Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo

8/3/2019 Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo

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VIABILITY OF PERMANENT SINGLE-PHASE

OPENING OF LINES IN EXTRA HIGH VOLTAGE

SYSTEMS

PART I – SECONDARY ARC EXTINCTION

F. A.T. Siha, Member IEEE J,A, Jardini, FellowMember IEEE

e-mall fats@!peausp br e-mad Jarduu(jpea,usp.br

University of S50 PauloAv, Prof. Luciano Gualberto, 158– trav.3

05508-900 – S2ioPaulo, SP, Brazil

Abstract: This paper discusses the viability of permanent single-

phase opening of lines in extra high voltage systems as a system

planning criterion. To apply such criterion it is necessary that :

(i) the secondary arc that appears after a single-phase fault

clearing is quenched; (ii) after a single-phase opening, the

current unbalances of negative and zero sequence in the electric

system are compensated. Power electronics are used to meet

targets. Only the secondary arc extinction condition is analyzed

in this part.

Key words: single-phase opening, secondary arc, unbalances

I. INTRODUCTION

The most common practice when a fault in a transmission

line causes its tripping is the three-phase opening, even if the

problem is in one phase only. Once the fault is eliminated,

the line reclosure occurs after a certain dead time when the

extinction of the secondary arc current is expected.

If there are multiple circuits in a section and the permanent

fault is in one phase, there is no interruption in the flow of

tran:jmitted power even when the three phases are opened.However, there will be a reduction of the transmitted power

during a the initial period after the line opening. This

situation is even more critical when there is only one circuit,

between sections, because the three-phase opening will

interrupt the power flow completely.

The single-phase opening can thus be seen as a way to

minimize this problem, since most faults in Extra High

Voltage (EHV) lines are of single-phase type.

However, the arc extinction conditions are more critical at

the single-phase opening than at the three-phase opening. Inthe latter there will be arc current due to oscillations of the

trapped charges in the line capacitances with their reactors;

these oscillations decrease over the time. In single-phase

opening, voltages in untripped phases may maintain the

secondary arc in values above the extinction limit.

If the permanent single-phase opening is chosen (a

practice not fully established), the load flow disturbance is

smaller than three-phase opening; therefore, more favorable

for the system stability. On the other hand, in the permanent

single-phase opening, there will be distortions in the system

(upstream and downstream the disconnected line), where

negative and zero sequence current and voltage components

will appear. The zero sequence components are blocked in

AY transformer; however, they might interfere in the

protection system. The negative sequence components pass

through to generators and loads being responsible sometimes

for undesired heating at the machines that may be

disconnected by negative sequence protections.

As a conclusion, there are two aspects to be considered in

the use of a permanent single-phase opening (with or

without reclosingj: (i) the extinction of the secondary arc in

the faulty phase (even Z~there is no reclosing), and (ii) the

elimination of current distortions downstream and upstream

the faulted line.

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Fig. 1. 765 kV Transmission SystemSingleLine Diagram

‘Thisarticle discusses a methodology for the compensation

of the arc current. The compensation I minimization of the

distortions in the system upstream and dowmtrea~ the

disconnected line is discussed in another article pI also by the

use of Power Electronics.

‘This cmnpensation of the secondary arc k obtained by

inserting a voltage source in the reactor, in the same phase as

the faulty phase. This source is constituted by a capacitor and

power transistors, thus providing the control of the moduleand phase angle of generated voltage.

‘The simulations here reported were performed using the

ATP Alternative Transient Program. The test system has

similar characteristics to the real 6300 MV& 765 kValternating current (AC) system transmission from Itaipu to

Siio PauI~ Brazil, with”a detaded representation of the-first

section with an approximate length of310 km. An equivalent

impedance represents the two remaining sections and the

receiving system (Fig. 1).

