Hi all,

I want to know why neutral to ground resistance are used for higher VA (MVA) transformer. And how to calculate value for it.

Regards,
Shailesh C Patel

 

Responding to SC Patel's Feb 21, 11:31pm query... the List Archives contain pro/con views regarding safety, transient reduction, and calculation methods.

Dismissing the above, then, the greatest benefit of resistance grounding is an economic one... to reduce iron-core damage.

Larger transformers produce higher fault-energy, consequently, greater damage to electric machinery. In most cases insulation failures in large machines can be fixed with winding replacement. But if iron-core loss is
significant the machine must be replaced. Thus, one can see that reducing ground-fault current from say 10kA, to 100A, is advantageous!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])