This document summarizes the design of a 1000 KVA, 33KV/11KV power transformer. Key details include: - Core and winding designs to meet specifications like voltage ratio and impedance - Calculations of losses, efficiency, and temperature rise - Dimensions of the transformer and its components like the core, windings, and tank - Additional specifications like no load current and impedance voltage are verified to meet requirements.

1. EE 3220 Electrical Machine Design
Project on Transformer Design
Submitted To:
DR.MD.HABIBULLAH
PROFESSOR,
DEPT OF EEE,
KUET
MD.ABU SAYED JANNATUL ISLAM
ASSISTANT PROFESSOR,
DEPT OF EEE,
KUET
Submitted by:
Group – 13
Members:
1. Mainul Islam [1703032]
2. Asif Rahman [1703046]
3. Asif Adnan Tajwer [1703069]
4. Al Mamun Sarker [1703070]
Date of Submission: 18 June 2021

2. PROBLEM
Design a 1000 KVA, 33KV/11KV, 50hz, 3-phase, core type,
delta/star and ONAN cooling based power transformer. Use
5% tapping at HV side and also ensure that the impedance
voltage is below 6%.

3. CORE DESIGN
THE VALUE OF K IS TAKEN FROM THE TABLE K=0.45 FOR 3PHASE CORE TYPE DISTRIBUTION
TRANSFORMER.
VOLTAGE PER TURN ET =K 𝑄 =.7 1000=22.14 V
THEREFORE FLUX IN THE CORE , ΦM=
𝐸𝑇
4.44×𝑓
=
22.14
4.44×50
= 0.0997WB
HOT ROLLED SILICON STEEL GUARD 92 IS USED . THE VALUE OF FLUX DENSITY BM IS ASSUMED
AS 1.45WB/M2.
NET IRON AREA AI=
0.0997
𝟏.𝟒𝟓
= 0.06878=68.78 ×103MM2
USING A CRUCIFORM CORE , AI =0.56D2
DIAMETER OF CIRCUMSCRIBING CIRCLE , D =
68.78×103
..
56
=350.46 MM
REFERENCE WIDTHS OF LAMINATIONS:
A=.85D=.85×350.46=297.9 MM
B=.53D=.53×350.46=185.7 MM
THE LAMINATIONS ARE PUNCHED FROM 750 MM WIDE PLATES AND THE NEAREST STANDARD
DIMENSIONS ARE:
A=298 MM AND B =186 MM

4. WINDOW DIMENSION
THE WINDOW SPACE FACTOR FOR THE REQUIRED RATING TRANSFORMER IS 𝐾𝑤=12/(30+KV)=.19
THE CURRENT DENSITY IN THE WINDINGS IS TAKEN 3.2 A/MM2
OUTPUT OF TRANSFORMER, Q =3.33FBMKWSAWAI×10-3
THEREFORE WINDOW AREA, AW=
1000
3.33×1.45×50×.19×3.2×106×.06878×10^−3
= .09905 M2
=99.05× 103MM2
TAKING THE RATIO OF HEIGHT & WIDTH OF WINDOW AS 4.0;
HW×WW=99.05× 103 MM2 OR, 4×WW²= 99.05× 103
THEREFORE WIDTH OF WINDOW , WW=157.4 MM &
HEIGHT HW=
99.05× 10^3
157.4
= 629.3 MM
AREA OF WINDOW PROVIDED ,AW =629.3*57.4
= 99.05 M2
DISTANCE BETN ADJACENT CORE CENTER, D =WW+D=157.4+351
=508.4MM

5. YOKE DESIGN
THE AREA OF YOKE IS TAKEN AS 1.2 TIMES THAT OF LIMB.
THEREFORE FLUX DENSITY IN YOKE = 1.45/1.2 = 1.208 WB/M2
NET AREA OF YOKE =1.2×68.78 ×103 =82.53×103 MM2
GROSS AREA OF YOKE = 76.59×103/0.9=91.7×103MM2
TAKING THE SECTION OF YOKE AS RECTANGULAR ,
DEPTH OF YOKE , DY=A=298 MM
THEREFORE, HEIGHT OF YOKE ,HY =
91.7×103
298
=307.71MM

