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Transformer
Load Short Circuit Calculator
07/24/2019, 13:28:12, puu8oy-xfmr1-xls.xls, Cover Sheet Simple Calculations Detailed Calculations Transformer Tables Simple Calculations will furnish base current and extend current capability for identified transformers as well as maximum short circuit current based on infinite MVA at transformer pirmary. Detailed Calculations will provide base load current and short circuit currents for identified transformers considering primary MVA and impedance details for transformer and Utility. Transformer Tables will provide based and extend rating currents for various sizes and types of transformers.
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Transformer Load And
Short Circuit Current Calculator
07/24/2019, 13:28:12, puu8oy-xfmr1-xls.xls, With Utility and XR ratios Source Data Select worse case or known source Impedance Additional Source Data: Primary Short circuit Amps = 20000 Reactance/Resistance Ratio (range 5-12): X/R1 = 10 Transformer Data Capacity: kVA= Transformer Primary Voltage: Volts (kV) line-line= Transformer Secondary Voltage: Volts (kV) line-line= Transformer Impedance: %Z= (^5) Impedance Tolerance: %= Reactance/Resistance Ratio (range 5-12): X/Rt= 12 Rated transformer secondary current (calculated): I(xfrmr)= 1519 Amps Calculated Source Impedance Calculation (%Z1): Primary Short Circuit kVA: SCkVA1 = SCAmps1 x Primary Volts (kV) x 1.732 = 478046 kVA Source Impedance: %Z1= kVAt X 100% = 0.00000 %Z SCkVA Vector Components of Source Impedance (%Z1): %X1 = %Z1 x sin[arctan(X/R1)] = 0. %R1 = %X1 = 0. X/R Transformer Impedance Calculation (%Zt): Vector Components of Transformer Impedance (%Zt): 5 %Z Including Tolerance %Xt = %Zt x sin[arctan(X/Rt)] = 4. %Rt = %Xt = 0. X/Rt Total System Impedance Calculation(%Ztot): Add vector components: %Xtot = %X1 + %Xt = 4. %Rtot = %R1 + %Rt = 0. %Ztot = 5. Short Circuit Availability at Transformer Secondary SC Amps2= 100 x I(xfrmr) = 30,387 Amps Calculated %Ztot Resistance/Reactance Ratio: X/R2 = 12.00 Calculated Motor Contribution Calculation Motor Contribution: 2.0 x rated motor load current at 208Y/120 volts 4.0 x rated motor load current at 240, 480, and 600 volts SCAmps(motor)= 4 X 0 Amps = - Amps Calculated Total System Short Circuit Availability SC Amps2 + SCAmps(motor) = 30,387 Amps Calculated Are you assuming Infinite Source? If KNOWN , enter Additional Source Data below.... Enter Data Here Enter Data Here Enter Data Here
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Revision 2 July 2 , Transformer cheat sheet data\xfmr_01.xls GE Industrial Systems (^) Page 4 By Marcelo E. Valdes, PE.
e GE Transformer Currents for Substation & Pad Mount Transformers
kVA 13,800 12,470 12,000 4,160 480 380 208 Volts 40000 1,675 1,854 1, 25000 1,047 1,159 1,204 3, 20000 838 927 963 2, 15000 628 695 723 2, 10000 419 464 482 1, 7500 314 348 361 1, 5000 209 232 241 695 6,021 7, 4000 168 185 193 556 4,817 6, 3750 157 174 181 521 4,516 5, 3000 126 139 145 417 3,613 4, 2500 105 116 120 347 3,011 3, 2000 84 93 96 278 2,408 3,042 5, 1500 63 70 72 208 1,806 2,282 4, 1000 42 46 48 139 1,204 1,521 2, 750 31 35 36 104 903 1,141 2, 500 21 23 24 69 602 761 1, 300 13 14 14 42 361 456 834 Amps = kVA X 0.042 0.046 0.048 0.139 1.204 1.521 2. kVA Nominal X 1.25 (or 1.15) 10000 524 579 602 1,737 1.25 X FA 7500 393 435 452 1,303 1. 5000 262 290 301 868 1. 4000 209 232 241 695 1. 3750 196 217 226 651 5,645 1. 3000 157 174 181 521 4,516 5,704 1. 2500 131 145 151 434 3,763 4,754 1. 2000 96 107 111 320 2,770 3,499 6,392 1. 1500 72 80 83 240 2,077 2,624 4,794 1. 1000 48 53 55 160 1,385 1,749 3,196 1. 750 36 40 42 120 1,039 1,312 2,397 1. kVA Nominal X 1.12 X 1.25 (or 1.15) 10000 586 649 674 1,945 1.25 X FA 7500 440 487 506 1,459 1. 5000 293 324 337 973 1. 4000 235 260 270 778 1. 3750 220 243 253 729 1. 3000 176 195 202 584 5,058 1. 2500 147 162 169 486 4,215 5,324 1. 2000 108 119 124 358 3,102 3,918 1. 1500 81 90 93 268 2,327 2,939 5,369 1. 1000 54 60 62 179 1,551 1,959 3,579 1. Nominal amperes at nameplate kVA, all transformer types Maximum amps for Oil/Silicon filled 65 deg, fan rating Maximum amps for Oil/Silicon filled 65/55deg rise, fan rating
g Revision 2 July 2 , Transformer cheat sheet data\xfmr_01.xls GE Industrial Systems (^) Page 5 By Marcelo E. Valdes, PE.
