84 + Interview Questions in Rating And Heating Of Motors in Electric Drives Page 2 InterviewSolution

51.	The unit of the moment of inertia is Joule.(a) True(b) FalseI got this question in an international level competition.I would like to ask this question from Power Rating Determination of Electric Motors for Different Applications in division Rating and Heating of Motors of Electric Drives
Answer» The correct option is (B) False For explanation I would say: The moment of inertia is TAKEN as the sum of the product of the MASS of each particle with the square of their distance from the axis of the ROTATION. The UNIT of the moment of inertia is kg×m^2=kgm^2.

Discussion

52.	Calculate the 3-∅ power developed in the IM using the following data: VL=20 V, IL=5 A, cosΦ=.8.(a) 138.56 W(b) 128.41 W(c) 163.78 W(d) 177.59 WI had been asked this question by my school teacher while I was bunking the class.I would like to ask this question from Power Rating Determination of Electric Motors for Different Applications in chapter Rating and Heating of Motors of Electric Drives
Answer» RIGHT CHOICE is (a) 138.56 W Easy explanation: The power developed in the IM is √3VLILcos∅. The power is INDEPENDENT of TIME and frequency. P=√3VLILcos∅=√3×20×5×.8=138.56 W.

Discussion

53.	450-seconds rated motor is preferable for __________(a) Light duty cranes(b) Medium duty cranes(c) Intermittent duty cranes(d) Heavy duty cranesI had been asked this question in an international level competition.This intriguing question originated from Power Rating Determination of Electric Motors for Different Applications in chapter Rating and Heating of Motors of Electric Drives
Answer» RIGHT answer is (a) Light duty CRANES To elaborate: Light duty cranes are used in POWER plants, compressor plants. 450-seconds rated motor is preferable for light-duty cranes. They can safely operate for 450-seconds without exceeding the SPECIFIED temperature.

Discussion

54.	Voltage rating of the IM depends upon the insulation level.(a) True(b) FalseI had been asked this question at a job interview.Origin of the question is Power Rating Determination of Electric Motors for Different Applications topic in portion Rating and Heating of Motors of Electric Drives
Answer» CORRECT option is (a) True To explain: The voltage rating of the IM depends upon the INSULATION level. The insulation level is also decided on the BASIS of the over-voltages.

Discussion

55.	Current rating of the IM depends upon the cross-section area of the conductors.(a) True(b) FalseI had been asked this question in an online interview.The above asked question is from Power Rating Determination of Electric Motors for Different Applications topic in portion Rating and Heating of Motors of Electric Drives
Answer» The correct choice is (a) True Easy EXPLANATION: The CURRENT rating of the Induction motor depends UPON the cross-section AREA of the conductors. Resistance ∝ 1÷Area, I ∝Area.

Discussion

56.	Which motor is preferred for overhead traveling cranes?(a) Intermittent periodic motor(b) Continuous duty motor(c) Slow speed duty motor(d) Short time rated motorThe question was posed to me in quiz.Query is from Motors Rating and Heating in chapter Rating and Heating of Motors of Electric Drives
Answer» The correct answer is (a) Intermittent periodic MOTOR The BEST explanation: Intermittent periodic motor is preferred for overhead traveling CRANES. Cranes REQUIRE high starting torque for a short interval of time. Intermittent periodic motors have low SYNCHRONOUS speed.

Discussion

57.	Which one of the following motor is a 1-Φ AC motor?(a) Synchronous motor(b) Series motor(c) Shunt motor(d) Capacitor runI have been asked this question in an internship interview.I'm obligated to ask this question of Power Rating Determination of Electric Motors for Different Applications topic in chapter Rating and Heating of Motors of Electric Drives
Answer» Correct answer is (d) Capacitor RUN The best I can EXPLAIN: Capacitor run MOTOR is a 1-Φ AC motor. The capacitor is used to provide a 90° phase difference between the currents of MAIN and AUXILIARY winding.

Discussion

58.	The direction of the single-phase IM can be reversed by using which one of the method?(a) By interchanging the supply terminals(b) By removing the capacitor(c) By changing the direction of auxiliary winding current(d) By removing the main windingThe question was asked in an interview for job.Asked question is from Motors Rating and Heating topic in chapter Rating and Heating of Motors of Electric Drives
Answer» Correct option is (a) By interchanging the supply terminals Explanation: The direction of the single-phase IM can be reversed by changing the direction of AUXILIARY WINDING or main winding current.The net torque DEVELOPED in the IM is ImIasin(Φ).

