Transformer Design & Design Parameters
Transformer Design & Design Parameters- Ronnie Minhaz, P.Eng.Transformer Consulting Services Inc.
Power Transmission DistributionGENERATIONTRANSMISSION115/10 or 20 kV132161230345500Generator 0/115230/132Auto-transformerTransformer Consulting Services Inc.DISTRIBUTIONDISTRIBUTED POWER230/13.81611321156934Step-downtransformerpads
StandardsU.S.A. (ANSI) IEEE Std C57.12.00-2010, standard general requirements for liquidimmersed distribution, power and regulation transformers ANSI C57.12.10-2010, safety requirements 230 kV and below 833/958through 8,333/10,417 KVA, single-phase, and 750/862 through60,000/80,000/100,000 KVA, three-phase without load tap changing; and3,750/4,687 through 60,000/80,000/100,000 KVA with load tap changing (ANSI) IEEE C57.12.90-2010, standard test code for liquid-immerseddistribution, power and regulating transformers and guide for short-circuittesting of distribution and power transformers NEMA standards publication no. TR1-2013; transformers, regulators andreactorsCanadaCAN/CSA-C88-M90(reaffirmed 2009); power transformers and reactor;electrical power systems and equipmentTransformer Consulting Services Inc.
Transformer Design: Power rating [MVA]CoreRated voltages (HV, LV, TV)Insulation coordination (BIL, SIL, ac tests)Short-circuit Impedance, stray fluxShort-circuit ForcesLoss evaluationTemperature rise limits, Temperature limitsCooling, cooling methodSound LevelTap changers (DTC, LTC)Transformer Consulting Services Inc.
Transformer Design:Simple Transformer Left coil - input (primary coil)– Source– Magnetizing current Right coil - output (secondary coil)– Load Magnetic circuitTransformer Consulting Services Inc.
Transformer Design:Power rating [MVA]Power rating S [MVA] for three-phasetransformer is defined as:Where:U - rated line voltage (primary or secondary),I - rated line current (primary or secondary).Transformer Consulting Services Inc.
Transformer Design:Power rating [MVA] 30/40/50 MVA corresponding to differentcooling stages, e.g. ONAN/ONAF/ONAF(OA/FA/FA), 0.6/0.8/1.0 p.u. 60/80/100//112 MVA for 55/65oCtemperature rise units; 12% increase in powerrating for 65oC rise from 55oC rise, 24/12/12 MVA for three-circuit units (e.g. HVLV1-LV2).Transformer Consulting Services Inc.
Transformer Design:Core Form Concentric windings‘Set’ Winding GeometryCooling optionsCost considerationShipping differencesTransformer Consulting Services Inc.
Transformer Design:Type of Cores–3 legs Type 1 –––legs and yokes not of equal crosssectionsingle-phase2 legs Type 22 wound legs–legs and yokes of equal cross sectionsingle-phase–3 legs– Type 31 wound leg2 return legs––3 wound legslegs and yokes of equal cross sectionthree-phaseTransformer Consulting Services Inc.
Transformer Design:Type of Cores–4 legs Type 4 –legs and yokes not of equalcross sectionsingle-phase–5 legs– Type 52 wound legs2 return legs ––3 wound legs2 return legslegs and yokes not of equalcross sectionthree-phaseTransformer Consulting Services Inc.
Transformer Design:Core Form CutawayTransformer Consulting Services Inc.
Transformer Design:Insulation Coordination Basic Insulation Level (BIL) tested withlightning impulse 1.2/50 ms (FW, CW) Switching Insulation Level (SIL), switchingimpulse 250/2500 ms Induced Voltage (ac) Applied Voltage (ac)Transformer Consulting Services Inc.
Transformer Design:Insulation CoordinationWithstand voltage Impact on designBIL (LI)SILInduced voltageApplied voltageBushings, lead structure & its clearances,winding clearances, stresses to ground,neutral point insulationExternal clearances, lead clearances, phaseto-phase stressesInternal winding stresses (V/T), stresses toground, phase-to-phase stressStresses to ground (windings, leads)Transformer Consulting Services Inc.
Transformer Design:High Voltage (HV) Voltage class of the unit, levels of LI and SI, aredetermining selection of bushings, surgearrestors, insulating structure (graded or fullyinsulated, internal and external clearances, use ofbarriers, caps and collars, stress rings, etc.) impulse voltage distribution dictates the windingtype, main gaps, type of conductor (MW, Twin,Triple, CTC)Transformer Consulting Services Inc.
Manufacturing Process:Coil Winding(Disc inner and outer Crossovers)Transformer Consulting Services Inc.
Transformer Design:Low Voltage (LV) Low voltage generates the highest currents intransformer, determining selection ofbushings, lead structure, etc. Stray field problems have to be addressed i.e.use of non-magnetic inserts, magnetic shunts,e.t.c, selection of winding type (low temperaturerise - use of CTC, short-circuit withstand)Transformer Consulting Services Inc.
Manufacturing Process:CTC - epoxy bonded, netting tapeTransformer Consulting Services Inc.
