Family of Voltage-Limiting Devices (VLD):
Voltage-Limiting Device TZD-1NR
Voltage-Limiting Device TZD-1NR/T

TZD-1NR is the Voltage Limiting Device (VLD) type F. It may also work as type O in specified current range. According to EN-50562-2 it belongs to class 2.2 of VLD.
Primarily, it is intended for use in open group bonding system of 3kV railway traction, where earth-fault may occur, but direct connection to the running rails is unacceptable due to the stray current.
For tramway, metro and depots voltage limiting device TZD-1NR/T is offered, which has exactly the same functionality and parameters except reduced to 60 V triggering voltage.

Voltage limiting device TZD-1NR becomes conductive when the voltage at its terminals approaches triggering voltage. It happens when the earth-fault occurs. TZD-1NR conducts current till the opening of high speed circuit breaker in substation and then, it returns to non-conductive state (recovers).
Triggering of TZD-1NR may be also caused by other effects (e.g. over-voltages due to the commutations), and recovering to non-conductive state will happen when the flowing current approaches zero. TZD-1NR is repeatable and does not require external power supply.