Circuit Breaker

Part II

Circuit Breaker

Contents

Circuit breaker

Operating Principle

Interrupting principles for high-voltage circuit-breakers

Property of SF6

Advantages of SF6 breaker

Constructional design and operation

Major Supplier

Standards

Circuit breaker

In a simpler way a circuit breaker can be defined as an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

In electrical network a circuit breaker is defined as an mechanical switch device, capable of making, carrying and breaking currents under normal circuit conditions. Also capable of making and carrying current for a specified time and breaking currents under specified abnormal circuit conditions, such as those of a short circuit, without damage to itself.

Operating Principle

Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of "high voltage" varies but in power transmission work is usually thought to be 72,500 V or higher, according to a recent definition by the International Electro technical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers. In substations the protection relay scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault.

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

Oil-filled (dead tank and live tank)Oil-filled, minimum oil volume

Air blastSulfur hexafluoride

High voltage breakers are routinely available up to 765 kV AC. using SF6 gas as arc extinguishing media due to its high dielectric strength and other advantages.

Live tank circuit breakers are where the enclosure that contains the breaking mechanism is at line potential, that is, "Live". Dead tank circuit breaker enclosures are at earth potential.

Interrupting principles for high-voltage circuit-breakers

1

.

High-voltage circuit-breakers have greatly changed since they were first introduced and several interrupting principles have been developed that have contributed successively to a large reduction of the operating energy. Current interruption in a circuit-breaker is obtained by separating two contacts in a medium, such as sulfur hexafluoride (SF6),insulating oil and air having dielectrical and arc quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a blast of sufficient intensity.

Sulfur hexafluoride is generally used in present high-voltage circuit-breakers (of rated voltage higher than 52 kV).

Property of SF6

The dielectric strength of SF6 in on average 2.5 times that of air, and, by increasing pressure, it can be seen that the dielectric strength also increases and than around 3.5 bar of relative pressure, SF6 has the same strength as fresh oil.

Sound propagation in SF6 gas is about three times less than in air, at atmospheric pressure. The interruption of the arc will therefore be less loud in SF6 than in air.

It is non-toxic,

It is uninflammable,It will not explode.

It is a stable gas

Advantages of SF6 breaker

Advantages of SF6 circuit breakers can explain their success:

Simplicity of the interrupting chamber which does not need an auxiliary breaking chamber;Autonomy provided by the puffer technique;The possibility to obtain the highest performance, up to 63 kA, with a reduced number of interrupting chambers;Short break time of 2 to 2.5 cycles;

High electrical endurance.Possible compact solutions when used for GIS or hybrid switchgear.

2

Integrated closing resistors or synchronized operations to reduce switching over voltages.Reliability and availability

Low noise levels.

The reduction in the number of interrupting chambers per pole has led to a considerable simplification of circuit breakers as well as the number of parts and seals required. As a direct consequence, the reliability of circuit breakers improved, as verified later on by surveys.

Constructional design and operation

SF6 circuit breaker are divided mainly in two section i.e. interrupting chamber and operating mechanism

Construction of the interrupting chamber is more or less similar however design of operating mechanism varies manufacture to manufacture depending upon the type of mechanism.

Interrupting chamber

In modern SF6 circuit breaker interruption of the current are made on puffer principle wherein SF6 gas flow on to arcing zone is generated by puffer cylinder and piston. Stationary contacts and its assembly is suspended from the upper side of the interrupting porcelain. Over head conductors are connected to the upper and the lower terminal pads

6.1.1 Closed position

During this position current flow through stationary contact, moving contact, puffer cylinder and fixed finger contacts.

6.1.2 Opening operation

Opening is done by pulling down the insulating rod, piston rod, puffer cylinder moving contact, moving arc contact and nozzle. After some contact wiping stationary and moving arc contacts separate, thereby generating arc simultaneously gas pressure in puffer chamber builds up and high pressure gas flows through nozzle and quenches the arc.

