BHEL

G SAIKRISHNA 12121A0244CH.VAISHNAVIK.VASAVIG V AKHILB.NAVATEJA

12121A022312121A026512121A024512121A0220

INTERNAL GUIDEMr. U.KAMAL KUMAR, M.Tech., Assistant Professor,Department of EEE.

EXTERNAL GUIDEMr. G RAVI JATOTH M.Tech.,

Sr. Switchgear Engineer,BHEL- Ramachandrapuram...

A Mini project presentationOn

Submitted toJAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY ANANTAPUR, ANANTAPUR

In partial fulfillment of the requirementsfor the award of the degree of

BACHELOR OF TECHNOLOGYIN

ELECTRICAL AND ELECTRONICS ENGINEERINGBy

Under the esteemed guidance of

SREE VIDYANIKETHAN ENGINEERING COLLEGE(Autonomous)

Sree Sainath Nagar, Tirupati – 5171022011 – 2015

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

STUDY OF EHV CIRCUIT BREAKER

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04/18/2023

• About BHEL Hyderabad

• Introduction

• Circuit breakers classification

• Operating mechanism of BHEL EHV Circuit breaker

• Characteristics of SF6 gas

• Merits and demerits of SF6 gas circuit breaker

• Testing of EHV circuit breaker

• BHEL circuit breaker

• Conclusions

Contents

Dept of EEE2

04/18/2023Dept of EEE3

About BHEL Hyderabad

• The Hyderabad Unit of BHEL is located at Ramachandrapuram which is around 30KM from the

historic city of Charminar.

• Foundation Stone of the Plant was laid in 1959 and the production commenced in the year 1965.

• The Unit was set up mainly to manufacture 60MW and 110MW Steam Turbo Generator sets for

State Electricity Boards.

• From this small beginning, the Ramachandrapuram Unit has been growing steadily in different

phases of development and today it caters to a wide spectrum of business in Power, Industry,

Transmission, Oil and Gas.

04/18/2023Dept of EEE

Introduction

• Its basic function is to detect a fault condition and interrupt current flow. 

• A circuit breaker can be defined as an electromechanical device capable of

making, breaking and carrying currents under both normal and abnormal

conditions.

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04/18/2023Dept of EEE

• Unlike a fuse, which operates once and then must be replaced, a circuit

breaker can be reset (either manually or automatically) to resume normal

operation

• Circuit breakers are made in varying sizes, from small devices that protect

an individual household appliance up to large switchgear designed to

protect high voltage circuits feeding an entire city

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CONTD…

Dept of EEE

Classification of Circuit Breakers Based upon voltage :• Low voltage circuit breakers

• Medium voltage circuit breakers

• High voltage circuit breakers

• Extra High Voltage circuit breakers

• Ultra High Voltage circuit breakers

Based upon Location: 1) Indoor type

2) Outdoor type

Fig. 1: Indoor type

Fig. 2: Outdoor type 04/18/20236

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Based upon design:

• Dead tank circuit breaker : A switching device in which a vessel(s) at ground

potential surrounds and contains the interrupters and the insulating mediums

• Live tank circuit breaker : A switching device in which the vessel(s) housing the

interrupter(s) is at a potential above the ground

Fig. 3: Live tank circuit breaker

Fig. 4: Dead tank circuit breaker

Dept of EEE7

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Based upon interrupting medium

• Air blast circuit breaker

• Oil circuit breaker

1) Bulk oil circuit breaker

2) Minimum oil circuit breaker

• Vacuum circuit breakers

• SF6 gas circuit breakers

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Operating mechanism

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In Hydraulic mechanism moving parts are totally immersed in hydraulic

fluid and is a completely sealed system and protects the components

from corrosion.

The potential energy of the pressurised SF6 gas is used to operate the

contact system of the interrupter

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Fig. 5 BHEL Circuit breaker at site

04/18/2023Dept of EEE11 :Fig. 6: Hydraulic Mechanism of Circuit Breaker

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Fig. 7: ON and OFF positions of a circuit breaker

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Arc extinction in BHEL circuit breaker

Dept of EEE13

Fig.8: Arc extinction in BHEL circuit breaker

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Merits of SF6 gas circuit breakers

• SF6 is an electronegative gas and is excellent for use as an arc quenching

medium.

