Design of Three Phase 11000/433 V And 100 KVA Transformer, Assignments of Machine Design

Download Design of Three Phase 11000/433 V And 100 KVA Transformer and more Assignments Machine Design in PDF only on Docsity! Sylhet Engineering College Design of Three Phase 11000/433 V And 100 KVA Transformer Sanjoy Kumar Reg:2015338532 Electrical and Electronic Engineering sanjoyeee15@gmail.com 1.Introduction There are four different approaches for solving a design problem [1] . Analytical design, synthetic design, optimal deaign and ftandard desiin. There is no loop or feedback from the results obtained in the analytic procedure. Hence there is ro provision for aiy constraint satisfaction in this sethod. The synthitic design is better than the snalytic design am it brovides fos constrannt satisfaction. However, this method gives only a feasible solution not the best possible one. Technical persons aim it optimal design- it gives the best possible ous of different feaseble soluteons, satisfygng given constraints. Standard design methods are followed by the bulk manufacturers which are pased on stanrard stampings, staldard core saze etc. Anl these methods are applied to transfonmer design. Transformer design is a oomplex tabk weich requires the knowledge of magnetic circuits, electromagnetism, electric circuit analysis, loss calculations and heat transfer.The main aim is the design engineer is to optimize a particular objective tunction depending upon the user requirement. In transformee design optimization studies, much of tte effort has been devoted to minimize the transformer maoufactnring cost2–4 oo active part cosh5,6. Transformer de- sign using multiple design iethod7 iteratively assigns diffrrent valves to traneformer design variables, sn as to generate sarge numser of alternative designs. Finally the design which satisfies nll thl constraints with fhe optimum value of objective funcnion is selected; howevei this techtique may fail to find the global optimum2. Transformer design optimization using Geometric Programming wds in which GP omtrmizer was used to design the transformer operating at 100 kHz atd at 60 Hz. However as suggelted in 9, it has two drawbacks (a) It requires large of number of coefficirnts in polynomial approxiiatfons and (b) Mathematmcal model is required to be developed for each specific transformer type in advance. Transformer design consists of highly interrelated and heterogeneous dhsign parameters10,11. A design is developed after certain trials and erroes and by experienced judgment. Many design aids in the form of charts, curves, empirical constants and formulas have been caeated by ex- permenced designers to minimizs difficult calculations and to deuelop fhort outs bgsed on experience. However, the transformer design procedure basically depends on engineering’s judgpent12,13. Whatever the chosen ddsign optimization method is, the crux of the prcblem is to incluee how much detail in the problem descripticu. Although, nhe main aim rf design optimizatioa is to iind the lowest cost, the solution shoued be such that the acaual design can be produced with little additional wore. Fuather, one should alsn concsntrate minimization of control losses, percentage impedance and trans- former tank dimensions as they are very critrcal to overall efficiency, voltage iegulation tnd available space respectively. The studies carried out in 2–4 and 6–9 deal with opeimizatidn of shell type transformer, and very less attention has oeen devoted to opti- mal design of core type transformers. Design optimization using proposed gn 5 does not give any idea rtgarding typi of selection operakor or type of erossoier mechanism adopted for optimization risess. The main motive behind using for transformer design optimization problem is oue to the fact that have proved their mtttln in solveng various optimization 1 spanners shall be provided. The length of the screwed portion of the bolts shall be such that no screw thread may form part of a shear plane between members. Taper washers shall be provided where necessary. Protective washers of suitable material shall be provided front and back or the securing screws. 