SUPPRESSION OF VFT IN 11OOkV GIS BY ADOPTING resistor fitted disconnectors.pdf

7/27/2019 SUPPRESSION OF VFT IN 11OOkV GIS BY ADOPTING resistor fitted disconnectors.pdf

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872 IEEE Transactions on Power Delivery, Vol. 11. No. 2, April 1996SUPPRESSION OF VFT IN 11OOkV GIS BY ADOPTINGRESISTOR-FITTED DISC ONNEC TOR

Y. Yamagata K. Tanaka

Tokyo Electric Power CompanyTokyo, Japan

S. Nishiwaki N. Takahashi T. Kokum aiMemberI. Miwa T. Komukai K. ImaiMember

Toshiba CorporationKawasaki, Japan

Abstract - With lOOOkV transmission lines planned in Ja-pan, very fast transient (VFT) phenomena will be suppressedby installing a resistor in a disconnector O gas insulatedswitchgear (GIs). In this paper the VF T overvoltage suppress-ing effect of the resistor and the duty required of the resistorare clarified. A llOOkV resistor-fitted disconnector was testedby constructing a charging current interruption test circuit. Ithas been clarified that the disconnector accepts the requiredduty. The disconnector tested here wil l be used for the fieldtest.

circuit in the event of restriking, having no mechanical con-tacts to connect the resistor but only a movable electrode.

This paper investigates the surge suppression effect of theresistor, obtains the required duty of the resistor, and de-scribes the testcircuit, which can prove the resistor accepts the obtainedduty, and the test results. There is already a report on a scalemodel of a resistor-fitted disconnector and its test [7]. How-ever, here discussed is a full-voltage disconnector. Thedisconnector experimentally proved here will be used in afield proof test scheduled for 1995.

of the charging current

1. INTRODUCTIONIt is known that when switching a charging current, theGIS disconnector repeats restriking, generating a very fast

transient (VFT) overvoltage I l l and that such overvoltagescan cause ground faults from between disconnector contacts[2][3] or at a bus contaminated by metallic particles [4][5].This can develop into interference with the low-voltage cir-cuit of the control system [6].

In Japan, there are plans to provide lOOOkV transmission.The LIWL of the GIS (gas insulated switchgear) used thereis set as low as 2250kV. Thus, with disconnectors as an ex-tension of conventional technology, the overvoltage levelwill exceed the LIWL. With higher overvoltages, suchground faults and interference are more likely to be caused.To suppress such VFTs, it was decided to try to employ re-sistor-fitted disconnectors. The resistor-fitted disconnector,which is the subject of discussion here and has been manu-factured, is designed to connect a resistor in series with the

95 SM 499-4 PWRD A paper recommended and approvedby the IEEE Switchgear Committee of the IEEE PowerEngineering Society for presentation at the 1995IEEE/PES Summer Meeting, J u l y 23-27, 1995, Portland,OR. Manuscript submitted December 28, 1994; madeavailable for printing June 15, 1995.

2. SWITCHING PROCESS OF RESISTOR-FITTEDDISCONNECTOR

Fig. 1shows the full view of the llOOkV resistor-fitteddisconnector manufactured in the present study. Fig. 2 illus-trates the switching process of the disconnector; (a) showsthe closed state, (b) and (c) show mid courses of switchingand (d) shows the opened state. (b) shows that the head ofthe movable contact is in the resistor shield, where ignitionis repeated between the head of the resistor shield and the

OperatingmechanismInsulatingspacer 2(powersupply side)

MovableelectrodeShield onmovableside

Inter-electrodedischargeResistorshieldResistor

Tank

Stationaryelectrode

I I

Insulatingspacer 1(load side)Fig. 1 Full view of 1 lOOkV resistor-fitted disconnector

0885-8977/96/$05.000 1995 IEEE


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873

GISTransformer

Zn O surge arresterOverhead transmission line

BushingOpened circuit breakerDisconnector resistance

Resistor

(a) Closed stateRestriking arc

z = 9x2, 2) =27omlps460OpF

V ~ O ~ A1555kV, Vim* = lO8OkVZ =23052, 2)= 3Oomlps

5oopF400pF

50n-lkQ

Restriking arc

(b) Mid-course of switching

(c) Mid-course of switching (d) Opened stateFig. 2 Illustration of switching operation of resistor-fitted disconnector

movable contact. (c) shows that the head of the movablecontact is outside the resistor shield, where ignition is re-peated between the head of the movable contact and thehead of the resistor shield until sufficient insulation is recov-ered. Under a resistor insertion system like this, in the eventof a restriking, the resistor is inserted in series with the cir-cuit, enabling overvoltages to be suppressed.

