English Trans

12
Contents Page Introduction ....................................... 5/2 Product Range .................................. 5/3 Electrical Design .............................. 5/4 Transformer Loss Evaluation ......... 5/6 Mechanical Design ......................... 5/8 Connection Systems ....................... 5/9 Accessories and Protective Devices ........................ 5/11 Technical Data Distribution Transformers ............ 5/13 Technical Data Power Transformers ...................... 5/18 On-load Tap Changers .................. 5/26 Cast-resin Dry-type Transformers, GEAFOL .................. 5/27 Technical Data GEAFOL Cast-resin Dry-type Transformers .................. 5/31 Special Transformers .................... 5/35 Transformers Transformers 5

description

Trans

Transcript of English Trans

Page 1: English Trans

Contents PageIntroduction ....................................... 5/2

Product Range .................................. 5/3

Electrical Design .............................. 5/4

Transformer Loss Evaluation ......... 5/6

Mechanical Design ......................... 5/8

Connection Systems ....................... 5/9

Accessories andProtective Devices ........................ 5/11

Technical DataDistribution Transformers ............ 5/13

Technical DataPower Transformers ...................... 5/18

On-load Tap Changers .................. 5/26

Cast-resin Dry-typeTransformers, GEAFOL .................. 5/27

Technical DataGEAFOL Cast-resinDry-type Transformers .................. 5/31

Special Transformers .................... 5/35

TransformersTransformers

5Ohne Namen-1 22.09.1999, 16:22 Uhr1

Page 2: English Trans

1

2

3

4

5

6

7

8

9

10

5/2 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

Introduction

In addition, there are various special-purpose transformers such as convertertransformers, which can be both in therange of power transformers and in therange of distribution transformers as faras rated power and rated voltage are con-cerned.As special elements for network stabili-zation, arc-suppression coils and com-pensating reactors are available. Arc-sup-pression coils compensate the capacitivecurrent flowing through a ground fault andthus guarantee uninterrupted energy sup-ply. Compensating reactors compensatethe capacitive power of the cable networksand reduce overvoltages in case of loadrejection; the economic efficiency andstablility of the power transmission are im-proved.The general overview of our manufactur-ing/delivery program is shown in thetable ”Product Range“.

Standards and specifications, general

The transformers comply with the relevantVDE specifications, i.e. DIN VDE 0532”Transformers and reactors“ and the”Technical conditions of supply for three-phase transformers“ issued by VDEWand ZVEI.Therefore they also satisfy the require-ments of IEC Publication 76, Parts 1 to 5together with the standards and specifi-cations (HD and EN) of the EuropeanUnion (EU).Enquiries should be directed to the manu-facturer where other standards and spe-cifications are concerned. Only the US(ANSI/NEMA) and Canadian (CSA) stand-ards differ from IEC by any substantial de-gree. A design according to these stand-ards is also possible.

Important additional standards

■ DIN 42 500, HD 428: oil-immersedthree-phase distribution transformers50–2500 kVA

■ DIN 42 504: oil-immersed three-phasetransformers 2–10 MVA

■ DIN 42 508: oil-immersed three-phasetransformers 12.5–80 MVA

■ DIN 42 523, HD 538: three-phasedry-type transformers 100–2500 kVA

■ DIN 45 635 T30: noise level■ IEC 289: reactance coils and neutral

grounding transformers■ IEC 551: measurement of noise level■ IEC 726: dry-type transformers■ RAL: coating/varnish

Transformers are one of the primarycomponents for the transmission anddistribution of electrical energy.Their design results mainly from the rangeof application, the construction, the ratedpower and the voltage level.The scope of transformer types starts withgenerator transformers and ends with dis-tribution transformers.Transformers which are directly connectedto the generator of the power station arecalled generator transformers. Their powerrange goes up to far above 1000 MVA.Their voltage range extends to approx.1500 kV.The connection between the different high-voltage system levels is made via networktransformers (network interconnectingtransformers). Their power range exceeds1000 MVA. The voltage range exceeds1500 kV.Distribution transformers are within therange from 50 to 2500 kVA and max.36 kV. In the last step, they distributethe electrical energy to the consumersby feeding from the high-voltage into thelow-voltage distribution network. Theseare designed either as liquid-filled or asdry-type transformers.Transformers with a rated power up to2.5 MVA and a voltage up to 36 kV arereferred to as distribution transformers;all transformers of higher ratings areclassified as power transformers.