Discussion

59.	Calculate the value of the angular acceleration of the machine using the given data: J = .541 kg-m^2, load torque = 10 N-m, motor torque = 2 N-m.(a) 45 rad/s^2(b) The machine will fail to start(c) 30 rad/s^2(d) 51 rad/s^2I have been asked this question in exam.My doubt stems from Motors Rating and Heating topic in section Rating and Heating of Motors of Electric Drives
Answer» Correct choice is (b) The machine will FAIL to START Explanation: Using the dynamic equation of MOTOR J×(ANGULAR ACCELERATION) = Motor torque – Load torque: .541×(angular acceleration) = 2-10=-8, angular acceleration=-14.78 rad/s^2. The load torque is greater than the motor torque. The motor will fail to start.

Discussion

60.	Calculate the value of the angular acceleration of the Heavy duty crane using the given data: J = 5 kg-m^2, load torque = 30 N-m, motor torque = 80 N-m.(a) 10 rad/s^2(b) 20 rad/s^2(c) 30 rad/s^2(d) 50 rad/s^2The question was posed to me in an interview.This key question is from Motors Rating and Heating topic in division Rating and Heating of Motors of Electric Drives
Answer» The correct ANSWER is (a) 10 rad/s^2 Easiest EXPLANATION: Using the dynamic equation of MOTOR J×(angular acceleration) = Motor torque – Load torque: 5×(angular acceleration) = 80-30=50, angular acceleration=10 rad/s^2.

Discussion

61.	Calculate the resonant frequency if the values of the capacitor and inductor are 4 F and 4 H.(a) .25 rad/sec(b) .26 rad/sec(c) .28 rad/sec(d) .29 rad/secThis question was posed to me during an online interview.I would like to ask this question from Motors Rating and Heating topic in chapter Rating and Heating of Motors of Electric Drives
Answer» Correct ANSWER is (a) .25 rad/sec To EXPLAIN: During RESONANCE condition XL=Xc. The value of the resonant frequency is 1÷√LC=1÷√16=.25 rad/sec. The VOLTAGE across the capacitor and inductor becomes EQUAL.

Discussion

62.	Calculate the frequency of the stator side of the IM if the value of slip is 0.04 and rotor frequency is 2 Hz.(a) 50 Hz(b) 49 Hz(c) 45 Hz(d) 51 HzI have been asked this question in semester exam.My question is from Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives
Answer»

Discussion

63.	Calculate the frequency of the rotor side of the IM if the value of slip is 0.34 and the supply frequency is 70 Hz.(a) 23.8 Hz(b) 22.7 Hz(c) 24.5 Hz(d) 23.1 HzThe question was asked during an interview.The above asked question is from Motors Rating and Heating topic in chapter Rating and Heating of Motors of Electric Drives
Answer» Correct choice is (a) 23.8 HZ Easiest explanation: The frequency of the rotor SIDE is low as COMPARED to supply frequency. The rotor frequency is slip×(supply frequency)=.34×70=23.8 Hz.

Discussion

64.	1800 second rated motors are used for __________(a) Heavy duty cranes(b) Light duty cranes(c) Medium duty cranes(d) Intermittent duty cranesI got this question during an online interview.This key question is from Motors Rating and Heating in section Rating and Heating of Motors of Electric Drives
Answer» Correct answer is (C) Medium duty cranes To explain: Medium duty crane motor is used to develop high STARTING TORQUE. They PROVIDE the output for a specified interval of time without EXCEEDING a specified temperature.

Discussion

65.	The capacity of the Crane is expressed in terms of tonnes.(a) True(b) FalseThis question was posed to me in quiz.This intriguing question originated from Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives
Answer»

Discussion

66.	Induction motor is also known as__________(a) Frequency changer(b) Frequency remover(c) Time period remover(d) DC machineThis question was addressed to me during an online interview.The question is from Motors Rating and Heating topic in division Rating and Heating of Motors of Electric Drives
Answer» The correct answer is (a) Frequency CHANGER The EXPLANATION is: The Induction motor is ALSO known as frequency changer. The stator frequency can be changed USING the slip CONCEPT. The rotor frequency of IM is slip×(stator frequency).

