44 + Interview Questions in Design Of Permanent Magnet (Pm) Dc Motors in Design Of Electrical Machines Page 1 InterviewSolution

1.	How many principle types of lubricants are available in the PMDC motor?(a) 2(b) 3(c) 5(d) 7This question was posed to me during an online interview.Enquiry is from Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right ANSWER is (b) 3 The BEST I can explain: There are 3 PRINCIPLE types of LUBRICANTS in use. They are oil, dry film lubricants and GREASE.

Discussion

2.	How many types of bearings are made use of in the PMDC motors?(a) 2(b) 3(c) 4(d) 5This question was posed to me in an interview for internship.My question is based upon Design Steps and Considerations topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct OPTION is (a) 2 Easiest EXPLANATION: There are two types of BEARINGS used in the PMDC motors. They are BELL bearing and the journal bearing.

Discussion

3.	What type of gear is made use for the silent operation?(a) spur gears(b) helical gears(c) worm gears(d) spur gears and worm gearsI have been asked this question during an interview.Question is taken from Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (b) helical gears The explanation: There are THREE types of gears made use of in the GEARING system of the PMDC MOTORS. The helical gears is made use for the silent operation.

Discussion

4.	What type of gear is made use of in the high inertia motors?(a) spur gears(b) helical gears(c) worm gears(d) spur and helical gearsThis question was addressed to me in an interview for internship.My doubt is from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The CORRECT choice is (C) WORM gears The explanation: There are THREE types of gears made use of in the PMDC motors. The worm gears are used in the high inertia load.

Discussion

5.	What type of gears are used in the small loads and low inertia motors?(a) spur gears(b) helical gears(c) worm gears(d) worm gears and helical gearsThe question was asked by my school teacher while I was bunking the class.This interesting question is from Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct answer is (a) SPUR GEARS For explanation: Three types of gears are made USE of in the PMDC motors. The spur gears are made use of in the low inertia and SMALL load motors.

Discussion

6.	How many types of gears are made use of in the PMDC motors?(a) 1(b) 2(c) 3(d) 4This question was addressed to me in an interview for job.I'd like to ask this question from Design Steps and Considerations topic in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct option is (c) 3 The EXPLANATION is: Generally 3 types of GEARS are made use of in the PMDC MOTORS. They are spur gears, helical gears, and WORM gears.

Discussion

7.	What is the solution to prevent the increase of resistance of motor windings?(a) higher ventilation arrangement(b) reduction in the number of poles(c) increase the coil windings(d) insulate the windingsThis question was addressed to me in exam.My doubt stems from Design Steps and Considerations in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT CHOICE is (a) higher ventilation arrangement To explain: The increase of RESISTANCE of the motor winding is one of the cause of thermal failure. They can be reduced by providing a higher ventilation arrangement in the machine.

Discussion

8.	What does the inability of the motor to dissipate the heat cause?(a) causes high starting current(b) insulation failure(c) causes low starting current(d) causes high starting currentI got this question during an interview for a job.My question is from Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right option is (b) insulation FAILURE Explanation: The inability of the motor to DISSIPATE the HEAT is ONE of the causes of THERMAL failure. The inability of the motor to dissipate heat causes insulation failure.

Discussion

9.	What does the increase of the resistance of the motor winding cause?(a) high starting current(b) low motor torque(c) low starting current(d) high motor torqueI had been asked this question during an online interview.Origin of the question is Design Steps and Considerations in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct choice is (b) low MOTOR TORQUE For explanation: The increase of the resistance of the motor WINDING is one of the cause of THERMAL failure. This PRODUCES lower motor torque in the machine.

Discussion

10.	How many primary reasons are present for the thermal failure?(a) 3(b) 4(c) 2(d) 5This question was addressed to me during an internship interview.The origin of the question is Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (C) 2 Explanation: There are 2 primary reasons for the THERMAL failure. The first ONE is an increase of the RESISTANCE of motor winding and second one is the inability of the motor to DISSIPATE the heat generated.

Discussion

11.	How many number of poles should be used for large motors of relatively low speed?(a) should be equal to 2(b) should be lesser than 2(c) should be greater than 2(d) should be more than 4I had been asked this question by my college director while I was bunking the class.Enquiry is from Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct answer is (C) should be greater than 2 To ELABORATE: The number of poles should be greater than 2 for large motors with relatively LOW speed. The number of poles is equal to 2 for SMALL motors.

