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A

Method

to

Decide the Switching Instants of

Controlled Switching Circuit Breaker

for

Shunt Reactors

**

'W.Y.

Lee , 'K .Y. Park, 'J.K. Chong,

'B.Y.

L e e , H.

J. Kim

*L

Korea E lec t ro t ech n o lo g y

Research

In s t i t u t e , V i t z ro t ech Co. Ltd . , Sou th Korea

Abslrod his paper describes a method which determines

the operating instants

of

the circuit breaker for controlled

switching

of

shunt reactors independent of the network

configuration, in order

to

reduce overvoltages and inrush

currents. Some other previous papers offered the favorable

instants for both isolated and directly earthed neutral case, but

not for the earthed neutral through a reactor. The proposed

method in this paper is based on two facts. First, the instant

of

a

maximum voltage between contacts of the circuit hreake r(CB) is

the optimum point

for

closing to minimize the inrush current.

And secondly, both the minimum arcing time

of

the CB and the

current interruption instant of each

poles

should he considered as

the reference

for

the opening instant. The performance of the

proposed method was verified by the

results of

simulation studies

using the electromagnetic transien ts program (EMT P). The

behaviors of CB treated in the simulation involve the rate of

decay

of

dielectric strength between contacts and the scatter

of

the operating time. Especially, the results

of

EMTP show that the

closing and opening instants

of

the second one among the three

poles shift continuously with the r atio of the impeda nce of a shunt

reactor

to

that of the neutral reactor in the range of

30

phase

angle, respectively. And also the maximum scatter of the CB

dosing

time to ensure the inrush current of less than

a

certain

level can he provided.

Index Ierms-circuit breaker, controlled switching, inrush

current, optimum instant, reignition, shunt reactor.

I. INTRODUCTION

Since the reliability of a system for delivering the stable

electric energy should be considered as the most important

thing of all . the application

o f

the digital and intelligent

technology to the operation

of

circuit breakers has not been

in

common. But recently

in

conjunction with the development of

an electronic technology this barrier would be getting lower.

The con tro l led switch ing app l ied to c i rcu i t b reakers has

received considerable attention

as

an effective method to

reduce the switching surges and stresses

on

the apparatus

involved[l][2]. Especially, an inrush current on closing and

overvoltages due to current chopping or reignition during

opening have been recognized as the representative problems

in the shunt reactor switching. Up to date in order to reduce

the generation of these switching surges,

the

conventional

methods with a closing resister or an arrestor have been used.

but the recent evolution of the circuit breaker technologies, in

conjunction with the increased application of the electronics to

power system control, has made it possible

to

extend the

application

of

controlled switching to reduce switching

surges[3]-[7]. For the case of a network configuration with the

neutral earthed through the reactor in shunt reactor

applications, the magnitude and the instant of the crest voltage

across the contacts of circuit breakers are vaned as a function

of the ratio of a neutral reactor to shunt reactor. Th e optimum

instants for switching should be decided by the voltage across

the contacts or the anticipated current interruption m oments as

well as the characteristics of circuit breakers, namely the

scatter of the circuit breaker operating time and the slope

of

the dielectric strength

of

a contact gap. In the previous studies,

only the network configurations with both an isolated neutral

and

an

earthed neutral have been considered but the switching

of shunt reactors with neutral earthed through an reactor has

not been dealt with.

In this paper

a

method is proposed

which

determines the

operating instants of the circuit

breaker

for controlled

switching of shunt reactors independent of the network

configuration.

11. DETERMINING THE OPTIMAL SWITCHING INSTANTS

The controlled switching has been adopted as an effective

method to reduce either overvoltages or inrush currents at the

application of circuit breakers to the shunt reactor switching.

The optimal point-on-wave

for

switching should be determined

by the circuit configuration and the characteristics of circuit

breaker in use. Fig. I shows the simple circuit configuration

with variable neutral reactor(LG) which

is

considered for

calculating the switching instants in this paper. In this figure

if

the neutral reactor becomes to be a large extreme value, this

rcuit is similar to the isolated neutral condition and in the other

case

of

lower extreme values, earthed neutral condition may be

available. It is assumed that each pole of a circuit breaker

operates independently and the rate

of

decrease of dielectric

0-7803-7525-4/02/$17.00 Q 2002 IEEE.

