SWITCHGEARSWITCHGEAR

Gear for switchingGear for switching

CIRCUIT BREAKERSCIRCUIT BREAKERS

ISOLATORSISOLATORS

HV / EHV SWITCHGEARHV / EHV SWITCHGEAR

SWITCH

FUSE

NOT USED IN A TRANSMISSION NETWORK AS IT WOULD FAIL TO INTERRUPT.

CIRCUIT BREAKERCIRCUIT BREAKER

A circuit breaker is defined as a mechanical device capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specific time and breaking currents under specific abnormal circuit conditions such as those of short circuit.

The circuit breaker serves two basic purposes

Switching during normal operating conditions for the purpose of operation and maintenance.

Switching during abnormal conditions such as short circuit and interrupting fault currents.

CIRCUIT BREAKER (52)

•IEC62271-100

Origins

• An early form of circuit breaker was described by Edison in an 1879 patent application, although his commercial power distribution system used fuses. [1] Its purpose was to protect lighting circuit wiring from accidental short-circuits and overloads.

• The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials.

• When a current is interrupted, an arc is generated - this arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit.

ARC quench techniques

• Different techniques are used to extinguish the arc including:

• Lengthening of the arc

• Intensive cooling (in jet chambers)

• Division into partial arcs

• Zero point quenching

Power plant

Transformer Transformer Local distribution net work

Transmission

line

Switch

Yards

Switch

Yard

Power Transmission system

CLASIFICATIONN OF CIRCUIT CLASIFICATIONN OF CIRCUIT BREAKERSBREAKERS

Based on VoltageLow- Medium less than 1kV

HIGH - 1kV to 52kV

Extra High- 66kV to 765kV

Ultra High -above 765kV

Based on locationIndoor

Outdoor

Based on External designdead tank

Live tank

Based on Interrupting mediaAir break

Air blast

Bulk oil

Minimum oil

SF6 gas insulated

vacuum

DEAD TANK TYPE LIVE TANK TYPE

CLASIFICATION OF AIS BREAKERS

ACB AIR ABCB BOCB OIL MOCB SF6

VACUUM

Development of CB’S(1)

• Until recently oil circuit breakers were used in large numbers for in many voltage switchgears. There are number of disadvantages of using oil as quenching media in circuit breakers. Flammability and high maintenance cost are two such disadvantages!

Development of CB’S(2)

• Manufacturers and Users were forced to search for different medium of quenching. Air blast and air circuit breakers were developed but could not sustain in the market due to other disadvantages associated with such circuit breakers. (bulky and cumbersome,noisy). Further research were done and simultaneously two types of breakers were developed with SF6 as quenching media in one type and Vacuum as quenching media in the other .

Oil Circuit Breaker

Oil Circuit Breakers are extensively employed in our power systems until 1970s. In these the properties of the arc are employed for are extinction. Thus by using arc energy to crack the oil molecules, hydrogen gas may be generated which can be used to sweep, cool and compress the arc plasma and so deionize it in a self – extinguishing process.

BOCB

MOCB

Arc Rupture under oil •It should be noted that by immersing the interrupting contacts in oil, the production of an arc during contact separation cannot be prevented. However the heat of arc immediately evaporates the surrounding oil and dissociates it into carbon and a substantial volume of gaseous hydrogen at high pressure.,.

* Hydrogen by its high heat conductivity cools the arc so fast that the voltage required for reignition is 5 -10 times as high as that required for air and thus is best suited for interruption. Moreover it is produced spontaneously in arcs under oil.

Arc Extinction in Air BlastIn Air blast circuit – breakers the air flows from high pressure reservoir to the low atmospheric pressure during the arc extinction process. The flow rate is governed by the throat diameter of the nozzle, the pressure difference and the nozzle profile. The design is such that almost supersonic speeds of flow are achieved. The axial flow of air at high velocity causes rapid reduction in the diameter of the arc and the arc does not reappear after the final current zero.

