Open circuit CT's (again)
Open circuit CT's (again)
(OP)
Hi, Ive read all the posts on open circuit CT's already but they all refer to what happens when primary current is applied to them. My quick question is what happens in a power frequency withstand test, with the secondary open circuit, i.e. 11kV AC applied to primary conductor. Anyone?






RE: Open circuit CT's (again)
Most folks short and ground the secondary winding during this test.
RE: Open circuit CT's (again)
RE: Open circuit CT's (again)
RE: Open circuit CT's (again)
In other words, open-circuit voltage is not a concern....voltage rise of the entire secondary is.
RE: Open circuit CT's (again)
Just currious, you don't need to do this..for further how to test the CT, chek megger tester guidance
RE: Open circuit CT's (again)
Gunax, I wasnt testing the CT itself I was pressure testing the HV switchgear, theres no way of doing this without passing HT through the CT on this particular gear. We got talking as to the do's and donts and I said I wasnt sure what would happen if the CT was open circuit in this particular test, as above I normally ensure the shorting bar is in and earth link is in.
RE: Open circuit CT's (again)
RE: Open circuit CT's (again)
I don't really understand the problem here. You go from instruments connected with secondary neutral grounded to CT secondary short circuited and grounded. There is no step where the ground needs to be or should be removed.
RE: Open circuit CT's (again)
What Davidbeach has wrote seems to make perfect sense to me, which brought me to the question, would damage be caused by just applying HT to the primary?
RE: Open circuit CT's (again)
David is correct regarding the voltage across the winding. Scottf is correct about voltage to ground.
Damage to equipment? I suppose it depends on the equipment configuration. You have a capacitive voltage divider, with one side pulling the secondary voltage up, the other side pulling it down. How this divides out would not be easily calculated.
RE: Open circuit CT's (again)
If you apply on the primary/source side of the switchgear, you're probably doing voltage withstand normal frequency/insulation test, no current will be flowing through the bus, so no current/voltage will be built up at secondary side of the CT.
When you apply, current test to the source side of the switchgear/lets assume mommentary current test flowing through the switchgear, you would get high voltage at secondary side of the CT, if you failed to short & ground it, which may damage the CT/change its characteristic/blow out.