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strength(RDDS) between gap during contact traveling is

linearly proportional to the gap distance.

Ls LG

N

-

V

-

L pole

2

IVLj

Fig.

I.

i rcuit configuration for

the

eono o l ld sw i tch ing

of

a

shunt reactor

(L

ourcc

side

reactor, LR.s.T

:

shunt

reactor

of each phase)

Vp and

o

represent the peak value of the applied voltage

between the phase and the earth and an angular frequency,

respectively.

point

(VN)

is

also affected by

the

closing of the preceding

phases, it becomes as described in

(3).

In the following sections a

determining both

optimal closing and opening instants is described under some

assumed conditions

For the last phase to close, phase

S,

the voltage of

a

neutral

A. Optimum closing instant

The current should be initiated at voltage crest across each

contact in order to reduce or mitigate the inrush current of

shunt reactors. It is noted that these instants are not identical to

that of the mechanical contact touch because of the pre-strike

occurred at contact gaps subject to the applied voltage. Since i t

is

necessary to derive the magnitude and the instant

of

the

voltage crest of e ach pole for determining the optimal closing

instants, the influence

of

the value of the neutral reactor on the

instant of a voltage crest across the circuit breaker contacts

should be described. And also the RDDS of contacts and the

deviation of a closing time scatter should be considered to

decide the instants of mechanical contact touches.

In the controlled switching, the target instants are the

moment of contact touches. Even though the same target

instants are used for closing the shunt reactor, the moment at

which a current starts to flow could differ due to the effect of

RDDS

of circuit breakers. For simplification, the first pole to

close is assumed as phase

R

then consequently the next two

phases at which voltage crests are occurred would be noted as

phase T and S . For phase

R

the voltage waveform across the

contact gap can be easily estimated from the steady state

voltage. It is not affected by the value of the neutral reactor.

But for the case of a second closing pole, phase T, the

potential of a neutral point is changed due to the closing of

phase

R

and the magnitude therefore, the instant of crest

voltage between the contacts

on

phase T are also affected.

The voltage excursion across the contact of the second

operating pole

is

given by

I )

with respect to the phase angle

of the first pole as the reference and the instant at which the

peak voltage is appeared can be expressed as written in

(2)

where L c and L represent the inductance of a neutral and

a

shunt reactor, respectively. T he parameter m included

in

above

equations represents the ratio of the inductance of a shunt

reactor to that of a neutral reactor(LiLc).

771

W t

=

6

(OT ) = V If

s s .( y 2 1

From these equations it is known that the crest voltage across

the contact on phase S always occurred at the same instant(716

[ and only the magnitude is changed as

a

function of the

parameter m as shown

in

(4) and 5) . The voltages excursion

as described

in

above equations ar e shown in Fig.

2.

-

.

..

Vs.

VT: voltage

B C T OSS

the c ~ n t a c t f phare and T

Fig. 2. Voltages across he contacts

dunng

closing (Reference phare angle :

voltagezero

cross

of phase

R)

The possible range of the instants and magnitudes of voltage

crests are appeared in this figure as bold lines marked with 1 )

and

(2)

with the variation of m. The trajectory of optimum

closing instants which corresponds to the voltage peak of a

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second closing pole with respect to the preceding zero cross of

the reference voltage (phase

R) s

plotted as the curve I )

in

Fig.

3 

as the function of the parameter m.

In order to determine the optimum contact touch, the circuit

breaker behaviors such as a mechanical scatter( A T ) of

operation mechanism and the rate of decay of dielectric

strength(RDD.9) between the contact gap should be

appropriately considered. The relative value(K) of a circuit

breaker RDDS (Scs)with regard to the rate of voltage

approaching to the zero cros s

(SFO

VP) s represented as (6).

(6)

= -

s

In Fig. 4, the relationship between the contact touch and the

current initiation moment

is

illusuated and the instant of the

contact touch for the voltage peak point, marked

P,

corresponds to the moment of 16.

