The device monitors the insulation between return conductor and earth in direct current railways.
The device measures the voltage between a building and a reference electrode in the ground.
If the protection against voltage breakdown (SDS for short) is short-circuited, it learns the state of “reverse currents flow through the surrounding soil”.
In this state, the voltage increases significantly between the earth and the structure, as part of the return current flows through the earth.
This state is recognized again when the structure and return line are short-circuited. This means that every change that can be traced back to an earth fault is reliably detected.
Insulation faults between the return conductor and the structure are automatically detected and reported. This measure, combined with the elimination of the fault, can avoid corrosion damage caused by the permanent flow of current.