5.DESIGN OF HIGH VOLTAGE WINDING

Primary line voltage (V_l)=11000v                           

For high voltage delta side,primary phase voltage V_p=11000

Number of turns per phase of primary,T_p=(V_p/V_s)*T_s

                                                                         = (11000/250)*50

                                                                         = 2200 turns

Tapping ±2½%, ±5½%

Total number of primary turns for providing tapping=1.05*2200

                                                                                                =2310 turns

Selecting cross-over type of winding(from table)

Now, for cross-over type:

             Number of coil=voltage level / (800 to 1000)

                                        =11000/845 ≈13

Using  12 separate coils ,

  Number of turns per coil =2310/12 = 192.5 turns/coil

   Voltage per coil = 11000/12 =916.66 volt/coil

Taking 15 layers per coil

   Turns per layer =192.5/15 =12.83 13 turns per layer

 25 turns for first 10 layer and 27 turns for remaining  5 layers

High voltage winding current (phase current)

              I_p =125*10³/3*11000 =3.787A

Current density for LV winding = 2.35A/mm²

Taking current density of HV winding 10% greater than LV winding =1.1*2.35

                                                                                                                     =2.585A/mm²

Now, Area of primary conductor,a_p=I_p/

                                                                =3.787/2.585 =1.464mm²

For cylindrical conductor ,a_p= d²/4

                                                d= _p/

                                                   =1.365mm

From table :

Taking conductor of diameter,d=1.4mm(bare conducter)

From table: selecting a conductor of fine insulated cover having diameter=1.575mm

Now,modified  area of insulated conductor = d_new ²/4

                                                                                         = ²/4

                                                                                          = 1.5393 mm²

Actual value of current density =3.787/1.5393 = 2.46A/mm²

Axial depth of one coil = 15 * 1.575 mm

                                          =23.625mm

Total axial depth of HV winding

        L_cp=no of coil *axial depth of one coil +spacing *no of coils

             =12*23.625+12*5

              =305.7mm

Clearance,on each side of winding ,=(Height of window - L_cp)/2

                                                                  =55.65mm

Let the insulation between layers =0.3

Radial depth of HV winding =15*1.575+14*0.3

                                                    =27.825mm

Thickness of insulation between LV and HV winding

I.e. width of duct ,a=5+0.9*kv

                                =5+0.9*11 =15mm

Inside diameter of HV winding =(outside dia of LV winding +2*15)

                                                         =238.08mm

Outside diameter of HV winding =( inside dia of HVwinding +2*47.475)

                                                            =238.08+2*47.475

                                                               =333.03mm