IL FAULT AND ARC EVOLUTION

To have the phenomenon described, the following aspects

were considered:

- Singte-phase fault in bus B after 100ms steady state pre-fault condition;

- Single-phase opening (BI-B3) 50 ms after the fault

initiation, remaining the connection to earth in B;

- Elimination of the connection to earth in B, after 1000 ms

of the fault initiation instant;

The current value from B to earth is shown in Fig. 2 and

the voltage in B is shown in Fig. 3. The single-phase to earth

current peak r-s 16M* being high until the opening of

the circuit breakers at both ends of the faulty line. As fromthis instant there is still current from B to earth with muchlower level, the secondary arc. This swomlary arc current

results from the coupling of the sound phases with the faulty

phase and the transient of trapped charges at line

capacitances at the instant of the circuit breakers opening.

When the secondary arc extinguishes, a recovery voltage in

the faulty phase appears (Fig. 3). If this voltage is high the

arc regnishes.

*From this point ahead kV and A refer topeak values

D & ~>

-&l--+G’

a) Steadystate and short circuit– Oto 200 ms

‘ltl,

300 I

, “

‘I*,,!-..)m

1- ‘--,00

.,-

b)With uhme A of B1-B3 owned – 200to 1500~s.

Fi& 2. Clnnmt tiwmB to earth- single-phase fault am!s@le-phase opening

arc regnishes.

Note that this phenomenon is repeated at all arc current

crossing zero until extinction takes place, In Fig. 2 an arc

extinction was assumed at the instant 1100ms.

Fig. 4 shows the area as related to arc current and recove~

voltage, where the arc extinguishes [2].

III. TRANSIENT STADILI~Y

It is desired to comnare the effect in the system when a

single-phase or a three~phase breaker opening is adopted.

Therefore, the verification of influences of these types of

openings in power oscillations (transient stabili~), shall be

evaluated with proper program, However, a first insight can

“ ,,”,

O!---6,,

4,0

,00

20”

<“”

,0” J

r“-” ,..1Fig.3. Phaseto earth voltage at bus B

0-7803-5938-0/00/$10.00 (c) 2000 IEEE



180

i60

140

120

100

30

60

40

20

—

kV peak

!

10 20 30 40 50

Fig. 4 – Arc Extinction

Secondary arc current x Recovery voltage first peak

be c]btained by examining the power step at the instant just

after the three-phase or single-phase opening, without line

fault. The power variation is smaller when single-phase

opening is used as in the case of three-phase opening (813

MW against 410 MW arriving at Itaipu bus); therefore, better

for the system stability. However, currents (and voltages)

unbalances occur at the generator and at the receiving system

(Table I).Table I

Current from A to Itaipu at A

Positive sequence 4>70kA

I Negative sequence 0,35 kAI 7em seouence I (1

IV. CONDITION OF ARC EXTINCTION

For comparison the Base Case consisting of a single-phase

fault in B was run.

The three-phase line opening was simulated and it was

found that after 1600 ms the arc current is 35 A. Upon the arc

extinction the first peak of the recovery voltage at fault point

is 23 kV. The arc current and the recovery voltage valuesmeet the extinction criteria defined in Fig. 4.

With the single-phase opening the arc current remains 97

A (Fig. 2), and the first peak of the recovery voltage, (if the

arc extinguishes) 77 kV (Fig, 3). By the criterion defined on

Fig. 4 the arc is unlike to extinguish.

Note: Literature states that fast grounding switches mq

help arc extinction. It is also known that the

parameters represented in the simulation, like the

reactor resistance, may inruence the results. These

aspects will not be discussed here because this

work aims at using Power Electronics to get the

so-called extinction.

I,Al, ” B,

i

‘“~” –4 ‘-””4-”+ c-

+ ,3–~––-+--~ ; -

a..- .-

i

\

)--*+---”--

~)4 1 ;:“)[ H, - ‘:,( .-r _ _’H:-----

~1jc~.:~v=o”-’—Fig. 5. Arc compensation source scheme used forthe secondary arc

extinction

V. THE USE OF VOLTAGE SOURCE TO GET THE

SECONDARY ARC EXTINCTION

The aim is check the effectiveness obtained in the

reduction of the secondary arc current (Base Case single-

phase to ground fault – single-phase line opening condition)

by using a voltage source (arc compensation source) in series

with one of the reactors of the open line (Fig. 5).