0.05–2.5

2.5–3000

0.10–20

≤ 36

36–1500

≤ 36

Ratedpower

Max.operatingvoltage

[MVA] [kV]

Oildistributiontransformers

GEAFOL-cast-resintransformers

Powertransformers

5/13–5/17

5/18–5/25

5/27–5/34

Figs.onpage

Fig. 1: Transformer types

Ohne Namen-1 22.09.1999, 16:23 Uhr2

Page 3: English Trans

1

2

3

4

5

6

7

8

9

10

Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition 5/3

Product Range

Above 2.5 MVA up to more than 1000 MVA, above 30 kV up to 1500 kV(system and system interconnecting transformers, with separate windings orauto-connected), with on-load tap changers or off-circuit tap changers,of three- or single-phase design

Generator and powertransformers

50 to 2 500 kVA, highest voltage for equipment up to 36 kV,with copper or aluminum windings, hermetically sealed (TUMETIC®) orwith conservator (TUNORMA®) of three- or single-phase design

Oil-immerseddistribution transformers,TUMETIC, TUNORMA

Buchholz relays, oil testing equipment,oil flow indicators and other monitoring devicesFan control cabinets, control cabinets for parallel operation andautomatic voltage controlSensors (PTC, Pt 100)

Accessories

Advisory services for transformer specificationsOrganization, coordination and supervision of transportationSupervision of assembly and commissioningService/inspection troubleshooting servicesTraining of customer personnelInvestigation and assessment of oil problems

Service

Furnace and converter transformersTraction transformers mounted on rolling stock and appropriate on-load tap-changersSubstation transformers for traction systemsTransformers for train heating and point heatingTransformers for HVDC transmission systemsTransformers for audio frequencies in power supply systemsThree-phase neutral electromagnetic couplers and grounding transformersIgnition transformers

Special transformersfor industry, tractionand HVDC transmissionsystems

100 kVA to more than 20 MVA, highest voltage for equipment up to 36 kV,of three- or single-phase designGEAFOL®-SL substations

Cast-resin distributionand power transformersGEAFOL

Liquid-immersed shunt and current-limiting reactors up tothe highest rated powersReactors for HVDC transmission systems

Reactors

Fig. 2

Ohne Namen-1 22.09.1999, 16:23 Uhr3

Page 4: English Trans

1

2

3

4

5

6

7

8

9

10

5/4 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

Dy1

iii

Dy5

Dy11

Yd1

Yd5

Yd11

ii

i

III II

I1

iiiii

iIII II

I

5

iiiii

i

III II

I11

iii

iii

III II

I11

iiiii

iIII II

I

5

iii

ii

i

III II

I1

Electrical Design

Power ratings and type of cooling

All power ratings in this guide are the pro-duct of rated voltage (times phase-factorfor three-phase transformers) and ratedcurrent of the line side winding (at centertap, if several taps are provided), expres-sed in kVA or MVA, as defined in IEC 76-1.If only one power rating and no coolingmethod are shown, natural oil-air cooling(ONAN or OA) is implied for oil-immersedtransformers. If two ratings are shown,forced-air cooling (ONAF or FA) in one ortwo steps is applicable.For cast resin transformers, natural aircooling (AN) is standard. Forced air cooling(AF) is also applicable.

Temperature rise

In accordance with IEC-76 the standardtemperature rise for oil-immersed powerand distribution transformers is:■ 65 K average winding temperature

(measured by the resistance method)■ 60 K top oil temperature

(measured by thermometer)The standard temperature rise for Siemenscast-resin transformers is■ 100 K (insulation class F) at HV and

LV winding.Whereby the standard ambient tempera-tures are defined as follows:■ 40 °C maximum temperature,■ 30 °C average on any one day,■ 20 °C average in any one year,■ –25 °C lowest temperature outdoors,■ –5 °C lowest temperature indoors.Higher ambient temperatures require acorresponding reduction in temperaturerise, and thus affect price or rated poweras follows:■ 1.5% surcharge for each 1 K above

standard temperature conditions, or■ 1.0% reduction of rated power for each

1 K above standard temperature condi-tions.

These adjustment factors are applicableup to 15 K above standard temperatureconditions.