6.1.3 Closing operation

3

During this operation insulting rod is pushed up and all the parts moved in reverse direction of the opening operation simultaneously SF6 gas is taken in to the puffer chamber

The moving contact system is connected to operating mechanism housed in mechanism housing

Interrupting Chamber

Operating Mechanism

Various types of operating mechanism are used in present days

Pneumatic

Hydraulic

Spring Charged

Major Supplier

Major suppliers of circuit breaker in DTL are BHEL, CGL, ABB, AREVA etc

4

Standards

The Indian and international standard references for CB s are as given in the table below:

Standard

Title

Affirmed date

IS 1138 1991

General requirement of circuit breaker

Sept 2002

IEC 60056 (1987)

above 1000 volt

IS 15136 :1993

Method of Synthetic testing of high

April 2003

IEC 60247 (1989)

voltage AC circuit breaker

IS 14657: 1998

Gas insulated metal enclosed switch

April 2003

IEC 61259 (1994)

gear 72.5 kV and above requirement

of switching of bus charging current

IS 14658: 1999

High voltage AC circuit breakers

April 2004

IEC 61633 (1995)

guide for short circuit and switching

test procedure for metal enclose dead

tank circuit breaker

IS 14674: 1999

High voltage AC circuit breakers

April 2004

IEC 61166 (1993)

guide for seismic qualification

IS 60517 :1990

Gas insulated metal enclosed switch

Sep 2002

IS/IEC 60517 (1990)

gear 72.5 kV and above

5

Site Inspection Record (SFQP)

Equipment: Circuit Breaker

Doc No : SFQP/CB/IR/01

Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 1 of 11

I- RECEIPT AND STORAGE

1

Receipt

Remark

a

Check the serial number and accessories detail

Poles

Operating drives

Switch Cubicle

Air receiver

Compressor

b

Check the name plate details

Remark

Circuit breaker type :

Rated voltage:

Sr NO

Normal Current

Gas Pressure SF6/20 deg.C(abs)

Lightning impulse withstand voltage

Short circuit breaking current

Short time withstand current

Line charging breaking current

Closing & Opening supply voltage

Operating Sequence

First pole to clear factor

Manufacturing Year

c

Complete material is available as per packing list?

Yes

No

If NO, mention the shortfall

Remark:

d

Instruction manual is available?

Yes

No

e

G.A and erection drawing is available?

Yes

No

f

Schematic drawings available?

Yes

No.

2

Storage

Yes

No

a

Was operating drives box stored indoor?

b

Was accessories box stored indoor?

Yes

No

c

Was the outdoor equipments store above raised platform?

Yes

No

d

Any equipment damaged during re transportation/unloading at

Yes

No

site?

e

Is there any gas leakage /oil leakage/smell

Yes

No

f

Is CBs kept away from inflammable material

Yes

No

Note: Deficiencies to be brought to the knowledge of higher authorities.




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 2 of 11

II- ERECTION




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 3 of 11

1.

Foundation

Yes

No

Is foundation and location of equipments including location of

foundation bolts as per G.A drawing?

2.

Structure

a

Is length of the foundation bolts (projected outside) sufficient to

Yes

No

put check nuts?

b

Is there leveling nut available below structure?

Yes

No

c

Is the top side of the structure base plate as per G.A. Drawing?

Yes

No

d

Is direction of the structure as per G.A drawing ?

e

Is the structure leveled in x, y and z axis as per G.A drawing/

Yes

No

instruction Manual? X axis= Pole to pole distance ( Measuring

tape);Y axis= Structure Height ( Water tube level) & z axis =

Alignment of all the structures in one line ( Line thread).

f

Tightness of the nuts and check nuts done?

Yes

No

g

Are the foundation bolts filled with mortar?

Yes

No

3

Switch cubicle and compressor

Is the switch cubicle & compressor erected as per G.A. Drawing?

Yes

No

4.

Trench provision

Are the trenches provide with supporting device for copper pipe

Yes

No

5.

