Power Transformers10 to 100 MVA

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Transformer technologyat a glance

An extensive transmission system

with efficient transformers is indis-

pensable to ensure a reliable supply

of power. Consequently Siemens

will be found wherever

networks are being ex-

panded, updated or

established for the

first time.

All over the world,

power transformers

from Nuremberg

enjoy a great

reputation. What the

Nuremberg plant

manufactures

reflects today's

state of the art and

testifies to the

highest levels of

quality and

reliability. Our quality

management system is certified

to DIN ISO 9001, the world's most

stringent standard. Our accredited

test laboratories likewise meet the

latest specification.

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Components

Three-limb core

LV winding

HV winding

Tapped winding

Tap leads

LV bushings

HV bushings

Clamping frame

On-load tap changer

Motor drive

Tank

Conservator

Radiators

View into a 40-MVAnetwork transformer:

Voltage ratio:110 ± 16% / 21 kVVector group: YN d5Type of cooling: ONAN

In the 10 to 100 MVA ratedpower range, the mostcommon voltage ratio is from110 to 132 kV to 30, 20 or10 kV. These transformershave off-load or on-load tapchangers to adapt them tonetwork conditions.

We manufacture these unitsto VDE 0532, IEC 76 or tonational specifications. Weoffer individual solutions toproblems satisfying all therequirements with respect totype of operations, low noiseand low losses, connectiontechnology, type of cooling,transportation and installation.

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Iron core

Rapid and precise stacking of corelaminations on special stands:

The joints are step-lapped.

Computer-controlled longitudinaland cross-cutting equipment:

These are capable of cutting sheetsflexibly, without burr or bending, intotheir final shape.

Step-lapped core:

The best way to keep noise and losseslow.

Core of a 24-MVA transformer:

The cross-sections of the bolt-freelimbs are finely graded and arepractically circular in shape.

Transformers are of the coretype. Core limbs – wound andnon-wound – are arranged inone plane and connected byyokes.

As required by the loss eval-uation and the customer'snoise-emission requirements,0.3 mm and 0.23 mm thickHi-B laminations are used,which may also be laser orplasma-treated.

Step-lap stacking has provedto be the best technique andis standard in our company.

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Windings

Careful treatment is particularlyimportant:

The windings are subsequentlytested, pressed and dried.

For high voltages Um <= 145 kV,layer windings made of paper-insulated transposed copperconductors are preferred.

Low-voltage and high-voltagewindings as also the tapwindings, are wound on topof one another to form a com-pact integrated system.

The advantages: high short-circuit strength, compactdimensions, few solderedjoints.

The cylindrical windings arearranged concentrically andseparated by axial oil ducts.

Transposed conductors reducestray losses in the windings:

These consist of a number ofvarnish-insulated transposed flatconductors.

Winding benches for layer windings:

The insulated conductors are woundin layers under constant pressure andtension.

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Voltage variation

The on-load tap changer has amotor-drive mechanism:

It is mounted on the tank andconnected to the tap changer via abevel gear.

Drum-type no-load tap changer:

This is used for adjustment of thevoltage ratio when the transformer isde-energized.

On-load tap changer for large trans-formers:

Here, tap selector and diverter switchare separate and arranged on top ofone another. The oil in the diverterswitch compartment is kept apartfrom the transformer oil.

In order to adapt the voltageratio to the requirements ofthe system, the transformerhas a special winding withtappings. The voltage ratiocan thus be changed eitherby a no-load tap changer afterswitching off the transformer,or under load with an on-loadtap changer.

Motor drives are available foroperating the on-load tapchangers. These can be con-trolled either locally or by re-mote control. No-load tapchangers are normally setmanually.

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Tank

Perfect protection againstcorrosions is in demand:

The tanks are treated in the steel gritblasting chamber and are given theiranti-corrosive finish in the spray booth.If, additionally, galvanizing is alsorequired, we apply a standard zincdust paint coating.

View of the welding line:

This is where the tank segments arejoined together by submerged-arcwelding – mostly automatically.

The modern Surface-TreatmentCentre:

The tanks are given their finish in thesteel grit blasting chamber and thevarnishing chambers.

In addition to the core andwinding, the tank is the thirdmain component of a trans-former. It accommodates thecore-and-coil assembly andthe oil filling, often weighingseveral hundred tonnes. Thiscalls for a statically secureand oil-leak-proof design, withthe weight optimized.