Altitude of installation

The transformers are suitable for operationat altitudes up to 1000 meters above sealevel. Site altitudes above 1000 m necessi-tate the use of special designs and an in-crease/or a reduction of the transformerratings as follows (approximate values):

The primary winding (HV) is normallyconnected in delta, the secondary winding(LV) in wye. The electrical offset of thewindings in respect to each other is either30, 150 or 330 degrees standard (Dy1,Dy5, Dy11). Other vector groups aswell as single-phase transformers andautotransformers on request (Fig. 3).

Power transformers

Generator transformers and large powertransformers are usually connected in Yd.For HV windings higher than 110 kV, theneutral has a reduced insulation level.For star/star-connected transformers andautotransformers normally a tertiary wind-ing in delta, whose rating is a third of thatof the transformer, has to be added. Thisstabilizes the phase-to phase voltages inthe case of an unbalanced load and pre-vents the displacement of the neutralpoint.Single-phase transformers and autotrans-formers are used when the transportationpossibilities are limited. They will be con-nected at site to three-phase transformerbanks.

■ 2% increase for every 500 m altitude (orpart there of) in excess of 1000 m, or

■ 2% reduction of rated power for each500 m altitude (or part there of) in ex-cess of 1000 m.

Transformer losses and efficiencies

Losses and efficiencies stated in this guideare average values for guidance only. Theyare applicable if no loss evaluation figure isstated in the inquiry (see following chapter)and they are subject to the tolerances stat-ed in IEC 76-1, namely +10% of the totallosses, or +15% of each component loss,provided that the tolerance for the totallosses is not exceeded.If optimized and/or guaranteed losses with-out tolerances are required, this must bestated in the inquiry.

Connections and vector groups

Distribution transformers

The transformers listed in this guide areall three-phase transformers with one setof windings connected in star (wye) andthe other one in delta, whereby the neutralof the star-connected winding is fully ratedand brought to the outside.

Fig. 3: Most commonly used vector groups

Ohne Namen-1 22.09.1999, 16:23 Uhr4

Page 5: English Trans

1

2

3

4

5

6

7

8

9

10

Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition 5/5

Electrical Design

≤ 1.1

3.6

7.2

12.0

17.5

24.0

36.0

52.0

72.5

123.0

145.0

170.0

245.0

Highestvoltagefor equip-ment Um(r. m. s.)

[kV]

Ratedshort-durationpower-frequencywithstandvoltage(r. m. s.)

[kV]

Rated lightning-impulse with-stand voltage(peak)

List 1[kV]

List 2[kV]

3

10

20

28

38

50

70

95

140

185

230

275

325

360

395

20

40

60

75

95

145

40

60

75

95

125

170

250

325

450

550

650

750

850

950

Higher test voltage withstand requirements must bestated in the inquiry and may result in a higher price.

Fig. 4: Insulation level

Insulation level

Power-frequency withstand voltages andlightning-impulse withstand voltages are inaccordance with IEC 76-3, Para. 5, Table II,as follows:

Conversion to 60 Hz – possibilities

All ratings in the selection tables of thisguide are based on 50 Hz operation.For 60 Hz operation, the following optionsapply:■ 1. Rated power and impedance voltage

are increased by 10%, all other parame-ters remain identical.

■ 2. Rated power increases by 20%, butno-load losses increase by 30% andnoise level increases by 3 dB, all otherparameters remain identical (this lay-out is not possible for cast-resin trans-formers).

■ 3. All technical data remain identical,price is reduced by 5%.

■ 4. Temperature rise is reduced by 10 K,load losses are reduced by 15%, allother parameters remain identical.

Overloading

Overloading of Siemens transformers isguided by the relevant IEC-354 ”Loadingguide for oil-immersed transformers“and the (similar) ANSI C57.92 ”Guide forloading mineral-oil-immersed power trans-formers“.Overloading of GEAFOL cast-resin trans-formers on request.

