Electrical Design Process

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1 Electrical Design Process Jason Varnell Lead Design Engineer SPX Transformer Solutions, Inc. September 26, 2018

2 Agenda 1. Bid Design Process Parameters Affecting Bid Design 2. Final Design Process Design Parameters SPX Transformer Solutions, Inc. September 26,

3 Transformer Cutaway View SPX Transformer Solutions, Inc. September 26,

4 Bid Design Process SPX Transformer Solutions, Inc.

5 Summarize Bid Design Parameters Loss evaluation, existing size and weight restrictions shipping by rail/road Dielectric Requirements BILs-LI, SI, induced voltage, applied voltage Customer Specifications Normal operation MVA rating, voltage ratio, connection LTC/DETC, % impedance, parallel operation, sound levels Type of cooling temp rises, top oil rise, average winding rise, hot spot rise winding and core Short circuit, overloading, over fluxing, seismic conditions, any other specific requirement(s) SPX Transformer Solutions, Inc. September 26,

6 Parameters Affecting Bid Design Loss evaluation affects the selection of flux density for core and selection of current density for windings % impedance affects core and coil dimensions, leakage flux distribution, short circuit stresses and regulation % impedance depends on the following: Winding dimensions Voltage per turn Frequency Transformer rating SPX Transformer Solutions, Inc. September 26,

7 Parameters Affecting Bid Design (cont.) Basic insulation levels (BIL) affects the clearance between windings, phase to phase clearances, winding end clearances and tank clearances Over-excitation requirements affect selection of flux density, size and weight of core Taps purpose, type, range and location affect core and winding design Dimension and shipping weight limitations affect core dimensions, flux density and current density SPX Transformer Solutions, Inc. September 26,

8 Parameters Affecting Bid Design (cont.) Sound level affects the type of core construction, flux density, type of cooling fans Temperature rise and type of cooling affects the quantity of radiators and fans Overload requirement may increase the quantity of radiators, quantity of fans and winding conductor area Parallel operation with existing transformers affects placement of windings on core SPX Transformer Solutions, Inc. September 26,

9 Parameters Affecting Bid Design (cont.) No load loss = (along grain core weight * watt/lb + across grain weight * watt/lb)* correction factor, where: watt/lb. ~ flux density, core grade and correction factor ~ core dimensions and type of core construction No-load loss at 20 C = loss at T C*(1+ (T-20)*Kt), where, Kt = for grain oriented steel Load loss depends on winding dimensions, number of turns, current density, conductor type and frequency Load Loss = I 2 R loss + Eddy loss + Stray loss I 2 R depends on the number of turns, winding dimensions, area of copper conductor SPX Transformer Solutions, Inc. September 26,

10 Type of Core Construction - 1 A4 A A2t.707" 1/2" A2f ~ A1 ~ 5 1/2" A5 Mitered Core Construction SPX Transformer Solutions, Inc. September 26,

11 Type of Core Construction - 2 A2 Few steps shown only 4 ~ Total 3 Five Steps ~ 2 ~ A1 1 1 ~ ~ ~ 3 4 Remaining joints are same as shown. Step-Lap Core Construction SPX Transformer Solutions, Inc. September 26,

12 Step Lap Joint SPX Transformer Solutions, Inc. September 26,

Bid Design Steps Summarize design parameters Finalize winding arrangement Standard arrangement: Core TV TAP LV HV Select clearances between windings, winding to yoke, phase to phase and winding to

13 Bid Design Steps Summarize design parameters Finalize winding arrangement Standard arrangement: Core TV TAP LV HV Select clearances between windings, winding to yoke, phase to phase and winding to tank Select type of core construction mitered or step-lap Select type of material for core, winding (CTC/MW) Input limits for winding current density, flux density, core overall dimensions, if required SPX Transformer Solutions, Inc. September 26,

14 Typical Winding Arrangement C E A B D F Cyl Cyl G G Cyl G 3/8 1/2 3/8 3/8 1/2 1/2 3/8 3/8 D F B C A E TV COM SER 1/4" pb. cylinder SPX Transformer Solutions, Inc. September 26,

15 Bid Design Steps (cont.) Bid optimizer software computes different designs based on loss evaluation and meeting various limits set per specification, flux density, current density, dielectric design, short circuit and other design considerations Evaluate various design options, select the optimum feasible design meeting customer and design requirements with lowest total owning cost Total owning cost = Selling Price + Cost of Losses Cost of Losses = No load loss * No load evaluation $/KW + load loss * load loss evaluation $/KW SPX Transformer Solutions, Inc. September 26,

16 Final Design Process SPX Transformer Solutions, Inc.

17 Final Design Process Customer specifications and requirements Bid Design Review Bid Design /Requirements Finalize design Parameters Verification Design Review Design Sheets Mech Design Approval Drawings Release to Shop SPX Transformer Solutions, Inc. September 26,