Discussion

12.	What is the relation of the brush shift with the demagnetization effect?(a) brush shift is directly proportional to the demagnetization effect(b) brush shift is indirectly proportional to the demagnetization effect(c) brush shift is directly proportional to the square of the demagnetization effect(d) brush shift is indirectly proportional to the square of the demagnetization effectI had been asked this question in a national level competition.The above asked question is from Design Steps and Considerations topic in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct choice is (a) brush SHIFT is DIRECTLY proportional to the demagnetization EFFECT Explanation: The SECOND design consideration is the brushes in the PMDC motor. The brush shift increases the DEMAGNETIZING effect.

Discussion

13.	In the PMDC motors the brush shift should be approached with considerable caution.(a) true(b) falseThis question was addressed to me in final exam.My question is based upon Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right answer is (a) true For explanation: The brush SHIFT in the PMDC motor should be approached with considerable CAUTION. This is because as flux shift in the ceramic MAGNET will be found to be ALMOST negligible.

Discussion

14.	What is the relation between number of poles and flux reversal in the armature?(a) number of poles is directly proportional to the flux reversal in the armature(b) number of poles is indirectly proportional to the flux reversal in the armature(c) number of poles is directly proportional to the square of the flux reversal in the armature(d) number of poles is indirectly proportional to the square of the flux reversal in the armatureI have been asked this question in an interview for job.Enquiry is from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct answer is (a) NUMBER of poles is DIRECTLY proportional to the flux reversal in the armature Explanation: The first design CONSIDERATION in the PMDC motor is the number of poles. The flux reversal in the armature is directly proportional to the number of poles.

Discussion

15.	What is the formula for the length of the stator slots?(a) length of the stator slots = 2 * perimeter of one magnet(b) length of the stator slots = 1/2 * perimeter of one magnet(c) length of the stator slots = 1/3 * perimeter of one magnet(d) length of the stator slots = 3 * perimeter of one magnetThe question was asked in my homework.The above asked question is from Design Steps and Considerations topic in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right ANSWER is (b) length of the stator slots = 1/2 * perimeter of ONE magnet To explain: The length of the stator slots is REQUIRED in the calculation of the radial THICKNESS of the joke. The length of the stator slots is EQUAL to half the perimeter of one magnet.

Discussion

16.	What is the relation between number of poles and total volume of magnet?(a) number of poles is directly proportional to the total volume of the magnet(b) number of poles is indirectly proportional to the total volume of the magnet(c) number of poles is directly proportional to the square of the total volume of the magnet(d) number of poles is indirectly proportional to the square of the total volume of the magnetI had been asked this question in an online quiz.My question is based upon Design Steps and Considerations topic in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct choice is (B) number of POLES is INDIRECTLY proportional to the total volume of the magnet The BEST I can explain: The first design consideration in the PMDC motor is the number of poles. The volume of the magnet is indirectly proportional to the number of poles.

Discussion

17.	The radial thickness of the joke is directly proportional to the length of the stator slots.(a) true(b) falseI had been asked this question in an online quiz.Origin of the question is Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The CORRECT choice is (b) false For explanation: The last design STEP in the PMDC motor is the calculation of the radial THICKNESS of the joke. The radial thickness of the joke is indirectly proportional to the length of the STATOR SLOTS.

Discussion

18.	The radial thickness of the joke directly proportional to the flux.(a) true(b) falseThe question was asked by my college director while I was bunking the class.I'd like to ask this question from Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct answer is (a) true For explanation: The last design STEP in the PMDC MOTOR is the calculation of the radial thickness of the joke. The FLUX VALUE is directly proportional to the radial thickness of the joke.

Discussion

19.	What is the relation of the wire cross-section with respect to the armature resistance?(a) wire section is directly proportional to the armature resistance(b) wire section is indirectly proportional to the armature resistance(c) wire section is directly proportional to the square of the armature resistance(d) wire section is indirectly proportional to the square of the armature resistanceI had been asked this question during an interview for a job.The above asked question is from Design Steps and Considerations in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct option is (a) wire section is DIRECTLY PROPORTIONAL to the ARMATURE resistance For explanation: The 10th design STEP of the PMDC motor is the calculation of the wire cross section. The wire cross section is directly proportional to the armature resistance.

