Transformers
Transformers
Posted By MMASBA

Induced over voltage test of transformer


Induced over voltage test of transformer

Induced over voltage test of transformer is one of transformer testing that carry out at manufacture factory … and this test classified under routine test of transformer & type test of transformer >>> to see full details about transformer testing click here >>> transformer testing

 

Purpose of Induced over voltage test of transformer:

  1. To secure that the insulation between the phase windings, turns, coils, tapping leads and terminals.
  2. For non-uniformity insulated windings  the insulation between these parts and earth.
  3. Withstand the temporary over voltages and switching over voltages to which over voltages and switching over voltages subject to the transformer during its lifetime.
  4. Ensure that the transformer is not cut into one of the electrical supply lines.
  5. This causes the resonant effect to occur, causing high vibration voltage waves that may damage the transformer if there is a weak isolation.
  6. Discovering the air gaps between the layers of the windings to find out the efficiency of insulation between these layers and other layers and high voltage high-frequency we use will detect these air gaps.

Precautions before do this test:

  1. Disconnect the electrical current from the transformer.
  2. Clean the terminals of the transformer.

Steps of Induced over voltage test of transformer:

Induced over voltage test of transformer

  • Apply the excitation voltage to the terminals of the low voltage winding.
  • Left the other windings open circuited.
  • Normally, we use high frequency voltage source (the test frequency is typical 180 HZ) to prevent magnetic flux saturation, and the test voltage is twice rated voltage.
  • Select the tapping of the off-circuit tap changer.
  • So, in all windings the voltage during the test is as near as possible to the rated test voltage.
  • We can calculate the duration of the test from this relation:
  • T test = [rated frequency / test frequency] x 120 seconds = 40 s (min 15 sec, max 60 sec)
  • Repeat the test at each tap changer point of transformer.
  • The test is successful if no collapse of the test occurs.

 


Electrical Engineer