104 + Interview Questions in Design Of Single Phase Induction Motor in Design Of Electrical Machines Page 1 InterviewSolution

1.	The smaller values are applicable for lower rating machines.(a) true(b) falseThis question was addressed to me at a job interview.I need to ask this question from Output Equation topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» CORRECT answer is (a) true 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.

Discussion

2.	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 : 0.65This question was addressed to me in examination.My question is based upon Output Equation in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right answer is (C) 0.55 : 0.65 Easy EXPLANATION: The POWER FACTOR of the 75 watt motor is 0.55. The power factor of 750 watt motor is 0.60.

Discussion

3.	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 * diameterI got this question in an interview for internship.My question is based upon Operating Characteristics topic in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct option is (d) LENGTH = 0.63 * diameter Best 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.

Discussion

4.	What is the range of the frequency constant?(a) 0.86-1.0(b) 0.82-1.0(c) 0.9-1.0(d) 0.5-1.0This question was posed to me in my homework.I'd like to ask this question from Operating Characteristics topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct CHOICE is (a) 0.86-1.0 For 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.

Discussion

5.	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) 1.1-1.5I have been asked this question in an interview.The above asked question is from Operating Characteristics in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct answer is (C) 1.1-1.42 To elaborate: The MINIMUM value of the MOTOR TYPE constants is 1.1. The maximum value of the motor type constants is 1.42.

Discussion

6.	The loss for the sleeve bearing having stator outer diameter 150 mm and 1000 rpm is 3.7 W.(a) true(b) falseI have been asked this question during a job interview.Origin of the question is Operating Characteristics in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right choice is (a) true The explanation is: 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.

Discussion

7.	The high values actually apply for the small motors below 150 W.(a) true(b) falseI have been asked this question in an interview.I need to ask this question from Operating Characteristics topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT choice is (b) false The explanation is: 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.

Discussion

8.	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) 1.5-2I had been asked this question in class test.Question is from Operating Characteristics in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct choice is (b) 1.75-2.2 To explain I would SAY: 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.

Discussion

9.	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 outputThis question was addressed to me in a national level competition.I need to ask this question from Operating Characteristics topic in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct CHOICE is (c) 4-8% of watt output For explanation I would say: 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.

Discussion

10.	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 bearingThis question was addressed to me in class test.I'm obligated to ask this question of Operating Characteristics in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct CHOICE is (d) ball bearing or SLEEVE bearing The 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.

Discussion

11.	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 lossThe question was asked by my college director while I was bunking the class.The above asked question is from Operating Characteristics topic in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct option is (c) TOTAL IRON loss for induction motors = 1.5-2.5 times the sum of STATOR tooth and core loss Best 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.

Discussion

12.	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 weightsThis question was addressed to me by my college director while I was bunking the class.This intriguing question originated from Operating Characteristics topic in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right choice is (d) flux DENSITIES and WEIGHTS Best 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.

Discussion

13.	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 factorI got this question during an online interview.I would like to ask this question from Operating Characteristics topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» CORRECT option is (d) flux DENSITY is directly proportional to the SATURATION factor The 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.

Discussion

14.	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) 1.2-1.6I got this question by my college director while I was bunking the class.The query is from Operating Characteristics topic in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right CHOICE is (c) 1.1-1.35 The best 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.

Discussion

15.	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 gapI got this question in homework.Asked question is from Operating Characteristics in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT CHOICE is (a) saturation factor = TOTAL mmf required for the magnetic circuit/mmf required for air gap The explanation is: The total mmf required for the magnetic circuit and the mmf required for air gap is calculated. On substitution, the saturation factor is OBTAINED.

Discussion

16.	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 densityI got this question during an online interview.I want to ask this question from Operating Characteristics in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct ANSWER is (a) value of flux DENSITY = 1.67 TIMES of average flux density Easiest 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.

Discussion

17.	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 lengthThe question was posed to me by my school principal while I was bunking the class.Asked question is from Operating Characteristics in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right choice is (b) mmf REQUIRED for AIR gap = 8,00,000 * air gap FLUX density * air gap CONSTANT * air gap LENGTH Easy 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.

Discussion

18.	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°I have been asked this question in an online quiz.I want to ask this question from Operating Characteristics topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (b) 60° To explain: 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.