3. CALCULATION OF OVERVOLTAGESFig. 3 shows a typical llOOkV GIs. Overvoltages in

disconnectors were calculated at various points in this GIs.It has been shown that very fast transient overvoltagescaused when the disconnector restrikes in GIS can be calcu-lated very accurately [SI. n the present study, the calcula-tion was carried out using EMTP in accordance with thetechnique shown in the reference [8].

Overvoltage calculation was based on the assumption thatrestriking was caused when the residual voltage at the loadside and the voltage at the power supply side were -1.Opu(-898kV) and +l.Opu respectively. Table I shows the con-stants used in the calculation. Some waveforms in the calcu-lation results, which are for no resistance, 200Q and 1kQ indisconnector0 in Fig. 3 , are shown in Fig. 4. The calcula-tion here is for the case in which maximum overvoltageswere obtained when there is no resistor in the disconnectors.1) With no resistor in the disconnectors, the crest value of

overvoltages is 2.8(pu) x 898(kV) = 2510kV. This ex-ceeds LIWL = 2250kV.2) If the resistor is 200Q or lkQ, surges are nearlynonoscillatory. Overvoltages are reduced to almost lpu.

Fig. 4 hows the followings:

-The left:half issimilar jto therighthalf.

ES10 LAPD

1I* CT

kFig. 3 1 lOOkV GIS circuitry used for the surge calculation


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8742.8pu Load side

200.0 200.0z z9

* Nx-

Wm0 x=. 0

-EL

J (a1-i Surge voltage J (a)-2 Disconnector current(a) Without disconnector resistor

100.0z2

9

*xhWmL-

100.0

terminalmm-9t-IPU (b )- I Surge voltage J (b)-2 Resistor voltage

(b) With disconne ctor resistor 200Q

S L_i (c1-1 Surge vol tage9 -1PU (c)-2 Resistor voltage(c) With disconnector resistor 1kQ

Fig.4 Some waveforms from surge calculation4. DUTY OF RESISTORS

With insulation recovery characteristics betweendisconnector electrodes simulated, the repetitive generationof restriking was calculated during the intenuption and clos-ing operation. Fig. 6shows the insulation recovery charac-teristics used in calculation, with the movable electrode ofnegative and positive polarity with respect to stationary con-tact. At point A , the movable electrode separates from thestationary contact and at point B; its head is outside the re-sistor shield.

It is known that repetitive restrikings occur differently be-tween the case disconnector inter-electrode breakdown volt-age differs with polarity and the case the breakdown voltagedoes not differ with polarity [9]. If the breakdown voltagediffers with polarity, the maximum inter-electrode voltagethat causes resuikings is lower.As shown in Fig. 1, when the head of the movable elec-trode is outside the resistor shield, the inter-electrode formof the disconnector is nearly a rod-plane. That is, the mov-able electrode corresponds to a rod, and the resistor shield toa plane. Therefore, the electric field strength of the head ofthe movable electrode is higher. Thus, when the movableelectrode is positive, the breakdown voltages are higher thanwhen the movable electrode is negative.

The energy consumed by the resistor due to repetitive

None 50 200 1000Resistance (Q)

(a) Overvoltage multiple2000

1500- EQ)

Xs=: 1000-LAdOmm.-2 500-

050 200 1000

Resistance (Q)(b) Resistor voltage

2500-3L2 2000.-mE 1500-a$ 1 0 0 0SE 500FJ- 0a,

50 200 1000Resistance (Q)

( c ) Energy consumed by resistorFig. 5 Results of calculation

(In each case of calculation, th e maximum valuesat various points of GIS are plotted.)restriking was also calculated. As shown in Fig. 40)-1 nd(cl-1, restriking via the resistor causes the capacitance volt-age at the load side of the disconnector to vary from the ini-tial value before restriking to the value of the voltage at thepower supply side, which meanwhile remains nearly con-stant. This is because the impedance at the power supplyside is small and the capacitance at the power supply side ismuch larger than that at the load side. Energy ER consumedhere by the resistor is approximately given in a simple wayby


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875Fig. 7. This is a characteristic phenomenon whereby there isdifference between positive and negative breakdown volt-ages [9]. The results of 400 calculations are summarized inFig. 8.

