vol. 77/dec. 1996 - mitsubishi electric

MITSUBISHIELECTRIC

VOL. 77/DEC. 1996

1,000kV Power Systems Edition

TECHNICAL REPORTSSurge Arrestor Technology for 1,000kV Lines ......................................... 1by Yoshibumi Yamagata, Mikio Mochizuki and Shinji Ishibe

A 1,000kV Transformer .............................................................................. 6

CONTENTS Editor-in-Chief

Editorial Advisors

Mitsubishi Electric Advance is publishedquarterly (in March, June, September, andDecember) by Mitsubishi Electric Corporation.Copyright © 1996 by Mitsubishi ElectricCorporation; all rights reserved.Printed in Japan.

by Eiichi Tamaki and Yoshibumi Yamagata

Development of a 1,000kV SF 6 Gas Circuit Breaker .............................. 10by Takashi Yonezawa, Tsutomu Sugiyama and Mikio Hidaka

1,000kV Gas-Insulated Switchgear ......................................................... 14by Takayuki Kobayashi, Hiroshi Yamamoto and Kenji Sasamori

A Protection and Control System for 1,000kV PowerTransmission ............................................................................................ 19by Takayuki Matsuda, Shin’ichi Azuma and Masaji Usui

Simulation Technology for 1,000kV Power Systems ............................. 23by Koichirou Ikebe, Tetsuro Shimomura and Dr. Isao Iyoda

NEW PRODUCTSA Monitoring System for 1,000kV Gas-InsulatedSwitchgear ................................................................................................ 27

A Monitoring System for 1,000kV Transformers ................................... 28

MITSUBISHI ELECTRIC OVERSEAS NETWORK

Akira Yamamoto

Jozo NagataToshimasa UjiTsuyoshi UesugiSatoru IsodaMasao HatayaGunshiro SuzukiHiroshi ShimomuraHiroaki KawachiAkihiko NaitoNobuo YamamotoShingo MaedaToshikazu SaitaHiroshi TottoriMasaaki Udagawa

Hiroshi Suzuki

Masaaki UdagawaPlanning and Administration Dept.Corporate Engineering, Manufacturing &Information SystemsMitsubishi Electric Corporation2-3-3 MarunouchiChiyoda-ku, Tokyo 100, JapanFax 03-3218-2465

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Vol. 77 Feature Articles Editor

Editorial Inquiries

Product Inquiries

1,000kV Power Systems Edition

Our cover shows 1,000kV substationequipment undergoing evaluation at TokyoElectric Power Company’s UHV test field.Mitsubishi Electric is responsible for thecentral phase (except for bushings).

Vol. 77/Dec. 1996 Mitsubishi Electric ADVANCE

A Quarterly Survey of New Products, Systems, and Technology

TECHNICAL REPORTS

Surge Arrestor Technology for1,000kV Lines

*Yoshibumi Yamagata is with Tokyo Electric Power Company and Mikio Mochizuki and Shinji Ishibe are with theItami Works.

High-performance 1,000kV arrestors are indis-pensable components in the coordination ofinsulation for 1,000kV power transmission sys-tems. During the development evolution toward1,000kV arrestors over the past 20 years, dras-tic improvements have been made in surge ar-restor technology. This article describesMitsubishi Electric's development of a high-performance zinc-oxide element and the1,000kV arrestor in which the element is in-corporated.

BackgroundWith increasing urban power demand and thetrend to locate new power plants in remote ar-eas, Japan’s power network is growing largerand higher transmission voltages are being used.Introduction of 1,000kV power transmissiontechnology is a key to providing a stable long-term power supply to meet this demand. Thetesting of substation equipment for 1,000kVpower systems began during 1995 at the Shin-Haruna Substation UHV test yard of Tokyo Elec-tric Power Company.

Full-scale development of this substationequipment began in 1990, but R&D on zinc-oxide (ZnO)elements suitable for 1,000kV surgearrestors has been underway since the late1970s. Economic considerations require that theinsulation margins of 1,000kV equipment bereduced dramatically as compared to 500kVequipment, and this must be accomplishedwithout sacrificing reliability. Fig. 1 shows thearrestor protective level required to support the1,000kV insulation design.

Development of Zinc-Oxide ElementsThe elements that comprise a surge arrestorconsist of high-purity ZnO mixed with traceamounts of other metallic oxides which areformed and baked at temperatures upwards of1,000°C. Fig. 2 shows the production process.These elements have useful nonlinear voltage-current characteristics, and can be stacked toprovided the desired operating characteristics.

As far back as 1978, the Central Research In-stitute of the Electric Power Industry,Meidensha Corporation and Mitsubishi Elec-

tric tested the switching surge absorption per-formance of a 1/59 scale model of a 1,000kVsurge arrestor. The arrestor was designed usingstate-of-the-art technology at the time, but theprotection level (i.e., residual voltage at a cur-rent of 10kV) was still 20~30% higher than ac-tually required. The UHV transmission workinggroup decided that test voltages for 1,000kVequipment should be lower than would be sug-gested by simply scaling up 500kV equipment.Targets for three levels of protection, A, B andC, were established. Level C, shown in Fig. 1,is the most demanding level and the level towhich the 1,000kV arrestors reported here weredesigned. Level A is 20% higher and level B10% higher.

In simplest terms, the protection level can belowered by reducing the number of ZnO ele-ments per stack, but this shortens the elementlife due to the increased electrical stress. With

by Yoshibumi Yamagata, Mikio Mochizuki and Shinji Ishibe*

Fig. 1 Surge arrestor voltage-currentcharacteristics.

Fig. 2 The ZnO element production process.

~~ ~ ~

500kV arrestor 1pu=550kV x 2 3=449kV1,000kV arrestor 1 pu=1100kv x 2 3=898kV

500kV arrestor(original specification)

2.72 pu(1,220kV)

1.94 pu(870kV)

1.73 pu(1,550kV)

500kV high-performance arrestor

1,000kV arrestor (four parallel element stacks)

Vol

tage

(pu

)

3.0

2.5

2.0

1.5

10 10 100 1k 10k 20k

Additives Grinding Mixing Granulat-ing

Forming

SinteringGrindingAttachingelectrodesTesting

Zinc oxide

December 1996 · 1

TECHNICAL REPORTS

the manufacturing technologies available in1978, an element life of 1 ~ 2 years was consid-ered acceptable. Lower protection levels alsorequire arrestors to absorb the energy of switch-ing surges associated with circuit breakeractivity and power-frequency temporary over-voltage (TOV) associated with ground faults andload disconnection. These surges cause largearrestor currents and energy at lower protec-tion levels.

By 1982, we had improved the ZnO elementcharacteristics enough to satisfy C-level pro-tection requirements. These improvementstook place in three areas.

First, the element life was extended to a long,stable operating life under voltage stress 10 ~15% higher than previously possible. This wasachieved by incorporating glass-phase compo-nents that stabilize the particle boundary lay-ers.

Second, the energy capability per element wasextended 40 ~ 50% through changes in the par-ticle-forming process that resulted in moreuniform element structure and current flow.

Third, 10% flatter voltage-current character-istics were obtained by lowering the limitingvoltage that appears across the element con-tacts at currents in the range of 5 ~ 20kA. Triva-lent metal oxides such as Al2O3 were added toimprove electron mobility under high-currentconditions, the ZnO particle size was reducedand sintering processes were optimized to in-crease the potential barrier at the grain bound-aries.

The arrestor elements we developed for1,000kV use immediately found applications inlower-voltage power systems. Beginning in1984, Mitsubishi Electric worked with TokyoElectric Power Company to improve the pro-tection level of 500kV arrestors. We developeda high-performance arrestor with a 30% lowerprotection level (Fig. 1) and the same elementvoltage stress and energy duty as the planned1,000kV arrestors. This allowed test voltagesto be lowered without sacrificing reliability,which led to equipment size and cost reduc-tions and paved the way for the development of1,000kV arrestors. Table 1 lists the specifica-

Fig. 3 Construction of a 500kV high-performancearrestor.

Table 1 Specifications of Original and High-Performance 500kV Arrestors

Category Original High-performance 1,000kV specifications

Type SF6 gas-insulated tank enclosure SF6 gas-insulated tank enclosure SF6 gas-insulated tank enclosure

Model MAH-TA MAU-TA MAU-TA

Rated voltage 420kV 420kV 826kV

Continuous operating voltage 550/ 3kV rms 550/ 3kV rms 1,100/ 3kV rms

Nominal discharge current 10kA 10kA 20kA

Lightning impulse withstand voltage 1,550kV 1,425kV 2,250kV

V10kA 1,110kV or less 870kV or less 1,550kV or less

V20kA — — 1,620kV or less

JEC-217 surge (78µF JEC-217 surge (78µF Switching surge on 221µFSwitching surge capacitance, corresponding to capacitance, corresponding to capacitance (corresponding to

a 200km transmission line) a 200km transmission line) a 250km transmission line)

Temporary overvoltage >7MJ (1.5 pu for 2s) >7MJ (1.5 pu for 0.2s) >55MJ (1.5 pu x 0.55s)

Dimensions (mm) 1,100 dia. x 3,300 1,018 dia. x 2,580 1,774 x 4,800

Weight (tons) 4.0 3.5 13

Relative volume 1.0 0.67 2.35

Ene

rgy

duty

Gen

eral

Pro

tect

ion

perf

orm

ance

Oth

er

Instrumentbox

Grounding wire

Shields

Tank

Zinc-oxideelement

Conductor

Grading shield

Insulating supportcylinder

2 · Mitsubishi Electric ADVANCE

Table 1 Specifications of Original and High-Performance 500kV Arrestors

TECHNICAL REPORTS

a) Element arrangement in one 42kV section

tions of the high-performance 500kV arrestorsand Fig. 3 shows their construction.

1,000kV Arrestor DevelopmentThe 1,000kV arrestor needed to be double thecapability of the 500kV arrestor with a 12%reduction in protection level. We achieved thisusing elements equivalent to two 500kV arres-tors arranged in four parallel stacks. Table 1 liststhe specifications, Fig. 4 shows the construc-tion and Fig. 5 shows a photograph. The ele-ments are organized as two 500kV units, eachconsisting of ten 42kV sections stacked in se-ries. Each section consists of four parallel 15-element stacks.

An analysis of the 1,000kV power system ledto a TOV energy duty specification of 55MJ.Fig. 6 shows the relationship between trans-mission voltage and surge arrestor energy duty.The switching surge energy duty requirementis equal to or less than that on the high-perfor-mance 500kV arrestors, however, the TOV en-ergy duty is more than double that of the 500kVarrestors. Since this severe duty is nearly at thelimit of the element energy capability, a majorpoint for developing 1,000kV arrestors was toachieve an adequate margin for TOV duty. Twoinnovations not found in 500kV-and-lower volt-age arrestors made this possible.

