TRANSFORMER PART 4
[1] High frequency transformers sometimes make use of ferrite cores because it has
A. High specific gravity
B. High resistance
C. High hysteresis
D. low permeability
Ans:B
Answer
[2] Harmonics in transformer result in
A. Increased core losses
B. Increased I2R losses
C. Magnetic interference with communication circuits
D. All of the above
Ans:D
Answer
TRANSFORMER PART 4
[3] The full load copper loss of a transformer is 1600W. At half-load the copper loss will be
A. 6400W
B. 1600W
C. 800W
D. 400W
Ans:D
Answer
[4] Power transformers are generally designed to have maximum efficiency around
A. No load
B. Half load
C. Near full load
D. 10% overload
Ans: C
Answer
[5] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results
A. Short-circuiting of the secondaries
B. Power factor of one of the transformers is leading while that of the other lagging
C. Transformers having higher copper losses will have negligible core losses
D. Loading of the transformers not in proportion to their kVA ratings.
Ans:D
Answer
TRANSFORMER PART 4
[6] The changes in volume of transformer cooling oil due to variation of atmospeheric temperature during day and night is taken care of by which part of transformer?
A. Conservator
B. Breather
C. Bushings
D. Buchholz relay
Ans:A
Answer
[7] The transformer laminations are insulated from each other by
A. Mica strip
B. Thin coat of varnish
C. Paper
D. Any of the above
Ans:B
Answer
[8] Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
Ans: B
Answer
TRANSFORMER PART 4
[9] During open circuit test of a transformer
A. Primary is supplied rated voltage
B. Primary is supplied full load current
C. Primary is supplied current at reduced voltage
D. Primary is supplied rated kVA
Ans: A
Answer
[10] Which of the following is not standard voltage for power supply in India
A. 11kV
B. 33kV
C. 66 kV
D. 122 kV
Ans: D
Answer
[11] The low voltage winding of a 400/230 volt, 1-phase, 50Hz transformer is to be connected to a 25Hz supply in order to keep the magnetization current at the same level as that for normal 50Hz supply at 25Hz the voltage should be [Gate 1997]
a) 230V
b) 460V
c) 115V
d) 65V
Ans: C
Answer
TRANSFORMER PART 4
[12] The primary current in the current transformer is dictated by [Gate 1997]
a) The secondary burden
b) The core of the transformer
c) The load current
d) None of the above
Ans:A
Answer
