thoshiba power transformer

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POWER TRANSFORMERS

TOSHIBA TOSHIBA TOSHIBA TOSHIBA



1909 44kV, 4.5MVA Bank Hodogaya Substation, Yokohama Electric Co., Japan

1917 110kV, 13.2MVA Bank Inawashiro Hydroelectric Power Co., Japan

1926 154kV, 20MVA Bank Gifu Substation, Nihon Electric Power Co., Japan

1939 220kV, 80MVA Xu Chuna Jiang Power Station, Chang Jin Jiang Hydroelectric PowerCo.,China

1952 275kV, 117MVA Shin-Aimoto Substation, Kansai Electric Power Co., Japan

1958 275kV, 200MVA Chiba Thermal Power Station, Tokyo Electric Power Co., Japan

1960 275kV, 300MVA Yokosuka Thermal Power Station, Tokyo Electric Power Co., Japan

1961 330kV, 300MVA Bank Electricity Commission of New South Wales Substation, Australia

1963 275kV, 430MVA Owase-Mita Thermal Power Station, Chubu Electric Power Co., Japan

1967 275kV, 680MVA Anegasaki Thermal Power Station, Tokyo Electric Power Co., Japan

1967 512.5kV, 600MVA Bank B.C. Hydro & Power Authority Power Station, Canada

1968 525kV, 1200MVA Bank Bonneville Power Administration Substation, U.S.A.

1971 500kV, 1000MVA Bank Shin-Koga Substation, Tokyo Electric Power Co., Japan

1973 275kV, 1100MVA Kashima Thermal Power Station, Tokyo Electric Power Co., Japan

1974 275kV, 450MVA Sunen Substation, Chubu Electric Power Co., Japan

1974 525kV, 1100MVA Sodegaura Power Station, Tokyo Electric Power Co., Japan

1977 500kV, 1500MVA Bank Shin-Koga Substation, Tokyo Electric Power Co., Japan

1977 500kV, 680MVA Okuyoshino Pumped Storage Power Station, Kansai Electric Power Co.,

1977 525kV, 1200MVA Fukushima 1st Nuclear Power Station, Tokyo Electric Power Co., Japan1982 765kV, 805.5MVA Bank EDELCA Guri Power Station, Venezuela

1985 515kV, 1260MVA Tsuruga 2nd Nuclear Power Station, Japan Atomic Power Co., Japan

1988 765kV, 1650MVA Bank Furnas Foz do Iguacu Substation, Brazil

TOSHIBA POWER TRANSFORMERSIn 1894 Toshiba started producing transformers. Since then, we have successively completed the following

power transformers, each epoch-making when considering Japan's industrial level in those years.



Recently, with the sharp increase indemands for electric power, powertransformers have grown in scale

while unit capacity has shown asincreasing tendency.Especially, thermal/nuclear powerplant transformers have displayed anotable tendency toward largecapacity. Toshiba has successivelyrenewed its records on unit capacitysuch as 200MVA in 1958, 300MVA in1960, 430MVA in 1963, 680MVA in1967, 1100MVA in 1973, 1200MVA in1977. In 1985 we manufactured aworld-record product of 60Hz, 515kV,1260MVA delivered to Tsuruga 2ndNuclear Power Station, Japan AtomicPower Co., Japan.

While substation transformers aremostly equipped with on-load tapchangers, based on technical know-how under license of MaschinenfabrikReinhausen GmbH, Germany,Toshiba developed a resistance-typeon-load tap changer, which waspromptly standardized to ensure highreliability. A large number oftransformers providing on-load tapchangers up to 800 VIVA are beingproduced, and many auto-trans-formers up to 765 kV-1650 MVA bankare being manufactured by

Toshiba.Recently, transformers connected togas-insulated switchgear (GIS) are

being broadened in application. As to all voltage classes no largerthan 500kV, Toshiba established a GIS connection technique, resulting inthe successful manufacture anddelivery of 500kV, GIS direct-coupledtransformers. Transformers forpumped-storage power stations andunderground substations are subjectto strict restrictions on transportdimensions and weight. Throughadopting an innovative method ofdividing components to facilitatetransportation and assemblytechnique, Toshiba manufactured and

delivered three-section type 275kV,300MVA transformers to undergroundsubstations, 345kV, 300MVAtransformer to pumped-storage powerstation and a nine-section type 500kV,680MVA transformer to anunderground power station, whoseequivalent cannot be seen in any partof the world.By initiating research on 500kVtransformers early in 1955, andthrough exerting efforts subsequentlyseveral times in related research anddevelopment activities,

in 1967 Toshiba successfullycompleted and delivered a 500kVtransformer to the B.C. Hydro &Power Authority, Canada. This wasthe first practical model ever built inJapan for an ultra high-voltage powertransformer. Further, in 1971,500/275kV-1000MVA auto-transformer-banks were completed asthe first 500kV transformer product tobe delivered for domestic use. In1977, Toshiba also delivered1500MVA-bank autotransformers.In 1988, 765/525kV1650MVA auto-transformer-banks were delivered toBrazil as the first 765kVautotransformer product.Supported by such technology,

Toshiba successively manufacturedand delivered the aforementionedgigantic thermal, nuclear powerstation transformers and hydroelectricpower station transformers whichrequires the difficult transportationwith strict transport restrictions.Regarding transformers of the 500kVand above, Toshiba boasts one of theworld's largest supply record, havingexceeded 120,OOOMVA in totalcapacity of supplied transformers (330units).