18 Final Design Steps Review bid design, customer requirements Find a reference design, if available Compute the design insulation level for insulation design Finalize core diameter, winding turns, type of winding, gap between windings and end clearances Check voltage ratio error, change number of turns, if required Select number of turns/disk, tap sections, conductor paper, type of conductor, duct between sections/turns SPX Transformer Solutions, Inc. September 26,

19 Final Design Steps (cont.) Balance ampere-turns in LV windings, in case of de-energized taps in the main HV winding Calculate % impedance, core loss, load loss and compare with guaranteed parameters Change conductor size and winding height, as required Calculate impulse voltage distribution in winding and between gaps Finalize wound-in-shield requirement for HV winding SPX Transformer Solutions, Inc. September 26,

20 Ampere Turn Balance 26 SECTIONS 38 SECTIONS 76 TURNS TURNS.16 KSP.16 KSP 4 SECTIONS 16 SECTIONS TURNS TURNS KSP.16 KSP 26 SECTIONS 74 TURNS 38 SECTIONS.16 KSP TURNS.16 KSP LV WINDING HV WINDING TOP HALF OF CENTRE FED WINDING SPX Transformer Solutions, Inc. September 26,

21 Wound-in-Shield Arrangement SPX Transformer Solutions, Inc. September 26,

22 Final Design Steps (cont.) Review conductor insulation, gap between windings based on the calculated transient voltages Calculate % impedance at rated and tap extremes between windings and compute fault currents Perform short-circuit withstand calculations, analyze stresses in windings, key-spacers, end forces; based on results, change winding conductor if required and recalculate the stresses SPX Transformer Solutions, Inc. September 26,

23 Electrostatic Field Analysis SPX Transformer Solutions, Inc. September 26,

24 Final Design Steps (cont.) Recalculate impulse withstand, if required Perform leakage flux analysis, calculate tank losses, eddy losses, frame losses Calculate temperature rise of clamps and tank Increase end clearances and tank clearances, as required Calculate flitch plate and outer core temperature rise and split flitch plate/outer core packet, if needed SPX Transformer Solutions, Inc. September 26,

25 Leakage Flux Analysis SPX Transformer Solutions, Inc. September 26,

26 Final Design Steps (cont.) Perform temperature rise calculations and finalize number of radiators, fans to limit the guaranteed top oil rise, average winding rise, hot spot temperature; perform overload temperature rise calculations, if specified Prepare detailed design sheets which provide technical information for winding sheets, internal layout, external layout, controls and approval/manufacturing drawings Prepare detailed test specification based on ANSI and customer requirements SPX Transformer Solutions, Inc. September 26,

27 Design Parameters - 1 Voltage per turn ~ frequency * core area * flux density No. of turns = Phase voltage / voltage per turn Voltage ratio V 2 / V 1 = Turns ratio N 2 / N 1 No load loss = (along grain core weight * watt/lb + across grain weight * watt/lb) * correction factor watt/lb. ~ flux density, core grade correction factor ~ core dimensions, core construction No-load loss at 20 C = No load loss at T C*(1+ (T-20)*Kt) (Kt = for grain oriented steel) SPX Transformer Solutions, Inc. September 26,

28 Design Parameters - 2 Load Loss = I 2 R loss + Eddy loss + Stray loss Eddy losses depend on conductor thickness and width and the leakage flux distribution Stray loss ~ % impedance, winding dimensions and tank clearances % Impedance ~ (Current*turns*radial winding dimensions) / (axial dimensions * voltage per turn) SPX Transformer Solutions, Inc. September 26,

29 Design Parameters - 3 Sound-level ~ flux density, core construction & distance db 1 = 20 * log(x 2 /X 1 ) + db 2 where, X 2 or X 1 is the distance of point 2 or point 1 from center of transformer %Regulation = ( %X sinø + %R cosø +((%X cosø -% R sinø)²/200)) where, cosø = power factor %X = Reactance %R = (Total loss in kw/kva)*100 %Efficiency = (1 - Total loss in kw/kva)*100 SPX Transformer Solutions, Inc. September 26,

30 Questions? Thank you! SPX Transformer Solutions, Inc.

31 Annex A Additional Information SPX Transformer Solutions, Inc.

32 Electrical Design Process Jason Varnell Lead Design Engineer SPX Transformer Solutions, Inc. September 26, 2018

General Requirements Basics/ Physics of Transformer Design Step Down Transformer HV Winding MVA = V 1 * I 1 High Voltage (V 1 ) Low Current (I 1 ) V 1 N 1 ᴽ LV Winding MVA =

33 General Requirements Basics/ Physics of Transformer Design Step Down Transformer HV Winding MVA = V 1 * I 1 High Voltage (V 1 ) Low Current (I 1 ) V 1 N 1 ᴽ LV Winding MVA = V 2 * I 2 Low Voltage (V 2 ) High Current (I 2 ) V 2 N 2 ᴽ Power In Power Out MVA_In MVA_Out V 1 > V 2 N 1 > N 2 I 1 < I 2 SPX Transformer Solutions, Inc. September 26,