6. OVERALL DIMENSION OF FRAME
HEIGHT OF FRAME ,H=HW+2HY=629.3+2*307.71= 1243MM
WIDTH OF FRAME ,W=2D+A=2×351+298 =1000MM
DEPTH OF FRAME, DY=A= 298MM

7. L-V WINDING
SECONDARY VOLTAGE = 11KV
SECONDARY PHASE VOLTAGE ,VS=
11,000
3
=6350.85V
NUMBER OF TURNS PER PHASE, TS =
𝑉𝑠
𝐸𝑡
=
6350.85
22.14
=287
SECONDARY PHASE CURRENT, IS=
1000
3×6.35
=52.486 A
CURRENT DENSITY 3.2 A/MM2 IS USED.
AREA OF SECONDARY CONDUCTOR AS=52.486/3.2= 16.4MM2
USING A BARE CONDUCTOR OF 5.5×3.1 MM
AREA OF CONDUCTOR , AS=17 MM2
CURRENT DENSITY IN SECONDARY WINDING , ΔS=52.486/17 = 3.087 A/MM2
THE CONDUCTOR ARE PAPER COVERED. THE INCREASE IN DIMENSION ON ACCOUNT OF ACCOUNT OF PAPER COVERING
IS 0.5 MM.
THEREFORE DIMENSION OF INSULATED CONDUCTOR = 6×3.6 MM2
USING 3 LAYER WINDING LAYERS, HELICAL WINDING IS USED. THEREFORE SPACE HAS TO BE PROVIDED (
𝑇𝑠
3
+ 1)=(
287
3
+ 1) =
97
TURNS ALONG THE AXIAL DEPTH.
AXIAL DEPTH OF L.V WINDING LCS=97×6 =582
THE HEIGHT OF WINDOW IS 629.3 MM. THIS LEAVES A CLEARANCE OF (629.3-582)/2=23.7 MM OF EACH SIDE OF THE
WINDINGS.
RADIAL DEPTH OF LOW VOLTAGE WINDING,
BS=NO. OF LAYERS X RADIAL DEPTH OF CONDUCTOR + INSULATOR BETN LAYERS
=3×3.6+2×0.5 = 12 MM
DIAMETER OF CIRCUMSCRIBING CIRCLE , D =351 MM USING PRESSBOARD WRAPS
1.5MM THICK AS INSULATION BETNL.V. WINDING AND CORE.

8. H-V WINDING
PRIMARY LINE VOLTAGE =33000 ; DELTA
PRIMARY PHASE VOLTAGE ,VP=33000 V
THEREFORE NO. OF TURNS PER PHASE, TP=11000 ×
𝑇𝑠
𝑉𝑠
=
33×287
6.35
=1491.5
AS 5% TAPPINGS ARE TO BE PROVIDED, THEREFORE THE NO. OF TURNS IS INCREASED TO TP=1.05×1491.5=1567
THE VOLTAGE PER COIL IS ABOUT 1375 V THEREFORE USING 16 COILS,
VOLTAGE PER COIL 33000/16=2062.5V.
TURNS PER COIL 1492/16=94
USING 15 NORMAL COILS OF 90 TURNS AND 1 REINFORCED COIL OF 150 TURNS.
TOTAL H.V TURNS PROVIDED, TP=15 × 90 + 150=1500
TAKING 12 LAYERS PER COIL. TURNS/COIL=60/12=8 (APPROXIMATE)
MAXIMUM VOLTAGE BETN LAYERS = 2×8×22.14 =354.2 V
H.V. WINDING PHASE CURRENT, IP =(1000×1000)/(3×33000)=10.1A
AS THE CURRENT IS BELOW 20A, CROSS-OVER COILS ARE USED H.V WINDING
TAKING A CURRENT DENSITY OF 2.4 A/MM2
AREA OF H.V. CONDUCTOR , AP=10.1/2.4 = 4.2MM2
DIAMETER OF BARE CONDUCTOR = =2.02 MM

