Polarity Test of Current Transformer (CT)

Polarity Test of CT:

A DC source is connected with the positive terminal to P1 and the negative terminal to P2. An analog ammeter is connected to the secondary terminal of the CT. The positive terminal of the meter is connected to terminal S1 of the CT while the negative is connected to terminal S2. A contact is momentarily made through the switch. The contact is made for a second and broken. This is important as continuous contact can short-circuit the battery. The momentary make-break contact causes a deflection in the analog multimeter in the positive direction, if the polarity is correct. If the deflection is negative, it indicates that the polarity of the current transformer is reversed. The terminals S1 and S2 need to be reversed and the test can be carried out.

2.Ratio Test

The primary current of minimum of 25% rated primary current to be injected on primary side of CT with secondaries shorted and the secondary current can be measured by a multi meter or analog ammeter.

Kn = Ip/Is;

3.The Current Error or Ratio Error in Current Transformer 

Ratio error= ((Ip -KnIs)/Ip)x 100