# Electrical Machine Design MCQ (Multiple Choice Questions)

Here are 1000 MCQs on Electrical Machine Design (chapterwise).

1. Which of the following circuit is designed to dissipate heat produced in the machine?
a) Electric circuit
b) Magnetic circuit
c) Dielectric circuit
d) Thermal circuit

Explanation: A thermal circuit in electrical machine design deals with the mode and media to dissipate heat produced in the machine. The heat produced in the machine leads to losses.

2. Which of the following materials is generally used in the design of electromagnetic machines?
a) Paramagnetic materials
b) Diamagnetic materials
c) Ferromagnetic materials
d) Core-magnetic materials

Explanation: Ferromagnetic materials can strongly act like a magnet when placed in a magnetic field. They are exhibited by materials such as iron, cobalt, nickel, etc. Ferromagnetic materials are generally used in electromagnetic machines.

3. What must be mainly ensured to keep the temperature rise within limits?
a) Good efficiency of the machine
b) Proper cooling and ventilation
c) Proper saturation level
d) Good insulation

Explanation: Temperature rise will affect the life of the insulation. Thus, proper cooling and ventilation must be ensured according to electric machine design to keep the temperature rise within limits. The coolant flowing will absorb the heat from machine parts.

4. Which of the following kind of conductors will require thicker insulation?
a) Large sized conductor
b) Small-sized conductor
c) Conductors with high permeance
d) Conductors with low permeance

Explanation: Maximum voltage stress and mechanical stress is necessary to determine the size of insulation. Thus, if two electrical machines operate at the same voltage, large-sized conductors will need thicker insulation.

5. Which of the following factor mainly determines the type of insulation for an electrical machine?
a) Maximum allowable flux density
b) Maximum operating temperature
c) Maximum efficiency of the machine
d) Maximum allowable loss in machine

Explanation: Temperature rise affects the life of the insulation which can further reduce the operating life of the machine. Thus, maximum operating temperature determines the type of insulation for an electrical machine.

6. How should be the magnetic and electrical loadings in a highly efficient electric machine?
a) It must be small
b) It must be large
c) It must be equal to the current density
d) It must be equal to the flux density

Explanation: To reduce operating costs the efficiency of the machine must be made higher. The magnetic and electrical loadings in a highly efficient electric machine must be small and use more material.

7. What kind of emf is produced in an electric machine when the coil is stationary and flux varies with time?
a) Transformer emf
b) Motional emf
c) Interactional emf
d) Induction emf

Explanation: Transformer emf also called the pulsational emf is produced when the coil is stationary and flux varies with time. No energy conversion takes place in this process. This kind of emf is generated in a transformer.

8. What kind of materials are used to design electrical heating devices?
a) High Conductivity Materials
b) High Resistivity Materials
c) High Weldability Materials
d) High Solderability Materials

Explanation: High resistive materials are used to make resistances or heating devices as we require to dissipate electrical energy as heat. These are generally obtained by using an alloy of different metals.

9. What are the main dimensions of a rotating electric machine?
a) Field diameter and Armature core length
b) Armature diameter and Field core length
c) Armature diameter and Armature core length
d) Field diameter and Field core length

Explanation: The armature is the part of the machine that carries AC. The main dimensions in a rotating electric machine are said to be the Armature diameter and Armature core length.

10. What determines the output of a dc electric machine?

11. How will the size and cost of a rotating electric machine be if it is designed with greater speed?
a) small size and more cost
b) small size and less cost
c) large size and more cost
d) large size and less cost

Explanation: The rotating electric machine designed with greater speed will have a smaller size and lesser cost compared to other machines giving the same output but designed at lesser speeds. This is because the volume of active parts of the machine varies inversely with speed.

12. What is the relation between the output coefficient to the volume of active parts in a rotating electric machine?
a) directly proportional
b) inversely proportional
c) equal to
d) No relation can be established

Explanation: The output coefficient and the volume of active parts in a rotating electric is inversely proportional to each other. Thus, the size of the machine decreases with an increase in output coefficient.

13. How should be the output coefficient of a rotating electric machine from an economics point of view?
a) High
b Low
c) Moderate
d) Output coefficient does not affect the economics

Explanation: The rotating electric machine designed with a higher output coefficient will have a smaller size and lesser cost. This volume of active parts of the machine varies inversely with the output coefficient. Thus, the output coefficient of a rotating electric machine must be high.

