ELECTRICAL MACHINE DESIGN 4

31. The inductive reactance of a distribution core type transformer with concentric cylindrical coils of equal length can be reduced by
a) increasing the window height
b)  increasing the window  width
c) decreasing the yoke height.
d) increasing the operating flux density in the yoke.
ans. a

32. If all the dimensions of a transformer is doubled its iron loss will be
a) half
b) double
c) four times
d) 8 times
ans. d

33. The primary and secondary winding's are interlaced for
a) easiness of coil making
b) reduced leakage reactance
c) reduced cost.
d) uniform heating.
ans. b

34. It is necessary that magnetic coupling in a transformer is close. This is done to ensure
a) high efficiency
b) good regulation
c) good regulation and high efficiency
d) good regulation and high power factor.
ans. d

35. What is the arrangement of winding's in a core type single phase transformer?
a) Half lv inside and half hv outside on each core limb
b) LV on one code limb and hv on the other.
c) Sandwiched lv and hv discs on each core limb.
d) Half hv inside and half lv outside on each core limb.
ans. a

36. With increase in voltage , the window space factor of a transformer
a) decreases
b) increases
c) remains constant
d) decreases or increases depending upon whether it is a distribution or power transformer.
ans. a

37. No-load current in a large sized transformer is about
a) 10% of full-load current
b) 7% of full-load current
c) 4% of full-load current
d) 1% of full-load current
ans.d

38. A 200/400 ratio transformer has a secondary winding resistance of 0.5 ohms. The total resistance as referred to primary is about
a) 0.125 ohms
b) 0.5 ohms
c) 1 ohm
d) 2 ohms
ans. a

39. Typical value of per unit impedance for a transformer is
a) 0.2
b) 0.1
c) 0.05
d) 0.01
ans. c

40. If the iron loss in a transformer at full load is 600 W, the total  iron loss at 25% of overload will be
a) 600 W
b) 750 W
c) 1000 W
d) 400 W
ans. a