We have 6.6kV, 2500Amp, 40kA Switchgear fed through 33/6.9kV, 22/27.5MVA, ONAN/ONAF Transformer.
The transformer neutral is earthed through 400Amp, 30 sec. NER. The 6.6kV Switchgear has Bus differential protection vide ABB REF615_N for each bus section.
We have checked sensitivity of Bus Differential protection as per ABB manual.
https://techdoc.relays.protection-c...busbar-high-impedance-differential-protection
As per calculation, sensitivity of protection is obtained as Iprim= 1832.5Amp (refer attachment) which is higher than NER rarting of 400Amp.
Now, we are in receipt of comment from End user, that the sensitivity of protection should be such that it shall also detect any earth fault on busbar as well.
Not sure how to resolve this issue. Any suggestion on this is highly appreciated. Thank you !
The transformer neutral is earthed through 400Amp, 30 sec. NER. The 6.6kV Switchgear has Bus differential protection vide ABB REF615_N for each bus section.
We have checked sensitivity of Bus Differential protection as per ABB manual.
https://techdoc.relays.protection-c...busbar-high-impedance-differential-protection
As per calculation, sensitivity of protection is obtained as Iprim= 1832.5Amp (refer attachment) which is higher than NER rarting of 400Amp.
Now, we are in receipt of comment from End user, that the sensitivity of protection should be such that it shall also detect any earth fault on busbar as well.
Not sure how to resolve this issue. Any suggestion on this is highly appreciated. Thank you !