TESTING OF PHASE SHIFTING TRANSFORMERS BASIC AND TUTORIALS


Unless otherwise specified, all tests carried out at the factory should be made in accordance with IEEE Std C57.12.90-1993. Additional tests, particular to PSTs, are defined in 11.2, Special tests for PSTs.

Since the method of testing PSTs is dependent on the design, the testing methods will be mutually agreed upon by the user and manufacturer.

Resonant frequency and transient voltage tests
These tests are normally performed on the core and coil assembly in air. However, they can also be performed inside the tank filled with oil and fitted with temporary bushings to give access to required test points.

For a two-core design in one or more tanks, the windings must be interconnected as for impulse testing. These tests are intended to verify the transient voltages and natural frequencies at various points in the windings at all tap combinations and connections that can be compared and evaluated with studies.

Temperature tests and loss distribution
In most cases temporary bushings must be installed for connections to windings, which are not normally accessible, in order to determine the various resistances for the temperature tests and to determine the losses and the distribution of these losses.

The location of these temporary bushings depends on the design and winding configuration and is subject to agreement between user and manufacturer. For two-tank designs, the tanks may be separate to determine the losses in the various cores and windings and the temperature test.

This information will be provided by the manufacturer to the user during preliminary discussions.

Dielectric test
For dielectric tests each tank with its corresponding core and windings should be connected electrically and mechanically together as for the service condition. In most cases, temporary bushings must be installed on lower voltage windings in order to perform the IEEE standard low frequency induced test on the higher source and load side windings.

In very high voltage PSTs, it is sometimes necessary to install an auxiliary winding next to the core for shielding purposes. This auxiliary winding can then be used for performing the low-frequency induced test through the use of temporary bushings.

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