What is the minimum insulation resistance of a transformer?

What is the minimum insulation resistance of a transformer?

Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.

What is insulation resistance of power transformer?

Insulation Resistance Test or Megger Test of Transformer: Insulation resistance is the ratio of applied voltage to the resulting current at a specified time after the voltage is applied. Direct voltage are used for measuring insulation resistance values. Insulation resistance test of transformer is essential type test.

What is IR test in electrical?

An insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. Such tests are useful for checking the quality of insulation, not only when a product is first manufactured but also over time as the product is used.

How many test are there in transformer?

Transformer manufacturers perform two main types of transformer testing – type test of transformer and routine test of transformer. Some transformer tests are also carried out at the consumer site before commissioning and also periodically in regular and emergency basis throughout its service life.

What is the IRIR value for transformer insulation resistance?

IR Value for Transformer Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in megohms or may be calculated from measurements of applied voltage and leakage current.

What is the minimum Ir value required for a transformer?

There are no national or international standards prescribing minimum IR values. Nor is it an acceptance test for motors, generators or transformers. Yet this is a very important test which should be done invariably before conducting HV tests. The thumb rule is (KV + 1) Mega ohms.

What is the insulation resistance of the transformer at the test temperature?

Value at 60 seconds after application of the test voltage is referred to as the Insulation Resistance of the transformer at the test temperature. The transformer Neutral bushing is to be disconnected from earth during the test. All LV surge diverter earth connections are to be disconnected during the test.

What is a good pI value for a transformer?

A PI of more than 1.25 and DAI of more than 1.3 are generally considered satisfactory for a transformer when the results of other low voltage tests are found in order. PI less than 1 calls for immediate corrective action. For bushings, an IR value of above 10,000 MU is considered satisfactory.