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Controlled Switching of Circuit Breakers
R (
1)
June
29,
201
1©
INA
BB
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Wed
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ay,
Contents
• Basic principle of controlled switchingBasic principle of controlled switching
• Today‘s common applications and their benefit
• Future applications of controlled switching
• General trends
( 2)
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Literature
• CIGRE WG 13.07, "Controlled switching of HVAC circuit breakers. Guide for application. Lines, reactors, capacitors, transformers. Part I," Electra, 183:pp. 43-73 Apr 199973, Apr. 1999.
• CIGRE WG 13.07, "Controlled switching of HVAC circuit breakers. Guide for application. Lines, reactors, capacitors, transformers. Part II," Electra, 185:pp. 37-57, Aug. 1999., g
• CIGRE Task Force 13.00.1 of Study Committee 13, "Controlled switching—a state of the art survey. Part I," Electra, 162:pp. 65-96, Oct. 1995.
• CIGRE Task Force 13.00.1 of Study Committee 13, "Controlled switching—a state y , gof the art survey. Part II," Electra, 164:pp. 39-61, Feb. 1996.
• U. Krüsi, K. Fröhlich and J. H. Brunke, "Controlled Transformer Energization Considering Residual Flux—Implementation and Experimental Results,"
( 3)
Proceedings of IASTED int. Conf. on Power and Energy Systems, Tampa, Florida, USA, Paper Nr. 328-143, pp. 155-160, 19.-22. Nov. 2001.
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Purpose of Controlled Switching
Close and/or open the breaker precisely point on wave in order to
• avoid or reduce transients in the systemd t t b k d th i t• reduce stresses at breaker and other equipment
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LIMITATIONS FOR SUCCESSFUL INTERRUPTION
• Circuit breaker operation depends on
– Thermal Limit i e The magnitude of the current to be interruptedThermal Limit i.e. The magnitude of the current to be interrupted
– Dielectric Limit i.e. The magnitude of transient recovery voltage
Dielectric Limit
TransientRecoveryVoltage
( 5)
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Current to be interrupted
LIMITATIONS FOR SUCCESSFUL INTERRUPTION
• The magnitude of the current to be interrupted dictates the
t ti f th i it b kconstruction of the circuit breaker
– Large volume of interrupting medium (SF6) is required for faster
cooling and de-ionization of the contact gap.
– A puff with higher pressure is required to take away the ionized
gasses quickly and regain the dielectric property in contact gap.
• All the above requirements result in higher energy operating
( 6)
q g gy p g
mechanisms and larger size of interrupting chamber.
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LIMITATIONS FOR SUCCESSFUL INTERRUPTION
• The magnitude of the transient recovery voltage dictates
– High speed contact separation.
– A larger gap between the moving contact and the fixed contact.
– High TRV also requires that external insulation of the
interrupting chamber should withstand higher dielectric stressesinterrupting chamber should withstand higher dielectric stresses.
• All the above requirements also result in higher energy operating
( 7)
mechanisms and larger size of interrupting chamber.
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What can be done
• Can we increase the circuit breaker arc interrupting capability and
l i it i lif ith t h ialso increase its service life without having
– stronger operating mechanism and
– larger volume of the arc chamber
• Controlled switching is one such method that can be used to
enhance the breaking capabilities of a circuit breaker
( 8)
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Can Controlled interruption help
Additional performanceb t ll d i t ti ???
Random interruptionVoltage
Dielectriclimit
by controlled interruption ???
??
???
?Thermal
limit
?
( 9) Current
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How Controlled Switching work
• Traditionally the circuit breaker switching is controlled by substation control. i.e. either byCB substation control. i.e. either by protective relays or by manual switching
circuit• In controlled switching a local
breaker controller is place between the circuit breaker and
circuit breakercontrol
between the circuit breaker and the station control.
• It controls the exact instant of Controller
( 10
)
circuit breaker contact separation to achieve lower stresses on the
substation control
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Timing for controlled switching( 1
1)
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Cases of extending dielectric limits
Possible upgrading area byf t ll d it hi
Random interruptionVoltage
means of controlled switching
( 12
) CurrentNo thermal interrupting stress
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Cases of extending dielectric limits
• Energization and de-energization of capacitor banks
• Energization and de-energization of shunt reactors
• Energization of unloaded power transformers
• Energization and de-energization of unloaded transmission linesg g
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Energization of capacitor banks
• Problem: Excessive, high frequent inrush current• Solution: Close at zero of voltage across breakerSolution: Close at zero of voltage across breaker
voltage
ll duncontrolledcontrolled~
( 14
) current
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Controlled Capacitor Bank Energisation - Benefits
Technical Implication Monetisation
Breaker reduces contact burn 5k$ - 15k$reduced current forces in breakerno closing resistors(Increases availability of breaker)
qualitative15% - 30% of breakerqualitative
Adjacent Inrush current ages bank qualitativeAdjacentCompon.
