What is a magnetic balance test of power transformers

Please forward analysis of magnetic balance test of power transformer

magnetic balance test of transformer

The Magnetic Balance test is conducted on Transformers to identify inter turn faults and magnetic imbalance. The magnetic balance test is usually done on the star side of a transformer. A two phase supply 440V is applied across two phases, say, 1U and 1V. The phase W is kept open. The voltage is then measured
between U-V and U-W. The sum of these two voltages should give the applied voltage. That is, 1U1W + 1V1W will be equal to 1U1V.

For instance, if the voltage applied is 440V between 1U1V, then the voltages obtained can be

1U1V = 1U1W + 1V1W
440V = 260V + 180V

The voltages obtained in the secondary will also be proportional to the voltages above.

This indicates that the transformer is magnetically balanced. If there is any inter-turn short circuit that may result in the sum of the two voltages not being equal to the applied voltage.

The Magnetic balance test is only an indicative test for the transformer. Its results are not absolute. It needs to be used in conjunction with other tests.

For confirming the specifications and performances of an electrical power transformer it has to go through numbers of testing procedures. Some tests are done at manufacturer premises before delivering the transformer. Mainly two types of transformer testing are done at manufacturer premises- type test of transformer and routine test of transformer. In addition to that some transformer tests are also carried out at the consumer site before commissioning and also periodically in regular & emergency basis through out its service life.
Type of Transformer Testing

Tests done at factory

Type tests


Routine tests


Special tests


Tests done at site

Pre-commissioning tests


Periodic/condition monitoring tests


Emergency tests

Type Test of Transformer

To prove that the transformer meets customer’s specifications and design expectations, the transformer has to go through different testing procedures in manufacturer premises. Some transformer tests are carried out for confirming the basic design expectation of that transformer. These tests are done mainly in a prototype unit not in all manufactured units in a lot. Type test of transformer confirms main and basic design criteria of a production lot.
Routine Tests of Transformer

Routine tests of transformer is mainly for confirming operational performance of individual unit in a production lot. Routine tests are carried out on every unit manufactured.
Special Tests of Transformer

Special tests of transformer is done as per customer requirement to obtain information useful to the user during operation or maintenance of the transformer.
Pre Commissioning Test of Transformer

In addition to these, the transformer also goes through some other tests, performed on it, before actual commissioning of the transformer at site. The transformer testing performed before commissioning the transformer at site is called pre-commissioning test of transformer. These tests are done to assess the condition of transformer after installation and compare the test results of all the low voltage tests with the factory test reports.