Controlled Switching Simplified

Controlled Switching of Circuit Breakers

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Contents

• Basic principle of controlled switchingBasic principle of controlled switching

• Today‘s common applications and their benefit

• Future applications of controlled switching

• General trends

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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,"

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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

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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

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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

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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

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Can Controlled interruption help

Additional performanceb t ll d i t ti ???

Random interruptionVoltage

Dielectriclimit

by controlled interruption ???

??

???

?Thermal

limit

?

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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

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circuit breaker contact separation to achieve lower stresses on the

substation control

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Timing for controlled switching( 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

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) 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~

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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]

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Time [ms]

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No line compensation

Voltage across breaker at auto reclosing (3) ( 4

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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

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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

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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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