Zero Sequence / Earth Fault Setting
Zero Sequence / Earth Fault Setting
(OP)
Hi,
We have an exisitng installation with a soft started compressor (motor f.l.c. 515A) with a P&B Golds digital motor protection relay type PBSJ 3E5 N11. There are three CTs (750/5) residually connected one per phase. One setting in the relay relates to the zero sequence or earth fault setting. I understand the theory behing what it is but how is this value calculated? All the manual says is the value is ajustable over the range 0.06 to 0.6 x In.
Regards
We have an exisitng installation with a soft started compressor (motor f.l.c. 515A) with a P&B Golds digital motor protection relay type PBSJ 3E5 N11. There are three CTs (750/5) residually connected one per phase. One setting in the relay relates to the zero sequence or earth fault setting. I understand the theory behing what it is but how is this value calculated? All the manual says is the value is ajustable over the range 0.06 to 0.6 x In.
Regards





RE: Zero Sequence / Earth Fault Setting
David Castor
www.cvoes.com
RE: Zero Sequence / Earth Fault Setting
RE: Zero Sequence / Earth Fault Setting
There is no calculation.
David Castor
www.cvoes.com
RE: Zero Sequence / Earth Fault Setting
RE: Zero Sequence / Earth Fault Setting
It is not a matter of preference. There are competing goals while determining protection settings, such as degree of equipment protection, degree of availability ( avoiding nuisance trips), personal safety (e.g. arc flash hazard) and coordination with upstream and downstream devices. So there is seldom one answer that can be reached by calculation. There could be a range of settings that all could be acceptable or not acceptable. That is where the 'art' comes in. Work with one of your senior engineers, familiar with your system design and objectives.
Also look up applicable local codes.
Rafiq Bulsara
http://www.srengineersct.com
RE: Zero Sequence / Earth Fault Setting
Is the power system solid or resistance grounded? If this is a solidly grounded system and a low voltage application, the main breaker could easily trip as quickly or even quicker than that ground fault relay would operate.