Equipment matching

Are the serial nos of all the equipment matching with the serial

Yes

No

numbers mentioned in the packing list?

6

Pole

a

Is there any chipping on the petticoats of insulators?

Yes

No

* If Yes, what is the size of chipping?

Can erection work proceed further?

Yes

No

Do Not proceed further if chipping is unacceptable, immediately

report

b

Is

there positive pressure verified in all the three poles?

Yes

No

Verification to be done by pressing the gas valve/dilo after

opening the dummy cover.( in case of factory assembled pole)

c

Confirm no damages observed on gas valve/dilo coupling while

Yes

No

mounting the pole column on the structure?

Do Not proceed further, if unacceptable

d

Pole erection Details:

S No

R

Phase

Y

Phase

B

Phase

e

Is the direction of the pole gas valve/pressure gauge as per G.A

Yes

No

drawing?




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 4 of 11

f

Application of proper torque on all the mounting bolts?

Yes

No

*If YES, mention the values

1. Foundation bolts

Nm

2. Structure hardware

Nm

3. Pole mounting bolts

Nm

g

Whether

associated equipment are placed in their position during

Yes

No

the erection as per approved drawing and manual in correct phase

sequence

7.

Fixing of operating mechanism/ drive

a

Was there any ingress of water found inside the drives ?

Yes

No

Rectification /overhauling required

Yes

No

Do not proceed further before rectification/ overhauling of the drive

b

Threads of bottom seal rod found intact?

Yes

No

* if No, in which serial number of the drive is damage observed:

---------------------

Replacement of the bottom seal rod to be done in the above drive

c

Removal of the close interlock pipe done to avoid damage during

Yes

No

erection?

d

Matching of serial numbers done

with respective pole and drive?

Yes

No

e

Thorough cleaning of mounting surface done before mounting

Yes

No

f

Serial number details after fixing the drives:

R Phase

Pole:

Drive:

Y Phase

Pole:

Drive:

B Phase

Pole:

Drive:

g

Is the clearances between phases and with earth are conforming to

Yes

No

design value through out

h

Check that earthing of CB and structure done as per approved

Yes

No

earthing drawing?

i

Check connection in between individual pole unit and control unit

Yes

No

8.

Pneumatic piping (if applicable)

a

Availability of following material?

Yes

No

Bending machine, pipe cutter, hacksaw, flat & round file, emery

paper ,any special tools as per OEM manual , Mulmul cloth, pull

wire, petrol/CTC, bench vice and general purpose grease/oil.

* If No, to be arrange at site before starting the job.

b

Method used for bending the pipes

Remarks

*Avoid hot bending ,only cold bending

c

Are all the pipes flushed with water jet before starting bending?

Yes

No

*If No, first flush the pipe with water jet.

d

Cleaning of pipes with water jet after bending?

Yes

No

e

After bending are the pipes cleaned with pull through method

Yes

No

using mulmul cloth & petrol/CTC?

* If NO, reclean the pipe using above method

f

Is there

the emergency tripping unit in the breaker?

Yes

No

* If Yes, clean thoroughly

g

Procedure given in instruction manual for making ermetto joints

Yes

No

was followed?

* If No, cut the ermetto rings and follow the procedure with fresh

ring




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 5 of 11

h

Clamping of all pipe joints?

Yes

No

* If NO, to be done prior to air filling

9

Cabling

a

Availability of following tools for carrying out the cabling work?

Yes

No

Multi meter, hacksaw, Knife, set of pliers, set of screw drivers,

Insulation tape, ferrules, crimping tool and belt- button

*If No, arrange proper tools before commencing the cabling job.

b

Procedure for cable glanding being followed?

Yes

No

c

Identification of each core with suitable ferrules done as per

Yes

No

schematic drawing?

* If NO, check continuity of the cable and rework.

d

Is proper size of screw driver used for fixing wires in terminal

Yes

No

blocks and auxiliary switches ?