Features

High Reliability

Core Structure OffersSplendid Characteristics

Advanced Winding Application

Perfect Drying Process

Sufficient MechanicalStrength againstShort-circuiting

Highly Efficient Cooling

Perfect Measure againstLeakage Flux

Adequate Oil-leakagePreventive Structure

Simplified Installation Work

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to conventional technologies, the ability to designcapable transformers, an excellent workingenvironments and facilities, and thorough use ofinspection and testing system.

The high reliability of Toshiba products is widelyrecognized by users in Japan and abroad. It is backed

up by an accumulation of technology, which has beencarefully achieved by adding new technologies

utilized, displays with Toshiba transformers less no-loadloss and no-load current, as well as low noise.

Adopting of a miter-joint core, in which thecharacteristics of grain-oriented silicon steel are fully

The windings are manufactured by highly skilledworkers in a dust-proofed room.

Toshiba adopts the disk windings with optimuminsulation design based on the voltage oscillationanalysis by computer in high voltage winding.

Toshiba transformers offer excellent insulation, and arefree from shrinkage caused by aging.

Toshiba transformers are of the core type, in which thecore-and-coil assembly is independent of the tank, sothat the core-and-coil assembly can be completely driedthrough our unique vapor phase drying method.

hydraulic jack on a thick annular insulating plate set onthe top thereof. Further more, a perfectly dried,precompressed, pressboard is used, so that the windingis provided with adequate strength to withstand short-circuit mechanical force.

Efforts are now being exerted to ensure sufficient short-circuit strength by maintaining a balance of ampere-turns between windings, determining materials to beused on the basis of mechanical force calculated bycomputers, and exercising adequate care in thepretreatment fastened by applying pressure with a

winding conductors are uniformly insulated, and noreinforcement of insulation is necessary. Because ofthis favorable voltage distribution, the rise oftemperature is uniform.

Forced-cooling is used on the winding and inside thecore, with oil kept circulating through its interior in orderto achieve a large cooling effect. Since the windings areeffective in

voltage distribution, the

Slits are provided on core-leg clamping plates and soon, in order to reduce stray loss as a prevention againstlocal overheating. Further more, nonmagnetic steel isused as necessary in large-current bushing pockets andparts, in the vicinity of large-current lead.

In a large-capacity, high-impedance transformer,probable leakage flux is calculated by computers oneach part so that a magnetic shield, corresponding tothe result of each calculation, is provided on the innersurface of the tank and the clamp surface opposite ofthe coil, to prevent a large amount of leakage flux.

used in such openings as manholes and accessorymounting parts.

The tank is of all-welded construction in which there isno possibility of oil leakage. Nitrile rubber gaskets, excellent in oil resistance and weather resistance, are

advantage of being a built-in type, it is a standardpractice to transport the on-load tap changer asassembled in the main tank.

Since the transformer is transported with its core-and-coil assembly kept in the factory-assembled stage, highreliability is maintained and installation in the field issimplified.

Further more, by utilizing its

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Core

Three-phase transformers usuallyemploy three-leg core. Wheretransformers to be transported by railare large capacity, five-leg core isused to curtail them to within theheight limitation for transport.Even among thermal/nuclear powerstation transformers, which areusually transported by ship and freedfrom restrictions on in-land transport,gigantic transformers of the1000MVA class employ five-leg coreto prevent leakage flux, minimizevibration, increase tank strength, andeffectively use space inside the tank.Regarding single-phasetransformers, two-leg core is wellknown. Practically, however, three-leg core is used; four-leg core andfive-leg core are used in large-capacity transformers. The sectionalareas of the yoke and side leg are50% of that of the main leg; thus, thecore height can be reduced to alarge extent compared with the two-leg core.For core material, high-grade, grain-oriented silicon steel strip is

used.

connected by a core leg tie plate;fore and hind clamps by connectingbars. As a result, the core is soconstructed that the actual siliconstrip is held in a sturdy frame

consisting of clamps and tie plates,which resists both mechanical forceduring hoisting the core-and-coilassembly and short circuits, keepingthe silicon steel strip protected fromsuch force.I n large-capacity transformers,which are likely to invite increasedleakage flux, nonmagnetic steel isused or slits are provided in steelmembers to reduce the width forpreventing stray loss from increasingon metal parts used to clamp the

core and for preventing localoverheat. The core interior isprovided with many cooling oil ductsparallel to the lamination to which apart of the oil flow forced by an oilpump is introduced to achieve forcedcooling.When erecting a core afterassembling, a special device shownin Fig. 8 is used so that no strain dueto bending or slip is produced on thesilicon steel plate.

The steel strip surface is subjectedto inorganic insulation treatment.

