(A) To provide oxygen to the cooling oil
(B) To provide cooling air
(C) To arrest the flow of moisture when the outside air enter the transformer
(D) To filter the transformer oil
Ans: (C) To arrest the flow of moisture when the outside air enters the transformer
Explanation:
Breather is filled with silica gel, when atmospheric air enters into the transformer, it passes through the silica gel and all the moisture from atmospheric air is absorbed by silica gel.
2. Open circuit test of transformer gives
(A) Hysteresis loss
(B) eddy current loss
(C) Sum of Hysteresis and eddy current loss
(D) copper loss
Ans: (C) Sum of Hysteresis and eddy current loss
3. The power factor in a transformer
(A) is always unity
(B) is always leading
(C) Is always lagging
(D) Depends on the power factor of the load
Ans: (D) Depends on the power factor of the load
4. A short circuit test on transformer gives
(A) Copper losses at full load
(B) copper losses at half load
(C) iron losses at any load
(D) Sum of iron loss and copper losses
Ans: (A) Copper losses at full load
5. A tap changer used on a transformer for adjusting the .....voltage.
(A) Primary
(B) Secondary
(C) Both primary and secondary
(D) none of the above
Ans: (B) Secondary
6. High leakage reactance transformers are of
(A) small volt-ampere ratings
(B) High volt-amper ratings
(C) High voltage ratings
(D) low voltage rating
Ans: (A) small volt-ampere ratings
7. tappings of the transformer are provided
(A) at the phase end of Lv side
(B) at the phase end of Hv side
(C) at the neutral end of Hv side
(D) at the middle-end of Hv side
Ans: (D) at the middle-end of Hv side
8. Tappings are usually provided on the Hv winding of the transformer because it
(A) is easily accessible physically
(B) Has to handle low currents
(C) Has a large number of turns which allows smoother variation of voltage
(D) all of the above
Ans: (D) all of the above
9. For off load tap changing the best method is to use tap changers
(A) Outside the tank with no selector switch
(B) Outside the tank operated by selector switches
(C) Inside the tank operated by external selector switches
(D) inside the tank with no selector switches
Ans: (C) Inside the tank operated by external selector switches
10. On load tap changing the best method is to employ tap changers
(A) Outside the tank with no selector switch
(B) Outside the tank operated by selector switches
(C) Inside the tank operated by external selector switches
(D) inside the tank with no selector switches
Ans: (B) Outside the tank operated by selector switches
11. In a constant voltage transformer(CVT), the output voltage remains constant due to
(A) capacitor
(B) input inductor
(C) saturation
(D) tapped winding
Ans: (C) saturation
12. The output voltage can be varied by a variac transformer over a
(A) Very small range
(B) Wide range of 0 and 120 percent of input voltage
(C) Over a range of 0 and 50 percent
(D) over a range of 50 and 100 percent
Ans: (B) Wide range of 0 and 120 percent of input voltage
13. Overcurrents in a transformer adversely affect
(A) Insulation life
(B) Mechanical stresses
(C) both (A) & (B)
(D) none of these
Ans: (C) both (A) & (B)
14. The excessive temperature rise will cause maximum damage to
(A) Winding insulation
(B) Core laminations
(C) Copper winding
(D) Dielectric strength of oil
Ans: (A) Winding insulation
15. The rating of a transformer ....... when the supply frequency is increased.
(A) remain unchanged
(B) Decreases
(C) Increase
(D) none of these ]
Ans: (C) Increase