Potential transformer

                                                  Potential Transformer 

• The Potential transformer is another type of instrumentation transformer. It is used to measure high voltages.
• The construction of a potential transformer (P.T) is same as that of the normal transformer.

The connection of a potential transformer in a circuit to measure voltage is shown in fig.

Description :

• To measure high voltage, the potential voltage transformer which is a step down transformer is connected across high voltage terminals and voltmeter is connected on low voltage side.
• A potential transformer is an ordinary two winding transformer with high turns ratio, designed for low current carrying capacity.
• Due to P.T., voltage across voltmeter gets reduced by a factor equal to the turns ratio of P.T. 
• The scale of thr voltmeter is suitably calibrated by taking in to account the turns ratio of P.T.
• So if the ratio (N2/N1) is known and V2 is measured then we can obtain the voltage V1 accurately

Sources of error :

          There are two types of errors that are likely to occure in the potential transformer :

           1. Ratio error      2. phase angle error.

1. Ratio error :

          To ensure accurate measurement, the turns ratio of the P.T. should be very accurately adjusted. The error introduced due to incorrect ratio is called as the ratio error.

2. Phase angle error :

           A little deviation in the phase angle between voltage and current can affect the voltmeter reading considerably. Such an error is called as phase angle error.