And when concerning the scatter of operating time(*AT)

the span in w hich current could be initiated with symmetrical

making voltage around a peak voltage(P) is bounded with two

points as the left side lirnit(A) and the right side limit(B). And

the corresponding contact touch points would be t3 and 17,

respectively. The target point for a contact touch is set to 15

resulted from a m ean value of these two extreme cases in order

to keep a maximum margin. It is noted that the calculated

target point tS is not identical to t6 obtained from the voltage

peak point P.

This means that if the voltage applied to the contacts is

varied, K

is also

changed. The making target point for closing

around peak voltage was known as (7) through the previous

study[7].

Y

t = f ( K , AT)

t a r g e t

B x2.Y2)

F-W b

s i n

x

target

point

t5

)

t2

t3 t4 16 7 x

0

7\l \&

T

c o s ( w - A T )

4

O K

- _

+

1 ~ 1 ' 1 ' 1 ' 1

5 10 15 zo

Katio 1

Inductance m

Fig. 3. Optimum instant

for

switching with respect to the preceding zero

crossing function

of

the p a r m e t e r m

Although the circuit breaker behavior regarding to the rate

of decay of dielectric strength of contacts gap is not changed,

the

K

included in (7) should be modified according to the

magnitude of the applied voltage between contact gaps. The

results obtained from (7) are the calculated instants which do

not consider the relationship among the poles therefore,

it

is

necessary to use the same reference instant for three phase

controlled switching. In Fig. 5 the procedure for determining

the optimum closing instants of each poles is i l lusuated.

As the results from this procedure, the optimum contact

touches

tT,s )for

phase

T

and S are given in

(8)

and

(9)

with

respect to the preceding voltage zero cross on phase R as the

reference instant

(Step

1)

Determine

K

for the applied voltage

across the contacts.

(Step 2)

t,,,,.,=f(K. A T )

(Step

3)

Determine the optimum closing

instants for each poles with respect to

the preceding voltage zero crossing of

phase R o n the identical time axis

Fig. 5 . Procedure for determining he

optimum

dar ing ins tan ts for each phase

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B. Optimum opening insranr

Determining opening instants

is

purposed to reduce

overvoltages due to current chopping or reignition at the

current interruption and is dependent on the arcing time of

circuit breakers. But it is not possible to achieve the

elimination of both causes at the same time hence a

compromise solution which is suit to the requirements must be

reached. Since overvoltages caused by reignition are normally

severer than current chopping overvoltages,

it

is necessary to

increase the time interval between the contact separation and

following current zero to he larger than the minimum arcing

time of the circuit breaker. However, since the current zero

anticipation for each pole is needed for deciding the instants of

contact separations, the effect of neutral reactor on the current

zero is described in this section. For the first pole to

clear(phase R) the current zero is predictable from the normal

current waveform independently

of

the neutral condition of

shunt reactors. But for the second pole to clear(phase T), the

neutral condition affects the instant of current zeros which are

derived from IO ) and (11).

The potential variation of the neutral point due to the

opening

of

phase R leads the phase angle of a current through

a

pole T to be changed. Equation (10) describes the voltage

excursion on the phase T of a shunt reactor which is

represented as the VL in Fig. I . From IO ) , the instant of the

currenl zero on phase T

is

derived

as

one given in

I

I ) . The

curve noted as (2) in Fig. 3  presents the phase variation of a

current zero. The reference instant uscd in I

I )

corresponds to

the voltage zero on phase R and the estimated current zeros

of

each pole a re presented in Fig. 6. 

r,

f \

. ,

, ,

Fig. 6. Current interrupting instants of each poles with respect to the

reference

vo1rrgc zero

The instant of a current zero(t1') on phase

R is

delayed 90

from the reference point. For the phase T , the second operating

pole, the zero cross

of

its current is located within the region

between

12

and 13' and for the last operating pole the real

instant of a current zero occurs at 14 except for the isolated

neutral condition at which the current through both poles

is

interrupted simultaneously.

The minimum arcing time and the variation of the operating

time should be considered for determining the optimum instant

of contact separation.

