Answer / ksk

Mr.usman if u know the answer just tell the answer but dont
give unnecessary answers.

Answer / vinod

Good question,
Generator with Star point direct earth will have heavy
earth fault current during fault, so rating of the
equipment and protection elements required more and is not
economical. So by using suitable NGT/NGR the current can be
reduced a minimum possible value to detect the fault with
less protection unit cost.Also NGT out put is using for
start time protection of Generator.

Answer / sunil

NGR basically used for Star connected Generator. It is
basically limit the fault current and protect the
generator.Its value is calculated with the help of Generator
Core caring capability curve i.e. at what Amp you restrict to
flow in core. suppose you restrict 100A current and your
Generation voltage is 11 KV. then at the time of fault,
Voltage applied across the NGR is 6.35 KV. and with the help
of this voltage, Resistance will be V/I which is 63.50 ohms.
At the time of fault, normally Earth fault (Sensitive/stand
by)operated. and in case they not operated then current
having magnitude more than 100A will burn the resistance. and
system become unearth i.e. system will isolate from earth.

Answer / saad

NGR Neutral ground resister
NGR connected between earth and star point of generator
during normal condition only limited current or zero
current flow in the ground side but during fault there r
too much current that limit the NGR with the help of
resister and relay setting according to that minimize
current that tripped the breaker of generator
Have a good day man

Answer / avinash singh

Both NGR and NGT are used to for restricting earth fault current. The standard practice is to have a single grounding in a system with same voltage. If we generate 11kV through the generator and there is no step up transformer before connecting the generator to the generator Circuit Breaker than we will have to use NGR and restrict current at 100A instead of restricting it at 10A as the relay at the feeder side will not be able to detect such small fault current as the relay is getting its input reading from a CT which might be above 1000/1A rating. The relay will not be able to sense small value current as low as 10A as it is quite a low value. So we need to consider NGR considering the sensitivity of relay and CT.
When there is a transformer between generator and generator circuit breaker than you can have the secondary of the transformer grounded and you will get the path for earth fault at feeder end through that grounded system. Now in this case you need not protect the feeder from the generator side and you only need to protect the generator now. So, you will keep the current because of earth fault as low as possible which enters the generator. In this case you can use an NGT and lower the earth fault current to 10A. The CT for sensing earth fault current will be connected at secondary i.e. LT side of transformer and as the voltage is low there, the current will be more and CT can easily sense that much current and the relay will trip the generator as soon as the fault occurs. The resistance will also be connected on LT side of transformer as we can connect low value resistor there and it will have a higher value resistance effect on the primary side of NGT which is HT side which is connected to the main neutral line of generator. Hope this answer helps.

Answer / ahmed hussain

NGR is basically a resistor that Protects the Generator under Fault conditions, when phase to neutral fault occur ,the fault current is limited by NGR thus protecting the generator winding.
there are many NGR Configurations ,
1. LOW impedance
2.High impedance
3.Hybrid Impedance

Answer / prashant kaushik

For limiting fault current in generator

Answer / bharat

it is used for protection of generator from fault.In NGR
RESISTANCE VALUE WILL BE 153 OHMS For 6.6kv/22kv now u can
calculate fault current from this it is connected at 22kv
side.

Answer / usman batliwala

It is generally used for limiting the fault current.

Such a poor question. Go back to Engineering 2nd Year.

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