Outdoor Instrument Transformers - ABB

ExplanationsTechnical Specifications – Voltage TransformersVoltagesThe rated voltages are the values of primary and secondary voltages on which the performance isbased.Voltage factor (Vf)It is important that the voltage transformer, for thermal and protection reasons, can withstand andreproduce the continuous fault overvoltages that can occur in the net. The over-voltage factor isabbreviated as Vf.The IEC standard specifies a voltage factor of 1.2 continuously and simultaneously 1.5/30 sec. forsystems with effective grounding with automatic fault tripping, and 1.9/8 hrs for systems with insulated neutral point without automatic ground fault systems.Accuracy, according to IEC, for measuring windings is fulfilled between 0.8 and 1.2 x rated voltageand for protection windings up to the voltage factor (1.5 or 1.9 x rated voltage).ReconnectionThe voltage transformer can be designed with secondary reconnection.Secondary reconnection means that extra secondary terminals (taps) are taken out from thesecondary winding(s).Burden and accuracyclassBurdenThe external impedance in the secondary circuit in ohms at the specified power factor. It is usuallyexpressed as the apparent power – in VA -, which is taken up at the rated secondary voltage.(See Current Transformers above).The accuracy class for measuring windings, according to IEC, is given as 0.2, 0.5 or 1.0 dependingon the application. A rated burden of around 1.3-1.5 times the connected burden will give maximumaccuracy at the connected burden.For protection purposes the class is normally 3P or 6PSimultaneous burden(IEC)Thermal limit burdenVoltage dropFerro-resonanceMetering windings and protection windings not connected in open delta are considered as simultaneously loaded. A protection winding connected in open delta is not considered as a simultaneous load.Thermal limit burden is the total power the transformer can supply without excessively high temperature rise. The transformer is engineered so that it can be loaded with the impedance corresponding tothe load at rated voltage, multiplied by the square of the voltage factor. This means that at a voltagefactor of 1.9/8h, for example, the limit burden total rated burden x 1.92.The transformer cannot be subjected to a higher limit burden without being loaded higher than therated burden. Consequently, because of loading considerations, it is unnecessary to specify a higherthermal limit burden.The voltage drop in an external secondary circuit (cables and fuses) can have a significantly largerinfluence on the ratio error than incorrect burden.Ferroresonance is a potential source of transient overvoltage. Three-phase, single-phase switching,blown fuses, and broken conductors can result in overvoltage when ferroresonance occurs betweenthe magnetizing impedance of a transformer and the system capacitance of the isolated phase orphases. For example, the capacitance could be as simple as a length of cable connected to theungrounded winding of a transformer. Another example of ferroresonance occurring is when an inductive voltage transformer is connected in parallel with a large grading capacitor across the gap of acircuit breaker.Ferroresonance is usually known as a series resonance.B-3Edition 5, 2008-03ABB Instrument Transformers — Buyer’s Guide

ExplanationsTechnical Specifications – Voltage TransformersAdditional forCapacitor VoltageTransformers (CVT)and Capacitor VoltageDivider (CVD)Capacitancephase - groundRequirements for capacitance values can be applicable when using the CVT for communication overlines (for relay functions or remote control).PLC Power Line Carrier.Higher capacitance Smaller impedance for signal.Frequency ranges 50-500 kHz. The line matching unit can be adjusted to any capacitance.The lower applied frequency decide the minimum capacitance of coupling capacitor.More informationregarding instrumenttransformersMore detailed information about instrument transformers can be found in ourApplication Guide, Outdoor Instrument Transformers. Catalog Publication 1HSM 9543 40-00enABB Instrument Transformers — Buyer’s GuideEdition 5, 2008-03B-4