Nominal X 1. kVA 13,800 V 12,470 V 12,000 V 4,160 V 480 V 380 V 208 V 5000 279 308 320 924 4000 223 247 256 739 3750 209 231 240 693 6, 3000 167 185 192 554 4,805 6, 2500 139 154 160 462 4,004 5, 2000 111 123 128 370 3,203 4, 1500 84 92 96 277 2,402 3,035 5, 1000 56 62 64 185 1,602 2,023 3, 750 42 46 48 139 1,201 1,517 2, 500 28 31 32 92 801 1,012 1, 300 17 18 19 55 480 607 1, kVA Nominal X 1.15 X 1. 5000 320 354 368 1, 4000 256 284 295 850 3750 240 266 276 797 3000 192 213 221 638 5, 2500 160 177 184 531 4,605 5, 2000 128 142 147 425 3,684 4, 1500 96 106 111 319 2,763 3,490 6, 1000 64 71 74 213 1,842 2,327 4, 750 48 53 55 159 1,381 1,745 3, 500 32 35 37 106 921 1,163 2, 300 19 21 22 64 553 698 1, kVA Nominal X 1.30 X 1. 5000 362 401 416 1, 4000 290 321 333 961 3750 272 301 312 901 3000 217 240 250 721 2500 181 200 208 601 5, 2000 145 160 167 480 4,164 5, 1500 109 120 125 360 3,123 3,945 7, 1000 72 80 83 240 2,082 2,630 4, 750 54 60 62 180 1,562 1,973 3, 500 36 40 42 120 1,041 1,315 2, 300 22 24 25 72 625 789 1, Maximum amps for Dry type, 150 deg rise, FA rating Maximum amps for Dry type, 115 deg rise, FA rating Maximum amps for Dry type, 80 deg rise , FA rating
g Revision 2 July 2 , Transformer cheat sheet data\xfmr_01.xls GE Industrial Systems (^) Page 7 By Marcelo E. Valdes, PE.
Impedances and short circuit currents
Maximum AIC at the secondary terminals of a transformer can be derived as follows: with infinite short circuit kVA available on primary. Example: 1 nominal current 2500kVA at 480V is 3,011 amps, nominal Z% is 5. SCA = (3,011/5.75) X 100 X 1.075 = 56,293 amps symmetrical RMS 2 nominal current 3000kVA at 480V is 3,613 amps, nominal Z% is 5. SCA = (3,613/5.75) X 100 X 1.075 = 67,547 amps symmetrical RMS If primary short circuit current is limited it can be incorporated into the calculations as follows: SSCA = TFLC/((TkVA/PSCkVA)+(Z% X 0.925/100)) SSCA = Secondary short circuit amps. TFLC = Transformer full load current, secondary. TkVA = Transformer kVA. PSCkVA = Primary short circuit kVA. (In medium and high voltage parlance short circuit currents are expressed in MVA or kVA) Example: 1 Above 2500kVA with 400MVA available at medium voltage primary. SSCA = 3,011/((2500/400,000) +(5.75 X 0.925/100) SSCA = 3,011/((25/4,000) + (0.0532)) SSCA = 3,011/0. SSCA = 50,650 A RMS symetrical 2 Above 2500kVA with 200MVA available at medium voltage primary. SSCA = 3,011/((25/2,000) + (0.0532)) SSCA = 3,011/0. SSCA = 45,830 A RMS symetrical An additional consideration are motor loads connected on the low voltage side of the transformer. The conservative way to take motor contribution into consideration is to use the full load current of all the motors connected, multiply by 4 and add to the transformer supplied short circuit current. (Transformer nominal full load current/%Z) X 100 X 1.075 = Short circuit current. Note that above 2500 kVA you can easily have more than 65 kAIC!
