Air Blast Circuit Breaker PRESENTATION ON Air Blast Circuit Breaker under the guidance of:- Presented By:- Mr. B.R.Reddy Anuj Kumar Pandey EN-3rd year Roll No. 0813321016

OVERVIEW INTRODUCTION CLASSIFICATION ADVANTAGES DISADVANTAGES APPLICATIONS FUTURE PERSPECTIVE

Introduction An electrical power system is very complex. It needs some form of switchgear in order that it may be safely and efficiently controlled or regulated under both normal and abnormal operating conditions. Circuit breaker is an automatically operated electrical switch. It protects an electrical circuit from damage caused by overload and short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.

Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. It can be of various size , from small device that protects the appliances of an household to large to protect the entire city.   Need of a Circuit Breaker The power distribution grid delivers electricity from a power plant to your house. The power distribution grid delivers electricity at a consistent voltage but resistance (therefore current)varies in a house. All of the different light bulbs and electrical appliances offer a certain amount of resistance, also described as the load . This resistance is what makes the appliance work

FUNCTIONS:- It carries the full load current continuously without over heating or damage. It opens and closes the circuit on no load. It makes and breaks the normal operating current. It makes and breaks the short circuit current of magnitude up to which it is designed for.

Classification The circuit breaker can be classified on the basis of the quenching (cooling) medium: Air circuit breaker Air blast circuit breaker Tank type bulk oil circuit breaker Minimum oil circuit breaker SF6 circuit breaker Vacuum circuit breaker   A light bulb, for example, has a filament inside that is very resistant to flowing charge. The charge has to work hard to move along, which heats up the filament, causing it to glow. Appliances are designed to keep current at a relatively low level for safety purposes. Too much charge flowing through a circuit at a particular time would heat the appliance's wires and the building's wiring to unsafe levels, possibly causing a fire. Need of a Circuit Breaker(cont…)

AIRBLAST CIRCUIT BREAKER This keeps the electrical system running smoothly most of the time. But occasionally, something will connect the hot wire directly to the neutral wire or something else leading to ground. For example, a fan motor might overheat and melt, fusing the hot and neutral wires together. The circuit breaker's job is to cut off the circuit whenever the current jumps above a safe level . Need of a Circuit Breaker(cont…)

Introduction These type of breakers employ ‘air blast’ as the quenching medium. The contacts are opened by air blast produced by the opening of blast valve. The air blast cools the arc and sweeps away the arcing products to the atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc. So the arc is extinguished and the flow of current is interrupted.   Breaker Design A circuit breaker does the same thing as a fuse -- it opens a circuit as soon as current climbs to unsafe levels -- but you can use it over and over again. Fuses only work once. Every time you blow a fuse, you have to replace it with a new one. The basic circuit breaker consists of a simple switch , connected to either a bimetallic strip or an electromagnet. The diagram below shows a typical electromagnet design.

Classification Types of Air blast circuit breaker (1). Axial-blast type (2).Cross-blast type (3).Radial-blast type TYPICAL ELECTROMAGNET DESIGN

In which the air-blast is directed along the arc path as shown in Fig. Axial-blast type:- In which the air-blast is directed along the arc path as shown in Fig.  The electricity magnetizes the electromagnet When the current jumps to unsafe levels, the electromagnet is strong enough to pull down a metal lever connected to the switch linkage. The entire linkage shifts, tilting the moving contact away from the stationary contact to break the circuit. The electricity shuts off. Breaker Design(cont…)

Types of Air blast circuit breaker In which the air-blast is directed at right angles to the arc path as shown in Fig. 2) Cross-blast type:-

Types of Air blast circuit breaker In which the air-blast is directed radially as shown in Fig (3) Radial-blast type:-

1) Axial blast Air blast circuit breaker

2) Cross-blast air breaker

Advantages The risk of fire is eliminated. The arcing products are completely removed by the blast The growth of dielectric strength is so rapid that final contact gap needed for arc extinction is very small. This reduces the size of device. The arcing time is very small due to the rapid build up of dielectric strength between contacts Due to lesser arc energy, ABCB are very suitable for conditions where frequent operation is required The energy supplied for arc extinction is obtained from high pressure air & independent of the current to be interrupted

Disadvantages Air has relatively inferior arc extinguishing properties. Air blast circuit breakers are very sensitive to the variations in the rate of restriking voltage. Considerable maintenance is required for the compressor plant which supplies the air blast .

Application The air blast circuit breakers are finding wide applications in high voltage installations. Majority of the circuit breakers for voltages beyond 110 kV are of this type.

Future perspectives In the near future, present interrupting technologies can be applied to circuit-breakers with the higher rated breaking currents (63 kA to 80 kA) required in some networks with increasing power generation.

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