Discussion

19.	How many parts does the stator mmf passes through?(a) 3(b) 4(c) 5(d) 6I have been asked this question in quiz.Enquiry is from Operating Characteristics topic in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» RIGHT CHOICE is (c) 5 To explain I would say: The stator MMF produced in the motor PASSES through 5 parts. They are air GAP, stator teeth, stator core, rotor teeth, rotor core.

Discussion

20.	How many factors are present in the operating characteristics?(a) 2(b) 3(c) 4(d) 5I have been asked this question in unit test.This key question is from Operating Characteristics in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct choice is (c) 4 The 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.

Discussion

21.	What is the output equation of a single phase induction motor developed by P.H Tricky?(a) diameter^2 * length = 16.5 / H.P * output coefficient * frequency constant * motor type constants * rpm * 10^6(b) diameter^2 * length = 16.5 * H.P * output coefficient * frequency constant * motor type constants/rpm * 10^6(c) diameter^2 * length = 16.5 * H.P / output coefficient * frequency constant * motor type constants * rpm * 10^6(d) diameter^2 * length = 16.5 * H.P * output coefficient / frequency constant * motor type constants * rpm * 10^6I had been asked this question by my school principal while I was bunking the class.This key question is from Parameters topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct option is (b) diameter^2 * length = 16.5 * H.P * output coefficient * frequency constant * motor type constants/rpm * 10^6 The EXPLANATION is: The output coefficient, horse power, frequency constant, motor type constant along with the speed is calculated. On substitution we GET the diameter^2 * length VALUE.

Discussion

22.	What factor is the core length made equal to in theoretical conditions?(a) pole length(b) pole proportion(c) pole length(d) number of polesThe question was asked in semester exam.Enquiry is from Parameters topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct option is (c) POLE length The best 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.

Discussion

23.	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 gapThis question was addressed to me in unit test.My question comes from Parameters topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» RIGHT choice is (C) saturation factor = total mmf REQUIRED for MAGNETIC circuit / mmf required for air gap 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.

Discussion

24.	The magnetizing reactance is directly proportional to the saturation factor.(a) true(b) falseThe question was posed to me in an international level competition.My enquiry is from Parameters in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct OPTION is (b) false For 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.

Discussion

25.	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 pitchI had been asked this question in an online interview.Origin of the question is Parameters topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct option is (B) magnetizing reactance is directly proportional to the pole pitch The BEST EXPLANATION: The magnetizing reactance is ONE of the PARAMETERS in the leakage reactance calculation. The magnetizing reactance is directly proportional to the pole pitch.

Discussion

26.	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 slotsThe question was posed to me in a job interview.Origin of the question is Parameters in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right choice is (c) overhang leakage REACTANCE is directly PROPORTIONAL to the average COIL SPAN in SLOTS 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.

Discussion

27.	What is the value of the stator slot leakage factor?(a) 0.90(b) 0.80(c) 0.95(d) 0.85I got this question by my college professor while I was bunking the class.I'd like to ask this question from Parameters topic in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right choice is (C) 0.95 The 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.

Discussion

28.	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)The question was asked in quiz.Enquiry is from Parameters topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer»

Discussion

29.	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 factorThe question was asked during a job interview.This intriguing question comes from Parameters in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT OPTION is (a) SKEW leakage reactance is directly proportional to the stator slot leakage factor The explanation is: 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.

Discussion

30.	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 leakageThe question was asked by my college director while I was bunking the class.This intriguing question comes from Parameters topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (a) ZIGZAG reactance is DIRECTLY proportional to the SPECIFIC permeance for zigzag leakage Easy 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.

Discussion

31.	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 thesquare of the number of rotor slots(d) slot leakage reactance is indirectly proportional to the square of the number of rotor slotsThe question was asked in an internship interview.I'd like to ask this question from Parameters in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right OPTION is (B) slot leakage REACTANCE is INDIRECTLY proportional to the number of rotor slots 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.

Discussion

32.	What is the relation between slot leakage reactance and specific slot permeance?(a) slot leakage reactance is directly proportional to thespecific 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 permeanceThe question was posed to me during an interview for a job.The above asked question is from Parameters in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» CORRECT answer is (a) slot LEAKAGE reactance is directly proportional to thespecific slot permeance The explanation: Specific slot permeance is one of the PARAMETERS PRESENT in the leakage reactance calculation. It is directly proportional to the slot leakage reactance.

