In the case of railways wich are operated with direct current, the rail is used as a return conductor for the traction current. The rail is insulated from the ground, since stray currents that otherwise may occur cause corrosion on buildings and systems.
The return current flowing through the rail leads to a potential difference to earth due to the electrical resistance of the rail. This potential difference can be tapped as a voltage between the rail or the vehicle and buildings or the earth. This voltage is potentially dangerous to people. Therefore, according to DIN EN 50122, it is prescribed to reduce these voltages from a defined threshold value. This happens via a temporary short circuit between the rails and the surrounding earth.
The WITT EscS 7 is an automatically resetting earthing short-circuiter for the protection of people and systems. It is the only product available on the market that meets the latest requirements of DIN EN 50122-1 and DIN EN 50122-3. This means that not only direct and alternating voltages, but also the superimposition of these two types of voltage between return conductor and earth are monitored. The combination of anti-parallel arranged thyristors and a power contactor guarantees a short switching time as well as a high current carrying capacity. This earthing short-circuiter has a particularly compact design.
The WITT EscS 7 is approved by the Federal Railway Authority (ID no .: 3343340/0/016).
If the entered voltage curve is exceeded, the earthing short-circuiter starts up, i.e. when the switch-on criteria are met, the thyristors are ignited and the contactor switched at the same time. The thyristors switch in a few milliseconds; the contactor has a closing time of approx. 60 ms. When the thyristors fire, the voltage collapses to a few volts. The thyristors remain ignited until the closing of the contactor has been recognized based on the position of the auxiliary contacts of the contactor. The thyristors are then deleted. The contactor then takes over the load.
The properties described under the tab “Technical data” also contain possible options that we offer for the product. If you are interested, please contact us.