Transformers - Tekhar

Electrical DesignInsulation levelPower-frequency withstand voltages andlightning-impulse withstand voltages are inaccordance with IEC 76-3, Para. 5, Table II,as follows:Highestvoltagefor equipment Um(r. m. s.)[kV] 1.1Rated lightningimpulse withstand tandvoltage(r. m. s.)List 1[kV][kV]3List 2[kV]–Conversion to 60 Hz – possibilitiesAll 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 voltageare increased by 10%, all other parameters 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 layout is not possible for cast-resin transformers). 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.Transformer cell (indoor installation)The transformer cell must have the necessary electrical clearances when an open airconnection is used. The ventilation systemmust be large enough to fulfill the recommendations for the maximum temperatures 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 transformer ading 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 transformers“.Overloading of GEAFOL cast-resin transformers on request.56Routine and special tests145.0170.0245.0All transformers are subjected to thefollowing routine tests in the factory: Measurement of winding resistance Measurement of voltage ratio and checkof polarity or vector group Measurement of impedance voltage Measurement of load loss Measurement of no-load loss andno-load current Induced overvoltage withstand test Seperate-source voltage withstand test Partial discharge test (only GEAFOLcast-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.78910Higher test voltage withstand requirements must bestated in the inquiry and may result in a higher price.Fig. 4: Insulation level5/5Siemens Power Engineering Guide · Transmission and Distribution · 4th EditionOhne Namen-1522.09.1999, 16:23 Uhr

Transformer Loss Evaluation12345678910The 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 transformers 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 inquiry, the manufacturer receives the necessary incentive to provide a loss-optimized transformer rather than the lowcost model.Detailed loss evaluation methods fortransformers have been developed andare described accurately in the literature,taking the project-specific evaluation factors of a given customer into account.The following simplified method for a quickevaluation of different quoted transformerlosses is given, making the following assumptions: The transformers are operated continuously The transformers operate at partial load,but this partial load is constant Additional cost and inflation factors arenot 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 Cctaking into account the purchase priceCp, the interest rate p, and the depreciation 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 equivalent 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:A. Capital costCc CpCp · ramountyear100 purchase pricep · qn depreciation factorqn – 1pq 1 interest factor100r pn interest rate in % p.a. depreciation periodin yearsB. Cost of no-load lossCP0 Ce · 8760 h/year · P0Ce energy chargesP0 no-load loss [kW]amountyearamountkWhC. Cost of load lossCPk Ce · 8760 h/year · α2 · Pkamountyearconstant operation loadrated loadα Pk copper loss [kW]D. Cost resulting from demands chargesCD Cd (P0 Pk)Cdamountyear demand chargesamountkW · yearFig. 55/6Ohne Namen-1Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition622.09.1999, 16:23 Uhr

Transformer Loss EvaluationTo demonstrate the usefulness of suchcalculations, the following arbitrary examples are shown, using factors that canbe considered typical in Germany, andneglecting the effects of inflation on therate assumed:12Example: 1600 kVA distribution transformerDepreciation periodInterest rateEnergy chargen 20 yearsDepreciation factorp 12% p. a.r 13.39Ce 0.25 DM/kWhDemand chargeCd 350Equivalent annual load factorαA. Low-cost transformerP0 2.6 kWPk 20 kWCp DM 25 0003DMkW · yr4 0.8B. Loss-optimized transformerno-load lossload losspurchase priceCc 25000 · 13.39100P0 1.7 kWPk 17 kWCp DM 28 0005no-load lossload losspurchase price6Cc 28000 · 13.39100 DM 3348/year DM 3 749/yearCP0 0.25 · 8760 · 2.6 DM 5694/yearCP0 0.25 · 8760 · 1.7 DM 3 723/yearCPk 0.25 · 8760 · 0.64 · 20 DM 28 032/yearCPk 0.25 · 8760 · 0.64 · 17 DM 23 827/yearCD 350 · (2.6 20) DM 7910/yearCD 350 · (1.7 17) DM 6 545/yearTotal cost of owning and operating thistransformer is thus:Total cost of owning and operating thistransformer is thus:789DM 44 984.–/yearDM 37 844.–/year10The energy saving of the optimized distribution transformer of DM 7140 per yearpays for the increased purchase price in less than one year.Fig. 65/7Siemens Power Engineering Guide · Transmission and Distribution · 4th EditionOhne Namen-1722.09.1999, 16:23 Uhr