Assuming the residual voltage at the load side of thedisconnector is kl.Opu, calculations were made for repetitiverestrikings at the time of closing.For the case in which the positive breakdown voltage be-tween electrodes equals the negative one, calculations werealso carried out for repetitive restrikings for both interrup-tion and closing. Residual voltages of klpu were used forthe closing operation.

From the results of 400 calculations carried out withopening and closing phases varied, the maximum values ofinter-electrode breakdown voltage and the energy consumedby resistors are shown in Table 11.

Fig. 9shows the resistor manufactured to meet the above-mentioned required duty. It is a noninductive resistor made

1.35( 1.0closing

1k8 2000-22 1000-

.d-0c

U

1796 12.81796 17.6 )

. Measured data- urve used in calculationNegative

Time (ms)Fig. 6 Discon nector insulati on recovery characteristics used in asimula tion of repeti tive restrikings

1E --CVo2.where C: capacitance at the load side of the disconnectorand Vo: oltage between disconnector electrodes at the timeof restriking.

With the bus length at the load side and the capacitance ofthe open circuit breaker in the field taken into account, thecapacitance at the load side to be switched of thedisconnectors manufactured here was determined as 2000pF.Using this value for C, the energy consumed by thedisconnector resistors was calculated.

The opening phase for an ac voltage with an actual dis-connector is random. Repetitive restriking after disconnectoropening occurs differently with opening phase [9]. There-fore, the above-described computations were made 400times with the opening phase evenly divided within onecycle (20ms). An example of the waveforms obtained by thecalculation of interruption are shown in Fig. 7. In the inter-val between point A at opening and point B in Fig. 7, thehead of the movable electrode is inside the resistor shield.Subsequent to point B, the head of the movable electrodecomes out of the resistor shield. At point C, the last ignitiontakes place, completing the interruption. The energy con-sumed by the resistor grows as restriking takes place repeat-edly, reaching 11.4kJ.In all 400 calculations carried out with the opening phasevaried, the last load-side voltage was negative as shown in

(1)R - 2

, , I p u = l l O O X f i / f i = 8 9 8 k V ,Q

'I B Power supply side I 'Load side voltageA (conta cts separation) voltage c

4 Fig.7 An example of simulation results of repetltive restrikingsat interruption

Total 400 calculations Total 400 calculations1801 a

1_1800Voltage (kV) - Energ;(kJ)(b) Distribution of energy con-sumed by resistor

(a) Distribution of maximum valuesof restriking inter-electro devoltageFig. 8 Summarized results of 400 calculat ions about interruption

TABLE 11MAXIMUM ALUES IN THE RESULTSOF 400 CALCULATIONS

FOR EACHC A SEk = Positiv e Maximum inter- Maximumbreakdown voltag e/ electrode energyNegat ive breakdown consumed bbreakdown voltag e voltag e (kV) resistor (kTf

Interruption 1710 14.5 )

Metal Resistor wire

Fig. 9 Discon nector resistor manufactured


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876by winding, in opposite directions, two layers of metal resis-tance wires. Its resistance is l k a and two units are used inparallel, providing500Q.

5. CHARGING CURRENT INTERRUPTION TEST5.1 Test Circuit Structure

A full voltage test circuit was prepared to carry out acharging current interruption test with a 1OOkV resistor-fit-ted disconnector. The test circuit structure and a photographof it are shown in Figs. 10 and 11 respectively. A 900kVtesting transformer with a short-circuit generator was usedas the power supply. To obtain the large amount of con-sumed energy of disconnector resistor, the capacitance at thepower supply side of the disconnector was determined to be15times that at the load side.5.2 Merhod of Measuring Ver y Fast Transient Overvoltagesand Measured Wa veforms

To measure very fast transient overvoltages caused byrestrikings, the capacitance potential divider shown in Fig.12 was prepared using insulating spacers to support thehigh-voltage GIS conductor [SI [101. Signals were converted

