Leakage discrimination method of fixed capacitor and common fault treatment

Date：2022-09-16 17:22:13Views：848

Capacitors are widely used in life and industry, and many devices have capacitors. In the absence of special instruments, the quality of capacitors can be detected and judged with multimeter resistance. This paper collects and sorts out some materials, hoping to be of great reference value to all readers.

1、 Detection method of fixed capacitor

1. Detect small capacitance below 10pF: because the capacity of fixed capacitors below 10pF is too small, use a multimeter to measure, and only qualitatively check whether there is leakage, internal short circuit or breakdown. Multimeter R can be selected for measurement × In 10k gear, use two probes to connect two pins of the capacitor at random, and the resistance value should be infinite. If the measured resistance value (the pointer swings to the right) is zero, it indicates that the capacitor is damaged due to leakage or internal breakdown.

2. Detect 10PF ～ 001 μ F Fixed capacitor: judge whether it is good or bad by judging whether it is charged. Multimeter R × 1k gear. Two triode β The values are all above 100, and the penetrating current should be small. Composite tubes can be composed of 3DG6 and other silicon triodes. The red and black probes of the multimeter are respectively connected with the emitter e and collector c of the composite tube. Due to the amplification effect of the composite triode, the charging and discharging process of the measured capacitance is amplified, so that the pointer swing of the multimeter is increased, which is convenient for observation.

3. It should be noted that during the test operation, especially when measuring the capacitance of small capacity, the pin of the measured capacitance should be repeatedly changed to contact two points A and B, so as to clearly see the swing of the multimeter pointer. For 001 μ Fixed capacitance above F, R of multimeter can be used × 10k gear is used to directly test whether the capacitor has charging process and whether there is internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.

Common fault handling

1. Common faults of capacitor. The power supply shall be cut off immediately when one of the following conditions of the capacitor is found.

(1) The capacitor shell expands or leaks oil.

(2) The casing is broken, flashover and sparks occur.

(3) The internal sound of the capacitor is abnormal.

(4) The temperature indicator falls off when the shell temperature rises above 55 ℃.

2. Troubleshooting of capacitor

(1) When the capacitor explodes and catches fire, immediately disconnect the power supply and use sand and dry fire extinguisher to extinguish the fire.

(2) When the fuse of the capacitor is blown, it shall be reported to the dispatcher, and the circuit breaker of the capacitor shall be opened after obtaining consent. Cut off the power supply to discharge it, and conduct external inspection first, such as whether there is flashover trace on the outside of the bushing, whether the shell is deformed, whether there is oil leakage and whether the grounding device is short circuited, and shake the insulation resistance value between electrodes and between electrodes and ground, and check whether the capacitor bank wiring is complete and firm, and whether there is phase loss. If no fault is found, replace the fuse and put it into operation. If the fuse is still fused after power transmission, the fault capacitor shall be exited and power transmission to the rest shall be resumed. If the circuit breaker trips at the same time as the fuse is blown, forced transmission is not allowed at this time. It shall be put into operation after the above inspection is completed and the insurance is replaced.

(3) If the circuit breaker of the capacitor trips but the shunt fuse is not broken, discharge the capacitor for three minutes before checking the power cable of the circuit breaker current transformer and the outside of the capacitor. If no abnormality is found, it may be caused by voltage fluctuation of external fault bus. After inspection, it can be put into trial; Otherwise, further comprehensive power on test shall be conducted for the protection. Through the above inspections and tests, if the cause is still not found, it is necessary to act according to the system and gradually test the capacitor. No trial investment is allowed until the cause is found out.

3. Safety precautions when handling faulty capacitors. Since the two poles of the capacitor have the characteristics of residual charge, first try to discharge its charge, otherwise electric shock accident is likely to occur. When handling the fault capacitor, the circuit breaker of the capacitor bank and its upper and lower disconnectors shall be opened first. If fuse protection is adopted, the fuse tube shall be removed first. At this time, although the capacitor bank has discharged by itself through the discharge resistance, there will still be some residual charges, so it must be discharged manually. When discharging, first fix the grounding terminal of the grounding wire with the grounding grid, then discharge the capacitor for many times with the grounding rod until there is no spark and discharge sound, and finally fix the grounding wire. At the same time, it should also be noted that if the capacitor has internal disconnection, fuse fusing or poor contact of the lead, there may be residual charges between its two poles, which will not be discharged during automatic discharge or manual discharge. Therefore, the operation or maintenance personnel shall wear insulating gloves before contacting the fault capacitor, and use a short circuit to short circuit the two poles of the fault capacitor to discharge. In addition, capacitors connected in series shall be discharged separately.

The above is the relevant content of the "fixed capacitor leakage discrimination method and common fault handling" brought by the core creation detection. I hope it can be helpful to everyone, and we will bring more wonderful content later. The company's testing services cover: testing and verification of electronic components, IC authenticity identification, product design material selection, failure analysis, functional testing, factory incoming material inspection, tape weaving and other test items. Welcome to call Chuangxin Testing, we will serve you wholeheartedly.