The detection signal generated by the partial discharge is very weak, only in the microvolt range. In terms of value, it is easily overwhelmed by external interference signals. Therefore, it is necessary to consider the suppression of the influence of interference signals and take effective anti-interference measures.
Some interference suppression methods in partial discharge tester testing are as follows:
(1) The interference of the power supply can be suppressed by the filter. The filter should be able to reject all frequencies of the detector bandwidth, but test the voltage through low frequencies.
(2) The interference of the grounding system can be eliminated by connecting the test circuit to the appropriate grounding point through a separate connection. All nearby grounded metals should be well grounded without potential fluctuations.
(3) External interference sources introduced by the coupling of discharge test lines, such as high voltage test, nearby switching operation, static or magnetic induction caused by radio emission and electromagnetic radiation, are mistaken as discharge pulses. If these sources of interference cannot be removed, the test line should be treated to ensure good surface finish, large radius of curvature, and shielding. A well-designed thin metal plate, sheet metal or steel wire should be shielded. Sometimes the metal housing of the sample should be used as a shield. If possible, a shielded laboratory can be built.
Since the partial discharge pulse signal is a very weak signal, on-site electromagnetic interference can cause a large error in the measurement results, so it is difficult to measure accurately. In order to improve the measurement accuracy, in addition to the above anti-interference measures, the partial discharge meter should also take the following measures:
(1) The equipment used in the test should be as halo-free as possible, especially the test transformer and coupling capacitor Ck.
(2) The partial discharge tester has good filtering performance and high-frequency isolation between the power supply and the measurement circuit.
(3) The test time of the partial discharge tester should be selected at a time with less interference, such as at night.
