By hvhipot 
Before the partial discharge test, the transformer should be vented and allowed to stand for more than 24 hHV Hipot Electric Co., Ltd.s. The high voltage is placed at the 5th branch, voltage is applied from the low voltage side, all transformer bushings CT are short-circuited to ground, and all bushings end screens are grounded. The test is carried out according to the pressure of each phase; the neutral point of the high and medium voltage side is grounded: the bushing head of the high and medium voltage side is put on the shielding cover: the capacitive current of the transformer is compensated with a reactor (overcompensation is about 0.5-1A) ): Before the test, the partial discharge detector should be tested and pressurized. The high-voltage side is pressurized to about 50kV, and the test voltage is calibrated from the low-voltage side with a 100kV voltage divider.
Interference suppression, interference is divided into the following two categories:
(1) The interference that exists before the test circuit of the partial discharge detector is energized. Its main series resonances are switching operations in other circuits other than the test circuit, nearby high-voltage electric fields, motor rectification, and radio transmission.
(2) The interference generated after the partial discharge detector test circuit is energized, but not from the internal interference of the test product. This interference usually increases with the increase in voltage. This interference includes the partial discharge of the test transformer itself, the corona or poor contact discharge on the high-voltage conductor, and the partial discharge of the low-voltage power supply side, which is coupled to the test transformer or other connections. Measure the interference caused in the loop, etc.
According to the nature and series resonance of the interference, the following methods can be used to suppress the interference.
(1) For interference from the power supply, a low-pass filter can be set on the primary of the high-voltage test transformer, a high-voltage low-pass filter can be set on the high-voltage end of the test transformer, and a shielded isolation transformer can be set for the test power supply and the power supply for the instrument.
(2) The main measure to suppress the corona discharge at the high-voltage end is to select a suitable non-corona ball as the high-voltage connection.
(3) Suppress the interference of the grounding system of the test loop. Weiyi’s measure is to select one point of grounding in the entire test loop. Some instruments have the function of suppressing interference. At this time, the balanced wiring method and the time window method can be used to suppress the interference.