Discussion

67.	Which starting method is the worst method in Induction motor?(a) Direct online starting(b) Autotransformer starting(c) Reactance starting(d) Star-Delta startingI had been asked this question during an online interview.Enquiry is from Motors Rating and Heating topic in division Rating and Heating of Motors of Electric Drives
Answer»

Discussion

68.	A high starting torque is offered by the Belt Conveyors.(a) True(b) FalseI have been asked this question in an interview for job.This intriguing question originated from Motors Rating and Heating topic in section Rating and Heating of Motors of Electric Drives
Answer» RIGHT ANSWER is (a) True The BEST I can explain: The Belt Conveyors can provide continuous-flow transportation. The AMOUNT of material transported on a conveyor system DEPENDS upon belt speed, belt width.

Discussion

69.	Which motor is preferred for Jaw crushers?(a) WRIM(b) SCIM(c) Belt slip ring IM(d) DC shunt motorI got this question in examination.I want to ask this question from Motors Rating and Heating in section Rating and Heating of Motors of Electric Drives
Answer»

Discussion

70.	Which duty cycle has on load and off-loads period?(a) Intermittent duty(b) Short time duty(c) Continuous duty with constant load(d) Continuous duty with variable loadThe question was posed to me during an interview.This is a very interesting question from Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives
Answer» The correct option is (a) INTERMITTENT DUTY To explain: Intermittent duty CYCLE has frequent on load and off-loads period. The on-load period and off-loads periods are too short to ACHIEVE steady-state thermal CONDITION.

Discussion

71.	Convert 50℉ into Celsius.(a) 20 ℃(b) 10 ℃(c) 30 ℃(d) 40 ℃I have been asked this question in a job interview.My doubt is from Motors topic in section Rating and Heating of Motors of Electric Drives
Answer» Correct option is (a) 20 ℃ To explain: TEMPERATURE can be expressed in CELSIUS and Fahrenheit. The basic UNIT of temperature in SI is the Kelvin. The formula used is (50℉− 32) × 5/9 = 10℃.

Discussion

72.	What is the unit of power?(a) Joule/sec(b) Joule/sec^2(c) Joule/sec^3(d) Joule/sec^4I had been asked this question by my school teacher while I was bunking the class.I need to ask this question from Motors topic in portion Rating and Heating of Motors of Electric Drives
Answer» RIGHT answer is (a) Joule/sec The EXPLANATION is: The POWER is defined as the rate at which WORK is done. The ratio of energy and time is power. It is expressed in WATT or Joule/sec.

Discussion

73.	Convert 20 ℃ into Fahrenheit.(a) 68 ℉(b) 58 ℉(c) 78 ℉(d) 48 ℉This question was addressed to me at a job interview.This interesting question is from Motors topic in division Rating and Heating of Motors of Electric Drives
Answer» The correct choice is (a) 68 ℉ To EXPLAIN: Temperature can be expressed in Celsius and FAHRENHEIT. The Standard UNIT of the temperature is the Kelvin(K). (20℃ × 9/5) + 32 = 68℉.

Discussion

74.	Calculate the quality factor for the R-C circuit connected in the cooling system if R=1 Ω and C=10 F.(a) 0.1(b) 0.2(c) 0.3(d) 0.4I have been asked this question in my homework.Query is from Motors topic in portion Rating and Heating of Motors of Electric Drives
Answer» The correct answer is (a) 0.1 For explanation: The quality FACTOR is defined as the RATIO of the REACTIVE power to the ACTIVE power consumed. The resistor always absorbs active power and capacitor absorbs the reactive power. Quality factor=1÷RC=1÷10=.1.

Discussion

75.	Calculate the heat absorbed by a 3 Ω resistor when 6 V is applied across it.(a) 12 W(b) 10 W(c) 8 W(d) 11 WThe question was posed to me during an online interview.The doubt is from Motors topic in portion Rating and Heating of Motors of Electric Drives
Answer» The CORRECT option is (a) 12 W Easiest explanation: The RESISTOR always absorbs active POWER and dissipates in the form of the heat. Power ABSORBED by a 3 Ω resistor is 6×6÷3=12 W.

Discussion

76.	Calculate the steady state temperature value for T(t)=1.5(1-e^-17t).(a) 1.5(b) 4.8(c) 3.9(d) 2.4I got this question during an interview for a job.My question is based upon Motors topic in portion Rating and Heating of Motors of Electric Drives
Answer» Right CHOICE is (a) 1.5 For explanation: The steady STATE temperature value is obtained at t=∞. The value of T(t) at t=∞ is 1.5(1-e-∞)=1.5(1-0)=1.5. The TERM e^-17t is an EXPONENTIALLY decaying FUNCTION.

