what is the use of neutral displacement relay
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Answer Posted / loboreliance2003
The relay comprises an attracted armature element fed via a
rectifier and series resistor. It can be provided with
either a fixed
setting, or variable settings using a plug bridge. It has a
minimum
withstand of rated voltage continuously.
Operation of Neutral Voltage Displacement Relays
The zero sequence current that flows for an earth-fault on
an un-earthed network is determined by the capacitance of
the cable to earth. This flow of current leads to a rise in
the voltage of the neutral point of the incoming supply
(the star-point of either the generator or transformer). It
is this rise that is detected by a neutral voltage
displacement relay. If the network is quite small (i.e.
short cables), then the zero-sequence voltage will be
unstable. This is why an instantaneous relay is only
generally used to provide an alarm. In the event of a
fault, neutral voltage protection cannot detect the
location of a fault, so all sources of supply should be
disconnected.
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