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How to prevent leakage of mining cables
In the prevention experiment, it was found that the leakage current of phase A was too large (when the voltage was added to 26 kV, the leakage current had reached MA), so the maintenance was suspended. Measure insulation resistance: !a=!b==0M".
Measured process
Breakdown points. A-phase DC withstand voltage experiment was conducted. At 35kV, the leakage current was increased by the agile mA to break down.
Straight flash method. Because when the voltage rises to 35kV, the fault does not flash out, and the voltage cannot be increased because of the capacity of the equipment. Therefore, flashover is used instead.
Flash method. Select 2yF storage capacitor, the impact voltage of 35kV, the ball gap flashover, showing the discharge of imperfect waveform; with the ball gap discharge intensity gradually weakened, after a few discharge no longer discharge. Analysis of the situation: The above-mentioned experimental results indicate that there is no discharge or discharge of faults. Because the fault resistance is too large, the fault site does not discharge at 35kV voltage, mining cable leakage is also smaller; the ball gap discharge once, the cable is charged once, together with the cable potential increased, which is reduced ball gap two voltage . Therefore, the discharge of the ball gap is interrupted when the voltage at both ends of the ball gap is reduced to fail to break through the ball gap after several discharges.
Impact points, make it discharge outstanding. The impulse voltage is 35kV, the discharge frequency is & s), after half an hour of impact discharge (at the moment, the sampling resistance and the tester should not be connected in the test loop), measure the insulation resistance: !A=k!, immediately select the flash method test.
The flash test waveform at a surge voltage of 21 kV.
Sound measurement point. Impact voltage: 21kV. Discharge frequency: /4~l/5(l/s). Fault condition discharge: Outstanding. Fixed position: At - the point is fixed. The point of fault in practice is a direct head of Chen's vintage oil filling.
Quiz understanding
Leakage problems, because the fault resistance is too high (M! level), not easy to discharge or discharge is not perfect.
When the frequency and intensity of ball-gap breakdown gradually decline, it is clear that the fault point discharge is not sufficient, and methods should be adopted to improve the discharge status.
In the course of the test, the abnormality of the resistance of the faults, and even the greater the resistance of the impact of the discharge faults, the faults of this characteristic are located in the traditional joints, especially the oil-filled cable ends.