Testing of current transformer

Current transformers are generally used to measure currents of high magnitude. These transformers step down the current to be measured, so that it can be measured with a normal range ammeter. A Current transformer has only one or very few number of primary turns. The primary winding may be just a conductor or a bus bar placed in a hollow core (as shown in the figure). The secondary winding has large number turns accurately wound for a specific turns ratio. Thus the current transformer steps up (increases) the voltage while stepping down (lowering) the current.

 transformer testing

The following testing are done at the current transformer .Which is given below,

i) Type Testes:-

 

  1. Verification of terminal marking and polarity.
  2. High voltage power frequency test on primary windings.
  3. Over voltage inter-turn test.
  4. Determination of error according to requirements of appropriate accuracy class.
  5. Short time current test.
  6. Temperature rise test.
  7. Impulse voltage test for current transformer for service in electrically exposed installations.

Special type testing may be done on current transformer .

  1. High voltage power frequency wet withstand voltage test on outdoor current transformer.
  2. Partial discharge test.

(ii) Routine Tests:-

  1. Verification of terminal markings and polarity.
  2. High voltage power frequency test on primary windings.
  3. High voltage power frequency test on secondary windings.
  4. Over voltage inter turn test.
  5. Determination of error according to the requirements of appropriate accuracy class.
  6. Accuracy test.

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