111. RESULTSOFTHE

SIMULATION

For verifying the performance of the proposed method, the

simulation studies with electromagnetic transients

program(EMTP) are carried out. The making instants and

corresponding inrush currents are presented by using the

model circuit with the parameters of 550kV power system as

shown in Fig. 1. The inductance of a source side reactor and

that of a shunt reactor equal to 190mH and 6.0H, respectively

are used as significant system parameters. The parameter m

would he

all

possible values including the upper and the lower

extreme values. It is assumed that the slope of the dielectric

withstand between contact gap is identical to that of the

applying voltage at zero cross

T o assess the performance of the proposed method the

current initiation at the voltage peak due to the pre-strike is

confirmed under the several conditions of a neutral reactor and

with the variation of RDDS. The representative result of these

verifications is illustrated in Fig. 7. 

-2

I ) , (2). (3): he rate

of

decreaseofdielectric strength for contact gaps on each

pole

Fig. 7. Optimal contact touch instants obtained from the proposed method

(m=l)

The making instants(t1, 12, 13)

of

each pole resulted from

the target contact touches(t1'. 12'. 13') are at c rest voltage across

the contact and

this

means that the inrush current has the

minimum level and the symmetrical waveform.

Hence, the mechanical variation in closing time should be

also considered in order to limit the inrush current. The spread

of the operating instants of each pole is given by normally

distributed random numbers which have a mean and a standard

deviation(o ). It is assumed that the possible variation span of

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the closing time is within the range bounded by + A T round

the mean value as shown in Fig. 8. And the corresponding 30

in the given distribution is equal to A T . When the contacts are

close lo touching during the closing stroke the mean value of

the decrease in the withstand voltage can be approximated by a

linear function of time. The slope K(kV/sec) which is identical

to that of voltage at zero cross is depicted in Fig 8.

The calculated instant of a contact touch is set to the mean

value of the normal distribution which represents the statistical

scatter of operating time. The magnitude of inrush currents is

evaluated by the simulation studies with EM TP

negative

tolerance

nominal

posi t ive

tolerance

slope

:K

Fig.

8 .

Probability characteristics of e variation

in

closing times

The inrush current increases with the scatter of a closing

time. During the simulation study,

100

closing operations are

performed with the statistical variation of closing time under

the condition of the preset time tolerance(AT) varying from 0

to 2.0 ms. Typical ones among the results for the case of AT

equal to

1

.Oms and 2.0 ms are appeared in Fig. 9. 

For the case

of

AT equal to 2.0ms the maximum occurrence

locates

in

the range from 1.4 to

1.5

p.u. and the upper limiting

value i s

about 1.8p.u. with respect to a normal current. For the

other values of A T , the ranges bounded by

30

are marked

with bold lines in Fig.

10 

which correspond to the distribution

of

inrush currents.

z ,

,? ,

,?

,9

,  ,

,?

Inrush Current

(P.u.)

Fig. 9.

Number of ~ c c u r r e n ~ e

~ R U S

nrush currents

in

p.u .

AT=l.O, 2.Orns)

It means that if inrush current is required to be limited

below 1.5 p.u. the scatter of circuit breaker operating time

should be less than 1.4ms.

For the circuit breaker with no scatter of operating time, the

corresponding inrush current is almost 1.0 p.u,, Therefore, the

instant of the contact touch for each pole is verified to

be

calculated correctly.

2 1.8

1.6

1.4

g

1.2

8 1.0

1.0 2.0

Variation of Operating T ime

ms)

Fig

10.

Distribution of the inrush current with respect to

operating time

scattenng(K=l)

IV. CONCLUSION

The optimum closing and opening instants for shunt reactor

applications in the cases

of

earthed neutral through a reactor as

well as both the isolated and directly earthed neulral are

provided by the method proposed

in

this paper. From the

results of this study it is clear that the magnitude and the

instant of the peak voltage across the contacts are affected by

the ratio of the inductance

of

a shunt reactor to that

of

neutral

reactor. Therefore the relative slope(K)

of

RDDS should be

considered to calculate the optimum instants. The performance

of the proposed method was verified by the simulation studies

with EMT P considering the behaviors of circuit breakers such

as the rate of decrease of dielectric strength and the variation

in operation times

of

the circuit breaker as important

parameters.

Additionally,

t he operation

time scatter

to limit the

inrush

current to the level of less than a certain magnitude can be

established by using the obtained results.

