Design Of Electrical Machines MCQs – Design of Single Phase Induction Motor MCQs ( Design Of Electrical Machines ) MCQs
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Design Of Electrical Machines MCQs – Design of Single Phase Induction Motor MCQs ( Design Of Electrical Machines ) MCQs
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Types of Motor
1. What is the special feature of single phase induction motor?
a) high starting torque
b) low starting torque
c) average starting torque
d) zero starting torque
Answer: d
Explanation: The single phase induction motor has no inherent starting torque. Thus special means should be used to make it self starting.
2. How many methods are present in the self starting of the single phase induction motor?
a) 1
b) 2
c) 3
d) 4
Answer: c
Explanation: There are 3 methods involved in the self starting of the single phase induction motor. They are split phase starting, shaded pole starting, repulsion motor starting.
3. What are the names of the windings used in the split phase starting?
a) starting windings
b) auxiliary windings
c) starting or auxiliary windings
d) starting and auxiliary windings
Answer: c
Explanation: The single phase induction motor is not self starting. The starting or auxiliary windings are used along with the running or main windings.
4. What is the displacement of the running and the starting windings used?
a) running winding displaces the starting winding by 180°
b) running winding displaces the starting winding by 90°
c) starting winding displaces the running winding by 90°
d) starting winding displaces the running winding by 180°
Answer: b
Explanation: The split phase starting makes use of the starting windings along with the running windings. The running winding displaces the starting windings by 900.
5. How is the required phase displacement between the current in the running and starting windings obtained?
a) by connecting a suitable resistor
b) by connecting a suitable capacitor
c) by connecting a suitable inductor
d) by connecting a suitable impedance
Answer: d
Explanation: The running winding displaces the starting winding by 90°. The required phase displacement is obtained by connecting a suitable impedance in series with any of the windings.
6. When is the starting winding cut out of the circuit in the split phase motor?
a) when the motor speed reaches 65 % of the full load speed
b) when the motor speed reaches 75 % of the full load speed
c) when the motor speed reaches 50 % of the full load speed
d) when the motor speed reaches 85 % of the full load speed
Answer: b
Explanation: The single phase induction motor is not a self starting machine and hence starting windings are connected in series with the running winding. The starting windings are cut out when the motor speed reaches 75 % of the full load speed.
7. What is the shaded pole starting method?
a) part of the pole is shaded by open circuited copper ring
b) part of the pole is shaded by short circuited copper ring
c) the pole is shaded by open circuited copper ring
d) the pole is shaded by short circuited copper ring
Answer: b
Explanation: One of the starting methods of the single phase induction motor is the shaded pole starting method. Here the part of the pole is shaded by the short circuited copper ring.
8. What happens in the shaded pole starting method according to the displacement?
a) displacement between shaded and unshaded portion varies between 20°-25°
b) displacement between shaded and unshaded portion varies between 20°-35°
c) displacement between shaded and unshaded portion varies between 20°-30°
d) displacement between shaded and unshaded portion varies between 30°-45°
Answer: c
Explanation: The shaded pole starting method is that the part of the pole is shaded by short circuited copper ring. The displacement between shaded and unshaded portion varies between 200-300.
9. For what type of machines is the shaded pole starting method suitable?
a) for outputs below 60 watt
b) for output below 50 watt
c) for output below 40 watt
d) for output above 50 watt
Answer: a
Explanation: The efficiency of the shaded pole starting method is very low. The shaded pole starting method is used for outputs below 60 watts.
10. When is the repulsion motor starting method used?
a) when low starting torque is required
b) when high starting torque is required
c) when high running torque is required
d) when low running torque is required
Answer: b
Explanation: The repulsion motor starting method is one of the 3 methods of starting the single phase induction motor. It is used when the high starting torque is required.
11. What is the specialty in the repulsion motor starting method?
a) cage winding is replaced by armature windings
b) cage winding is replaced by field windings
c) cage winding is replaced by commutator windings
d) cage winding is replaced by bearings
Answer: c
Explanation: The repulsion motor starting method is one of the methods used in the starting of the single phase induction motor. Here the cage winding is replaced by the commutator windings.
12. What happens in the repulsion motor starting method?
a) the cage windings is dominant
b) the commutator windings are dominant
c) the rotor windings are dominant
d) the stator windings are dominant
Answer: b
Explanation: The repulsion motor starting method is one of the starting methods of single phase induction motor. The commutator windings are dominant and hence gives good starting torque.
13. What is the range of output watt for the shaded pole induction machine?
a) 0.37-50
b) 90-750
c) 90-3700
d) 7.5-370
Answer: a
Explanation: The range of output watt for capacitor type induction motor is 90-750 and that of the repulsion start motor is 90-3700. The range of output watt for resistor type induction motor is 7.5-370 and that of the shaded pole type is 0.37-50.