* If No., replace damage terminals and auxiliary switches

e

Are wires at safe distance from the cam of the aux. Switch, ON-

Yes

No

OFF indicator, space heaters/ variable resistors/thermostat, etc?

* If No, redress the cable

f

IR value of cables after completion of wiring by using 500 V megar.

Measured Value :

M ohm.

10

Gas

filling and leakage test

Prerequisite for SF6 gas filling: Thermometer, Temperature v/s pressure Chart from OEM

manual, SF6 gas cylinder, gas filling kit, suitable right/left connector, spanners, fresh cloth,

CTC/Petrol & Mulmul cloth etc.

a

Presence of pressure in all the three poles? For checking use

Yes

No

double spanners to open the dummy cover of gas valve/dilo

Coupling

* If NO, Fill the pressure in that particular pole up to 2.0 bar

absolute and sniff the complete pole with the leak detector and

find the leakage. If no leakage is found, continue gas filing and if

any leakage is found first attend the leakage point before

proceeding further. Decision for vacuum can vary case to case.

b

Is the gas monitoring system fixed as per G.A drawing?

Yes

No

c

Gas filling kit is Available at site

Yes

No

* If No, arrange gas filling Kit.

d

Calibration of density Monitor/ switch at ambient Temperature

Yes

No

Ambient temperature at

site substation control room --------Deg C

TB No

Absolute Bar

Low pressure alarm (connected between Terminals)

Opening Block- I (connected between Terminals)

Opening Block II (connected between Terminals)

Time at which Calibration done:

e

Is following procedure adopted for connection of gas pipes:

Yes

No

Ensure that gas pipe is through and without any blockage or

physical damage




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 6 of 11

Cleaning the sealing surfaces at both the ends of the gas pipes

as well as at density

monitor/block end and pole end with

petrol or CTC.

Applying thin layer of grease on the threads and also on the

O rings.

Holding the gas valve/ dilo with one spanner and tightening

the nut of the gas pipe with another spanner. Ensure That Gas

Valve/Dilo does not rotate during fixing the gas pipe.

f

SF6 gas leakage test

Is

Leak detector available in working condition?

Yes

No

* If NO, do not proceed further till leak detector is arranged.

Is the compete SF6 gas system in the breaker

( which includes

Yes

No

pole, gas pipes & density switch/ monitor) free from any SF 6 gas

leakage?

* If

No, describe leakage found from which joints:------------

Can these points be rectified at site?

Yes

No

* If No, does it needs replacement?

Is any material removed from spare breaker available at site?

Yes

No

Is material to be replenished/replaced

Replenish

Replaced

List of the material required to replenish/ replace

g

Check for tightening of all bolts and nuts

Yes

No

Remark:

III-COMMISSIONING CHECK




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 7 of 11

1

Compressor detail

Make

------------------

Serial number

------------------

Year of manufacturing

-----------------

Observation

Is oil filled up to required level?

Yes

No

Is quality of oil as per specification?

Yes

No

*If NO, drain the oil and fill the specified oil

up to

specific level.

Is the tension of the belt adequate?

Yes

No

*If NO, adjust the tension

2

Air filling

Presence

of mud/ dust or dirt in drive mechanism chamber

Yes

No

of any of the drive?

*If

YES,

proper cleaning is to be carried out in drive.

serial number:

Is the complete pneumatic system including air storage

Yes

No

receiver clean & free from foreign particles?

* If

NO, Repeat the cleaning exercise till satisfaction

Switch on AC supply

Measurement of 3 phase supply : Between phase to phase

:Between phase to neutral

Thermal over load relay settings done at

Measured motor current in all the 3 phase

R phase _____A

Y phase _____ A

B phase _____ A

Compressor stops at __

bar

Is there any air leakage detected with soap solution from any of

Yes

No

the joint?

* If YES, rectify the air leakage point. If required drain the air

Are all the pipes clamps firmly into the trench and with structure

Yes

No

angles?

IF NO, clamp the Pipes.

