MV Cable Sizing Ring Main

SYSTEM PARAMETERS

Nominal System Voltage System Configuration Connected Load Demand Load Power Factor (pf) Demand Ring Load Current (I) Ring Length (L) Maximum Permissible %Voltage Drop

kV MVA MW p.u Amp km %

11 Ring Main 9.35 5 0.85 309 1.575 3.5

MV CABLE SIZING

DERATING FACTORS

Meth Method od of Cabl Cable e Ins Insta tall llat atio ion n

The The cab cable le shal shalll be be bur burie ied d dir direc ectl tly y und under ergr grou ound nd at an aver averag age e dep depth th of 1000 1000 ~ 110 1100m 0mm m in in tre trefo foil il conf config igur urat atio ion. n.

Ground Temperature Correction Factor Depth of Laying Correction Factor Soil Thermal Resistivity Corr ec ection Factor Cable Grouping Correction Factor Harmonic Current Correction Factor Total Cable Current Derating Factor

0

Assuming a ground temperature of 50  C Assuming a burial depth of 1100 m Assuming dry soil with thermal resistivity of 2.0 K.m/W Only applicable to multiple circuits Assuming a third harmonic content of less than 15%

0.83 0.96 0.77 1.0 1.0 0.61

CABLE SIZING

Cable Voltage Grade

8.7/15 kV

Cable Construction

1 x 3 Core Cu/XLPE/SWA/XLPE 2

Cable Size (S) Cable Resistance (R ) Cable Reactance (X) Rated Current Carrying Capacity Derated Current Carrying Capacity Voltage Drop %Voltage Drop

mm ohm/km ohm/km Amp Amp Volt %

Short Circuit Current Rating for 1 sec Short Circuit Current Rating for 3 sec

kAmp kAmp

185 0.128 0.1 383 235 136 1.24

240 0.098 0.09 436 268 110 1.00

300 0.079 0.09 481 295 96 0.88

3 x 1 Core Core Cu/X Cu/XLPE LPE/AW /AWA/P A/PVC VC 185 0.127 0.12 405 248 144 1.31

240 0.098 0.11 463 284 119 1.08

300 0.078 0.11 516 317 105 0.95 45 25

3 x 1 Core Core Al/XLP Al/XLPE/A E/AWA/ WA/PVC PVC 300 0.13 0.11 405 248 142 1.29

400 0.102 0.11 454 279 122 1.11

500 0.08 0.1 507 311 102 0.92 47 28

SELECTED CABLES

300 mm 500mm

2

2

3 x 1 Core Cu/XLPE/AWA/PVC 3 x 1 Core Al/XLPE/AWA/PVC

The two selected cables (highlighed in green) satisfy the requsite current carrying and volatge drops demands of the envisaged system and also provide short circuit current capability equal to or beyond the 25 kA rating of 11kV feeder switchgear.