• Outdoor EHV SF6 has less number of interrupters per pole.

• The breaker is silent and does not make sound like air-blast circuit

breaker.

• The maintenance required is minimum, it may need once in four to ten

years.

Dept. of EEE14

04/18/2023Dept of EEE

Demerits of SF6 gas circuit breakers

• Sealing problems may arise. Imperfect joints lead to leakage of gas.

• Arced SF6 is poisonous and should not be inhaled.

• SF6 is a greenhouse gas.

• Influx of moisture in the breaker is very harmful and several failures

are reported due to this cause.

• Special facilities are needed for transport, transfer and maintenance of

gas.

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Characteristics of SF6 gas

Temperature in degree centigrade

• At high temperatures SF6 remains in gaseous state owing to high pressures.

Dept of EEE16

Pres

sure

in b

ar a

bsol

ute

Fig. 9: Characteristics of SF6 gas

04/18/2023

Gas pressure in gas absolute pressure

Uniform

field

bre

akd

ow

n v

olta

ge

Dept of EEE17

Fig.10: Comparison of SF6 with Air

• When compared with the air and water

SF6 has high breakdown voltage.

• Its relatively large molecules have a great

affinity for free electrons with which they

combine making the gas

• These properties remain effective up to a

temperature of 20000K and it is the reason

for the high dielectric strength of the gas.

04/18/2023Dept of EEE

Tests on BHEL Circuit breaker

Basically there are two types of tests

1) Type tests

2) Routine tests

Type Tests : These are like design validation test and are conducted only

once for a particular design until the standard gets revised.

Routine tests : These are to be conducted on every circuit breaker being

manufactured to ensure the breaker is manufactured as per the design.

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Type tests

Dept of EEE19

1. Switching performance test

2. Short circuit current test

3. High voltage test

4. Mechanical and environmental test

5. Temperature rise test

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Routine Tests

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• Mechanical operations test

• Measurement of contact resistance

• High pressure test on Hydraulic mechanism

• Power frequency withstand test on main circuit

• N2 leak test on accumulator

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BHEL Circuit Breaker

Dept of EEE21

• Circuit Breaker manufacturing was started in

1960s at Hyderabad. BHEL works in collaboration

with Sweden.

• In 1980s SF6 breakers were introduced by BHEL

in technical collaboration with Siemens Germany.

• Presently BHEL is manufacturing SF6 circuit

breakers with Hydraulic mechanism of 145kV,

245kV, 420 kV and 800kV Voltage ranges. They

manufacture only outdoor breakers and are of live

tank design.Fig. 11: BHEL 420kv circuit breaker

04/18/2023Dept of EEE

Electrical data of BHEL circuit breaker

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Specifications:

Rated voltage kV 420

Rated Insulation level

- lighting impulse withstand

voltage

kV

1425

- one minute power frequency

withstand voltage

kV 520-610

Rated frequency Hz 50

Rated normal current A 2000, 3150

Rated short - circuit breaking current kA 40

Rated short-circuit making current kA 2.5 times rated short-circuit breaking current

Rated short-circuit current duration Sec 1.0

Rated duty cycle --- O-0.3sec.-CO-3 min.-CO

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Closing time ms 100 max

Opening time ms 22 max

Arcing time ms 18 max

Closing and opening times of the BHEL manufactured circuit breakerCONT’D…

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Conclusions

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• From Primitive Air circuit breaker designs to Present day SF6 circuit breaker there is

lot of evolution in the breakers.

• As present day breakers are dominated by SF6 circuit breakers and it is a greenhouse

gas, there is a plenty of research is being carried out to replace this as the interrupting

media.

• But with available modern technology these obstacles may be over come and in near

future a solution with low cost, superior performance and reliability may arrive

marking a revolution in the breaker designs.

04/18/2023Dept of EEE

References

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B. M. Weedy, “Electric Power Systems Second Edition”, John Wiley and Sons, London, 1972, ISBN 0-471-92445-8 pp. 428-430 

D. Braun, W. Heilmann, A. Plessl, “Application criteria for SF6 and vacuum circuit-breakers”. ABB Review 4/89, 25–33

Sunil S Rao. "Switchgear protection and power systems", eighth edition.

Siemens ,“Basics of Circuit breakers” , STEP series.