only some transformers and some generator requires NGR why?

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only some transformers and some generator requires NGR why?..

NGR - Neutral Grounding Resistor is used to limit the fault
current of a sytem.

So generally a system with high line voltage of 3.3KV and
above normally comprises of high load equipment which
results in very high fault currents due to a Short-circuit
fault. Normally during a Earth fault the fault current
flowing through the earthed phase is to be carried by the
remaining phases which may be very much more than the
rating of the conductors. So we follow the Neutral
Grounding practice so that the fault current is carried by
the nuetral.

Now this current carried by the nuetral is to be limited
such that this high fault current does not damage the
grounded equipment so in the neutral we insert a resistance
which is the NGR.

So for any high voltage system to limit the fault current
NGRs are used. for the equipment working at lesser voltage
normally can withstand the short circuit currents for short
time.