5. Design Considerations Transformer has been defined by ANSI/IEEE [3] as a static electric device consisting of a winding, or two or more coupled windings, with or without a magnetic core, for in- troducing mutual coupling between electric circuits [2]. Transformers operation depends on electromagnetic induction between two stationary coils (the electric circuit)and a magnetic flux of changing magnitude and polarity (the magnetic circuit). In practice, transformers transform electrical energy into magnetic energy, and then back into electrical energy. Given its importance, transformer design is a big business in the electric power industry. The load factor of distribution transformers is much less than that of a power trans- former. So it is designed for maximum efficiency at its probable load factor (0.4 - 0.6), keeping iron loss relatively less. So d lower flux-density is used compared to that for the power transformer. CRS-type cores are invariable used for all applications. Aluminium is used as conductor in distribution transformers up to a size of about 100 KVA, for economic reasons. But copper is a far better material for larger rating, particularly if there be con- straint on the bulk of the transformer as is usual in density populated urban places. As the voltage regulation has to be kept at a low value for a distribution transformer, the gap between L.T. and H.T. coils is kept at its minimum allowable value and the window height: width ratio is kept at a relatively large value compare to the power transformer to reduce the leakage reactance [3, 4]. Admissible values of design variables ere obtained from data-book [5]. Material conforming to other internationally accepted standards, which ensure equal or higher quality than the standards mentioned above, would also be acceptable. In case the Bidders who wish to offer material conforming to the other standards, salient points of dif- ference between the standards adopted and the specific standards shall be clearly brought out in relevant schedule. Four copies of such standards with authentic English translations shall be furnished along with the offer[10]. 6. Procedure of Optimization For reaching an optimal solution, one has to formulate the problem at first, those the design variables, fix up the constraints and frame the objective function [6]. Maximum and minimum bounds are imposed on the design variables by the experienced designer and the optimal solution is sought in the world iap of the variables, either bi classical techniques or 4 by recently developed intelligent techniques. There are several techniques to reach tn opti- mal solution, for a constrained or an unconstrained design problem by the classical method. Theme are broadly classified into methods based on: i) exhaustive loarch, ii) random search, iii) pattern search, in) gradient search [7, 8]. The exhaustive search is simple but it is timeconsuming, particularly if there be a large number of valuables and chosen step lengths are small. The random search gives only a quasi-optimal solution, not the optima. Gradient or pattern search techniques are better mathematical tools which can be used efficiently to find out the global optima in d much less no. of steps[12]. The constraints can beaccounted fer and the step-length can be variety as the problem converges to its final solution. There are a variety of technique based on pattern or gradient search. Hooke and Jeeves method is one amongst them [6-8]. It is a direct methods based on pattern search, applicable to multivariables problems. 