CT Metering Class

Hi I want to know that what is used for covering the usual range of metering and relay applications in the current transformers does the accuracy classes used ??

[Rajkumar Agarwal]

Well for current transformers a set of burdens is used covering the usual range of metering and relay applications.

One set of accuracy classes is used.

For potential transformers a set of burdens is used covering the usual range of metering and relay applications.

In the case of metering CT s, accuracy class is typically, 0.2, 0.5, 1 or 3.

It means that the errors have to be within the limits specified in the standards for that
particular accuracy class.

CT for Metering




The metering CT has to be accurate from 5% to 120% of the rated primary current, at
25% and 100% of the rated burden at the specified power factor.

In the case of protection CT s, the CT s should pass both the ratio and phase errors at the
specified accuracy class, usually 5P or 10P.

The value of primary current up to which the CT complies with composite error requirements.

This is typically 5, 10 or 15, which means that the composite error of the CT has to be within specified limits at 5, 10 or 15 times the rated primary current.