MV cable sizing sheet

MEDUIM VOLTAGE CABLE SIZING 1- Assumptions: 1.1 Minimum cable size for Meduim Voltage feeders is 50 sq.mm 1.2 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- Calculations 3.1 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 (KA) 10 16 20 25 31.5 40 50 65 80

Cable C.S.A (mm2) calculated designed 31.27 3x50 50.04 3x70 62.55 3x70 78.18 3x95 98.51 3x120 125.09 3x150 156.37 3x185 203.28 3(1x240) 250.19 3(1x300)

CB opening

XLPE

time (sec)

CONST

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

143 143 143 143 143 143 143 143 143

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 (sq.mm) 3 x 50 3 x 70 3 x 95 3 x 120 3 x 150 3 x 185 3(1 x 240) 3(1 x 300)

Ic in air (Amps) 220 270 330 375 430 490 650 740

De-rating Factor 0.683 0.683 0.683 0.683 0.683 0.683 0.683 0.683

Imax (Amps) 150.26 184.41 225.39 256.125 293.69 334.67 443.95 505.42

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 (sq.mm) 3 x 50 3 x 70 3 x 95 3 x 120 3 x 150 3 x 185 3(1 x 240) 3(1 x 300)

R (uohm/m) 494 343 248 196 159 128 98 80

X Voltage (uohm/m) (kVolts) 107 3.3 101 3.3 95.3 3.3 92.2 3.3 89.9 3.3 87.3 3.3 105 3.3 103 3.3

Power FLC Cable lengthVoltage Factor (Amps)(meter) Drop 0.8 0.00 0.8 0.00 0.8 0.00 0.8 0.00 0.8 0.00 0.8 0.00 0.8 790 150 0.88 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

(sq.mm)

(uohm/m)

(uohm/m)

Running

Starting

(Amps) (meter)

3 x 50 3 x 70 3 x 95 3 x 120 3 x 150 3 x 185 3(1 x 240) 3(1 x 300)

494 343 248 196 159 128 98 80

107 101 95.3 92.2 89.9 87.3 105 103

0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8

0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

VoltageV. Drop V. Drop

Cable length Ist

136

500

500

1000

790

100

(%Ifl)

(kVolts) Running

5 5 5 5 5 5 5 5

3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3

0.00 1.20 0.00 5.57 0.00 0.00 0.59 0.00

Starting

0.000 3.556 0.000 19.256 0.000 0.000 2.686 0.000