3

Pressure switch setting in

bar ( reference pressure gauge of cubicle)

Pressure in bar

Decrease

Increase

Trip block- I

Trip block- II

Close block

Auto re-close

Low Pressure alarm

Compressor start/ stop




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 8 of 11

4

Operation of the compressor safety valve is satisfactorily

Yes

No

* If yes, what is blow-off pressure

------- bar

* If NO, any required setting done /

What is the Re- setting pressure

------- bar

5

Is the inter cabling between operating drives and the switch

Yes

No

cubicle complete?

* If No, complete the wiring

Checking of complete wiring done as per schematic drawing

number--------

Connection of density switch/monitor cables:

Setting of the variable resisters ( Measuring of coil resistance)

Ambient temperature during measurement of resistance ___ at degree centigrade

What is the control voltage

___ V DC

Current across the control circuit

---- A DC

CLOSE COIL

R Phase -Coil resistance_____

+Variable Resistance

Total

_____Ohms

Resistance

Y Phase Coil resistance ____ + Variable Resistance

Total

_____Ohms

Resistance

B Phase coil resistance:_____ + Variable Resistance

Total

_____Ohms

Resistance

TRIP COIL-1

R Phase - Coil resistance_____ +Variable Resistance

Tot

_____Ohms

Resistance

Y Phase Coil resistance ____ + Variable Resistance

Total

_____Ohms

Resistance

B Phase coil resistance:_____+ Variable Resistance

Total

_____Ohms

Resistance

TRIP COIL-2

R Phase - Coil resistance_____

+Variable Resistance

Total

_____ Ohms

Resistance

Y Phase Coil resistance ____

+ Variable Resistance

Total

_____ Ohms

Resistance

B Phase coil resistance:_____

+ Variable Resistance

Total

_____Ohms

Resistance

Requirement of DC control voltage in ideal condition: (220 VDC)

Actually measured at site with multimeter _________ VDC

Switch ON DC supply

Local Operation of The Breaker (Electrically):

Local closing operation

OK

Local tripping operation for trip coil 1

OK

Anti pumping function

OK

Trip command provided directly on terminal number:

--------




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 9 of 11

9

Pole discrepancy relay operation

OK

Timer

Timer setting ------------- sec

10

Remote operation

Closing command given on terminal number

______

Tripping command (T1) given on terminal number

______

Tripping command (T2) given on terminal number

_____

11

Post clos. Trip circuit

supervision checked on terminal numbers

For Trip Coil 1

_______________________

For Trip Coil 2

_______________________

Pre

close Trip circuit

supervision checked on terminal numbers

12

Breaker position indication (electrical)

Which colour of the lamp glow when breaker

is TRIP

--------------

Which colour of the lamp glow when breaker

is CLOSE --------------

13

Spare Contact Checking:

Position of the breaker

TRIP

Serial number of contacts found

NC:

Serial number of contacts found

NO:

Position of the breaker

CLOSE

Serial number of contacts found NC:

Serial number of contacts found NO:

14

Is the breaker with Emergency Tripping Unit (ETU)?

Yes

No

*If Yes, follow procedure listed below to test the ETU:

Close the breaker electrically.

Switch OFF the DC Supply

TRIP the breaker through Emergency trip Unit

Check whether all the 03 poles are in trip position

15

Check number of operations,

in case of failure of compressor.

(i) Breaker in close position

Build up the normal

operating pressure as per OEM manual

Number of Trip & close

operations performed till blocking.------------------

(ii) Breaker in open position

Build up the normal

operating pressure as per OEM manual

Number of Trip & close

operations performed till blocking. -----------------

16

Breaker Timing

Serial number of the Timer

Last date of calibration

Operation

Limit

Phase

Measured value

Closing

millisecond

R

______

m sec

Y

______

m sec

B

______

m sec




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 10 of 11

Tripping(T1))

millisecond

R

_______ m sec.

Y

_______ m sec

B

________m sec

Tripping (T2)

millisecond

R

________m sec

Y

_______ m sec

B

_______ m sec

CO ( through T1)

millisecond

R

_______ m sec

Y

_______ m sec

B

________m sec

CO ( through T2)

millisecond

R

_______ m sec

Y

________ m sec

B

________ m sec

17

If closing and tripping time need to be adjusted (Procedure of

Yes

No

Adjustment as per OEM manual to be recoded)

R

________

Y

________

B

________

18

Pressure Drop During Operation :

Close

________

Trip

_______

CO

________

19

Tightness of all the electrical terminals of switch cubicle and

Yes

No

drive

20

Is Gas leakage, once again verified after timing and operation?