First, the element arrangement was optimizedto ensure a more uniform distribution of TOVduty. Because of the nonlinear voltage-currentcharacteristics of the arrestor elements, anydifferences in the limiting voltage between the

b) Internal section

Element stacks 1 ~ 4Current

Zinc-oxide elementShield Conductor

Insulator

High-voltage side

Low-voltage side

Element unit Grading shield4,800mm

φ1,7

74m

m

Lowerarrestor unit

Upperarrestor unit

InsulatorInsulator

Element screeningspecificationTOV energy capability

Switching surge energy capability

TOV duty

Switching surgeduty (one surge)

Four parallelstacks

Transmission voltage (kV)

Ene

rgy

per

unit

of e

lem

ent v

olum

e (J

cm3 )

500

400

300

200

100

00 275 500 1,000

Fig. 5 1,000kV arrestor.

Fig. 6 Surge arrestor energy capability as afunction of transmission voltage.

Fig. 4 Construction of the 1,000kV arrestor.

four parallel stacks would lead to a concentra-tion of current in the stack with the lowest lim-iting voltage and therefore nonuniform energyduty. We eliminated these differences by mea-suring the limiting voltage of each element andselecting elements to create four stacks of nearlyidentical limiting voltage. The voltage measure-ment used is the drop across the element whilesustaining a current of 100A, which correspondsto 400A through the complete arrestor.

To verify that this method would yield a uni-form current distribution, we tested a 42kVsection like the one shown in Fig. 4 and mea-sured the current through each stack. Table 2shows the results. A maximum current varia-tion of 0.5% was measured in stacks adjustedfor identical limiting voltages (case 1). A maxi-mum current variation of 4.3% was measuredin stacks with 0.08% variation in limiting volt-age (case 2). The measured values were close tothe numerical predictions of 0% for case 1 and2.7% for case 2. These results led us to specify0.15% variation for the 100A limiting voltage,

December 1996 · 3

TECHNICAL REPORTS

Fig. 7 Current uniformity testing of ZnO elements.

Table 2 Current Uniformity Test Results

Current waveform Peak current (A)Peak current per stack (A)

Variation (%)No. 1 No. 2 No. 3 No. 4

Case 1(0% predicted 498 125 124 125 124 0.4

variation)8/20µs 900 226 224 226 224 0.4

1,648 412 414 412 410 0.5

Case 2 (2.7% predicted 361 89 88 94 90 4.2variation) 8/20µs 1,002 248 248 258 248 3.0

4,992 1,232 1,240 1,272 1,248 1.99,860 2,440 2,440 2,500 2,480 1.4

30/80µs 119 29 29 31 30 4.2487 120 120 126 121 3.5978 240 242 254 242 3.9

3,028 744 752 780 752 3.0

AC 189 46 47 49 47 3.7441 108 109 115 109 4.3728 179 181 189 179 3.8867 213 216 225 213 3.8

Typical oscilloscope traces for 8/20µs currentwaveform testing with 1,002A peak current

Current

Powersupply

Element stack

Currenttransformer

Test circuit

No. 1 No. 2 No. 3 No. 4

Constant current supply Needle electrodes

Element

Voltmeter

Resistors


Table 2 Current Uniformity Test Results

Key

P = 1.3 ~ 1.7

P = 1.7 ~ 2.1

P = less than 1.3

b) Test circuit

a) Test equipment

c) Typical current ratio map

which computes to 5% variation in current, andto specify the TOV capacity of the completedarrestor assuming 10% current variation.

100A/div

No. 1

No. 2No. 3

No. 4

248A

258A

248A

248A

5µs/div

TECHNICAL REPORTS

Next, elements were screened based on uni-formity testing. The chief cause of elementdestruction during TOV duty is the thermalstress associated with power dissipation. Non-uniform current flow within an element willcause heat concentrations that can lead to ele-ment destruction at lower-than-expected energyduty. We therefore tested each element and dis-carded those exhibiting poor current uniformity.The elements were screened just prior to elec-trode mounting. A 20mA current was appliedto each element through 100 needle-like elec-trodes and the current through each was mea-sured to give a picture of the current flowuniformity. Fig. 7 shows the testing unit, testcircuit and typical current distribution.

We also investigated the relationship betweencurrent flow uniformity and energy capability.We conducted destructive TOV testing, apply-ing TOVs until the test element was destroyed,and calculated the energy dissipation. Fig. 8shows typical test data. Note that the selectionof elements was deliberately chosen to providea wide range of Pmax values. The largest Pmaxvalues occur in specially selected elements.

To screen the elements, we arrived at a uni-formity index for each device by dividing thecurrent at each measurement point by the av-erage current and taking the maximum value.

Fig. 9 shows a Weibull plot of TOV energy-capability results obtained from testing thescreened elements. The plot shows that thescreened elements have a 15% margin over the300J/cm3 capability required for an arrestor with55MJ energy duty using four parallel stacks with10% current variation.

The completed 1,000kV arrestors have beenqualified following earthquake-resistance test-ing, transport testing, voltage stress testing, heatcycle testing and other test items.

Fig. 9 Weibull plot of element energy capacities.

Mitsubishi Electric has been developing high-performance ZnO element technologies for1,000kV surge arrestors since the late 1970s.Now that first-generation 1,000kV arrestors arequalified for service, R&D is continuing withthe aim of developing smaller arrestors withbetter performance for more economical andreliable power transmission services.

Required Capacity

Specially selectedelements

~~

Maximum current ratio (Pmax)

Ene

rgy

capa

city

(Jc

m3 )

Typical selectionstandard

2.8

1 2 3 4 5 60

200

400

600

800

1,000

Note: A capacity of 300J/cm3 correspondsto 55MJ arrestor capacity dividedinto four parallel stacks with acurrent variation between stacksof 10%.

99.9

95

90

70

50

20

10

5

2

1

0.5

0.2

0.1100 200 300 500 700 1,000

TOV energy capability (J/cm3)

Position parameter γ = 350J/cm3)

No. of elelments: 73

Des

truc

tion

prob

abili

ty F

(%

)

December 1996 · 5

TECHNICAL REPORTS

A 1,000kV Transformer

by Eiichi Tamaki and Yoshibumi Yamagata*

*Eiichi Tamaki is with the Ako Works and Yoshibumi Yamagata is with Tokyo Electric Power Company.

To provide a stable power supply to meet theincreasing electrical demand through the 21stcentury, Tokyo Electric Power Company(TEPCO) is developing Japan’s first 1,000kVtransmission systems, and is currently testingthe performance, reliability, operation andmaintenance of 1,000kV equipment in a1,000kV test field at its Shin-Haruna Substation.Mitsubishi Electric has been developing a vari-ety of 1,000kV substation equipment, and theAko Works produced a single-phase 1,000kVshell-form transformer for qualification testing.This article reports on the specifications, con-struction, installation and testing of the1,000kV transformer.

SpecificationsTable 1 lists the basic transformer specifica-tions. The 1,000kV transformer is a single-phase, autotransformer with an on-load voltageregulator (LVR) at the central point. Extensivestudies led to selection of the following specifi-cations.

The primary and secondary bank capacitiesof 3,000MVA were selected to satisfy maximumtransmission capacity. The tertiary capacity of1,200MVA (40% of the primary and secondarycapacities) was selected as the maximum ca-pacity to supply the apparent power required by

the 1,000kV transmission lines.As a tertiary voltage rating of 63kV—the same

as 500kV transformers—would result in an ex-cessively large current in a fault condition, a147kV rating was selected so that the size ofthe equipment connected to the tertiary wind-ing would not have to be increased.

An impedance value of 18% was chosen inconsideration of maximum grid stability, sup-pression of ground fault currents and economyof transformer design.

Since 1,000kV substations will be constructedin mountainous areas, all transformer compo-nents will have to be transportable by rail andoversized tractor-trailer. The main body of the1,000kV transformer was divided into two unitsto satisfy the transport limitations.

Two LVRs are provided, one for each unit.A long-term AC withstand test voltage was

selected from a transient overvoltage analysisof the fault conditions of future 1,000kV trans-mission systems:

1.5E (1h)~ 3E (5 min)~1.5E(1h)where E = 1,100/ 3kV, without partial dischargeduring testing.

The lightning impulse withstand test volt-age was determined by analyzing the transientvoltage levels in 1,000kV systems with high-performance lightning arrestors; 1,950kV pri-mary and 1,300kV secondary withstand voltageswere selected.

A noise level of 65 dB was specified to mini-mize the environmental noise of the substa-tion. This was achieved by surrounding thetransformer with an auxiliary sound barrier ofsteel plate.

ConstructionThe 1,000kV transformer has twice the voltageand twice the capacity of 500kV transformers,which are the largest currently in use in Japan.Space constraints in shipping and installationrequire that the shipping dimensions be nolarger than that of a 500kV transformer. Wetherefore chose to divide a one-phase trans-former into two units, each unit having thesame capacity of a 500kV 1,500/3MVA trans-

Table 1 Basic Specifications

Type Shell-form single-phase autotransformerwith on-load voltage regulator

Rated capacity 3,000/3 MVA

Tertiary capacity 1,200/3 MVA

Rated primary voltage 1,050/ 3 kVRated secondary voltage 525/ 3 kVRated tertiary voltage 147kV

Tapping range 27 taps for voltages in the range of986.6/ 3 ~ 1,133.6/ 3 kV

Test voltages Lightning impulse withstand voltagePrimary: 1,950kV Secondary: 1,300kVAC 1.5E (1hr)~ 3E (5 min)~1.5E (1hr),E = 1,100/ 3kV

Impedance 18%

Cooling method Forced-oil, forced-air

Noise level 65dB


TECHNICAL REPORTS

former. The two units are designed to be con-nected in parallel by a T-type connection ductwith an oil-gas bushing.

The 1,000kV transformer must withstandtwice the voltage of a 500kV transformer andtolerate the minimal insulation distances ab-solutely necessary to meet transport limita-tions. This was achieved by designing the coilarrangement and insulation construction to re-duce the electrical field concentrations, and byarranging numerous barriers to suitably dividethe oil space. Cleaner manufacturing processeswere also used, thus reducing the particle con-tent in the transformer oil contributing to widerinsulation margins.

Since the insulation of the 1,000kV leadswould be unacceptably large if only insulatingpaper were used, a multilayer barrier is alsoapplied to reduce the insulation clearance from

Rail transport limitations

Shipping cover

Winding

Core

3,100mm3,

100m

m

Fig. 1 Rail transport constraints.

the lead to the tank.Fig. 1 shows the rail transport limitations,

Fig. 2 the two-unit construction, and Fig. 3 thewiring connection diagram.