Discussion

77.	A circuit consists of two 7 F capacitors connected in series and 12 H inductor. Determine the order of the circuit.(a) 1(b) 2(c) 0(d) 3The question was posed to me in examination.I want to ask this question from Motors topic in portion Rating and Heating of Motors of Electric Drives
Answer» The correct choice is (b) 2 To elaborate: The order of the circuit is the NUMBER of memory/storing elements which are non-separable present in the circuit. In mathematics, the order is DEFINED as the highest order DERIVATE in the differential equation. The order of the circuit is 2 because TWO 7 F capacitors COMBINE to form a single capacitor.

Discussion

78.	Insufficient rating of the machine can damage the windings.(a) True(b) FalseI got this question during an online exam.I want to ask this question from Motors in portion Rating and Heating of Motors of Electric Drives
Answer» Right CHOICE is (a) True Best explanation: The inadequate rating of the equipment can damage the winding and halt the MACHINE OPERATION. The WINDINGS can burn out and lead to the breakdown of the machine.

Discussion

79.	What is heating time constant of the machine?(a) The ratio of the thermal capacity and heat dissipation constant value(b) The ratio of the thermal capacity and heat dissipation constant value(c) The ratio of the thermal capacity and heat dissipation constant value(d) The ratio of the thermal capacity and heat dissipation constant valueI got this question in an interview for job.Enquiry is from Motors in portion Rating and Heating of Motors of Electric Drives
Answer» Correct choice is (a) The RATIO of the thermal capacity and HEAT dissipation constant VALUE Easy EXPLANATION: The heating time constant of the machine is the ratio of the thermal capacity of the machine and heat dissipation constant value. Τ = c÷D. It has a unit of second.

Discussion

80.	Inadequate rating of the equipment can___________(a) Increase the speed(b) Decrease the speed(c) Damage the winding(d) Increase the efficiencyI have been asked this question by my college professor while I was bunking the class.The query is from Motors topic in section Rating and Heating of Motors of Electric Drives
Answer» RIGHT CHOICE is (c) Damage the winding To EXPLAIN I would say: The INADEQUATE rating of the equipment can damage the winding and stops the MACHINE operation. The windings can burn out.

Discussion

81.	Calculate the heating time constant of the machine if the thermal capacity (c) of the machine is 24 watts/℃ and heat dissipation constant value (D) is 3 watts/℃.(a) 8 sec(b) 7 sec(c) 6 sec(d) 9 secThis question was posed to me by my school principal while I was bunking the class.I would like to ask this question from Motors topic in section Rating and Heating of Motors of Electric Drives
Answer» CORRECT choice is (a) 8 sec Easiest EXPLANATION: The heating TIME constant of the machine is the ratio of the thermal CAPACITY of the machine and HEAT dissipation constant value. Τ = c÷D=24÷3 = 8 sec.

Discussion

82.	Cooling air travels 10 m distance in 5 sec from point A to point B. Calculate the velocity of the cooling air.(a) 2 m/s(b) 4 m/s(c) 6 m/s(d) 10 m/sThe question was asked in exam.My question is based upon Motors in section Rating and Heating of Motors of Electric Drives
Answer» The CORRECT option is (a) 2 m/s The best explanation: The velocity of the cooling air can be CALCULATED USING the ratio of displacement and TIME. The value of the displacement is 10 m. The value of the velocity is 10÷5=2 SEC.

Discussion

83.	Which of the following are the classes of insulating material in electrical machines?(a) Γ, A, E, F, H, C(b) Γ, E, B, F, H, C(c) A, E, B, F, H, C(d) Γ, A, E, F, CI have been asked this question by my school principal while I was bunking the class.The question is from Motors in section Rating and Heating of Motors of Electric Drives
Answer» The correct answer is (a) Γ, A, E, F, H, C To elaborate: DEPENDING upon the temperature limits, insulating materials are classified into seven classes Γ, A, E, B, F, H, C. The insulation has the lowest temperature limit.

Discussion

84.	Iron losses occur in the machine are variable losses.(a) True(b) FalseI got this question during an online exam.Query is from Motors in chapter Rating and Heating of Motors of Electric Drives
Answer» Right answer is (b) False Explanation: Iron losses CONSIST of eddy CURRENT and hysteresis losses. These are constant losses. Iron losses are independent of the LOAD current. The copper losses are VARIABLE losses.

Discussion

Explore topic-wise InterviewSolutions in .

