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:
- To secure that the insulation between the phase windings, turns, coils, tapping leads and terminals.
- For non-uniformity insulated windings the insulation between these parts and earth.
- Withstand the temporary over voltages and switching over voltages to which over voltages and switching over voltages subject to the transformer during its lifetime.
- Ensure that the transformer is not cut into one of the electrical supply lines.
- This causes the resonant effect to occur, causing high vibration voltage waves that may damage the transformer if there is a weak isolation.
- 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:
- Disconnect the electrical current from the transformer.
- Clean the terminals of the transformer.
Steps of 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.