Life of Capacitors

In this theory, effect of temperature, voltage and current on the life of capacitor is given. The life of capacitor is affected by

Factors affecting life of capacitor

Effect of Temperature on life of capacitor

The temperature depends upon following parameters.

Ambient temperature at which capacitor is operated

Over current flows through capacitor

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

 

Effect of voltage on life of capacitor

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

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 flow through capacitor

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.

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 lead to life of capacitor.

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