# Electric Machines Past Papers Exam Questions

By Prof. Fazal Rehman Shamil

## Guess Paper 1: Electric Machines Fall – 2020 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1. Briefly define each of the following:
a. Armature
b. Brushes
d. Induction motor
e. Torque
f. Shunt Motor
g. Henry

Q2. Differentiate between AC and DC generator.

Q3. What is the counter-electromotive force (CEMF) and speed of rotation?

Q4. What are mechanical and electrical losses? Explain

Q5. Discuss the Wye and Delta connections briefly.

Q6. Explain the three phase induction motor and their principle components.

Q8. Write short Notes on any TWO.
a. Magnetism
b. Compound Generator
c. Current Transformer

## Guess Paper 2:Electric Machines Spring – 2020 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1. Briefly define each of the following:
a. Armature
b. Brushes
d. Induction motor
e. Torque
f. Shunt Motor
g. Henry

Q2. Differentiate between AC and DC generator.

Q3. What is the counter-electromotive force (CEMF) and speed of rotation?

Q4. What are mechanical and electrical losses? Explain

Q5. Discuss the Wye and Delta connections briefly.

Q6. Explain the three phase induction motor and their principle components.

Q8. Write short Notes on any TWO.
a. Magnetism
b. Compound Generator
c. Current Transformer

## Guess Paper 3: Electric Machines Fall – 2019 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1. Briefly define each of the following:
a. Slip
b. Rotor speed
d. Synchronous speed
e. Torque
f. Shunt Motor
g. Mutual Induction

Q2. (a). Briefly explain the construction and working of DC generator .
(b) A dc generator delivers a load of 450 A at 230V and the resistance of shunt field and armature are 50Ω and 0.03Ω respectively. Calculate the generated e.m.f..

Q3. What is the counter-electromotive force (CEMF) and speed of rotation?

Q4. (a) Discuss the different losses in the transformer.
(b) In no load test of single phase transformer the following test data were obtained. Primary voltage
=220 V, Secondary Voltage = 110V Primary Current =0.5A, Power input = 30 W Find the following.
(i) The turn’s ratio. (ii) The magnetizing components of no load current.

Q5. Discuss the Wye and Delta connections briefly.

Q6. Explain the three phase induction motor and their principle components.

Q8. Explain any two of the following topics.
(i) Shunt generator under load (ii) Transformer cooling methods. (iii) Current transformer

## Guess Paper 4: Electric Machines Fall – 2019 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1:

• Auto transformer is used for which of the following schemes explain?

(220kV/132kV or 132kV/11Kv)

• Purpose of commutator in a DC machine?
• What are the advantages of stationary armature in a machine?
• Which on of the DC motors has high starting torque?
• What is residual magnetism. Why property of material retain magnetic flux?
• The rotor of synchronous machine is supplied with DC supply.                    True/False
• Transformer is an AC machine                                                                      True/False
• Copper losses are occurs in iron core.                                                   True/False
• Armature copper losses are called permanent losses.             True/False
• Open circuit test on transformer is performed in order to find core losses        True/False
• Squirell cage induction motor has wound rotor             True/False
• One unit of energy meter is equal to………?
• Core is laminated in order to minimize………?
• Synchronous condenser is used for ………….?

Q2.      What is synchronous machine? Explain principle of operation and types?

Q3.       Derive equation for short and open circuit test on transformer also draw equivalent circuit diagram?

Q4.       What are available techniques to start a synchronous motor?

Q5.      Write four conditions for parallel operation?  Discuss parallel operation advantages ?

Q6.      Explain Speed control methods of wound induction motor with the help of diagram?

Q7.     Briefly explain the construction of DC machines with help of diagram?

Q8.      Write short note on any two of the following:

(a) What is dynamic braking or Regenerative braking of DC motor, elaborate with atleast on example.

(b) Types of three phase induction motor and its construction.

(c)  Wave winding and lap winding

## Guess Paper 5: Electric Machines Fall – 2018 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1:

• Auto transformer is used for which of the following schemes explain?

(220kV/132kV or 132kV/11Kv)

• Purpose of commutator in a DC machine?
• What are the advantages of stationary armature in a machine?
• Which on of the DC motors has high starting torque?
• What is residual magnetism. Why property of material retain magnetic flux?
• The rotor of synchronous machine is supplied with DC supply.                    True/False
• Transformer is an AC machine                                                                      True/False
• Copper losses are occurs in iron core.                                                   True/False
• Armature copper losses are called permanent losses.             True/False
• Open circuit test on transformer is performed in order to find core losses        True/False
• Squirell cage induction motor has wound rotor             True/False
• One unit of energy meter is equal to………?
• Core is laminated in order to minimize………?
• Synchronous condenser is used for ………….?