Silicone Rubber InsulatorsSilicone Rubber as an InsulatorWide range of instrumenttransformers with silicone rubber(SIR) insulatorsABB AB, High Voltage Products can supplymost of our instrument transformers withpatented helical extrusion-moulded siliconerubber insulation.ABB Manufacturing TechniqueThe patented helical extrusion moulded siliconerubber insulators without joints (chemical boundsbetween spirals) minimizes electrical field concentrations and reduces build-up of contamination. The cross-laminated fiberglass tube insidethe insulator provides high mechanical strength.Completed TestsCT IMB 36-800 kVVT EMF 52-170 kVCVT CPA/CPB 72-800 kVWhy Silicone Rubber Insulators?Ceramic (porcelain) insulators have performedwell for several decades, but one of the disadvantages with porcelain is its fragility.Listed below are some of the advantagesof silicone rubber insulators compared toporcelain: Non-brittle Minimum risk for handling and transportdamages Minimum risk for vandalism Light-weight Explosion safety Excellent pollution performance Minimum maintenance in polluted areas HydrophobicThere are several polymeric insulatormaterials available, of which siliconehas proven to be superiorThe silicone material used for ABB AB, HighVoltage Products, Instrument Transformers isapproved according to IEC and ANSI/IEEE standards.Tests performed: Accelerated ageing test (1,000 h) Lightning impulse test, wet power frequencytest and wet switching impulse test Short circuit test Temperature rise testColorThe (SIR) insulators for the instrument transformers are supplied in a light gray color.DeliveriesABB in Ludvika has supplied instrument transformers with (SIR) insulators for the most severeconditions, from marine climate to desert and/orpolluted industrial areas.A reference list can be provided on request.Comparison of Polymeric GoodGoodExcellentWeightMech. strengthMaintenanceAgeingUV-resistanceExperience of MaterialABB has used silicone rubber (SIR) insulatorssince 1985, starting with surge arresters, andhas gained considerable experience.C-1Edition 5, 2008-03More InformationFor additional information please refer topublication 1HSM 9543 01-06en.ABB Instrument Transformers — Buyer’s Guide

sustN omot ees r CABB Instrument Transformers — Buyer’s GuideEdition 5, 2008-03C-2

DesignCurrent TransformerIMB Design Features and AdvantagesABB’s oil minimum current transformers type IMB is based on a hairpindesign (shape of the primary conductor) also known as tank type. Thebasic design has been used by ABBfor 60 years, with more than 160,000units delivered.The design corresponds with the demandsof both the IEC and IEEE standards. Specialdesign solutions to meet other standardsand/or specifications are also available.The unique filling with quartz grains saturated in oil gives a resistant insulation in acompact design where the quantity of oil iskept to a minimumThe IMB transformer has a very flexibledesign that, for example, allows large and/ormany cores.Primary WindingThe primary winding consists of one or moreparallel conductor of aluminum or copperdesigned as a U-shaped bushing with voltage grading capacitor layers.The insulation technique is automated to givea simple and controlled wrapping, which improves quality and minimizes variations.The conductor is insulated with a specialpaper with high mechanical and dielectricstrength, low dielectric losses and goodresistance to ageing.This design is also very suitable for primarywindings with many primary turns. This isused when the primary current is low, forinstance unbalance protection in capacitorbanks. (Ex. ratio 5/5A)ImpregnationHeating in a vacuum dries the windings. Afterassembly all free space in the transformer(app. 60%) is filled with clean and dry quartzgrain. The assembled transformer is vacuumtreated and impregnated with degassed mineral oil. The transformer is always deliveredoil-filled and hermetically sealed.Tank and InsulatorThe lower section of the transformer consistsof an aluminum tank in which the secondarywindings and cores are mounted. The insulator, mounted above the transformer tank,consists as standard of high-grade brownglazed porcelain. Designs using light grayporcelain or silicon rubber can be quoted onrequest.The sealing system consists of O-ring gaskets.Expansion SystemThe IMB has an expansion vessel placed ontop of the insulator. A hermetically sealedexpansion system, with a nitrogen cushioncompressed by thermal expansion of the oil,is used in the IMB as the standard design.An expansion system with stainless steel expansion bellows can be quoted on request.On Request – Capacitive Voltage TapThe secondary winding consists of doubleenameled copper wire, evenly distributedThe capacitive layers in the high voltage insulation can be utilized as a capacitive voltagedivider. A tap is brought out from the secondto last capacitor layer through a bushing onthe transformer tank (in the terminal box or ina separate box, depending on the IMB tankdesign). An advantage of the capacitive terminal is that it can be used for checking thecondition of the insulation through dielectricloss angle (tan delta) measurement withoutdisconnecting the primary terminals. The tapcan also be used for voltage indication, synchronizing or similar purpose, but the outputis limited by the low capacitance of the layers.The load connected must be less than10 kohms and the tap must be groundedwhen not in use.Edition 5, 2008-03ABB Instrument Transformers — Buyer’s GuideCores and Secondary WindingsThe IMB type current transformers are flexible and can normally accommodate anycore configuration required.Cores for metering purposes are usuallymade of nickel alloy, which features lowlosses ( high accuracy) and low saturationlevels.The protection cores are made of highgrade oriented steel strip. Protection coreswith air gaps can be supplied for specialapplications.D-1around the whole periphery of the core. Theleakage reactance in the winding and alsobetween extra tapping is therefore negligible.