A. Determination of the Voltage Source Characteristics

The Base Case was run, in steady state condition, andfollowed the procedures bellow described:

- With single-phase fault in B, and without arc compensation

source, the arc current was determined.

- The same case was run with generators (G1 and G2)

bypassed and with the voltage source on (connected to the

reactor in B1).

Testing different values, the source voltage (module and

phase) that feeds a current opposed to the arc current of the

previous step was determined. Note that, the principle of the

superposition of the sources (G1, G2 ~d VsouRcE ) was

therefore considered.

- Then the case with all system sources and with the presence

of VsOuRcE connected to the reactor at Itaipu was again run

so that the results in this step contain the new value of the arc

current modified by VsouRcE

This procedure was repeated for all other fault locations

down the line as for the arc compensation source connected

to the two line reactors, one at a time, The result with the arc

compensation source at B1 side is shown in Table II, being:

IARC= arc current without V~ouRc~

VsouRc~= voltage source determined for secondary arc

cancellation

I*Rc~= arc current with VSOUKE connected

IREACTOR= reactor cmrrentwithout VSOUKCE

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TABLE II

ARC CURRENT ANDVOLTAGE SOURCEFORSECONDARYARCEXTINCTION (CONNECTED AT B1 SIDE)

Fault location I~~c(A, “cl) VSOURCE (kV,Oel) IM,C,.(A, “cl) Iw~c~o~(A,”el)

B 97I@ 193Im 0,4 Im 14l=B1 95 Ifl 1811~ 0,7 IN 25 l=

B2 99 IQ 195 lx 3,0 IN 8 IW

l/4(B 1-B2) 96 Ifl 1891+J!WJ 0>6Ifi 19\w

3/4(Bl-B2) 100 I@ 195Im 0,3 Im o

Note that, in the table, the value of ( 360° +@IREACTOR,

where @~R~Ac-rO~s the phase angle Of IREACTOR is

closed to the desired V50URCE phase angle, and will be

referred here as Reference Phase.

B. Xensibi[ity analysis

The calculation was repeated with fault at various points

down the line.

The arc compensation source voltage applied was:

‘SOURCE = ‘13600+ ‘IREACTOR (1)

The reason for such angle choice was because it is closed

to the determined ideal value and that @ImAc~oRcan be

measured. The magnitude of E is to be determined. The

results are presented in Fig. 6.

Next, the sensibility to arc compensation source voltage

phme angle was determined by applying:

V50URCE= 200 kV 1360°+ @lREAcToR+ A@” (2)

Being: A@= variation of angle for the sensibility analysis

(in electrical degrees),

The 200 kV was chosen, because this value, is within the

range where the arc value is very low for the various

fauhlocations (Fig. 6).

The secondary arc current sensibility to the phase angle of

the source is shown in Fig. 7, to the arc compensation sourcekAULr

LO CA I ’1ON

1

“’%-5+-=J

125 175 225 275

E (kIJ)

From figures, one realizes that even with a t 20%

variation in E the arc current is bellow 50 A.

Similarly a + 20° variation in the arc compensation source

voltage phase angle as related to the Reference Phase does

not lead to arc current above 50 A.

C. Secondary Arc Extinction - Transient Analysis

For the performance analysis of the arc compensation two

tests were carried out: one using an ideal AC voltage source;

and then a power electronic based DC-AC source.

1) Ideal AC source : In the Base Case, at the instant t = 498 ms,

the ideal AC voltage source of 193 1201Q kV is

inserted inthe system. In an almost steady state condition the

arc current value is 32 A and the recovery voltage in the first

half cycle afler the arc extinction is 1.8kV. Therefore, the arc

current extinction is expected.

Having the same procedure repeated, but

V50URCE= 2001218° kV ( average value, passible of

adoption), the values 32 A and 25 kV for the arc current and

the recovery voltage, respectively, are obtained. Being also

satisfactory the conditions for arc extinction.