14. What is the range of the starting current of capacitor type induction motor?
a) 5-7
b) 4–6
c) 2-6
d) 2-3
Answer: b
Explanation: The range of starting current is 5-7 for resistor type induction motor and that of the repulsion start motor is 2-3. The range of the starting current of capacitor induction motor is 4-6.
15. What is the range of the starting torque of shaded pole induction motor?
a) 2-4
b) 2-3.5
c) 0.2-0.3
d) 0.25-0.5
Answer: c
Explanation: The range of starting torque in the capacitor induction motor is 2-3.5 and that of the repulsion start induction motor is 2-4. The range of the starting torque of the shaded pole induction motor is 0.2-0.3.
Single Phase Induction Motor Construction
1. How many steps are involved in the construction of single phase induction motor?
a) 3
b) 4
c) 5
d) 6
Answer: c
Explanation: There are 5 steps in the construction of the single phase induction motor. They are stator, stator windings, rotor, starting switches, electrolytic capacitor.
2. What is the lamination used for the stator?
a) cast iron
b) die cast aluminium alloy frame
c) cast iron or die cast aluminium alloy frame
d) cast iron and die cast aluminium alloy frame
Answer: c
Explanation: The stator is made up of a block of laminations. The block of laminations are made up of cast iron or die cast aluminium alloy frame.
3. What type of coils are used for winding the single phase induction motor generally?
a) rectangular coils
b) square coils
c) cruciform coils
d) circular coils
Answer: d
Explanation: The slots house the starting and running windings. The single phase induction motors are generally wound with concentric coils.
4. How many kinds of single phase windings are present?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: There are basically 3 kinds of single phase windings. They are concentric, progressive and skein.
5. How are the poles and pitches in the concentric windings?
a) single pole, different pitches
b) different pole, different pitches
c) different pole, single pitch
d) single pole, single pitch
Answer: a
Explanation: The concentric windings have a single pole for a common centre. They have different pitches for each individual coil.
6. What is the form of the progressive windings?
a) double layer diamond coil windings
b) single layer diamond coil windings
c) multi layer diamond coil windings
d) three layer diamond coil windings
Answer: b
Explanation: The progressive windings is one kind of the stator windings. They are in the form of the single layer diamond coil windings.
7. When is the skein winding made use of?
a) when small amount of relatively small size wire is used
b) when large amount of relatively small size wire is used
c) when large amount of relatively large size wire is used
d) when small amount of relatively large size wire is used
Answer: a
Explanation: Skein winding is one of the 3 kinds of single phase windings used. It is used when small amount of relatively small size wire is used.
8. What kind of motor employs the skein winding made use of?
a) maximum horse power single phase induction motor
b) fractional horse power single phase induction motor
c) minimum horse power single phase induction motor
d) zero horse power single phase induction motor
Answer: b
Explanation: The skein winding is one of the 3 kinds of single phase induction motor. The skein winding is used when fractional horse power single phase induction motor is used.
9. Which winding is mostly used winding in the single phase induction motor?
a) circular winding
b) concentric winding
c) progressive winding
d) skein winding
Answer: b
Explanation: The concentric winding is the most widely used winding. It is also the most flexible winding of the windings used in the single phase induction motor.
10. What is/are the advantages of the skein winding?
a) low cost to wind
b) low cost to insert
c) permits some freedom of choice of distribution
d) low cost to wind, low cost to insert, permits some freedom of choice of distribution
Answer: d
Explanation: The skein winding is the low cost to wind and to insert. It also permits some freedom of choice of distribution.
11. What material is used in the tunnel of the rotor of the single phase induction motor?
a) aluminium
b) copper
c) steel
d) wood
Answer: a
Explanation: The rotor consists of a block of slotted laminations. The slots form a series of tunnels that are filled with aluminium in its molten state.
12. What type of operations are used in the starting switches?
a) mechanical operation
b) electrical operation
c) centrifugal operation and mechanical operation
d) centrifugal operation
Answer: c
Explanation: The starting switch is used to cut the auxillary winding when the motor attains 75% of the full load speed. The switches operate in both the centrifugal as well as mechanical operation.
13. The ac electrolytic capacitor is formed by winding two sheets of etched aluminium foil.
a) true
b) false
Answer: a
Explanation: Modern capacitor start motors employ ac electrolytic capacitors. The ac electrolytic capacitor is formed by winding two sheets of etched aluminium foil, separated by two layers of insulating paper, into a cylindrical shape.
14. The electrolytic capacitor and insulator unit is impregnated using ethylene glycol or a derivative.
a) true
b) false
Answer: a
Explanation: The electrolytic capacitor and insulator unit is impregnated using the ethylene glycol. It is also impregnated using the derivative of ethylene glycol.
15. What is the range of the power factor of electrolytic capacitors?
a) 2-4
b) 4-6
c) 6-8
d) 7-9
Answer: c
Explanation: The minimum power factor of the electrolytic capacitor is 6. The maximum power factor of the electrolytic capacitor is 8.
