Answer / mashani

when you see transformer(Medium Viltage Transformer) which
conneted as Y(star) the netral is connected on something
like box....actually its not a box...inside the box is some
inductance which have a value of OHM(it's called NGR"Netral
Grounded Resistance).....
this NGR is used to limited current which will arrived on
netral line.....
it means...when there is fault from phase to ground the
current will be back to the transformer by the netral line
so this NGR is needed installed before this current arrived
to the transformer becoz this fault current is so big and
can destroy the transformer thats why we need NGR

Answer / navin

NGR = NEUTRAL GROUND RESISTANCE

Answer / venkatesh a

NGR- Neutral ground resistor.

Used to limit the ground fault current.
If the Line voltage getting leakage or shorted with ground
then fault curretn will flow.
If it is High voltage system this fault current will be
very high (KAmps). So this much high value fault current
will demage the fault current sensing devices (relays).
This fault current will reach the transformer Neutral
through the Neutral earth pits.
By adding the NGR in between the Transformer neutral and
Neutral earth pit, resistance of the fault current path
getting increase.
we Know that, resistance is more then the (fault) current
flow will be less.
Then easy to sence. Normally resistance will be 12 to 15
ohms depends upon the setting made at relays.

Answer / 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.

Answer / venkatesh kulkarni

Used to limit the ground fault current.
If the Line voltage getting leakage or shorted with ground
then fault curretn will flow.
If it is High voltage system this fault current will be
very high (KAmps). So this much high value fault current
will demage the fault current sensing devices (relays).
This fault current will reach the transformer Neutral
through the Neutral earth pits.
By adding the NGR in between the Transformer neutral and
Neutral earth pit, resistance of the fault current path
getting increase.
we Know that, If resistance is more then the (fault) current
flow will be less.Then easy to sence. Normally resistance
will be 12 to 15 ohms depends upon the setting made at
relays.

Answer / vishal essar

th e NGR is Neutral gorunding resistor connected to the
Neutral of the star side of the transformer. It si so
connected to limit the fault current getting reflected beoz
of Phase to gnd fault on the Delta side of the Transformer
and also Gnd fault on the same side of the transformer.
Such transformers are for specific loads
like...Motors...specially higher rating motors. The mototr
staring current is very high and a fault at this point can
definnitely destroy the trafo. Hence a NGR is rpovided to
limit the fault current. NGR is a Box having resistor and
Inductors in series parallel connection.

Answer / dhannnuu

NGR 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.

Answer / farhad

A suitably rated power resistor that is connected
between the neutral of a transformer (or generator) and
the system ground. It serves to limit fault currents and
prevent damage to the equipment

Answer / dipak

NGR:- Neutral grounding resister
In high voltage or extra high voltage line NGR is used.
Mainly this NGR are used for to decrease leakege current.
So that current cant able to come to Neutral of the trafo.
so we can save our trafo.
If any big earth fault occur in system that more amount of
current will flow in neatral (Ia+Ib+Ic) so that comes to
Neutaral of the trafo so if we put some resistance than it
disappiate this cuurent in heat purpose not able this
current to trafo.
so that's why NGR rating also have temprature stability and
withstand time.

Answer / md79

Mr. Venkatesh A

Thank you.

i have one transformer 1000kva, 11/.433kv. we are using 200/5 amp. ct unit for measuring purpose, & one 800 amp. V.C.B Unit for the same t/f operate, i wants to known the primary current of T/F is only 53 amp. why we used 800 amp. V.C.B ? & 200/5 amp. CT Unit.

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