/////////////////////////////////////////Ge Tr L Cs Bg BS DS BS Bg CI

Ge s hort- circui t generator, Tr t esting transform er 900kV, L protectivereactor 9OOpH, Cs powe r supply side capacitor 33,OOOpF, Bg bushi ng1 OOkVac, BS SF gas-insulated bus lorn, DS resistor fitted disconnector,CI load side capacitor 1150pF

Fig. 10 Structure of test circuit

Fig. 11 1 00kV charging current interruption test

Copper.boxC

/ / Tanke

C = 4000pFR, = 50kQR,=IkQV = 30V

Oscrllo-converter scopeOptical fiber cableFig. 12 Potential divider using spa cer

into light for transmission. The frequency response of theoverall voltage divider was 16MHz (-3dB). Overvoltageswere measured at two points using spacers at the load andpower supply sides of the disconnector, as shown in Fig. 1.The voltage applied to the resistor when the disconnectorwas restruck was obtained from the differences betweenwaveforms at these two points. Some of the results of mea-surements obtained at restriking in the charging current in-terruption test are shown in Fig. 13 (a), (b ) and (c). Thewaveform in (b) is for the resistor voltage obtained by de-ducting the load-side voltage in (c) from the power supplyside voltage in (a). The dc voltage before restriking was noton the resistor.

To check the measured waveforms at spacer potential di-viders, waveforms were measured additionally with a lowvoltage using a mercury switch and the results were com-pared [ 2 ] . With the window of the disconnector tank open,the power supply and the load sides were charged with 50Vand -5OV respectively and the mercury switch, which wasconnected between electrodes, was closed. Fig. 14. (a) and(b) show measured waveforms. In Fig. 14 (a), waveforms

(a) Power supply side voltage1

vz Resjriking -1018kV

(b) Differential voltage of (a) and (c)T,=l. 1 5p (resistor voltage)v3(c) Load side voltage 1.00 u d d i u

Fig. 13 Very fast transient voltage w aveforms at restriking obtained witha spacer potential divider


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, 4 8 7 7

(a)-1 Vo ltage at point F in Fig. 1 (power supply side voltage)0

IOOV0 -(a)-2 Difference voltage between (a)-1 and (a)-3 (resistor voltage)0 0$-50v

&3 Voltage at point H in 1. a@ us/d vI Fig. 1 (load side voltage) -SW ON

(a) Measured waveforms 1

I (b)-1 Voltage at point G in Fig. 1(power supply side voltage)0--.-b)-2 Difference voltage between (b)-I and (b)-3 (resistor voltage)-b)-3 Voltage at point H in 1 Fig. 1(load side voltage) --SW ON(b) Measured waveforms 2

Fig. 1 4 Waveforms measured with low voltage

were measured at point F in Fig. 1 for the power supply sidevoltage and at point H for the load side voltage, and the re-sistor voltage was obtained as the difference between them.The waveforms are similar to those measured with an actualvoltage using the spacer potential dividers shown in Fig. 13.In Fig. 14 (b), the waveform for the power supply side wasmeasured at point G. By obtaining the difference betweenthis voltage and the measured waveform at point H, the riseportion of the voltage on the resistor could also be observedas shown in Fig. 14 @)-2.5.3 Characteristics of Test Circuit

a) Rise of Voltage Applied to Resistor: The actual GIS infield has buses on both the load and the power supply sidesof the dinconnector. In a simplified way, the moment thedisconnector restrikes via the resistor, voltage VR of equa-tion (2) is applied to the resistor. Its rise is very fast.

where Z : surge bus, R: resistance of

10m gas ins/ul&ed bus was installed at either side of thedisconnector as shown in Fig. 10or 11. As a result, a fastrising voltage was obtained as shown in Fig. 14 (b)-2. Su-perimposed at the rise portion here is a very fast transientcomponent, which is probably caused by local reflections ofthe complicatedly shaped disconnector.