High volume of air resorvoirs,pipes,compressor plant--- disadvantages.when pr is low,br recloses.

VCB(1)

• In a Vacuum circuit breaker, vacuum interrupters are used for breaking and making load and fault currents. When the contacts in vacuum interrupter separate, the current to be interrupted  initiates a metal vapour arc discharge and flows through the plasma until the next current zero. The arc is then extinguished and the conductive metal vapour condenses on the metal surfaces within a matter of micro seconds. As a result the dielectric strength in the breaker builds up very rapidly

Mainfeatures:High quality vacuum interrupter design

•Simplified arc quenching method

•Robust compact construction  

•No evacuation tube

•Slim body design

•High reliability

•Contacts touch each other

•Normal position is close.

Rating of VCB Voltage range : 3.3 kV to 36 kV

Current range: 200 A to 4000 A

Breaking current range : up to 50 kA

Impulse withstand voltage (BIL) : up to 325 kV

VCB(2)

• The properties of a vacuum interrupter depend largely on the material and form of the contacts.. At the moment it is accepted that an oxygen free copper chromium alloy is the best material for High voltage circuit breaker.

• Gap maintains normally 6mm for 11KV• Gap maintains normally 18mm for 33KV• Gap is the limitation for EHV breakers

SF6 CB HIGHLIGHTS

• ELECTRONEGATIVE• HIGH THERMAL CONDUCTIVITY• HIGH DIELECTRIC• NON-TOXIC• STABLE,CHEMICALLY INERT• NO CONTAMINATION TAKES PLACE• Affects the ozone layer (It has a global warming

potential that is 23,900 times worse than CO2).

Arc Extinction in SF6 Gas

In plasma, most of the current is carried by electrons. In certain gases like SF6, the atoms and molecules have the property of attracting electrons to form negative ions. Negative ions are heavier than electrons and move slowly, thereby the resistance of plasma increases rapidly. Therefore, electronegative gas like SF6 is excellent arc extinction medium.

Two sets of contacts High resistance solid comes inside and low

resistance hallow cylindrical comes outside

Puffer cylinder,piston arrengment causes to increse the pressure inside from 8kg to 15kg

momemtararyly, thus dielectricstrenth increases rapidly helps in arc quenching.

SF6 GAS PROPERTIES

• Normally Gap is 38mm in 132kv CB’S,

•50mm in 220KV and,

•70mm/break in 400kv

•Pr’s 6kg/sq.mtr—8kg/sq.mtr

• Till now what we have seen will happen inside the chamber called arcing chamber.this is top portion of pole unit. Arcing takes place in top arcing chamber only.but entire pole contains dielectric media.pole is a part of CB.

Types of mechanisms

• Hydraulic

• Pneumatic

• Spring

• Mixed

72.5kV Minimum Oil Circuit Breaker type HLC

145kV Minimum Oil Circuit Breaker type HLD

145kV SF6 Circuit Breaker type 3ARI-EG

145kV hydraulic mechanism operated SF6 gas breaker

245kV SF6 Circuit Breaker type 3AV1

420kV SF6 Circuit Breaker type 3AT2/3

800kV SF6 Circuit Breaker type 3AT4/5

800kV Type 3AT4/5 SF6 gas circuit breaker

Schedule Of Guaranteed Technical Particulars Of 12kv,800/1250,25KA Indoor Metalclad Vacuum Circuit

BreakerS l. No DESCRIPTION DETAILS

1 Manufacturer's type designation

WMS 12/1250

2 Applicable technical standards

I.E.C 62271-100, I.E.C 62271-200 & TS 11118 10Q1

3 Type of breaker offered Indoor Draw out type Metal clad VCB

4 Rated voltage (kV) 12

5 Rated frequency (Hz) 50

6 Number of poles Three

7 Class (indoor/outdoor) Indoor

8 Rated normal current

(a) Under site conditions(Amps) 800/1250

(b) Rated current (Amps) 800/1250

9 Rated short circuit breaking current

(a) rms value of A.C. component of rated short circuit current (kA)

