ISF for Current Transformers

Dear Sh.M.Vasan,

ISF means Instrument Safety Factor.The Ammeter connected to Current transformer shall be protected in case secondary current exceeds to say normal secondary current of 1Amp.The ammeters are designed to take overload of 5 times secondary current.Above that value CT will saturates and protect the connected Ammeter.Usually ISF=5 is used.Sometimes ISF-10 also used.

In the design of CT, the CT shall be designed to saturate if Sy current goes beyond 5 or10 times rated value inorder to protect the conneced instruments.It will not in any way affect the performance of CT and measuring core.

V.Ambarani

Dear Mr.Ambarani,

I have clearly understood about significance of ISF from your clarification. What will happen to the CT after saturation. Can CT regain its Original charecteristics once fault is cleared?

Can u pls explain me about CT saturation?

Regards,

Manimaran.V

DearSh.Manimaran,

As i had already informed that CT is designed for such overload and will regain its normal rated current linear working zone once the fault is cleared.

Regards

V.Ambarani

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If an MFM Panel meter is connected to the CT, the MFM should be capable of withstanding the over current value inline with ISF value of CT..Correct??

How does one get <...over current...> from the output of a <...CT...>?