I. C o W.T.I. C o Ambient C c) Maximum temperature after 24 hours. C o Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ¦ÉÉMÉ-4 +xÉÖ®úIÉhÉ B´ÉÆ {ÉÊ®úSÉɱÉxÉ SECTION-4 MAINTENANCE AND OPERATION Prepared By Samvet Lahari, Bhopal. Phone- 5277412 SECTION 4 4. MAINTENANCE AND OPERATION 4.1 SUPERVISION OF TRANSFORMER/REACTOR 4.1.1 GENERAL In order to avoid faults and disturbances, it is important that a careful and regular supervision and control of the reactor and its components is planned and carried out. The frequency and extent of such a supervision and control is dependent on climate, environment and service conditions etc. The directions for a certain transformer/reactor are therefore preferably based on experiences from comparable transformer/ reactor installations. A supervision and maintenance program according to schedule in ANNEXURE 4.1 is recommended. Spare transformers/reactors are supervised and maintained according to the same schedule as transformers/ reactors in service. 4.1.2 GENERAL MAINTENANCE Dirt/Dust The external transformer surfaces shall be inspected regularly and when required cleaned from dust, insects, leaves and other airborne dirt. Possible Leakage After energising of the transformer, a certain settling may appear in sealing joints. These should therefore be retightened according to schedule in ANNEXURE 4.1. This applies especially to sealing joints with plain gaskets that are not placed in grooves. Rust damages, touch-up painting A regular inspection of the external surface treatment of the reactor should be carried out. Possible rust damages are removed and the surface treatment restored to original state by means of primer and finish paints. 4.1.3 OIL PRESERVATION SYSTEM, MOISTURE ABSORPTION Transformer oil absorbs easily moisture from the surrounding air. The moisture absorption has been prevented by means of rubber sack in convservator which acts as a separating wall between the oil and the surrounding air. The moisture absorption is further prevented by a breather connected to the conservator. The active drying agent (silica gel) should be exchanged or regenerated when 2/3 of the agent has been red-coloured by absorbed moisture. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 The breather contains also an oil-seal that prevents spontaneous air circulation. This seal should be filled with oil to the level specified. 4.1.3.1 OIL LEVEL INDICATOR FOR OIL CONSERVATOR The Transformer oil conservator is provided with an oil-level indicator. At an oil temperature of 45oC, the conservator should be half filled. If the level exceeds the value full, oil must be drained off. If the value is low, oil must be filled in, Normal oil level should be at 35oC mark. 4.1.3.2 GAS-OPERATED RELAY (BUCHHOLZ RELAY) The use of gas-operated relay as protection for oil-immersed transformers is based on the fact that faults as flash over, short-circuit and local overheating normally result in gas- generation. The gas- bubbles gathering in the gasoperated relay affect a float- controlled contact which gives an alarm signal. 4.1.3.3 MOISTURE If the oil has been subjected to moist air, the moisture content and the electric strength of the oil shall be checked. 4.1.3.4 SLUDGE, ACID Normally the BHEL transformers have uninhibitated oil. Sometimes inhibited oil is used. The inhibitor works so that it breaks the chain reaction by which sludge and acid are produced. This retards the ageing process and extends the utilization time of the oil. If sludge is being produced in the oil, the oil changes colour and becomes darker and turbid. The sludge can be removed by means of filtering, but if the sludge formation has started, it will increase with time. The oil should therefore be exchanged if the neutralisation value according to IS:1866 exceeds 0.5 mg KOH/g or precipitable soluble sludge is produced. The oil exchange should preferably be carried out when the transformer is warm and the oil viscosity is low. The exchange should be as complete as possible, because old oil will affect the new one, speeding up the ageing. Oil which is not too much oxidized may in certain cases be regenerated, but this is economical only for large oil quantities. 4.1.3.5 OIL, MISCELLANEOUS For supplementary information about transformer oil, see clause 4.2 Supervision and control of oil. 4.1.4 TEMPERATURE SUPERVISION The service life of a transformer is highly dependent on the temperature prevailing in the core and windings under operation. It is thus important to keep the oil and winding temperatures under observation continuously. The temperatures should be read regularly and the measured values registered. These values will give guidance for judging the service life of the transformer, cooling system functions etc. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 4.1.4.1 OVERLOAD A Transformer can normally be overloaded at a low ambient temperature. However, the permissible overload must not be judged only with regard to the oil temperature. We must also consider that the temperature difference between winding and oil will increase with the load. Therefore, also the winding temperature must be supervised during overloading. For determination of the overload capacity for modern transformers refer IS:6600. If the temperature in a transformer shows a tendency of rising without a corresponding increase of the load, this may be caused by a reduction of the cooling ability of the cooling equipment (dirt, dust). The thermometer should also be checked in this case. 4.1.4.2 THERMOMETER FOR MEASUREMENT OF TOP-OIL TEMPERATURE The thermometer consists of a cylindrical sensing body with a flange, a capillary tube, and a thermometer housing with dial and contact-device. The measuring system is filled with a liquid, which changes its volume at temperature variations, and affects spring bellows. The movements of the bellows are transferred to the pointer and signal contacts via a link system. The thermometer is provided with two signal contacts of mercury switches. The contacts can be set independently of each other. For control and adjustment of the thermometer, see OTI leaflet. 4.1.4.3 WINDING-TEMPERATURE INDICATOR The thermometer system consists of a sensitive body with assembling details, a capillary tube and a thermometer housing, which contains a scale with an indicating pointer and a max. pointer, heating and adjusting resistor, as well as contact- device for four switches. For further information about function, control and adjustment of winding temperature indicator, see WTI Leaflet. 4.1.4.4 REMOTE CONTROL OF WINDING TEMPERATURE For remote control of winding temperature a resistance temperature device has been used with a heating element built into the same housing. The heating element is fed by the secondary current of a current transformer. For setting of the heating element there is a parallel connected adjusted resistor installed in the control cabinet. For further information about function and calibration, see RTD Leaflet. 4.1.4.5 RADIATORS The external cooling surfaces shall be inspected regularly and when required cleaned from dust, insects, leaves or other airborne dirt. This is especially important in case of fan cooling. The cleaning is suitably carried out by means of water flushing at high pressure. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Normally, no measures are necessary for keeping the internal cooling surfaces clean as long as the oil is in good condition. If, however, sludge formation has set in, the sludge may deposit on horizontal surfaces in radiators. In such a case, the radiator should be flushed internally with clean oil. If the sludge does not loosen, we can firstly flush with petrol etc. and then with oil. 4.1.4.6 CONTROL CABINET The operation of the control cabinet and devices normally included, are described in Vol. I. 4.1.4.7 BUSHINGS Bushing porcelains shall be cleaned from dust and dirt regularly. In areas where the air contains impurities as salt, cement dust, smoke or chemical substances, shorter intervals are required. See also the Instructions in the special information documents about bushings that are included in vol.I. 4.1.4.8 CONNECTIONS In order to avoid prohibited temperature rises in the electrical connections of the transformers/reactor, all screw-joints should be checked and re-tightened according to schedule enclosed. 4.1.4.9 ACCESSORIES Separate leaflet/instructions should be followed for various fittings (as applicable) for Fans, Pumps, Flow indicators, Pressure Gauges, Oil Gauge, Pressure reducing valve, OLTC, Off circuit tap switch, OFAF/OFWF Coolers etc. These leaflet are enclosed with Vol I. 4.1.5 MAINTENANCE SCHEDULE Maintenance schedule given at Annexure 4.1 should be followed. With proper maintenance as per this schedule normal life of Transformer or reactor can be expected. 4.1.6 IR TEMPERATURE RELATION It has always been the question from our customers as to how the IR value can be converted at different temperatures. We have drawn a curve (Fig. 4.1) for guidance of the operating staff on the basis of our experience. So that they can judge the IR Value at any temperature. This curve cannot be taken for absolute value but will serve as a good guide for conversions of IR values at different temperatures. A simple example is given as to how to calculate the value at different temperature. Suppose IR value of 70oC is 300 M Ohms and we want to convert at o 40 C, the curve will give you a factor K for difference in temperature i.e. (70oC-40oC)=30oC. K for 30oC temperature difference = 4.2 So the value at 40oC = 4.2x300 = 1260 M. Ohms. Value thus converted fairly tally with the actual Value when cooling the transformer. The factors are tabulated as below: Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Difference in temp. Factor K 4.2 10oC 1.65 20oC 2.6 30oC 4.2 40oC 6.6 50oC 10.5 SUPERVISION AND CONTROL OF OIL 4.2.1 GENERAL The oil in a reactor provides an electrically insulating and a cooling medium. The service reliability of an oil-immersed transformer/reactor is therefore mainly, depending on the oil quality. In service, oil is subjected or normal deterioration due to the conditions of use mainly due to air, water and solid particles/sediment. 