Transformer Design:Tertiary Voltage (TV)TV can be brought out to supply tertiary circuit, or can benot brought out (buried). For brought out TV design follows the rules as for LV,i.e. sizing the bushings, leads, short-circuit faults Tertiary voltage generated at buried TV winding has noimportance for user; typically such TV winding is deltaconnected and provides the path for zero-sequencecurrents during short-circuit and suppresses thirdharmonic (and its multiples) currents.Transformer Consulting Services Inc.
Transformer Design:Geometry of end insulationTransformer Consulting Services Inc.
Transformer Design:End insulationElectric field distributionTransformer Consulting Services Inc.
Transformer Design:Short-circuit impedance Determines the regulation (voltage drop acrosstransformer) under load conditions Limits the short circuit currents and resulting forces Specified by customer (can be per IEEE Std) Can be expressed in % of rated impedance (equal to %value of short-circuit voltage), or in [W] related toprimary or secondary side In general Z R jX, but resistance is negligible %IX depends on: geometry, amp-turns, base power,frequencyTransformer Consulting Services Inc.
Transformer Design:Short-circuit impedanceShort-circuit reactance is calculated using the magnetic field programs (finiteelement, Rabins); can be estimated using simple formulas;High value of stray reactance in design results in: high leakage flux, leading to high additional (eddy) losses in windings andconstructional parts, can result in increase in the highest (hot-spot) temperature rises; use ofCTC is expected (also in HV winding) - higher manufacturing cost; the value of voltage regulation is high short-circuit current are limited, forces are low.Low value of impedance may result in large short-circuit currents, leading tohigh forces; the designing is difficult, more copper must be added, epoxybonded CTC cables have to be used, more spacers are added.Transformer Consulting Services Inc.
Transformer Design:Short-circuit DesignBasic theory Current carrying conductors in a magnetic field experienceforce in accordance with Fleming’s left hand rule. Axial flux produces radial force and radial flux producesaxial force Conductors are attracted to each other when currents arein same direction Conductors are pushed away from each other whencurrents are in opposite direction Force is proportional to square of currentTransformer Consulting Services Inc.
Transformer Design:Short-circuit DesignTypes of forces Radial force due to axial flux Axial Compressive force due to current in same winding Axial force due to unbalance ampere turns in the windings(radial flux condition)Transformer Consulting Services Inc.
Transformer Design:Short-circuit DesignRadial forcesStresses due to radial forces Hoop stress in outer winding Buckling stress in inner windingSupported buckling and free bucklingStresses due to axial forcesAxial compressiveforce at center Compressive stress on key spacers Tilting of conductors Axial bending between key spacersTransformer Consulting Services Inc.
Transformer Design:Radial ForcesBucklingHoopTransformer Consulting Services Inc.
Transformer Design:Transformer Consulting Services Inc.
Transformer Design:Loss EvaluationCost of ownership capital cost cost of lossesCost of losses cost of no-load loss cost of load loss cost of stray lossThe load loss and stray loss are added together as theyare both current dependent Ownership of Transformer can be more than twicethe capital cost considering cost of power losses over20 years Modern designs low-loss rather than low-costdesignsTransformer Consulting Services Inc.
Transformer Design:Loss EvaluationTransformer as energy converter dissipates losses;depending on operation of the unit (load characteristics)the losses can have significant economical cost for users.Losses are divided into: no-load loss load lossTransformer also consumes some auxiliary power,resulting in auxiliary lossesTransformer Consulting Services Inc.
Transformer Design:Loss EvaluationNo-load lossLosses generated in the core sheets by main (working) flux of a transformerare called no-load losses. They include the histeresis loss and the eddycurrent loss.No-load losses do not depend on: load core temperature (there is though a correction factor)No-load losses depend on: voltage, these losses increase dramatically with increase in voltage if fluxdensity is approaching the saturation, frequency, core material: its properties, the lamination thickness, mass of the core.Because most transformers are energized (under voltage) at all times, whatresults in continuous generation of no-load losses, these losses have high costevaluation.Transformer Consulting Services Inc.
Transformer Design:Loss Evaluationload lossLosses generated in transformer by load currents, bothprimary and secondary, are called load losses.Load losses consist of fundamental (ohmic) losses I2R in each phase, whileresistance R is measured at DC voltage; additional (eddy) losses, generated by the eddycurrents induced by the stray flux in all metallicelements (leads, windings, constructional parts, tank,shields) penetrated by this fluxTransformer Consulting Services Inc.
Transformer Design:Loss Evaluationload loss Ohmic losses increase with resistance R which increaseswith the temperature t as follows: According to standards the additional losses decrease withincrease in temperature (with reversed factor used forohmic losses) Combined ohmic and eddy losses, giving total load loss, areincreasing with square of load current; i.e. the load lossesdepend heavily on loading of the unit The standard reference temperature for the load losses ofpower and distribution transformers shall be 85oCTransformer Consulting Services Inc.
Transformer Design:Stray flux distributionFlux distribution with the tapping winding in position:(i) full rise, (ii) neutral, (iii) full buckTransformer Consulting Services Inc.
Transformer Design:Summary of LossesTransformer Consulting Services Inc.