25

(b) percentage of D.C. component 45

10 Rated short circuit making current (kAp) 62.5

11 First pole to clear factor 1.5

12 Rated operating sequence O-0.3sec-CO-3min-CO

13 Rated duration of short circuit(sec) Upto3

14 Rated out of phase breaking current (kA) 6.25

15 Opening tune (ms) 35 +/- 5

22 Short tune current rating for 3 seconds 25 kA rms with 62.5 kA p

17 Arcing time (ms)

(a) At 100% rated breaking current (ms) 8-11

(b)At 50% rated breaking current (ms) 7-10

(c) At 25% rated breaking current (ms) 6-8

(d) At 10% rated breaking current(ms) 5-6

18 Total Break Time (ms)

(a) At 100% rated breaking current (ms) 47-49

(b) At 50% rated breaking current (ms) 50

(c) At 25% rated breaking current (ms) 48

s(d) At 10% rated breaking current (ms) 45

19 Closing time (ms) 45 +/- 5

20 Minimum reclosing time at rated interruption capacity from the instant of trip coil energisation (ms)

21 Minimum dead time for reclosing (ms) 250

22 Rated shunt capacitor bank switching capacity (single bank) in Amps

400

23 Max. Rise of temperature over ambient (°C) 58

24 Length of contact travel (mm)

25 Rate of contact Travel

(a) At tripping(meters/sec) 0.8 to 1

(b) At closing (meters/sec): 0.7 to 0.9

26 Type of main contact Butt type

27 Material of the contact

(a), main contacts Copper-Chromium

(b). whether contacts are silver coated No

(c). Contact pressure (Kg/sq.mm) 230

28 Insulation level of the breaker

(a) 1 minute power frequency withstand voltage 28

28 (b) Impulse withstand test voltage (kV peak) 75

Minimum clearances

29 (a) Between phases s(live parts) (mm) 130

(b) Between live parts and Earth (mm) 120

(c) Centre to centre distance between phases (mm) 190

30 Whether circuit breaker is fixed trip or trip free Trip free

31 Method of closing

(a) Normal Shunt release

(b) Emergency Manual

32 Type of closing mechanism Motor wound spring

33 Normal voltage of closing pick up range (volts) 220/110/48/30

34 (a) Power at normal voltage of closing mechanism (watt) 200

35 (b) Power at 85% of normal voltage, (watts) 144.5

36 Type of tripping mechanism Toggle Trip

37 Normal voltage of tripping coils (volts) 220/110/48/30

(a) Power at normal voltage for tripping coils (watts) 200

(b) Power at 70% normal voltage for tripping coil (watt)

98

38 Recovery voltage when circuit breakers tested at 100% rated

6.9

39 Rate of rise of restriking voltage at breaking

(a) for 30% breaking capacity,( kV/Micro sees) 1.7

(b) for 100% breaking capacity, (kV/Micro sees ) 0.34

40 No. of openings circuit breakers is capable of performing without inspection, replacement of contacts or other main parts

(a) at 50% rated current >20000

(b) at 100% rated current 10000

(c) at current corresponding to 50% rated breaking capacity

200 to 400

(d) at current corresponding to 100% rated breaking capacity

100

41 Weight of complete circuit breaker(kg) 850

42 Impact loading for foundation design to include dead load plus impact value on opening at maximum interrupting ratings, in terms of equivalent static load (kg)

1700

43 Overall dimensions

(a) Height (mm) 1253

(b) Width (mm)((‘ 630

[c) Length (mm) 1562

44 Spring charging motor rating 220 V, C/DC,250watts

45 Busbar material Copper

46 Busbar material 80x8 2 bars of 80x8

47 Busbar insulation Heat shrinkable PVC

48 Power required for heater(watts) 80

49 Whether heater is continuously rated Yes

CLAUSE NO. 33 kV VACUUM CIRCUIT BREAKERS

19.00.00

19.01.00

20.00.00

20.01.00

21.00.00

SITE TESTS ON CONTROL AND AUXILIARY CIRCUIT

The following tests shall be conducted at site before commissioning.

1) Voltage tests on control and auxiliary circuit.

2) Measurements of resistance of the main circuit.

3) Mechanical Operation Tests.

4)Insulation Resistance test

NAMEPLATE

Equipment should be provided with name plate giving full details of manufacture, capacities and other details as specified in the relevant IS.

SI. No.

DESCRIPTION VALUES |

i) Rate Voltage (kV rms) 36 kV

ii) Rated frequency (Hz) 50

iii) System neutral earthing Solidly grounded system

iv) Type of arc quenching medium Vacuum

v) Rated normal current at site conditions (Amps) 630 Amps

vi) Number of poles 3

vii) Installation Outdoor type

viii) Temperature rise As per IEC 56 (Table-4) Page- 19

ix) Rated short circuit

a) Interrupting capacity at 36 kV 25 kA

b) The percentage DC components As per IEC 56 & (Ref. Page 5 1 , 21 of JEC)

x) Rated short circuit making 63 kA

xi) First pole to clear factor 1.5

xii) Rated short time current 25 kA

xiii) Rated duration of short circuit 3 Seconds ^

xiv) Total break time for any current upto the rated breaking current with limiting condition of operating and quenching media

<80ms

21.01.00 TECHNICAL PARAMETERS 36 kV Circuit Breakers

33 kV VACUUM CIRCUIT BREAKERS pressure (ms)

xv) Closing time (rms) <150ms

xvi) Mounting Hot dip galvanized lattices steel support structured bolted type

xvii) Phase to phase spacing in the switch yard i.e., interpole spacing for breaker (min.)

400

xviii) Required ground clearance from the lowest line terminal if both the terminals are not in same horizontal plane (cum)

2820

xix) Height of concrete plinth (mm) 150

xx) Minimum creepage distance of support insulator (mm)

900

xxi) Standard value of rated transient recovery voltage for terminal fault

As per IEC-56

xxii) Standard value of rated line RRRV

Characteristics Surge Peak Factor

For Short Line faults ImpedanceFactor K= 1.6 A KV/ms = 0.214 Z (ohms) = 450

xxiii) Rated operating

a) duty cycle 0-0.3 Second - CO-3 Minutes-CO

b) Auto reclosing Suitable for three phase Auto / reclosing duty

xxiv) Rated insulation level under heavy pollution condition 1.2/50 micro second lightening Impulse withstand voltage (kV Peak) to earth

170 kV

s 1 min. Power Frequency Withstand Voltage kV (rms) to Earth (kV rms)

70 kV

xxvi) Rated Characteristics for out of Phase breaking

a) Out of phase breaking capacity

25% of rated breaking capacity

b) Standard values of transient recovery

As per IEC-56 ,

c) Operating mechanism

Spring operated, Anti pumping and Trip free mechanism

33 kV VACUUM CIRCUIT BREAKERS

d) Power available for operating mechanism Three phase 415 Volts 50 C/S or single phase 50 C/S 240 Volts

xxvii) a) Rated supply voltage of closing and operating devices and auxiliary circuits110 V DC/30 VDC

1)110 V DC/30 VDC

2) Series Trip Type system requiring no DC supply. Closing in this case shall be operating on 240 Volts AC 5( C/S single phase

3) 415 Volts 50 Hz three phase

b) Permissible voltage variation 1) In case of DC Power supply voltage variation shall be between 85% to 110% of normal voltage.

