How to calculate cable size in HT?

kVA X0.8 PF =Kw =W            

 P=RT3 V I COS fi              

SO, I = P / RT3 x V x COSfi

I = /1.xx0.8= A

Now take cable table and select the suitable xlpe cable.

Cable sizing is done based on three parameters:

1. Load current,
2. Short circuit current carrying capacity,
3. Voltage drop.

Step 1:

Calculate the load current from the load data available. Formula is,

I=Load (in kW)/(sqrt(3)*V(in kV)*p.f) (A)

The current obtained has to derated since the cable is designed to operate at a defined temperature. Derating factors will be available in cable catalog.

Get the cable size corresponding to this derated current from the catalog.

Step 2:

Next, find the cable size for the short circuit capacity of the system. Formula used is,

Cable size= (Fault current(in kA)*Fault clearing time)/K

where, K-constant depending on the conductor and insulation used. K=90 (for Al cables), K=140 (for Cu cables)

Choose the cable size whichever is greater in step 1 or step 2.

Step 3:

Check for voltage drop with the cable size chosen.

If the cable is connected to a HT motor load, then the voltage drop from transformer to motor should not exceed 5%.

Also, if it is a motor load, the voltage drop for motor starting has to be checked. It has to be less than 15%.

1. You Can use i\\this for less than 1 kV cable-sizing-calculator
2. For XlpE Calucation