• 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. 

Protection against over load, short circuit & single phasing provided.

Metering: Digital frequency meter, ammeters & voltmeters. Ammeter and voltmeters are connected to CT &  PT of proper current and voltage ratio.

Duty cycle  -    Suitable for 1 minute withstand test of transformer