Components in a substation -

CIRCUIT BREAKER

Components in a sub - stationComponents in a sub - stationCircuit Breaker IsolatorsLightning ArrestorsPower TransformerCurrent TransformerPotential Transformer

Auto Transformer Control & Relay panelBatteries & ChargerBus barInsulatorsConnectorsControl cables

CIRCUIT BREAKERSCIRCUIT BREAKERS Switching and current interrupting device Serves two basic purposes Switching normal operating conditions - for operation & maintenance Switching abnormal operating conditions Clearing short circuits & Interrupting fault

currentsContd…

CIRCUIT BREAKERS(contd.,CIRCUIT BREAKERS(contd., Should be capable of :

Carrying normal load current Make and Break load current Make and Break abnormal fault current Performing few or many operations in a year Operating in elevated & reduced temperature

areas

HISTORY OF CIRCUIT BREAKERHISTORY OF CIRCUIT BREAKER

Knife & Mercury Switches Oil Circuit Breakers (1885) Minimum Oil Circuit Breakers Air Blast Circuit Breaker (1930) SF6 Breakers (1950) Double pressure type SF6 Breakers Puffer type SF6 Breakers Vacuum Circuit Breakers

CLASSIFICATION OF CIRCUIT BREAKERSCLASSIFICATION OF CIRCUIT BREAKERS

Based on Construction Indoor application Outdoor application

Based on method of Arc ExtinctionHigh Resistance InterruptionZero Point Interruption

Dielectric Medium used for Arc ExtinctionDielectric Medium used for Arc Extinction

Air Break CBs - (LT Application)Air at atmospheric Pressure

Air Blast CBs- High Pressure AirOil CBs - Dielectric OilSF6 CBs -SF6 Gas at 4-7Bar PressureVacuum CBs - Vacuum

Functions of operating mechanismFunctions of operating mechanism

To provide means whereby the CB can be CLOSED rapidly without hesitation

To HOLD the CB in closed position by latches till a trip signal is received

To allow the CB to OPEN without delay on receiving the trip signal

To have Sufficient energy to operate the moving parts rapidly and smoothly.

Contd…

Functions of operating mechanism (contd…)Functions of operating mechanism (contd…)

Mechanism should be capable of operating by conventional low power control circuits

Mechanism should have a positive action (ON or OFF - not in between)ReliableCapable of performing auto reclose cycle

TYPES OF MECHANISMTYPES OF MECHANISM

“Dependable”-Continuity of power supply (Manual & Power)

“Stored Energy type”- Energy is stored in Charged Spring/

Compressed Air / Hydraulic Oil - Independent of continuity of power supply

Types of stored Energy Mechanism used in Types of stored Energy Mechanism used in

Circuit BreakersCircuit Breakers

Spring Closed, Spring Opened Solenoid Closed, Spring Opened Hydraulic Pneumatic Pneumatic Closed, Spring Opened Spring Closed, Pneumatically Opened

ARCARC EXTINCTION IN C.BEXTINCTION IN C.B

In AC (50 Hz) current will be Zero at the end of each half cycle(i.e 100 times / Sec.)

For efficient Arc Extinction, Breaker must establish good insulation between contacts very quickly. This is achieved by removing any ionised material from between contacts and replacing it with insulating material

(Contd..)

ARC EXTINCTION IN C.B (Contd..)ARC EXTINCTION IN C.B (Contd..)

Arc Extinction in Oil Arc Extinction in Air Blast Arc Extinction in Vacuum- No free Electrons Arc Extinction in SF6 SF6-atoms-molecules–attract & hold free electrons Arc Extinction with multiple breaks Resistor interruption To reduce the over voltages & transients because of rapid changes in current level

Advantages of SF6 Circuit BreakerAdvantages of SF6 Circuit Breaker

More compact design than other CBs of similar capacity.

Operation is relatively quiet. High pressure Air compressors and large

reservoirs not required. Fewer moving parts hence lesser maintenance. Gas is stable - absence of contact erosion.

