Generally HT cable sizing is not done based on the full
load current of the equipment but based on the prospective
fault level. For a 11kV network, generally it shall not be
less than 150sqmm XLPE.

Fault level at 11kV(furnished by respective EB)=100 MVA(say)

Details on EB's fault level can be obtained from EB.

Therefore fault current= 100*1000/(SQRT(3)*11000)
= 5.25 kA

Short circuit current rating (for 3-sec duration)of HT 11kV
XLPE cables with Alu conductor is as below:
95 sqmm: 5.16 kA
120 sqmm: 6.51 kA
150 sqmm: 8.14 kA

First calculate the current of primary side(HT) and derate the cable by atleast 0.7.
Eg:1500*1000/(1.732*11000)=78.73A
Current I after Derating =78.73/.7 =112A (0.7 if laid on the trays or value will vary if buried in the ground).
Cable equivalent to rating has to be selected.
Now Short circuit withstand capacity (sq. of I X t in sec) has to be checked from the cable catalogue.This value of cable should be higher then SC withstand capacity of the ground usually it is 50KA.it less go for next size and finalise.

HT Cable select, its depend of incoming capacity of feeder
line. say feeder capacity 100 MVA SO Calculate current I=
100*100/11*1.73=5.25kA. So we can select of HT Cable for
minimum short ckt current carrying capacity of minimum 5.2kA.

Assume PF of transformer is .8.
rating of transformer=1500kVA=1500X.8=1200kW
V=433(3phase)
So that maximum current-
I= P/V*PF
=1200*1000/1.732*433*.=1600A
So cable size required if copper cable
1mm=4amp= 400sqmm(by consedering all factors)
For aluminium cable
1mm=2.5A=640sqmm