The detection signal produced by partial discharge is very weak, only in the microvolt range. In terms of value, it can easily be overwhelmed by external jamming signals. Therefore, it is necessary to consider the suppression of the influence of interference signals and take effective anti-interference measures.
The suppression methods of some interference in the partial discharge tester test are as follows:
(1) The interference of the power supply can be suppressed by the filter. The filter should reject all frequencies of the detector bandwidth, but test the voltage at low frequencies.
(2) Interference from the grounding system can be eliminated by connecting the test circuit to the appropriate grounding point through a separate connection. All nearby grounding metals should be well grounded without potential fluctuations.
(3) External interference sources introduced by the coupling of discharge test lines, such as high-voltage tests, nearby switching operations, static or magnetic induction and electromagnetic radiation caused by radio emission, are mistaken for discharge pulses. If these interfering sources cannot be removed, the test line should be treated to ensure a good surface finish, a large radius of curvature, and shielding. Thin, well-designed sheets, plates, or wires should be shielded. Sometimes the metal casing of the sample should be used as a shield. If possible, a shielding laboratory can be built.
Since the partial discharge pulse signal is a very weak signal, electromagnetic interference in the field can cause large errors 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 stun-free equipment as much as possible, especially the test transformer and coupling capacitor Ck.
(2) The partial discharge tester(partial dishcarge detector) 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 night.