Ground Resistor for Generators

No idea about 460 voltios generator. A grounding resistor for two generators?? You want somebody as a guide for selecting resistors?

What is the desired ground fault current?

TAKE CARE!! IF you get told a resistance which limits current to less than minimum to operate "ground fault protection" you will just get a melted grounding resistor and still have an earth fault!! Are we talking a "3 terminal" generator or a "4 terminal" generator?? It has an effect on how you can earth.

BEFORE YOUR QUESTION IS ANSWERED

TWO GENERATORS ARE RUNNING IN PARALLEL .

IF BOTH THE GENERATORS ARE SYNCHRONISED IN THE SAME BUS DIRECTLY WITHOUT A GENERATOR TRANSFORMER .

IN THAT CASE ONLY ONE GENERATOR NEUTRAL IS SUPPOSED TO BE GROUNDED (FOR PROPER SHARING OF REACTIVE KVAR).

IN THIS RANGE GENERATOR NEUTRAL SHOULD BE GROUNDED THROUGH A HIGH IMPEDANCE GROUNDING THROUGH NGT .

THE SECONDARY WINDING OUTPUT OF NGT SHALL BE USED FORV 59G PTROTECTION.

THE NGT RATING FOR EACH GENERATOR SHOULD BE 270 VOLT-14KVA.

THE SECONDARY OUTPUT SHOULD BE MAX-60VOLT(THIS SHOULD BE ADJUSTABLE ACROOS A VARIABLE RESISTANCE)

THE NGT OTHER END SHOULD BE CONNECTED THROUGH A KNIFE SWITCH TO A DEDICATED TREATED EARTHPIT.

I never heard of such resistors. your question is confusing. Have you done any homework before posting this Q? if yes details please!

Post #4 from Guest is good (For 4 terminal generator with neutral). But, if you have only one ground resistor, the NGT (Neutral Grounding Transformer) must be switched by contactor or manual changeover switch to neutral of running generator (You may operate with only one generator on-line). Or else, if you have NGT on each generator neutral, only one must be connected in normal operation.

Generator neutral is grounded through an impedance to limit the fault current. This fault current is also used for tripping the set where an overcurrent relay is used. Generally the neutral is grounded through a distribution transformer secondary of which is loaded through a resistor and a current coil of the earth fault relay. Transformer is used so that a low value resistance may be used which offer higher impedance on primary side to limit the fault current. The value of resistor is chosen based on the principle that power loss in resistor is equal to the capacitive charging VA of the generator. So to design the grounding resistor value of generator, connecting cables (or bus duct etc.) would have to be considered. The resistor is rated for short time power dissipation.