What is a Doble test on a transformer?

The Doble test is basically a power factor test performed on transformers to ensure they are functioning correctly. This dissipation testing can also be performed on MV cables and motors. Some techs use the term as a catchall phrase for a breaker’s timing test using a shunt trip.

What is a doble power factor test?

POWER FACTOR TESTING Insulation power factor tests are used to measure dielectric losses, which relate the wetness, dryness or deterioration of transformer insulation. Both factory and field testing are performed to verify the insulation integrity of substation transformers.

What are the proper steps of testing a transformer?

Four Methods for Testing Transformers

  1. Turns Ratio Testing. Turns ratio transformer testing is commonly used to ensure that the winding ratio between the primary and secondary coils are aligned to recommended specifications.
  2. Insulation Resistance Testing.
  3. Power Factor Testing.
  4. Resistance Testing.

What is UST mode?

UST mode is used to measure insulation between two ungrounded terminals of the apparatus, isolate an individual section of insulation and test it without measuring other connected insulation.

Why transformer testing is required?

The need for transformer testing is to check the functioning of the transformer and to decrease the chance of failure. All electrical equipment needs to be maintained safely from some of the failures. Transformer failure can happen because of electrical, thermal, or mechanical factors.

What is Megger test of transformer?

The insulation resistance test (meggering) is of value for future comparison and also for determining if the transformer is to be subjected to the applied voltage test. The winding insulation resistance test is a DC high voltage test used to determine the dryness of winding insulation system.

How do you test the power factor of a transformer?

Note // Transformer windings provided with neutral insulation rating which is less than the line insulation rating should be tested below the neutral insulation rating level….Power factor test.

Winding rating Line-to-line, kV Test Voltage Line-to-ground, kV
5.04 to 8.72 2 and 5
2.4 to 4.8 2
Below 2.4 1

Which test is more important in testing of transformer?

The insulation power factor test provides more useful information about gradual insulation deterioration than other tests, such as the DC winding insulation resistance test.

What does a Doble test measure?

Fundamentally, the tests are used to assess the AC characteristic of the dielectric; one such value is dielectric losses, the real component of the current, which relates to contamination and/ or deterioration of dielectric.

What is Tangen Delta test?

Tan Delta, also called Loss Angle or Dissipation Factor, is a diagnostic method of testing cables to determine the quality of the cable insulation. This is done to try to predict the remaining life expectancy and in order to prioritize scheduled maintenance, replacement, or rejuvenation of the cable system under test.

How do you test a de-energized transformer?

Doble tests are conducted in the field on de-energized transformers using special test equipment. The testing software automatically performs analysis of test results and responds with a four letter code as shown in table 10.

How can temperature correction be done on the Doble test set?

Temperature correction of test results can be done automatically on the Doble test set. The values obtained at each test are compared to previous tests and baseline factory tests, and a trend can be established as the insulation system ages.

What are the SFRA tests for a delta/wye transformer?

For a delta/wye transformer, a test voltage of variable frequency, normally 20 Hz to 2 MHz, is placed across each phase of the high voltage winding. The SFRA sets of tests are as follows:

What is the purpose of a transformer test?

The purpose of this test is to detect short-circuited turns, poor electrical connections, core de-laminations, core lamination shorts, tap changer problems, and other possible core and winding problems. On three-phase transformers, results are also compared between phases.