Earth faulth protection in a ungrounded system 1

[Kevin Mejia]

Hello everybody,

I have to adjust the relay settings in a ungrounded system at 13,2 kV, and I want to know if there is a stardard setting for 3V0 (using broken delta for the measurement) in the detection of ground faults. I think an adjustment at 0,1*Vnominal must be right considering that: in normal operation 3V0=0 and, in fault condition it would be 3*VLN.

Thanks in advance.

 

[RRaghunath]

Earth fault protection 59G for unearthed / high resistance earthed Generators is based on broken delta voltage measurement and is used to be set at 5% pickup.
This is to ensure that 95% of the generator winding is protected.

 

[cranky108]

Note you can't get 100% protection with this scheme.
Also, there needs to be a resistor across the open to pass third harmonic current.