Quiz: Electrical Engineering

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)

  1. 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.

 

 

 

 

 

 

 

 

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