All cores employ miter-joint coreconstruction. Yokes are jointed at

an angle of 45 ｰ to utilize the

magnetic flux directionalcharacteristic of steel strip.

A computer-controlled automaticmachine cuts grain-oriented siliconsteel strip with high accuracy andfree of burrs, so that magneticcharacteristics of the grain-orientedsilicon steel remains unimpaired.(Fig. 6)Silicon steel strips are stacked in acircle-section. Each core leg isfitted with tie plates on its front and

rear side, with resin-impregnatedglass tape wound around the outercircumference. Sturdy clampsapplied to front and rear side of theupper and lower yokes are boundtogether with glass tape.

And then, the resin undergoesheating for hardening to tighten theband so that the core is evenlyclamped (Fig. 7).

Also, upper and lower clamps are

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Fig.6 Computer-controlled Core Lamination Line

Fig.7 Bind-type Core

Fig.8 Core Erecting Cradle

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Winding

Continuous Disk Winding

This capacitance acts as seriescapacitance of the winding to highlyimprove the voltage distribution forsurge.Unlike cylindrical windings,hisercap disk winding requires noshield on the winding outermostside, resulting in smaller coiloutside diameter and thus reducingtransformer dimension.Comparatively small in windingwidth and large in space betweenwindings, the construction of thistype of winding is appropriate forthe winding, which faces to aninner winding of relatively highvoltage. Thus, general EHV or UHVsubstation transformers employhisercap disk winding to utilize itsfeatures mentioned above.

Various windings are used as shownbelow. According to the purpose ofuse, the optimum winding is selectedso as to utilize their individual

features.

Hisercap Disk Winding

(Interleaved disk winding)

In hisercap disk winding,electrically isolated turns arebrought in contact with each otheras shown in Fig. 9.Thus, this type of winding is alsotermed "interleaved disk winding."Since conductors 1 - 4 and

conductors 9 - 12 assume a shapesimilar to a wound capacitor, it isknown that these conductors havevery large

capacitance.

This is the most general typeapplicable to windings of a widerange of voltage and current(Fig.10). This type is applied towindings ranging from BI L of 350kV

to BI L of 1550kV. Rectangular wire is used where

current is relatively small, whiletransposed cable is applied to largecurrent. When voltage is relativelylow, a transformer of

100MVA ormore capacity handles a large

current exceeding 1000A. In thiscase, the advantage of transposedcable may be fully utilized.Further, since the number of turnsis reduced, even conventional

continuous disk construction issatisfactory in voltage distribution,thereby ensuring adequatedielectric characteristics. Also, whenever necessary, potentialdistribution is improved byinserting a shield between turns.

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Helical Coil

For windings of low voltage (20kVor below) and large current, ahelical coil is used which consists of

a large number of parallelconductors piled in the radialdirection and wound. Adequatetransposition is necessary toequalize the share of current amongthese parallel conductors.Figure 12 illustrates the transposingprocedure for double helical coil.Each conductor is transposed atintervals of a fixed number of turnsin the order shown in the figure, andas a result the location of eachconductor opposed to the high

voltage winding is equalized fromthe view point of magnetic fieldbetween the start and the end ofwinding turn.

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Insulation Structure

On parts where the electric field isliable to be concentrated, such asthe winding ends of disk windings,detailed electric field analysis by

computer determines the optimumshield shape and the insulationdistance so that the surrounding oilis kept free from excessive electricstress (Fig. 13).Further, spaces between windingsclose to a uniform field employ abarrier insulation structure in whichan oil gap is formed by pressboard(Fig. 14), so that partial dischargecharacteristics and dielectricstrength are improved through anadequate barrier arrangement,

resulting in stabilized insulatingperformance. The windings areclamped according to the followingsteps.When the annular, thick insulatingplate placed on the coil top hasbeen clamped by a hydraulic jack,insulator wedges and blocks areinserted between the insulating plateand the underside of the upper yokeand clamp, so that each coil isclamped uniformly and completely.Regarding pressboard to be used

for spacers and duct pieces on thecoil, precompressed pressboard isused. Coils maintaining adequateshort-circuit strength for many yearsand free from shrinkage throughaging have been realized throughuniformly, completely clampedconstruction and insulating materialsexcellent in compressivecharacteristics combined withadequate drying.Further, all insulating materials usedfor clamping these coils are oil

impregnable and the optimum typefor applications under high electricfields.The connective parts of coil leadsare likely to invite electric fieldconcentration as a result of theedges of terminals and clampingbolts. To alleviate stressconcerntration, each connection iswound with aluminum-foil-laminatedcrepe paper into a streamlinedshape and completely covered withinsulating paper.

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Prevention of Internal Partial Dischargeand Insulation TreatmentIn the case of transformers specifiedwith several reduced-insulationlevels, such as EHV or UHVtransformers, the ratio between

testing voltage and operating voltageis small. To ensure high reliability inextended operation under highvoltage, thorough quality control mustbe effected to prevent dangerouspartial discharge. Main causes ofpartial discharge include:● Incompletely dried insulations● Voids in insulations● Electrically floating metals and

incomplete contact under electricfield of high intensity

● Edged electrodes

● Concentrated electric stress appliedto oil gap

● Intermixed foreign matter or dustTo eliminate these causes, thefollowing measures are taken in theprocess of design and manufacture;to confirm reliability, a partialdischarge test is conducted at thefinal stage.

