Question { Assam Electricals, 99258 }

what is the purpose of NGR?

Answer

NGR (Neutral Grounding Resistors )is employed in AC
distribution networks to limit the fault current which
would flow from the transformer or generator neutral star
point in the event of an earth fault in the systems. It is
used when the neutral of supply transformer is accessible
and its own impedance is not enough to limit fault current.
The rating of the protection relays within the required
time.
For Grounding Neutral of Transformer or Generator,
Resistors upto 33 KV are offered for fault of short
duration like 10 sec., 30 sec., 60 sec., continuous etc.

Question { 8050 }

How can we calculate the current if we have load in KVA and if
the load in KW then what formula will be use for calculating
the current. please give both the formula for calculating the
current.

Answer

For KVA rating,
The formula for determine the current is:

I = KVA/(1.732 x Voltage) (For three phase system)
I = KVA/Voltage (For Single Phase)

For KW rating
The Formula for current is

I= KW/(1.732 x Voltage x Power factor)(for three phase system)
I = KW/(Voltage X Power factor)(For Single Phase)