24-12-2012, 06:51 PM
AC VACUUM CIRCUIT BREAKER
AC VACUUM CIRCUIT.pptx (Size: 5.32 MB / Downloads: 58)
INTRODUCTION
The vacuum circuit breaker (VCB) is a single phase 25 KV circuit breaker used to protect power circuit for application on electric locomotives and electrical multiple units (EMU’S).
The device is used as a line circuit breaker to close and open the power circuit and also to break the circuit under overload, short circuit conditions or any other abnormal working conditions defined and implemented for the application.
DOUBLE BOTTLE VACUUM CIRCUITBREAKER.
It offers a high degree of insensitivity to climatic conditions, has a compact design, high rupture capacity, long life-span, reduced maintinance
CONSTRUCTION
The vacuum circuit breaker comprises three main parts which are the upper part, which is the high voltage circuit (HT), the intermediate part, which assures isolation from earth and the lower part with the electro-pneumatic and the auxiliary circuit (LT).
UPPER PART
A vacuum switch tube moving contact is fitted with pushed screw, flexible shunts to carry the current from moving contact to shafting head. Spring box houses the contact springs and operating cam to transfer the vertical motion into horizontal direction.
INTERMEDIATE PART
It serves to isolate the upper part (HT) from the lower part (LT) i.e. it isolates the vehicle roof, which is earthed with the high tension part of the circuit breaker.
VACUUM SWITCH TUBE CONSTRUCTION
The vacuum switch tube comprises two copper alloy contacts, one fixed and the other moving.
The fixed contact is mounted on a metal flange which carries the ceramic outer cover of the chamber.
The ceramic cover is generally in two parts with the metal screen fixed between them.
This screen protects the ceramic parts against deposition of metallic vapours produced by the arc when the contacts are open.
CONCLUSION
The fish bone auxiliary switch is used instead of rotary switch which over comes all the problems of overheating to its inadequate designing.
The efficiency of fish bone can be increase by paralleling of pins in the fish bone thus we currently used it in VCB more efficiently.