AUXILIARY TRANSFORMER TESTING METHODS

1. Insulation Resistance Test.
2. Ratio Test.
3. Vector Group Test.
4. Winding Resistance Test.
5. Magnetizing Current Test.
6. Magnetic Balance Test.


1.Insulation Resistance Test:

To check the insulation level of transformer winding & oil this test is conducted
Apply the 5 KV on the primary to earth for 15 seconds & 60 seconds values to find polarization index value
Apply 2.5KV between primary to secondary and note down the 15 seconds & 60 second value.
Apply 1 KV between secondary to earth and note down the 15 seconds & 60 seconds value.

2.Ratio Test:

To find the transformation error this test is carried out. Apply 3-phase Voltage on the primary side and measure the secondary side voltage in TAP 3 & TAP 5.Calculate the ratio error by actual and measured value.

3.Vector Group Test:

To verify the vector group as specified by the manufacturer this test is carried out.
For example: Dyn11 Transformer
To verify, superimpose the 1U and 2U terminals and measured the voltages as per below equation and justify

Equation:
1.1U 1V = 1U 2n + 1V 2n
2.1V 2W=1V 2V
3.1W 2W < 1W 2V.

4.Magnetic Balance Test:

To verify the correct identification of cores and phases and to verify mutual flux inductance, this test is carried out.
Apply the voltage on one winding and measure the voltage sharing on the other windings. By theory the adjacent placed winding should share more flux than the other. That is if we apply on 1U –1V winding, 1V-1W should share  more voltage than 1W-1U. Note done and verify the magnetic balance as below

APPLIED VOLTAGE (V)			Measured  voltage(V)
1U-1V	1V-1W	1W-1U	1U1V	1V1W	1W1U
415	__	__	__
__	415	__		__
__	__	415			__

 5.Magnetizing Current Test:

To Asses the no load losses of the transformer this test is carried out. Measure the magnetizing current of the each winding / phase by tong tester or multimeter and verify with factory report.

6. Winding Resistance Test:

To verify the resistance value as specified by the manufacturer and to asses any damage on winding this test is carried out. Apply the DC current of 10Amps through the winding with the feedback of voltage drop the kit will calculate winding resistance value. Compare and verify with factory test report.