Demagnetising a saturated CT

[appunni]

Sir,
Please explain the method for demagnetising a saturated CT. Can we assure 100% success in demagnetising the saturated CTs of all types with these methods?

with regards,
appunni

 

[peterb]

Connect a variable AC supply to the CT secondary, with the CT primary open circuited. Increase the supply voltage gradually, measuring the current supplied to the CT, up to the rated CT secondary current.
Slowly reduce the supply voltage to zero. You have cycled the CT through the B-H curve and this should remove any residual magnetism. You can confirm this by plotting the voltage-current characteristic before and after the procedure - the difference in magnetizing curve will demonstrate the demagnetization, assuming that you did in fact start with a Ct that had remanent magnetism present.

 

[busbar]

See

http://www.geindustrial.com/products/applications/GET-97D.pdf

under “Magnetic Bias.”