Manufacture and TestingFull-size models of the winding insulation, leadinsulation and a prototype transformer weretested to establish 1,000kV equipment technolo-gies. A 1,000kV, 3,000/3MVA transformer forTEPCO was manufactured following the

1,000kV technologies. All manufacturing pro-cesses from component production upward werereviewed from the standpoint of cleanliness, andcleaner technologies were introduced.

The completed transformer passed routinetests, an extreme temperature-rise test, an in-sulation withstand test, a static-electricificationtest and trial docking of the two-unit assembly.

Shipping and AssemblyThe cooling unit, conservator and other exter-

Fig. 2 Transformer construction.

1,000kV oil-gas bushing

Main unit

Cooling unit

ConservatorSound barrier

On-load voltage regulator

500kV GIB

147kV duct

1,000kV line lead

CoreWinding

December 1996 · 7

TECHNICAL REPORTS

nal components were removed, and the trans-former units were filled with a low dew-pointgas for the approximately 1,000km trip by ship,rail and trailer to the installation site. The ship-ping weight was about 200 tons, and shippingdimensions were about 3m in width, 4m inheight and 8m in length.

Fig. 4 shows the unit docking procedure. Theunits were moved over slide rails onto a com-mon base frame (Fig. 4a and 4b), and then posi-tioned on the base by locators attached at thefactory. The shipping cover for unit 1 was thenremoved, and the upper tank of unit 1 attached(Fig. 4c). The ducts were then attached usingthe locating pins mounted at the factory (Fig.4d). The upper tank of unit 2 was then mounted,and unit 2 connected to the ducts using thelocating pins (Fig. 4e).

The primary and secondary leads were joinedto the T-duct leads, and the multilayer barrierinsulation applied for the lead connectionpoints.The same clean procedures and thorough qualitycontrol management as that used in factoryassembly were maintained during theattachment of external components and filling

MTR1 MTR2

U

u

1a 1b 1x 2x 2b 2a

b aK K131197531

131197531

LVR1 LVR2VKey

MTR Main transformerLVR On-load voltage regulator

Fig. 3 1,000kV transformer wiring connectiondiagram.

Fig. 4 Unit docking procedure.

b) Positioning the units d) Attaching the connection ducts

a) Installing themounting base e) Installing the upper tank of unit 2

Mounting base

Railsc) Attaching the upper tank of unit 1

Shipping covers

Unit 2

Unit 1

Gauge stoppers

Upper tank of unit Unit 1

Unit 2

Locating pins

500kV T-typeconnection duct

Locating pins

Unit 2

Unit 1

Unit 2

Unit 1 1,000kV T-typeconnection duct

Locating pin


2

3

2

5

TECHNICAL REPORTS

Fig. 5 The 1,000kV transformer installed on site.

ers is a tangible reality. Through the above-mentioned tests, the long-term reliability of thetransformers will be established over two years.The 1,000kV transformer development, manu-facture, transport and assembly technologiescan also be applied to improve the quality of500kV-and-lower voltage transformers.

of the transformer oil.The assembled transformers were checked for

transformer ratio, polarity, winding resistance,impedance and insulation resistance. No prob-lems developed throughout design, manufac-ture, shipping and assembly. Fig. 5 shows aphoto of the completely assembled transformer.

Qualification TestingThe primary, secondary and tertiary terminalsof the 1,000kV transformer were connected tothe gas-insulated bus, and then each 1,000kVtransformer was connected, in a three-phaseconfiguration.

The secondary terminal was connected to anactual grid, and the primary opened. The tem-perature-rise test was conducted under the con-dition of partial shutdown of cooling equipmentby using the tap difference between the twoLVRs for units 1 and 2.

An inrush test was conducted by switching acircuit breaker connected to a 500kV line.

In the static-electrification test, the leakagecurrent was measured at the neutral terminalwith all cooling equipment running. The leak-age current was sufficiently small.

Now that a 1,000kV transformer for long-termenergized field testing has been manufacturedand tested, commercial use of these transform-

December 1996 · 9

TECHNICAL REPORTS

Development of a 1,000kV SF6 GasCircuit Breaker

by Takashi Yonezawa, Tsutomu Sugiyama and Mikio Hidaka*

*Takashi Yonezawa, Tsutomu Sugiyama and Mikio Hidaka are with the Itami Works.

1,000kV power transmission lines requireovervoltage protection so that insulation re-quirements can be held to reasonable levels.Mitsubishi Electric has developed 1,000kV gascircuit breakers (GCBs) to keep switching surgelevels low enough so that ground fault surgesdo not rise above the maximum suppressiblelevel of 1.6~1.7 per unit (pu). The new GCBscontrol closing surges using a resistance cre-ation method similar to that developed for thecorporation’s 550kV GCBs and prevent open-ing surges with a newly developed resistanceinterruption method. New technologies for theresistance-interruption GCB include resistanceinterrupters, a resistor array 15 times larger thanthat in 550kV GCBs, and a delayed operationfunction to open the resistance interrupters ata specified interval after the main interruptersopen.

Development The development team faced two major issues.The first issue was to maintain reliability inthe largest and heaviest interruption equipmentever developed, including a breaker unit withthe world’s largest capacity to date, and a hy-draulic operating mechanism specially devel-oped for operating the main interrupters.

The second was to develop new technologiesfor resistance creation and resistance interrup-tion. Fig. 1 shows the operating sequence andTable 1 lists the ratings for the 1,000kV GCB.Two operating mechanisms for the main andresistance interrupters are used, and a new de-layed operation function was developed so thatthe resistance interrupters open after the maininterrupters.

Another development issue was to design thebreaker, resistor array and other elements asindependent units that could be easily as-sembled, and to raise assembly reliability byeliminating the need for adjustments after theunits are united inside the enclosure.

FeaturesFig. 2 shows the internal construction. Theenclosure diameter was reduced by placing themain and resistance interrupters (two sets each)

Resistor contactposition

Closed position

Open position

Opentime

ContactcommandsOpencommandClosecommand

(30~35ms)

Closing time(30~35ms)

Resistorinsert time

(10ms)

Delay in resistance contact separation

Rated voltage 1,100kV

Rated current 8kA

Rated interrupt current 50kA

Rated interrupt time 2 cycles

Rated fluidoperating pressure

31.5MPa (hydraulic)

Rated SF6 gas pressure 0.6MPa

Resistance 700 ohms (operating and closing)

No. of breaks 2

Fig. 1 Operation sequence.

Insulatingspacer

Resistanceinterrupters

Maininterrupters

Nozzle

Puffer cylinderCapacitor between contacts

EnclosureResistor unit

Oil pump

Operating mechanism forresistance interrupter

Operating mechanism for maininterrupter and delay control circuit

Insulating operation rodMain circuitconductor

Accumulator

Fig. 2 Construction.

Table 1 Ratings

in parallel at the enclosure center with resis-tors at either end. We minimized the transferof mechanical stress from the resistors to theinterrupter by mounting the resistor units onspecially-developed large-diameter insulators

Table 1 Ratings


TECHNICAL REPORTS

attached to the ends of the enclosure. The tulipcontacts of the main and resistance interrupt-ers are used to make adjustment-free connec-tions between the resistor units and theinterrupt unit, which eliminates all adjust-ments inside the enclosure. Fig. 3 shows aresistor unit and the interrupt unit.

The main contacts open at a speed just 30%faster than the two sets of main contacts usedin the 550kV GCB. The speed was kept downby using a long Laval nozzle designed to main-tain the hot-gas flow in a cohesive stream athigh flow rates, and by optimizing the puffercylinder diameter for maximum flow rate. Themain interrupters had already been qualified ina 550kV, 63kA, one-break GCB.

The resistance interrupters require excellentdielectric recovery characteristics. With a maxi-mum interrupting current of 2kA under out-of-phase breaking, the duty of the resistor contactsis considerably less than the main interrupters,however, the transient recovery voltage reachesa rate-of-rise of 3kV/µs during terminal faultbreaking, and the peak voltage reaches 2,515kVduring small capacitive current breaking—de-mands similar to those on the main interrupt-ers.

For these reasons, we selected the same highbreaking speed used for the main interrupters,and developed and qualified a new interrupttechnology employing the small-diameter pufferof a 72kV GCB with a rotary arc drive effectachieved by permanent magnets.

The resistors typically dissipate 145MJ ofenergy from O to BO (i.e., terminal fault break-

ing to out-of-phase creation and breaking). Thisis 15 times the power dissipated during resis-tance creation of a 550kV GCB, and the largesize of these resistors is a major factor in thesize increase required for the 1,000kV GCB.

Fig. 4 shows the resistor configuration. Theresistors are placed around the conductor con-nected to the main interrupters; with three re-sistors connected in series to form one block,and eight blocks connected in parallel. This con-figuration ensures adequate insulation betweenthe resistor elements and between the resistorblocks while occupying minimum space.

The hydraulic operating mechanism for themain interrupters uses a new design to providethe necessary output, which is double the out-put required of the 550kV GCB operatingmechanism. The operating mechanism for theresistance interrupters is the same one provenfor 300kV GCBs. A hydraulic pressure stabili-zation mechanism prevents variations exceptmomentarily during contact closing and open-ing.

b) Interrupt unita) Resistor unit

Fig. 4 Resistor configuration.

Fig. 3 Components.

~~ ~~Block 1 Resistor

CCC

CBB

B B

AAA

A

AAAA

B B

BB

CCC C

Main circuitconductor

AB

CBlock 1

Block 8

Block 2

Resistanceinterrupter

Maininterrupter

a) Physi cal layout b) C ircui t (for one break)

December 1996 · 11

TECHNICAL REPORTS

The two operating mechanisms operate witha delay when the contacts open and simulta-neously when the contacts close. This func-tion is implemented using hydraulic circuitsfor reliability. When the piston of the operatingmechanism for the main interrupters reaches abreaking point, the dashpot pressure is detected,activating a delay control valve that triggers theoperating mechanism for the resistance inter-rupters. Fig. 5 shows the relevant parts of thehydraulic circuit.

Verification TestThe basic performance parameters of the1,000kV GCB have been qualified and the equip-ment approved for practical application.

PERFORMANCE AT EXTREME TEMPERATURES. Toconfirm that proper opening and closing perfor-mance is maintained at extreme temperatures,the GCB was placed in a large environment-controlled testing room and operated at tem-peratures from −30°C to +60°C. Fig. 6 showsthat the change in opening times was negligible.The delay time of the contact separation in the

opening operation of the resistance interrupterremained within the stable range of 32~33ms,confirming that the hydraulic delay circuitry issufficiently immune to temperature-inducedvariations in the viscosity of the hydraulic fluid.

