What are the methods to eliminate the interference sources when measuring partial discharge of transformer?

The interference sources during the measurement of partial discharge of transformer include the interference of power supply network, interference of various electromagnetic field radiation, poor contact of test circuit, corona at various parts and internal discharge of test equipment, interference of earthing system, and interference of suspended discharge of metal objects.

During the partial discharge test of the transformer, the power interference mainly comes from two aspects: one is from the power supply network, that is, the on-site maintenance power supply, which uses low-voltage low-pass filter and shielded isolation transformer to filter the interference; the other is from the test power supply network, that is, the test transformer and voltage regulating device, which can use high-voltage low-pass filter to filter the interference signal.

When conducting on-site tests, the interference not only comes from the power supply, but also from spatial interference, that is, the interference generated by various electromagnetic field radiation in the test circuit induction. At this time, the interference generated by filters and other components of the spatial electromagnetic field in the test object, coupling capacitors, and other parts of the circuit cannot be suppressed. When such interference affects the measurement, the balanced wiring method and the function of the partial discharge instrument can be used to suppress the interference and improve the detection sensitivity. When the interference source comes from the power supply, the balance circuit should include a high-voltage circuit, that is, both devices should use the same power supply to apply high voltage, and the grounding side should be connected to the balance input unit to achieve the best balance effect. When the interference source is from the coupling effect of electromagnetic waves, one of the two test objects of the grounding balance circuit can be left without high voltage, and the rest of the circuit remains unchanged. The non pressurized test object acts as an antenna, which is phase equilibrium with the same high-frequency signal coupled to the test object, reducing interference signals, but this method has no inhibitory effect on the power supply.

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