Transformer Design:Loss EvaluationAuxiliary lossesAuxiliary losses are generated by cooling equipment: fans, pumps.Typically, these losses are not significant whencompared to no-load and load losses.The auxiliary losses depend on the cooling stage of theunit, reaching maximum for top power rating.Transformer Consulting Services Inc.
Transformer Design:Loss EvaluationExampleTypically, the losses are evaluated (in ) usingcustomer-defined factors and are added to theprice of transformer during bid evaluationFor example:Price adder KNLL x NLL KLL x LL KAuxL x AuxLwhere:NLL, LL, AuxL- no-load, load and auxiliary losses [kW]KNLL, KNLL, KNLL - loss evaluation factors [ /kW]Transformer Consulting Services Inc.
Transformer Design:Temperature rise limits Winding Temperature Rise:- average, 55/65oC, 95/115oC(nomex)- hot-spot, 65/80oC, 130/150oC (nomex)- hotspot, during short circuit 210oC Oil Temperature Rise:- top, 55/65oC Metal parts not in contact with insulation, 100oC Reference ambient temperatures40oC max, 30oC daily average, 20oC yearly averageAny other ambient condition, the temperature rise limits to bereduced For water cooled units the ambient is considered that of coolingwaterTransformer Consulting Services Inc.
Transformer Design:Temperature limits Oil temperature 100/105oC Average winding temperature( paper) 85oC for normal paper &95oC for thermally upgraded paper & 125 or 145oC for nomex Hotspot winding temperature (paper) based on daily averageambient 95oC for normal paper & 110oC for thermally upgradedpaper Maximum allowed hotspot based on maximum ambient 105oC fornormal paper & 120oC for thermally upgraded paper Maximum allowed hotspot 250oC for very short time, during shortcircuit Temperature limit for metal parts in contact with insulation is sameas for winding Other metal parts limit is 140oCTransformer Consulting Services Inc.
Transformer Design:Cooling Both no-load and load losses are converted into heat whichincreases the temperature of active parts (core and windings),constructional parts (clamps, tank), as well as of the oil. Next, the heat has to be dissipated by cooling system (tank,radiators, etc.) to cooling medium, e.g. to surrounding air. Thetemperature rises of all components are limited by appropriatestandards. These criteria have to be satisfied during thetemperature rise test (heat run). Intensity of cooling has to be increased together with increase inrated power, in order to sustain allowable temperature rises. Inpower transformers one may utilize: (i) radiators, or coolers, (ii)forced air flow, (iii) forced oil flow (preferably directed flow), (iv)water cooling, (v) “loose” structure of windingsTransformer Consulting Services Inc.
Transformer Design:Cooling methodsCooling medium A - air cooling, O - oil cooling, K, L - cooling withsynthetic fluid, W - water coolingCooling mode N - natural cooling, F - forced cooling,
Transformer Design & Design Parameters - Ronnie Minhaz, P.Eng. Transformer Consulting Services Inc. Power Transmission Distribution Transformer Consulting Services Inc. Generator Step-Up Auto-transformer Step-down pads transformer transformer 115/10 or 20 kV 500/230 230/13.8 132 345/161 161 161 230/115 132 230 230/132 115 345 69 500 34 GENERATION TRANSMISSION SUB-TRANSMISSION DISTRIBUTION .
3. Instrument transformer: Used in relay and protection purpose in different instruments in industries . . Current transformer (CT) . Potential transformer (PT) . Open circuit and Short circuit Test on transformer . These two transformer tests are performed to find the parameters of equivalent circuit of transformer and losses of the transformer.
Transformer Lab 1. Objectives: 1.1 Comparison of the ideal transformer versus the physical transformer 1.2 Measure some of the circuit parameters of a physical transformer to determine how they affect transformer performance. 1.3 Investigate the ideal transformer and ca
transformer there are hysteresis and eddy current losses in transformer core. Theory of transformer on no-load, and having no winding resistance and no leakage reactance of transformer Let us consider one electrical transformer with only core losses. That means it has only core losses but no copper lose and no leakage reactance of transformer.
Step 13: Now click on the 2-Winding Transformer icon . Place the 2-winding transformer in the same way that you placed the previous two components. Join the primary of the transformer to the Main Bus. Double click the transformer icon and set the following properties: On the Info Tab o Change the transformer ID to "Main Transformer".
the distribution magnetic flux in the transformer. It has been used ANSYS Package Version 11 to model the distribution transformer.Table (1) shows the data of distribution transformer. 3.1 Transformer Geometry (Building and meshing): The transformer study is 250 kVA, three phase distribution core type "stacked core" transformer.
A transformer-based UPS may use a transformer before the rectifier and requires an isolation transformer after the inverter to derive the voltage being delivered to the critical load. Transformer-free UPS designs use power and control electronics technologies to eliminate the need for an isolatio
6. Disconnect all the SCG transformer primary leads. 7. Remove the three remaining screws securing the transformer. Remove the transformer from the enclosure. To install the transformer assembly (see Figure 1 & 2, page 7 & 8): 1. Mount the transformer onto the back panel of the enclosure. Secure the
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