9. H-V WINDING(CONT.)

10. RESISTANCE
MEAN DIAMETER OF PRIMARY WINDING =
491.2+427
2
=459.1 MM
LENGTH OF MEAN TURN OF PRIMARY WINDING LMTP=⺎×459.1×10-3
=1.44 M
RESISTANCE OF PRIMARY WINDING AT 75℃,RP=
𝑇𝑝×⍴×LMTP
𝑎𝑝
=
1500×0.021×1.44
3.46
= 12.49 Ω
MEAN DIAMETER OF SECONDARY WINDING=
377+254
2
=315.5MM
LENGTH OF MEAN TURN OF SECONDARY WINDING LMTS=⺎×315.5×10-3
=0.99M
RESISTANCE OF SECONDARY WINDING AT 75℃,RS=
𝑇𝑠×⍴×LMTS
𝑎𝑠
=
287×0.021×.0.99
17
=0.351Ω
THEREFORE TOTAL RESISTANCE REFERRED TO PRIMARY SIDE ,
RP=12.49+
1500
287
2
× .351=35.07 Ω
P.U. RESISTANCE OF TRANSFORMER ΕR=
𝐼𝑝×𝑅𝑝
𝑉𝑝
=
10.1 ×35.07
33000
=0.0107

11. LEAKAGE REACTANCE
MEAN DIAMETER OF WINDINGS =
491.2+354
2
=422.6 MM
LENGTH OF MEAN TURN,LMT =⺎×422.6×10-3=1.32 M
HEIGHT OF WINDING ,LC =( LCP+LCS) /2 =(585.6+582)/2
= 584 MM(APPROX.)
THEREFORE LEAKAGE RESISTANCE REFERRED TO PRIMARY SIDE ,
XP=2×⺎×50×4×⺎×10-7 ×15002×
1.32
.584
× 15 +
32.1+12
3
× 10−3
=22.76Ω
P.U. LEAKAGE RESISTANCE OF TRANSFORMER ΕR=
10.1 ×22.76
33000
=.00717
P.U IMPEDANCE ΕS= .0107 2 + .00717 2=0.013
HERE IMPEDANCE IS 1.3% WHICH IS BELOW 6%.

12. REGULATION
P.U REGULATION, E=ERCOSØ+EXSINØ
PER UNIT REGULATION AT UNITY POWER FACTOR, E=ER=0. 00717
AT ZERO P.F LAGGING, E=𝐸𝑥 = .00697
AT 0.8 P.F LAGGING, E= 0.00717×0.8+0.00697×0.6
=0.0099

13. LOSSES
I2R loss:
I2R loss at 75℃ = 3 × 𝐼𝑝2 × 𝑅𝑝=3 × 10.12 × 35.07
=10732.5 W
Taking stray loss 15% above.
Total I2R loss,Pc=1.15 X 10732.5 =12342.4 W
Core Loss:
Taking density laminations as 7.6X103kg/m3
Weight of 3 limbs =3X0.06878X0.0997 ×7.6X103=156.35 kg
Core loss in limbs=156.35X1.2=187.6 W
Weight of two Yokes = 2X.08253X1X7.6X103=1254.5 kg
Core loss in Yoke=1254.5X1.8= 2258.1W
Total core loss,Pi=187.6 + 2258.1 =2445.7W

14. EFFICIENCY
TOTAL LOSSES AT FULL LOAD = 12342.4+2445.7
= 14788W=14.788KW
EFFICIENCY AT FULL LOAD UNITY P.F. =
1000
1000+14.788
× 100%
=98.5 %
FOR MAXM EFFICIENCY ,𝑥2
𝑃𝑐 = 𝑃𝑖
OR, 𝑥 =
𝑃𝑖
𝑃𝑐
=
2445.7
12342.4
=0.445
THE MAXIMUM EFFICIENCY OCCURS AT 44.5% OF FULL LOAD.
THIS IS GOOD FIGURE FOR POWER TRANSFORMER.

