ge transformer and short circuit calculator

g TransformerLoad Short Circuit Calculator

11/02/2015, 18:36:45, 293334669.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.

g Transformer Load And Short Circuit Current Calculator

11/02/2015, 18:36:45, 293334669.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 DataCapacity: kVA=

Transformer Primary Voltage: Volts (kV) line-line=

Transformer Secondary Voltage: Volts (kV) line-line=

Transformer Impedance: %Z= 5.75

Impedance Tolerance: %=

Reactance/Resistance Ratio (range 5-12): X/Rt= 12

Rated transformer secondary current (calculated): I(xfrmr)= 3007 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% = 0.52296 %ZSCkVA1

Vector Components of Source Impedance (%Z1):

%X1 = %Z1 x sin[arctan(X/R1)] = 0.52037

%R1 = %X1 = 0.05204X/R1

Transformer Impedance Calculation (%Zt):Vector Components of Transformer Impedance (%Zt): 5.675 %Z Including Tolerance

%Xt = %Zt x sin[arctan(X/Rt)] = 5.65540

%Rt = %Xt = 0.47128X/Rt

Total System Impedance Calculation(%Ztot):Add vector components: %Xtot = %X1 + %Xt = 6.17576

%Rtot = %R1 + %Rt = 0.52332

%Ztot = 6.19790

Short Circuit Availability at Transformer SecondarySC Amps2= 100 x I(xfrmr) = 48,517 Amps Calculated

%Ztot

Resistance/Reactance Ratio: X/R2 = 11.80 Calculated

Motor Contribution CalculationMotor 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 1504 Amps = 6,014 Amps Calculated

Total System Short Circuit AvailabilitySC Amps2 + SCAmps(motor) = 54,531 Amps Calculated

Provided Courtesy of GE Industrial SystemsContact [email protected] if you have any comments

Are you assuming Infinite Source?

If KNOWN, enter Additional Source Data below . . . .

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g TransformerLoad Current and Short Circuit Calculator

11/02/2015, 18:36:45, 293334669.xls, Simple Xfmr Calcs

Go To Detailed Calculations Go to Main SheetClick above if you wish to include X/R ratios and better Utility information.Choose from the drop down menue or fill in the blnk were required.Red triangles indicate additional comments.

Transformer Type

Transformer KVA kVA

Secondary Voltage Volts

Nominal Impedance 5.75 %

Impedance Tolerance %

Motor load % of xfmr kVA

Nominal Secondary Amperes 3,007 Amps Calculated

Maximum SC Current 56,218 Amps Calculated

Max SCA with Motor Contribution 68,247 Amps Calculated

Extended current rating 140 % Calculated

Extended Rating Amperes 4,210 Amps CalculatedProvided Courtesy of GE Industrial SystemsContact [email protected] if you have any comments

g Revision 2July 2 ,1996 Transformer cheat sheetdata\xfmr_01.xls

GE Industrial Systems Page 4 By Marcelo E. Valdes, PE.

e GE Transformer Currents for Substation & Pad Mount TransformerskVA 13,800 12,470 12,000 4,160 480 380 208 Volts40000 1,675 1,854 1,92725000 1,047 1,159 1,204 3,47420000 838 927 963 2,77915000 628 695 723 2,08410000 419 464 482 1,3907500 314 348 361 1,0425000 209 232 241 695 6,021 7,6064000 168 185 193 556 4,817 6,0853750 157 174 181 521 4,516 5,7043000 126 139 145 417 3,613 4,5632500 105 116 120 347 3,011 3,8032000 84 93 96 278 2,408 3,042 5,5581500 63 70 72 208 1,806 2,282 4,1691000 42 46 48 139 1,204 1,521 2,779750 31 35 36 104 903 1,141 2,084500 21 23 24 69 602 761 1,390300 13 14 14 42 361 456 834

Amps = kVA X 0.042 0.046 0.048 0.139 1.204 1.521 2.779

kVA Nominal X 1.25 (or 1.15)10000 524 579 602 1,737 1.25 X FA 7500 393 435 452 1,303 1.255000 262 290 301 868 1.254000 209 232 241 695 1.253750 196 217 226 651 5,645 1.253000 157 174 181 521 4,516 5,704 1.252500 131 145 151 434 3,763 4,754 1.252000 96 107 111 320 2,770 3,499 6,392 1.151500 72 80 83 240 2,077 2,624 4,794 1.151000 48 53 55 160 1,385 1,749 3,196 1.15750 36 40 42 120 1,039 1,312 2,397 1.15

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 1.255000 293 324 337 973 1.254000 235 260 270 778 1.253750 220 243 253 729 1.253000 176 195 202 584 5,058 1.252500 147 162 169 486 4,215 5,324 1.252000 108 119 124 358 3,102 3,918 1.151500 81 90 93 268 2,327 2,939 5,369 1.151000 54 60 62 179 1,551 1,959 3,579 1.15750 40 45 47 134 1,163 1,469 2,685 1.15

