This article introduces to affect four factors of electrical life of the contactor,that is usage category;rated current;operating frequency and working environment,and improves the electrical life of the contactor from this analysis.

This paper presents capacity calculation and selection of a frequency converter under seven different conditious,and discusses relations between capacity of the frequency converter and motor rated current and load torque etc,.

This article discusses the choice of rated current when low voltage circuit breaker is used in main or branch lines.

Firstly,the paper described problems of how to select frequency converter according to(require) of practical engineering from nominal power of AC motor,current rating of motor,practical(current) of(motor) and torque overload capability.

Enhancement of ripple current capacity of electrolytic capacitors;

They are higher ESR, overload ripple current, destruction by the foreign maters, abnormal voltage variation in the local power supply network, etc.

In practical,taken in the rectifi- er ripple current of the DC bus and the ripple current created by the inverter are the most important functions of electrolytic Capacitor used in three phase bridge rectifier output bus.