15. IMPEDANCE VOLTAGE OF
TRANSFORMER:
THE IMPEDANCE VOLTAGE SHOULD BELOW 6%. So We Find impedance voltage of
Transformer is 1.3%.
%Z=impedance Voltage.
Rated Voltage at H.V. Winding=33000V
As we know, %Z=(Impedance Voltage / Rated Primary Voltage) x 100
1.3= (Impedance Voltage / 33000) x 100
Impedance Voltage= 429
This means there would be a 429 voltage drop in the high-voltage winding at full load
due to losses in the windings and core.

16. NO LOAD CURRENT
CORRESPONDING TO FLUX DENSITY OF 1.45 WB/M2 AND 1.208 WB/M2 IN THE CORE AND
YOKE RESPECTIVELY
ATC =420 A/M & ATY =130 A/M
TOTAL MAGNETIZING MMF =3*420*0.0997+2*130*1
= 385.62A
MAGNETIZING CURRENT IM=
𝐴𝑇𝑂
2𝑇𝑃
=
385.62
3∗ 2∗1500
=0.0606A
LOSS COMPONENT OF NO LOAD CURRENT, IL=
2445.7
3∗33000
= 0.025A
NO LOAD CURRENT, IO= 0.0606 2 + 0.025 2
= 0.065A
NO LOAD CURRENT AS A PERCENTAGE OF FULL LOAD CURRENT=
0.065
10.1
∗ 100=.644%
ALLOWING FOR JOINTS ETC THE NO LOAD CURRENT WILL BE ABOUT 2% OF FULL LOAD
CURRENT.

17. TANK
HEIGHT OVER YOKE,H = 307.71MM
ALLOWING 150MM AT THE BASE & 350 MM FOR OIL,
HEIGHT OF OIL LEVEL =307.71+150+350= 807.71 MM
ALLOWING 450MM HEIGHT FOR LEADS ETC
HEIGHT OF TANK HT=807.71 + 450 =1257.71 MM
WIDTH OF THE TANK , WT=2D+DE+2L=2 × 491.2 + 508.4 + 2 × 85
=1660.8 MM
LENGTH OF THE TANK,LT=DE+2B=491.2+2X125 =741.2 MM
TOTAL LOSS DISSIPATING SURFACE OF TANK =2 1.66 + .7412 × 1.257 = 6.036M2
SPECIFIC LOSS DISSIPATION DUE TO RADIATION & CONVENTION IS 30W/M2-℃
TEMPERATURE RISE =
14788
30×6.036
= 81.65℃
THIS IS ABOVE 50℃ & THEREFORE PLAIN TANK IS SUFFICIENT FOR COOLING & TUBES
ARE REQUIRED.

18. NO OF TUBES CALCULATIONS
TUBES HEIGHT, Ht= 1.257M &WIDTH, Wt=1.66M
SO, AREA OF PLANE TANKS, St= 2(.74+1.66)*1.257= 6.03 M2
LET, TUBE AREA BE XSt.
TOTAL DISSIPATING SURFACE= (1+x)St = 6.03(1+x).
SPECIFIC LOSS DISSIPATION=
14788
4.34 1+𝑥 ∗35
=
68.14
1+𝑥
ASSUME THAT, TEMPERATUIRE RISE TO BE LIMITED TO 50oC AND TOTAL LOSS IS 14788W.
LOSS DISSIPATION =
12.5+8.8𝑥
1+𝑥
W/M2-oC
So,
12.5+8.8𝑥
1+𝑥
=
68.14
1+𝑥
=> X = 6.32
IF DIAMETER OF EACH TUBE BE 100MM AND AVERAGE HEIGHT IS 2M THEN,
WALL AREA OF EACH TUBE = πdtlt = π*0.1*2
= 0.63 M2
TOTAL NUMBER OF TUBES REQUIRED =
6.32
0.63
=10(APPROX.)
SO, NEARLY 10 TUBES ARE RUQUIRED.