4.2.2 SCHEDULE The oil should be maintained as per the guidelines of IS:1866. Periodicity of test and permissible limits for important parameters of oil - electric strength, water content, resistivity, tan-delta, neutralization value, sediment and precipitable sludge, flash point and interfacial tension are given in Annexure 4.2. Health of reactors can be effectively monitored by Dissolved Gas Analysis (DGA) technique described in detail in IS:9434 and IS:10593. This technique helps in detection of incipient faults in reactors. 4.3 TROUBLE SHOOTING General measures for trouble shooting are described in this section. 4.3.1 Items to be informed to BHEL in case of trouble. Followings are items to be informed to BHEL. 1. Transformer or Reactor specifications Capacity Serial number & work order No. Year of manufacture. 2. Load current (A) or load (kW) 3. Operating tap position (In case of Transformer) 4. Conditions at time of trouble. a) Date, time b) Trouble phenomena c) Checked items and results 4.3.2 Transformer troubles and check items. Troubles, their possible causes and items to be checked are given in Table 4.1 & 4.2. 4.3.3 Detective devices and their functions. Refer to table 4.3 4.3.4 Check items and judging standard Refer to table 4.4. 4.3.5 Detection method of oil or gas leaks. Refer to table 4.5. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Table 4.3: Detective devices and their functions No. Detective device Description 1. Buchholz relay (1st stage) This relay detects the gas evolution due to internal trouble and gives alarm, and is suited to the detection of minor or slowly developing faults. The nature of the detected fault can be judged to an extent by analyzing the gas and oil. In case of nitrogen gas sealed transformer, part of dissolved nitrogen gas comes out due to the sudden temperature drop, which sometimes results in the actuation of this relay. 2. Buchholz relay (2nd stage) When a major fault suddenly takes place inside the transformer, oil flows suddenly from the transformer tank to the conservator. The second stage of Buchholz relay is actuated by this oil flow. If the second stage of the relay functions independently, check the air breather, nitrogen gas sealing device etc. If it functions combinedly with the over current relay etc. it is suspected that a serious internal defect is existent. In such a case take all tentative measures and contact BHEL immediately. 3. Pressure relief device When the internal pressure of the transformer rises above the set value, the pressure relief device functions. It also functions, though occasionally by the choking of the air breather. The self- excited pressure relief plate is subject to brittleness caused by secular change. Comprehensive judgment based on the inspection of other protective relays is the key to determining whether the function of this device is an erroneous operation or a normal operation caused by internal defect. 4. Differential relay This relay detects the internal defect by comparing the input current and the output current of the transformer. If it functions combinedly with other protective devices, it is indicative, in almost all cases, of an internal fault. Note that this relay sometimes operates due to inrush current when the transformer is energized, and this is of course not an internal fault. 5. Dial thermo meter alarm contact This thermometer gives alarm when the temperature rises beyond the preset value. Insufficient cooling effect of cooling equipment due to contamination of cooling fins, Stoppage of oil pumps, fans and so forth is one of the reasons that operates this device. 6. Overcurrent relay, ground fault relay These are intended for detecting faults in the electric system connected with the transformer. A fault in the transformer results in the function of these relays, which is always accompanied by the actuation of protective devices of the transformer. Detection of the fault in the electric system should therefore be made on the basis of a comprehensive judgment of these functions. 7. Voltmeter ammeter If a sudden change in voltage or current is noted when no abnormalities are detected in the electric system, or an abnormal unbalance of voltage or current is noted between phases, investigate the cause. 8. Human senses Note that human senses also play an important role in fault detection. Following are the points to be checked by your senses. 1) Discolouration or odour of insulation oil (blackening or stink). If pieces of insulating materials or copper particles are found in the oil, it is suspected that an internal defect has developed. 2) Abnormal vibration or sound. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Table 4.4: Check and refer standards No. Check Point Description Judging standard 1. Measurement of insulation resistance Grounding fault can be detected by this measurement, though to some extent. The measurement must be proceeded after disconnecting the transformer from lines and cleaning of bushing surfaces. Judgment to be made by comparison with values obtained by periodical inspection. 2. Measurement of winding resistance This is a primary means to be employed for detecting the fault of windings. The resistance should preferably be measured independently by the D.C. drop of potential method. Judgment to be made by comparison with the factory test report. 3. Measurement of voltage ratio This can be conducted by applying a voltage of about 200V which can be readily obtained at job-site. Accurate measurement at job site entails some difficulties due to source voltage variation and errors of instruments. In case of 3 phase transformers, it is essential to measure the ratio phase by phase and check the variation of the ratio between phases. Judgment to be made by comparison with the factory test report. This measurement is very useful to detect fault in windings and/or cores. Local short- circuit in windings or cores often causes an increase in the exciting current. The test can be made by applying a low voltage (200-400 volts) to a winding. 1 Measure dielectric strength and check for carbon sludge, offensive odour and discoloration. Judgment to be made with reference to Annexure 4.1 & 4.2. 4. Measurement of exciting current 2 Comparison of the measured values with previously obtained ones. Significant difference in value among phases. 5. Checking of insulation oil 6. Measurement of dielectric loss factor, tan 7. Analysis of gas accumulated in Buchholz relay When gas is accumulated in the Buchholz relay,its composition must be clarified by the gas chromatograph analyzer to check for the possible internal defect. Contact BHEL 8. Analysis of dissolved gas in oil Existence of internal defect can be judged, though to a limited degree, by sampling and analyzing oil by a gas chromatograph. (Refer 4.3.2). Contact BHEL Judgment to be made by comparison with values obtained by periodical inspection. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Table 4.5 Method for detecting oil or nitrogen leaks Leak Measures Description Oil leak Clean the suspected leak part with thinner or gasoline apply chalk powder to it. The leak part will present itself as a soiled spot. The following are susceptible to leakage. (1) Gasketed joints. (2) Welded parts. Nitrogen leak (in case of Nitrogen sealed system) Step up Nitrogen gas pressure to 0.17 kg/cm2 The following are susceptible to leakage (1) Accessories for pressure relief (2) Flanges (3) Welded parts 4.3.6 GAS ANALYSIS ON TRANSFORMER OIL Incipient faults in oil filled transformer are usually the result of electrical or thermal excess stress of either the transformer oil or insulating materials. It is known that such excessive stresses produce a mixture of gases characteristic of which give an indication of the type of faults, and materials associated with the faults. It is recommended that analysis of dissolved gases in transformer oil by gas chromatographic equipment is made, the time of commissioning and then after an interval of one year for transformers of 145 kV class and above. 4.3.7 ANALYSIS METHOD 4.3.7.1 SAMPLING OF OIL FROM TRANSFORMERS Oil in transformers can be sampled through drain or sampling valve near bottom of the tank. Special care shall be taken not to introduce air, foreign matter, or dirty oil into sampling container. For this purpose, first 0.5-1.0 litre of oil from the transformer shall be over-flown through the oil container. Shape of the sampling container may be that of shown in Fig. 4.2 and sampling method shall be in accordance with Fig. 4.3. See also IS:9497 Sampled oil shall not be exposed to air before analysis. 4.3.7.2 GAS ANALYSIS Gases to be analysed and criteria for the gases found in transformer oil are tabulated in table 4.6. 4.3.8 ASSESING THE TEST RESULTS Test results on gas contents in oil by some typical faults in transformer active part models are shown in table 4.7. Table 4.6 and table 4.7 may by referred to evaluate transformer condition. To analyse DGA test results, flow chart given at Appendix A of IS:10593 should be followed. Standard values may be taken from CBIP Technical report no. 62 of April 88 titled "Guide for testing of Transformer by Sampling and analysis of free and dissolved gases" Ratio technique of IS:10593 should be used to know the nature of fault. IS:9434 and IS:10593 have been adopted from IEC pub 567 and IEC pub 599. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Table 4.6 Gases to be analysed and criteria 1. Gases to be analysed normally O2, N2, H2, Co, Co2, CH4 2. Gases to estimate abnormality H2, CH4, C2H2, C2H4, C2H6 3. Gases to estimate deterioration Co, Co2, CH4 Table 4.7 Gas content in oil by faults Sl. Type of faults Decomposable gases in transformer oil 1. Overheat of oil CH4, C2H4, H2, (C2H6, C2H2,C3H6 C3H8) 2. Arcing in oil H2, C2H2, (CH4, C2H4) 3. Overheat of solid insulating materials CO, CO2, (H2, C2H4) 4. Overheat of oil and paper combination CH4, C2H4, CO, CO2, H2 5. Arcing of oil and paper combination ( 4.4 (i) H2, C2H2, CO, CO2, (C2H4) ) shows gas contents which appear rarely. PARALLEL OPERATION If it is desired to parallel a transformer which is not identical in design with BHEL transformer, it is preferable to refer the matter to BHEL for advice. (ii) The voltage ratings/ratios and impedance values at all taps should match for the two transformers that are to be paralleled. Only certain combinations of vector groups are capable of being paralleled. The table 4.8 below indicates the more common permissible combinations. Table 4.8 TRANSFORMER (B) H.V. Delta Star Delta Star L.V. Star Delta Delta Star Yes Yes No No Yes Yes No No No No Yes Yes No No Yes Yes H.V./L.V. Delta/Star TRANSFORMER (A) Star/Delta Delta/Delta Star/Star Prepared By Samvet Lahari, Bhopal. Phone- 5277412 (iii) Reference to the connection diagrams of two transformers should indicate the terminals to be paralleled. (iv) The reversal of two leads on either side of a three-phase transformer will reverse the polarity changing them in sequence (e.g. form UVW to VWU or WUV) will swing the vectors through 120. (v) Phase sequence and polarity can be checked by energising both transformers on the primary side before paralleling and measuring the open-circuit voltage appearing across each pair of terminals which will ultimately be paralleled. (vi) IS:2026 and IS:10561 may also be referred. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 4.1 MAINTENANCE SCHEDULE SI Items to be inspected Inspection notes HOURLY 1. 2. 3. 4. Ambient temperature Winding temperature Oil temperature Load amps/Load voltage - - Check that temperature rise is reasonable. Shutdown the transformer and investigate, if either is persistently higher than normal. Check against rated figures An improper tap position can cause excessive core loss. Voltage and tap position should be corrected. DAILY 1. 2. 3. 4. Oil level in transformer conservator Oil level in tap changer diverter switch. Oil level in bushings. Check oil level from oil gauge Top up, if found low. Check oil level from the gauge glass. Top up, if found low. Check the oil level from gauge glass/gauge. Top up, if found low. Pipework and accessories for leakages Inspect the transformer for leakages. If leakages are observed tighten evenly the gasket joints. Replace O ring or washer suitably. Replace gasket if needed. MONTHLY 1. 2. Buchholz Relay Dehydrating breather Leakages of water into cooler. Check oil level Check colour of silicagel. 1. Bushings 2. Transformer oil and tap changer oil Cooler fan, bearing and controls, pumps. Examine for dirt deposition and tightness of oil filling plugs. Examine for cracks in porcelain.Clean and tighten plugs. Check for di-electric strength and moisture content. Check contacts, manual control and interlocks. 3. 3. Action required - Release collected gas/air Reactivate/replace with new charge, if found pink Investigate and rectify after taking shutdown. QUARTERLY Cracked porcelain should be rectified/replaced. Take suitable action to restore quality of oil. Lubricate the fan bearings. Replace worn out contacts and other parts. Clean/ adjust controls and interlocks. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 4. On load tap changer Examine contacts, check step by step mechanism operation, end position limit switches and brakes. Also check oil in driving gear mechanism. Replace all worn out and burnt contacts. Set limit switches in position. Clean/ replace brake shoe lining. Lubricate all bearing and coupling points suitably. (Refer Separate leaflet.) 5. Dehydrating breather Check oil level in the cup and ensure air passages are free. Top up, if found low. Clean air passages. YEARLY 1. Transformer oil Check for characteristics in line with IS:1866 Filter/replace as required to restore the quality. 2. Cable box Check for proper scaling of compound filling holes. Check for cracks in the compound (if used). Replace sealing washer, if found damaged. 3. Alarm and protection circuits. Check all protections and alarm circuits by actual external initiation. Check operation of relays and their sensitivity. Replace burnt out fuses Adjust the setting and check wiring circuits. Adjust relay setting, if needed. Replace damaged relays. 4. OTI & WTI pockets Check oil in the WTI and OTI pockets. Replenish, if required 5. Earth strip Check earthing resistance 6. Packing gaskets of fans Inspect the condition of packing gaskets. Take suitable action, if resistance is noted high. Replace if worn out or resilience lost. 7. Fan motors Check IR value of motor winding after rainy season. Noise & vibration of fans. Dry out, if found low, check balancing of fans. 8. Tank and accessories Check painting and surface finish. Mechanical inspection of all accessories. Touch up/repaint, if required Replace any component found damaged. 