There are power distribution networks which feed certain earth-fault
prone zone where the earth-fault may cause fire hazards and or damage
to the cables and equipment. In those zones as a safety measure, the
neutral terminal (star point) of the power transformer secondary is
grounded through a suitable neutral grounding resistor (N.G.R.) to
restrict the earth-fault current within a certain stipulated limit so that the
fire hazards and damage to the equipment may not take place.
The above neutral grounding system alone cannot provide with a longterm
safety assurance. In outdoor distribution station there are many
possibilities of damage in the neutral grounding connections due to
various environmental effects causing open circuit and burning of NGR.
This may also result in failure of earth-leakage protection operating through neutral CT or CBCT as the leakage current may not be
able to flow through open circuit of neutral grounding connection.
In view of the above, it becomes necessary to incorporate a device that will ensure a fail-safe operation of N.G.R. and the grounding
system. The device will continuously monitor the continuity of NGR and neutral grounding connections and will trip the feeder circuit
breaker as and when any open circuit occurs in neutral grounding connection or in neutral grounding resistor (NGR). The device will
ensure failsafe operation of neutral grounding system.