Phasing Test & equipment for MV Power system

[power2engineer]

We have a 13.8KV MAIN1-TIE-MAIN2 Switchgear Fed from Utility's Two, 20MVA, 115KV/13.8KV Delta-Wye Grounded transformers both fed from single utility 115KV line. Upon fault on one of the transformer 13.8KV Bus to MAIN1 breaker we closed the tie breaker.

Question is when we replace the failed 13.8KV bus duct the plant does not want another outage. A colleague is insisting that we should first open the TIE before closing the MAIN1. He thinks that not knowing if the phasing verification was ever done on the two 13.8 KV buses this would be safest approach. I looked at Hubbell-Chance Phase tester see link.

http://www.hubbellpowersystems.com/lineman/meters/digital-phasing-testers.asp

Which tests the phase sequence on both the Transformer (Line) and Bus (Load) side of MAIN1 breaker. I am not sure if this instrument will also identify A B and C buses on both sides of the breaker Can I also use this equipment to measure phase angles between phase As on Line and Load side of the breaker?

Thanks to all my learned colleague.

 

[Marmite]

As part of the commissioning of the site you would expect the phasing to have been proven. Have the utility transformers never been taken out on a planned basis for maintenance by closing the tie and opening the transformer 13.8kV C/B without a complete site shutdown? That being said, if there are any doubts, by all means get hold of some phasing sticks and prove it again. If there was any chance of the connections being altered during the fault repair then this should be done anyway. If the circuit breaker is isolatable and the spouts are accessible then phasing sticks like those in your link would do the job. They work by comparing voltages rather than phase angle, but this is exactly the application they are used for.
Regards
Marmite

 

[rbulsara]

Your colleague is right and engage services of a testing company to perform "Hot Phasing" check across the open breaker(s).

You need to get both the phase rotation and the sequence right. Relying on instrumentation alone is dangerous.


Rafiq Bulsara

http://www.srengineersct.com