9. Gasket joints 10. Divert servicing 11. Diverter switch of on-load tap changer Check the tightness of bolts One year commissioning after Check the contacts for burning or pitting marks. Tighten evenly all loose bolts, nuts, locking etc. Draw out diverter, clean, tighten contacts. Recondition/replace if required. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 12. Diverter switch oil Filter oil irrespective of strength. Replenish with new oil,if oil is too much contaminated. 13. Tank cover and conservator Dirt, Dust, Surface Clean touch-up painting. 14. Bushing top connectors. Check contact joints Retighten. 1. Oil conservator General Inspection including checking the operation of gauges on it. Check heathiness of air cell. Clean, if required. Ensure proper functioning of indicator/Replace if punctured. 2. Transformer oil Examine values as per IS:1866 Filter oil if required. 3. Buchholz relay Mechanical inspection of buchholz Set floats, if required. TWO YEARLY 7-10 YEARLY 1. Transformer and tap changer Assembly Overall internal inspection including lifting of core and coil assembly Tighten all clamping arrangement, loose cleatings etc. Tighten all nuts and bolts and check locking arrangements and fasteners. Wash core and coil with dry transformer oil. NOTES: 1. In addition to the above instructions, reference should be made to IS:10028 Code of practice for selection installation and maintenance of transformer 2. Reference of IS:1866 "Code of practice for Maintenance and Supervision of Mineral insulating oil in equipments'' should be made for maintenance of oil while transformer is in service. Table 1&2 of IS:1866 are given at annexure 4.2 & 4.3 for ready reference. 3. The inspection schedule specified for longer periods automatically includes those specified for shorter period. 4. All maintenance test results and observations should be specifically recorded. 5. Where matter given in the inspection book differs from that given in standards referred to, the transformer user should follow the instruction book. 6. In case of anything abnormal occuring during service, advice from BHEL should be obtained giving them complete particulars as to the nature and extent of occurrence, together with the name plate particulars in order to assist identification of the transformer. 7. As efforts are being constantly made to improve designs and service, the transformer supplied may differ in minor details from data given herein. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 4.2 APPLICATION AND INTERPRETATION OF TESTS ON OIL IN TRANSFORMERS AND REACTORS (INCLUDING SELECTOR TANKS OF ON-LOAD TAP CHANGERS (CLAUSE 5.1 (a), 5.2, 6.0 and 7.1) Sl.No CHARACTERISTIC (1) (2) (i) Electric strength (breakdown voltage-kV) EQUIPMENT VOLTAGE TEST METHOD (REF TO IEC/ISO TEST VENUE F=FIELD OR APPENDIX) L=LABORATARY SUGGESTED INITIAL PERIODICITY OF TESTS (3) (4) (5) 145 kV and above IS:6792-1972* (average of 6 brealdowns on one cell filling with 2.5 mm gap spacing) F/L 72 kV and less than 145 kV Below 72.5 kV (ii) water content (ppm) 145 kV and above PERMISSIBLE LIMIT SATISFACTORY FOR USE ACTION IF OUTSIDE PERMISSIBILE LIMIT SEE ALSO (6) (7) (8) After filling or re-filling prior to energizing, then after three months and after one year 50 kV (Min) Recondition or alternatively If more econmic or other tests dictate, replace oil. 40 kV (Min) 30 kV (Min) IS:335-1983 L After filling 25 PPM or re-filling (Max) prior to energizing, 35 PPM 3 months and after one year Recondition oil or alternatively If more econmic or other tests dictate, replace oil. Below 145 kV (iii) Specific resistance (resistivity ohm-cm) at 900C (see Note 9) All voltages IS:6103-1971 L After filling or re-filling prior to energizing, 3 months and after 2 years 0.1X1012 ohm-cm (Min) at 900C Recondition if the value of the DDF permits, reclaim or replace if not. (iv) Dielectric dissipation factor (tan δ) at 900C 145 kV and above Below 145 kV IS:6262-1971 L After filling or re-filling prior to energizing, then after 2 years 0.2 (Max) Reclaim or replace oil (limit to be adopted depends on the type of equipment and instructions from the manufacturer). (v) Neutralisation value (total acidity (see Note 10) All voltage IS:1448 (P:2) 1967 F or L do 0.5 mg KOH/g (Max) Reclaim or replace oil (vi) Sediment and/ or precipitable sludge All voltage Appendix A L do No sediment or precipltable sludge should Recondition oil if sediment is detected be detectable 1.0 (Max) alternatively if more economic or other test dictate replace oil. Reclaim or replace oil if precipitable sludge is detected. (vii) Flash point (see Note 11) All voltage IS:1448 (P:21) 1970 L do Decrease in the flash point 15oC (Max) of the inital value minimum value 125oC Reclaim or replace oil after knowing causes. (viii) Interfacial tension at 27oC All voltage IS:6104-1971 L do 0.018 N./m (Min) Reclaim or replace oil. (ix) Dissolved gas analysis 145 kV and above IS:9434-1979 L After filling or re-filling prior to energizing, 3 months and after one year. IS:10593 1983 Reclaim or replace oil. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Note 1 Note 2 The voltages indicated in col 3 are highest system voltages. The full application of these recommendations to small transformers upto 1 MVA or below 36 kV will be technically necessary only in cases where high reliability is required. It will normally be uneconomic. In most cases, it could be limited to the simpler field tests and the periodicity of tests will be determined with relation to the reliability required. Inspection of oil in pole- mounted transformers is assumed to be uneconomic. Note 3 Characteristics are normally well above the permissible limits given in col 7 at the time of test of transformer in the manufacturers works. However, no separate limits have been fixed for this stage. Note 4 Higher limits may be required for electric strength and lower limits for water content prior to testing in the factory and prior to energizing the transformer. Special instructions given by the manufacturer may be followed. Note 5 Suggested initial periodicity of tests have been given in col. 6. Subsequent intervals may vary depending on previous test results (progress of ageing) and on changed service conditions. Note 6 Instructions of equipment manufacturers should be taken into account in adoption of the recommendation of this table. Note 7 For application and interpretation of test in diverter tanks of on-load tap changers, guidance shall be taken from the manufacturer. Note 8 Alternatively an indication of the presence and effect of water content can be obtained from a resistivity comparison at 27oC and 90oC (see 6.4.1.2). Note 9 Water content and acidity influence the values of the specific resistance. The limit is indicative only and when value falls below this limit the cause should be ascertained by other tests. Note 10 Perform test more frequently when value exceeds 0.3 mg KOH/g. For transformers subject to test (ii), method(s) it will be necessary to test more frequently to establish when neutralization value (total acidity) exceeds 0.1 mg KOH/g. Note 11 This test may also be required when an unusual odour is noted or when an internal fault has occured. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 ANNEXURE 4.3 GUIDELINES FOR THE CHARACTERISTICS OF OIL TO BE OBTAINED BEFORE ENERGIZING NEW TRANSFORMERS USING NEW INSULATING OILS ACCORDING TO IS:335-1983 SL. NO. CHARACTERISTIC EQUIPMENT VOLTAGE TEST METHOD (REF TO IS:OR APPENDIX) PERMISSIBLE LIMIT SATISFACTORY FOR USE (1) (1) (2) Electric strength (breakdown voltage kV) (3) (4) Below 72.5 kV (5) IS:6792-1972 40 kV (rms) min 72.5 kV and less than 145 kV 50 kv (rms) min 145 kV above 60 kV (rms) min and (ii) Specific resistance (resistivity ohmcm at 90oC) All voltages IS:6103-1971 1X10 12 (min) (iii) Dielectric dissipation factor (tanδ) at 90oC Max. All voltages IS:6262-1971 0.05 (iv) Water content, ppm Max. Below 72.5 kV IS:335-1983 25 ppm 72.5 kV and less than 72.5 kV 20 ppm 145 kV above 15 ppm (v) Interfacial tension at 27oC (Min) N/m All voltages (vi) Dissolved gas content 145 kV above and IS:6104-1971 and ohm-cm 0.030 (Under Consideration) Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 Prepared By Samvet Lahari, Bhopal. Phone- 5277412 4.5 DOS AND DONTS 4.5.1 DONTS FOR POWER TRANSFORMER/REACTOR 1. Do not energise without thorough investigation of the transformer/reactor, whenever any alarm of protection has operated. 2. Do not re-energise the transformer/reactor, unless the Buchholz gas is analysed. 3. Do not re-energise the transformer/reactor without conducting all pre-commissioning checks. The results must be comparable with results at works. 4. Do not handle the off-circuit tap switch when the transformer is energised. 5. Do not energise the transformer, unless the off-circuit tap switch handle is in locked position. 6. Do not leave-off circuit tap switch handle unlocked. 7. Do not leave tertiary terminals unprotected outside the tank, connect them to tertiary lightning arrestors protection scheme, when connected to load. 8. Do not allow WTI/OTI temperature to exceed 55oC during dryout of transformer, and filter machine temperature beyond 60oC. 9. Do not parallel transformers which do not fulfil the condition given in clause 4.4. 10. Do not use low capacity lifting jacks on transformer/reactor for jacking. 11. Do not move the transformer/reactor with bushings mounted. 12. Do not overload the transformer other than the specified limits as per IS:6600. 13. Do not change the settings of WTI and OTI alarm and trip frequently. The setting should be done as per the site condition. 14. Do not leave red pointer behind the black pointer in OTI and WTI. 15. Do not leave any connection loose. 16. Do not meddle with the protection circuits. 17. Do not allow conservator oil level to fall below 1/4 level. 18. Do not allow oil level to fall in the bushings, they must immediately to be topped up. 19. Do not leave marshalling box doors open, they must be locked. 20. Do not switch off the heater in marshalling box except to be periodically cleaned. 21. Do not allow dirt and deposits on bushings, they should be periodically cleaned. 