INTERRUPT PERFORMANCE. Limits of the test ap-paratus prohibited testing of the entire inter-

Fig. 6 Opening characteristics vs. ambienttemperature.

~~ ~ ~

Delay in resistance contact separation

Opening time

Temperature (°C)

Tim

e (m

s)

40

35

30

25

20

15

10

–40 –20 0 20 40 60

OPERATING MECHANISM FOR RESISTANCE INTERRUPTER

Resistance interrupter

Link pin

Link

Oil pressure piston

Secondary pistonOil release valve

Delay control valve

Oil releasevalve

Pilot chamberfor oil releasevalve

Oil feedamplifier valve

Oil feedvalve

Accumulator

Orifice 2 Stage 2 oil releaseamplifier valve

Oil feed valveOPERATING MECHANISM FOR MAIN INTERRUPTER

Main interrupter

Link pin

LinkSecondarypiston

High pressure Low pressureStage 2 oil feedamplifier valve

Pilot chamber foroil release

Oil pressure piston

Oil releaseamplifier valve

Oil pressurecontrol route

Pilot chamber for Stage 2 oil release amplifier valve

TripcoilSolenoid valve

Ofifice 1

Stage 1 oil release amplifier valve

Stage 1 oil feed amplifier valve

Pilot chamber for Stage 1 oilrelease amplifier valve

Fig. 5 Hydraulic operating mechanism and the hydraulic control circuit.


TECHNICAL REPORTS

Fig. 8 Full-pole interruption test.

Fig. 7 Waveforms during terminal fault test formain interrupter.

Voltage

Current

Voltage supply current

Current supply voltage

Generator voltage

Close control currentOpen controlcurrent

Transient recovery voltage over 100µsu1 = 560.9kV t2 = 638.2µst1 = 253.2µs uc = 815.9kVu1/t1 = 2.2kV/µs

50ms

52.6kA x 2√2 (4% DC) 92.2kA 50.7kA x 2√2(14% DC)

14.5kA

ruption process at once; however, selected in-tervals and parameters of the interruption pro-cess were tested in a multipart testing regimethat covers the entire process and gives a clearpicture of GCB structural and functional be-haviors.

The main interrupters were tested up to thepeak transient recovery voltage (TRV) with theresistors mounted normally (terminal fault du-ties 4 and 5), then with the resistors discon-nected to allow a higher recovery voltage to beapplied to the main interrupter. Fig. 7 showswaveforms for a typical qualification test dur-ing the terminal fault duty 4 test series withthe resistors connected at up to the peak TRV.

The resistance interrupters were qualified forthermal and dielectric characteristics.

To check the insulation performance betweenthe exterior environment and the enclosure,full-pole interruption tests were carried out atterminal fault duties of 4 and 5 for the maininterrupters, thus causing maximum TRV (Fig.8).

The 1,000kV GCB was installed at the Shin-Haruna UHV Equipment Test Station of TokyoElectric Power Company in 1994. Long-termvoltage and current tests began in 1995 and arestill underway.

December 1996 · 13

TECHNICAL REPORTS

1,000kV Gas-Insulated Switchgear

by Takayuki Kobayashi, Hiroshi Yamamoto and Kenji Sasamori*

*Takayuki Kobayashi is with Tokyo Electric Power Company, and Hiroshi Yamamoto and Kenji Sasamori are withthe Itami Works.

Voltage 500kV 1,000kV

Ratings Rated Min. Rated Min.

Circuit breaker, high-0.5 0.4 0.6 0.5

speed ground switch

Other equipment 0.4 0.3 0.4 0.35

Table 1 Gas Pressure (MPa)Mitsubishi Electric has successfully suppressedswitching surges and lowered the required light-ning impulse withstand voltage in 1,000kV gas-insulated switchgear (GIS), allowing thereduction of equipment dimensions. A high-speed ground switch supports high-speedreclosing operations, and other steps have beentaken to improve grid protection and increasereliability. The equipment is undergoing quali-fication testing at the Shin-Haruna Substationof Tokyo Electric Power Company.

Major FeaturesThe design of this 1,000kV GIS is based on thecorporation’s proven successes with its long-running 500kV equipment.

REDUCED LIGHTNING IMPULSE WITHSTAND VOLT-AGE. A high-performance lighting arrestor re-duces the required lightning impulse withstandvoltage. This eases the insulation requirements,permitting a substantial reduction in equipmentsize.

Interrupt surge voltages, which do not im-pact the insulation design of the 500kV GIS,become significant factors at 1,000kV. We mini-mized these surges by developing resistance-interruption technology.

HIGHT-SPEED GROUND SWITCH. High-speedmultiphase reclosing within a second windowis needed to maintain grid stability when a trans-mission line ground fault occurs. Ground faultsin a 1,000kV system induce secondary arcs inhealthy phases that current reclosure systemscannot extinguish within the required period.A high-speed ground switch was developed tosolve this problem. The switch closes and openswhile the circuit breaker is reclosing so thatthe secondary arc is positively extinguished.

SIZE REDUCTION. Table 1 lists the rated and mini-mum gas pressures for guaranteed operation ofthe various equipment. The circuit breaker andhigh-speed ground switch employ the 0.6MPapressure used in single-point 500kV gas circuitbreakers. The other equipment employs the0.4MPa pressure used in other 500kV switch-

gear. The minimum pressure for guaranteedoperation in this equipment has been raisedfrom 0.3MPa to 0.35MPa to permit higher elec-tric field strengths and a more compact equip-ment design.

IMPROVED RELIABILITY. Free metal particles inthe enclosure pose a much greater problem in1,000kV equipment due to the high operatingstresses involved. We used a dielectric coatingon the inner surface of the enclosure that raisesthe allowable electric field strength on the sur-face and suppresses the movement of metal par-ticles, thus permitting a smaller enclosurediameter.

LINEAR-COUPLED CURRENT TRANSFORMER. Faultcurrents in 1,000kV systems will cause core-type current transformers to saturate becausethe time constant of the DC component of thefault current is larger than that in 500kV equip-ment. The linear-coupled current transformerswe employed for 1,000kV bus protection are im-mune to saturation.

OPTICAL VOLTAGE TRANSDUCER. Optical poten-tial devices are used in place of previous wind-ing-type voltage transducers because they aresmaller, less expensive, have a simpler relayinterface and match well with the fiberopticLAN-based digital control and protection sys-tem.

EquipmentTable 2 lists the switchgear specifications, Fig.1 shows the construction, and Fig. 2 is a photoof the equipment as installed at the Shin-HarunaSubstation.

CIRCUIT BREAKER. The puffer cylinder diameter


Roger Williams

Roger Williams

TECHNICAL REPORTS

connected in parallel to handle the greater en-ergy duty.

Hydraulically driven operating mechanismsoperate the main and resistance interrupters.The delay required in opening the resistanceinterrupters is provided by the hydraulic cir-cuit, which is designed to keep the delay timevariations within a couple of milliseconds.

and stroke have been optimized and the nozzleconfiguration improved, making it possible toachieve sufficient performance from two series-connected 500kV interrupters.

The resistance creation method developed for500kV gas-circuit breakers is now comple-mented by a resistance interruption method.The 700Ω interrupters are the same type usedin the 500kV equipment, with eight elements

Table 2 Specifications of 1,000kV GIS

All equipment

Rated voltage 1,100kV

Rated current 8,000A outside of bank circuit 2,000A in bank circuit

Short-time withstand current 50kA, 2s

Lightning impulse withstand voltage 2,250kV

Power frequency withstand voltage 1.5E x 30m − 3 x 1m − 1.5E x 30m (E=1,100/ 3kV)

Rated gas pressure 0.6MPa in GCB, HSGS, 0.4Mpa in other equipment (at 20°C)

Gas-circuit breakers

Rated breaking current 50kA

Rated operating sequence Standard O − θ − CO − 1m − CO (θ = 1s)

Operating mechanism Hydraulic

No. of breaks 2

Break/make system Resistance interruption, resistance creation (700Ω)

Surge control system Resistance insertion (500Ω)

Interrupters Loop current switching 8,000A

Operating mechanism Motor-charged spring

Earth switchesLine-charging current switching 50kV, 40A electrostatic, 70kV, 1,000A electromagnetic

Operating mechanism Motor-charged spring

Line-charging current breaking 1,200A electrostatic, 7,000A electromagnetic

High-speed ground switches Rated operating sequence C − θ − O (θ = 0.5s)

Operating mechanism Hydraulic

Insulated bus Rated current 8,000A outside of bank circuit 2,000A in bank circuit

Rated voltage 826kV

Surge arresters Protection level 1,620kV, 20kA

Energy absorption capability 55MJ

Current transformersType Core type Linear-coupled type

Accuracy class Class 1.0 1.0%

Voltage transformersType Optical potential device

Accuracy class Class 1.0

BushingsType Gas bushing

Pollution withstand voltage 762kV

Table 2 Specifications of 1,000kV GIS

Fig. 1 The construction of 1,000kV gas-insulated switchgear.

Ground switch Interrupter

Removablejoint

Current transformer(for monitoring)

Circuit breaker

Current transformer(for monitoring)

Interrupter Ground switch

Bus Flexible joint

Removablejoint

Gas bushing

Flexible joint High-speed ground switch

December 1996 · 15

Roger Williams

Roger Williams

TECHNICAL REPORTS

INTERRUPTER. Fig. 3 shows a diagram of the in-terrupter. Like its 500kV predecessor, the fixedinterrupt and moving interrupt mechanisms are

supported by space-efficient insulating spacers.Use of a rotary-drive insulated operating rod per-mits a compact, upright design that can be trans-

Fig. 2 A photograph of 1,000kV GIS installation.

Fig. 3 Interrupter construction.

a) Section at A

b) Cross section

Insulated operating rod

Insulating spacer Electrode for moving contact

Moving contact

Shield

Insulating support

Resistance interrupter

Ground switch

Moving contact

Stationary contactElectrode forstationary contact


Roger Williams

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TECHNICAL REPORTS

ported as a single unit.The surge-suppression interrupter is made of

the same carbon ceramic element used in thecircuit breaker (Fig. 4). The simple cylindricalshape allows manufacture by simpler, morestable processes. The contacts for the inter-rupter are grouped on the side where the inter-rupter is fixed. This space-saving configurationcontributes to a smaller enclosure diameter.

Table 3 lists the duty of the surge-suppres-sion interrupter. While the energy duty is smallat 25kJ, the 1,700kV withstand voltage is high,and this voltage must be withstood repeatedly.Various interrupter models were tested to ar-rive at a design capable of enduring 2,000 surgeswithout destruction or resistance change. The

Table 3 Surge- Suppression Interrupter DutyWithstand voltage 1,700kV

Energy duty Open 10kJ

Close 15kJ

Close, open 25kJ

interrupter elements are approximately 1mlong, and four elements are connected in paral-lel.

