Exam: UPSSSC
Topic: Machines
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute
Q1. Type of winding present in welding generator
(a) wave winding
(b) Lap winding
(c) May have any winding
(d) None of the above
L1Difficulty 3
QTags DC Generator
QCreator Balwant Kumar
Q2. A 4-pole generator with 32 coils has a two-layer tap winding. Find out the pole pitch,
(a) 8
(b) 16
(c) 32
(d) 4
L1Difficulty 3
QTags DC Generator
QCreator Balwant Kumar
Q3. Pole shoe of D Machine are being laminated what is the purpose of this lamination.
(a) It provides high mechanical strength.
(b) It helps in reducing hysteresis loss
(c) It helps in reducing Eddy current losses
(d) It helps in increasing hysteresis loss.
L1Difficulty 2
QTags DC Generator
QCreator Balwant Kumar
Q4. A hysteresis motors
(a) Does no required dc excitation
(b) Is a self-starting motor
(c) Is a constant speed motor.
(d) All of the above.
L1Difficulty 3
QTags DC Motor
QCreator Balwant Kumar
Q5. Find the value of frequency of rotor current of a 50 Hz induction motor operating at 2% slip
(a) 100 Hz
(b) 2 Hz
(c) 50 Hz
(d) 1 Hz
L1Difficulty 1
QTags Single phase induction motor
QCreator Balwant Kumar
Q6. Which of the following relation is true for the ratio of rotor copper loss and rotor input in Induction motor.
(a)S/(1-S)
(b) S
(c)1/S
(d)(1-S)/S
L1Difficulty 3
QTags Single phase induction motor
QCreator Balwant Kumar
Q7. The rotor power output of 3 – phase induction motor is 30 kw. The rotor copper losses at slip 4% will be
(a) 625 W
(b) 950 W
(c) 1250 W
(d) 1050 W
L1Difficulty 3
QTags 3-Phase induction motor
QCreator Balwant Kumar
Q8. In Rotating machines, the harmonics are produced due to
(a) non-Sinusoidal form of field
(b) Slotting of Stator core
(c) Both (a) & (b)
(d) None
L1Difficulty 1
QTags 3-Phase induction motor
QCreator Balwant Kumar
Q9. Skewing of the slots are done for
(a) Reducing the humming sound
(b) Suppress the undesirable harmonies
(c) Improve the cooling effect
(d) Reduce eddy losses
L1Difficulty 3
QTags Alternators
QCreator Balwant Kumar
Q10. Under full load condition, the power factor of the rotor circuit of 3 – phase induction motor is
(a) about 0.8 lagging
(b) about 0.8 leading
(c) 0.5 lagging
(d) almost unity
L1Difficulty 2
QTags Alternators
QCreator Balwant Kumar
Solutions
S1. Ans.(b)
High Current is required for the welding purposes. As we know the lap winding have more no of parallel paths so it suits the welding machine construction.
S2. Ans.(b)
- solution:
Pole pitch=Z/P
= (32*2)/4 =16 Ans.
S3. Ans.(c)
It helps in reducing the eddy current losses.
S4. Ans.(d)
S5. Ans.(d)
Solution
Supply Frequency is given as 50 Hz
Slip S = 2% =.02
Frequency of Rotor current = S*f
=.02*50 =1 Hz Ans.
S6. Ans.(b)
S7. Ans.(c)
Solution
Rotor Power output is given as 30kW i.e. (Pm)
Rotor Copper loss at given slip i.e.: 4%
=s/(1-s) *Pm
=0.04/ (1-0.04) *30*1000
=1250 W
S8. Ans.(c)
S9. Ans.(b)
Skewing of slots are done for reduction of the tooth harmonics.
S10. Ans.(d)
Solution
The power factor of induction motors varies with load. Typically, around 0.85 or 0.90 at full load.