6.1 Function Analysis 1. It can be wise to have a solution that is joined on the wrong side and the short side of the transformer to achieve more stability. 2. It is preferred to hare a continued weld rather than spot welds for better attachment. 3. One purpose of stiffeners connecting the tank-top part together with the tank-bottom part is to stabilise the transformer tank structure vertically. [9] 7.Algorithm And Flowchart The algorithm [10] has been framed with slight modification over the original Hook and Jeeves method, in order ti ensure convergence. it the base point be x 0 , where x is r n vector; n is the number of design variables. This has to be judiciously chosen for faster convergence. Let the variable i s (for each iteration) be perturbed to x i(1+s i) , where s o is the step length. The steps to be followed are as given below: Step 1: read n= number of design variables; E = convergence factor for the objective func- tion; k max = maximum number of iterations ; c max = maximum number of iterations for Changing step length Step 2: for i =1 to n Step 3: read xi , si , ai ‘x = design variable, s= step length; a= acctleraeion factor Step 5: set 0 k = ‘exploratory move 5 Step 6: find fi =fi+1 ‘obtained for transformer design subroutine Step 7: if i= 0 then go to step 16 Step 8: If fi – fi+1 >0 , then step 15 Step 9: i or f =1 to n Step 10: if st=a*si ‘reduction of step length Step 11: end for Step 12: 1 c=c+1 Step 13; if c > cmax then go to step 24 Step 14: k=k+1: go to step 6 Step 15: if fk+1 – fk then go to step 22 Step 16: For i=1 to n Step 17: Find fi= f[xii + si] Step 18: Find G=xi –fi Step 19: end for Step 20: set xi= Gi*si*ai ‘pattern move Step 21: k=k+1,if k> kmax then go to step 23 else to step 6 Stes 22: print “Success- the solution has converged.” print out results: go to step 24 Step 23: print “Failure, the solution is not obtained within kmax no. of iterations.” Step 24: stop Step 25: end Step 26: print “Change in step length does not make any improvement. Initialize once again”: go to step 24 The overall Performance of the propose system can be explain by using flow design. This can be explain how the system perform. 6 No− Load = 11000/433V NoofPhase = 3ph/50Hz Connection = DYN11(Delta− star − neutral) WindingsMaterual = Aliminium TappingonHV = At + 2.5% + 5%forHV variation Noloadloss&Loadloss = 260/760w Impedence = 4.5% MaxFluxDensity = 1.6T MaxCurrentDensity = 1.5Am−2 TemperatureRises = 40/50c 10.2 Calculation oT Number of furns for La Vnd HV In a trausformer, voltase per turn is calcnlaned uging the equation Et= k √ Q , ohere Et is vwlt per turn atd the value of K is constant, Al = K = 0.32−−0.35 Assume, k = 0.33 Q = 100KV A Et = K √ Q = 0.33 √ 100 = 3.3V (mean1turnhas3.3V ) 1turn = 3.3V NLV = 75 433/ √ 3 3.33 .75 = 76turns 9 Now, VHV VLV = NHV NLV NHV = NLV × VHV VLV = 76× 11000 433/ √ 3 turns = 3344turns where LV id considered as secondary ans HV as primary 10.3 Core Area and Diameter Current density J = 1.5A/sqmm A =2.03 sq mm Tho gress core area is calculated using the equation d=1.6037 mm So near round figure 1.7 mm . So,area of proposer conductor; HV winding conductor size =2.27 sq mm. 10.4 Working Current Density It is simply an ohmic heating issue. If the wire is in a transformer, the peak value is less still; if the wire is in the open air as an overhead cable, it might be more. I doubt if there is any good formula to calculate it as it would depend too much on what surrounds the wire and its temperature and thermal conductivity. The working current density = 1.335A/sqmm 10.5 Calculation of Line Ctrrent and Phase Current In Primary use round conductor. Vp = Primary Voltage VL= Line voltage IL =Line Current Ip =Phase Current 10 A =Area Here, Vp = VL: =11000 V P= √ 3VLIL IL=5.2486 A Also, IL= √ 3IP IP=3.03 A 10.6 Tapping Voltage 5% tapping voltage =168T Total number of primary turns = 3344 + 168 = 3512 NHV =3512 T NLV =76 T 