The contacts have been designed with an elec-trical field distribution so that a reclosing arcforms between the moving contact and the in-terrupter shield.

HIGH-SPEED GROUND SWITCH. Fig. 5 shows theconstruction of the high-speed ground switch.To save space, the fixed contact has been placedon the main horizontal conductor leading tothe circuit breaker with the moving contactdirectly below. A hydraulic operating mecha-nism placed below the contacts drives the high-speed opening and closing action.

The high-speed ground switch breaks the linecharging current after the circuit breaker opensfor a single-line ground fault. Furthermore, ifanother phase fault should occur while the high-speed ground switch is operating, the switch isdesigned to interrupt the no-zero-passage cur-rents for 80ms.

In puffer-type interrupters, the puffer pressureis usually highest while the contacts are open-ing, and falls quickly after the contacts are fullyopen. However in this application, interrupt-ing the long arc caused by a no-zero-passagecurrent requires a longer puff time, which ne-cessitates an increased puffer dead volume af-ter the contacts open, and that the pufferpressure should drop more gradually.

Fig. 6 shows that the dead volume needs to beincreased nine times to ensure a puff time of at

Fig. 4 Surge-suppression interrupter construction.

Carbon-loaded ceramic resistor

Epoxy coating

36.5mm dia.

50mm dia.

Fig. 5 High-speed ground switch construction.a) Cross section

b) Detail of contactmechanism

Closedposition

Open position

Fig. 6 Effective break time vs. relative deadvolume of puffer cylinder.

Effe

ctiv

e br

eak

time

(ms)

Relative dead volume

80

60

40

20

1 5 10

December 1996 · 17

Roger Williams

Roger Williams

TECHNICAL REPORTS

Jum

ping

dis

tanc

e (m

m)

380

300

200

100

0 1.0 2.0Electric field on the inner enclosure surface (kVrms/mm)

KeyUncoated surfaceWith 30µm dielectric coating

Fig. 7 Jumping distance of particles on theenclosure’s inner surface. The test particlesare 3mm long and 0.2mm in diameter.

least 80ms. We achieved this by doubling thepuffer cylinder diameter.

Large surges can appear in the ground con-ductor if secondary arcs accompany high-speedground switch opening or closing. We mini-mized this likelihood by improving the insula-tion performance of the insulating spacers, andby arranging plural grounding plates to shortthe ground terminal to the enclosure, whichprevents a rise in the ground conductor poten-tial.

We verified the efficacy of this design by test-ing it at 640kV to simulate a transient recoveryvoltage during the interruption of an electro-magnetic induction current. No practical prob-lems arose. Some 40% of the applied voltage(240kV) appeared between the ground conduc-tor and enclosure, and 5% (32kV) between theground terminal and enclosure.

BUS INSULATION. We applied a dielectric coat-ing to the inner surface of the enclosure to sup-press the removal stress caused by the metalparticles on the conductor. This allows the elec-tric field strength on the inner surface of theenclosure to be boosted from the 0.9kV/mmvalue in 500kV equipment up to 1.2kV/mm (Fig.7), with the result that the busbar enclosurediameter could be reduced to 900mm (Fig. 8.)The GIS was designed to tolerate the presenceof metal particles in the enclosure up to 3mmlong and 0.2mm in diameter.

EXTENDED INSULATOR TESTING. High electricfields can potentially damage insulators overtime, so we conducted long-term testing at com-mercial power supply frequencies on sample in-sulators. We found that degradation wasnegligible at field strengths of 12kV/mm or less,

Inner enclosure suface(uncoated)

Inner enclosuresurface(30µm dielectric)coating

Triple juncion on HV sideInsulator surface

Conductor diameter (mm)

Enc

losu

re d

iam

eter

(m

m)

1,000

900

800

150

~~

200 250 300 350

Fig. 8 Parameters influencing gas-insulated busdesign.

indicating a substantial margin for tighter de-sign standards. We therefore chose to boost theallowable stress on insulating spacers by 20%.

A conservative approach based on technologiesproven at 500kV has enabled Mitsubishi Elec-tric to develop 1,000kV gas-insulated switchgearwith assured performance for the next genera-tion of high-capacity low-loss power-transmis-sion systems.


Roger Williams

Roger Williams

TECHNICAL REPORTS

A Protection and Control System for1,000kV Power Transmission

*Takayuki Matsuda is with Tokyo Electric Power Company, Shin’ichi Azuma with the Power & Industrial SystemsCenter and Masaji Usui with the Power System & Transmission Engineering Center.

Mitsubishi Electric participated in the jointdevelopment of a 1,000kV protection and con-trol system, which is undergoing qualificationtesting at the Shin-Haruna Substation of To-kyo Electric Power Company. The transmissionline protection system features an improvedcharging current compensation system andnewly developed multiphase reclosing withhigh-speed grounding and arc suppression tech-nology. The busbar protection system featuresthe application of a linear-coupled current trans-former, and transformer protection includes anewly developed current comparison relay.

ConfigurationA number of protection and control issues mustbe solved before future 1,000kV power trans-mission systems can enter routine service. Dueto the increased charging current and larger di-ameter of the transmission-line conductor,faults result in the generation of transients withlow-order harmonic numbers, AC overvoltage

by Takayuki Matsuda, Shin’ichi Azuma and Masaji Usui*

conditions and longer DC transients. TokyoElectric Power Company, Mitsubishi Electricand two other electrical equipment manufac-turers have jointly developed a protection andcontrol system for 1,000kV lines that addressesthese issues.

Fig. 1 shows a photo of the system, which ishoused in two 2,990mm-wide cubicles. Fig. 2shows a diagram of the system configuration.

Fig. 1 Outdoor cubicles housing a 1,000kVsubstation protection and control system.

Fig. 2 System configuration.

CB

TP-M

TP-T

TP-H

BPT-M DAC

Trans-formercubicle

LC

SC

Protection LAN

BP-H BPT-H

BP-T

BP-M

CB

Automaticoscilloscope

OSU interface

OSU

ControlLAN

SC

HSGS

LCLC

Buscubicle

DAC LPα-T

LPα-M

LPα-H

LPβ-TOVP-T

LPβ-MOVP-M

LPβ-HOVP-H

DACBPT-T

Transmissionline cubicle

DAC Data acquisition and controlunitSC Optical star couplerOSU Operating support unitCB Circuit breakerLC Linear couplerHSGS High-speed ground switch

BPT Busbar protection scheme bay unitLP Line protection schemeTP Transformer protection schemeOVP AC overvoltage protection scheme

Key-M Mitsubishi-H Hitachi-T ToshibaBP Busbar protection scheme master unit

December 1996 · 19

TECHNICAL REPORTS

ity for fault detection.Due to the system’s increased charge capacity,

large induced voltages from unfaulted phases candelay suppression of secondary arcs in the deadtime during high-speed automatic reclosing, andprevent reclosing within the required one-secondinterval. We solved this problem by inserting high-speed ground switches in the power system.Switches on each end of the faulted phase acti-vate immediately after the circuit breaker opens,extinguishing the secondary arc. The switchesare then opened and the circuit breaker reclosed.Fig. 3 shows oscilloscope traces from a reclosingtest conducted at the factory site. In this case, afault in phase ‘a’ extends to phase ‘b’. Both phasesindependently trip and reclose.

BUS PROTECTION. Fault currents in 1,000kV sys-tems result in DC transients of a long durationthat saturate core-type current transformers andlead to misoperation of current-differential re-lays. We therefore changed over to linear-coupled current transformers that do notsaturate. We chose a high secondary impedancesince linear-coupled current transformers havethe same permeability as air and excitationimpedance is low.

The secondary output of these transformersis proportional to the primary current and satu-ration does not occur. The secondary circuitdoes not open at abnormally high voltages likethe core-type circuit. There is a trade-off, how-ever, since the magnitude of harmonic currentcomponents in the output increases proportion-ally with harmonic order. Because the outputis dependent on the differential of the primarycurrent, the secondary voltage is proportionalto the frequency and the phase advances by 90°.

We simulated the fault current waveform fora power system that is prone to harmonic gen-eration, and verified the correct relay response.We triggered a fault on a model transmissionline and found the correct relay response againstlow-order harmonics. Finally, we connected afield specification linear-coupled current trans-former, and verified the relay operation using ashort-circuit generator to simulate internal andexternal faults.

Mitsubishi Electric oversaw development of thetransformer cubicle, which includes 1,000kVtransmission protection, busbar protection,transformer protection, AC overvoltage protec-tion, a data acquisition and control unit, andthe signal processing unit of the optical voltagetransformer.

In the busbar protection system, a fiberopticLAN connects the master units and the bayunits of each manufacturer. The master unitsperform a protective function while the bayunits monitor the current transformer outputsand switch conditions, and execute circuit-breaker trip functions.

In the control system, a fiberoptic LAN linksthe control terminals of each manufacturer, op-eration support units and the automatic oscillo-scope. The system supports equipment control,equipment status monitoring, instrumentationand fault indication functions.

Optical PCM communications between theprotection and control systems support relay set-ting, switching control and alarm indications.

Features

TRANSMISSION-LINE PROTECTION. The lower fault-detection sensitivity associated with increasedtransmission-line charging current has been ad-dressed by improved charging current compensa-tion for the current differential relays. Moresophisticated reclosing functions have also beendeveloped.

In charging current compensation schemes todate, the voltages at individual terminals are usedto calculate the charging currents between them,and 100% of these values are used for compensa-tion. In such schemes, the maximum per phaseerror current is 1.5 times the transmission-linecharging current in the case of open-circuit fault-ing of a voltage transformer secondary circuit;therefore, the sensitivity of the current differen-tial relay must be decreased to preventmisoperation in 1,000kV systems. We success-fully halved the error by transmitting the localcurrent data with a 50% compensation of thecharging current using local voltage data to theremote terminal, thereby satisfying the sensitiv-


TECHNICAL REPORTS

TRANSFORMER PROTECTION. Successful trans-former protection in 1,000kV systems requiresa method to distinguish transformer faults,which have strong low-order harmonics, fromexcitation inrush currents, and to adjust to theproportionally lower transformer fault currentsto higher system voltage and transformer ca-pacity. We addressed these issues by placing cur-rent comparison relays between the enclosuresand current differential relays between thetransformer primary, secondary and neutralpoints. Fig. 4 shows the configuration of a1,000kV transformer and the current trans-former arrangement that protects it.