Output Equation
1. What is the formula of the output equation of ac machines?
a) kVA input Q = output coefficient * diameter2 * length * synchronous speed
b) kVA input Q = output coefficient / diameter2 * length * synchronous speed
c) kVA input Q = output coefficient * diameter2 / length * synchronous speed
d) kVA input Q = output coefficient * diameter2 * length / synchronous speed
Answer: a
Explanation: The output coefficient, diameter, length and synchronous speed are first calculated. Then on substitution gives the kVA input and in turn gives the output equation.
2. What is the formula for the output coefficient of the output equation?
a) output coefficient = 11 * winding space factor * specific magnetic loading / specific electric loading * 10-3
b) output coefficient = 11 * winding space factor * specific magnetic loading * specific electric loading * 10-3
c) output coefficient = 11 * winding space factor / specific magnetic loading * specific electric loading * 10-3
d) output coefficient = 11 / winding space factor * specific magnetic loading * specific electric loading * 10-3
Answer: b
Explanation: The winding space factor, specific magnetic loading, specific electric loading is calculated. On substitution gives the output coefficient used for the calculation of output equation.
3. What is the formula of the kVA input if the rating of the machine is given in horse power?
a) kVA input = horse power / 0.746 * efficiency * power factor
b) kVA input = horse power * 0.746 * efficiency * power factor
c) kVA input = horse power * 0.746 / efficiency * power factor
d) kVA input = horse power * 0.746 * efficiency / power factor
Answer: c
Explanation: The horse power rating of the machine along with the efficiency and power factor is calculated. On substitution the kVA input can be obtained.
4. What is the ratio of the efficiency for 75 watt to 750 watt motor?
a) 4:7
b) 5:7
c) 6:7
d) 3:7
Answer: b
Explanation: The efficiency of the 75 watt motor is 50%. The efficiency of the 750 watt motor is 70%.
5. What is the ratio of power factor of the 75 watt to 750 watt motor?
a) 0.55 : 0.60
b) 0.50 : 0.60
c) 0.55 : 0.65
d) 0.50 : 0.65
Answer: c
Explanation: The power factor of the 75 watt motor is 0.55. The power factor of 750 watt motor is 0.60.
6. The smaller values are applicable for lower rating machines.
a) true
b) false
Answer: a
Explanation: The smaller values are applicable for lower rating machines. The power factor is 0.55 for 75 watt motor and the efficiency is 50% for the 75 watt motor.
7. What is the efficiency for the output watt of 180?
a) 0.38
b) 0.48
c) 0.57
d) 0.65
Answer: c
Explanation: The efficiency of the output watt of 37 is 0.38 and the efficiency of output watt of 90 is 0.48. The efficiency of the output watt of 180 is 0.57.
8. What is the power factor of output watt of 90?
a) 0.46
b) 0.51
c) 0.56
d) 0.62
Answer: b
Explanation: The power factor of output watt of 37 is 0.46 and the power factor for 180 output watt is 0.56. The power factor of the output watt of 90 is 0.51.
9. What factor does the output coefficient depend upon?
a) specific magnetic loading
b) specific electric loading
c) specific electric loading or specific magnetic loading
d) specific electric loading and specific magnetic loading
Answer: b
Explanation: The output coefficient depends upon the specific electric loading. The output coefficient also depends upon the specific magnetic loading.
Design of Permanent Magnet (PM) DC Motors
10. What is the range of the average flux density used in the output equation?
a) 0.30-0.55 weber per m2
b) 0.30-0.50 weber per m2
c) 0.35-0.45 weber per m2
d) 0.35-0.55 weber per m2
Answer: d
Explanation: The minimum value of the average flux density is 0.35 weber per m2. The maximum value of the average flux density is 0.55 weber per m2.
Design of Stator
1. What type is the stator windings of the single phase induction motor?
a) hollow
b) cylindrical
c) concentric
d) rectangular
Answer: c
Explanation: The stator windings are also known as the running winding or the main winding. The type of stator winding used is concentric type
2. How many coils are present in the stator windings?
a) 2
b) 3
c) 2 or more
d) 3 or more
Answer: d
Explanation: The stator windings of single phase induction motors are concentric type. There are usually 3 or more coils per pole each having same or different number of turns.
3. How much of the total slots are used for the reduction of the mmf wave harmonics?
a) 60%
b) 65%
c) 70%
d) 80%
Answer: c
Explanation: 70% of the total slots are used for the reduction of the mmf wave harmonics. The remaining 30% are used for accommodating the starting windings.
4. How can the small single phase motor reduce the harmonics still much further?
a) removing the winding
b) insulating the winding
c) grading the winding
d) shading the winding
Answer: c
Explanation: 70% of the total slots are used for the reduction of the mmf wave harmonics. The mmf wave harmonics can be still further reduced by grading the winding.