Drying/Oil Filling Treatment

I n the core-type transformer, thecore-and-coil assembly isindependent of the tank, so that theassembly is allowed to completelydry. When drying the core-and-coilassembly, Toshiba's innovative vaporphase drying method is used, inwhich special oil vapor is sprayed onthe assembly to utilize latent heat

produced when the oil vaporcondenses.Since heating is effected deep insideevenly and quickly, the assembly canbe completely dried

without causing damage to theinsulations.Upon completion of drying, the coil isclamped in a low-humidity room

adjusted to 5% or below relativehumidity to prevent any reabsorptionof humidity (Fig. 17).When a core-and-coil assembly hasbeen installed in a tank, the tank isevacuated to a high vacuum state toremove reabsorbed humidity on theinsulations surface and voids inimpregnated insulation; thendeaerated oil is filled under the highvacuum.Upon completion of a factory test, thetransformer is transported to the site

(with its accessories disassembledand packed as required) forinstallation and assembly. Duringinstallation and assembly at site,adequate care is taken to dehydrationand the prevention of waterabsor tion as in the case of factor

Removing Voids

Voids in impregnated insulation suchas paper and pressboard can becompletely removed by oil filling

under a vacuum. Depending on theglue material and the using method,there is a possibility of creating voidsinside. Thus, oil-impregnable glue isused and due care is exercised toavoid using excessive glue.

Electric Field ControlInsulation between high- and lowvoltage windings, between windingsand the tank/core, and between coil

layers depends mainly on the oilimpregnated paper and oil gaps.Unless voids are created in layers ofinsulation paper, partial dischargeoccurs first on oil gaps. The electrodeshape and insulation dimensionsmust be carefully selected to keep theoil free from excessive stress.The electric field tends to concentrateon the small shaped lead wires fromcoils and lead wire connections,edges of terminals and clampingbolts, and metal structures such as

cores, clamps, and the tank which arefacing these high-voltage electrodes.

As to parts liable to invite electric fieldconcentration, detailed electric fieldanalysis is conducted

by computer to determine theoptimum electrode shape, insulationconstruction, and insulationdimensions to ensure careful control

of the electric field.

Dust ControlThe penetration of all sorts of dustand foreign matter, as well as metallicparticles, is unfavorable totransformers; such matter incurspartial discharge. To avoid thispenetration, the transformer core-and-coil is assembled in a dust-controlled dust-proofed room; windingoperations are performed in a double-ceiling room -a dust-proofed room

provided with an additional ceiling(Fig. 16).Dust is further controlled by coatingmetal structures of the core-and-coilassembly and the tank interior withwhite paint; should dust or foreignmatter penetrate from the exterior, itcan be readil detected.

Fig. 15 Wave Form of Partial Discharge

Fig.16 Dust-proofed Workshop

Fig.17 Vapor-phase Drying Oven

Fig.18 Transformer Final Testing

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With the increase in transformer capacity,the leakage flux also rises, so that strayloss is increased or local overheat iscaused. For large-capacity transformers, it

becomes very important from thestandpoint of improved reliability tothoroughly comprehend leakage flux andto take measures to minimize stray loss. At Toshiba, careful measures againstleakage flux are taken on the basis of theresults of computer-aided analysis onleakage flux distribution and eddy currentloss on each part of the transformer, fullyutilizing our rich experience in producing ahuge number of large-capacitytransformers. As to eddy current loss in coil conductors,the loss of each coil part is determinedfrom leakage flux distribution. Transposedcable and various types of transpositionare applied in accordance with results ofthe above-mentioned loss analysis toprevent local overheat from being causedby excessive loss.Generally made of mild steel, tanks andother structural members are high inpermeability and liable to invite leakage

flux concentration.Thus, the tank inner surface is providedwith a shield made of conductor platesuch as aluminum or a laminated shieldmade of silicon steel strips to preventleakage flux from penetrating the tank,thus reducing a large eddy current losscreated on steel members. As to other structural members, efforts areexerted to prevent local overheat orexcessive deterioration of adjacentinsulation from being caused by eddy

current loss, while employingnonmagnetic materials in accordance withleakage flux on each part, providing slitsin steel members to narrow the width asdescribed in the section on "Core " andadopting other measures appropriate forrespective parts.

Measures against Leakage Flux

Fig.19 Example of Leakage Flux Distribution Analysis by a Computer

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Tank

The tank is manufactured byforming and welding steel plate tobe used as a container for holdingthe core and coil assembly together

with insulating oil. The Toshibatransformer tank offers thefollowing features:● Subjected to automatic beam

welding machine (Fig. 20) andother special facilities, the tankpossesses high quality andstrength.

● Transformers to be transported byship are structured in a semiovalshape on both ends of the tankand provided with reinforcement

members rationally arranged,resulting in increased strength anddecreased weight.