Routine and special tests

All transformers are subjected to thefollowing routine tests in the factory:■ Measurement of winding resistance■ Measurement of voltage ratio and check

of polarity or vector group■ Measurement of impedance voltage■ Measurement of load loss■ Measurement of no-load loss and

no-load current■ Induced overvoltage withstand test■ Seperate-source voltage withstand test■ Partial discharge test (only GEAFOL

cast-resin transformers).The following special tests are optional andmust be specified in the inquiry:■ Lightning-impulse voltage test (LI test),

full-wave and chopped-wave (specify)■ Partial discharge test■ Heat-run test at natural or forced cooling

(specify)■ Noise level test■ Short-circuit test.Test certificates are issued for all theabove tests on request.

Transformer cell (indoor installation)

The transformer cell must have the neces-sary electrical clearances when an open airconnection is used. The ventilation systemmust be large enough to fulfill the recom-mendations for the maximum tempera-tures according to IEC.For larger power transformers either anoil/water cooling system has to be used orthe oil/air cooler (radiator bank) has to beinstalled outside the transformer cell.In these cases a ventilation system hasto be installed also to remove the heatcaused by the convection of the transform-er tank.

Ohne Namen-1 22.09.1999, 16:23 Uhr5

Page 6: English Trans

1

2

3

4

5

6

7

8

9

10

5/6 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

q = p100

+ 1

A. Capital cost

B. Cost of no-load loss

C. Cost of load loss

D. Cost resulting from demands charges

Cc =Cp · r

100

= purchase price

= depreciation factor

= interest factor

= interest rate in % p.a.= depreciation period in years

Cp

r = p · qn

qn – 1

pn

CP0 = Ce · 8760 h/year · P0

= energy charges

= no-load loss [kW]

Ce

P0

amountkWh

CPk = Ce · 8760 h/year · α2 · Pk

amountyear

amountyear

amountyear

α

Pk

=

= copper loss [kW]

constant operation loadrated load

CD =amount

yearCd (P0 + Pk)

Cd = demand charges amountkW · year

Transformer Loss Evaluation

The sharply increased cost of electricalenergy has made it almost mandatory forbuyers of electrical machinery to carefullyevaluate the inherent losses of theseitems. In case of distribution and powertransformers, which operate continuouslyand most frequently in loaded condition,this is especially important. As an example,the added cost of loss-optimized trans-formers can in most cases be recoveredvia savings in energy use in less than threeyears.Low-loss transformers use more andbetter materials for their construction andthus initially cost more. By stipulating lossevaluation figures in the transformer in-quiry, the manufacturer receives the nec-essary incentive to provide a loss-opti-mized transformer rather than the low-cost model.Detailed loss evaluation methods fortransformers have been developed andare described accurately in the literature,taking the project-specific evaluation fac-tors of a given customer into account.The following simplified method for a quickevaluation of different quoted transformerlosses is given, making the following as-sumptions:■ The transformers are operated con-

tinuously■ The transformers operate at partial load,

but this partial load is constant■ Additional cost and inflation factors are

not considered■ Demand charges are based on 100%

load.The total cost of owning and operating atransformer for one year is thus defined asfollows:■ A. Capital cost Cc

taking into account the purchase priceCp, the interest rate p, and the depre-ciation period n

■ B. Cost of no-load loss CP0,based on the no-load loss P0, andenergy cost Ce

■ C. Cost of load loss Cpk,based on the copper loss Pk, the equi-valent annual load factor a, and energycost Ce

■ D. Demand charges Cd,based on the amount set by the utility,and the total kW of connected load.