22. Do not allow unauthorised entry near the transformer/reactor. 23. Do not leave ladder unlocked, when the transformer/reactor is ON in service, in case it is provided. 24. Do not change the sequence of valve opening for taking standby pump and motor into circuit. 25. Do not switch on water pump unless oil pump is switched on. 26. Do not allow water pressure more than oil pressure in differential pressure gauge. 27. Do not mix the oil, unless it conforms fully to IS:335. 28. Do not allow inferior oil to continue in transformer/reactor. The oil should be immediately processed and to be used only when BDV/ppm conforms to IS:1866. 29. Do not continue with pink silicagel, this should immediately be changed or regenerated. 30. Do not leave secondary terminal of an unloaded CT open. 31. Do not store transformer/reactor for long after reaching site. It must be erected and commissioned at the earliest. 32. Do not keep the transformer/reactor gas filled at site for a longer period. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 4.5.2 DOS FOR POWER TRANSFORMER/REACTOR 1. Check and thoroughly investigate the transformer/reactor whenever any alarm or protection operated. 2. Check air cell in conservator. 3. Attend the leakages on the bushing immediately. 4. Examine the bushings for dirt deposits and coats, and clean them periodically. 5. Check the oil in transformer and OLTC for di-electric strength and moisture content and take suitable action for restoring the quality. 6. Check the oil level in oil cup and ensure air passages are free in the breather. If oil is less, make up the oil. 7. Check the oil for acidity and sludge as per IS:1866. 8. If inspection covers are opened or any gasket joint is to be tightened, then tighten the bolts evenly to avoid uneven pressure. 9. Check and clean the relay and alarm contacts. Check also their operation, and accuracy and if required change the setting. 10. Check the protection circuits periodically. 11. Check the pointers of all gauges for their free movement. 12. Clean the oil conservator thoroughly before erecting. 13. Check the buchholz relay and readjust the floats, switches etc. 14. Inspect the painting and if necessary retouching should be done. 15. Check the OTI and WTI pockets and replenish the oil, if required. 16. Remove the air through vent plug of the diverter switch before you energise the transformer. 17. Check the oil level in the diverter switch and if found less, top up with fresh oil conforming to IS:335. 18. Check the gear box oil level, if less top up with specified oil. 19. Examine and replace the burnt or worn out contacts as per Annexure 4.1 of Maintenance Schedule. 20. Check all bearings and operating mechanism and lubricate them as per schedule. 21. Open the equalising valve between tank and OLTC, wherever provided at the time of filling the oil in the tank. 22. Connect gas cylinder with automatic regulator if transformer is to be stored for long, in order to maintain positive pressure. 23. Fill the oil in the transformer/reactor at the earliest opportunity at site and follow storage instructions. 24. Check the door seals of marshalling Box. Change the rubber lining if required. 25. Equalise the diverter compartment of the OLTC by connecting equalising pipe between flange joints provided on the tap changer head. Prepared By Samvet Lahari, Bhopal. Phone- 5277412 4.6 DISPOSAL The items to be disposed off are mineral oil, silicagel, gasket and other insulating material. For disposal of these items, following procedure is recommended. 4.6.1 INSULATING OIL : The transformer oil is mineral Hydro Carbon (Petroleum) oil. No special risks are involved in the handling and use of transformer oil. Howerver, attention is drawn to the need for personnel hygiene i.e washing of skin & clothing, which has come in contact with oil by personnel dealing with these products. Hands in such cases should be washed carefully before eating and drinking and contaminated clothing should be changed. Also inhalation of fumes or vapours should be avoided. When used oil has to be disposed off, certain precautions are necessary to avoid risk of environmental pollution such as large spillage and leakage from the containers, which may otherwise result into destruction of greenary, water birds, fishes. Normally, non contaminated oil free of PCB (Poly Chlorinated Biphenyls) can be destructed by burning or sent to local authorities for asphalt production. However contaminated oil containing PCB shall be filled in drums and sent to local authorities for disposal. 4.6.2 SILICAGEL : When silicagel can not be regenerated and to be disposed off, it can be dumped in a pit and covered with earth. 4.6.3 GASKET AND OTHER INSULATING MATERIAL : Crok Gaskets & Nitrile Rubber Gaskets can be disposed off by burning in a place separately marked and prepared for the purpose. In case these can not be burnt, these can be dumped in a pit and covered with earth. Prepared By Samvet Lahari, Bhopal. Phone- 5277412