Question { Texmo, 9648 }

How to calculate the Sizes of the cable required for one
specific load? Is there any formula for that? ( EX: For
400KW load,50mtr Length, What is the LT cable Size
required?)

Answer

Yes we have formula.....

Power P =400KW, Length L =50 Mtr, Voltage V =415V

ANSWER:-------

First find current,

Current I= 695.65A

Apply the factors in the below mentioned formula:-

R = pL/a

Where R=Resistance, p=Resistivity, L=Length, a=Area

Since p=12 for Aluminiun and 14 for Copper.

Then, R= pL/a

We know that V=IR

Apply "R" in Ohms Law

V = IR

V = I pL/a

Therefore ,

Area "a"= (IpL/V) / 1.732 (since 3 phase)

a = (695.65 x 12 x 50 / 415)/1.732

a = 580.69 ( Approximately 600 Sq.mm )

a = 600 ( 2 x 300 Sq.mm)

Therefore 2R, 3.5C X 300 Sq.mm cable is required.

Question { Trident, 17751 }

What is the formula to find out the kvar required to
improve the powerfactor from .85 to .99 at 1500kw, 415v.

Answer

The KVAR required is:

KVAR=KW(tan@1-tan@2) (where @1=cos-1(p.f1)& @2=cos-1(p.f2)

Therefore,

KVAR=KW {tan[cos-1(p.f1)]-tan[cos-1(p.f2)]}

=KW {tan[cos-1(0.85)]-tan[cos-1(0.99)]}

=KW {tan[31.79]-tan[8.11]}

=KW {0.48}

=1500 {0.48}

=720

Therefore 720 KVAR is required to improve powerfactor from
0.85 to 0.99 for 1500KW load.

NOTE:-
Excuse me if the answer is wrong.