6 ) Energy Consumed by Resistor: In the test circuit shownin Fig. 10,the capacitance of capacitor C1, bushing Bg andgas insulated bus BS, at the load side of the disconnectorwas determined as 2230pF. This is above the specificationvalue: 2000pF. To obtain a high voltage to be applied to theresistor and large energy consumed by the resistor, at thepower supply side of the disconnector, capacitor Cs, havinga capacitance 15 times larger than that at the load side, wasconnected. This made, as shown in Fig. 13, the voltage atthe load side vary from the initial value V, before restrikingto V3, nearly equal to V , at the power supply side. However,what differs here from the phenomena in the actual GISshown in Fig. 4 (b)-1 or (b)-2 is that the power supply sidevoltage after restriking is not constant, but oscillatesslightly, producing the peak at point R in Fig. 13. This is be-cause of the inductance of the circuit, which causes high-fre-quency transient oscillations, or the Cs-Bg-BS-DS-BS-Bg-C1 circuit in Fig. 10.The resistor voltage also produced peakS for point R. This makes it impossible to represent the en-ergy consumed by the resistor in the test circuit by equation(1). The energy consumed by the resistor was obtained as1.46kJ from the resistor voltage waveform in Fig. 13 (b). Itis obtained as 1.16k.l from equation (l), with C: 2230pF andV: 1018kV. Thus, the energy consumed by the resistor in thetest circuit is 1.46/1.16= 1.26 times larger than that in actualGIs.

c ) Damping of the Resistor Voltage: When thedisconnector discharged between the head of the movableelectrode and the resistor shield, the discharge arc propa-gated while branching, causing the resistor to short-circuit.This was observed in the initial phases of the disconnectordevelopment. Fig. 15 illustrates this phenomenon.

In Fig. 15 (b), the branching leader grows because a volt-age is generated at the resistor by a discharge current flow-ing through it. The faster the damping of the discharge cur-rent flowing through the resistor, the slower the growth ofthe branching leader.

If phenomena like this are taken into account, it is neces-sary to fit damping of the discharge current through the re-sistor at the time of restriking in the test circuit LO that in ac-tual systems. As shown in Fig. 4, the damping time constant


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(4 (b ) (4Fig. 15 Illustration of resistor short-circuit caused by branching leader

of the discharging current through the resistor in actual G Isis represented as approximately by CR , where C is the ca-pacitanceat the load side of the disconnector and R is the re-sistance of the disconnector resistor. The specified vdues inthe present test are C: 2000pF and R: 500Q which makeCR: 1ps.

In the test circuit, damping time constant T, is 1 . 1 5 ~sshown in Fig. 13 (b) and there is peak portion S . This provesthat the phenomenon shown in Fig. 15 is more likely to takeplace in the test circuit than in actual GIs .5.4 Test Results

With the power supply voltage raised 1.1 times (11OOkV/6 x 1.1 = 700kV), 400 charging current interruption testswere carried out with the opening phase left at random. Anexample of oscillograms showing how repetitive restrikingtook place is shown in Fig. 16. The load side residual volt-ages after the interruptions were consistently negative,which agrees with the results of simulation shown in Fig. 7.

Fig. 17 shows the photograph of observed arcs betweendisconnector electrodes. It was taken with the camera placedat the observation window of the disconnector tank and itsshutter left open. It corresponds to the test yielding the oscil-lograms in Fig. 16.

During the test, all repetitive restrikings above a certainlevel were observed with a digital memory oscilloscope. Ateach restriking, the waveform was observed by triggering

0" v v v v w w u w v v v v v v v v(a ) Power supply side voltage988kV

0w I%& Contact: opening (b) Load side voltage

Fig. 16 Measured oscillogram

Fig. 17 Photographed arcs between electrodes

the digital oscilloscope and dividing the memory. The arcobservation, one result is shown in Fig. 17, was continuedthroughout the 400 tests.

Fig. 18(a) shows the test results for the distribution ofmaximum values of the restriking voltage between elec-trodes. 2pu = 2 (1100/6 x f i x 1.1) = 1980kV. Becausethere is a difference between the positive and negative val-ues of the inter-electrode breakdown voltage, even the maxi-mum was 1680kV, lower than the value above. Fig. 18 (b)shows the results of calculations, which were conducted us-ing a power supply voltage of 1100kV/& x 1.1 instead of110OkV/& in the calculation shown in Fig. 8(a).

Fig. 19shows the results of a calculation of the distribu-tion of the energy consumed by the resistor, which isequivalenr to the calculation in Fig. 8 (b). In the calculation,the same conditions were used as in the test: the power sup-ply voltage was 1.1 times higher and the energy consumed

200v )VI,L

800z 40

0

Total 400 tests Total 400 calculations

1200 1400 1600Voltage (kV) Voltage (kV)

(a) Test results (b) Results of calculationFig. 18 Distributions of maximum values ofrestriking inter-electrode voltagePower supply voltage: 1.1 x 1 1 0 0 k V/ f i


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879cuit was carried out, proving that the resistor-fitteddisconnector withstood the required duty.