Discussion

20.	What is the relation between axial dimension and the area of the magnet?(a) area of the magnet is directly proportional to the axial dimension(b) area of the magnet is indirectly proportional to the axial dimension(c) area of the magnet is directly proportional to the square of the axial dimension(d) area of the magnet is indirectly proportional to the square of the axial dimensionThe question was asked in an internship interview.Question is taken from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT CHOICE is (a) area of the magnet is directly proportional to the axial DIMENSION Easy explanation: The calculation of the axial dimension is ONE of the steps in the PMDC MOTORS. The axial dimension is directly proportional to area of the magnet.

Discussion

21.	What is the formula for the armature resistance?(a) armature resistance = running armature resistance / 1.0 to 1.0(b) armature resistance = running armature resistance * 1.3 to 1.5(c) armature resistance = running armature resistance * 1.4 to 1.5(d) armature resistance = running armature resistance / 1.3 to 1.3I had been asked this question during an interview.Question is taken from Design Steps and Considerations in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT option is (d) armature resistance = RUNNING armature resistance / 1.3 to 1.3 The explanation: The running armature resistance is FIRST calculated in the PMDC MOTOR. It is DIVIDED by 1.3 and that gives the armature resistance of the machine.

Discussion

22.	What is the formula of the number of turns per coil?(a) number of turns per coil = number of conductors/2coils/slotnumber of armature teeth(b) number of turns per coil = number of conductors2coils/slotnumber of armature teeth(c) number of turns per coil = number of conductors2coils/slot/number of armature teeth(d) number of turns per coil = number of conductors/2coils/slot/number of armature teethThe question was posed to me by my college director while I was bunking the class.I need to ask this question from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» RIGHT answer is (a) NUMBER of turns per COIL = number of conductors/2coils/slotnumber of ARMATURE teeth Best explanation: The number of conductors is CALCULATED along with the coils per slot is calculated. Next, the number of armature teeth is calculated, and on substitution gives the number of turns per coil.

Discussion

23.	What is the relation between the flux and the no local speed?(a) flux is directly proportional to the no local speed(b) flux is indirectly proportional to the no local speed(c) flux is directly proportional to the square of the no local speed(d) flux is indirectly proportional to the square of the no local speedThis question was addressed to me in semester exam.This interesting question is from Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT choice is (B) FLUX is indirectly proportional to the no local speed Best explanation: The calculation of the flux VALUE is one of the DESIGN steps. The flux is indirectly proportional to the no local speed calculated.

Discussion

24.	What is the formula of the length of the magnet?(a) length of the magnet = sum of the volume of air gap and magnet * Area of the magnet + 0.06(b) length of the magnet = sum of the volume of air gap and magnet / Area of the magnet + 0.06(c) length of the magnet = sum of the volume of air gap and magnet / Area of the magnet – 0.06(d) length of the magnet = sum of the volume of air gap and magnet * Area of the magnet – 0.06The question was posed to me in an interview for job.I would like to ask this question from Design Steps and Considerations topic in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right answer is (c) LENGTH of the MAGNET = SUM of the VOLUME of air gap and magnet / Area of the magnet – 0.06 The explanation is: The sum of the volume of the air gap and magnet is FIRST calculated. Next, the area of the magnet is calculated from its formula and on substitution gives the length of the magnet.

Discussion

25.	What is the range of length of the magnet in the PMDC motors?(a) 2.5-4 cm(b) 2-3 cm(c) 2.5-3 cm(d) 1.5-4 cmThis question was addressed to me during an online exam.The origin of the question is Design Steps and Considerations topic in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The CORRECT choice is (a) 2.5-4 cm Best explanation: The MINIMUM VALUE of the length of the MAGNET in the PMDC motor is 2.5 cm. The maximum value of the length of the magnet in the PMDC motor is 4 cm.