2) DC-AC Source : With a DC-AC inverter source, it is

possible to produce a device (Fig. 8) which generates a

sinusoidal waveform similar to the one of the ideal AC

source. This inverter has PWM (pulse width modulatecJ

control with a pulse frequency larger than the network’s. The

generated voltage therefore is not a pure sinusoidal waveFAULT

LOCATION

!

o—

!25 1/5 — 225 275 325

PHASE (degrees)

Fig. 7. Arc currentx Voltage source phase

(source in the reactor at Bl)Fig, 6. AJ-Ccurrent x Source voltagemodule(source in the reactor at B 1)

connected to the reactor at B1,

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rlTAIPU B, B B2 03 c

F’~+””+ -

b

7---”--”&R~---..

-. — .)

I

n “,.”,,,“1,...,;:S;1

T,II CH4!

-< ->

, r-t ‘“”o”’”_

~~.,

Fig. 8. DC-AC arc compensationsource

I1 1

1

Fig. 10. Current at the fault point (B to earth), phase a,Btie Casewith the insertionof Vs&acE= 153kV (DC).

The extinction can be facilitated when an opposed current

to the arc is injected through a power electronics based

device.

VII. ACKNOWLEDGMENTSx–a I

n–d

cl, m, a, .–a,

111 1dIGNALI

IT LnSIGNAL2 UI

~_...t (.s)

Fig. 9. SwitchingControl Signals

and contain different harmonics. Some harmonics can be

eliminated by selecting appropriate switching times @ing

angles) as shown in Fig. 9.

For a square wave of 153 kV (equivalent to AC source of

193kV peak) the arc current is of 40 A and the recovery

voltage is of 2.3 kV, satis~ing the condition for arc

extinction (Fig. 10).

The required power of this inverter is about 10 MVA (200

kV and 100 A). This device could be obtained by using a

10~200kV transformer ratio, with the source located in the

low voltage side supplying a 2 kA current.

VI. CONCLUSIONS

After single-phase opening in EHV AC systems, the

secondary arc current resulted fi-om the capacitive coupling

of the sound phases with the faulty phase, can reach values

where there is no guarantee of its extinction in due time.

The authors gratefidly acknowledge the contributions of

Edson H. Watanabe, Clovis Goldemberg and Carlos M. V.

Tahan for their suggestionsfor this work and the CNPQ for its

sponsorship.

VIII. REFERENCES

[1] F. A. T, Silva and J, A, Jardini, “Viability of permanent single-phase

opening of lines in extra high voltage systems, Part II – Unbalance

cancellation”. Submitted for publication, IEEE, PES, 1999.

[2] W. Sate, J, A. Lima and G, Borgonovo. “Interconnection ; An

alternative using static compensation”. In: SEMINARIO

NACIONAL DE PRODU@O E TRANSMISS~O DE ENERGIA

ELETRICA, 5. Recife, 1979.Anais. s.n.t. (inPortuguese)

[3]O. A. Ciniglio and D. P. Carroll “Improved power transfer during single

pole switching a symmetrical sequence filtering approach.” IEEETransactions on Power Delivery, v.8, n.1, p. 454-460, January

1993.

[4] E. W. Kimbark, “Suppression of ground-fault arcs on single-pole-switched EHV lines by shunt reactors”. IEEE Transactions onPower Apparatus and Systems, v.83, p, 285-290,March 1964.

[5] B, R. Shperling, A. Fakheri, and B. J, Ware. “Compensation scheme for

single-pole switching on untransposed transmission lines”. IEEE

Transactions on Power Apparatus and Systems, v.97, n.4, p.

1421-1429,July/August 1978.

[6]N. Knudsen “Single-phaseswitchingon transmis~ionlines using reactors

for extinction ofthe secondaryarc”, CIGRE, Report 310,1962.

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Viability of Permanent Single Phase Opening of Lines in Extra High Voltage un s. Paulo