14. How should be the specific loadings to design a machine with reduced dimensions?

Explanation: The output coefficient is proportional to the product of specific magnetic loading and specific electric loading. The output coefficient of a rotating electric machine is inversely proportional to the output coefficient. Thus, increased values of specific loadings will give a small size machine.

15. Where does maximum flux density occur in a well-designed electric machine?
a) In the rotor
b) In the air gap
c) In the teeth
d) In the poles

Explanation: The maximum flux density in a well-designed electric machine occurs in the teeth of the machine. The flux density in teeth is directly proportional to the specific magnetic loading.

16. Which of these factors does not determine the specific magnetic loading in rotating machines?
a) Magnetizing current
b) Core loss
c) Maximum flux density in iron parts
d) Number of parallel paths

Explanation: The Magnetizing current, Core loss, and Maximum flux density in iron parts of the machine are the factors that help in determining the specific magnetic loading in rotating machines.

17. What is the other name for a short-pitched coil electrical machine?
a) Coiled
b) Commutated
c) Winded
d) Chorded

Explanation: Two coil sides can form a full pitched coil when they are spaced one pole pitch apart. A coil span less than a pole pitch is called a short-pitched coil or chord.

18. What kind of layer winding does a closed winding of an electric machine usually have?
a) Single layer
b) Double layer
c) Single layer or Double layer
d) Mixture of single layer and double layer

Explanation: A double layer winding has identical coils where one coil side of each coil lies in the top half portion of slot and another side on the bottom half of another slot. Such a winding is used to make closed winding.

19. Why are tapered interpoles used in large DC electric machines?
a) To eliminate saturation at root of pole
b) To obtain higher speeds
c) To obtain maximum torque
d) To eliminate eddy current loss

Explanation: At heavy overloads saturation at the root of the pole may occur. Thus, tapered interpoles are used to eliminate saturation at root of the pole.

20. Which part of an electric machine is designed to give the main magnetic flux?
a) Interpoles
b) Frame
c) Main poles
d) Commutator

Explanation: Main poles is the part of an electric machine that is designed to give the main magnetic flux. This is present in the field system of the dc machine which is responsible to produce magnetic flux for the necessary excitation.

21. Which of the following is used to connect the armature conductors to the commutator?
a) vee-ring
b) Equalizer ring
c) Banding
d) Risers

Explanation: A commutator helps in rectifying the alternating current that is induced in armature. A riser is used to connect the armature conductors to the commutator. Riser segments are made of copper strips in a large machine.

22. What process takes place in an electric machine when stationary is kept in a time-varying field?
a) Energy conversion
b) Energy transference
c) Rotation of coil
d) Movement of coil

Explanation: Transformer emf is produced when the coil is stationary and flux varies with time. No energy conversion takes place in this process thus, only energy transference takes place. This kind of emf is generated in the transformer.

23. Which of the following is the same as the transformer emf?
a) Pulsational emf
b) Induction emf
c) Interactional emf
d) Motional emf

Explanation: Pulsational emf is also called the transformer emf. It is produced when the coil is stationary and flux varies with time. Such emf is produced in a transformer and no motion takes place in this machine.

24. How will be the size and cost of a rotating electric machine that has a higher output coefficient be?
a) small size and more cost
b) small size and less cost
c) large size and more cost
d) large size and less cost

Explanation: The rotating electric machine designed with a higher output coefficient will have a smaller size and lesser cost compared to other machines having a lower output coefficient. This is because the volume of active parts of the machine varies inversely with the output coefficient.

25. How will high specific loading according to rotating electric machine affect the efficiency?
a) Efficiency increases
b) Efficiency decreases
c) Efficiency may increase or decrease
d) Efficiency is not affected

Explanation: Higher the specific loading, lower will be the size and cost of the machine but the efficiency, power factor, commutation conditions in dc machines are affected. Thus, a suitable value of specific loadings needs to be selected.

26. What kind of layer winding in an electric machine occupies the whole slot by one coil side of the coil?
a) Single layer
b) Double layer
c) Single layer or Double layer
d) Mixture of single layer and double layer

Explanation: A single layer winding occupies the whole slot by one coil side of the coil. Such a winding is used to make open windings but is not used for closed windings.