Q2.      What is synchronous machine? Explain principle of operation and types?

Q3.       Derive equation for short and open circuit test on transformer also draw equivalent circuit diagram?

Q4.       What are available techniques to start a synchronous motor?

Q5.      Write four conditions for parallel operation?  Discuss parallel operation advantages ?

Q6.      Explain Speed control methods of wound induction motor with the help of diagram?

Q7.     Briefly explain the construction of DC machines with help of diagram?

Q8.      Write short note on any two of the following:

(a) What is dynamic braking or Regenerative braking of DC motor, elaborate with atleast on example.

(b) Types of three phase induction motor and its construction.

(c)  Wave winding and lap winding

## Guess Paper 6: Electric Machines Fall – 2018 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1:

1. Define types of Alternator?
2. Purpose of Sumpner or Back-to-Back Test?
3. Define unity power factor?
4. Define difference between relay and fuse?
5. What is auto-transformer?
6. A transformer is a static piece of equipment used either for raising or lowering
the voltage of an AC supply with a corresponding decrease or increase in
True/False
7. Buchloz relay is used as sensing device in transformers only                  True/False
8. Core loses are permanent loses           True/false
9. Core losses occur in armature winding.           True/False
10. Squirrel cage induction motor is rarely used in industry. True/False
11. To determine the iron losses ………. test is performed.
12. Synchronous motor and induction motor rotational speed are …….
13. Armature reaction distorts …………    field
14. Split phase induction motor has two windings i.e. main winding and ………

Q2.      Draw the equivalent circuit of transformer from open and short circuit test?

Q3.      Derive formula for Induction Motor Torque i.e Shaft torque and rotor torque?

Q4.      What is the main difference between salient and non-salient pole type synchronous machines? Explain its

uses with respect to generator?

Q5.      What are the problems associated with Y-Y three phase transformer connections?

Q6.      Explain power stages of a three phase induction motor.

Q7.      Differentiate universal and series motor with the help of circuit diagram

Q8.      Write short note on any two of the following

1. Write four conditions for parallel operation
2. Why Transformer Rating in KVA?
3. Applications of 3 phase induction motor

## Guess Paper 7: Electric Machines Fall – 2017 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q.1      a) chose the correct answer

1. A single phase induction motor employs ……………… rotor
2. Squirrel cage b) wound        c) both          d) none
• An alternator is sometimes called …………………. Generator
1. Synchronous b) asynchronous   c) either a & b   d)  none
2. The field winding of an alternator is ……………………. excited
3. a) D.C b)  A.C             c) Both a & b             d) None
• The Frequency of an EMF generated in an 8-pole alternator running at 900 RPM is …………………
• a) 50 Hz b) 60 Hz         c) 120 Hz      d) 100 Hz
1. When a 3-Phase induction motor is at no load the slip is ………………….
2. a) 1 b) 0.5         c) 0       d) Maximum
3. b) Fill in the blanks
4. The stator of a 3 phase induction motor produces ……………..Magnetic field.
5. The primary and secondary of a transformer are ……………………….Coupled.
• A transformer is a efficient device because it is ……………………..
1. 3-phase wound motors are also called ……………………..motor.
2. Most of the single phase induction motor are ………………….pole machine.

Q.2      Discuss the characteristics and application of synchronous motors.

Q.3      Draw equivalent circuit of transformer on no load, and its phasor diagram.

Q.4      Derive formula for induction motor torque i.e. shaft torque and rotor torque?

Q.5      Explain synchronous impedance method of an alternator.

Q.6      Explain universal motor in detail (construction, operation & characteristics).

Q.7      Explain the operation of 3 phase induction motor and the effect of load on the motor.

Q.8      Write short notes on any TWO

1. Stepper motor
2. Write four conditions for parallel operation
• Voltage regulation of Alternator.

## Guess Paper 8: Electric Machines Fall – 2017 Past Papers

Time Allowed: 3 hours

Total Marks:    70, Passing Marks (35)

Q1. Briefly define each of the following:
a. Current
b. Transformer
c. Turns Ratio
d. Motor
e. Pole
f. Rotor
g. Carbon Brush

Q2. What are magnetic circuits? Differentiate between AC and DC Machines.

Q3. Explain the parallel operation of the generators.

Q4. What are open and short circuit tests and for what purpose they have been used?

Q5. Discuss the principle of operation of a synchronous motor.

Q6. Differentiate between testing of machines by direct and indirect methods.

Q7. What is auto transformer? What are the advantages and uses of auto transformers?

Q8. Write short Notes on any TWO.
a. Principle of DC machines
b. Types of Starter
c. Common faults in DC machines

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29. Professional Ethics Past Papers Prof.Fazal Rehman Shamil (Available for Professional Discussions)
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