5. What is the formula for the mean pitch factor?
a) mean pitch factor = pitch factor of each coil per pole group + turns in the coil / total number of turns
b) mean pitch factor = pitch factor of each coil per pole group / turns in the coil * total number of turns
c) mean pitch factor = pitch factor of each coil per pole group * turns in the coil * total number of turns
d) mean pitch factor = pitch factor of each coil per pole group * turns in the coil / total number of turns
Answer: d
Explanation: The pitch factor of each coil per pole group, turns in the coil and total number of turns are obtained. On substitution, it gives the mean pitch factor.
6. What is the range of the winding factor for the usual windings distribution?
a) 0.70-0.80
b) 0.75-0.85
c) 0.70-0.85
d) 0.70-0.75
Answer: b
Explanation: The minimum value of the winding factor of the usual winding distribution is 0.75. The maximum value of the winding factor of the usual winding distribution is 0.85.
7. What is the formula of the maximum flux in the running winding?
a) maximum flux = flux * pole
b) maximum flux = flux/pole
c) maximum flux = flux / turns
d) maximum flux = flux * turns
Answer: b
Explanation: First the flux is calculated along with the number of poles used. On substituting the values the maximum flux value is obtained.
8. What is the value of the stator induced voltage with respect to the supply voltage?
a) stator induced voltage = 95% of supply voltage
b) stator induced voltage = 90% of supply voltage
c) stator induced voltage = 85% of supply voltage
d) stator induced voltage = 80% of supply voltage
Answer: a
Explanation: The winding factor is assumed to be 0.75-0.85 for the running winding. The stator induced voltage is 95% of the supply voltage.
9. How many design data are present in the design of the stator?
a) 6
b) 7
c) 8
d) 9
Answer: c
Explanation: There are 8 design data available in the design of the stator. The design data are running winding, number of turns In running winding, running winding conductors, number of stator slots, size of stator slot, stator teeth, stator core, length of mean turn.
10. What is the range of the current density for the open type motors split phase, capacitor and repulsion start motors?
a) 4-5 A per mm2
b) 3-4 A per mm2
c) 2-4 A per mm2
d) 1-4 A per mm2
Answer: b
Explanation: The minimum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 3 A per mm2. The maximum value of the current density for the open type motors split phase, capacitor and repulsion start motors is 4 A per mm2.
11. What is the relation of the number of slots with the leakage reactance?
a) small number of slots, high leakage reactance
b) large number of slots, high leakage reactance
c) large number of slots, small leakage reactance
d) small number of slots, small leakage reactance
Answer: c
Explanation: The number of slots is indirectly proportional to the leakage reactance. The larger the number of slots, the lower will be the leakage reactance.
12. What is the formula for the area required for the insulated conductors?
a) area required for the insulated conductors = total number of conductors per slot * 0.785 / diameter of insulated conductor2
b) area required for the insulated conductors = total number of conductors per slot / 0.785 * diameter of insulated conductor2
c) area required for the insulated conductors = total number of conductors per slot * 0.785 * diameter of insulated conductor2
d) area required for the insulated conductors = 1/total number of conductors per slot * 0.785 * diameter of insulated conductor2
Answer: c
Explanation: The total number of conductors per slot and the diameter of insulated conductors are calculated. On substitution the area required for the insulated conductors are calculated.
13. The flux density of the high torque machines is 1.8 weber per m2.
a) true
b) false
Answer: a
Explanation: The flux density of the general purpose machine is 1.45 weber per m2. The flux density of the high torque machines is 1.8 weber per m2.
14. The flux density of the stator core should not exceed 1.3 weber per m2.
a) true
b) false
Answer: b
Explanation: The flux density of the stator core should not exceed 1.5 weber per m2. The range lies between 0.9 – 1.4 weber per m2.
15. What is the formula for the flux density in stator core?
a) flux density in stator core = maximum flux / length of the iron * depth of stator core
b) flux density in stator core = maximum flux * length of the iron * depth of stator core
c) flux density in stator core = maximum flux / 2 *length of the iron * depth of stator core
d) flux density in stator core = maximum flux * length of the iron / depth of stator core
Answer: c
Explanation: The maximum flux, length of iron and depth of stator core is calculated. On substitution it provides the flux density in stator core.
Design of Rotor
1. How many design steps are available for the design of rotor?
a) 5
b) 6
c) 7
d) 8
Answer: b
Explanation: There are 6 design steps involved in the design of the rotor. They are number of rotor slots, area of rotor bars, area of end rings, rotor resistance, rotor teeth, rotor core.
2. What is the main motive while choosing the number of rotor slots?
a) increasing the efficiency
b) decreasing the losses
c) no noise is produced
d) high output is produced
Answer: c
Explanation: There are basically 6 steps involved in the rotor design. The number of slots is chosen such that no noise is produced.
3. What is the formula for the harmonic poles due to slots?
a) harmonic poles due to slots = 2 * (number of slots ± number of poles / 2)
b) harmonic poles due to slots = 2 / (number of slots ± number of poles / 2)
c) harmonic poles due to slots = 2 * (number of slots ± number of poles * 2)
d) harmonic poles due to slots = 1/ 2 * (number of slots ± number of poles / 2)
Answer: a
Explanation: First the number of slots and number of poles are first calculated. On substitution we get the harmonic poles due to the slots.
