2. Components in a sub - stationComponents in a sub - station
Circuit Breaker
Isolators
Lightning Arrestors
Power Transformer
Current Transformer
Potential Transformer
Auto Transformer
Control & Relay panel
Batteries & Charger
Bus bar
Insulators
Connectors
Control cables
3. 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
currents
Contd…
4. 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
5. 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
6. CLASSIFICATION OF CIRCUIT BREAKERSCLASSIFICATION OF CIRCUIT BREAKERS
Based on Construction
Indoor application
Outdoor application
Based on method of Arc Extinction
High Resistance Interruption
Zero Point Interruption
7. 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 Air
Oil CBs - Dielectric Oil
SF6 CBs -SF6 Gas at 4-7Bar Pressure
Vacuum CBs - Vacuum
8. 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…
9. 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)
Reliable
Capable of performing auto reclose cycle
10. 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
11. Types of stored Energy Mechanism used inTypes 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
12. 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..)
13. 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
14. 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.
15. 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
16. 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
17. 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.
18. 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.
19. RATED CHARACTERISTICS OF CIRCUITRATED 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.
20. RATED CHARACTERISTICS OF CIRCUITRATED CHARACTERISTICS OF CIRCUIT
BREAKERSBREAKERS
Rated Frequency:
Standard frequency of the power system
Rated Current: (rms value of the current)
CB can carry continuously with temperature rise
of the various parts within specified limits
Rated S.C. Current:
Highest value of short circuit current which the
CB is capable of breaking.(Expressed in KA).
21. RATED CHARACTERISTICS OF CIRCUITRATED 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.
22. RATED CHARACTERISTICS OF CIRCUITRATED CHARACTERISTICS OF CIRCUIT
BREAKERSBREAKERS
Rated 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.
23. TESTS ON CIRCUIT BREAKERSTESTS ON CIRCUIT BREAKERS
Type test – Capability of the Breaker
Routine test – Proper functioning of the Breaker
24. 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
25. 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
31. with smallwith small
currentcurrent
with smallwith small
currentcurrent
with short-circuitwith short-circuit
currentcurrent
with short-circuitwith short-circuit
currentcurrent
GL 312GL 312
Closed positionClosed position
InterruptionInterruption
Open positionOpen position
Closed positionClosed position
InterruptionInterruption
Open positionOpen position
Interruption