Mechanical Design1General mechanical designfor oil-immersed transformers: Iron core made of grain-oriented2 3 4 5678910electrical 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 systemSealed-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 expansion 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.5/8Ohne Namen-1Distribution transformers withconservator, TUNORMA This is the standard distribution transformer design in all ratings. The oil level in thetank and the top-mounted bushings is keptconstant by a conservator vessel or expansion 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 oiltraps and dehydrating breathers.Tanks from 50 to approximately 4000 kVAare preferably of the corrugated steel design, 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 transformersPower 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 compensated with an air bag. (This design isalso available for greater distribution transformers 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 necessary 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 standard. For monitoring and protective devices,see the listing on page 5/11.Fig. 7: Cross section of a TUMETIC three-phasedistribution transformerFig. 8: 630 kVA, three-phase, TUNORMA20 kV 2.5 %/0.4 kV distribution transformerFig. 9: Practically maintenancefree: transformer withthe TUPROTECT air-sealing system built into the conservatorSiemens Power Engineering Guide · Transmission and Distribution · 4th Edition822.09.1999, 16:23 Uhr

Connection SystemsDistribution transformers1All Siemens transformers have top-mounted HV and LV bushings according to DIN intheir standard version. Besides the openbushing arrangement for direct connectionof bare or insulated wires, three basic insulated termination systems are available:2Fully 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 enclosed 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. Suitable 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. Removal of transformer by simply bendingback the cables.34Fig. 11: Fully enclosed cable connection box56Insulated plug connectors (Fig. 12)For substation installations, suitableHV can be attached via insulatedelbow connectors in LI ratings up to170 kV.7Flange connection (Fig. 13)Air-insulated bus ducts, insulated busbars,or throat-connected switchgear cubiclesare connected via standardized flanges onsteel terminal enclosures. These can accommodate either HV, LV, or both bushings. Fiberglass-reinforced epoxy partitionsare available between HV and LV bushingsif flange/flange arrangements are chosen.The following combinations of connectionsystems are possible besides open bushing arrangements:HVLVCable boxCable boxCable boxFlange/throatFlangeCable boxFlangeFlange/throatElbow connectorCable boxElbow connectorFlange/throatFig. 10: Combination of connection systems8Fig. 12: Grounded metal-elbow plug connectors910Fig 13: Flange connection for switchgear and bus ducts5/9Siemens Power Engineering Guide · Transmission and Distribution · 4th EditionOhne Namen-1922.09.1999, 16:23 Uhr

Connection SystemsPower transformers12345The most frequently used type of connection for transformers is the outdoor bushing.Depending on voltage, current, systemconditions and transport requirements, thetransformers will be supplied with bushings arranged vertically, horizontally or inclined. 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 considerations often make it necessary to connectcables directly to the transformer. For voltages 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 eliminates the need for an intermediate link(cable, overhead line) between transformer and system (Fig. 15).6Fig. 14: Transformers with oil-filled HV cable boxes78910Fig. 15: Direct SF6-connection of the transformer to the switchgear5/10Ohne Namen-1Siemens Power Engineering Guide · Transmission and Distribution · 4th Edition1022.09.1999, 16:23 Uhr

