Electrical transformer related questions with answers #2

1.Why the cross-section of the yokes are made larger than limbs area ?

Ans.

       If we provided large cross-section for yokes than that of the limbs the flux density in the yokes will be reduced.This will result in a reduction of specific core loss in the yokes,hence a reduction in total core loss is obtained.This will be economic if the capital cost of the iron will saved.And also it will reduces magnetising current and no load current.

 

2.What is window space factor ?

Ans.

        It is the ratio of copper area in window to the total area of window of the transformer.It is denoted by K_w.

 

K_w=Copper area in window/Total window area

     =A_c/A_W

And the choice of window space factor depends upon the Voltage rating and KVA rating.

 

3.What are the windings used in transformer ?

Ans.

       It is necessary to select proper type of windings to be used in the transformer.The windings are chosen such that the desired electrical characteristics and mechanical strength is obtained.

High voltage windings are:

•  Cylindrical winding with circular conductors.

•  Continuous disc type winding with rectangular conductors.

•  Cross-over winding with either circular or small rectangular conductors.

 

Low voltage windings are:

•  Helical winding (mostly double helical)

•  Cylindrical winding with rectangular conductors.

 

4.What are the results of higher flux density in transformer ?

Ans.

       Higher values of flux density results in:

• Smaller core area

• Area of core becomes small hence material requirement is less hence cost is reduced.

• Reduction in length of mean turn of winding.

• Iron losses increases

• Large magnetising current produced

 

5.What is the cause of noise in transformer ?

Ans.

• Mechanical forces developed during working

• Expansion and contraction of oil level due to heating of transformer oil.

• Loosening of stampings in the core