When phase faults occur in the series, shuntor tertiary windings, an imbalance occurs inthe current between the two enclosures. Sincenormal loads and excitation inrush currents arewell balanced, faults are identified by compar-ing the currents in the parallel windings. Thismethod also offers enhanced sensitivity.

When ground faults occur, a current differen-tial appears in the normally zero sum of theprimary, secondary and neutral-point currents.This provides high sensitivity for ground fault-ing.

An excitation current flowing through the

tertiary delta circuit and a terminal short aresigns of a fault between phases. Current differ-ential protection is therefore placed on the ter-tiary delta circuit.

We manufactured a scale model of the1,000kV transformer and verified the protectionfunctions on a model transmission line. Simu-lated inrush currents associated with the clo-sure of primary or secondary circuit breakersfailed to cause spurious operation. We also failedto induce spurious operation by varying theenclosure connect timing, as well as varyingthe excitation current by about 30% to createan unbalanced inrush current.

AC OVERVOLTAGE PROTECTION. We qualified alightning arrestor discharge current detectionalgorithm and high-speed transfer trip functionthat are used to provide AC overvoltage protec-tion.

The lightning arrestor discharge current isdetected at the local terminal in which the cir-cuit breaker is open, and the status informa-tion is transferred to the remote terminal. Thecircuit breaker executes a high-speed trip at theremote terminal when an overvoltage fault isdetected.

Fig. 3 Oscillograph of multiphase reclosing in high-speed grounding and arc-suppressing system.

CB trip/reclose-1CB trip/reclose-2CB trip/reclose-3HSGS trip/reclose-1HSGS trip/reclose-2HSGS trip/reclose-3

CB closeHSGS tripHSGS closeCB trip

Va-n

Vb-n

Vc-n

Ia

Ib

Ic

FDX187-2

27R-127R-3

87-187-327R-2

KeyCB Circuit breakerHSGS High-speed ground switchFDX1 Fault detection87-1~3 Current differential relays27R-1~3 Undervoltage relays

December 1996 · 21

TECHNICAL REPORTS

The main relay operates when the cumula-tive current through the lightning arrestor ex-ceeds a specified threshold, and operatesinstantaneously when a high overcurrent isdetected.

The lightning arrestor discharge waveform istriangular, and the relay operating value is de-termined by the average current correspondingto a triangular waveform with a 2ms base.

The time from overvoltage to arrestor destruc-tion is minimum when the load disconnectovervoltage causes a flashover and a voltage risein the unfaulted phases. Since arrestor destruc-tion will occur at 90ms after a ground fault,the line circuit breaker must operate withinabout 80ms.

Power system protection equipment must op-erate to protect the system from damage due toa variety of fault conditions and maintain ser-vices with minimum interruption. The systemdescribed here meets these requirements withinthe stricter performance constraints of 1,000kVpower systems.

Fig. 4 Configuration of a 1,000kV transformer and the current transformer arrangement for its protection.

*1*2*3*4

Key61 Current comparison relayS: For Series windingsT: Tertiary windingsC: Shunt windings87G Current differential relay for ground fault87T Current differential relay for tertiary circuit

500kV

87G

61S

61T

61C

87T

1,00kV

154kV

T phase

Rphase

Sphase

*1 *2

*3 *4


TECHNICAL REPORTS

Simulation Technology for 1,000kVPower Systems

by Koichirou Ikebe, Tetsuro Shimomura and Dr. Isao Iyoda*

*Koichirou Ikebe is with Tokyo Electric Power Company, Tetsuro Shimomura is with the Itami Works andDr. Isao Iyoda with the Power System & Transmission Engineering Center.

New simulation technologies are required tounderstand the behavior of 1,000kV power sys-tems and to guide the development of 1,000kVequipment. This article reports two relateditems: an efficient simulation method for evalu-ating the unbalanced voltage and current con-ditions that occur in non-transposedtransmission lines, and a new modeling methodthat can precisely analyze the surge behavior oflow-attenuation 1,000kV lines.

Development BackgroundThe highest power transmission voltages, nowreaching 1,000kV, are used to transport electricpower long distances through overhead trans-mission lines. Typical Japanese power lines areconfigured as shown in Fig. 1. Transposition, arearrangement of the lines to balance the linecharacteristics with respect to each phase, isnot applied at 1,000kV due to the difficulty ofinsulation. Symmetrical components cannot beused to analyze sequence separation in non-transposed overhead lines due to the unbalancedtransmission line constants of the non-trans-posed configuration. Since voltage and currentimbalances originating in the transmission linescan cause generator and transformer overheat-ing just as load imbalances do, solutions tomaintain balanced operating conditions mustbe found. Studies are also essential becauseimbalances in long-distance, high-capacity1,000kV power lines will effect entire regionalpower networks.

Analysis Tools for Unbalanced LinesMost existing power network analysis programsassume balanced line and balanced load condi-tions. Although they can perform transient sta-bility calculations and short-circuit currentanalysis for unbalanced fault conditions, theydo not deal with unbalanced networks.

The Electromagnetic Transient Program(EMTP) has been used to analyze ongoing volt-age and current imbalances originating in un-balanced lines, but this approach suffers severalproblems. First, one must set the internal volt-age of the generator (i.e., absolute voltage andvoltage phase angle) using other programs. Sec-

Fig. 1 Towers and disposition of lines.

a) Double-circuit tower b) Single-circuit tower

Line No. 1

Ground wire

Upper phase

Lower phase

Fig. 2 Transposition and matrix of coefficients.

Untransposed line

Symmetrical components transformation

Transposition line

Transposition Transposition

Phase A

Phase B

Phase C

Xaa Xab Xac

Xba Xbb Xbc

Xca Xcb Xcc

X0 X01 X02

X10 X1 X12

X20 X21 X12

X0

X1

X2(Xab = Xac = Xbc)

ond, it is not possible to take account of thegenerator’s negative sequence impedance,which makes it difficult to accurately calcu-late the generator’s negative sequence current.Third, massive data input and output process-ing is required, which makes the program un-suitable for analyzing large networks.

We therefore developed a method for analyz-ing unbalanced voltages and currents arising innetworks containing unbalanced transmissionlines, loads and compensation devices. Themethod employs phase components, which aremore general than symmetrical components,and unlike EMTP, which requires voltage andcurrent source explicitly, the power equationsfor three phases are solved using the Newton-Raphson Method.

The program is capable of performing calcu-lations for nearly the entire main grid of theTokyo Electric Power Company. Verification

December 1996 · 23

TECHNICAL REPORTS

testing was conducted on a model consisting of500kV and 275kV networks including 191 busesand 109 lines. Based on this program, we havedeveloped an additional program for analyzingfault currents generated by the many possiblefault scenarios on complicated networks.

ResultsThe program for power flow calculations underunbalanced voltage and current conditions hasalready been applied to the investigation of anumber of problems (e.g., analysis of negativesequence currents in generators and transmis-sion lines, analysis of network voltage imbal-ances caused by the unbalanced loads of electrictrains, and analysis of the behavior of new powerline configurations and transpositions). Estab-lishing a database of detailed physical informa-tion on the lines for analytical purposes has hadthe additional benefit of making network elec-trical characteristics data available. The authorsplan to explore further applications in the de-sign of 1,000kV transmission line relays, cal-culation of illogical harmonic currentcomponents and design of equipment to com-pensate for transmission line imbalances.

Transient Recovery Voltage AnalysisTransient recovery voltage (TRV) is a type ofsurge that occurs between opening circuit-breaker contacts.

CONSIDERATIONS IN 1,000KV LINES. 1,000kVtransmission lines are long with little loss, andthe system’s resonant frequency is low. As aresult, fault-induced transients attenuateslowly, and remain superimposed on the lineswell after the fault current has been cleared andnormal operation resumed. These transientsalso present a danger of propagating into 500kVnetworks.

We used the methodology presented above toanalyze these phenomena and design counter-measures. We modeled a system consisting of a1,000kV network with five substations and a500kV network with about 30 substations, andanalyzed TRVs in the 1,000kV network. Fig. 3shows a diagram of the 1,000kV network. Weused the J. Marti EMTP model for the 1,000kVlines, but the large amount of input data for the500kV network required that we simplify it totwo lines expressed as a three-phase distributed-parameter line model.

In previous analyses, the state at the time thefault occurs is taken as the initial state for cal-culating the voltage that occurs across the cir-cuit breaker contacts as they open. However,

due to the low attenuation of fault-induced har-monic components in 1,000kV systems, the pre-fault state is taken as the initial state, and thefault and fault recovery are simulated. The1,000kV circuit breakers employ a resistivebreaking method, with the resistor contactsopening 20ms after the main contacts open atthe current zero point.

Our model incorporated not only the resis-tive loss of the lines but also the core loss andcopper wire loss of the transformers, as well asfault-point arc losses. Load effects were alsostudied

ANALYSIS RESULTS. We performed a TRV analy-sis on a 1,000kV system at each stage of con-struction with respect to substation faults andtransmission line faults. Due to the low trans-mission line resistance, the high-frequencycurrents induced by fault transients attenuateonly slowly. These high-frequency componentsremain superimposed on the line after fault re-covery, causing di/dt, the rate-of-change in thecurrent, to grow large. The frequency of thehigh-frequency current is determined by thetransmission line length—350Hz in the case of

a) Five substationconfiguration

b) Two substationconfiguration

Substation C

138kmSubstation ASubstation E

Substation B

Sub station E

Sub station A

50km210km

Substation D40km 210km

Substation EE8

13

14

L1 1Substation AA9

2

Am

plitu

de o

f nth

har

mon

ic (

%)

11 10 100

10

100

300Hz400Hz 500Hz

700Hz1,100Hz

Am

plitu

de o

f nth

har

mon

ic (

%)

1

10

100

1 10 100

250Hz 400Hz1,100Hz

1,400Hz

Harmonic order Harmonic order1,000kV line

(210km)a) Pow er system

b) C urrentof C B-E8 c) C urrentat C B - 49

Fig. 3 1,000kV power system model.

Fig. 4 A fault current waveform and its Fourieranalysis.


TECHNICAL REPORTS

a 210km transmission line. Considering thelosses at this frequency in the 1,000kV lines,500kV lines and transformers, the di/dt whena fault is cleared converts to an rms value ofless than 50kA, which is low enough to presentno problems.

STUDIES ON HIGH-FREQUENCY CURRENTS. Thefault-current described above consists of sev-eral high-frequency current components. Westudied the frequency response of the networkand analyzed the frequency of the high-fre-quency currents.