gnuisance relay tripping qualitative
System avoidance of overvoltages in remote places qualitative
( 15
)
SystemAspects
avoidance of overvoltages in remote placesPower auality improvement
qualitative
qualitative
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Example
Estimate of economical benefits due to Controlled S it hi
Investment: -25%( )
Switchingin the Furnas power system (10 capacitors banks)
•Elimination of:•pre-insertion resistors•auxiliary chambers
(Compared to CB costs)
•Reduction of:•dielectric strength capability in capacitors cells
-45%(Compared to capacitor costs)
( 16
)
Operation costs:•elimination of maintenance costs for resistors and auxiliary chambers
Not considered
Total: 7 MUS$
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Controlled Capacitor Bank De-Energisation
+ +
I + UB -
+
_~ US UC
_
IInterruption
I
U Load side voltage
Voltage across CB
( 17
)
time
UCLoad side voltage
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US = UC USBus voltage
De-energization of capacitor banks
•Problem: Potential jeopardy of restrikes•Solution: Avoid small arcing time
t1
t
t2
current
tArc voltage
RV
( 18
)
recoverycontact separation
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T/2 100
Controlled Capacitor Bank De-Energisation
T/2 = 10 msat 50 Hz
Recovery voltages
Time0
Capacitive current case
RRDS: - Rate of Rise of Dielectric Strength
ntac
tsge
acr
oss
co
( 19
)
Volta
g
Typical RRDS starting at minimum arcing time (0 ms)
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Typical RRDS starting several ms prior to current zero resulting in proper interruption
Controlled Capacitor Bank De-Energisation - Benefits
Technical Implication Monetisation
Breaker reduces restrike probabilitynozzle puncture, maintenance interv.
Qualitative??
AdjacentCompon
nuisance relay trippingavoids step voltage fronts in bank
qualitativequalitativeCompon.
SystemAspects
avoidance of voltage transients andvoltage escalation, saves arrestors
qualitativequalitative
( 20
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Aspects power quality improvement qualitative
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De-energization of a shunt reactor
rent
curr
UR~
Critical windowAccepted zone
oltage
( 21
)
UR
vo
UR20 s
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De-energization of a shunt reactor
Typical: TARCMIN 4 ms
RRDS at min. arcing time
Voltage withstand characteristic of the
circuit-breaker contact gap at opening,
RRDSyp ARCMIN
(Shorter arcing times will result in re-ignition)SAFE contact parting areaContact separation
Instant 1Contact separation
Instant 2
CurrentUacross CB
REACTOR CURRENT INTERRUPTION
Uacross CBUacross CBUacross CB
( 22
)
Tarcmin
Wi d ll i
USource
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Reignition-free operation
Controlled Reactor De-Energisation Benefits
Technical Implication Monetisation
Breaker Increase of Maintenance interval, Catastrophic failure
several k$l 100k$failure
(probability < 0,3 o/oo reduced by factor 100)several 100k$
Adjacent potential of reactor failure several 100k$AdjacentCompon. risk unknown – significantly reduced
System Reduction of transients, qualitative
( 23
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SystemAspects
,EMI in secondary system
q
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Nozzle and contact burn after numerous reactor de-energisations
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Rough Estimate of the probability for a catastrophic breaker failure
•20 reactors in the system switched twice daily over 30 yrs
21900 operationsx 3
•Critical window 1ms•2 breaker explosions occured
= 65700 single phase operations 6500 reignitions probability for an explosion is 1/3000
P b bilit f l f
( 25
)
Probability for loss of several 100 k$ is > 0.3 o/oo
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Energization of shunt reactors
Problem: Inrush current up to 3.5 puSolution: Close at voltage peakSolution: Close at voltage peak
Disadvantage:Transient overvoltage of steep wave front
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Inrush current and overvoltage versus closing angle
4.0
nt [pu]
I h C
3.0
3.5
h Curren Inrush Current
2.5
3.0
/ Inrus
1.5
2.0
rvoltage
Overvoltage
( 27
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1
0 1 2 3 4 5
Over
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Deviation from optimum switching instant [ms]
Magnetic flux in steady state
Symmetrical Flux Hysteresis
Flux
Voltage
Currenttime
Magnetizing currenttime
( 28
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Magnetizing currenttime
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time
Inrush currents (2)Flux
Asymmetrical magnetical flux
Hysteresis
Flux
currenttime
Some problems caused by inrush currents:
• Damage to the transformer
Inrush Current•False operation of transformer protections
• Adverse effects on power quality
Di t t bl
( 29
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• Direct current problems
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time
Inrush current of an unloaded power transformer with controlled switching (state of the art)
voltage12 3
3
.2000
.1000
.0900.0700
.0500.0300.0100 SECONDS
1
1
2
2
3
3
0.0
-.1000
-.2000
kV x 10**3
.8000
( 30
) .0900.0700
.0500.0300.0100SECONDS
current
1 112 2 3
.4000
0.0
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3 3-.4000
-.8000
kA 500A
Advantages of controlled reactor energization
•Technical Consequence– Reduced current forces in
reactor (inrush)A id i l t i i
•Financial consequence– Increase of life expectancy– Reduced failure risk
– Avoid nuissance relay tripping– Reduced contact burn– Increase of power quality
A id th ti i h i t
– Reduced maintenance
– Avoid sympathetic inrush into other transformer
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Optimum closing moment
1
Residual flux
[p.u.]