4. What factors are used fixing the number of stator slots?
a) winding arrangement
b) number of poles
c) winding arrangement or number of poles
d) winding arrangement and number of poles
Answer: d
Explanation: The number of poles are fixed according to the winding arrangement. The number of poles are also fixed according to the number of poles.
5. Which condition satisfies the quiet operation in machines?
a) number of stator slots is divisible by number of pairs of poles
b) number of rotor slots differs from the number of stator slots by more than the number of poles
c) number of rotor slots is not divisible by number of pairs of poles
d) number of stator slots differs from the number of rotor slots by more than the number of poles
Answer: b
Explanation: The number of rotor slots are decided for quieter operation of the machine. The number of rotor slots differs from the number of stator slots by more than the number of poles.
6. What among the following are considered for the selection of number of rotor slots?
a) magnetic locking
b) cusps
c) magnetic locking or cusps
d) magnetic locking and cusps
Answer: d
Explanation: The selection of number of rotor slots depends on the magnetic locking. The selection of number of rotor slots depends on the cusps also.
7. What is the formula for the total stator copper section for main winding?
a) total stator copper section for main winding = number of turns in the running winding * area of the running winding conductor
b) total stator copper section for main winding = 2 * number of turns in the running winding * area of the running winding conductor
c) total stator copper section for main winding = number of turns in the running winding / area of the running winding conductor
d) total stator copper section for main winding = 2* number of turns in the running winding / area of the running winding conductor
Answer: b
Explanation: First the number of turns in the running winding is calculated along with the area of the running winding conductor. On substitution it gives the total stator copper section for main winding.
8. What is the formula for the total cross section of rotor bars?
a) total cross section of rotor bars = number of rotor slots * area of each bar
b) total cross section of rotor bars = number of rotor slots / area of each bar
c) total cross section of rotor bars = number of rotor slots + area of each bar
d) total cross section of rotor bars = number of rotor slots – area of each bar
Answer: a
Explanation: The number of rotor slots and area of each bar is first calculated. On substitution it gives the total cross section of rotor bars.
9. What is the range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding for copper?
a) 0.4-0.8
b) 0.3-0.7
c) 0.5-0.8
d) 0.8-0.9
Answer: c
Explanation: The minimum value of range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding is 0.5. The maximum value range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding is 0.8.
10. What is the formula of the end ring current?
a) end ring current = number of rotor slots * bar current * 3.14 * number of poles
b) end ring current = number of rotor slots * bar current * 3.14 / number of poles
c) end ring current = number of rotor slots / bar current * 3.14 * number of poles
d) end ring current = number of rotor slots * bar current / 3.14 * number of poles
Answer: d
Explanation: The number of rotor slots and the bar current along with the number of poles is calculated. On substitution it gives the end ring current value.
11. What is the range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding for aluminium?
a) 1-1.3
b) 1-1.4
c) 1-1.6
d) 1.2-1.5
Answer: c
Explanation: The minimum value of range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding is 1. The maximum value range of the ratio of the total cross section of rotor bars to the total stator copper section for main winding is 1.6.
12. What is the formula for the area of each bar?
a) area of each bar = current through each bar / current density through each bar
b) area of each bar = current through each bar * current density through each bar
c) area of each bar = current density through each bar / current through each bar
d) area of each bar = current density through each bar * current through each bar
Answer: a
Explanation: The current through each bar and the current density through each bar is calculated. On substitution the area of each bar is obtained.
13. What is the formula of the area of each end ring?
a) area of each end ring = 0.32 * total cross section of rotor bars * number of poles
b) area of each end ring = 0.32 / total cross section of rotor bars * number of poles
c) area of each end ring = 0.32 * total cross section of rotor bars / number of poles
d) area of each end ring = 1/0.32 * total cross section of rotor bars * number of poles
Answer: c
Explanation: First the total cross section of rotor bars along with the number of poles are calculated. On substitution the area of each end ring is obtained.
14. What is the formula of the rotor teeth flux density?
a) flux density of rotor teeth = maximum flux / (number of rotor slots / number of poles) * length of the teeth * depth of rotor core
b) flux density of rotor teeth = maximum flux * (number of rotor slots / number of poles) * length of the teeth * depth of rotor core
c) flux density of rotor teeth = 1/maximum flux * (number of rotor slots / number of poles) * length of the teeth * depth of rotor core
d) flux density of rotor teeth = maximum flux / (number of rotor slots * number of poles) * length of the teeth * depth of rotor core
Answer: a
Explanation: The maximum flux, the number of rotor slots per pole and the length of teeth along with the depth of rotor core is calculated. On substitution the flux density of the rotor teeth is obtained.