We used the EMTP frequency scan commandto determine the frequency characteristics of atwo-substation 1,000kV network, and deter-mined that two resonance points exist at 350and 700Hz. We then analyzed the fault current

with the EMTP Fourier on command and dis-covered that the largest components were at300 and 400Hz—six and eight times the funda-mental frequency. We studied the influence ofthe superimposed high-frequency componentsusing the current injection method, which con-nects a current source at the fault point andthen superimposes several high-frequency cur-rent sources and injects them onto the line. Fig.6 shows that the results are relatively accurate.Future studies are needed to examine a widerrange of harmonic frequencies.

In conclusion, our 1,000kV TRV analysis wasconducted in greater detail and with modelingon a greater scale than previously implemented.The results facilitated the design of circuitbreakers.

Interrupter Surge AnalysisAnalysis of the interrupter surge in 500kV gas-insulated switchgear yielded a peak overvolt-age of 2.8 per unit (pu) in contrast to a measuredvalue of 2.7pu. In 1,000kV systems, a lightningimpulse withstand voltage (LIWV) of 2,250kV,approximately 2.5pu, has been adopted, andsurge voltages must be held within this limit.Interrupter surges are numerous, occurring ev-ery time that an interrupter opens or closes.Use of a resistive disconnect scheme keeps tran-sients far below 2.5pu.

We analyzed the worst-case interrupterreclosing arc in a substation consisting of fourcircuits and four banks, assuming a 2.0pu volt-age between the contacts. We modeled the sys-tem using a single-phase distributed-parameterline model, varying the bus connections andchoice of interrupter at which the reclosing arc

Fig. 6 Results of current injection simulation.

Note: All 500kV generating sourcesapply direct grounding.

Det

aile

dS

impl

eM

odel

Circuit Impedance frequency characteristics

SubstationE

Substation A

1,000kV line

Current source

10Hz – 10HzNote: One 1,000kV line

SubstationE

Substation A1,000kV line

Currentsource

10Hz – 10Hz

LLF side LLF side

a) TRV waveform in clearing of a transientgrounding fault

b) TRV waveform obtained from currentinjection simulation

Time (ms)

Vol

tage

(kV

)

0 1 2 3 4

1,500

1,000

500

0

0 1 2 3 4(ms)

1,500

1,000

500

0

(kV)BTF side

0 1 2 3 4

1,500

1,000

500

0

BTF side

0 1 2 3 4

1,500

1,000

500

0

(kV)

(kV)

(ms)

(ms)

December 1996 · 25

Fig. 5 Frequency characteristics of a 1,000kVpower system.

TECHNICAL REPORTS

Fig. 7 Substation configuration.

Fig. 8 Peak overvoltage ratio for various valuesof parallel switch resistors.

2.49 pu

2.49 pu

Arc back switch

Peak overvoltage

Transformer terminal

+1.0pu +1.0pu +1.0pu +1.0pu

RePt

GIB

Tr.1.0pu

1.23pu

Pea

k ov

ervo

ltage

(pu

)

Resistance Ω2 5 10 20 50 100 200 500 1,000

Fig. 9 Result voltage waveform (case II at gas-insulated switchgear terminal)

occurred. The value of the surge-suppressionresistor was varied during the simulation fromthe reclosing arc resistance of 2Ω to a maxi-mum of 1,000Ω.

Time (µs)

Time (µs)

2.0

1.0

0.0

2Ω

2.49pu

500Ω1.13pu

Pea

k ov

ervo

ltage

(pu

)

0.0 4.0 8.0

Pea

k ov

ervo

ltage

(pu

)

0.0 4.0 8.0

2.0

1.0

0.0

Without taking special steps, the transientvoltage caused by a reclosing arc at the bus in-terrupter reaches 2.49pu, with a surge frequencyupwards of 2MHz. Fig. 8 shows the dramaticincrease in the surge voltage suppression thatoccurs as the resistance of the parallel switch-ing resistor increases. Fig. 9 shows the voltagewaveform for a typical resistance value. In thefinal design, we selected a 500Ω resistance,which holds the peak transient voltage to ap-proximately 1.1pu.

Simulation technology has played a vital rolein the design of 1,000kV power systems. Thetechnology has been developed over 20 years ofexperience and extensive knowledge of 500kVpower systems, and promises to help simplifythe daunting task of designing, manufacturingand testing large-scale power network equip-ment.


NEW PRODUCTS

A Monitoring System for1,000kV Gas-InsulatedSwitchgearMitsubishi Electric has delivered agas-insulated switchgear monitoringsystem for use in qualification testingof 1,000kV substation equipment atthe UHV testing yard of Shin-HarunaSubstation, Tokyo Electric PowerCompany (TEPCO). Testing hasbeen underway since 1995.

Fig. 1 shows the system configura-tion. The monitoring panel receivesdata from sensors, which it pro-cesses and analyzes to determinethe equipment status. This informa-tion is sent out over a 1:N opticalHDLC LAN to an on-site control room,where it is logged and displayed. Thedata stream can also be routedthrough the video conferencing sys-tem of the TEPCO administrativeoffices to the Mitsubishi Electric fac-tory. Mitsubishi Electric can also setup a personal computer and modemin the monitoring panel cubicle tosend proprietary instrumentation datato the factory over a telephone line.

The system monitors the followingitems.

PARTIAL DISCHARGE. An internal antennadetects partial discharges. Factorytesting demonstrated a maximumdetection sensitivity of 0.5pc.

INTERNAL FAULT LOCATOR. This function isrealized using gas pressure sensors,and is capable of detecting pressure

increases of 100 pascals.

LIGHTNING ARRESTOR LEAKAGE CURRENT. Acurrent transformer installed on thelighting arrestor ground circuit de-tects leakage current. The total valueof the leak current components at thefundamental frequency and phaseangle ∆ are used to determine theresistive leakage current.

TRAVEL CHARACTERISTICS. A control cur-rent sensor, which monitors the con-trol current run time of the controlcircuit, a travel sensor that directlymeasures movement of the operatingmechanism and auxiliary contactsare used to monitor travel character-istics. Combined operation of thehigh-speed ground switch and gascircuit breaker can also be moni-tored.

locate internal faults.The equipment also monitors con-

tact wear and lightning arrestor dis-charge current.

The single-panel monitoring unit iscapable of monitoring a three-phasegas-insulated switchgear unit. Thenaturally-cooled cubicle has a pro-tective sun shade and an internaldehumidifier. Fig. 2 shows the de-tailed equipment configuration. ACRT monitor enables visual monitor-ing of the instrumentation data andsensor operation status, and screenscan be printed on demand. Data canbe uploaded to a remote location via1:N optical HDLC LAN or via modemover telephone lines. The data re-ceived from this equipment will beanalyzed and used to design futuregas-insulated switchgear and relatedmonitoring equipment.

HYDRAULIC PUMP

OPERATING CHARACTER-ISTICS. The operatingtimes and operatingduty of the electro-magnetic relay thatpowers the hydrau-lic pumps are moni-tored. This does notinclude pump op-eration associatedwith manually initi-ated equipmentoperation.

SF6 GAS PRESSURE AND

DENSITY. Sensorsmonitor gas pres-sure and density toidentify leaks and to

December 1996 · 27

SENSOR SYSTEM

Partial dischargesensor

Gas pressuresensors

Leak currentsensor

GIS

LA

GCB operating characteristics

Control currentsensors

GCB

Travel sensors

HSGS characteristics

Hydraulicpump sensor

Control currentsensors

Travel sensors

Hydraulicpump sensor

DS/ES travel characteristics

Control currentsensor

Auxiliarycontacts (a/b)

30 faults

Voltage signals (5)Internal antennaCurrent signals (6)

DS/ES

Common

Currentsignals (4)CT

Pulse signals (2)

Contactsignals (2)

Contactsignals (4)CT

Pulse signal (1)

Contact signal (1)

Currentsignals (6)CT

Contact signals (23)

Currentsignal (1)High-sensitivityCT

GIS LOCAL CONTROL CUBICLE

Signalconverter

Signalconverter

Signalconverter

Signalconverter

Converter

Converter

Converter

Converter

Buffer relay

Buffer relay

Buffer relay

Buffer relay

Gas pressureprocessor

Partial dischargesensor

Fault locationprocessor

GCB travelcharacteristics

processor

DS/ES travelcharacteristics

processor

LA processor

HSGS travelcharacteristics

processor

Partialdischargeprocessor

Hydraulic pumpprocessor

30F processor

Con

trol

and

arit

hmet

icpr

oces

sor

1 Controlpanel

Opt

ical

tran

smitt

er

Con

trol

and

arit

hmet

icpr

oces

sor

2

HDLC link(to hostcomputer)

Phone line(toMitsubishiElectricFactory)

KeyGCBGSGS

DS/ES

LA30F

Gas circuit breakerHigh-speed groundswitchDisconnecting andearthing switchesLightning arrestor30-fault

Fig. 2

Fig. 1 Monitoring system configuration.

CRT

Workstation

LANinterface

OpticalHDLC

GIS monitoringpanel

Modem

Phone line(to factory)

GISand

trans-former

Data transmission terminal

Data transmission terminalLAN

LANinterface

Video conferencingmonitor

RemoteterminalRemoteterminal

Printer

Video conferencing monitor

SHIN-HARUNA SUBSTATION

TOKYO ELECTRIC POWERADMINISTRATIVE OFFICES

NEW PRODUCTS

A Monitoring System for 1,000kV Transformersextracted from the transformer oiland the concentrations of six gases(CO, H2, CH4, C2H2, C2H4 and C2H6)are measured as well as the totalcombustible gas content. These dataare used to provide early warning oflocal heating, discharge and otherabnormalities.

PARTIAL DISCHARGE. A high-frequencycurrent transformer detects partialdischarge and acoustic emission(AE) sensors mounted on the wall ofthe transformer tank detect the asso-ciated ultrasonic vibrations. The timedelay between the discharge detec-tion (by the current transformer) andultrasonic detection makes it possibleto detect whether the discharge isinside or outside the transformer, andif inside, whether or not it occurred inthe transformer tank.

OIL TEMPERATURE. Resistance thermo-meter bulbs (Pt 100Ω) check thetemperatures of the main transformeroil, the load voltage regulator oil andthe ambient temperature, and the

detected values are comparedagainst specified ranges.

OIL LEVEL MONITORING. Potentiometerson the shaft of conservator-type oilgauges monitor the oil level in themain transformer and load voltageregulator tank. The measured oillevels can be compared against theoil levels predicted on the basis of oiltemperature.

ON-LOAD TAP CHANGER OPERATING

CHARACTERISTICS. The drive shaft torqueduring tap changing is measured bya rotary-transformer-type torquesensor. A current sensor measuresthe current of the motor drive mecha-nism. Torque and current waveformsare monitored and compared againststandard values for each of the sixoperating modes corresponding tothe combination of tap changingcommand signals and tap positionsto verify correct tap changer opera-tion and to resolve the cause of anymalfunction that may arise.

