06/01/2021

On which factors the life of capacitor depends?

 

The life of capacitor is affected by

  • Temperature
  • Voltage
  • Current

Temperature

The temperature depends upon following parameters

( 1 ) Ambient temperature at which capacitor is operated

( 2 ) Over current flows through capacitor

( 3 ) Dielectric and resistive power loss in the capacitor

  • As the temperature increases, there is fast degradation of the dielectric. The life of capacitor is reduced to half for every 10 degree increases in the temperature. 
  • The life of capacitor reduces for faster degradation of the dielectric. There is expansion of impregnation and dielectric material if the temperature increases beyond its limit. 
  • The capacitor may be burnt in the worst condition. The classification of capacitor is done according to ambient maximum temperature operating condition.

Symbol

Maximum ambient temperature

A

40

B

45

C

50

D

55

 Voltage

  • If the voltage increases beyond its specific limit, the dielectric of capacitor may breakdown. 
  • This will result in capacitor may short circuit permanently.

Current flow through capacitor

  • If the voltage increases beyond its specific limit, the capacitor current increases because the XC of the capacitor remains same. 
  • This will reduce the life of capacitor.
  • Voltage limit for capacitor

+ 10%

8 hours in 24 hours

+15%

30 min in 24 hours

+20%

5 min in 24 hours

+30%

1 min in 24 hours

 Current

( 1 ) Over load current

  • The over load current of capacitor is due to over voltage and harmonics. This may lead to local hot spot and internal short circuit of the capacitor.

( 2 ) Inrush current

  • When capacitor is switched on, a very high inrush current flows which may be 100 times rated current of capacitor. 
  • If the inrush current is not limited during frequent switching operation, it may leads to life of capacitor.

 

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