REFERENCES120

Inc.-;;i 80% 400

-=I5z

0 8 12 16 20Energy (kJ)Fig. 19 Distribution of energy consumed by resistorsResults of calculation under the sa me conditions as in the test

by the resistor per restriking was 1.26 times the value inequation (1). The maximum in Fig. 19 is higher than that inTable 11 Thus, the consumed energy is larger in the test thanin the actual GIs .As described above, 400 interruption tests were completedwithout trouble under severer conditions than in actual GIS.In other words, there were no resistor flashovers, no resistorshort-circuits due to branching arcs, no disconnector groundfaults, etc.

6. CONCLUSIONA study proved the effectiveness of a 1 OOkV resistor-fit-

ted disconnector for suppressing very fast transient overvolt-ages due to restrikings at the time of switching charging cur-rents and the required duty of resistors. A charging currentinterruption test circuit was prepared and tests were carriedout, proving that the disconnector manufactured withstoodthe required duty. The discussion in this paper can be sum-marized as follows:1) An actual 1OOkV GIS unit was taken up and a surge cal-

culation was carried out for a number of disconnectors.2) Simulating the operation and inter-electrode breakdownvoltage characteristics of a resistor fitted disconnector,multiple calculations were carried out on repetitiverestrikings, obtaining the distributions of energy con-sumed by resistors and restriking voltages betweendisconnector electrodes.3) A charging current interruption test circuit using a short-circuit generator and a testing transformer for the powersupply was prepared. The disconnector was flanked by10m gas insulated buses and provided with a 1150pF ca-pacitor at the load side and a 33 OOOpF capacitor at thepower supply side. Total capacitance of the load side was2230pF.4) Very fast transient phenomena at restrikings were mea-sured and the results showed that the test circuit met therequirements for the following: (1) rising speed of thevoltage on the resistor, (2) energy consumed by the resis-tor and (3) damping t ime constant of resistorvoltage.

5) A test with 400 interruptions using the prepared test cir-

[l] Working Group 33/13-09, Very Fast Transient Phenomena Associ-ated with Gas Insulated Substations, CIGRE, 1988.33-13.[2 ] S . Nishiwaki, Y. Kanno, S . Sato, E. Haginomori, S.Yamashita, and S.Yanabu. Ground Fault by Restriking Surge of SF6Gas-insulated Dis-connecting Switch and Its Sy nthetic Tests, IEEE Trans. on PAS,Vol.PAS-102, No. 1, January 1983, pp. 219-227.[3] S . Narimatsu, K. Yamaguchi, S.Nakano, and S . Maruyama, Inter-rupting Performance of Capacitive Current by Disconnecting Switchfor Gas Insulated Switchgear, IEEE on PAS,Vol. PAS-100, No. 6,June 1981, pp. 2726-2732.[4] S . Kobayashi, Y. Yamagata, S . Nishiwaki, H. Okubo, Y. Kawaguchi,Y. Murakami, and S . Yanabu, Particle-Initiated Flashover Caused byDisconnector Restriking Surges in GIS, 5t h ISH, 1987, Paper 12.03.[SI W. Boeck , W. Tashner, I. Gorablenkow, G.F. Luxa, and L. Menten,Insulation Behavior of SF6 with and without Solid Insulation in Caseof Fast Transients, CIGRE, 1986, 15-07.[6] J. Meppelink and H. Remde, Electromagnetic Compatibility in GISSubstations, Brown Boveri Review, No. 9, 1986, pp. 498-502.[7 ] J. Ozawa, T. Yamagiwa, M. Hosokawa, S . Takeuchi and K. Kozawa,Suppression of Fast Transient Overvoltage during Gas DisconnectorSwitching in GIs, IEEE PES 1986 Winter Meeting, 86 WM 138-2.[8 ] S . Ogawa, E. Haginomori, S . Nishiwaki. T. Yoshida, and K. Terasaka,Estimation of Restriking Transient Overvoltage on DisconnectingSwitch for GIS, IEEE PES 1985 Summer Meeting, Vancouver, 85[9] S.A. Boggs, F.Y. Chu, and N. Fujimoto, Disconnect Induced Tran-sients and Trapped Cha rge in Gas-Insulated Substation, IEEE Trans.