19. DESIGN SHEET
Delta
/
Star
KVA
1000
Frequency
50 HZ
Type of
cooling:
ONAN
Other
ratings:
Type:
Core
Phase
3

20. DESIGN SHEET(CONT.)
Line
Volage
HV:33000V
LV:11000V
Phase
voltage
HV:33000V
LV:6350.8V
Line
current
HV:17.5A
LV:52.48A
Phase
current
HV:10.1A
LV:52.48A

21. DESIGN SHEET(CONT.)
CORE
1 Material --- 0.35mm thick 92 grade
2 Output Constant K 0.7
3 Voltage per turn Et 22.14 v
4 Circumscribing circle
diameter
d 350.46 mm
5 No. of steps --- 2
6 Dimensions a 297.9 mm
b 185.7 mm
7 Net iron area Ai 68.78*10^3 mm2
8 Flux density Bm 1.45Wb/m2
9 Flux Φm 0.0997 wb
10 Weight 1410.95Kg
11 Specific iron loss 1.733 W/kg
12 Iron loss 2445.7 W

22. DESIGN SHEET(CONT.)
YOKE
1 Depth of Yoke Dy 137 mm
2 Height of Yoke Hy 307.71mm
3 Net Yoke area Ay 82.53x103 mm2
4 Flux density 1.208 Wb/m2
5 Flux 0.0996 Wb
6 Weight 627.75kg
7 Specific iron loss 3.60W/kg
8 Iron loss 2258.1 W

23. DESIGN SHEET(CONT.)
WINDOWS
1 Number 2
2 Window space factor Kw 0.19
3 Height of window Hw 629.3 mm
4 Width of window Ww 157.4 mm
5 Area of window Aw 99.05*103 mm2

24. DESIGN SHEET(CONT.)
FRAME
1 Distance btn adjacent limbs D 311 mm
2 Height of Frame H 1243 mm
3 Width of Frame W 1000 mm
4 Depth of wondow Dy 298 mm

25. DESIGN SHEET(CONT.)
WINDINGS
Sl no. Properties L.V. H.V.
1 Type of winding Helical Cross-over
2 Connections Star Delta
3 Conductor Dimensions bare 5.5*3.1 mm2 Diameter= 2.02 mm
insulated 6x3.6 mm2 Diameter= 2.1mm
Area 17.05 mm2 3.2 mm2
No. in parallel None None
4 Current Density 3.087 A/mm2 2.4 A/mm2
5 Turns per phase 287 1492
6 Coils total number 3 16
per core leg 1 5
7 Turns Per coil 287 15 of 90,1of 150
Per layer 96 8
8 Number of layers 3 12
9 Height of winding 582 mm 585.6 mm
10 Insulation Btn layers 0.5 mm press board 0.3 mm paper
Btn coils 5 mm spacers
11 Coil Diameters Inside 354 mm 427mm
Outside 377 mm 491 mm
12 Depth of winding 12 mm 32.1 mm
13 Length of mean turn 0.99 m 1.44 m
14 Resistance at 75℃ 0.351Ω 12.49 Ω

26. DESIGN SHEET(CONT.)
INSULATIONS
1 Btn L.V. winding & Core Press board wraps 1.5mm
2 Btn L.V. winding & H.V. winding Bakelized paper 5mm
3 Width of duct btn L.V & H.V. 5mm

27. DESIGN SHEET(CONT.)
TANK
1 Dimensions Height Ht 1257.71 m
Length Lt 0.748 m
Width Wt 1660.8 m
2 Oil level --- 0.8077 m
3 Tubes 10
4 Temperature rise --- 81.65℃
5 Impedance P.U. Resistance --- 0.0107
P.U. Reactance --- 0.00697
P.U. Impedance --- 0.013
6 Losses Total Core loss --- 2445.7 W
Total copper loss --- 12342.4 W
Total losses at full
load
--- 14.78 kW
Efficiency at full
load & u.p.f.
--- 98.5%

28. THAT’S IT!!🙂
THANK YOU!!😁