PRESENTATION ON SUMMER TRAINING PROGRAM TRAINING PLACE : ELECTRICAL LOCO SHED KANPUR ON THE BEHALF OF KANPUR INSITUTE OF TECHNOLOGY , KANPUR PRESENTED TO.. (HOD) RAKESH KUMAR PANDEY

AC VACUUM CIRCUIT BREAKER

INTRODUCTION I Fig :- placement of VCB on loco 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.

The distinguishing features of the circuit breaker are 1 The distinguishing features of the circuit breaker are 1.It’s vacuum switch tube(VST), 2.It’s electric pneumatic control. TYPES OF VCBS 1,Single bottle vacuum circuit breaker

2. 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.

2. 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.

3. LOWER PART THE PNUEMATIC CIRCUIT THE DRIVE MECHANISM THE AUXILIARY CIRCUIT (LT)

THE AUXILIARY CIRCUIT (LT) Auxiliary switch (AS) which changes it’s status depending on the position of circuit breaker. Auxiliary switch is configurable and is of proven fish bone type. Auxiliary switch drive (AD) mechanism which is linked with opening function.

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.

OPERATION The method of operation of circuit breaker is 1 OPERATION The method of operation of circuit breaker is 1. CLOSING OF VCB a) VCB OPEN Status of VCB in open condition is shown below:

b)ORDER (PULSE) TO CLOSE THE VCB Here we first energise the electro-pneumatic valve solenoid coil, operating of the electro-pneumatic valve (EP), air flows from air tank (AR) to the piston drive.

c) HOLDING THE VCB IN CLOSE POSITION Holding of VCB in close position is achieved by the compressed air, VCB switched on.

2. OPENING OF VCB a) Status of VCB in close condition as shown in previous figure b) Intruption of Current Supply of EP Valve Solenoid Coil Denergisation of EP valve solenoid coil Air supply from air tank is blocked and exhaust port open of the EP valve. Exhaust of the compressed air available in pneumatic cylinder (PN). Related figure shown below

Fig: interruption of current supply of EP valve Start the return of piston stroke through above mentioned action ensures safe opening of contacts. Fig: interruption of current supply of EP valve Fig: rapid movement of piston c) RAPID MOVEMENT OF PISTON The piston is accelerated by the release of the air pressure and release of contact pressure springs stored energy.

Fig: rapid movement of piston d) END OF PISTON STROKE

VACUUM CHARACTERISTICS According to Paschen’s law, the voltage applied between contacts in a vacuum varies as a function of the gas pressure and the distance between the contacts

CHARACTERISTIC OF THE AUXILIARY SWITCH The circuit breaker is equipped with 9 auxiliary contacts controlled by the cam drive linked with operating rod. Auxiliary switch can be configured to any combination of NO & NC as per requirement of application. State of contact : 5NO (normally open) : 4NC (normally closed) Number of contacts available for customer : 4NO (normally open) Now modified :6NO (normally open) :2NC (normally closed) Characteristics – Test voltage : 2.0 KV Continuous current : 10A Nominal current & breaking capacity : 2A@110V DC L/R=15ms

TYPICAL CLOSER TIME tcm Mechanical time for contact closing tce Total closing time

TYPICAL OPENING TIME tcm Mechanical time for contact closing tce Total closing time

MOUNTING ARRANGMENT Fig. Instalation of VCB on loco Fig: mounting arrangemgement of VCB

ADVANTAGES The main advantages of fish bone in vacuum circuit breaker as compared to rotary switch in vacuum circuit breaker are as follows The case of failure of fish bone circuit breaker is less as compared to rotary switch as in rotary switch there is very less crushing (less contact pressure) The life of fish bone circuit breaker is more as compared to the rotary switch, The maintinance required in case of fish bone is less as compared to rotary switch, The contacts are not visual in rotary switch but in fish bone ,the contacts can be visualised easily, The reliability of fish bone auxiliary contact increase by doing paralleling of spare contacts.

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.