● The tank bottom is fitted with a skidbase by welding and provided withpull lugs to facilitate rolling in thelongitudinal and transversedirections.

● Capable of withstanding a highvacuum of 0.1 torr or below, thetank can be filled with oil under avacuum; to thoroughly removegases and moisture from theinsulation.

● The tank is of completely enclosed,welded construction.Oilproof nitrile rubber gaskets areused on those parts which must beremoved from the standpoint ofassembly in the field or duringmaintenance; flanges thereon areprovided with accurately machinedgrooves or gasket retainers toensure proper tightening ofgaskets. Consequently, there is no

possibility of oil leakage over anextended period (Fig. 21, 22).

● The tank internal surface and themetallic part of the core-and-coilassembly are coated with whitepaint to help observe dustaccumulation.

Fi .20 Automatic beam weldin machine

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Cooling System

Panel type radiators are mounted onthe tank.

Since any cooling fans and oilpumps are not used, this type iswidely applied owing to its facilitatedmaintenance, Panel type radiatorshave features of decreasing oilvolume and withstanding a vacuum(Fig. 23).

Self-cooled Type

Cooling fans are installed on the

radiators to increase the coolingeffect. Usually, the cooling fans willbe put into service when naturalcooling becomes inadequate tomaintain the oil and/or windingtemperature within the specified limitunder a heavy load (Fig. 24).

This is a system in which unitcoolers, each consisting of a coolingtube, fan, oil-submerged pump, andoil flow indicator assembled as aunit, are arranged around the tank inthe necessary amount. Steel pipefitted with fins and dipped in zinc,with an excellent corrosionproofcharacteristics, is adopted ascooling pipe.In the tank cooled oil is delivered tothe windings and ducts on the core,so that each part is cooled uniformlyand effectively (Fig. 25).In some cases, a cooling deviceconsisting of a combination of oil-submerged pumps and radiatorswith cooling fans is used as acooling device for multirating of aforced-oil, forced-aircooled/forced-aircooled/self-cooled transformer(Fig. 26).

In case that a large amount ofcooling air is unavailable such asin underground substations, watercooled type is applied. The oilcirculates through the casingoutside the water tubes, and thewater circulates through the waterto be.Where the cooling water pressureis maintained at a higher levelthan oil pressure, a double-tube-type cooler is applied (Fig. 27).

Cooling System Capacity Cooling equipment

Self-cooling type

(ONAN) 30,000kVA or below Panel-type radiators

Forced-air-cooledtype (ONAF)

30,000kVA~150.000kVA Panel-type radiators and cooling fans

Forced-oil, forced-air-cooled type (OFAF)

150,000kVA or moreUnit cooler or panel-type radiator, andInstallation of cooling fans and pumps

Air-cooled-air-cooled

Forced-oil,Forced-air-cooled T e

Forced-oil,Water-cooled T e

Table 1 Standard design of cooling system

In addition to the above, a forced-oil, water-cooled type (OFWF) and forced-oil, self-cooled type(OFAN) are available.

Fig.23 Self-cooled type Transformer Fig.24 Forced-air-cooled type Transformer14



Fig.25 Forced-oil, Forced-air-cooled type Construction Fig.26 345kV-75MVA Forced-oil, Forced-air-cooled type Transformer

Fig.27 Forced-oil, Water-cooled type Construction

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Accessories

Oil Preservation System

Oil conservator type, nitrogen-enclosed type, and diaphragm type(Type OH-D), are employed for the oil

preservation system.

Diaphragm-type Oil PreservationSystem (Type OH-D)

The oil preservation system Type OH-Dis provided with a synthetic rubber air cellstretched over the oil surface in theconservator to completely isolate theinsulating oil from outside air. This ismost suitable for high-voltage, large-capacity transformers (Fig. 28).Since air in the air cell is connected to theopen atmosphere through a dehydratingbreather, the air cell shape variesaccording to expansion and contractionof the oil, keeping pressure in the air cellat the atmospheric pressure.Diaphragm-type oil preservation systemType OH-D offers the following features:

• Oil can be filled into the transformertank without being exposed to the air.

• Since insulating oil is completelyisolated from the atmosphere by an aircell, there is no possibility of oxygen or

moisture penetrating the oil.• Pressure on the surface of the oil is

constantly maintained at theatmospheric pressure, offering nopossibility of the oil becomingsupersaturated and forming bubbles;thus, high dielectric strength can bemaintained.

• No need to refill nitrogen gas ormeasure the gas purity simplifiesmaintenance.

• No need of attachments to beseparately installed results in less floor

area.• The air cell is made of nitrile rubber

reinforced with nylon cloth, ensuringsplendid oil-proofing and high strength.

Dehydrating Breather (Types FG,FP, FS)

Air in the air cell of conservator TypeOH-D is exposed to the openatmosphere through a dehydratingbreather to prevent dew condensation.

Regarding moisture absorbent, agranular type free from deliquescenceis used.To display the extent of moisture

absorption of the moisture

absorbent, it is also mixed the kindof moisture absorbent which is bluecolor under a dry state and changesto pink as moisture absorption

progresses. When no breathing is

conducted, the breather is isolatedfrom the open air by oil to prevent themoisture absorbent from needlesslyabsorbing moisture (Fig. 30).