34 Winding Design Requirements Disc Winding Helical Winding Layer Winding Ideal for HV Wdg More Turns Less CSA Few Conductor per Turn Multiple Turns per Disc Typical min 160 Turns Keyspacers Used Ideal for LV & TV Wdg Ideal for LV & TV Wdg Less Turns Less Turns More CSA More CSA Many Conductor per Turn Many Conductor per Turn One Turn per Disc One Turn per Disc Typical max 160 Turns Typical max 200 Turns Keyspacers Used No Keyspacers Used SPX Transformer Solutions, Inc. September 26,

35 Core Design Requirements Core Flux Density Size of Core is dependent on Flux Density (B) Core Loss (P o ) Turns (N) Laser Scribed Steel Saturates at about 2.03 Tesla B = V 4.44 f A c N A c is in square meters B is in Tesla Flux Density at rated voltage shall be set to avoid saturation or excessive temperatures during all over-excitation conditions Sound Level or Loss Evaluation may drive the design flux density down Optimizer program may increment core diameter for a given number of turns over a range of 85% to 100% of B design B design = 2.03 SF V OV B design = B design = 1.76 Tesla SPX Transformer Solutions, Inc. September 26,

36 B Flux Density Core Design Requirements Core Loss (P o ) P o Mass core Watts/Pound Ways to Reduce Core Loss 1.76 T Decrease Core Mass Decrease Flux Density Ways to Reduce Flux Density Increase Core Area with Turns Fixed Increase Turns with Core Area Fixed 0.5 W / lb Watts / Pound If you want a low core loss design then the unit will have a small core area meaning the number of turns is higher which also means the transformer will be taller and skinnier to meet the impedance requirements SPX Transformer Solutions, Inc. September 26,

37 LV WINDING HI-LO GAP HV WINDING General Requirements - Impedance Impedance %IX = 1 2 V N 1 3 LV BLD + Hilo HV BLD EL EL To Increase the Impedance then: Shorten EL Increase Hilo or LV/HV Radial Builds Increase Turns These Gaps are Prime Real Estate Optimize by Reducing the Gaps Magnetic Field SPX Transformer Solutions, Inc. September 26,

General Requirements Impedance Consequences Low Impedance High Impedance Standard Impedances are tabulated in C57.12.10-2010 Section 4.6.

38 General Requirements Impedance Consequences Low Impedance High Impedance Standard Impedances are tabulated in C Section Standard Impedances are classified by HV BIL and whether or not the unit has an LTC Standard Impedances are tabulated for the self-cooled (ONAN) rating SPX Transformer Solutions, Inc. September 26,

LV WINDING HV WINDING Dielectric Withstand Requirements Determine All Service and Test Voltages Equate All to AC Equivalent Voltage (Eav) Find Max Eav Calculate Stress in Oil Gaps* Calculate Strength

39 LV WINDING HV WINDING Dielectric Withstand Requirements Determine All Service and Test Voltages Equate All to AC Equivalent Voltage (Eav) Find Max Eav Calculate Stress in Oil Gaps* Calculate Strength of Oil Gaps* Check Local Stress *Alternatively Can Use Average Oil Stress Method for Approximation of Required Gap EXAMPLE: Hilo Min = Eav Edim + ins 2 = 100kv 5kv/mm + 3mm 2 = 21.5mm 3mm ins 100kV SPX Transformer Solutions, Inc. September 26,

40 Performance Requirements: Load Loss Load Loss (Pk) 2 Primarily I R In our design (I) is fixed, R can vary What factors influence (R)? R = ρ L A The rest is eddy loss and stray loss What factors influence eddy and stray loss? SPX Transformer Solutions, Inc. September 26,

41 Selecting an Optimized Design Determine the bounds limited by the design: Volts Amps Flux Density Impedance Minimum Gaps Current Density Determine the bounds limited by manufacturing: Core diameter, mass, height Winding diameter, mass, height Wire dimensions, ratios, hardness Overall core and coil assembly Height Weight Dimensional restrictions Paint booth Vapor phase Crane Capacity SPX Transformer Solutions, Inc. September 26,

42 Selecting an Optimized Design Core Diameter LV Turns Po Pk First Cost (Material) Loss Cost Total Owning Cost kW 75kW 300, , , kW 78kW 295, , , kW 80kW 290, , ,000 This process may take several iterations as the following is checked: Final Cooling Limited Space, Sound Level, Overload Customer Physical Constraints Multiple Loss Evaluations for Multiple Offers SPX Transformer Solutions, Inc. September 26,

43 Questions? Thank you! SPX Transformer Solutions, Inc.

Transformer Winding Design. The Design and Performance of Circular Disc, Helical and Layer Windings for Power Transformer Applications

Transformer Winding Design. The Design and Performance of Circular Disc, Helical and Layer Windings for Power Transformer Applications The Design and Performance of Circular Disc, Helical and Layer Windings for Power Transformer Applications Minnesota Power Systems Conference November 3 5, 2009 Earl Brown Heritage Center University of