## Current Transformer Turns Ratio and current ratio

## Current Transformer Turns Ratio and current ratio

(OP)

Dear Friends,

Could someone tell me the reason for following:

In PX class Current transformer ,as per IEC the acceptance criteria for error is turns ratio error shall be less than .25%. But in class x CT it is current ratio error as the deciding criteria. why in PX class it is Turns ratio and in Class X current ratio.

Please clarify.

thanks

Could someone tell me the reason for following:

In PX class Current transformer ,as per IEC the acceptance criteria for error is turns ratio error shall be less than .25%. But in class x CT it is current ratio error as the deciding criteria. why in PX class it is Turns ratio and in Class X current ratio.

Please clarify.

thanks

## RE: Current Transformer Turns Ratio and current ratio

Hopefully somebody who has a better handle on IEC will drop by soon.

## RE: Current Transformer Turns Ratio and current ratio

If so then that may be your answer.

Bill

--------------------

"Why not the best?"

Jimmy Carter

## RE: Current Transformer Turns Ratio and current ratio

class PX protective current transformer:protective current transformer of low-leakage reactance without remanent flux limit for which knowledge of the excitation characteristic and of the secondary winding resistance, secondary burden resistance and turns ratio, is sufficient to assess its performance in relation to the protective relay system with which it is to be used.

class P protective current transformerprotective current transformer without remanent flux limit, for which the saturation behavior in the case of a symmetrical short-circuit is specified

## RE: Current Transformer Turns Ratio and current ratio

Thank you for the reply .

But I know that protection class CT(PX class) error is measured in terms of Turns ratio not current ratio , unlike 5P20 and class x CT.

My doubt is why we use

Turns ratio for PXwhereas Current ratio for others?Any significant reason to do so?

Regards,

## RE: Current Transformer Turns Ratio and current ratio

## RE: Current Transformer Turns Ratio and current ratio

Class P is defined as an accuracy limit up to a over-current factor, therefore and accuracy test is done measuring current ratio error and phase angle error. For example, 5P20 means <5% error up to 20 times over-current.

The error is defined as composite/total error and the limits at rated current at +/-1% ratio error / +/-50 min phase error at rated current and <5% composite error at accuracy limit primary current (20 x Inom in this case).