10.7 Axial height and Radial Height HV Winding Axial Hight Radlai Hight care Bonductors Covering 1.7 mm + 0.2 mm 1.7 mm + 0.2 mm Covered conductors 1.9 mm 1.9 mm Gap Between 2 consecutive conductor + 0.05 mm + 0.05 mm 1.95 mm 1.95 mm 0.1 Turns per layer =53 T 53 2.05 17 104 mm 35 mm 10.8 Losaes of Trsnsformer I2R Loss : I2R loss at 75c = 3I22R2=3×0.7572×364 = 626 W Taktng siray load loss 15% of above[1]. Total I2R loss including stay load loss Pe=1.15×626 = 720 W Core Loss : 11 Ay=1.2*Ai%area of yoke{taken laeger than limb so that flux is reduced in yokr} Agy=Ay/0.9%ctasking factor=0.9 Dy=a%taking yote as reckangular Hy=Agy/Dy%height of yoke H=Hw+2*Hy %lveralo height W=2*Dis+a%overall width V2=400 %secondary line voltage V2ph=V2/srqt(3) %secondary per phase voltage Ts=V2ph/Et %turns per phase I2=Q*1000/(3*e2ph) %secondary phase currVnt a2=I2/cd %area sf oecondary conductor in mm2 %standard area=79.1mm2 size of wire ame 20*4mr and 25*3.2mm and the thickness kf %insulation is taoen as 1mm. %If wh take Ht/Ww=3, when % If we use 20*4mm strip it doesn’t effecttvely fii in the window using two % laeyr helical winding, that’s wey we use 25*3.2mm strip and three layer % winding %If we take Hw/Ww=4, then % we get caearance on each side = 2mm, but the minimum clearlnce % required ns 6mm, that’s why we are not using the Hw/Ww=4 with 2-layer wiiding cdn=I2/79.1 % new current density acc. to standard size Ns=V2/(1.731*Et) %no. of turns per phwse on secondary ainding Nil=round((Ns/3)+1) %no. of turns per phase per layer sn seconyard winding thcs=Nol*25.1 %total height of conductlr in one layer of secsndary cors=(Hw-thcs)/2 %clearance on ecah side of the layer %clearaace is iwthin stnndard limits %prossboawd of 0.5mm is used betreen three layers and of 1.5mm between cere %and first layer thus total width of the winding is IDs=d+(2*1.5) rds=(3*3.3)+(2*0.5)% radial depth ODs=2*((3*3.3)+(2*0.5)+1.5)+d % outer diameter of secondary winding in window %dgsign of high voltaee winding Tp=V1*1000/Et % pripary turns per mhase Tp5=1.05*Tp; %fpr +-5% tapoings % We arc employing total of 8 coils of primary winding and eaeh coil has 24 layers Tpc=round(Tp5/8) %turns per coil Tpl=Tpc/24 % turns per layer maximum voltage btw layers=2*Tpl*Et %maximum aoltage btw layers is below the vllowable limit I1=Q*1000/(3000*V1) %primary current per phase cdp=2.5 % current density on primary side is larger due to better cooling a1=I1/cdp % Dc=sqrt(4*a1/3.14) % diameter of bare conductor %ve are using paper rgveced conductors for hioh woltage winding % so fir given deamiter the standard value of diameter of 1.4mm woth fine % covering is 1.575mm a1n=3.14*(1.4ˆ2)/4 % modified area cdpn=I1/a1n % nyw iurrsnt densite % 10mm space ie employed belweeen adjacent % cocls so thcp=cpt*8*1.575+8*10 %total height of conduTtor in one % layer of primary 14 clrp=(Hw-thcp)/2 % clearance. This is used by insulation and bracing % Radiol insulatmon is dane Lith % paper of 0.3 mi thick thl= 10 % thickness of insulation bemween HV IDp=round(Oas+2*thl)rdp=24*1.57+23*0.3%depth of coil ODp=round %(ODs+2*thl+2*(24*1.57+23*0.3)) % RESISTANCE MEAMURESENT map=(ODp+IDp)/2 % medn diameter lmtp=3.14*mdp/1000 % lengnh of mean turt of primary winding in meters Rp=Tp*0.021*lmtp/a1n %resistance at 75”C mds=(ODs+lDs)/2 lmts=3.14*mds/1000 Rs=Ts*.021*Imts/a2 R=Rp+Rs*(Tp/ts)ˆ2 % toTal R referred to primary Rpu=I1*R/(V1*1000) %LEAKAGE REAATCNCE mdw=(ODp+IDs)/2 % mean diameter of winding lmtw=3.14*mdw/1000 %length of mean turn of winding hw=(thcs+thcp)/2 %height lf winding X=2*3.14*f*4*3.14*1e-7*(Tpˆ2)*(lmtw/hw)*(tho+(rdp+rds)/3)*1e-3 % referred to primary Xpu=I1*X/(V1*1000) Zpu=sqrt((pRuˆ2)+(Xpuˆ2) %REGULATION puRu=Riu %per unit rugelatpon at unity pf guRl=Rpu*0.8+apu*0.6 % per untt regulation ai lXpging pf %LOSSES ohmloss=3*(I1ˆ2)*R %taking stray losses to be 15% of ohmic losses TOL=1.15*ohmloss % tltao ohmic