Discussion

26.	What is the formula for the area of the magnet in the design of PMDC motors?(a) area of magnet = flux * 4.95 * residual flux density(b) area of magnet = flux / 4.95 * residual flux density(c) area of magnet = flux * 4.95 / residual flux density(d) area of magnet = 1/flux * 4.95 * residual flux densityI had been asked this question in a national level competition.This key question is from Design Steps and Considerations topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct choice is (b) area of magnet = flux / 4.95 * residual flux density Explanation: FIRST the residual flux density is CALCULATED. NEXT, the flux is calculated and substitution in the formula GIVES the area of magnet.

Discussion

27.	What should be the minimum value of the ratio of the magnetic to electric loading?(a) 40(b) 30(c) 50(d) 60This question was addressed to me in examination.My doubt is from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right choice is (c) 50 Explanation: The calculation of the ratio of the magnetic to electric loading is the SECOND step in the DESIGN of the PMDC motors. It should have a MINIMUM value of 50.

Discussion

28.	What should be the range of the product of the magnetic field and magnetic flux density?(a) 4-4.5 * 10^6(b) 4-4.3 * 10^6(c) 4.3-4.6 * 10^6(d) 4.2-4.5 * 10^6This question was addressed to me by my college professor while I was bunking the class.I'd like to ask this question from Design Steps and Considerations in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right CHOICE is (c) 4.3-4.6 * 10^6 The best I can explain: The product of the MAGNETIC field and magnetic FLUX DENSITY has a minimum VALUE of 4.3 * 10^6. The product of the magnetic field and magnetic flux density has a minimum value of 4.6 * 10^6.

Discussion

29.	What happens to the armature diameter and the volume of air gap and magnet when the angle is lower in value?(a) volume of air gap and magnet increases, armature diameter increases(b) volume of air gap and magnet increases, armature diameter decreases(c) volume of air gap and magnet decreases, armature diameter decreases(d) volume of air gap and magnet decreases, armature diameter increasesThe question was asked in quiz.My query is from Design Steps and Considerations in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (d) volume of air gap and magnet DECREASES, armature DIAMETER increases To explain I WOULD say: The lower values of angle, reduces the volume of air gap and magnet. The reduction of volume of air gap and magnet, increases the armature diameter.

Discussion

30.	How many design steps are present in the design of PMDC motors?(a) 8(b) 9(c) 10(d) 11The question was posed to me in homework.This interesting question is from Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right OPTION is (d) 11 To explain: There are 11 steps involves in the design of the PMDC motors. They are minimum sum of air gap volume and magnet volume, ratio of magnetic to electric loading, area of magnet, length of magnet, value of flux, number of turns PER COIL, running armature resistance, armature diameter, axial dimensions, wire cross section and radial thickness.

Discussion

31.	What is the formula for the flux density for the PM motors?(a) flux density = residual flux density / 1 + (1.11/permeance coefficient)(b) flux density = residual flux density * 1 + (1.11/permeance coefficient)(c) flux density = residual flux density / 1 + (1.11permeance coefficient)(d) flux density = residual flux density 1 + (1.11*permeance coefficient)I had been asked this question in examination.This question is from Design Preliminaries topic in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT option is (a) flux DENSITY = residual flux density / 1 + (1.11/PERMEANCE coefficient) EASY explanation: The residual flux density is calculated first along with the permeance coefficient to obtain the flux density of the PMDC motor. The flux density is 0.85 times the residual flux density.

Discussion

32.	For good performance the small dc motor should have magnetic to electrical boarding ratio greater than 70.(a) true(b) falseI had been asked this question in a job interview.My question comes from Design Preliminaries topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (b) false The best explanation: The PERFORMANCE of the small DC motor depends on the MAGNETIC to electrical BOARDING ratio. The magnetic to electrical boarding ratio should be GREATER than 50 for good performance.

Discussion

33.	How is the value of the magnetic to electrical boarding ratio related with the volume of iron and volume of copper?(a) high magnetic to electrical boarding ratio gives high copper volume and high iron volume(b) high magnetic to electrical boarding ratio gives low copper volume and high iron volume(c) low magnetic to electrical boarding ratio gives low copper volume and low iron volume(d) low magnetic to electrical boarding ratio gives low copper volume and high iron volumeThis question was addressed to me in an online quiz.My question is based upon Design Preliminaries topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (B) HIGH magnetic to electrical boarding ratio gives low copper VOLUME and high IRON volume To ELABORATE: The high value of magnetic to electrical boarding ratio gives a high volume of iron. But the high value of magnetic to electrical boarding ratio gives low copper volume.

