what is potential transformer

~ potential transformer (pt) use for measurement of line and step down the voltage.

~ measurement PT attached with voltmeter , wattmeter, energy meter.  

                        what is error in PT

~ two types of error in PT

1) Ratio error

2) phase error


1) Ratio error : in a potential transformer theoretically Kn = Np/Ns = Vp/Vs turn ratio and voltage ration should be equal. but in a fact this does not happen, because the impedance drops in the primary and secondary winding


2) phase error : ideal transformer has reverse secondary voltage vector v and primary voltage vector ,in phase but in real transformer there is phase difference between the two . this is called phase error. tis is phase error is shown in angle and shown in minutes