Before the partial discharge test, the transformer should be deflated and left standing for more than 24 hours. When the high voltage is placed at 5 points, the voltage is applied from the low voltage side, all transformer bushings CT are short-circuited to ground, and all bushing terminal boards are grounded. The test is pressurized according to each stage; the neutral point of the high and medium voltage sides is grounded: the bushing head of the high and medium voltage sides has a shield: the reactor is used to compensate the capacitive current of the transformer (the overcompensation method is about 0.5-1A): The partial discharge detector was pressurized before the test, the high voltage side was pressurized to about 50kV, and the test voltage on the low voltage side was calibrated with a 100kV voltage divider. Interference suppression, interference is divided into the following two categories:
(1) Partial discharge detectors test for disturbances before the circuit is energized. The main sources are switching operations in circuits other than the test circuit, nearby high voltage electric fields, motor rectification, and radio transmissions.
(2) The interference generated after the partial discharge detector test circuit is energized, but not the internal interference from the test object. This disturbance usually increases with increasing voltage. The interference includes the partial discharge of the test transformer itself, the corona or poor contact discharge on the high-voltage wire, the partial discharge of the low-voltage power supply side, and the interference caused by coupling to the measurement circuit through the test transformer or other connecting lines.
Depending on the nature and source of the disturbance, the following methods can be used to suppress the disturbance.
(1) For power supply interference, a low-pass filter can be set on the primary side 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 shielding isolation transformer can be set for the test power supply and the instrument power supply.
(2) The 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) The only measure to suppress the interference of the grounding system of the test circuit is to select a grounding point in the entire test circuit. Some instruments have the function of suppressing interference. At this time, the balanced routing method and the time window method can be used to suppress interference.