DIGITAL TESTING OF HIGH VOLTAGE CIRCUIT BREAKER

MADE BY:-NEERAJ PRASADROLL NO:-183ND YEAR EESURENDRA INSTITUTE OF ENGINEERING & MANAGEMENT

CONTENT• Origin• Introduction• Types of HV circuit breaker• Oil circuit breakers • Air blast circuit breakers• Sulphur hexafluroide circuit

breakers(SF6)• Vacuum circuit breakers

• Need for testing• Digital testing• Testing of circuit breaker• Aim of digital testing• Advantages &Disadvantages• Conclusions

Origin

• An early form of circuit breaker was described by Thomas Edison in an 1879 patent application, although his commercial power distribution system used fuses.

• Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads.

Introduction

What is a circuit breaker?

• A circuit breaker is a device which can make or break a circuit, either manually or automatically under all conditions .Like no-load, full-load and short-circuit conditions.

High-voltage breakers are broadly classified by the medium used to extinguish the arc.

• Oil circuit breakers• Air blast circuit breakers• Sulphur hexafluroide circuit

breakers(SF6)• Vacuum circuit breakers

Oil circuit breakersIt is designed for 11kv-765kv.These are of two types

• BOCB (Bulk oil Circuit Breaker)• MOCB (Minimum oil Circuit Breaker)

The contacts are opened under the oil and arc is struck between them.The heat of arc evaporates the surrounding oil and dissociates it into a substantial volume of gases hydrogen at high pressure.The hydrogen gas occupies a volume about one thousand times that of oil decomposed.The oil is ,therefore pushed away from the arc and expanding hydrogen gas bubble surrounds the arc region and adjacent portions of the contact as see in fig.

• Advantages:1.Oil has good dielectric strength. 2.Low cost.3.It has wide range of breaking capability.

Disadvantages:1.Slower operation , takes about 20 cycles for arc quenching.2.It is highly inflammable , so high risk of fire.3.High maintenance cost.

VACCUM CIRCUIT BREAKER

It is designed for medium voltage range (3.3-33kv).

This consists of vacuum of pressure (1*10-

6) inside arc extinction chamber.The arc burns in metal vapour when the

contacts are disconnected.At high voltage , it’s rate of dielectric

strength recovery is very high.Due to vacuum arc extinction is very fast.The contacts loose metals gradually due to formation of metal vapours.

Advantages:

1.Free from arc and fire hazards.2.Low cost for maintenance & simpler mechanism.3.Low arcing time & high contact life.4.Silent and less vibrational operation.

Disadvantages:

1.High initial cost due to creation of vacuum.2.Surface of contacts are depleted due to metal vapours.3.High cost & size required for high voltage breakers.

AIR BLAST CIRCUIT BREAKERS

This operates using high velocity blast of air which quenches the arc.

It consists of blast valve , blast tube & contacts.

Blast valve contains air at high pressure.Blast tube carries the air at high pressure

& opens the moving contact attached to spring.

There is no carbonization of surface as in VCB.

Air should be kept clean & dry to operate it properly.

Advantages:1.High speed operation as compared to OCB.2.Ability to withstand frequent switching.3.Facility for high speed reclosure.4.Less maintenance as compared to OCB.Disadvantages:1.Little moisture content prolongs arcing time.2.Pressure should be checked frequently for frequent operation.3.Risk of fire hazards due to over voltages.4.It can’t be used for high voltage operation due to prolonged arc quenching.

SF6 CIRCUIT BREAKERS It contains an arc interruption chamber containing

SF6 gas. In closed position the contacts remain surrounded

by SF6 gas at a pressure of 2.8 kg/cm2 . During opening high pressure SF6 gas at 14 kg/cm2

from its reservoir flows towards the chamber by valve mechanism.

SF6 rapidly absorbs the free electrons in the arc path to form immobile negative ions to build up high dielectric strength.

It also cools the arc and extinguishes it. After operation the valve is closed by the action of

a set of springs. Absorbent materials are used to absorb the

byproducts and moisture.

Advantages:

1.Very short arcing period due to superior arc quenching property of SF6 .2.Can interrupt much larger currents as compared to other breakers.3.No risk of fire.4.Low maintenance cost.5.No over voltage problem.6.There are no carbon deposits.Disadvantages:

1.SF6 breakers are costly due to high cost of SF6 gas.2.SF6 gas has to be reconditioned after every operation of the breaker, additional equipment is required for this purpose.

Need for testing HV circuit breaker:-

• When an overload or a short circuit occurs in the home or industry, the usual result is a blown fuse or a tripped circuit breaker.

• Circuit breakers are mechanical devices, which are subject to deterioration due to wear, corrosion and environmental contamination, any of which could cause the device to remain closed during a fault condition.

Testing of circuit breakers:-

• Routine tests • Type tests

Digital testing

A project started with the following parties :

• KEMA high power laboratories The Netherlands.

• Delft University of technology, The Netherlands.• Siemens AG, Germany• RWE Energy ,Germany

Aim of digital testing:-

• Developing digital testing of HV circuit breakers. I.e. , a software product for testing a model of such a device , once its characteristic fingerprints are obtained from refined measurements during standard tests.

• Digital offers a wide range of new possibilities for users , manufactures, standardizing bodies and test laboratories for fine tuning circuit breaker abilities in relation with standard and real power systems.

Advantages:-• Evaluation of the relevance of future standards for

different circuit breaker technologies and extinguishing media.

• Reduction of full scale testing in high-power laboratories.• Identification of network topologies that can pose special

difficulties to a circuit breaker.• Acceleration at development of new circuit breaker

design.• Monitoring the aging process of circuit breaker in

service.

Disadvantages:-

• Testing in costlier• Testing is time consuming• A tough procedure

Conclusion:-

• Digital testing gives precise information about the breaker, as obtained from laboratory tests.

• This is useful for the development of future standards.

• Powerful possibilities with digital testing are created when arc model and data analysis is coupled with a circuit analysis package.