These individual costs are calculated asfollows:

Fig. 5

Ohne Namen-1 22.09.1999, 16:23 Uhr6

Page 7: English Trans

1

2

3

4

5

6

7

8

9

10

Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition 5/7

Transformer Loss Evaluation

To demonstrate the usefulness of suchcalculations, the following arbitrary exam-ples are shown, using factors that canbe considered typical in Germany, andneglecting the effects of inflation on therate assumed:

A. Low-cost transformer B. Loss-optimized transformer

Depreciation periodInterest rateEnergy charge

Demand charge

Equivalent annual load factor

npCe

Cd

α

= 20 years= 12% p. a.= 0.25 DM/kWh

= 350

= 0.8

DMkW · yr

P0 = 2.6 kWPk = 20 kWCp = DM 25 000

P0 = 1.7 kWPk = 17 kWCp = DM 28 000

no-load lossload losspurchase price

no-load lossload losspurchase price

Cc25000 · 13.39

100

DM 3348/year

CP0 0.25 · 8760 · 2.6

DM 5694/year=

=

=

=

CPk 0.25 · 8760 · 0.64 · 20

DM 28 032/year=

=

CD 350 · (2.6 + 20)

DM 7910/year=

=

Total cost of owning and operating thistransformer is thus:

DM 44984.–/year

Cc28000 · 13.39

100

DM 3 749/year

CP0 0.25 · 8760 · 1.7

DM 3 723/year=

=

=

=

CPk 0.25 · 8760 · 0.64 · 17

DM 23 827/year=

=

CD 350 · (1.7 + 17)

DM 6 545/year=

=

Total cost of owning and operating thistransformer is thus:

DM 37 844.–/year

The energy saving of the optimized distribution transformer of DM 7140 per yearpays for the increased purchase price in less than one year.

Example: 1600 kVA distribution transformer

Depreciation factorr = 13.39

Fig. 6

Ohne Namen-1 22.09.1999, 16:23 Uhr7

Page 8: English Trans

1

2

3

4

5

6

7

8

9

10

5/8 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

Mechanical Design

Fig. 9: Practically maintenancefree: transformer withthe TUPROTECT air-sealing system built into the con-servator

General mechanical designfor oil-immersed transformers:

■ Iron core made of grain-orientedelectrical sheet steel insulated on bothsides, core-type.

■ Windings consisting of copper sectionwire or copper strip. The insulationhas a high disruptive strength and istemperature-resistant, thus guaranteeinga long service life.

■ Designed to withstand short circuit forat least 2 seconds (IEC).

■ Oil-filled tank designed as tank withstrong corrugated walls or as radiatortank.

■ Transformer base with plain or flangedwheels (skid base available).

■ Cooling/insulation liquid: Mineral oilaccording to VDE 0370/IEC 296. Siliconeoil or synthetic liquids are available.

■ Standard coating for indoor installation.Coatings for outdoor installation andfor special applications (e.g. aggressiveatmosphere) are available.

Tank design andoil preservation system

Sealed-tank distribution transformers,TUMETIC®

In ratings up to 2500 kVA and 170 kV LIthis is the standard sealed-tank distributiontransformer without conservator and gascushion. The TUMETIC transformer isalways completely filled with oil; oil expan-sion is taken up by the flexible corrugatedsteel tank (variable volume tank design),whereby the maximum operating pressureremains at only a fraction of the usual.These transformers are always shippedcompletely filled with oil and sealed fortheir lifetime. Bushings can be exchangedfrom the outside without draining the oilbelow the top of the active part.The hermetically sealed system preventsoxygen, nitrogen, or humidity from contactwith the insulating oil. This improves theaging properties of the oil to the extentthat no maintenance is required on thesetransformers for their lifetime. Generallythe TUMETIC transformer is lower thanthe TUNORMA transformer. This designhas been in successful service since 1973.A special TUMETIC-Protection device hasbeen developed for this transformer.

Distribution transformers withconservator, TUNORMA®

This is the standard distribution transform-er design in all ratings. The oil level in thetank and the top-mounted bushings is keptconstant by a conservator vessel or expan-sion tank mounted at the highest point ofthe transformer. Oil-level changes due tothermal cycling affect the conservator only.The ambient air is prevented from directcontact with the insulating oil through oil-traps and dehydrating breathers.Tanks from 50 to approximately 4000 kVAare preferably of the corrugated steel de-sign, whereby the sidewalls are formed onautomatic machines into integral coolingpockets. Suitable spot welds and bracesrender the required mechanical stability.Tank bottom and cover are fabricated fromrolled and welded steel plate.Conventional radiators are available.

