transformer design

Q .Design a 125KVA , 11000/433, 50Hz, 3 phase delta/star core type oil immersed natural cooled distribution transformer .The transformer is provided with tapping ±2½%, ±5½% on the HV side. Maximum temperature rise not to exceed 45 ̊C.

Solultion

1.FOR DESIGN OF CORE

We have,

E_t=k  Q

For 3-phase distribution transformer k=0.45

Q=125KVA

E_t=0.45* 125 =5.03115 V/T

Now, _m=E_t/4.44f =5.03115/4.44*50 =0.0227 wb

Selection of material of core   Hot rolled silicon steel of grade 92

Flux density (B_m) =1.25 wb/m                [data from page 5.59]

Now, area of core (iron),A_i= _m/B_m

=0.0226/1.25

=0.0182m²

Assuming 3-stepped,

Area, A_i=0.6*d²

D

d= A_i/0.6

d=0.174

And , a=0.9*d = 0.9*0.174= 0.1566           b=0.7*d = 0.7*0.174=0.1218

           c=0.42*d= 0.42*0.174=0.07308