Voltage limiting device HVL consists of the parallel connection of a metal-oxide (MO) surge arrester with no spark gaps and two anti-parallel connected thyristors. Transient surges caused by lightning and switching operations in the system are limited by the MO arrester. If surges occur for a longer period of time (milliseconds to hours) due to faults in the system or for operational reasons, the thyristors fire to limit touch voltages. As soon as a zero-current transition occurs, the thyristors cut off the current flow and the original condition is restored. The whole device is molded in silicone, designed and tested according to EN 50122-1 (IEC 62128-1), EN 50123-5 (IEC 61992-5), EN 50526-1 (IEC 62848-1).
Voltage limiting devices are used to prevent impermissible touch voltages in DC traction systems in normal operations and in fault conditions by bonding the return circuit of a DC railway system to the earthing system or to the exposed conductive parts.
Voltage limiting devices are available for nominal triggering voltage 60 V and 120 V.