Make Break In Power Circuit Breaker.pdf 364q60

Make/Break s By: Emile Nasrallah, Fouad Brikci, Stéphan Perron, P.Eng., Circuit Ph.D., Zensol Hydro-Québec Breaker Specialist Automation Inc. teacher

In Power Circuit Breakers

PREFACE

OIL CIRCUIT BREAKER

The interruption of electric power circuits has always been an essential function, especially in cases of overloads or short circuits when immediate interruption of the current flow becomes necessary as a protective measure. In earliest times, circuits could be broken only by separation of s in air followed by drawing the resulting electric arc out to such a length that it can no longer be maintained. This means of interruption soon became inadequate and special devices called circuit breakers had to be developed.

INTRODUCTION

S

In oil circuit breakers, the arc is drawn in oil inside a special compartment of the interrupting

ince the beginning, scientists based

chamber called the explosion pot. The intense

their

the

heat of the arc decomposes the oil and produces

capabilities of the available quenching

gases, mainly composed of hydrogen, generating

quench or extinguish the high power arc, which

mediums. Hence the breakers are classified

high pressure that produces a fluid flow through

necessarily occurs at the separating s of a

accordingly.

the arc and out of the explosion pot through vents

The basic problem has been to control and

research

on

exploring

breaker when opening high current circuits.

situated on its walls. Thus extending the arc’s colThe arc quenching ambients are numerous.

Since arcs generate a great deal of heat energy,

umn and carrying its energy away until its total extension see Fig 3.

most often destructive for the breaker's s,

Historically, it should be mentioned that pure

technology had to find ways to limit the arc

water has had some use in Europe. The arc

At transmission voltages below 345 kV, oil

duration and develop s that can withstand

produced gases, steam and hydrogen, which are

breakers used to be popular. They are increasing-

the arc effect time after time.

as effective as the vapor and hydrogen from oil in

ly losing ground to gas-blast circuit breakers such

quenching the arcs, but insulation problems have

as air-blast breakers and SF6 circuit breakers.

limited the use of this medium and at present no breakers are being built that use this technique.

AIR-BLAST CIRCUIT BREAKER

For the purpose of the present article, we will limit our quest to those most popular: Oil, Compressed air, SF6 and Vacuum. In the present article you will find a summarized

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BREAKER CATEGORIES

description of the different designs of make/break

Breaker development research has explored

s found in the modern power circuit

the available mediums and has come up with a lot

breakers and the key factors influencing their

of breaker designs but most of them fall into four

architecture and material choice.

major categories:

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In air-blast circuit breakers, air is compressed

electrodes. Vapor particles expand into the

limited and of short duration. They cause no dep-

to high pressures. When the s part, a blast

vacuum and condense on solid surfaces. At a

osition of by-products.

valve is opened to discharge the high-pressure air

natural current zero the vapor particles disappear,

to the ambient, thus creating a very-high-velocity

and the arc is extinguished. Vacuum breakers of

flow near the arc to dissipate the energy.

up to 242 kV have been built.

ARCHITECTURE FOR HIGH-PRESSURE ARCS: The s have to withstand the arc’s heat

SF6 CIRCUIT BREAKER

without excessive damage. They also need to have

MAKE/BREAK S The breaker’s heart is the switching element.

good conduction properties.

It is where the arc quenching takes place. It mainly contains the make/break s and the

Tungsten and tungsten alloys have good

interrupting medium. The make/break s’

resistance-to-arc properties but less conductivity.

functions can be reduced to:

Copper and silver have great conductivity but

• Conduct the electric current when the

relatively poor resistance-to-arc properties.

breaker is closed. • Withstand the arc’s destructive effect while

The s have also to overcome the deposition of by-products that may become a

interrupting.

problem if not wiped off before an insulating layer Generally, the make/break s have a

is built.

stationary part and a moving part. By bringing the In SF6 circuit breakers, the same principle is employed, with SF6 as the medium instead of air.

moving part to touch the stationary one, electric current flows and the breaker is closed.

The type of s that are commonly found in these types of devices are:

In the “puffer” SF6 breaker, the motion of the SLIDING S

s compresses the gas and forces it to flow

By driving the moving away from the

through an orifice into the neighborhood of

stationary the electric arc develops and by

As their name indicates, the moving

the arc. Both types of SF6 breakers have

quenching it the current stops flowing and the

and the stationary touch on closing and

been developed for EHV (extra high voltage)

breaker is open.

slide into each other to a certain distance before stopping at closed position. On opening, they

transmission systems. VACUUM CIRCUIT BREAKER

design and choice of materials are

slide out until their separation and the arc's

greatly affected by the arc's energy, duration and

ignition. The sliding action helps to wipe off the

the chemical reactions that may occur with the

deposited by-products, to make better on

ambient medium under the arc’s effect.

closing.