tt
dtUw1
( 32
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Prospective magnetic Steady state magnetic
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fluxSteady state magnetic flux
Peak inrush current
Peak Inrush Current as a Function of Closing Time Scatter
ent
1200
1400
nrush Curre
600
800
1000
se Peak In
peres 2%
Zero Residual
70% Residual
200
400
600
Worst Phas
Am
( 33
)
00 0.5 1 1.5 2 2.5
Closing Time Scatter (3 sigma) - ms
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Transformer burn in Montana
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Controlled Reactor Energisation Benefits
Technical Implication Monetisation
Breaker No significant impact no
Adjacent Inrush current (< 3pu) ages reactor qualitativeAdjacentCompon.
( ) gqualitative
System sympathetic inrush to transformer in case of series Qualitative
( 35
)
SystemAspects
sympathetic inrush to transformer in case of series compensationnuisance relay tripping
Qualitative(loss of power delivery)
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Energization of unloaded transmission lines
• Problem: Excessive overvoltagesS l ti Cl t f lt b k• Solution: Close at zero of voltage across breaker
transmission line
t
( 36
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system
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Voltage across breaker at auto reclosing (1)
1
2
0
1
olta
ge
[p.u
.]
-2
-1
0 50 100 150 200 250
Vo
T im e [m s]0 50 100 150 200 250
( 37
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line compensation 30%
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Voltage across breaker at auto reclosing (1)
1800kV
Field test in 500 kV system of BC-Hydro, Canada
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Voltage across breaker at auto reclosing (2)
2,5
1,5
2
.u]
1
1,5
Volta
ge [p
.
0
0,5
0 25 50 75 100Time [ms]
( 39
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Time [ms]
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No line compensation
Voltage across breaker at auto reclosing (3) ( 4
0)
50 100
time [ms]No line compensation
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Decay of trapped charge
Controlled Energisation of Unloaded Transmission lines- Benefits
Technical Implication Monetisation
Breaker no closing resistors 15% - 30% of breaker(Increases availability of breaker) qualitative
Adjacent Overvoltage reduction on line 20k$ / km (at 500kV)AdjacentCompon. Reduction of phase to phase clearing
System Avoid nuisance relay tripping qualitative
( 41
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SystemAspects
Avoid nuisance relay tripping qualitative
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Advantages of unloaded line energization
•Technical Consequence– Reduces transients phase to
ground– Reduced risk of fault re-
inception at O-C
•Financial consequence– Saves closing resistors
De rating of surge arrestors– De-rating of surge arrestors– Reduced line dimensions
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FUTURE? Controlled fault interruption?
I d l t i l lif d i d f d tIncreased electrical life and improved performance compared to random fault interruption?
Blast
Pressure at current zero,new CB
pressure
Pressure required for interruption
Reduced pressure build-upat current zero in worn CB
Narrow window with increased interrupting
capability
( 43
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Normal "arc extinguishing window” >1/2 cycle
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Tarc
Future potential of controlled switching
• Load interruptionp
• Fault interruption
• Energization of unloaded power transformers considering remanence flux
• Control for existing breakers
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Conclusion
I f t t ll d it hi ill b ft i th th h d•In future controlled switching will be a software issue rather than a hardware problem
•Controlled switching will become a normal feature for a CBCo t o ed s tc g beco e a o a eatu e o a C
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