15. What is the range for the ratio of the resistance to reactance in the split phase motors?
a) 0.40-0.55
b) 0.45-0.55
c) 0.45-0.8
d) 0.45-0.6
Answer: b
Explanation: The range for the ratio of the resistance to reactance in the split phase motors is 0.45-0.55. The range for the ratio of the resistance to reactance in the capacitor start motors is 0.45-0.8.
Parameters
1. What is the formula for the resistance of running winding?
a) resistance of running winding = 0.021 * no of turns in running winding * length of mean turns of running winding * area of running winding conductor
b) resistance of running winding = 0.021 / no of turns in running winding * length of mean turns of running winding * area of running winding conductor
c) resistance of running winding = 0.021 * no of turns in running winding / length of mean turns of running winding * area of running winding conductor
d) resistance of running winding = 0.021 * no of turns in running winding * length of mean turns of running winding / area of running winding conductor
Answer: d
Explanation: First the no of turns in running winding along with length of mean turns of running winding and area of running winding conductor is calculated. On substitution the resistance of running winding is calculated.
2. How many parameters are present in the single phase induction motor?
a) 2
b) 3
c) 4
d) 5
Answer: b
Explanation: There are 3 parameters in the single phase induction motor. They are running winding resistance, rotor resistance and leakage reactance calculations of single phase motor.
3. How many parameters are present under the leakage reactance calculations?
a) 6
b) 5
c) 7
d) 4
Answer: c
Explanation: There are 7 parameters present under the leakage reactance calculations. They are slot leakage reactance, rotor slot leakage reactance, zigzag leakage reactance, overhang leakage reactance, skew leakage reactance, magnetizing reactance, total leakage reactance.
4. How is the winding arrangement and how is the conductors in each slot?
a) circular winding and same conductors in each slot
b) circular winding and different conductor in each slot
c) concentric winding and same conductor in each slot
d) concentric winding and different conductor in each slot
Answer: d
Explanation: The winding of the induction motors are concentric type. The different conductors are being used in each slot.
5. What is the relation of the total slot leakage reactance with number of stator slots?
a) slot leakage reactance is directly proportional to the number of stator slots
b) slot leakage reactance is indirectly proportional to the number of stator slots
c) slot leakage reactance is directly proportional to the square of the number of stator slots
d) slot leakage reactance is indirectly proportional to the square of the number of stator slots
Answer: b
Explanation: The slot leakage reactance is one of the parameters used in the leakage reactance calculations. The slot leakage reactance is indirectly proportional to the number of stator slots.
6. What is the relation between slot leakage reactance and specific slot permeance?
a) slot leakage reactance is directly proportional to the specific slot permeance
b) slot leakage reactance is indirectly proportional to the specific slot permeance
c) slot leakage reactance is directly proportional to the square of the specific slot permeance
d) slot leakage reactance is indirectly proportional to the square of the specific slot permeance
Answer: a
Explanation: Specific slot permeance is one of the parameters present in the leakage reactance calculation. It is directly proportional to the slot leakage reactance.
7. What is the relation of the total slot leakage reactance with number of stator slots?
a) slot leakage reactance is directly proportional to the number of rotor slots
b) slot leakage reactance is indirectly proportional to the number of rotor slots
c) slot leakage reactance is directly proportional to the square of the number of rotor slots
d) slot leakage reactance is indirectly proportional to the square of the number of rotor slots
Answer: b
Explanation: The slot leakage reactance is one of the parameters in the leakage reactance calculation. The slot leakage reactance is indirectly proportional to the number of rotor slots.
8. What is the relation of the zigzag reactance with the specific permeance for zigzag leakage?
a) zigzag reactance is directly proportional to the specific permeance for zigzag leakage
b) zigzag reactance is indirectly proportional to the specific permeance for zigzag leakage
c) zigzag reactance is directly proportional to the square of the specific permeance for zigzag leakage
d) zigzag reactance is indirectly proportional to the square of the specific permeance for zigzag leakage
Answer: a
Explanation: Zigzag reactance is one of the parameters used in the leakage reactance calculation. The zigzag reactance is directly proportional to the specific permeance for zigzag leakage.
9. What is the relation of the stator slot leakage factor with the skew leakage reactance?
a) skew leakage reactance is directly proportional to the stator slot leakage factor
b) skew leakage reactance is indirectly proportional to the stator slot leakage factor
c) skew leakage reactance is directly proportional to the square of stator slot leakage factor
d) skew leakage reactance is indirectly proportional to the square of stator slot leakage factor
Answer: a
Explanation: Skew leakage reactance is one of the parameters used in the leakage reactance calculation. The skew leakage reactance is directly proportional to the stator slot leakage reactance.
