Thursday, April 28, 2016

3.DESIGN OF YOKE
Taking 20% greater area than that of core for yoke
Area of yoke (Ay)  = 1.2*Ai (take assumption into consideration)
                                 = 1.2*0.0182
                                 = 0.2184m2
Cross area of yoke =Net area/stacking  factor
                                   =0.02184/0.9   =0.0243m2
Taking shape of yoke is rectangular
Here,depth of yoke is equal to depth of core
        Dy= a=0.1567m
Height of yoke(Hy)= Ay/Dy
                                  = 0.0243/0.1567

                                   =0.15507m
  2. DESIGN OF WINDOW
 We know, Q=3.33*f* m*Aw*kw* *10-3
For 125KVA transformer ,kw=10/(30+KV)
                                                    =10/(30+11)  =0.2439s
 Assuming the value of current density
 current density , = 2.3 N/mm2[for distribution transformer]
Aw= Q/(3.33*f* m*kw* *10-3)
      =125/(3.33*50*0.0226*2.3*103)
       =0.0577m2
Assume , window height to width ratio =3
           i.e  Hw/Ww=3
    where Hw=height of window
                Ww=width of window
Assuming window height to width ratio=3  Then, HW=3*Ww
        Now Aw= Hw*Ww
               Aw=3* Ww2
Ww= Aw/3)
Ww= (0.0577/3)
Ww=0.139
And Hw=3* Ww
               =3*0.139
               =0.417
Distance between adjacent limb(D)= Ww+d =0.139+0.174 =0.312m

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,
Et=k  Q
For 3-phase distribution transformer k=0.45
Q=125KVA
Et=0.45* 125 =5.03115 V/T
Now, m=Et/4.44f =5.03115/4.44*50 =0.0227 wb
Selection of material of core   Hot rolled silicon steel of grade 92
Flux density (Bm) =1.25 wb/m                [data from page 5.59]
Now, area of core (iron),Ai= m/Bm
=0.0226/1.25
=0.0182m2
Assuming 3-stepped,
Area, Ai=0.6*d2
D
d= Ai/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