Protection Engineering Basics and Schemes Protection Engineering | Page 43

Ratio error is the difference between the primary voltage and secondary voltage vector

Ratio Error = K V P − V s

V P

K = nominal Ratio V p = Primary Voltage V s = Secondary Voltage Ratio and phase displacement errors are combined to form composite error, and on the basis of composite error we defined classes or accuracy classes of PT

Metering PT Accuracy Classes: � 0.1 � 0.2 � 0.5 � 1 � 3

Protection PT Accuracy Classes � 3p � 6p

Whenever you used PT, please read nameplate data before to use it

pg. 43