Different CT Ratio for Generator Differential Protection
Different CT Ratio for Generator Differential Protection
(OP)
Today I started up generator but ACB for generator has been tripped due to Differential Ocurrence. The reason is that CT's ratio are different from each other, which means that CT from Generator is 1250/5A and CT from Switchboard is 1250/1A. The protection relay is Alstom P343.
I am not sure if I am able to set two different CT setting and P343 is able to calculate equivalent current from two different CTs. At the moment, is P343 able to resolve problem by itself ?
If not, is there no other solution other than replacing same CT ratio ?
If any, can anybody advise any other protection to protect against differential ocurrence ?
I am not sure if I am able to set two different CT setting and P343 is able to calculate equivalent current from two different CTs. At the moment, is P343 able to resolve problem by itself ?
If not, is there no other solution other than replacing same CT ratio ?
If any, can anybody advise any other protection to protect against differential ocurrence ?






RE: Different CT Ratio for Generator Differential Protection
RE: Different CT Ratio for Generator Differential Protection
I'm not familiar with this relay, but as David Beach mentioned, some auxiliary CTs could be used to correct the ratio problem, at least temporarily.
So short answer: I don't know.
RE: Different CT Ratio for Generator Differential Protection
RE: Different CT Ratio for Generator Differential Protection
RE: Different CT Ratio for Generator Differential Protection
Pick your solution wisely- either program it into the relay or put in new CTs
JTK
RE: Different CT Ratio for Generator Differential Protection
RE: Different CT Ratio for Generator Differential Protection
I have not used this relay, so the solution you suggest may be the best course of action. Like I said- program the relay to handle the mis-match.
JTK
RE: Different CT Ratio for Generator Differential Protection
Be careful with CTs of different type/class, as they can always mismatch and create problems in case of a through fault.
RE: Different CT Ratio for Generator Differential Protection
Change the conection in the relay- the wiring from 1250/1 to the analog input for CT 1 A secondary. the same for the CT 1250/5 to input for CT 5 A secondary. Then check the differential current with secondary inyection.
Please respond if works.
Good luck
Milko
Melquiades
Protective Relay
Testing and Commissioning