27. What are the different types of interpoles in DC electric machines?
a) Parallel sided and Tapered
b) Open and closed
c) Single layer and double layer
d) Armature and field

Explanation: Interpoles are placed in a machine to improve the commutation conditions. The two types of interpoles are Parallel sided and Tapered where tapered are generally used for large machines.

28. What is the relation between hysteresis and the number of poles?
a) hysteresis loss decreases with an increase in number of poles
b) hysteresis loss increases with an increase in number of poles
c) hysteresis loss remains constant with an increase in number of poles
d) hysteresis loss may increase or decreases with an increase in number of poles

Explanation: Keeping the core area the same, the hysteresis loss for a 4 pole machine will be half of that in a 2 pole machine. Thus, hysteresis loss decreases with an increase in the number of poles.

29. Which of these will increase with an increase in the number of poles?
a) Weight of field copper
b Number of commutator segments
c) Overall diameter of machine
d) Weight of armature copper

Explanation: The weight of field copper, armature copper, and the overall diameter of the machine decreases with an increase in the number of poles. The number of commutator segments will increase with an increase in the number of poles.

30. How should be the value of field mmf to prevent excessive distortion of field form by armature reaction in an electric machine?
a) large compared to armature mmf
b) small compared to armature mmf
c) zero
d) large or small compared to armature mmf

Explanation: The field mmf must be large compared to armature mmf to prevent excessive distortion of field form by armature reaction. The air gap length can be made large to reduce the distortion effect of armature reaction as a long air gap needs a large field mmf.

31. Which of these windings are said to be bifurcated windings?
a) Whole coil winding
b) Semi-closed winding
c) half-coil winding
d) Hemitropic windings

Explanation: In electric machine design whole coil windings are also called bifurcated windings. In such a winding, it can be seen that the coils that comprise a pair of pole phase group are split into 2 sets of concentric coils.

32. How will the length of the air gap in a DC electric machine affect pulsational loss in pole faces?
a) Pulsational loss increases with an increase in air gap length
b) Pulsational loss decreases with an increase in air gap length
c) Pulsational loss does not change with an increase in air gap length
d) Pulsational loss may increase or decrease with an increase in air gap length

Explanation: The change in air gap flux density is small when the length of the air gap is increased. This is due to slotting. The pulsational loss in the pole face decreases with an increase in air gap length.

33. Which of these options are correct for a DC electric machine with a large air gap?
a) More pulsational loss in pole face
b) Quieter operation of the machine
c) Distorting effect of armature reaction more
d) No proper ventilation

Explanation: A DC electric machine with a large air gap has less pulsational loss in pole face, quieter operation of the machine, less distorting effect of armature reaction, and improved ventilation.

34. How should be the number of slots in a DC electric machine for better cooling of armature conductors?
a) Large number of slots
b) Less number of slots
c) Slots equal to the number of poles
d) Number of slots depends on commutation

Explanation: A large number of slots will require fewer conductors per slot and only fewer conductors are bunched together. For better cooling of armature conductors, a large number of slots are needed.

35. Which of the following circuit is made to insulate one conductor from another?
a) Electric circuit
b) Magnetic circuit
c) Dielectric circuit
d) Thermal circuit

Explanation: A dielectric circuit in electrical machine design has insulation that is used to insulate one conductor from another. They are also used to insulate the windings and the core.

36. How is the saturation level of ferromagnetic materials determined in electrical machines?
a) Using maximum allowable flux density
b) Using specific permeance
c) Using the linear velocity of material
d) Using maximum allowable loss

Explanation: The maximum allowable flux density helps in determining the saturation level of ferromagnetic materials. More the flux density more will be the excitation.

37. What part of electric machines will the temperature rise mainly affect?
a) Conductance of winding
b) Insulation of machine
c) Speed of machine
d) Torque of machine

Explanation: Temperature rise will affect the life of the insulation. If insulation is affected the life of the machine also decreases. Proper cooling and ventilation must be ensured according to electric machine design to keep the temperature rise within limits.

