1. Test purpose and significance

Dielectric loss measurement is more sensitive to finding distribution defects such as moisture and aging of the insulation or air gap discharge defects in the insulation. It has been widely used in the factory inspection and operation maintenance test of transformers.

2. Test procedure

1. Measure and record the ambient temperature, relative humidity, transformer nameplate, instrument name and serial number. And disconnect the high and low voltage measuring windings and neutral wires.

2. Short-circuit the three-phase windings on the high-voltage side of the transformer, connect the high-voltage output terminal of the instrument to the high-voltage side winding of the transformer via the high-voltage test wire (core wire), short the three-phase winding on the low-voltage side of the transformer, and ground the ground terminal of the instrument.

3. Turn on the power switch of the instrument, set the parameters, select the reverse connection method, internal standard, frequency conversion, internal high voltage, and test voltage (10kV).

4. Press the high voltage switch of the instrument, click to start the test, and wait for about 30 seconds to display the test results, including the capacitance value C and the dielectric loss tgδ.

5. After the test is completed, save or print the results as required, turn off the instrument, and then remove the wires.

Three, matters needing attention

1. Ensure that the instrument and the low-voltage side winding of the transformer are reliably grounded, and scrape the paint and rust on the grounding point.

2. In reverse connection test, use core wire for high voltage test wire, and suspend the shield wire.

3. When the rated voltage of the high-voltage side winding of the transformer is 10kV and above, the test voltage is 10kV. Below 10kV, the test voltage is equal to its rated voltage.

4. If the transformer has a neutral point, short-circuit it with the winding on the same side when wiring.

5. For oil change, try to measure when the oil temperature is lower than 50℃, and the tgδ at different temperatures needs to be converted.

6. During the test, the high-voltage test wire should not be in contact with the transformer shell, and a certain distance should be kept there.