Yes

No

21

SF6

gas pressure

after completion of job :

Bar

Time

at which the final pressure noted:

PM

22

Is air leakage, once again verified after timing and operation?

Yes

No

23

Are all the petticoats of insulators, switch cubicle , drive

Yes

No

mechanism are thoroughly cleaned and free

from dust and dirt?

* If No, clean it thoroughly with dry cloth, before charging

24

Operational counter reading as on Date:

R phase

Y phase

B phase

25

Are all the covers of drive mechanism closed properly & firmly?

Yes

No




Site:

Bay:

Equipment Sr No.:

Make:

Rating:

Voltage level:

Page 11 of 11

Remark:

IV- COMMISSIONING

1

Breaker cleared for charging?

Yes

No

* If No, mention the reason/ pending points

2

Date and time of breaker charging

Signature

Signature

OEM Engineer

JE DTL

DELHI TRANSCO LTD

Standard Field Quality Plan

Name of Equipment: Circuit

Breaker

Doc No: SFQP/CB/01

Page 1 of 2

Sl

Characteristic /Item

Reference

Remark

No

document

/acceptance norms

RECEIPT & STORAGE

1.

Receipt

BOM/Packing

2.

Storage

list/manufactures

instruction manual

IIERECTION

1.

Foundation

BOM/Packing

2.

Structure erection

list/manufactures

3.

Switch cubical & compressor

instruction

4.

Trench provision

manual/approved

5.

Equipment Matching

drawing

Pole erectionFixing of operating mechanism/ drive.Pneumatic pipingCabling

10 Gas filling & leakage test III COMMISSIONING CHECK

1.

Compressor

Approved drawing/

2.

Air filling

Manufactures

3.

Pressure switch setting

instruction

4.

Compressor safety valve

manual/Test report

Inter-cablingMeasurement of coil resistanceDC control supplyLocal operation of breakerPole discrepancy operationRemote OperationTrip circuit supervisionBreaker position indicationSpare contacts checkingEmergency tripping unitNumber of operation in case of compressor failureBreaker timingClosing tripping time adjustmentPressure Drop during operation.Tightness of electrical terminals.

Re-checking of Gas leakage

Recording of SF6 gas pressure

Re-checking of air leakage.

Cleanliness of petticoats of insulator, switch cubical & drive mechanism

Operational counter reading

DELHI TRANSCO LTD

Standard Field Quality Plan

Name of Equipment: Circuit

Breaker

Doc No: SFQP/CB/01

Page 2 of 2

Sl

Characteristic /Item

Reference

Remark

No

document

/acceptance norms

Closing of covers of drive Mechanism

IV

COMMISSIONING

1. Clearance of breaker charging

Approved drawing/

2. Date and time of charging

Manufactures

instruction

manual/Test

report/Check list

Notes:

DTL specification shall mean DTL Technical Specification, approved drawings, LOA provision for specific contracts.Tests/Checks indicated at column No.2 of SFQP are only generally required to be conducted. However, any other test /check required may be carried out as per site requirement.All the testing and measuring equipment for testing should be calibrated.Test check which is not applicable for particular equipment/mode/contract shall be considered to have omitted.Latest revision/amendment of specification/standard/drawings shall be followed.For all checks suitable record shall be maintained.) Test /check indicated in column no 2 of

SFQP should be carried as per 100% sampling planning basis

Circuit Breaker

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