TRANSFORMER DESIGN SIMULATION REPORT ==================================== Run mode : optimize Requested sections: frame, no-load, lv, hv, performance, tank Calculated chain : frame, no-load, lv, hv, performance, tank Rating : 630.0 kVA, 11000 / 415 V, 50 Hz, 3 phase Connection : Delta-Star (Dy11) Cooling : ONAN Reference temp. : 75.0 C for winding-loss comparison 1. MAGNETIC FRAME ----------------- Volts per turn Et = K*sqrt(kVA/ph) 8.6961 V/turn Net core area Ai = Et/(4.44*f*Bm) 0.024482 m2 Gross core area Ac = Ai/ki 0.027203 m2 Core diameter d = sqrt(Ai/k) 0.2020 m Window space factor kw = 10/(30+HV[kV])*multiplier 0.2805 Window area Aw 0.132454 m2 Core/window height L 0.6310 m Core-centre distance D 0.4120 m Window proportion L/(D-d) 3.0048 Yoke length W = 2D + yoke-width-factor*d 1.0060 m Yoke gross area Ay 0.031283 m2 Yoke width / height by / hy 0.1818 / 0.1721 m Core flux density Bm 1.6000 T Yoke flux density By 1.3913 T Specific core/yoke loss 1.4000 / 1.1162 W/kg Core / yoke mass 404.23 / 494.09 kg Core / yoke iron loss 565.93 / 551.50 W Total iron mass 898.32 kg Total iron volume 0.114436 m3 Iron loss Pi 1.117 kW 2. NO-LOAD CURRENT ------------------ LV phase voltage 239.600 V LV turns T2 = ceil(Vphase/Et) 28 turns LV phase current 876.459 A Core/yoke AT per m atC / atY 200.00 / 110.00 AT/m Core/yoke AT ATC / ATY 378.60 / 221.32 AT Total AT per phase (ATC+ATY)/ph 199.973 AT Wattful component Iw 1.5546 A Magnetizing component Im 5.8076 A No-load current I0 = sqrt(Iw2+Im2) 6.0121 A No-load ratio I0/I2 0.6859 % 3. LOW-VOLTAGE WINDING ---------------------- Turns / phase current 28 / 876.459 A LV phase voltage 239.600 V Available winding height 504.80 mm Turns radial / axial 7 / 4 Conductor arrangement 18 parallel, 3 x 6 strands Space per turn ALT 126.20 mm Bare strand size 20.00 x 1.00 mm Conductor area / density 349.272 mm2 / 2.509 A/mm2 Active / total axial height 497.60 / 597.60 mm Axial slack 33.40 mm Radial width 31.20 mm Inner / outer diameter 228.00 mm / 290.40 mm Mean turn / conductor length 0.814301 / 22.800423 m Copper volume / mass 0.00796355 m3 / 71.353 kg Resistance at 20 C / 75 C 0.001125 / 0.001368 ohm Copper loss at 20 C / 75 C 2.5936 / 3.1530 kW 4. HIGH-VOLTAGE WINDING ----------------------- Turns / phase current 1286 / 19.091 A HV phase voltage 11000.000 V Available winding height 441.70 mm Coils / axial x radial strands 12 / 4 x 28 Coil layout 112 middle turns, 83.0 end turns Space per coil ALT 36.81 mm Bare conductor / area 8.00 x 1.00 mm / 7.840 mm2 Current density 2.435 A/mm2 Active / total axial height 469.20 / 599.20 mm Axial slack 31.80 mm Radial width 39.20 mm Inner / outer diameter 322.40 mm / 400.80 mm Adjacent winding clearance 11.20 mm Mean turn / conductor length 1.136000 / 1460.895876 m Copper volume / mass 0.01145342 m3 / 102.623 kg Resistance at 20 C / 75 C 3.212480 / 3.905368 ohm Copper loss at 20 C / 75 C 3.5125 / 4.2701 kW 5. PERFORMANCE -------------- LV / HV copper loss at 20 C 2.594 / 3.512 kW LV / HV copper loss at 75 C 3.153 / 4.270 kW Total copper loss at 20 C / 75 C 6.411 / 7.794 kW Iron / load / total loss 1.117 / 7.794 / 8.912 kW Full-load efficiency at unity PF 98.605 % Maximum efficiency / load 98.910 % / 238.54 kVA Mean turn / active coil length 0.97515 / 0.46920 m HV ampere-turns per phase 24550.91 AT Resistance / reactance / impedance 1.237 / 9.142 / 9.225 % Regulation at 0.85 PF / unity PF 5.867 / 1.237 % PF load pu loss kW output kW efficiency 1.00 1.00 8.912 630.00 98.605 % 0.85 1.00 8.912 535.50 98.363 % 0.85 0.75 5.502 401.62 98.649 % 0.85 0.50 3.066 267.75 98.868 % 6. TANK, COOLING AND MASS ------------------------- Tank dimensions L x W x H 1.365 x 0.581 x 1.475 m Configured clearances L x W x H 0.140 x 0.180 x 0.500 m Tank volume / plain surface 1.169 m3 / 5.740 m2 Plain tank rise / cooled rise 124.20 C / 49.90 C Tube diameter / height 0.050 / 1.250 m Area per tube / required area 0.196 / 12.135 m2 Cooling tube count 62 Active / shipping mass 1083.02 / 2433.56 kg Oil volume / oil mass 1.035 m3 / 890.50 kg Specific active mass 1.719 kg/kVA BILL OF MATERIALS ----------------- HV copper 102.62 kg LV copper 71.35 kg Active core steel 898.32 kg Fabricated tank steel 460.04 kg Insulating oil 890.50 kg Material cost index 4990.33 ENGINEERING ASSESSMENT ---------------------- Status Metric Result Expected / benchmark PASS Core window proportion 3.005 ratio 2.500 to 4.000 Meaning: L/(D-d) checks whether the magnetic window is sensibly proportioned. Verdict: Inside the 2.5 to 4.0 design band. Basis: Academic design rule PASS No-load current 0.686 % 0.500 to 1.000 Meaning: Excitation current as a percentage of rated LV phase current. Verdict: Inside the textbook 0.5 to 1.0 percent band. Basis: Academic design rule PASS LV current density 2.509 A/mm2 2.300 to 3.500 Meaning: Copper loading determines conductor heating and material use. Verdict: Within the selected transformer-design band. Basis: Academic design rule PASS LV axial slack 33.400 mm >= 7.000 Meaning: Remaining axial allowance for insulation and assembly tolerance. Verdict: At least 7 mm remains. Basis: Academic design rule PASS HV current density 2.435 A/mm2 2.300 to 3.500 Meaning: Copper loading determines conductor heating and material use. Verdict: Within the selected transformer-design band. Basis: Academic design rule PASS HV axial slack 31.800 mm >= 7.000 Meaning: Remaining height after coils, end ring and insulation are placed. Verdict: At least 7 mm remains. Basis: Academic design rule FAIL Adjacent HV winding clearance 11.200 mm >= 15.000 Meaning: Clearance between adjacent HV winding envelopes on neighbouring limbs. Verdict: Winding envelopes are too close. Basis: Academic design rule FAIL No-load loss vs local benchmark 1117.429 W <= 680.000 Meaning: Core loss compared with the interpolated 11/0.420 kV utility benchmark. Verdict: Above the local benchmark; improve core material or flux selection. Basis: Kenya Power 2025, Table 6 FAIL Load loss at reference temperature 7794.230 W <= 5600.000 Meaning: Copper and stray loss corrected to the configured reference temperature. Verdict: Above the local benchmark; review conductor area and current density. Basis: Kenya Power 2025, Table 6 FAIL Total loss vs local benchmark 8911.659 W <= 6280.000 Meaning: Full-load loss at unity power factor, compared with the local rating curve. Verdict: Does not meet the local total-loss benchmark. Basis: Kenya Power 2025, Table 5 FAIL Short-circuit impedance 9.225 % 3.600 to 4.400 Meaning: Impedance affects fault current and voltage regulation. Verdict: Calculated 9.23% against a 4.00% local benchmark target. Basis: Kenya Power 2025, Table 5 INFO Full-load efficiency at unity PF 98.605 % <= 100.000 Meaning: Useful output divided by electrical input at rated load. Verdict: Higher is better; loss limits provide the formal local comparison. Basis: Calculated result PASS Calculated oil temperature rise 49.904 C <= 50.000 Meaning: Estimated steady rise after the calculated cooling tubes are included. Verdict: Cooling area holds the estimate within the target. Basis: Configured thermal target / IEC 60076-2 context PASS Usable oil volume 1.035 m3 >= 0.000 Meaning: Tank volume remaining after active-material displacement. Verdict: Positive oil volume is available. Basis: Calculated geometry PARETO OPTIMIZATION ------------------- Evaluated 294 designs; 7 passed the hard geometry and thermal constraints. The first row is the normalized knee-point recommendation. Bm(T) J(A/mm2) window ratio loss(W) active kg cost index eff(%) Z(%) * 1.700 2.600 2.800 8809.3 1012.7 4765.8 98.621 9.044 NOTES ----- - Local loss values are interpolated from Kenya Power's 2025 11/0.420 kV tables. - The project LV rating is configurable and may differ slightly from the 420 V benchmark. - This analytical model supports design comparison; type tests and detailed mechanical, dielectric, short-circuit and thermal verification remain necessary before manufacture.