2) In case of AC power supply voltage variation shall be of the normal voltage as per IS-15% to +10%

c) Permissible frequency ±3% from normal 50 Hz as per IS 2026 Part-11977 para 4.4

d) Combined variation of frequency and voltage

±15%

xxviii) Number of auxiliary contactsa 10 NO and 10 NC on each pole Continuous current rating 10 Amps, DC at 110/30 volts DC or 240 V AC

xxix) Number of coils 2 (Two) trip coils and 1 close coil 100kg. Static.

The breaker shall be designed to withstand the rated terminal load, wind, load, earthquake load and short circuit forces.

xxx) Rated terminal load The breaker shall be designed to withstand the rated terminal load, wind, load, earthquake load and short circuit forces.

16.01.00 Technical Parameters16.01.01 11 KV Circuit Breakers

SI. No DESCRIPTION VALUES

i) Rate Voltage (kV rms) 21 kV

ii) Rated frequency (Hz) . 50

iii). System neutral earthing Solidly grounded system

iv) Type of arc quenching medium

Vacuum

v) Rated normal current at site conditions (Amps)

630 Amps

vi) Number of poles 3

vii) Installation Indoor type

viii) Temperature rise As per EEC 56

ix) Rated short circuit

a) Interrupting capacity at 11 kV 25 kA

b) The percentage DC components

As per IEC 56 & (Ref. Page 51, 21 of IEC)

c) Minimum number of Short Circuit operation the Circuit Breaker can withstand

100

x) Rated short circuit making capacity

62,5 KA

xi) First pole to clear factor 1.5

xii) - Rated short time current -carrying capacity

25 kA

xiii) Rated duration of short circuit 3 Seconds

xiv) Total break time for any current upto the rated breaking current with limiting condition of operating and quenching

As per IS/EC

media pressure (ms)

XV) Closing time (rms) As per IS/DSC

xvi) Standard value of rated transient recovery voltage for terminal fault . ,

AsperIEC-56

xvii) Standard value of rated line Characteristics for short line faults

RRRV KV/ms=0.214

- Surge Peak Factor. Factor K=1.6 A

Impedance Z (ohms) = 450

xyiii) Rated operating

a) Duty cycle O-0.3 Second-CO-3 Minutes-CO

b) Auto reclosing Suitable for three phase Auto reclosing duty

xix) Rated insulation level under heavy pollution condition 1.2/50 micro second lightening Impulse withstand voltage (kV Deak) to earth

75 kV

xx) Power frequency withstand voltage kv (rms) to earth (KV)

28 KV

11 KV VACUUM CIRCUIT BREAKER xxi) Rated characteristic for out of Phase

breaking

a) Out of phase breaking capacity 25% of rated breaking capacity

b) Standard values of transient recovery AsperIEC-56

c) Operating mechanism Spring operated, Anti pumping and Trip free mechanism

d) Power available for operating mechanism

Three phase 415 Volts' 50 C/S or single phase 50 C/S 240 Volts

xxii) a) Rated supply voltage of (closing and operating devices and auxiliary circuits ~

1)1 10 y dc/so vdc 2) 240 Volts AC 50 C/S single phase 3) 415 Volts 50 Hz three phase

b) Permissible voltage variation 1) m case of DC Power supply voltage 11 variation shall be between 85% to 1 10% 1 of normal voltage. If 2) In case of AC power supply voltage jj variation shall be of the normal voltage asperIS-15%to+10%

c) Permissible frequency ±3% from normal 50 Hz as per IS : 2026 Part-11 977 para 4.4

d) Combined variation of frequency and voltage

±15%

xxiu) Number of auxiliary contacts 1 0 NO and 10 NC on each pole Continuous current rating 10 Amps, DC breaking rating capacity shall be 2 Amps with circuit time constant less man 20 ms at 220/30 volte DC

xxiv) Number of coils 2(Two) trip coils and 1 close coil with anti-pumping arrangement

xxv) Rated terminal load 100kg. Static. The breaker shall be designed to withstand the rated terminal load, wind, load, earthquake load and short circuit forces.