How to demagnetize the core of a current transformer

[RGarcia]

1. Which of the following conditions tends to demagnetize the core of a current transformer?

I answered passing a dc current through the windings.

[michaellabeit]

1. Which of the following conditions tends to demagnetize the core of a current transformer?

I answered passing a dc current through the windings.

My understanding is that DC will *magnetize* the core. Demagnetizing the core involves applying AC voltage to the CT secondary and increasing the voltage in steps. When the CT is saturated, you then decrease the voltage slowly back to zero and the core is no longer magnetized. Chris Werstiuk has a great pdf on CT testing.

[Kalbi_Rob]

My understanding is that DC will *magnetize* the core. Demagnetizing the core involves applying AC voltage to the CT secondary and increasing the voltage in steps. When the CT is saturated, you then decrease the voltage slowly back to zero and the core is no longer magnetized. Chris Werstiuk has a great pdf on CT testing.

Technically, both are correct. AC will de-magnetize the core. DC will magnetize the core, but there is a procedure in which you continuously swap polarity, while continually reducing the magnitude of the voltage, causing the core to de-magnetize, essentially simulating AC current at a much reduced frequency.