Controlled Switching Simplified

Controlled Switching of Circuit Breakers

R (

1)

June

29,

201

1©

INA

BB

/CT

Wed

nesd

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)

© IN

AB

B/C

TR (

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.

© IN

AB

B/C

TR (

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

( 4)

© IN

AB

B/C

TR (

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)

© IN

AB

B/C

TR (

Current to be interrupted


• 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.

© IN

AB

B/C

TR (


• 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.

© IN

AB

B/C

TR (

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)

© IN

AB

B/C

TR (

Can Controlled interruption help

Additional performanceb t ll d i t ti ???

Random interruptionVoltage

Dielectriclimit

by controlled interruption ???

??

???

?Thermal

limit

?

( 9) Current

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR ( breaker

Timing for controlled switching( 1

1)

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR ( No thermal interrupting stress

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

( 13

) ©

INA

BB

/CTR

(

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

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR (

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$

© IN

AB

B/C

TR (

Controlled Capacitor Bank De-Energisation

+ +

I + UB -

+

_~ US UC

_

IInterruption

I

U Load side voltage

Voltage across CB

( 17

)

time

UCLoad side voltage

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR (

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)

© IN

AB

B/C

TR (

Typical RRDS starting several ms prior to current zero resulting in proper interruption

Controlled Capacitor Bank De-Energisation - Benefits


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

)

Aspects power quality improvement qualitative

© IN

AB

B/C

TR (

De-energization of a shunt reactor

rent

curr

UR~

Critical windowAccepted zone

oltage

( 21

)

UR

vo

UR20 s

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR ( Window allowing

Reignition-free operation

Controlled Reactor De-Energisation Benefits


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

)

SystemAspects

,EMI in secondary system

q

© IN

AB

B/C

TR (

Nozzle and contact burn after numerous reactor de-energisations

( 24

) ©

INA

BB

/CTR

(

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

© IN

AB

B/C

TR (

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

( 26

) ©

INA

BB

/CTR

(

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

)

1

0 1 2 3 4 5

Over

© IN

AB

B/C

TR (

Deviation from optimum switching instant [ms]

Magnetic flux in steady state

Symmetrical Flux Hysteresis

Flux

Voltage

Currenttime

Magnetizing currenttime

( 28

)

Magnetizing currenttime

© IN

AB

B/C

TR (

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

)

• Direct current problems

© IN

AB

B/C

TR (

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

© IN

AB

B/C

TR (

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

( 31

) ©

INA

BB

/CTR

(

Optimum closing moment

1

Residual flux

[p.u.]

tt

dtUw1

( 32

)

Prospective magnetic Steady state magnetic

© IN

AB

B/C

TR ( Prospective magnetic

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

© IN

AB

B/C

TR (

Transformer burn in Montana

( 34

) ©

INA

BB

/CTR

(

Controlled Reactor Energisation Benefits


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)

© IN

AB

B/C

TR (

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

)

system

© IN

AB

B/C

TR (

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

)

line compensation 30%

© IN

AB

B/C

TR (


1800kV

Field test in 500 kV system of BC-Hydro, Canada

( 38

) ©

INA

BB

/CTR

(


2,5

1,5

2

.u]

1

1,5

Volta

ge [p

.

0

0,5

0 25 50 75 100Time [ms]

( 39

)

Time [ms]

© IN

AB

B/C

TR (

No line compensation

Voltage across breaker at auto reclosing (3) ( 4

0)

50 100

time [ms]No line compensation

© IN

AB

B/C

TR ( p

Decay of trapped charge

Controlled Energisation of Unloaded Transmission lines- Benefits


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

)

SystemAspects

Avoid nuisance relay tripping qualitative

© IN

AB

B/C

TR (

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

( 42

) ©

INA

BB

/CTR

(

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

)

Normal "arc extinguishing window” >1/2 cycle

© IN

AB

B/C

TR (

Tarc

Future potential of controlled switching

• Load interruptionp

• Fault interruption

• Energization of unloaded power transformers considering remanence flux

• Control for existing breakers

( 44

) ©

INA

BB

/CTR

(

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

( 45

) ©

INA

BB

/CTR

(

Documents

Controlled Switching Simplified