PAS,Vol. PAS-101, No. 10, October 198 2, pp. 3593-3602.[10]K. Nojima, S . Nishiwaki, H. Okubo, and S . Yanabu, Measurement ofSurge Current and Voltage Waveforms Using Optical-transmissionTechniques IEE Proceedings, Vol. 134, Pt. C, No. 6, November1987, pp. 415-42 2.

SM 367-8.

Yoshibumi Yam aga ta was bom in Ibaragi Prefecture, Japan on Novem-ber 3, 1953. He received his B.S. and M.S. d egrees in electrical engineer-ing from the Yokohama National University in 1976 and 1978 respec-tively.He joined the Tokyo Electric Power Co., nc., Japan in 1978. Sincethen he has been engaged in the construction of substations and the devel-opment of substation apparatus. Since 199 2 he has been a manager ofTransmission & Substations Construction Division.Kouji Tanaka was bom in Miyagi Prefecture, Japan on April 23, 1957.He received his B.E. degree in electrical engineering from Waseda Uni-versity, Tokyo, Japan in 1981.He joined the Tokyo Electric Power Co., Inc., Japan in 198 1 as an en-gineer engaged in work related to engineering and development of substa-tion equipment. At present, he is an as sistant manager of Transmission &Substations Construction Division.Mr. Tanaka is a member of IEE of Japan.Susumu Nishiwaki (M75) was bom in Kanagawa Prefecture, Japan onJanuary 3, 1947. He received his B.S. degree in electrical engineeringfrom Yokohama National University in 1969 and his Ph.D. degree fromNagoya University in 1982.In 1969 he joined the Heavy Apparatus Engineering Laboratory ofToshiba Corporation, Kawasaki, Japan, where he has been engaged in re-search and development of gas-insulated switchgear and lightning arrest-ers.Dr. Nishiwaki is a member of IEE of Japan and IEEE.


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880Nobuyuki Takahashi was horn in Kanagawa Prefecture, Japan on Janu-ary 10, 1946. He graduated from Kanagawa Technical High School,Kanagawa, Japan in 1965.He joined Toshiba Corporation in 1965. Since then, he has been en-gaged in short circuit test in the High Power Laboratory. Presently, he is asenior specialist in the power engineering section of the Heavy ApparatusEngineering Laboratory.Mr. Takahashi is a mem ber of IEE of Japan.Tsuyoshi Kokuma i was bom in Okayama Prefecture, Japan on March 19,1956. He graduated from Mizushima Technical High School, Okayama,Japan in 1974.He joined Toshiba Corporation in 1974. Since then, he has been en-gaged in short circuit test in the H igh Power Laboratory.Mr. Kokumai is a member of IEE of Japan.Ikuo Miwa was bom in Aichi Prefecture, Japan on December 8, 1952. Hereceived his B.S. degree in electrical engineering from Saga University,Japan in 1975.In 1975 he joined Toshiba Corporation, Hamakawasaki Works, where

he has been engaged in the development and design of GIS. He is pres-ently a manager of the GIS Designing Section.Mr. Miwa i s a member of IEE of Japan.Toshihiko Komukai (M70) was bom in Iwate Prefecture, Japan on Janu-ary 6, 1937. He received his B.S. degree in electrical engineering fromIwate University, and the Dr. of engineering degree from Tohoku Univer-sity, Japan in 1959 and 1981 respectively.Since 1959 he has been with Toshiba Corporation, Tokyo and engagedm power system analysis and development of power system co ntroller.Dr. Komukai is a mem ber of IEE of Japan and IEEE.Kensuk e Im ai was bom in Kanagawa Prefecture, Japan on July 4, 1961.He received his B.S. (1985) and M.S. (1987) degrees in electrical engi-neering from Yokohama National U niversity, Japan.In 1987, he joined Toshiba Corporation. Since then, he has been en-gaged in engineering of substation equipment such as gas-insulatedswitchgear and power transformers.Mr. Imai is a member of IEE of Japan.

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SUPPRESSION OF VFT IN 11OOkV GIS BY ADOPTING resistor fitted disconnectors.pdf