Current TransformerDesignIMB Design Features and AdvantagesClimateThe transformers are designed for, and areinstalled in, widely shifting conditions, frompolar to desert climates all over the world.Service LifeSeismic StrengthThe IMB has a mechanically robust construction, designed to withstand high demandsof seismic acceleration without the need ofdampers.The IMB transformer is hermetically sealedand the low and even voltage stress in theprimary insulation gives a reliable productwith expected service life of more than 30years. The IMB and its predecessors havesince the 1930s been supplied in more than160,000 units.1892103Expansion SystemThe expansion system, with a nitrogen gascushion, increases operating reliability andminimizes the need of maintenance andinspections. This type of expansion systemcan be used in the IMB since the quartz fillingreduces the oil volume and a relatively largegas volume minimizes pressure variations.For higher rated currents an expansionvessel with external cooling fins is used toincrease the cooling area and heat dissipation to the surrounding air.An expansion system with stainless steelexpansion bellows surrounded by the oil canbe quoted on request.4Quartz FillingMinimizes the quantity of oil and provides amechanical support for the cores and primary winding during transport and in the eventof a short-circuit.5FlexibilityThe IMB covers a wide range of primary currents up to 4,000 A. It can easily be adaptedfor large and/or many cores by increasing thevolume of the tank.6711Resistance to CorrosionThe selected aluminum alloys give a highdegree of resistance to corrosion, without theneed of extra protection. Anodized parts forIMB 36-170 kV can be offered on request.For use in extreme environmentsIMB 170 kV can be delivered with a protective painting.ABB Instrument Transformers — Buyer’s GuideCurrent Transformer Type IMB1.2.3.4.Gas cushionOil filling unit (hidden)Quartz fillingPaper-insulated primaryconductor5. Cores/secondarywindingsEdition 5, 2008-036. Secondary terminal box7. Capacitive voltage tap(on request)8. Expansion vessel9. Oil sight glass10. Primary terminal11. Ground terminalD-2

DesignInductive Voltage TransformerEMF Design Features and AdvantagesABB’s inductive voltage transformersare intended for connection betweenphase and ground in networks withinsulated or direct-grounded neutralpoints.The design corresponds with the requirements in the IEC and IEEE standards. Special design solutions to meet other standardsand customer requirements are also possible.The transformers are designed with a lowflux density in the core and can often bedimensioned for 190% of the rated voltagefor more than 8 hours.former consists of an aluminum tank in whichthe winding and core are placed. The tankconsists of selected aluminum alloys thatgive a high degree of resistance to corrosion,without the need of extra protection. Anodized details can be offered on request. Thesealing system consists of O-ring gaskets.The insulator, in its standard design, consists of high quality, brown glazed porcelain.The voltage transformers can also be supplied with silicone rubber insulators.Expansion SystemPrimary WindingsThe primary winding is designed as a multilayer coil of double enameled wire with layerinsulation of special paper. Both ends of thewindings are connected to metal shields.The EMF has an expansion vessel placedon the top section of the porcelain. The EMFhas a closed expansion system, withoutmoving parts and with a nitrogen cushion,that is compressed by the expansion of theoil. A prerequisite for this is that the quartzsand filling reduces the oil volume, and theuse of a relatively large gas volume, whichgives small pressure variations in the system.Secondary and Tertiary WindingsFerro-ResonanceIn its standard design the transformer has asecondary measurement winding and a tertiary winding for ground fault protection, butother configurations are available as required.(2 secondary windings in a design accordingto IEEE standard)The windings are designed with doubleenameled wire and are insulated from thecore and the primary winding with pressboard (presspahn) and paper.The windings can be equipped with additional terminals for other ratios (taps).CoreThe transformer has a core of carefully selected material, to give a flat magnetizationcurve. The core is over-dimensioned with avery low flux at operating voltage.The design of the EMF notably counteractsthe occurrence of ferro-resonance phenomena:- The low flux in the core at the operatingvoltage gives a large safety margin againstsaturation if ferro-resonance oscillationsshould occur.- The flat magnetization curve gives asmooth increase of core losses, whichresults in an effective attenuation of the ferroresonance.If the EMF transformer will be installed in anetwork with a high risk for ferro-resonance,it can, as a further safety precaution, beequipped with an extra damping burden, ona delta connected tertiary winding. See thefigure below.ImpregnationHeating in a vacuum dries the windings. Afterassembly, all free space in the transformer(approximately 60%) is filled with clean anddry quartz grains. The assembled transformer is vacuum-treated and impregnatedwith degassed mineral oil. The transformeris always delivered oil-filled and hermeticallysealed.Tank and InsulatorEMF 52-170: The lower section of the transE-1Edition 5, 2008-03Damping of ferro-resonanceABB Instrument Transformers — Buyer’s Guide