Accessories and Protective DevicesAccessories not listed completely.Deviations are possible.Double-float Buchholz relay (Fig. 16)For sudden pressure rise and gas detection 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. Discoloring of two liquids indicates either arcing byproducts or insulation decomposition products in the oil. No change in color indicatesan air bubble.1234Fig. 16: Double-float Buchholz relayDial-type contact thermometer (Fig. 17)Indicates actual top-oil temperature viacapillary tube. Sensor mounted in well intank cover. Up to four separately adjustable alarm contacts and one maximumpointer are available. Installed to be readable from the ground.With the addition of a CT-fed thermal replica circuit, the simulated hot-spot winding temperature of one or more phasescan be indicated on identical thermometers. These instruments can also beused to control forced cooling equipment.5678Fig. 17: Dial-type contact thermometerMagnetic 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 contacts; devices supplied with limit (position)switches for high- and low-level alarm areavailable. Readable from the ground.910Fig. 18: Magnetic oil-level indicator5/11Siemens Power Engineering Guide · Transmission and Distribution · 4th EditionOhne Namen-11122.09.1999, 16:23 Uhr

Accessories and Protective DevicesProtective device (Fig. 19) for hermetically sealed transformers (TUMETIC)1For use on hermetically sealed TUMETICdistribution transformers. Gives alarmupon loss of oil and gas accumulation.Mounted directly at the (permanentlysealed) filler pipe of these transformers.2Pressure relief device (Fig. 20)Relieves abnormally high internal pressureshock waves. Easily visible operationpointer and alarm contact. Reseals positively after operation and continues tofunction without operator action.3Dehydrating 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 dehydrating breather contributes to safe andreliable operation of the transformer.456Fig. 19: Protective device for hermetically sealedtransformers (TUMETIC)Fig. 20: Pressure relief device with alarm contact andautomatic resettingBushing current transformerUp to three ring-type current transformersper phase can be installed in power transformers on the upper and lower voltageside. These multiratio CTs are supplied inall common accuracy and burden ratingsfor metering and protection. Their secondary terminals are brought out to shortcircuiting-type terminal blocks in watertightterminal boxes.78Additional accessoriesBesides the standard accessories and protective devices there are additional itemsavailable, especially for large power transformers. 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.910Fig. 21: Dehydrating breather A DIN 42 567up to 5 MVA5/12Ohne Namen-1Fig. 22: Dehydrating breather L DIN 42 562over 5 MVASiemens Power Engineering Guide · Transmission and Distribution · 4th Edition1222.09.1999, 16:23 Uhr

Technical Data Distribution TransformersTUNORMA and TUMETICOil-immersed TUMETICand TUNORMA three-phasedistribution transformers1211103182N 2U 2V 2W Standard:DIN 42500Rated power:50–2500 kVARated frequency: 50 HzHV rating:up to 36 kVTaps on 2.5 % or 2 x 2.5 %HV side:LV rating:400–720 V(special designs for upto 12 kV can be built)Connection:HV winding: deltaLV winding: star(up to 100 kVA: zigzag)Impedance4 % (only up to HVvoltage at rated rating 24 kV andcurrent: 630 kVA) or6 % (with rated power 630 kVA or withHV rating 24 kV)Cooling:ONANProtection class: IP00Final coating:RAL 7033 (othercolours are available)H11U 2U 1WB1279E23678682Oil drain plugThermometer pocketAdjustment for off-load tap changerRating plate (relocatable)Grounding terminalsEA19101112Towing eye, 30 mm dia.Lashing lugFiller pipeMounting facility forprotective device34Fig. 24: TUMETIC distribution transformer (sealed tank)5415103 82N 2U 2V 2WH11U 2U 0LI Lightning-impulse test voltageAC Power-frequency test voltageFig. 23: Insulation level (IP00)92E12345A1EOil level indicatorOil drain plugThermometer pocketBuchholz relay (optional extra)Dehydrating breather (optional extra)678910137Adjustment for off-load

2.5 MVA and a voltage up to 36 kV are referred to as distribution transformers; all transformers of higher ratings are classified as power transformers. 0.05-2.5 2.5-3000 .10-20 36 36-1500 36 Rated power Max. operating voltage [MVA] [kV] Oil distribution transformers GEAFOL-cast-resin transformers Power transformers 5/13- 5 .