Power transformers

Power transformers of all ratings areequipped with conservators. Both the openand closed system are available.With the closed system ”TUPROTECT®“the oil does not come into contact with thesurrounding air. The oil expansion is com-pensated with an air bag. (This design isalso available for greater distribution trans-formers on request).The sealing bag consists of strong nylonbraid with a special double lining of ozoneand oil-resistant nitrile rubber. The interiorof this bag is in contact with the ambientair through a dehydrating breather;the outside of this bag is in direct contactwith the oil.All tanks, radiators and conservators(incl. conservator with airbag) are designedfor vacuum filling of the oil.For transformers with on-load tap changersa seperate smaller conservator is neces-sary for the diverter switch compartment.This seperate conservator (without air bag)is normally an integrated part of the mainconservator with its own magnetic oil levelindicator.Power transformers up to 10 MVA arefitted with weld-on radiators and areshipped extensively assembled; shippingconditions permitting.Ratings above 10 MVA require detachableradiators with individual butterfly valves,and partial dismantling of components forshipment.All the usual fittings and accessories for oiltreatment, shipping and installation ofthese transformers are provided as stand-ard. For monitoring and protective devices,see the listing on page 5/11.

Fig. 8: 630 kVA, three-phase, TUNORMA20 kV ± 2.5 %/0.4 kV distribution transformer

Fig. 7: Cross section of a TUMETIC three-phasedistribution transformer

Ohne Namen-1 22.09.1999, 16:23 Uhr8

Page 9: English Trans

1

2

3

4

5

6

7

8

9

10

Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition 5/9

Connection Systems

Distribution transformers

All Siemens transformers have top-mount-ed HV and LV bushings according to DIN intheir standard version. Besides the openbushing arrangement for direct connectionof bare or insulated wires, three basic insu-lated termination systems are available:

Fully enclosed terminal box for cables(Fig. 11)

Available for either HV or LV side, or forboth. Horizontally split design in degreeof protection IP 44 or IP 54. (Totally en-closed and fully protected against contactwith live parts, plus protection against drip,splash, or spray water.)Cable installation through split cable glandsand removable plates facing diagonallydownwards. Optional conduit hubs. Suit-able for single-core or three-phase cableswith solid dielectric insulation, with orwithout stress cones. Multiple cables perphase are terminated on auxiliary busstructures attached to the bushings. Re-moval of transformer by simply bendingback the cables.

Insulated plug connectors (Fig. 12)

For substation installations, suitableHV can be attached via insulatedelbow connectors in LI ratings up to170 kV.

Flange connection (Fig. 13)

Air-insulated bus ducts, insulated busbars,or throat-connected switchgear cubiclesare connected via standardized flanges onsteel terminal enclosures. These can ac-commodate either HV, LV, or both bush-ings. Fiberglass-reinforced epoxy partitionsare available between HV and LV bushingsif flange/flange arrangements are chosen.The following combinations of connectionsystems are possible besides open bush-ing arrangements:

Cable box

Cable box

Flange

Flange

Elbow connector

Elbow connector

HV

Cable box

Flange/throat

Cable box

Flange/throat

Cable box

Flange/throat

LV

Fig 13: Flange connection for switchgear and bus ductsFig. 10: Combination of connection systems

Fig. 11: Fully enclosed cable connection box

Fig. 12: Grounded metal-elbow plug connectors

Ohne Namen-1 22.09.1999, 16:23 Uhr9

Page 10: English Trans

1

2

3

4

5

6

7

8

9

10

5/10 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

Connection Systems

Power transformers

The most frequently used type of connec-tion for transformers is the outdoor bush-ing.Depending on voltage, current, systemconditions and transport requirements, thetransformers will be supplied with bush-ings arranged vertically, horizontally or in-clined. Up to about 110 kV it is usual touse oil-filled bushings according to DIN;condenser bushings are normally used forhigher voltages.Limited space or other design considera-tions often make it necessary to connectcables directly to the transformer. For volt-ages up to 30 kV air-filled cable boxes areused. For higher voltages the boxes areoil-filled. They may be attached to the tankcover or to its walls (Fig. 14).The space-saving design of SF6-insulatedswitchgear is one of its major advantages.The substation transformer is connecteddirectly to the SF6 switchgear. This elimi-nates the need for an intermediate link(cable, overhead line) between transform-er and system (Fig. 15).