10. What is the formula for the rotor bar skew angle?
a) rotor bar skew angle = 3.14 / rotor slot pitches through which bars are skewed * (no of rotor slots / number of poles)
b) rotor bar skew angle = 3.14 * rotor slot pitches through which bars are skewed * (no of rotor slots * number of poles)
c) rotor bar skew angle = 3.14 * rotor slot pitches through which bars are skewed / (no of rotor slots * number of poles)
d) rotor bar skew angle = 3.14 * rotor slot pitches through which bars are skewed / (no of rotor slots / number of poles)
Answer: d
Explanation: The rotor slot pitches through which bars are skewed, number of rotor slots and number of poles are calculated. On substitution the rotor bar skew angle is obtained.
11. What is the value of the stator slot leakage factor?
a) 0.90
b) 0.80
c) 0.95
d) 0.85
Answer: c
Explanation: Stator slot leakage factor is used in the calculation of the skew leakage reactance. The value of the stator slot leakage factor is 0.95 in the single phase induction motor.
12. What is the relation of the overhang leakage reactance with the average coil span in slots?
a) overhang leakage reactance is directly proportional to the square of the average coil span in slots
b) overhang leakage reactance is indirectly proportional to the square of the average coil span in slots
c) overhang leakage reactance is directly proportional to the average coil span in slots
d) overhang leakage reactance is indirectly proportional to the average coil span in slots
Answer: c
Explanation: The overhang leakage reactance is one of the parameters used in the leakage reactance calculation. The overhang leakage reactance is directly proportional to the average coil span in slots.
13. What is the relation between pole pitch and the magnetizing reactance?
a) magnetizing reactance is directly proportional to the square of the pole pitch
b) magnetizing reactance is directly proportional to the pole pitch
c) magnetizing reactance is indirectly proportional to the pole pitch
d) magnetizing reactance is indirectly proportional to the square of the pole pitch
Answer: b
Explanation: The magnetizing reactance is one of the parameters in the leakage reactance calculation. The magnetizing reactance is directly proportional to the pole pitch.
14. The magnetizing reactance is directly proportional to the saturation factor.
a) true
b) false
Answer: b
Explanation: The magnetizing reactance is one of the components used in the leakage reactance calculations. The magnetizing reactance is indirectly proportional to the saturation factor.
15. What is the formula of the saturation factor?
a) saturation factor = total mmf required for magnetic circuit * mmf required for air gap
b) saturation factor = total mmf required for magnetic circuit – mmf required for air gap
c) saturation factor = total mmf required for magnetic circuit / mmf required for air gap
d) saturation factor = total mmf required for magnetic circuit + mmf required for air gap
Answer: c
Explanation: The total mmf required for the magnetic circuit and the mmf required for air gap is calculated. On substitution of the values the saturation factor is calculated.
16. What factor is the core length made equal to in theoretical conditions?
a) pole length
b) pole proportion
c) pole length
d) number of poles
Answer: c
Explanation: The core length is made equal to the pole length in theoretical conditions. But in practical the exact dimensions are governed by manufacturing conditions.
17. What is the output equation of a single phase induction motor developed by P.H Tricky?
a) diameter2 * length = 16.5 / H.P * output coefficient * frequency constant * motor type constants * rpm * 106
b) diameter2 * length = 16.5 * H.P * output coefficient * frequency constant * motor type constants /rpm * 106
c) diameter2 * length = 16.5 * H.P / output coefficient * frequency constant * motor type constants * rpm * 106
d) diameter2 * length = 16.5 * H.P * output coefficient / frequency constant * motor type constants * rpm * 106
Answer: b
Explanation: The output coefficient, horse power, frequency constant, motor type constant along with the speed is calculated. On substitution we get the diameter2 * length value.
Operating Characteristics
1. How many factors are present in the operating characteristics?
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: There are 4 operating characteristics present in the single phase induction motor. They are mmf for air gap, saturation factor, iron loss, friction and windage loss.
2. How many parts does the stator mmf passes through?
a) 3
b) 4
c) 5
d) 6
Answer: c
Explanation: The stator mmf produced in the motor passes through 5 parts. They are air gap, stator teeth, stator core, rotor teeth, rotor core.
3. What is the angle at which the value of the flux density should be for the calculation of mmf?
a) 40°
b) 60°
c) 80°
d) 70°
Answer: b
Explanation: The calculation of mmf should be based upon the value of the flux density. The value of flux density at 60° from the interpolar axis as far as gap and teeth are concerned.
4. What is the value of the flux density with respect to average flux density?
a) value of flux density = 1.67 times of average flux density
b) value of flux density = 1.70 times of average flux density
c) value of flux density = 1.60 times of average flux density
d) value of flux density = 1.50 times of average flux density
Answer: a
Explanation: The value of flux density at 60° from the interpolar axis as far as gap and teeth are used in the calculation of mmf. The value of flux density = 1.67 times of average flux density.
5. What is the formula for the mmf required for air gap?
a) mmf required for air gap = 8,00,000 * air gap flux density * air gap constant / air gap length
b) mmf required for air gap = 8,00,000 * air gap flux density * air gap constant * air gap length
c) mmf required for air gap = 8,00,000 * air gap flux density / air gap constant * air gap length
d) mmf required for air gap = 8,00,000 / air gap flux density * air gap constant * air gap length
Answer: b
Explanation: The air gap flux density, air gap constant, air gap length are calculated first. On substitution, the mmf required for air gap can be obtained.