Disadvantages of SF6 Circuit BreakerDisadvantages of SF6 Circuit Breaker

SF6 gas is expensive Some toxic products are produced under

operating conditions Gas filling and emptying requires skill and costly

gas filling and evacuating equipments Leakage may cause serious problem & very

difficult to find out

Properties of SF6 Gas:Properties of SF6 Gas:Physical:

Colourless, odourless, nontoxic Pure gas is not harmful to health, Non-inflammable Gas at normal pressure & Temperature Gas density - 5 times that of air at 20 deg.C and

atmospheric pressure

Properties of SF6 GasProperties of SF6 Gas Chemical: Stable upto 500 Deg. Centigrade. Inert – Chemical inert – Metallic parts, contacts have

longer life. Electronegative. Does not react with structural materials upto 500 Deg.

Centigrade. Products of decomposition SF2 & SF4 recombine on

cooling. Metallic Fluorides are good insulators.

Dielectric properties of SF6Dielectric properties of SF6

DE strength of SF6 at atmospheric pressure is 2.35 times that of air and 30 % less than that of oil.

At high pressure DE strength increases. At 3 kg/cm2 DE strength is more than that of oil. This property permits smaller clearances and

smaller equipment.

RATED CHARACTERISTICS OF CIRCUIT RATED CHARACTERISTICS OF CIRCUIT

BREAKERSBREAKERS

Rating denotes C.Bs capabilities under specified conditions. Ratings are based on IEC recommendations.Rated Voltage: Corresponds to the highest system voltage for which the CB is intended.Rated insulation level: Power frequency withstand voltage Impulse withstand voltage.

RATED CHARACTERISTICS OF CIRCUIT RATED CHARACTERISTICS OF CIRCUIT

BREAKERSBREAKERS

Rated Frequency: Standard frequency of the power systemRated Current: (rms value of the current)CB can carry continuously with temperature rise of the various parts within specified limitsRated S.C. Current: Highest value of short circuit current which the CB is capable of breaking.(Expressed in KA).

RATED CHARACTERISTICS OF CIRCUIT RATED CHARACTERISTICS OF CIRCUIT

BREAKERSBREAKERS

Rated SC making current:At times the CB close on to a existing fault.CB must be capable of closing without hesitation.CB must be able to withstand high Mechanical forces. Rated SC making current should be at least 2.5 times SC current.

RATED CHARACTERISTICS OF CIRCUIT RATED CHARACTERISTICS OF CIRCUIT

BREAKERSBREAKERSRated duration of SC:

1 Sec. Or 3 Sec.

Rated operating duty:

i. o- t – co – T – co t = 0.3 Sec. T = 3 Min.

ii. co – t’ – co t’ = 15 Sec.

TESTS ON CIRCUIT BREAKERSTESTS ON CIRCUIT BREAKERS

Type test – Capability of the Breaker

Routine test – Proper functioning of the Breaker

TYPE TESTTYPE TEST

Mechanical Endurance Test Temp Rise Test Measurement of DC Resistance Milli volt Drop Test No load operation test(includes closing opening

operating sequence) Dielectric tests Basic Short circuit test

Routine TestRoutine Test

Mechanical test MV drop test Measurement of DC Resistance Power Frequency withstand test Voltage test on Aux Circuits IR Value of main & Aux. Circuits

1

GL 312GL 312

399 0

2300

2905

123/145 kV • 3150 A • 40 kA

Q

GL 312- Three-Phase AssemblyGL 312- Three-Phase Assembly

GL314 SF6 Circuit breaker GL314 SF6 Circuit breaker

GL314 on site

Interrupting chamber - GL314 Interrupting chamber - GL314

‘CLOSED’ position

Thermal effect + compression stage

Thermal effect ‘OPEN’ position

Vt

Vc

Vt : thermal volume

Vc : compression volume

InterruptingInterrupting..\7.Electrical Pres_Supporting\valcbtemp.mpg

chamber - GL314 chamber - GL314

with smallwith smallcurrentcurrent

with short-with short-circuit currentcircuit current

GL 312GL 312

Closed position Closed position Interruption Interruption

Open position Open position

Interruption

Circuit Breaker Testing.mp4

Testing Electrical Substations.mp4