How to Test Power Transformers

A meggar "a dc generator self contained meter primarily usedfor checking insulation values to ground"

Between phases very low resistance use ohm scale between Prim and Secondary better be close to infinate on meg scale test at or near transformer rated voltage ,

Primary leads to ground meggar resistance at voltage rating of transformer

reading should be infinate

Secondary leads to ground meggar reading at voltage rating of transformer reading should be infinate to ground.

Since you have several transformers if rated the same winding resistance will be close for all within 5-7% variance no real problem.

There are of course other "Toys" that can be used if you have the budget $. but a meter and a meggar do do the trick..........................

Hi os

The transformer manufacturers normally carry out standard routine test prescribe by the specification before final dispatch to the site. If there are orders for many transformers , the purchaser can ask for conducting heat run test and the type test of transformer ( to be carried out in presence of the purchaser at manufacturers premises)

At site before commissioning Insulation test of the windings must be carried with the help of megger of requireed voltage level. The transformer oil must be tested before charging with the help of standard transformer oil testing machine. If required filtration of oil need to be carried out if the oil testing results are below the required value .

In the electric utility where I work, we have 3 tests we always conduct on our transformers from 10 kVA to 500 kVA.

These are:

1. Insulation resistance test - HV-G, LV-G, HV-LV; minimum value: 2000 megOhms

2. Transformer turns ratio test - on all tap positions; minimum deviation from computed values: 5%

3. Oil Dielectric Breakdown Voltage test - to test the dielectric strength of the oil; minimum value: 30 kV (ASTM 877)

This tests worked for us. This may not work for others.