V. ACKNOWLEDGMENI

This work was supported by the components and material

technique development program sponsored by the Ministry

of Commercial, Industry and Energy of South Korea.

VI. REFERENCES

[ I 1

Task Force 13.00,

Conuolled

switching - A state-of-the-an survey

(pan

I

) ELECTRA No.162. October 1995

Task Force 13.00, Controlledswitching - A state-of-the-an survey

(pun

I I Y

ELECTRA No. 164 , February

1996

D.F. Peelo. J .H .

Sawuda.

Exoerien ce with controlled transmission

l ine

121

131

1

.

autoreclosing und controlled shunt reactor switching on B.C.Hydro

system .CIGRE,

13-101,

1998

141 Y. Fushirni. T. Kobayashi. E. Haginomon, A. Kobayashi

and

K.

Suzuki. Re-ignition r& controlled s&ching of EHV high power shunt

reac tor ,

CIGRE. 13-106.

1998

R.J. Rajotte,

C.

Charpentier.

S.

Breault, H. Hai Le

and

H.Huynh. Field

tests of a circuit breaker synch ronous controlll. IEEE Trans. on Power

IS1

~ e i i ~ e ~ .

ol. n,

NO. 3 ,

iU iy

1995

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(61

Working Group 13.07. Control led switching of HV AC CBs guide for

Jin-Kyo Chong received the B.S and M.S

application lines,

reactors.

capacitors,

transformers (1st PmY,

degree n

clecttical

engineering f rom Kangwon

ELECTRA, No.183. April

1999

i National University in 1991 and 1994

Working Group 13.07, Controlled switching of H VA C CBs guide for

respectively. Since 1994. he h a

been

with KERI,

application

l ines, remors.

capacitors. transformers 2nd

P m Y , as

a senior research engineer in the advanced

ELECTRA. No.185, August

1999

power apparatus research group.

His

research

interests are t he mdys is o f an slrctromngnetic

field and

the

test

o f circuit breakers.

'7

\

i

-..

1

[7]

Tel:055-280-1564.ux:O55-28O-I

89

E-mail: ikchone@keri.re.kr

VII. BIOGRAPHIES

Woo-Young

Lee received the B.S and

M.S

degree in electronic

engineering

f rom Kyungbook

National University

in 1980 and 1982

respectively.

Since

1982 he has

becn

with KERI,

principle

research engineer in the advanced

power apparatus research group. His research

inlcrests me

controlled

switching, measuring

techniques i n hig h power, partial discharge

mwurement .

Tel:055-280-1572. Fax:055-280-1589

E-mail: wylee@ksn.rc.kr

Kyong-Yop Park eceived the B.S degree i n

electrical engineering from Seoul Nat ional

University in 1979, the M.S and Ph.D degree from

Liverpool Univrsity, U.K. Since

1981

he has

been

with KERI. 8s a execut ive director of [he

advanced

power apparatus research group.

H i s

research interests are flow

field

analysis, analysis

of

lest results and

arc

phenomena in

gas

circuit

breakers.

Tel:055-280-1561,Fsx:055-280-1589

E-mail: kypwkI3kcr i. re.b

Byeong-Yoon

Lee

received the B.S. M.S and

Ph.D degree i n

el rcrr ica l

engineering from Seoul

National University in

1990.1992

and

1997

respectively. Since

1996,

he has

been

with KERI.

iv B senior research

cngincer

i n

the advanced

power apparvtus research group.

His research

interests are flow f ie ld analysis.

electric

magnetic analysis and arc phenomena in gas

circuit breakers.

TcI:O55-280~1565.ax:055-280-1589

Hee-Jim Kim eceived the B.S and

M.S

dzgrec

in

electrical mginzeting from K wangwm n and

lnhv

University

in

1980

and

1982

rcspcct ivr ly.

Since 1994.

he has

hem

wi t h Vilrro Tech Co.. as

a manager of the technical institute in

this

company.

His

research

interests

are the design

of

a vacuum interrupicr and D circuit

breaker

and

plasma applications.

Tel:03l-489-2004. Fm031492-2216

E-mail: hikim@vitrrotech.com  

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