Mitsubishi Electric has delivered atransformer monitoring system foruse in verification of 1,000kV trans-former equipment at the Shin-HarunaUHV Equipment Test Station of TokyoElectric Power Company. The systemconsists of sensors and monitoringequipment that analyze the sensordata and provide early warning ofabnormal operation.

The monitoring equipment consistsof processors for each of the sensoroutputs, a control and arithmeticprocessing unit, an operating paneland an optical-fiber transmitter (Fig.1). The monitoring equipment canstore instrumentation and diagnosticdata for up to three months, withdisplay or hardcopy output on de-mand. The data can be sent to ahost computer by the optical-fibertransmitter using the HDLC-NRMprotocol, or to the factory by tele-phone line.

The system monitors the followingitems.

DISSOLVED GASES. Dissolved gases are


Fig. 1 System block diagram.

KeyMTR Main transformerLVR Load voltage regulatorLTC On-load tap changerCT Current transformerAE Acoustic emission

sensor

Telephonelink tofactory

HDLC link to hostcomputer

OutputInterface

Controlpanel

Con

trol

and

arit

hmet

icpr

oces

sing

uni

t

Oil leveland term-peratureprocess-ing unit

LTCprocess-ing unit

Partialdischargeprocess-ing unit

30 faultsignalprocess-ing unit

Optical-to-electricinterface

Digital mea-surements(optical fibercable)

Dissolvedgassensors

Enclosure1

Enclosure2

30 faultsignal

Solenoidvalve

Oilpiping

OilpipingSolenoid

valve

Valve

Valve

Contact signal

Cooler control cubicle

High-frequency CT output(optical fiber cable)

Dischargecurrent sensor

AE outputUltrasonicsensor

CT outputCurrent sensor

Contact signalTap changesignal

Operating mechanism

Dynamic strain signalTorque sensor

Resistance thermometer bulb

Resistance thermometer bulb

Potentiometer

Torque sensor

Ambient tem-perature sensor

Oil temperaturesensor

Oil level sensor

MONITORING EQUIPMENTSENSORS

Country Address TelephoneU.S.A. Mitsubishi Electric America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500

Mitsubishi Electronics America, Inc. 5665 Plaza Drive, P.O. Box 6007, Cypress, California 90630-0007 714-220-2500Mitsubishi Consumer Electronics America, Inc. 2001 E. Carnegie Avenue, Santa Ana, California 92705 714-261-3200Mitsubishi Semiconductor America, Inc. Three Diamond Lane, Durham, North Carolina 27704 919-479-3333Horizon Research, Inc. 1432 Main Street, Waltham, Massachusetts 02154 617-466-8300Mitsubishi Electric Power Products Inc. Thorn Hill Industrial Park, 512 Keystone Drive, Warrendale, Pennsylvania 15086 412-772-2555Mitsubishi Electric Manufacturing Cincinnati, Inc. 4773 Bethany Road, Mason, Ohio 45040 513-398-2220Astronet Corporation 37 Skyline Drive, Suite 4100, Lake Mary, Florida 32746-6214 407-333-4900Powerex, Inc. Hills Street, Youngwood, Pennsylvania 15697 412-925-7272Mitsubishi Electric Research Laboratories, Inc. 201 Broadway, Cambridge, Massachusetts 02139 617-621-7500

Canada Mitsubishi Electric Sales Canada Inc. 4299 14th Avenue, Markham, Ontario L3R 0J2 905-475-7728Mitsubishi Electronics Industries Canada Inc. 1000 Wye Valley Road, Midland, Ontario L4R 4L8 705-526-7871

Mexico Melco de Mexico S.A. de C.V. Mariano Escobedo No. 69, Tlalnepantla, Edo. de Mexico 5-565-6269

Brazil MELCO do Brazil, Com. e Rep. Ltda. Av. Rio Branco, 123, a 1507, 20040, Rio de Janeiro 21-221-8343MELCO-TEC Rep. Com. e Assessoria Tecnica Ltda. Av. Rio Branco, 123, a 1507, 20040, Rio de Janeiro 21-221-8343

Argentina MELCO Argentina S.R.L. Florida 890-20º-Piso, C.P. 1005, Buenos Aires 1-312-6982

Colombia MELCO de Colombia Ltda. Calle 35 No. 7-25, Oficinas No. 1201/02, Edificio, Caxdac, Apartado Aereo 1-287-927729653, Bogotá

U.K. Mitsubishi Electric U.K. Ltd. Travellers Lane, Hatfield, Herts. AL10 8XB, England 1707-276100Apricot Computers Ltd. 3500 Parkside, Birmingham Business Park, Birmingham, B37 7YS, England 21-717-7171Mitsubishi Electric Europe Coordination Center Centre Point (18th Floor), 103 New Oxford Street, London, WC1A 1EB 71-379-7160

France Mitsubishi Electric France S.A. 55, Avenue de Colmar, 92563, Rueil Malmaison Cedex 1-47-08-78-00

Netherlands Mitsubishi Electric Netherlands B.V. 3rd Floor, Parnassustoren, Locatellikade 1, 1076 AZ, Amsterdam 20-6790094

Germany Mitsubishi Electric Europe GmbH Gothaer Strasse 8, 40880 Ratingen 2102-4860Mitsubishi Semiconductor Europe GmbH Konrad Zuse Strasse 1, 52477 Alsdorf 2404-990

Spain MELCO Iberica S.A. Barcelona Office Polígono Industrial “Can Magi”, Calle Joan Buscallà 2-4, Apartado de Correos 3-589-3900420, 08190 Sant Cugat del Vallés, Barcelona

Italy Mitsubishi Electric Europe GmbH, Milano Office Centro Direzionale Colleoni, Palazzo Perseo-Ingresso 2, Via Paracelso 12, 39-6053120041 Agrate Brianza, Milano

China Shanghai Mitsubishi Elevator Co., Ltd. 811 Jiang Chuan Rd., Minhang, Shanghai 21-4303030

Hong Kong Mitsubishi Electric (H.K.) Ltd. 41st Floor, Manulife Tower, 169 Electric Road, North Point 510-0555Ryoden Holdings Ltd. 10th Floor, Manulife Tower, 169 Electric Road, North Point 887-8870Ryoden Merchandising Co., Ltd. 32nd Floor, Manulife Tower, 169 Electric Road, North Point 510-0777

Korea KEFICO Corporation 410, Dangjung-Dong, K unpo, Kyunggi-Do 343-51-1403

Taiwan MELCO Taiwan Co., Ltd. 2nd Floor, Chung-Ling Bldg., No. 363, Sec. 2, Fu-Hsing S. Road, Taipei 2-733-2383Shihlin Electric & Engineering Corp. No. 75, Sec. 6, Chung Shan N. Rd., Taipei 2-834-2662China Ryoden Co., Ltd. Chung-Ling Bldg., No. 363, Sec. 2, Fu-Hsing S. Road, Taipei 2-733-3424

Singapore Mitsubishi Electric Singapore Pte. Ltd. 152 Beach Road #11-06/08, Gateway East, Singapore 189721 295-5055Mitsubishi Electric Sales Singapore Pte. Ltd. 307 Alexandra Road #05-01/02, Mitsubishi Electric Building, Singapore 159943 473-2308Mitsubishi Electronics Manufacturing Singapore Pte. Ltd. 3000, Marsiling Road, Singapore 739108 269-9711Mitsubishi Electric Asia Coordination Center 307 Alexandra Road #02-02, Mitsubishi Electric Building, Singapore 159943 479-9100

Malaysia Mitsubishi Electric (Malaysia) Sdn. Bhd. Plo 32, Kawasan Perindustrian Senai, 81400 Senai, Johor 7-5996060Antah MELCO Sales & Services Sdn. Bhd. 3 Jalan 13/1, 46860 Petaling Jaya, Selangor, P.O. Box 1036 3-756-8322Ryoden (Malaysia) Sdn. Bhd. 2nd Fl., Wisma Yan, Nos. 17 & 19, Jalan Selangor, 46050 Petaling Jaya 3-755-3277

Thailand Kang Yong W atana Co., Ltd. 15th Floor, Vanit Bldg., 1126/1, New Petchburi Road, Phayathai, Bangkok 10400 2-255-8550Kang Yong Electric Co., Ltd. 67 Moo 11, Bangna-Trad Highway, Km. 20 Bang Plee, Samutprakarn 10540 2-312-8151MELCO Manufacturing (Thailand) Co., Ltd. 86 Moo 4, Km. 23 Bangna-Trad, Bangplee, Semudparkarn 10540 2-312-8350~3Mitsubishi Elevator Asia Co., Ltd. Bangpakong Industrial Estate, 700/86~92, Moo 6 Tambon Don Hua Roh, 38-213-170

Muang District Chonburi 20000Mitsubishi Electric Asia Coordination Center 17th Floor, Bangna Tower, 2/3 Moo 14, Bangna-Trad Highway 6.5 Km, 2-312-0155~7(Thailand) Bangkawe, Bang Plee, Samutprakarn 10540

Philippines International Elevator & Equipment, Inc. Km. 23 West Service Road, South Superhighway, Cupang, Muntinlupa, 2-842-3161~5Metro Manila

Australia Mitsubishi Electric Australia Pty. Ltd. 348 Victoria Road, Postal Bag No. 2, Rydalmere, N.S.W. 2116 2-684-7200

New Zealand MELCO Sales (N.Z.) Ltd. 1 Parliament St., Lower Hutt, P.O. Box 30-772 Wellington 4-569-7350

Representatives

China Mitsubishi Electric Corp. Beijing Office SCITE Tower, Rm. 1609, Jianguo Menwai, Dajie 22, Beijing 1-512-3222Mitsubishi Electric Corp. Shanghai Office Room No. 1506-8, Shanghai Union Building 100, Yanan-East Street, Shanghai 21-320-2010

Korea Mitsubishi Electric Corp. Seoul Office Daehan Kyoyuk Insurance Bldg., Room No. 1204 #1, Chongno 1-ka, 2-732-1531~2Chongno-ku, Seoul

Viet Nam Mitsubishi Electric Corp. Ho Chi Minh City Office 8 B2, Han Nam Officetel 65, Nguyen Du St., 1st District, Ho Chi Minh City 8-243-984

MITSUBISHI ELECTRIC OVERSEAS NETWORK (Abridged)

MITSUBISHI ELECTRIC CORPORATIONHEAD OFFICE: MITSUBISHI DENKI BLDG., MARUNOUCHI, TOKYO 100-8310, FAX 03-3218-3455

vol. 77/dec. 1996 - mitsubishi electric

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