This test set provides a continuously variable output voltage at double frequency to test the insulation between turns of coils, layer to layer, terminals of windings with either uniform or graded insulation and also between the windings and earth, with graded insulation of both Distribution and Power transformers.
An alternating voltage of sine wave form (as much as possible) at double frequency (100 Hz.) and double in amplitude can be applied at one side of the transformer under test while the windings, which are not connected to the source of excitation, are left on open circuit. This higher frequency is considered to avoid excessive excitation current during the testing.

Voltage source:

To generate a voltage at 100 Hz., one 3-phase squirrel cage induction motor is given a supply through a star-delta switch. This motor drives the slip ring induction motor (generator). A variable voltage is also supplied to the generator thereby producing double frequency, which along with the output voltage of the generator is available across the terminals of the Set.

Selection chart: