MEDUIM VOLTAGE CABLE SIZING

1- Assumptions:1.1 Minimum cable size for Meduim Voltage feeders is 50 sq.mm1.2 Circuit breaker tripping time on short circuit is 200ms.1.3 Constant reflecting conductor material constant and temperature rise during short circuit condition is 143 for XLPE.1.4 As per client requirement, cable sizes above 185 sq.mm shall be single core installed in trefoil.1.5 Starting current for medium voltage motors are equals to 5 times the full load current.

2- References:2.1 Electrical design basis specification no.. 24613-200-3DR-E12F-00001.2.2 PIRELLI Cables catalogue for 300V-33000V cables

3- Calculations3.1 Medium Voltage Cable size based on short circuit current check: Table below reflects the designed cable sizes for diffirent effective short circuit current values.

Ieffective Cable C.S.A (mm2) CB opening XLPE(KA) calculated designed time (sec) CONST

10 31.27 3x50 0.2 14316 50.04 3x70 0.2 14320 62.55 3x70 0.2 14325 78.18 3x95 0.2 14331.5 98.51 3x120 0.2 14340 125.09 3x150 0.2 14350 156.37 3x185 0.2 14365 203.28 3(1x240) 0.2 14380 250.19 3(1x300) 0.2 143

3.2 Medium Voltage cable size based on current carrying capacity check: Table below reflects the designed cable sizes based on the maximum premissible current through the MV cable after consideration of de-rating factor.

cable size Ic in air De-rating Imax(sq.mm) (Amps) Factor (Amps)3 x 50 220 0.683 150.263 x 70 270 0.683 184.413 x 95 330 0.683 225.393 x 120 375 0.683 256.1253 x 150 430 0.683 293.693 x 185 490 0.683 334.673(1 x 240) 650 0.683 443.953(1 x 300) 740 0.683 505.42

3.3 Medium Voltage power feeder cable size based on voltage drop check: a) Table below reflects the designed cable sizes based on the maximum premissible voltage drop for the medium voltage power feeders.

cable size R X Voltage Power FLC Cable lengthVoltage(sq.mm) (uohm/m) (uohm/m) (kVolts) Factor (Amps)(meter) Drop3 x 50 494 107 3.3 0.8 0.003 x 70 343 101 3.3 0.8 0.003 x 95 248 95.3 3.3 0.8 0.003 x 120 196 92.2 3.3 0.8 0.003 x 150 159 89.9 3.3 0.8 0.003 x 185 128 87.3 3.3 0.8 0.003(1 x 240) 98 105 3.3 0.8 790 150 0.883(1 x 300) 80 103 3.3 0.8 0.00

b) Table below reflects the designed cable sizes based on the maximum premissible voltage drop for the medium voltage motor feeders.

cable size R X PF PF FLC Cable lengthIst VoltageV. Drop V. Drop(sq.mm) (uohm/m) (uohm/m) Running Starting (Amps) (meter) (%Ifl) (kVolts) Running Starting

3 x 50 494 107 0.8 0.3 5 3.3 0.00 0.0003 x 70 343 101 0.8 0.3 136 500 5 3.3 1.20 3.5563 x 95 248 95.3 0.8 0.3 5 3.3 0.00 0.0003 x 120 196 92.2 0.8 0.3 500 1000 5 3.3 5.57 19.2563 x 150 159 89.9 0.8 0.3 5 3.3 0.00 0.0003 x 185 128 87.3 0.8 0.3 5 3.3 0.00 0.0003(1 x 240) 98 105 0.8 0.3 790 100 5 3.3 0.59 2.6863(1 x 300) 80 103 0.8 0.3 5 3.3 0.00 0.000