INDUCED OVERVOLTAGE WITHSTAND TEST
   
 
PURPOSE OF THE TEST
 

The object of the test is to secure that the insulation between the phase windings, turn, coils, tapping leads and terminals, withstand the temporary overvoltages to which the transformer may be subjected during its lifetime.
   
 
PERFORMANCE
 

The excitation voltage is applied to the terminals of the low-voltage winding. The other windings are left open-circuited.

The duration of the test is:

rated frequency . 120 seconds
test frequency

The test is successful if no collapse of the test voltage occurs.

The test voltage connection is essentially the same as in service. A three phase winding is tested with symmetrical three-phase voltage induced in the phase windings. If the winding has a neutral terminal, may be it is earthed during the test.
   
 
The test voltage is twice the rated voltage. However, the voltage developed between line-terminals of any winding shall not exceed the rated short duration power-frequency withstand voltage.
 

 
 
The voltage is measured between terminals of the low voltage winding using a voltmeter at r.s.m. value. The voltage is so adjusted, that the average to the voltage value measured between terminals is equal to the required test voltage value.
   
 


Fig. 5.1
 Test circuit for induced overvoltage withstand test on three-phase transformer.
G1 supply generator, T1 transformer undertest, T2 current transformer, P1 ammeter, P2 voltmeter (r.s.m. value).
   
 
TEST REPORT
  The test voltage, frequency and test duration are stated in the report.