Abstract :
Capacitors are made with a wide range of materials to achieve specific types of performance. Their reliability is a function of the voltage and temperature operating conditions of the dielectric and the climatic and mechanical environmental conditions of the encapsulation. About one-seventh of all equipment failures are due to capacitors and half of these are due to improper selection or application. In choosing a capacitor for a given operation it is important to recognize that the limits given in specifications are statistical quantities. Particular care is necessary to establish the correct operating conditions of voltage and temperature. With proper care in selection, rating and application reliability of about 0.01% per 1000 hours is achievable but in extreme conditions this may rise to 1% per 1000 hours or more. The conditions for open or short circuit failure are given for various types of capacitor. The other main causes of failure are ingress of moisture and mechanical failure. New series of specifications are developing which will ensure the provision of more data for the circuit designer. The main need is for regular and systematic testing and the feedback of fault data to improve the control of the manufacturing processes. Reliable components can only be produced by fully optimized manufacturing techniques. Economic considerations show that it is unreasonable to expect a component to be significantly better than the specification to which it is bought. The reliability of a component is thought to be optimum for given application when first cost plus replacement cost plus the cost of the loss of equipment time is minimum.