Fig.28 Construction of Oil Preservation System Type OH-D

Fig.29 Oil Preservation System Type OH-D

Fig.30 Dehydrating Breather

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Dial Oil Level IndicatorFor indicating on the dial a changeof oil in the conservator, theindicator is tilted downward topermit easy supervision of the oillevel even if it is installed at a highlevel. Any change in the oil level is

detected by a float, converted intorotary motion by a gear, andtransmitted to the external pointerthrough a magnet. The float side iscompletely isolated from the pointerside by a partition through which therotary shaft does not pass,preventing oil leakage. The pointerside is of airtight construction withmoisture absorbent containedtherein to prevent the glass innerside from clouding (Fig. 31).

Protective Rela sThe following protective devices areused so that, upon a faultdevelopment inside a transformer,an alarm is set off or thetransformer is disconnected fromthe circuit. In the event of a fault, oilor insulations decomposes by heat,producing gas or developing animpulse oil flow. To detect thesephenomena, a Buchholtz relay isinstalled.

Buchholtz Relay

The Buchholtz relay is installed atthe middle of the connection pipebetween the transformer tank andthe conservator. There are a 1ststage contact and a 2nd stagecontact as shown in Fig. 32.The 1st stage contact is used to

detect minor faults. When gasproduced in the tank due to a minorfault surfaces to accumulate in therelay chamber within a certainamount (0.3Q-0.35Q) or above, thefloat lowers and closes the contact,thereby actuating the alarm device.The 2nd stage contact is used todetect major faults. In the event of amajor fault, abrupt gas productioncauses pressure in the tank to flowoil into the conservator. In this case,the float is lowered to close the

contact, thereby causing the circuitbreaker to trip or actuating thealarm device.

Fig.31 Construction of Dial Oil Level Indicator

Fig.32 Buchholtz Relay

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Temperature Measuring Device

Liquid Temperature Indicator Liquid temperature indicator (BMSERIES) is used to measure oiltemperature as a standard

practice. With its temperaturedetector installed on the tank coverand with its indicating part installedat any position easy to observe onthe front of the transformer, the dialtemperature detector is used tomeasure maximum oil temperature.Thanks to its double construction,the indicator can be removedregardless of oil in the transformertank. The indicating part, providedwith an alarm contact and amaximum temperature pointer, is of

airtight construction with moistureabsorbent contained therein; thus,there is no possibility of the glassinterior collecting moisture wherebyit would be difficult to observe theindicator (Fig. 33).Further, during remotemeasurement and recording of theoil temperatures, on request asearch coil can be installed whichis fine copper wire wound on abobbin used to measuretemperature through changes in itsresistance.

The winding temperature indicatorrelay is a conventional oil

temperature indicator supplementedwith an electrical heating element.The relay measures thetemperature of the hottest part ofthe transformer winding. Ifspecified, the relay can be fittedwith a precision potentiometer withthe same characteristics as thesearch coil for remote indication.The temperature sensing system isfilled with a liquid, which changes involume with varying temperature.The sensing bulb placed in a

thermometer well in thetransformer tank cover senses themaximum oil temperature. Theheating element with amatching resistance is fed with

current from the transformerassociated with the loaded winding of

the transformer and compensate theindicator so that a temperatureincrease of the heating element isthereby proportional to a temperatureincrease of the winding-over-the-maximum-oil temperature. Therefore,the measuring bellows react to boththe temperature increase of thewinding-over-the-maximum-oiltemperature and maximum oiltemperature. In this way theinstrument indicates the temperaturein the hottest part of the transformer

winding.The matching resistance of theheating element is preset at thefactory.

Winding Temperature Indicator Relay (BM SERIES)

Fig. 34 Construction of Winding Temperature Indicator Relay

Fig.33 Oil Temperature Indicator Fig.35 Winding Temperature Indicator

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Pressure Relief DeviceWhen the gauge pressure in the tankreaches abnormally to 0.35-0.7kg/c m2the pressure relief device startsautomatically to discharge the oil.

When the pressure in the tank hasdropped beyond the limit throughdischarging, the device is automaticallyreset to prevent more oil than requiredfrom being discharged.

Tap ChangerOff-circuit Tap ChangerOff-circuit tap changer is used forregulating the voltage after thetransformer has been completelyde-energized.

At Toshiba, two standard types of off-

circuit tap changers are available: awedge-type off-circuit tap changer anda slide-type off-circuit tap changer.The wedge-type is used when taps areprovided halfway on the winding; theslide-type is used when taps areprovided on the end of the winding.The wedge-type is shown in Fig. 37.The spring, which applies a contactpressure to the contact piece, is mosthighly compressed at its regularposition. Thus, in conjunction withwedge action of the contact piece, a

sufficiently high amount of contactpressure can be obtained, negatingthe possibility of incomplete contact.To prevent oil leakage, an oil seal isused on that part of the tank coverthrough which the operating shaftpasses.

