Grounding transformers

[lume7006]

Hello,

I would like to receive your feedback about grounding transformers:

1) Do you usually have them grounded through a resistance or reactance?
What is it better, reactance or resistance?

2) Have you experienced some transient overvoltages when a single phase to ground along the circuits despite being solidly grounded the grounding transformer?

I thank you in advance your comments and observations!

 

[rbulsara]

Refer to the IEEE Green book for starters.

 

[RRaghunath]

Resistance grounding is preferred when it comes to avoidance of over voltages.
When it comes to System earthing through grounding transformers, the system zero sequence impedance is a finite value as decided by the grounding transformer design and not zero.
IEEE62.92.1/Table-1 says that if the available earth fault current in the system is more than 60% of the phase fault current then the system qualifies to be Effectively earthed system and the over voltages will be limited to 2.0pu.