Discussion

33.	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 slotThe question was asked in an international level competition.This interesting question is from Parameters in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT choice is (d) CONCENTRIC WINDING and different conductor in each slot The EXPLANATION is: The winding of the induction MOTORS are concentric type. The different conductors are being used in each slot.

Discussion

34.	How many parameters are present in the single phase induction motor?(a) 2(b) 3(c) 4(d) 5I had been asked this question during an online interview.Query is from Parameters topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right option is (B) 3 For 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.

Discussion

35.	How many parameters are present under the leakage reactance calculations?(a) 6(b) 5(c) 7(d) 4This question was addressed to me in an internship interview.This key question is from Parameters in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (C) 7 The best I can explain: 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.

Discussion

36.	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 conductorI got this question in my homework.Query is from Parameters in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right answer is (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 Easy 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.

Discussion

37.	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) 0.45-0.6This question was addressed to me in an online quiz.This intriguing question comes from Design of Rotor topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» RIGHT option is (b) 0.45-0.55 The best I can explain: 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.

Discussion

38.	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 coreThis question was posed to me in class test.The question is from Design of Rotor in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct ANSWER is (a) flux density of ROTOR teeth = maximum flux / (number of rotor slots / number of poles) * LENGTH of the teeth * DEPTH of rotor core The best 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.

Discussion

39.	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 barI had been asked this question in my homework.The query is from Design of Rotor topic in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» RIGHT choice is (a) area of each BAR = current through each bar / current DENSITY through each bar Easiest explanation: The current through each bar and the current density through each bar is CALCULATED. On substitution the area of each bar is obtained.

Discussion

40.	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 polesThis question was posed to me at a job interview.Query is from Design of Rotor in chapter Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (c) area of each end ring =0.32 * TOTAL CROSS SECTION of rotor bars / number of POLES The best I can explain: 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.

Discussion

41.	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) 1.2-1.5The question was asked at a job interview.This interesting question is from Design of Rotor in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct ANSWER is (c) 1-1.6 The best 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.

Discussion

42.	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 polesI got this question in an interview for job.My doubt stems from Design of Rotor in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT ANSWER is (d) end ring current = number of rotor slots * bar current / 3.14 * number of poles To EXPLAIN: 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.

Discussion

43.	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) 0.8-0.9This question was posed to me in an interview for job.Query is from Design of Rotor in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct choice is (C) 0.5-0.8 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.

Discussion

44.	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 barThe question was asked in exam.This question is from Design of Rotor topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer»

Discussion

45.	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 conductorThe question was posed to me in quiz.My question is based upon Design of Rotor in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (b) total stator copper SECTION for main winding = 2 * number of turns in the RUNNING winding * AREA of the running winding conductor 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.

Discussion

46.	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 polesI had been asked this question in an interview.My question is from Design of Rotor topic in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The CORRECT OPTION is (d) winding arrangement and NUMBER of poles Easy 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.

Discussion

47.	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 cuspsThis question was posed to me by my school teacher while I was bunking the class.This interesting question is from Design of Rotor in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct choice is (d) MAGNETIC locking and cusps Easy 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.

Discussion

48.	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 polesThis question was posed to me in semester exam.Question is from Design of Rotor topic in division Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» The correct option is (b) NUMBER of rotor slots differs from the number of stator slots by more than the number of POLES The EXPLANATION is: 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.

Discussion

49.	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)The question was posed to me in a job interview.The origin of the question is Design of Rotor in section Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Right CHOICE is (a) harmonic poles due to slots = 2 * (NUMBER of slots ± number of poles / 2) The BEST EXPLANATION: First the number of slots and number of poles are first calculated. On substitution we GET the harmonic poles due to the slots.

Discussion

50.	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 producedI have been asked this question in my homework.My doubt is from Design of Rotor in portion Design of Single Phase Induction Motor of Design of Electrical Machines
Answer» Correct answer is (c) no NOISE is PRODUCED The BEST explanation: There are basically 6 STEPS involved in the rotor design. The number of slots is chosen such that no noise is produced.

Discussion

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