In DC traction systems, impermissible touch voltages may occur between the return circuit and the structure earth due to operational and short-circuit currents. In this case, a voltage-limiting device must be used between the return circuit and the structure earth in accordance with IEC 62128-1 / EN 50122-1. The Sitras® SCD reduces excessively high voltages by reliably short-circuiting the return circuit and structure earth temporarily. Furthermore, the formation of stray currents is minimized by automatic opening of the short-circuiting device. Features Fulfills all the criteria according to IEC 62128-1 / EN 50122-1; is also type-tested according to IEC 61992-6 / EN 50123-6 Maximum protection for personnel and equipment due to rapid response time Low maintenance requirement thanks to the use of a hybrid switching element which eliminates the need for maintenance-intensive voltage fuses High functionality and ease of use due to programmable controller with display and keypad Earthquake tested versions available Electrical data Steel cabinet Plastic housing Maximum system voltage [V] 3,000 3,000 Rated current [A] 800 400 Rated short-time withstand current 1 s [kA] 5 5 Rated short-time withstand current 10 ms* (peak value sinusoidal half-wave) [kA] 36 / 50 36 / 50 [switching operations] 1.5 x 106 1.5 x 106 [switching operations/h] 120 120 Steel cabinet Plastic housing Mechanical lifespan Operating frequency Mechanical data Dimensions (H x W x D)* [mm] Color* Degree of protection Weight [kg] 1,800x600x500 1,000x1,000x450 RAL 7047 RAL 7032 IP40 IP55 150...170 120...140 * other values on request Sitras SCD – Short-circuiting device Voltage-limiting device for DC traction power supply Product Information / Version 2.1.2 www.siemens.com/mobility Short-circuiting device Sitras SCD U t Hybrid switching element Return circuit, rail Equipotential bonding busbar Earth, structure earth Contact resistance between rail and structure earth Block diagram Sitras SCD Application Protection against personal injury: Impermissible touch voltages are prevented Monitoring of the potential of the return circuit: Earth faults in the contact line are detected, thus enabling them to be cleared by feeder substations Protection of installation: Overvoltages in the installation, e.g. due to lightning, are prevented Design/main components Hybrid switching element, consisting of DC contactor and thyristor instantaneous trip Measuring circuits for voltage (redundant) and current Programmable controller, optionally with Profibus interface Function In its basic state, the main contact of the DC contactor is open and the thyristor instantaneous trip is not conductive. The voltage between the return circuit and the equipotential bonding busbar is measured and displayed and the voltage over time evaluated. If one of the limits stored in the programmable controller is exceeded, the DC contactor closes. The limits are stored in the form of voltage-time characteristic curves. For AC and DC voltages, there are characteristic curves which can be parameterized differently. For the workshop area, it is possible to change over to an additional, separate characteristic curve. In the short-time range, voltage evaluation takes place in parallel as control by the programmable controller in a hardware circuit which directly triggers the thyristor instantaneous trip. The flow of current is detected by a programmable controller and the DC contactor is then switched. The Sitras SCD opens automatically when the set closing time expires, the current is not critical and a blocking condition does not exist. Blocking If the number of trips within a specific time is unusually high, opening of the DC contact is blocked and the Sitras SCD remains in a state that ensures the safety of persons. The same applies if there is a very high current for a long time. All the values can be parameterized. Blocking can be acknowledged locally or via a remote control link and thus cancelled. Control voltage failure The Sitras SCD operates on the closedcircuit principle. This ensures that even if the control voltage fails, the return circuit and the equipotential bonding busbar are automatically short-circuited and that the system is safe for persons. After the control voltage has been connected, the Sitras SCD returns to the state it was in before failure of the control voltage. All the states of the Sitras SCD can be signaled remotely. Siemens AG Industry Sector Mobility Division Electrification P.O. Box 32 40 91050 Erlangen Germany electrification.mobility@siemens.com www.siemens.com/mobility/ electrification www.siemens.com Version 2.1.2 / No. A6Z08100028228 The information in this document contains general descriptions of the technical options available, which do not always have to be present in individual cases. If not stated otherwise, we reserve the right to include modifications, especially regarding the stated values and dimensions.
