On DC railways, the immediate connection of the return conductors to the ground has to be prevented because hazardous stray currents may occur. Stray currents could damage buildings, bridges and other metallic (electrically conducting) facilities or parts of facilities by corrosion. Danger also emerges from occurrence of impermissibly high contact voltages. One of the measures to protect humans from impermissible contact voltages is the temporary short-circuit of the various grounding systems according to DIN EN 50122.
The VL is a self-resetting earth arrestor according to DIN EN 50122. The product is parameterisable. The monitoring of the DC- and AC – voltage differences is carried out between the return conductor and ground. The combination of anti-parallel arranged thyristors and a power contactor guarantees a low switching time as well as a high current load capacity.
When the entered voltage curve for DC or ACis exceeded the earth arrestor responds, meaning after the turn on criteria are fulfilled the thyristors are triggered and the power contactor is switched simultaneously. The thyristors have a switching time of a couple of milliseconds and the power contactor has a closing time of approx. 150 ms. By triggering the thyristors the voltage drops down to only a few volts. The thyristors stay triggered until the helping contacts of the power contactor detect its closure. Afterwards the thyristors are stopped the power contactor takes over the load.
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