38. How is the size of insulation determined?
a) By maximum voltage stress and maximum saturation
b) By mechanical stress
c) By maximum saturation and mechanical stress
d) By maximum voltage stress and mechanical stress

Explanation: Maximum voltage stress and mechanical stress is necessary to determine the size of insulation. In case if two machines operate at the same voltage, large-sized conductors will need thicker insulation.

## Chapterwise Multiple Choice Questions on Electrical Machine Design

Our 1000+ MCQs focus on all topics of the Electrical Machine Design subject, covering 100+ topics. This will help you to prepare for exams, contests, online tests, quizzes, viva-voce, interviews, and certifications. You can practice these MCQs chapter by chapter starting from the 1st chapter or you can jump to any chapter of your choice.

## 1. MCQ on Electrical Engineering Materials

The section contains Design of Electrical Machine multiple choice questions and answers on electrical conducting materials, high conductivity materials, temperature rise, magnetic and insulating materials.

## 2. Multiple Choice Questions on Thermal Design Aspects of Electrical Machines & D.C. Machines

The section contains Electrical Machine Design questions and answers on machines rating, armature design, commutator and brushes design, dc machines output equation design, poles number selection and pole design.

## 3. Design of Electrical Machines MCQ on Design of Transformers

The section contains Design of Electrical Machine MCQs on window space factor, core and winding design, transformers temperature rise, tank design, transformers cooling methods and overall dimensions.

## 4. Electrical Machines Design Multiple Choice Questions on Three Phase Induction Motor

The section contains Electrical Machine Design multiple choice questions and answers on three phase induction motor dimensions, rotor bars and slots design, wound rotor design, no load current, dispersion coefficient, stator windings, losses and efficiency.

## 5. Design of Synchronous Machines MCQ

The section contains Design of Electrical Machine questions and answers on synchronous machines types, hydro generators construction, turbo alternators construction, armature design, field winding design, rotor design, losses and temperature rise, synchronous machines output equation and slot dimensions.

## 6. Design of Permanent Magnet (PM) DC Motors Multiple Choice Questions

The section contains Electrical Machine Design MCQs on design preliminaries, design steps and considerations of permanent magnet dc motors.

## 7. Design of Electromagnets MCQ

The section contains Design of Electrical Machine multiple choice questions and answers on electromagnets types, electromagnets construction and magnet coils design.

## 8. Design of Current Transformers (CT) Multiple Choice Questions

The section contains Electrical Machine Design questions and answers on current transformers errors and construction, design principles and turns compensation.

## 9. Aspects of Design of Mechanical Parts MCQ

The section contains Design of Electrical Machine MCQs on shaft design, bearings, ac and dc machines frames, rotor windings bracing and fan design.

## 10. Design of Single Phase Induction Motor Multiple Choice Questions

The section contains Electrical Machine Design multiple choice questions and answers on motor types, single phase induction motor construction and output equations, stator and rotor design, single phase induction motor parameters and operating characteristics.

## 11. Multiple Choice Questions on Design of Small Electrical Machines, Starters and Field Regulators

The section contains Design of Electrical Machine questions and answers on small reluctance motor and small universal commutator designs, motor starters, calculation of resistance steps & field regulators design.

## 12. Computer Application in Electrical Machine Design MCQ

The section contains Electrical Machine Design MCQs on computer aided design, transformers computer aided design, dc motor and synchronous machine designs.

## 13. Fundamental Aspects of Electrical Machine Design Multiple Choice Questions

The section contains Design of Electrical Machine multiple choice questions and answers on machines designs, designs limitations, machine design modern trends and magnetic leakage.

## 14. Principles of Magnetic Circuit Design MCQ

The section contains Electrical Machine Design questions and answers on iron losses determination, slot leakage, pulsation losses, leakages types, field form, flux distribution curve harmonic analysis, specific permeance and magnetizing current calculations.

## 15. General Concepts and Constraints in Design of Rotating Machines Multiple Choice Questions

The section contains Design of Electrical Machine MCQs on relation between rating and dimensions, rotating machines output variation, standard frames, separation of d and l.

If you would like to learn "Design of Electrical Machines" thoroughly, you should attempt to work on the complete set of 1000+ MCQs - multiple choice questions and answers mentioned above. It will immensely help anyone trying to crack an exam or an interview.

Wish you the best in your endeavor to learn and master Design of Electrical Machines!