Power Fittings Megohmmeter To Measure The Insulation Of Oil-immersed Self-cooling Transformer

Copper Terminal block megohmmeter to measure the insulation of oil-immersed self-cooling transformer:
(1) When measuring the insulation resistance of oil-immersed self-cooling transformer, a 2500V megohmmeter with a scale range of 1000Mn should be used.
(2) Measurement items
① The insulation resistance of the high-voltage winding to the low-voltage winding and the shell, referred to as high to low and ground. ② The insulation resistance of the low-voltage winding to the high-voltage winding and the shell, referred to as low to high and ground. (3) Requirements for the qualified value of transformer insulation resistance
The qualified values ​​of insulation resistance of newly installed and overhauled 3~10kV transformers under different temperature conditions are shown in Table 7-4.
Table 7-4 Qualified value of transformer insulation resistance under different temperature conditions
Temperature/C 20 30 40 50 60 7 80Good value/MO 900 450 725 120 64 3 15 12Minimum value/MA 600 300 150 80 43 2 8
The insulation resistance value measured this time shall not be 30% lower than the value measured last time when converted to the same temperature.
(4) Absorption ratio R6o/R1s
The absorption ratio is the ratio of the insulation resistance at 60s and 15s in the shaking test. At 10~30C, it should be 1.3 times or more.
(5) Shaking test process
①The transformer to be tested shall be taken out of operation, and safety technical measures such as power outage, power test, discharge, and installation of temporary grounding wire shall be implemented; the shaking test shall be carried out by two people, and insulating gloves shall be worn.
❷Remove the busbars or wires on both sides of the high and low voltage of the transformer.
③ Clean the high and low voltage porcelain bushings of the transformer, and then use a wire to wrap 2~3 turns around the porcelain skirt of each porcelain bushing to connect the high and low voltage porcelain bushings respectively.
④ Short-circuit the high voltage terminals A, B, C and low voltage terminals a, b, C,
N of the transformer with steel wire.
The high voltage environment group of Zhongyangxi is connected to the low voltage temporary group and the external ground, as shown in Figure 7.10, the E terminal of the megohmmeter is connected to the low voltage group and the external ground, and the G terminal is connected to the porcelain skirt of the high voltage porcelain bushing. ⑥ Measure the insulation resistance of the low voltage winding to the high voltage winding and the shell, and the wiring is shown in Figure 7.11. The E terminal of the megohmmeter is connected to the high voltage winding and the shell, the 1 terminal is connected to the low voltage winding, and the G terminal is connected to the porcelain skirt of the low voltage porcelain bushing.
Wire connection
Figure 7-10 Measure the wiring of high-voltage winding to low-voltage winding and shell insulation resistance
Figure 7-11 Measure the wiring of low-voltage winding to high-voltage winding and shell insulation resistance
⑦ When measuring, the E terminal and G terminal should be connected to the connection wire of the object to be measured. One person uses an insulating rod to pick up the connection wire on the working terminal, and the other person shakes the meter to the rated speed (120r/min), then connects the L line to the high-voltage winding (or low-voltage winding), and reads the reading after the megohmmeter pointer stabilizes for 1 minute. Then remove the L line first, and then stop shaking the meter.
⑧ After the shaking test is completed, the high and low voltage windings must be discharged to the ground, the short-circuit wires between each phase are removed, and the original wiring is restored.