Quiz-1 ( Subject -ELECTRICAL MACHINES)
Hello students,this is the practice Quiz -1 for You Related with Electrical Machines Subject Hope this is beneficial for your practice work.
Manisha tyagi
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1. Iron losses are considered to be the constant losses. It depends on
Voltage
Frequency
Both (a) and (b)
None of these
Correct Answer
Wrong Answer
2. Copper losses in a rotating machine are
Variable losses
Constant losses
Both (a) or (b)
None of these
Correct Answer
Wrong Answer
3. Stray losses are the losses which vary with the load but their relationship with load current cannot be identified. Stray losses is maximum in
Synchronous machines
D.C. machines
Induction machines
Equal in all types of machines
Correct Answer
Wrong Answer
4. The brush contact losses in a d.c. Machine is
Inversely proportional to the square of current
directly proportional to the square of current
inversely proportional to the current
directly proportional to the current
Correct Answer
Wrong Answer
5. Electrical power output in a d.c. generator is equal to
Electrical power developed in armature – copper losses
Mechanical power input – iron and friction losses
Electrical power developed in armature – iron and copper losses
Mechanical power input – iron and friction losses – copper losses
Correct Answer
Wrong Answer
6. Mechanical power developed in armature of a d.c. motor is given by
Electrical power input to motor – copper losses
Motor output + iron and friction losses
Both (a) & (b)
None of these
Correct Answer
Wrong Answer
7. Out of electrical, mechanical and magnetic losses, the losses which is minimum is
All are equal
Electrical losses
Magnetic losses
Mechanical losses
Correct Answer
Wrong Answer
8. If % ηm is the mechanical efficiency of a DC machine and % ηe is the electrical efficiency. Then the overall efficiency of DC machine is given by
% η m + % η e
% η m X % η e
(% η m + % η e) / % η m
(% η m + % η e) / % η e
Correct Answer
Wrong Answer
9. The current flowing through the armature of a d.c. shunt machine at maximum efficiency is given by
√(Pi / Ra)
√(Ra / Pi)
√(Pi / R2a)
√(Ra / P2i)
Correct Answer
Wrong Answer
10. The speed in d.c. machine can be measured by using
Anemometer
Tachometer
Voltmeter
Ammeter
Correct Answer
Wrong Answer
11. Brushes in d.c. machines are made up of
Cast iron
Mild steel
Copper
Carbon
Correct Answer
Wrong Answer
12. If A is the number of parallel paths and P is the number of poles, then the number of parallel path in lap winding and in wave winding is
A = P, A = 2
A = 2P, A = P
A = 2, A = P
A = P, A = 2P
Correct Answer
Wrong Answer
13. In a d.c. machine, the current rating and voltage rating of wave winding is
Low, high
High, low
High, high
Low, low
Correct Answer
Wrong Answer
14. In electric traction, which type of motor is generally used?
Shunt motor
Series motor
Cumulative compound motor
Differential compound motor
Correct Answer
Wrong Answer
15. Speed of d.c. shunt motors are controlled by
Flux control method
Rheostatic control method
Voltage control method
All of these
Correct Answer
Wrong Answer
16. In the flux control method for controlling the speed of d.c. shunt motor, the speed control is not possible
Below normal rated speed
Above normal rated speed
Both (a) and (b)
None of these
Correct Answer
Wrong Answer
17. Which method is suitable for the speed control, below and above the normal rated speed of d.c. shunt motor?
Flux control method
Rheostatic control method
Voltage control method
All of these
Correct Answer
Wrong Answer
18. Which starter does not provide high speed protection to the d.c. shunt motor?
Three point starter
Four point starter
Two point starter
None of these
Correct Answer
Wrong Answer
19. Open circuit test is to be performed on transformer to find
Constant losses
Copper losses
Both (a) and (b)
None of these
Correct Answer
Wrong Answer
20. If the transformer is step – up transformer then for performing short circuit test meter is connected to the
H.V. side
L.V. side
Any side
Test cannot be performed on step up t / f
Correct Answer
Wrong Answer
21. In a 20 kVA, 2200 / 220 volts transformer iron and copper losses are 300 and 400 watts respectively. Its efficiency at half load and unity power factor is
95.11%
96.15%
97.77%
98%
Correct Answer
Wrong Answer
22. Two transformers are operated in parallel, most essential condition to be satisfied is
Polarities should be same
Leakage reactance should be equal
Turns ratios should be equal
Impedances should be in proportion to their kVA rating
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