Grounding of star neutral

220KV is not HT distribution voltage. I think it should be 220 volts? Normally the distribution system is 11KV(HT)/400V(LT). 220KV is termed as Extra High Voltage(EHV). The Distribution in our region is done on ∆ Y configuration.

Grounding of primary distribution circuits has 2 principal purpose: stabilizing circuit potentials to ground to avoid overstressing insulation,and providing a path for ground faults to aid in the operation of overcurrent devices and to secure prompt disconnecting under fault conditions. The second function is important to providing safety to the public.

You said:

"The second function is important to providing safety to the public."

May I ask for more explanation please.

Samak

The 220KV side needs to be able to generate enough fault currrent to clear the faults quickly in the event of faulted cables or transmission lines. Some manufacturers recommend star point resistors to limit the damage to the transformer core if the fault is inside the transformer and prevent fires if the protection does not clear fast enough.

The secondary side of the transformer may have the grounding resistor .In the protection system , the protection relay will be connected across the 3 ohm rsistor.if a fault or unbalance occurs on the secondary circuit, the voltage will develop across the 3 ohm resistor and the relay will operate.

11KV overhead lines which come into contact with trees or other obstructions will not result in a spurious trip.