Electric Power Generation, Transmission, and Distribution

23.3.3 Potential Transformers

IN

OUT

Ratio correction factor (RCF)¼

true ratio

marked ratio

(RCF generally>1)

Burden is measured in VA ;VA¼

E^2

Assume Zb

10:1

10 V 0.9 Zb

RX

True ratio¼

10

0 : 9

¼ 11 : 1

)RCF¼

11 : 1

10

¼ 1 : 11

Marked ratio¼

10

1

¼ 10

Voltage at secondary is low and must be compensated by 11% to get the actual primary voltage using the
marked ratio.

23.3.4 Current Transformer

True ratio¼marked ratioRCF

;RCF¼

true ratio

marked ratio

23.3.5 H-Class

Vs is fixed

Is varies Nearly constant ratio error in %