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



Nominal X 1.33kVA 13,800 V 12,470 V 12,000 V 4,160 V 480 V 380 V 208 V

5000 279 308 320 9244000 223 247 256 7393750 209 231 240 693 6,0063000 167 185 192 554 4,805 6,0692500 139 154 160 462 4,004 5,0582000 111 123 128 370 3,203 4,0461500 84 92 96 277 2,402 3,035 5,5441000 56 62 64 185 1,602 2,023 3,696750 42 46 48 139 1,201 1,517 2,772500 28 31 32 92 801 1,012 1,848300 17 18 19 55 480 607 1,109

kVA Nominal X 1.15 X 1.335000 320 354 368 1,0634000 256 284 295 8503750 240 266 276 7973000 192 213 221 638 5,5262500 160 177 184 531 4,605 5,8162000 128 142 147 425 3,684 4,6531500 96 106 111 319 2,763 3,490 6,3761000 64 71 74 213 1,842 2,327 4,251750 48 53 55 159 1,381 1,745 3,188500 32 35 37 106 921 1,163 2,125300 19 21 22 64 553 698 1,275

kVA Nominal X 1.30 X 1.335000 362 401 416 1,2014000 290 321 333 9613750 272 301 312 9013000 217 240 250 7212500 181 200 208 601 5,2052000 145 160 167 480 4,164 5,2601500 109 120 125 360 3,123 3,945 7,2071000 72 80 83 240 2,082 2,630 4,805750 54 60 62 180 1,562 1,973 3,604500 36 40 42 120 1,041 1,315 2,402300 22 24 25 72 625 789 1,441

Maximum amps for Dry type, 150 deg rise, FA rating





Nominal X 1.12kVA 13,800 V 12,470 V 12,000 V 4,160 V 480 V 380 V 208 V

5000 235 260 270 7784000 188 208 216 622 5,3953750 176 195 202 584 5,0583000 141 156 162 467 4,046 5,1112500 117 130 135 389 3,372 4,2592000 94 104 108 311 2,697 3,407 6,2251500 70 78 81 233 2,023 2,556 4,6691000 47 52 54 156 1,349 1,704 3,112750 35 39 40 117 1,012 1,278 2,334500 23 26 27 78 674 852 1,556300 14 16 16 47 405 511 934

Extended ratings formulas

Liquid filled, 2500-10,000kVA Liquid filled, 750-2000kVAFans = 125% Fans = 115%55/65deg rise = 112% 55/65deg rise = 112%

Dry type Padmount, 55/65 deg riseFans = 133% At 65 deg rise = 112%115deg rise = 115%80deg rise = 130%

Cast coilFans = 140%For some manufacturers can vary from 133% to 150%.

Liquid fill primary substation 12MVA and largerTwo levels of fans are available each 33% of base kVA., 166% max.55/65 deg rise rating provides an additional 12% for a maximum of 186%.

Notes:

*Padmount transformers larger than 2500 kVA are not specifically described in the ANSI standardsneither are fan cooled ratings. Installation of fans would specifically contravene the tamper resis-tant requirements of the ANSI standards. Fans are not recommended for Padmounted transformers.*Padmount transfomers loadbreak separable connectors are limited to 200 amperes maximum.*Padmount transfomers dead front primary bushings are limited to 600 amperes maximum.*Padmount primary under oil switches are limited to 400 amperes maximum.*Padmount transformer's internal fuses are very limited above 1500kVA, separate protection is oftenrequired.

All transformer secondaries are, generally, limited to 5000 amperes maximum.

For all 480V transformers 3000 kVA & larger take consideration of secondary short circuit currentas it could exceed 65,000 amperes and hence require special secondary distribution equipment.Motor contribution not included !

Maximum amps Oil filled Padmount, 55/65 deg rise



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 5.75

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 5.75SCA = (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 calculationsas 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 = 3,011/0.05945SSCA = 50,650 A RMS symetrical

2 Above 2500kVA with 200MVA available at medium voltage primary.SSCA = 3,011/((25/2,000) + (0.0532))SSCA = 3,011/0.0657SSCA = 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 ofall 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!

Cover SheetWith Utility and XR ratiosSimple Xfmr CalcsAmp tables

Drop Down 6: 2500Drop Down 8: 13800Drop Down 9: 480Drop Down 11: 7.5Drop Down 13: KnownDrop Down 22: 50% of Xfmr CurrentDrop Down 8_2: 2500Drop Down 9_2: 480Drop Down 11_2: 7.5Drop Down 17: Cast coil, with fans, 40%Drop Down 21: 100

ge transformer and short circuit calculator

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