6. What is the formula for the saturation factor?
a) saturation factor = total mmf required for the magnetic circuit/mmf required for air gap
b) saturation factor = total mmf required for the magnetic circuit + mmf required for air gap
c) saturation factor = total mmf required for the magnetic circuit – mmf required for air gap
d) saturation factor = total mmf required for the magnetic circuit * mmf required for air gap
Answer: a
Explanation: The total mmf required for the magnetic circuit and the mmf required for air gap is calculated. On substitution, the saturation factor is obtained.
7. What is the range of the saturation factor in the single phase induction motor?
a) 1.1-1.3
b) 1.0-1.2
c) 1.1-1.35
d) 1.2-1.6
Answer: c
Explanation: The minimum value of the saturation factor in the single phase induction motor is 1.1. The maximum value of the saturation factor in the single phase induction motor is 1.35.
8. What is the relation between flux densities with respect to saturation factor?
a) flux density is indirectly proportional to the square of the saturation factor
b) flux density is directly proportional to the square of the saturation factor
c) flux density is indirectly proportional to the saturation factor
d) flux density is directly proportional to the saturation factor
Answer: d
Explanation: The saturation factor is kept low if the flux densities in the teeth and core are low. The saturation factor is kept high if the flux densities in the teeth and core are high.
9. What factors are considered while calculating iron loss in stator teeth and core?
a) flux densities
b) weights
c) flux densities or weights
d) flux densities and weights
Answer: d
Explanation: The iron loss in stator teeth and core are found by calculating their flux densities. The iron loss in stator teeth and core are found by calculating their weights.
10. What is the relation between total iron loss for induction motors and the sum of stator tooth and core loss?
a) total iron loss for induction motors = 1.3-2.3 times the sum of stator tooth and core loss
b) total iron loss for induction motors = 1.4-2.4 times the sum of stator tooth and core loss
c) total iron loss for induction motors = 1.5-2.5 times the sum of stator tooth and core loss
d) total iron loss for induction motors = 1.3-2 times the sum of stator tooth and core loss
Answer: c
Explanation: The total iron loss for induction motors is 1.5-2.5 times the sum of stator tooth and core loss. The total iron loss is due to fundamental frequency flux.
11. What is the range of the multiplying factor when test data is not available?
a) 1.7-2
b) 1.75-2.2
c) 1.6-2.3
d) 1.5-2
Answer: b
Explanation: The multiplying factor should be obtained from tests of motors of similar design. When test data is not available, a value of 1.75 to 2 may be used.
12. What are the factors which result in the bearing friction and windage loss?
a) ball bearings
b) sleeve bearing
c) ball bearing and sleeve bearing
d) ball bearing or sleeve bearing
Answer: d
Explanation: The bearing friction and windage loss will depend upon the ball bearings. The bearing friction and windage loss will also depend upon the sleeve bearings.
13. What is the friction and windage loss for a 1500 rpm machine?
a) 3-7% of watt output
b) 3-9% of watt output
c) 4-8% of watt output
d) 1-5% of watt output
Answer: c
Explanation: The friction and windage loss and a speed of 1500 rpm, it is usually minimum 4% of the watt output. The friction and windage loss and a speed of 1500 rpm, it is usually maximum of 8% of the watt output.
14. The high values actually apply for the small motors below 150 W.
a) true
b) false
Answer: b
Explanation: The friction and windage loss and a speed of 1500 rpm, it is usually 4-8% of the watt output. The high values apply to small motors below 180 W.
15. The loss for the sleeve bearing having stator outer diameter 150 mm and 1000 rpm is 3.7 W.
a) true
b) false
Answer: a
Explanation: The sleeve bearing having a stator outer diameter of 150 mm has losses at different running speed. The 1000 rpm machine gives loss of 3.7 W.
16. What is the range of the frequency constant?
a) 0.86-1.0
b) 0.82-1.0
c) 0.9-1.0
d) 0.5-1.0
Answer: a
Explanation: The minimum value of the frequency constant used in the output equation of P.H Tricky is 0.86. The maximum value of the frequency constant used in the output equation of P.H Tricky is 1.0.
17. What is the range of the motor type constant?
a) 1.1-1.3
b) 1.0-1.4
c) 1.1-1.42
d) 1.1-1.5
Answer: c
Explanation: The minimum value of the motor type constants is 1.1. The maximum value of the motor type constants is 1.42.
18. What is the formula of the most economical relation between D and L?
a) length = 0.6 * diameter
b) length = 0.5 / diameter
c) length = 0.6 / diameter
d) length = 0.63 * diameter
Answer: d
Explanation: The length and the diameter are the 2 main dimensions of the single phase induction motor. The most economical relation between length and diameter is length = 0.63 * diameter.