The unit of the moment of inertia is Joule.(a) True(b) FalseI got this question in an international level competition.I would like to ask this question from Power Rating Determination of Electric Motors for Different Applications in division Rating and Heating of Motors of Electric Drives

Voltage rating of the IM depends upon the insulation level.(a) True(b) FalseI had been asked this question at a job interview.Origin of the question is Power Rating Determination of Electric Motors for Different Applications topic in portion Rating and Heating of Motors of Electric Drives

Which motor is preferred for overhead traveling cranes?(a) Intermittent periodic motor(b) Continuous duty motor(c) Slow speed duty motor(d) Short time rated motorThe question was posed to me in quiz.Query is from Motors Rating and Heating in chapter Rating and Heating of Motors of Electric Drives

Calculate the frequency of the stator side of the IM if the value of slip is 0.04 and rotor frequency is 2 Hz.(a) 50 Hz(b) 49 Hz(c) 45 Hz(d) 51 HzI have been asked this question in semester exam.My question is from Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives

1800 second rated motors are used for __________(a) Heavy duty cranes(b) Light duty cranes(c) Medium duty cranes(d) Intermittent duty cranesI got this question during an online interview.This key question is from Motors Rating and Heating in section Rating and Heating of Motors of Electric Drives

The capacity of the Crane is expressed in terms of tonnes.(a) True(b) FalseThis question was posed to me in quiz.This intriguing question originated from Motors Rating and Heating in portion Rating and Heating of Motors of Electric Drives

Induction motor is also known as__________(a) Frequency changer(b) Frequency remover(c) Time period remover(d) DC machineThis question was addressed to me during an online interview.The question is from Motors Rating and Heating topic in division Rating and Heating of Motors of Electric Drives

A high starting torque is offered by the Belt Conveyors.(a) True(b) FalseI have been asked this question in an interview for job.This intriguing question originated from Motors Rating and Heating topic in section Rating and Heating of Motors of Electric Drives

Which motor is preferred for Jaw crushers?(a) WRIM(b) SCIM(c) Belt slip ring IM(d) DC shunt motorI got this question in examination.I want to ask this question from Motors Rating and Heating in section Rating and Heating of Motors of Electric Drives

Convert 50℉ into Celsius.(a) 20 ℃(b) 10 ℃(c) 30 ℃(d) 40 ℃I have been asked this question in a job interview.My doubt is from Motors topic in section Rating and Heating of Motors of Electric Drives

What is the unit of power?(a) Joule/sec(b) Joule/sec^2(c) Joule/sec^3(d) Joule/sec^4I had been asked this question by my school teacher while I was bunking the class.I need to ask this question from Motors topic in portion Rating and Heating of Motors of Electric Drives

Convert 20 ℃ into Fahrenheit.(a) 68 ℉(b) 58 ℉(c) 78 ℉(d) 48 ℉This question was addressed to me at a job interview.This interesting question is from Motors topic in division Rating and Heating of Motors of Electric Drives

Calculate the quality factor for the R-C circuit connected in the cooling system if R=1 Ω and C=10 F.(a) 0.1(b) 0.2(c) 0.3(d) 0.4I have been asked this question in my homework.Query is from Motors topic in portion Rating and Heating of Motors of Electric Drives

Calculate the heat absorbed by a 3 Ω resistor when 6 V is applied across it.(a) 12 W(b) 10 W(c) 8 W(d) 11 WThe question was posed to me during an online interview.The doubt is from Motors topic in portion Rating and Heating of Motors of Electric Drives

Calculate the steady state temperature value for T(t)=1.5(1-e^-17t).(a) 1.5(b) 4.8(c) 3.9(d) 2.4I got this question during an interview for a job.My question is based upon Motors topic in portion Rating and Heating of Motors of Electric Drives

A circuit consists of two 7 F capacitors connected in series and 12 H inductor. Determine the order of the circuit.(a) 1(b) 2(c) 0(d) 3The question was posed to me in examination.I want to ask this question from Motors topic in portion Rating and Heating of Motors of Electric Drives

Insufficient rating of the machine can damage the windings.(a) True(b) FalseI got this question during an online exam.I want to ask this question from Motors in portion Rating and Heating of Motors of Electric Drives

Cooling air travels 10 m distance in 5 sec from point A to point B. Calculate the velocity of the cooling air.(a) 2 m/s(b) 4 m/s(c) 6 m/s(d) 10 m/sThe question was asked in exam.My question is based upon Motors in section Rating and Heating of Motors of Electric Drives

Iron losses occur in the machine are variable losses.(a) True(b) FalseI got this question during an online exam.Query is from Motors in chapter Rating and Heating of Motors of Electric Drives