Causes of capacitor failure
Technical Support
Initial failure
The capacitor has potential defects. If an abnormal situation occurs in the early stage of power supply, it will accelerate deterioration and cause failure.
Occasional failure
The wiring is not secure or damaged by external force during installation.
Failure caused by overload
- The installation location is poorly ventilated and the surrounding temperature is too high.
- Overvoltage operation: The operating voltage includes power supply voltage fluctuations, harmonic voltages, and fundamental voltage rise after series reactors, which exceeds the maximum allowable overvoltage limit.
- Overcurrent operation: When the capacitor charging current contains harmonics, the effective value of the current shall not be greater than the allowable overcurrent limit.
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Capacitors used in automatic power factor controllers are frequently switched on and off as the load changes. If the sudden increase in current at the moment of switching on is not suppressed, it is very easy to cause capacitor failure and contactor contact damage.
Aging failure
After the capacitor has been used for many years, the electrical insulation strength is reduced due to aging of the insulation strength and internal free factors, causing damage.
Top ten reasons for starting capacitor failure
1. Environmental and temperature effects
◎Ambient temperature is too high
◎Poor heat dissipation of capacitor plate
◎Insufficient installation distance between adjacent capacitors, poor heat dissipation
2. Improper human operation
◎The low voltage capacitor should drop to 1 minute after power is cut off 50V or less
◎The high voltage capacitor should be reduced to 10 minutes after power is cut off 75V or less
◎The residual voltage has not dropped below the safe value,Reinvest
3. Improper selection of protective equipment
◎High voltage switch, Fuse or NFB
◎Wire diameter selection
◎Contactor (MC) level (at least AC3 level)
◎Selection of UV, OV and timer
◎Unbalance protection
4. Overcurrent
◎Due to the influence of harmonic effect
◎Resonance phenomenon causes harmonic value amplification
5. Inrush current
◎ According to IEC 60947-4-1 Table7b
6.Inrush current value:
◎The maximum value can reach 100 times of Isc rating
◎Improper selection of capacitor withstand voltage
7. Series resonance
◎Mutual influence between harmonics and capacitors in power supply systems
◎It will cause overvoltage
8. Parallel resonance
◎The impact of harmonic generation equipment and capacitors
◎It will cause overcurrent
9. Improper matching
◎No series reactor
◎ Improper selection of reactor specifications, 6%, 8% or 13%
◎The current carrying capacity of the reactor is insufficient
◎Controversy over impedance matching between reactors and capacitors
10. Equipment factors
◎Capacitor failure and aging
◎The reactor has insufficient current carrying capacity and the magnetic field is saturated
◎Poor manufacturing quality, C or XL/XC value fluctuation
◎Resonance frequency changes or is out of control