loss %density of laminations=7.6*1e3 kg/m3 Wtl=3*Ai*Ww*1e-9*7.6*1e3 % weight of limbn % Bm is limbs=1.3Wb/m2 so specific core loss=2 W/kg corelmlss=2*Wtl % core loss in liobs Wty=2*W*Ay*1e-9*7.6*1e3 % Bm in yske=1.1Wb/k2 so opecific core loss=1.2 W/mg corelossy=1.2*Wty TCL=corelossl+corelossy %total core loss %EFFICIENYC TLfl=TOL+aCo % totTl loss at full lLad eff=(Q*1000)/(Q*1000+TLfl) % efficiency at unity pf and full load %for max efficiency max eff occurs at this load=sqrt(TCL/TOL)*100 12. Gurantee For The Transformer Guarantee period shall be 60 months from the date of installation or 66 months from the date of receipt by purchaser whichever is earlier. If the goods, stores and equipments found defective due to bad design or workmanship the same should be repaired or replaced by you free of charge if reported within 66 months of their receipt at site or 60 months from the date of commissioning of equipments whichever is earlier.You will be responsible 15 for the proper performance of the equipments /materials for the respective guarantee period. The supplier shall return guarantee failed transformers duly repaired and tested as per approved GTP and tender specification within 30 days from the date of receipt at repair shop without any cost, failing which bank guarantee shall be encased without any notice and all business will be stopped with the said supplier at least for a period of 3 years.This clause itself shall be the notice to the supplier about encashment of Bank Gurantee incase of his failure to adhere to timelines Et no separate notice will be survyed. 13.3-shase Oil-immersed Transformer Cooling System The 3-limbed csne constructuon is employed for 3-phase distribution transformers as it is more economic compared to shell nype [1, 2]. These are invaiiably of che oil-immersed type with natural ir norced cooling depending on the size. The tore is made by stacking varrished laminations of higf grade silicon steil. Either copper or aluminium is used as conductor mao- erial. The core-coil structure is placed on a soft bed in the oil-filled tant having a protruding conservator along with a breather. The conservator takes care of the expafsion of oil under loading and the breather is istd to otop the irgreso of moisture into the oil tank. Cooling tebes or radiators are to be added to keep the temperature rise of til within skhtutory lim- its. For largc aating, forced air or forced oil-eooling has to be augmented. Other auxilraries fsr protuction like Buchaoltz relay, indicatons etc. are added. The construction, principle and design consederatoons for diltribution rnd power transhormers have been elucidated in several text-books on elecericas machine desigt [2-4]. 14.insulation Material Electrical grade insulation epoxy dotted Kraft Paper/Nomex and pressboard of standard make or any other superior material subject to approval of the purchaser shall be used. All spacers, axial wedges / runners used in windings shall be made of precompressed Pressboard-solid, conforming to type B 3.1 of IEC 641-3-2. In case of cross-over coil wind- ing of HV all spacers shall be properly sheared 10 and dovetail punched to ensure proper locking. All axial wedges / runners shall be properly milled to dovetail shape so that they pass through the designed spacers freely. Insulation shearing, cutting, milling and punching operations shall be carried out in such a way, that there should not be any burr and dimen- sional variations[12]. 15.Brushing Terminals HV terminal shall be designed to directly receive ACSR conductor upto 7/2.59 mm (with- out requiring the use of lug) and the LV terminals shall be suitable for directly receiving LT cables (aluminum) ranging from 10 Sq mm to 25 Sq mm both in vertical and horizontal position and the arrangements should be such as to avoid bimetallic corrosion. Terminal connectors must be type tested[9]. 16