Fig.36 Pressure Relief Device

Fig.37 Construction of Wedge-type Off-circuit Tap Changer

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On-load Tap ChangerDeveloped on the basis of technicallicense from MR Co., Germany,Toshiba On-load Tap Changer FKSeries boasts the following features:

• The entire on-load tap changercan be built in a tank to facilitateassembly and transport of thetransformer.

• By performing resistance-typebreaking, arcing time is short, andboth oil contamination and contactwear can be considerablyreduced. Further, this tap changerensures high reliability and longlife.

• The tap selector is provided with

contact pieces structured to permitconducting large current; eachcontact piece is provided with ashield electrode on its upper andlower sides for needs of insulation.

•

The mechanical parts areprovided with adequate strength tomeet torque as required, thusensuring high reliability duringextended operation.

• The three-phase tap changer is

split into three segments,becoming suitable for changingthe neutral-point tap on star-connection winding. This type oftap changer can also be used as alarge-capacity, single-phase tapchanger with current shunted byimpedance of the transformerwindings.

• The diverter switch can be lifted

from the tap changer, offeringmaintenance ease.

Type Max, step voltage (V) Max, load current (A)

FKT-M100J 3,300 550

FKT-T100M 4,000 1,120

Table 2 Standard Types of On-load Tap Changers

Fig, 38 On-load Tap Changer Type FKT-T100M Fig, 39 Section of On-load Tap Changer

20



BushingHaving manufactured various typesof bushings ranging from 6kV-classto 800kV-class, Toshiba hasaccumulated many years of splendidactual results in their operation.

Plain-type Bushing Applicable to 24kV-class or below,this type of bushing is available in astandard series up to 25,OOOArated current. Consisting of a singleporcelain tube through which passesa central conductor, this bushing isof simplified construction and smallmounting dimensions; especially,this type proves to be advantageouswhen used as an opening ofequipment to be placed in a busduct (Fig. 40).

Oil-impregnated, Paper-insulatedCondenser Bushing The oil-impregnated, paper-insulated condenser bushing, mainlyconsisting of a condenser cone ofoil-impregnated insulating paper, isused for high-voltage application

(Fig. 41, 42). This bushing, ofenclosed construction, offers thefollowing features:

• High reliability and easymaintenance.

• Partial discharge free at testvoltage.

• Provided with test tapping formeasuring electrostatic capacityand tan δ.

• Provided with voltage tapping forconnecting an instrumenttransformer if required.

Fig.42 345kV Oil-impregnated Paper-insulated Condenser Bushing (SF6 Gas-Oil)

21



From the standpoint of protectingthe surrounding living environment,the problem of noise is attachedmuch importance.

Thanks to a combination ofToshiba's excellent coreconstruction and assemblingtechnique, our large-capacitytransformers are manufactured atlower noise level than the standardlevel for transformers specified inNEMA-TR1.However, when a transformer isinstalled close to the boundary lineof a power station/substation, orwhen several transformers areinstalled at the same station, it may

be necessary to employtransformers with even less noise. According to the required decrease

of noise, large-capacity

transformers are decided thecombination of various noiseenclosed constructions and cooler.

Curtain-type enclosureThe transformer tank side wallsare covered with steel plate panelsaround their outer circumference.The steel plate interiors are linedwith sound-absorbent material toprevent noise from built-up.Steel-panel noise enclosureThe transformer tank side wallsand covers are entirely coveredwith steel plate panels. Weldedconstruction is used in all assemblyof steel plate panels to minimizenoise, resulting in a highnoiseproofing effect.

Concrete-panel noise enclosureThe transformer tank side wallsand covers are entirely coveredwith a noise enclosure consisting ofconcrete and steel plate combined.Since mass of concrete-panel isgreater than that of steel plate, theconcrete-panel noise enclosureachieves greater noise reductionthan the steel-panel noiseenclosure.Concrete noise enclosureThe transformer tank side wallsand covers are entirely coveredwith a reinforced concrete wall.This construction achieves the

greatest noise-reducing effect.

Low-noise Transformer

Fig.43 Construction of Low-noise Transformer

Construction of Noise Enclosure

22



Low-noise CoolerTypical coolers applicable to low-noise transformers include thefollowings:● Low-noise unit cooler with low-

speed cooling fan● Low-noise unit cooler with sound-

absorbing duct on the frontof cooling fan

● Independent radiator of self-cooled type or forced-oil,self-cooled type

● Water-cooled unit cooler

Large-capacity transformers of the100-300MVA class adopt thefollowing various types ofcombination in accordance withnoise level requirements:● Noise level: 70-80 dB

The transformer tank side wallsare covered with a curtain-typeenclosure; a low-noise unitcooler with low-speed coolingfan is installed.

● Noise level: 60-70 dBThe transformer tank is covered

with a steel-panel noiseenclosure; a low-noise unitcooler with low-speed cooling

fan or noise-absorbing duct isinstalled.