Inductive Voltage TransformerDesignEMF Design Features and AdvantagesClimateThese transformers are designed for, and areinstalled in a wide range of shifting conditions, from polar to desert climates all overthe world.1923Service LifeThe low and even voltage stresses in theprimary winding give a reliable product witha long service life. EMF and its predecessorshave been supplied in more than 55,000units since the 1940s.Expansion System45The expansion system based on the nitrogencushion gives superior operating reliabilityand minimizes the need of maintenance andinspection of the transformer.Quartz FillingMinimizes the quantity of oil and provides amechanical support to the cores and primarywinding.10116Resistance to CorrosionEMF 52-170: The selected aluminum alloysgive a high degree of resistance to corrosionwithout the need of extra protection. Anodized details can be offered on request.12ABB Instrument Transformers — Buyer’s Guide148Seismic StrengthEMF is designed to withstand the high demands of seismic acceleration.13715Voltage transformer EMF 1451.2.3.4.5.6.7.8.Primary terminalOil level sight glassOilQuartz fillingInsulatorLifting lugSecondary terminal boxNeutral end terminalEdition 5, 2008-039.10.11.12.13.14.15.Expansion systemPaper insulationTankPrimary windingSecondary windingsCoreGround connectionE-2

DesignCapacitor Voltage TransformerCPA and CPB Design FeaturesABB’s capacitor voltage transformers(CVTs) and coupling capacitors areintended for connection betweenphase and ground in networks withisolated or grounded neutral.ABB offers a world-class CVT with superiorferro-resonance suppression and transientresponse.The design corresponds to the requirements of IEC and ANSI and all nationalstandards based on them. Special designs tomeet other standards and customer specifications are also available.Due to the design of the capacitor elements, described below, CPA and CPBare, with regard to temperature stability andaccuracy, equivalent to inductive voltagetransformers.Difference and Composition ofCPA and CPBA capacitor voltage transformer with an electromagnetic unit (EMU), type EOA is calledCPA and with EMU, type EOB is called CPB.The design of the EOA and EOB is basicallyidentical, however the EOB has a larger tankand core, with space for larger windings,making it capable of withstanding higher burdens.Our standard voltage divider, type designation CSA (high capacitance) or CSB (extrahigh capacitance) is mounted on an electromagnetic unit (EMU), making a completecapacitor voltage transformer.A coupling capacitor (without an EMU) iscalled CCA (high capacitance) or CCB (extrahigh capacitance).Capacitor Voltage DividerThe capacitor voltage divider (CVD) consistsof one or two capacitor units, assembled ontop of each other. Each unit contains a largenumber of series-connected, oil-insulatedcapacitor elements. The units are completelyfilled with synthetic oil, which is kept undera slight overpressure by the design of theexpansion system. O-ring seals are usedthroughout the design.F-1Edition 5, 2008-03The capacitor elements are designed withrespect to the demands made by revenuemetering, and their active component consists of aluminum foil, insulated with paper/polypropylene film, impregnated by a PCBfree synthetic oil, which has better insulating properties than normal mineral oil and isrequired for the mixed dielectric. Due to itsunique proportions between paper and polypropylene film, this dielectric has proven itselfvirtually insensitive to temperature changes.Electromagnetic UnitThe voltage divider and the electromagneticunit are connected by internal bushings,which is necessary for applications with highaccuracy.The EMU has double-enameled copperwindings and an iron core made of high quality steel sheet and is oil insulated in a hermetically sealed aluminum tank with mineral oil.The primary coil is divided into a mainwinding, and a set of externally connectedtrimming windings. The nominal intermediatevoltage is approx. 22/ 3 kV.The EOA and EOB have a reactor, which isconnected in series between the voltage divider and the high voltage end of the primarywinding. This reactor compensates for theshift in phase angle caused by the capacitivevoltage divider. The inductive reactances aretuned individually on each transformer beforeaccuracy testing.For special applications, HVDC stations,me

ABB Instrument Transformers — Buyer’s Guide Edition 5, 2008-03 A-2 Introduction Day after day, all year around— with ABB Instrument Transformers ABB has been producing instrument trans-formers for more than 60 years. Thousands of our products perform vital functions in electric powe