Ground Fault Protection for the Petersen Coil Applied 6kV System

[sykimk]

My client's existing 6kV system had consisted of 110/6kV main transformers (Primary side(110kV)-grounded wye / Secondary side(6kV)-delta winding) and Petersen coil to their 6kV system.

In this regards, I think there may be very few grounding fault currents when ground fault currents occurred on the existing 6kV system, and new 6kV switchgear 1,000 meters far from the existing 6kV system will be conneted through cables. My protection schemes for new 6kV switchgear are to use by combination of 67G (directional ground overcurrent relay) via ZCT and 64 (ground overvoltage relay) via grounding potential transformer (GPT) because I don't think that ground fault protection can be done by use of overcurrent ground fault rely (50G/51G).

I do not consider to use 67G for incoming CBs at new 6kV switchgear because it will be protected by upstream switchgear.

Do you have any idea for further consideration to properly protect new 6kV switchgear against ground faults?

Thank you very much for you kind advice in advance

 

[DiscoP]

Contact Areva (Alstom).

They have some MiCOM protection relays suitable for use on Petersen Coil Earthed networks.

Their website is

http://www.areva-td.com

 

[DNMak]

I have heard of use of Peterson's on the neutral of a 4WY, but how are they utilized on a 3WD?

 

[sykimk]

I understand your comments, please note that my client uses Peterse coils through zig-zag transformer connected to main bus. I think it is very unusual case.
Finally, I decided that 64 & 67G relays will be suitable for protection against ground fault on 6kV system.
Do you have any comments or advice?