The tank parts are made ofblast-cleaned steel plates upto 30 mm thick. These platesare first put together to formsegments and then weldedoil-tight to form the tank.

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Assembling the components

The heart of the transformer – thecore-and-coil assembly – is put to-gether out of the various compo-nents:

The assembly team on the workingplatforms is always at the right height.These platforms have motor drives toadjust their height.

The quality of manufacture is as-sured from materials ordering totransformer delivery to the cus-tomer:

The final mechanical and electricalcheck of the finished product is aparticularly important phase.

The last step of manufacturing:

The core-and-coil assembly, driedunder vacuum at 135 °C in the vapour-phase plant, is inserted into the tank.

In the preassembly shop, thecore-and-coil assembly of thetransformer is put togetherfrom the core, windings,clamping devices, on-load tapchanger and the leads.

After the dried core-and-coilassembly has been insertedinto the tank, the transformeris evacuated and filled withtransformer oil. Then acces-sories like motor drive, controlcabinets, bushings, monitor-ing devices, etc. are attachedto the tank.

Before the transformer leavesthe factory, it is subjected toexhaustive final testing in thetest bay.

Cooling

Conservators for open or closedsystems are available:

With the closed TUPROTECT®

system, the oil does not come intocontact with the surrounding air.The oil expansion is compen-sated by an air bag.

Better heat dissipation:

Additional, temperature-controlledfans providing vertical air flow tocool the radiators.

For particularly low-noiseinstallations:

Enclosed transformers withseparate radiator banksoutdoors.

Water as the external coolant:

Oil-to-water coolers are attachedto the transformer.

The efficiency of the coolingis a crucial factor determiningthe operational safety and thelife span of a transformer.

The type most frequentlyused is ONAN (natural) cool-ing. The heat loss is absorbedby the transformer oil and giv-en off to the surrounding airvia radiators. With ONAF cool-ing the radiators are addition-ally cooled by fans. The cool-ing system may also consistof separate radiator banks, orwater coolers.

Types of cooling:

a natural air cooling with radiators (ONAN)b radiators additionally cooled by fans (ONAF)c cooling by separate radiator banksd water instead of air as cooling medium.

a b

c d

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Operating worldwide

Electric power is generated andimmediately consumed here:

Numerous transformers are in opera-tion in Jeddah's industrial area. Theillustration shows 73-MVA generatortransformers.

Our Company's experiencein the transformer field goesback one hundred years.Tens of thousands of instal-lations are equipped withour transformers. Their tech-nology, quality and reliabilityare appreciated around theglobe.

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Siemens‘ good reputation hasspread to Latin America too:

10-MVA transformers in a Venezuelansubstation.

Particularly environmentallyacceptable:

This 25-MVA network transformerin a south German substation hasan exceptionally low sound pressurelevel: 36 dB (A).

In Switzerland:Two 40-MVA transformers withseparate radiator banks for theBurgdorf substation.

A transformer for the desert:

Wide temperature fluctuations, sand-storms. No problem. Siemens tech-nology is good for decades.

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An 80-tonne crate for Pennsylvania,USA:

Its contents: a 43-MVA transformer,made in Germany.

In Africa too:

The distribution of electric energyvia Siemens transformers. 15 and30-MVA units in Nigeria.

Tailor-made for narrow space:

Where space is scarce thetransformer is being tailor-made.The illustration shows a 73-MVAgenerator transformer.

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15m below ground:

These two 40-MVA powertransformers (on the left)are situated 15 m belowground in the town of St. Gall,Switzerland. In 1996, a mobilecrane was required for preciseinstallation of the two 72-tonnedevices (on the right). Anadditional feature of thesetransformers: their dissipatedheat is used to heat thesurrounding buildings.

In Germany:

The likelihood that the powerfrom the socket is delivered bya Siemens transformer is par-ticularly high in this country.

One customer requirement:

A colored transformer designfor an environmentally friendlypower station in SouthGermany.

Siemens AGPower Transmission andDistribution GroupTransformers DivisionKatzwanger Strasse 150D-90461 Nurembergwww.ev.siemens.de

Powerto the

Siemens Aktiengesellschaft Subject to change without prior notice Order-Nr. E50001-U420-A22-X-7600Printed in GermanyDispo-Stelle 1920061D6317 Ra/Br 101744 PA 04003.