Fig. 14: Transformers with oil-filled HV cable boxes

Fig. 15: Direct SF6-connection of the transformer to the switchgear

Ohne Namen-1 22.09.1999, 16:23 Uhr10

Page 11: English Trans

1

2

3

4

5

6

7

8

9

10

Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition 5/11

Accessories and Protective DevicesAccessories not listed completely.Deviations are possible.

Fig. 16: Double-float Buchholz relay

Fig. 17: Dial-type contact thermometer

Double-float Buchholz relay (Fig. 16)

For sudden pressure rise and gas detec-tion in oil-immersed transformer tanks withconservator. Installed in the connectingpipe between tank and conservator andresponding to internal arcing faults andslow decomposition of insulating materials.Additionally, backup function of oil alarm.The relay is actuated either by pressurewaves or gas accumulation, or by loss ofoil below the relay level. Seperate contactsare installed for alarm and tripping.In case of a gas accumulation alarm, gassamples can be drawn directly at the relaywith a small chemical testing kit. Discolor-ing of two liquids indicates either arcing by-products or insulation decomposition prod-ucts in the oil. No change in color indicatesan air bubble.

Dial-type contact thermometer (Fig. 17)

Indicates actual top-oil temperature viacapillary tube. Sensor mounted in well intank cover. Up to four separately adjust-able alarm contacts and one maximumpointer are available. Installed to be read-able from the ground.With the addition of a CT-fed thermal re-plica circuit, the simulated hot-spot wind-ing temperature of one or more phasescan be indicated on identical thermo-meters. These instruments can also beused to control forced cooling equipment.

Magnetic oil-level indicator (Fig. 18)

The float position inside of the conservatoris transmitted magnetically through thetank wall to the indicator to preserve thetank sealing standard device without con-tacts; devices supplied with limit (position)switches for high- and low-level alarm areavailable. Readable from the ground.

Fig. 18: Magnetic oil-level indicator

Ohne Namen-1 22.09.1999, 16:23 Uhr11

Page 12: English Trans

1

2

3

4

5

6

7

8

9

10

5/12 Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition

Accessories and Protective Devices

Protective device (Fig. 19) for hermeti-cally sealed transformers (TUMETIC)

For use on hermetically sealed TUMETICdistribution transformers. Gives alarmupon loss of oil and gas accumulation.Mounted directly at the (permanentlysealed) filler pipe of these transformers.

Pressure relief device (Fig. 20)

Relieves abnormally high internal pressureshock waves. Easily visible operationpointer and alarm contact. Reseals posi-tively after operation and continues tofunction without operator action.

Dehydrating breather (Fig. 21, 22)

A dehydrating breather removes most ofthe moisture from the air which is drawninto the conservator as the transformercools down. The absence of moisture inthe air largely eliminates any reduction inthe breakdown strength of the insulationand prevents any buildup of condensationin the conservator. Therefore, the dehy-drating breather contributes to safe andreliable operation of the transformer.

Bushing current transformer

Up to three ring-type current transformersper phase can be installed in power trans-formers on the upper and lower voltageside. These multiratio CTs are supplied inall common accuracy and burden ratingsfor metering and protection. Their second-ary terminals are brought out to short-circuiting-type terminal blocks in watertightterminal boxes.

Additional accessories

Besides the standard accessories and pro-tective devices there are additional itemsavailable, especially for large power trans-formers. They will be offered and installedon request.Examples are:■ Fiber-optic temperature measurements■ Permanent gas-in-oil analysis■ Permanent water-content measurement■ Sudden pressure rise relay,etc.

Fig. 20: Pressure relief device with alarm contact andautomatic resetting

Fig. 19: Protective device for hermetically sealedtransformers (TUMETIC)

Fig. 21: Dehydrating breather A DIN 42 567up to 5 MVA

Fig. 22: Dehydrating breather L DIN 42 562over 5 MVA

Ohne Namen-1 22.09.1999, 16:23 Uhr12