Answer Posted / venkatesh a
For the low voltage systems NGR is not required. If it
necessary then We should consider the relay/Numerical relay
time of fault current allowable, sensing capacity.
In some industries, where the critical areas even though
fault happens they didn't allowing to trip the circuit by
relays.
They maintaining the supply as it is till the next
shutdown.
These resistance are calculated depends upon the fault
current, time delay of fault current, Relay settings.
In my site, we are using the 12.7Ohms NGR for 33/6.6Kv
6.3Mva transformer.
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