AC MACHINES
1.The supply to one terminal of delta-wye connected 3-phase core type transformer which is on no-load fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be
a) 230,230,115
b) 230,115,115
c) 345, 115,115
d) 345,0,345
ans. b
2. In a transformer fed from a fundamental frequency voltage source, the source of harmonics is the
a) overload
b) poor insulation
c) iron loss
d) saturation of the core.
ans. d
3. The magnetizing current in a transformer is rich in
a) 3rd harmonic
b) 5th harmonic
c) 7th harmonic
d) 13th harmonic
ans. a
4. Which of the following conditions is/are necessary for the parallel operation of two transformers?
a) percentage impedance should be the same
b) polarities of both secondaries should be the same.
c) voltage ratings should be the same.
d) All the above
ans. d
5. Two transformers of identical voltages but of different capacities are operating in parallel, for satisfactory load sharing
a) impedance's must be equal
b) per unit impedance's must be equal
c) per unit impedance's and X/R ratio must be equal
d) impedance's and X/R ratio must be equal.
ans.c
6. Two transformers are to be operated in parallel such that they share the load in proportion to their kVA ratings. The rating of the first transformer is 500 kVA and its pu leakage impedance is 0.05 pu. If the rating of the second transformer is 250 kVA, its pu leakage impedance is
a) 0.20
b) 0.10
c) 0.05
d) 0.025
ans. b
7. An auto-transformer having a transformation ratio of 0.8 supplies a load of 10 kW. The power is transformed inductively from the primary to secondary is
a) 10 kW
b) 8 kW
c) 2 kW
d) zero
ans. c
8. The coils are to be connected to obtain a single-phase,400V/1000V, auto-transformer to drive a load of 10kva. Which of the given options should be exercised to realize the required auto-transformer?
a) Connect A and D; Common B
b) Connect B and D; Common C
c) Connect A and C; Common B
d) Connect A and C; Common D.
ans. a
9. In the auto-transformer obtained in question 48, the current in each coil is
a) Coil-1 is 25 A and Coil-2 is 10A
b) Coil-1 is 10 A and Coil-2 is 25A
c) Coil-1 is 10 A and Coil-2 is 15A
d) Coil-1 is 15 A and Coil-2 is 10A
ans.d
10. Constant current transformer is of ____ type.
a) core
b) shell
c) core or shell
d) None of these
ans. b
a) 230,230,115
b) 230,115,115
c) 345, 115,115
d) 345,0,345
ans. b
2. In a transformer fed from a fundamental frequency voltage source, the source of harmonics is the
a) overload
b) poor insulation
c) iron loss
d) saturation of the core.
ans. d
3. The magnetizing current in a transformer is rich in
a) 3rd harmonic
b) 5th harmonic
c) 7th harmonic
d) 13th harmonic
ans. a
4. Which of the following conditions is/are necessary for the parallel operation of two transformers?
a) percentage impedance should be the same
b) polarities of both secondaries should be the same.
c) voltage ratings should be the same.
d) All the above
ans. d
5. Two transformers of identical voltages but of different capacities are operating in parallel, for satisfactory load sharing
a) impedance's must be equal
b) per unit impedance's must be equal
c) per unit impedance's and X/R ratio must be equal
d) impedance's and X/R ratio must be equal.
ans.c
6. Two transformers are to be operated in parallel such that they share the load in proportion to their kVA ratings. The rating of the first transformer is 500 kVA and its pu leakage impedance is 0.05 pu. If the rating of the second transformer is 250 kVA, its pu leakage impedance is
a) 0.20
b) 0.10
c) 0.05
d) 0.025
ans. b
7. An auto-transformer having a transformation ratio of 0.8 supplies a load of 10 kW. The power is transformed inductively from the primary to secondary is
a) 10 kW
b) 8 kW
c) 2 kW
d) zero
ans. c
8. The coils are to be connected to obtain a single-phase,400V/1000V, auto-transformer to drive a load of 10kva. Which of the given options should be exercised to realize the required auto-transformer?
a) Connect A and D; Common B
b) Connect B and D; Common C
c) Connect A and C; Common B
d) Connect A and C; Common D.
ans. a
9. In the auto-transformer obtained in question 48, the current in each coil is
a) Coil-1 is 25 A and Coil-2 is 10A
b) Coil-1 is 10 A and Coil-2 is 25A
c) Coil-1 is 10 A and Coil-2 is 15A
d) Coil-1 is 15 A and Coil-2 is 10A
ans.d
10. Constant current transformer is of ____ type.
a) core
b) shell
c) core or shell
d) None of these
ans. b
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