To understand these crucial elements,

This type of usually separates the

it is necessary to review the electric arc’s

resistance-to-arc role from the current carrying

characteristics.

role, by using tungsten alloy based s called arcing s that are meant to close first on closing and separate last on opening and are

ELECTRIC ARC The electric arc is a natural phenomenon.

submitted to the arc. The current carrying role is

Despite its destructive nature it is of great use to

attributed to copper or silver plated copper

current switching in circuit breakers. It acts as

s called main s. These s are

variable impedance from zero value when the

not subjected to the arc and therefore not eroded

breaker is closed to infinity when the breaker is

by it.

open. DESIGN EXAMPLES Designers worked hard to reach effective

HIGH-PRESSURE ARC The vacuum breaker uses the rapid dielectric

Found in blast type circuit breakers (air-blast,

recovery and high dielectric strength of vacuum.

SF6 and oil circuit breakers). Great heat

A pair of s is hermetically sealed in a

generation

durations

In the KSO type oil circuit breaker by the

vacuum envelope.

characterize them. They also generate deposition

General Electric company, the stationary

of solid by-products that may affect the

is a ring of sprung copper (or sliver plated)

conductivity of the s.

fingers where two of them have a

Actuating motion is transmitted through

and

relative

long

tungsten tip (see Fig 7).

bellows to the movable . When the

56

designs exploit these principles.

s are parted, an arc is produced and

VACUUM ARC

ed by metallic vapor boiled from the

Found in vacuum circuit breakers. They are

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The moving is a solid rod of copper (or silver-plated) with the upper part made of tungsten (see Fig 7a)

In the Dell-Alsthom, PKV type air-blast circuit

In SF6 ABB, HPL Type circuit breaker, The ABB, DLF Type air-blast circuit breaker uses butt s which are particularly shaped to achieve these goals. breaker, the stationary is a tulip made of sliver plated copper fingers where two of these s are arcing fingers made of tungsten. The moving is a tube of silver-plated copper with the upper part made of tungsten (see Fig 8a).

For main s the stationary is a tulip made of sliver plated copper fingers, the moving is silver-plated copper tube The arcing is completely separate from the main . The stationary is a tungsten rod and the moving one is a tulip consisting of tungsten fingers.(see Fig 10a)

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To overcome this problem, the arc root must be made to move over the surface.

FOR VACUUM ARCS: none of the above conditions are present. Two plates of conductive material can constitute the moving and the stationary s. Generally we need to separate them to a short distance (3mm to 20mm).

In order to achieve this, s are so shaped, as in Fig 12, that the current flow

In a vacuum circuit breaker, vacuum

through them results in a magnetic field being

interrupters are used for breaking and making

established which is at right angles to the arc

load and fault currents. When the s in

axis. This radial field causes the arc root to rotate

vacuum interrupter separate, the current to be

rapidly around the resulting in a uniform

interrupted initiates a metal vapor arc discharge

distribution of the heat over its surface. s

and flows through the plasma until the next

of this type are called radial magnetic field

current zero. The arc is then extinguished and the

electrodes and they are used in the majority of

conductive metal vapour condenses on the metal

circuit breakers for medium voltage applications.

surfaces within a matter of microseconds. As a result the dielectric strength in the breaker builds up very rapidly.

A

new

design

has

come

in

vacuum

interrupters, in which switching the arc from diffusion to constricted state is done by subjecting

The properties of a vacuum interrupter

the arc to an axial magnetic field. Such a field

depend largely on the material and form of the

can be provided by leading the arc current

s.

through a coil suitably arranged outside the vacuum chamber. Alternatively the field can be pro-

Over the period of their development, various

vided by deg the to give the

types of material have been used. At the

required path. Such s are called

moment it is accepted that an oxygen free copper

axial magnetic field electrodes.

chromium alloy is the best material for high voltage circuit breakers. In this alloy, chromium is distributed through copper in the form of fine grains.

This

material

combines

good

arc

extinguishing characteristic with a reduced

All of these s use a wiping action when the moving gets inserted in the stationary

TESTING

tendency to welding and low chopping

Make/break s as presented need to be

current when switching inductive current. The use

tested periodically to assess their condition.

of this special material is that the current

These s have to keep their good conduc-

chopping is limited to 4 to 5 Amps.

tive properties when the s are fully closed.

as we see the traces of this action in Fig 11.

This principle has advantages when the short circuit current is in excess of 31.5 kA.

The conductive properties may be affected by the At currents under 10kA, the vacuum arc burns as a diffuse discharge. At high current values the

mechanical wear due to friction on operation or electrical wear caused by the electrical arc.

arc changes to a constricted form with an anode spot. A constricted arc that remains on one spot for too long can thermally overstress the s to

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RESISTANCE MEASUREMENT: The

best

method

for

testing



such a degree that the deionization of the

resistance is to put in application Ohm’s law.

zone at current zero can no longer be guaranteed.

It consists of applying a current, usually 100

Electric Energy T& D Magazine l May-June 2007 Issue

59

Amps, and to measure the voltage drop in volts across the closed s. The resistance is then calculated in dividing the voltage by the current. The resulting value is read in micro-ohms, 1 micro-ohm= 10-6 ohms. This measurement is used on all types of s.