Discussion

34.	What is the value of the reluctance factor in the calculation of the intensity of magnetic field?(a) 1(b) 2(c) 1.15(d) 1,45I have been asked this question in a national level competition.Question is from Design Preliminaries in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right option is (c) 1.15 Easiest EXPLANATION: The RELUCTANCE FACTOR is one of the factors made use of in the calculation of the intensity of magnetic field. The value of the reluctance factor is around 1.15 GENERALLY.

Discussion

35.	What is the formula of the magnetic to electrical boarding ratio?(a) magnetic to electrical boarding ratio = number of poles * permeance coefficient * flux per pole/number of conductors * armature current(b) magnetic to electrical boarding ratio = number of poles / permeance coefficient * flux per polenumber of conductors armature current(c) magnetic to electrical boarding ratio = number of poles + permeance coefficient * flux per pole/number of conductors * armature current(d) magnetic to electrical boarding ratio = number of poles * permeance coefficient / flux per polenumber of conductors armature currentThe question was asked during a job interview.This interesting question is from Design Preliminaries in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct CHOICE is (a) magnetic to electrical boarding ratio = number of poles * permeance coefficient * flux per POLE/number of CONDUCTORS * ARMATURE current For explanation: The permeance coefficient is first calculated along with the number of poles and the flux per pole. Then the number of conductors are NOTED and the armature current is calculated to give the magnetic to electrical boarding ratio.

Discussion

36.	What is the value of the demagnetizing coefficient if the total number of teeth is greater than 10^7?(a) d = angle/360(b) d = angle/240(c) d = angle/540(d) d = angle/720I got this question in an interview for job.Question is taken from Design Preliminaries in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct ANSWER is (d) d = angle/720 To elaborate: If the total number of teeth is greater than 10^7 then the demagnetizing COEFFICIENT become the ratio of the angle and 720. Otherwise d is ONE half the ratio of the maximum number of teeth that can be situated WITHIN the angle to the total number of teeth.

Discussion

37.	The field current flowing in the conductor’s acts as demagnetizing force on the fraction tips of the magnet.(a) true(b) falseThe question was asked in an internship interview.I'd like to ask this question from Design Preliminaries in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» CORRECT choice is (B) false To explain I would say: The armature current flowing in the conductors ACTS as demagnetizing force. Its acts on the fraction tips of the magnets present.

Discussion

38.	What is the usual value of the permeance coefficient of the PMDC motor?(a) 4(b) 5(c) 6(d) 7I have been asked this question in an online quiz.My query is from Design Preliminaries in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right choice is (C) 6 The best I can explain: The range of the permeance COEFFICIENT for the PMDC motor is 4-8. The value is USUALLY around 6 for most of the APPLICATIONS.

Discussion

39.	What is the range of the permeance coefficient in the PMDC motors?(a) 3-5(b) 4-9(c) 4-8(d) 3-9The question was posed to me in unit test.Enquiry is from Design Preliminaries topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Right choice is (c) 4-8 The best EXPLANATION: The minimum VALUE of the permeance coefficient used in the PMDC MOTORS is 4. The maximum value of the permeance coefficient used in the PMDC motor is 8.

Discussion

40.	What factor does the permeance coefficient depend upon?(a) geometry of the magnet(b) geometry of the magnet, airgap, associated non-portions of the magnetic circuit(c) airgap(d) associated non-portions of the magnetic circuitI got this question by my college professor while I was bunking the class.My enquiry is from Design Preliminaries in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct answer is (b) GEOMETRY of the magnet, airgap, ASSOCIATED non-portions of the magnetic CIRCUIT The best explanation: The PERMEANCE coefficient depends upon the geometry of the magnet and the airgap. It also depends on the associated non-portions of the magnetic circuit.

