During initial loading of 6.6 kV Medium Voltage Switchgear we discovered that the main incoming circuit breaker protection current transformer (CT 2500:1 A) secondary circuits were open at 40A on primary current for 2 hrs and our EE engineer reconnect it with 40A still remain on primary (unsafe condition).

1. Dose this CT damage by abnormal high voltages ?

2. Whether this current transfomlers should be replaced or retested. If retesting, how to prove this CT still OK

 

Responding to Chakrit's Sep 23 query... it probably was not damaged having been subjected to only about twice its rated excitation ampere-turns!

However, testing requires three essential factors: sophisticated test equipment; skilled and knowledgeable test personnel; and great care. So, unless you possess or can obtain all three of the enumerated factors the CT should be replaced!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])