Dielectric Frequency Responce

The dielectric test of transformer is generally performed in two different steps, likewise, separate source voltage withstand test and induced voltage withstand test of transformer, which we have discussed one by one below.

Separate source voltage withstand test of transformer
This dielectric test is intended to check the ability of main insulation to earth and between winding.

Procedure
1) All three line terminals of the winding to be tested are connected together.
2) Other winding terminals which are not under test and also tank of the transformer should be connected to earth.
3) Then a single-phase power frequency voltage of shape approximately sinusoidal is applied for 60 seconds to the terminals of the winding under test.
4) The test shall be performed on all the windings one by one.
5) The test is successful if no break down in the dielectric of the insulation occurs during test.