Discussion

41.	What happens to the diameter when the poles are more than 2?(a) diameter = 2 * diameter * (number of armature teeth embraced by one coil/total number of armature teeth)(b) diameter = 2.32 * diameter * (number of armature teeth embraced by one coil/total number of armature teeth)(c) diameter = 2.32 * diameter * (number of armature teeth embraced by one coil * total number of armature teeth)(d) diameter = 2 * diameter / (number of armature teeth embraced by one coil/total number of armature teeth)I got this question in final exam.My question is taken from Design Preliminaries topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct option is (B) diameter = 2.32 * diameter * (number of ARMATURE teeth embraced by one coil/total number of armature teeth) EXPLANATION: The diameter is the exact calculated value for 2 pole MOTORS. But when the poles are more than 2, the above formula is made use of to calculate the armature RESISTANCE.

Discussion

42.	What is the formula for the armature resistance in PMDC motor?(a) armature resistance = (Diameter + length)total number of armature conductors/1.2 10^4 * number of parallel paths in the armature^2(b) armature resistance = (Diameter + length)total number of armature conductors1.2 * 10^4 * number of parallel paths in the armature^2(c) armature resistance = (Diameter + length)total number of armature conductors/1.2 10^4 + number of parallel paths in the armature^2(d) armature resistance = (Diameter + length)+total number of armature conductors/1.2 * 10^4 * number of parallel paths in the armature^2I got this question in an online quiz.My doubt stems from Design Preliminaries topic in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct option is (a) ARMATURE resistance = (Diameter + length)total number of armature CONDUCTORS/1.2 10^4 * number of parallel paths in the armature^2 To EXPLAIN: First the diameter, length and the total number of armature conductors are obtained. Next the number of parallel paths in the armature is calculated and on SUBSTITUTION it provides the armature resistance.

Discussion

43.	What is the range of the copper factor in PMDC motors?(a) 0.1-0.3(b) 0.1-0.2(c) 0.1-0.4(d) 0.2-0.4This question was posed to me by my college professor while I was bunking the class.This intriguing question comes from Design Preliminaries topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» The correct CHOICE is (B) 0.1-0.2 The explanation is: The copper factor represents the fraction of the armature circular area for CONDUCTORS. The RANGE of the copper factor is between 0.1-0.2.

Discussion

44.	What does the copper factor in PMDC motors represent?(a) it represents the armature circular area for conductors(b) it represents the field circular area for conductors(c) it represents the fraction of the armature circular area for conductors(d) it represents the fraction of the field circular area for conductorsThis question was posed to me in an interview for job.Query is from Design Preliminaries topic in chapter Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines
Answer» Correct choice is (c) it represents the FRACTION of the armature circular area for conductors To explain I would say: The COPPER factor represents the fraction of the armature circular area for conductors. It is REPRESENTED by the LETTER K.

Discussion

Explore topic-wise InterviewSolutions in .

How many principle types of lubricants are available in the PMDC motor?(a) 2(b) 3(c) 5(d) 7This question was posed to me during an online interview.Enquiry is from Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

How many types of bearings are made use of in the PMDC motors?(a) 2(b) 3(c) 4(d) 5This question was posed to me in an interview for internship.My question is based upon Design Steps and Considerations topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

How many types of gears are made use of in the PMDC motors?(a) 1(b) 2(c) 3(d) 4This question was addressed to me in an interview for job.I'd like to ask this question from Design Steps and Considerations topic in section Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

How many primary reasons are present for the thermal failure?(a) 3(b) 4(c) 2(d) 5This question was addressed to me during an internship interview.The origin of the question is Design Steps and Considerations in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

In the PMDC motors the brush shift should be approached with considerable caution.(a) true(b) falseThis question was addressed to me in final exam.My question is based upon Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

What should be the minimum value of the ratio of the magnetic to electric loading?(a) 40(b) 30(c) 50(d) 60This question was addressed to me in examination.My doubt is from Design Steps and Considerations in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

How many design steps are present in the design of PMDC motors?(a) 8(b) 9(c) 10(d) 11The question was posed to me in homework.This interesting question is from Design Steps and Considerations topic in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

What is the usual value of the permeance coefficient of the PMDC motor?(a) 4(b) 5(c) 6(d) 7I have been asked this question in an online quiz.My query is from Design Preliminaries in portion Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines

What is the range of the permeance coefficient in the PMDC motors?(a) 3-5(b) 4-9(c) 4-8(d) 3-9The question was posed to me in unit test.Enquiry is from Design Preliminaries topic in division Design of Permanent Magnet (PM) DC Motors of Design of Electrical Machines