BIBLIOGRAPHY The present article is based on our personal experience. • Power circuit breaker theory and design,

maintenance. Since graduation in 1984 he worked as a field

edited by C.H. Flurscheim, revised edition

engineer. In1990 he ed the worldwide circuit

1982;

breaker manufacturer GEC ALSTHOM as a

• Circuit Interruption theory and techniques, edited by Thomas E. Browne Jr., edition 1984;

DYNAMIC RESISTANCE:

Emile Nasrallah is an electrical engineer specialized in Power circuit breakers

• material, Proc. 9th Int. Conf.

specialized field engineer. In 1997 he became the manager of MV & HV circuit breaker SF6 division of ALSTOM, responsible of technical , maintenance and training for SF6

For some breakers, especially those that use

Electr. phenom./24th Holm Conf.

circuit breakers. In 2001 he became manager

an arcing nozzle to drive the flow of the

Electr. s, IIT, Chicago, September

of Air blast circuit breaker division for AREVA.

quenching medium (puffer type SF6 breakers for

1978, pp. 81-86.

He was in charge of the Air blast (PK and PKV) refurbishing program in partnership with

example, see fig 10b), the wear of arcing

• JK. Lemelson, The failure of closed heavy

s, if excessive, may affect the arc

current pieces in insulating oil at

hydro-Quebec and introduced a unique

quenching capability of the interrupter, resulting

high temperature, Proc. 6th Int. Conf.

istration system for the program

in its destruction.

Electric phenom., IIT, Chicago,

(average of 35, 735 kV PK air blast circuit

June 1972, pp. 252-258;

breaker per year). In 2005 he ed General

So the assessment of the arcing

• R. Holm and E. Holm, Electric s:

Electric Company of Canada as a senior circuit

cannot be done by simply measuring the

Theory and Application, Springer-Verlag,

breaker specialist and is in charge of the circuit

resistance in the classic way as described

New York, 1967, pp. 89, 136, 161, 438;

previously. A new method is developed called the

• COMPARISON BETWEEN VACUUM AND

dynamic resistance. It consists of

SF6 CIRCUIT BREAKER FOR MEDIUM

measuring the resistance as described

VOLTAGE on

above but continuously while the is

http://www.panickker.net/article6.htm

breaker division of the Montreal service centre, responsible of the remanufacturing program for Oil circuit breakers Dr. Fouad Brikci is the president of Zensol Automation Inc. He was the first to introduce

moving from the first touch until the fully

• Circuit breaker: Definition and Much More

closed position. This method permits to measure

from Answers.com Science and Technology

the concept of truly-computerized test

the length of the arcing and by comparing

Encyclopedia.

equipment in the field of circuit breaker analyzers. As a former university teacher in

it to a value measured when new, helps determine its state of erosion. It is important to state that this method does not apply to butt-type s. SUMMARY The electric arc plays an important role in the

About the Authors

Ecole Polytechnique — Algiers and CNRS -

Stéphan Perron, Hydro-Québec teacher, High

LAAS researcher in , Dr. Brikci has

Voltage breaker maintenance

developed experience in the fields of

Stéphan Perron has been teaching maintenance

electronics, automation, and computer science.

and trouble shooting of High Voltage Circuit

Most activities were focused on the industrial

Breakers and Thermography for more than 7

application of computers. Among his

years at the Hydro-Quebec Competence Center

achievements are the development of fully

choice of material and shape of the make/break

based in Saint Antoine des Laurentides, QC,

comput¬erized measuring systems for quality

s.

Canada. He developped his expertise by working

control in circuit breaker manufacturing,

In high-pressure arcs, intense heat is

on the maintenance side of the High Voltage

laboratories, and maintenance services of

Circuit Breakers of Hydro-Quebec for 18 years.

electric utilities. Dr. Brikci holds a PhD in

generated, which the s have to resist and

His specialties are the ABB (models SFE, HPL,

Electronics and a Master in Sci¬ences in EEA

keep their conductive properties. This is achieved

ELF and DLF) breakers, the GE (models KSO,

(electronics, electrotechnics, and automation)

by using tungsten alloys and copper or silver-

AT) breakers and all the related test instruments,

from the University of Bordeaux, .

plated copper and tulip s shape.

as well as the sectionnors Joslyn VBM, the

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In vacuum arcs, the choice of materials is

handling and behavior of the SF6 gaz and

email : [email protected]

interpretation of thermagraphic readings

Fouad Brikci, Zensol Automation Inc.

crucial to limit vapor emissions and favor their

(Level 1) on breakers. Stéphan Perron holds

condensation within microseconds otherwise the

a DEC degree in Electronics from the

s are destroyed. Oxygen-free copper

CEGEP St Jérome, QC, Canada

chromium alloy is the best material for high voltage circuit breakers and butt shape is commonly used .

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