● Noise level: 55-65 dBThe transformer tank is covered

with a concrete-panel noise

enclosure; a radiator bank orlow-noise unit cooler with noise- absorbing duct is installed.● Noise level: 50- 60 dB

The transformer tank is placedin a concrete noise-enclosure.Generally, an forced-oil, self-cooled system is employed withthe radiator bank installedoutside the concrete noise-enclosure. If circumstancesrequire, a unit cooler of thewater-cooled type or super low-

noise type is installed.

Low-noise Combination of Transformer

Fig.44 Steel-panel Noise Enclosure Fig.45 Concrete-panel Noise enclosure

23



Construction of Cable ConnectionAnd GIS Connection

Cable ConnectionIn urban-district substationsconnected with power cables and

thermal power stations suffered fromsalt-pollution, cable direct-coupledconstruction is used in which atransformer is direct-coupled with thepower cable in an oil chamber.Toshiba employs an indirectconnection system in which, with acable connecting chamber attachedto the transformer tank, a coilterminal is connected to the cablehead through an oil-oil bushing in thecable connection chamber.Construction of the connection

chamber can be divided intosections. Cable connections and oilfilling can be separately performedupon completion of the tankassembling.

GIS (Gas InsulatedSwitchgear) ConnectionThere is an increasing demand for

GIS in substations from thestandpoint of site-acquisitiondifficulties and environmentalharmony. In keeping with thistendency, G IS connection-typetransformers are ever-increasing intheir applications.

At Toshiba, the SF6 gas bus isconnected directly with thetransformer coil terminal through anoil-gas bushing.Toshiba's oil-gas bushing support iscomposed of a transformer-side

flange and an SF6 gas bus-sideflange, permitting the oil side and thegas side to be completely separatedfrom each other.

Fig.46 Indirect Cable Connection Fig.47 Direct GIS Connection24



Transportation

It is important to transport atransformer in the same conditionas it was completely assembled,dried and tested at the factory. Thismakes it possible to ensure highreliability and to shorten the periodfor on-site installation.

A Toshiba transformer istransported in the same uprightposition as it was in finalassembling so that on-siteinstallation becomes very simple,requiring no special operations.While a transformer is intransportation, its main tank is filledwith dry air or dry nitrogen to

completely prevent the core andcoils from absorbing

moisture until final on-site oil filling.When extreme transportrestrictions are imposed, as in thecase of power stations inmountains or when roads aresubjected to weight restrictions orwhen the entrance for undergroundhoisting is narrow in the case ofinstallation with urban undergroundsubstation, the following transportprocedure is employed: A three-phase transformer is divided intosections so that one-phase sectionhoused in a tank is carried into thesite at a time, and the threesections are assembled

into the original three-phasetransformer at the site.The transformer core and coils aretransported to the site in the samecondition as it was assembled andtested at the factory, and they areoined to each other using specialducts and leads submerged in oil.When further strict transportrestrictions are imposed, a single-phase unit may be divided into twoor three sections. Toshibadelivered a 500kV, 680MVA three-phase transformer in nine sections- a record-breading product!

Fig.48 Loading a 50Hz, 420kV, 700MVA Transformer

25



Research and Development

For the research and developmentof equipment coping with thetendency toward high voltage andlarge capacity, the cooperation ofengineers in every field is

necessary -such as electrical,mechanical, chemical and metalengineering, as well as statistics.Toshiba Heavy ApparatusEngineering Laboratory is exertingefforts to cultivate basic techniquescovering various fields in close cooperation with the manufacturingdepartment including the design,

production, and test/inspectionsections, thereby playing a majorrole in new product development,improved product performance,and enhanced reliability. The

world-prominent, latest testingfacilities in this Laboratory are fullyutilized in the development ofultrahigh-voltage insulationstructures represented by ToshibaUHV transformers and 500kVtransformers, as well as infundamental research concerningvarious types of discharge and

breakdown, including breakdown inoil which supported development.Further, all possible efforts areexerted by the staff of thisLaboratory in basic to applied

research on extensive engineeringfields ranging from electromagneticphenomenon, structural strength,heat transfer and cooling, noise,vibration, and earthquake proofing -including insulation and metallicmaterials.

Fig.49 UHV Laboratory

Fig.50 2300kV AC Testing Facilities Fig.51 6000kV Impulse Generator26



Fig.52 Analysis with Computer

Fig.53 UHV Prototype Auto-transformer 500/3MVA-1200/√3kV-50Hz

27



1-1, SHIBAURA 1-CHOME, MINATO-KU, TOKYO, 105-8011, JAPAN

TEL: 03(3457)3612 FAX: 03(5444)94196

Overseas Office:London, Moscow, Vienna,Beijing Shanghai, Guangzhou,Hong Kong, New Delhi,Bangkok, Taipei, Manila,Jakarta, Colombia,Rio de Janeiro, Buenos Aires

● For further information, please contact your nearest Toshiba Liaison Representational or International Operations-Energy System.● The data given in this catalog are subject to change without notice.

Toshiba International Corporation:San Francisco, Houston,VancouverToshiba International CorporationPty. Ltd.: Sydney, MelbourneToshiba International CompanyLimited: London

TOSHIBA TOSHIBA TOSHIBA TOSHIBA

thoshiba power transformer

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