163 + Interview Questions in Induction Machines in Electrical Machines Page 3 InterviewSolution

101.	In a three phase induction motor, voltage between the slip rings at standstill is 50 V. At full load the slip is 0.04. The voltage between slip rings at full load is?(a) 2V(b) 50V(c) 20V(d) 5VI got this question by my college professor while I was bunking the class.Question is taken from Rotor EMF, Current and Power topic in section Induction Machines of Electrical Machines
Answer» CORRECT choice is (a) 2V The BEST I can explain: E2 = sE = 0.0450 = 2V.

Discussion

102.	A three phase induction motor is connected to 400V, 50 hz supply. If the stator to rotor turn ratio is 2, the standstill rotor induced voltage per phase is?(a) 115.5 V(b) 231 V(c) 346 V(d) 200 VI had been asked this question during an interview for a job.The query is from Rotor EMF, Current and Power in division Induction Machines of Electrical Machines
Answer» Right choice is (a) 115.5 V To ELABORATE: Emf at SECONDARY PER phase = (400/1.73)/2 = 115.47 V.

Discussion

103.	In an induction motor slip will be negative when the _________(a) rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field(b) stator magnetic field and rotor rotate in opposite direction(c) rotor rotates at speed less than synchronous speed and in the opposite direction of the rotation of stator field(d) rotor rotates at speed more than synchronous speed and in the opposite direction of the rotation of stator fieldThis question was addressed to me in an interview.This intriguing question originated from Rotor EMF, Current and Power topic in chapter Induction Machines of Electrical Machines
Answer» Right option is (a) rotor rotates at speed more than SYNCHRONOUS speed and in the direction of the rotation of STATOR field Easy explanation: s = (NS-Nr)/Ns;SLIP is negative when rotor rotates at speed more than synchronous speed and in the direction of the rotation of stator field.

Discussion

104.	A 3-phase induction motor is operating at slip ‘s’. If the slip is reversed, its slip at the instant will be _________(a) 2-s(b) zero(c) 2+s(d) 1-sThe question was asked during an interview for a job.My question is taken from Rotor EMF, Current and Power in division Induction Machines of Electrical Machines
Answer» The correct answer is (a) 2-s To explain: For the REVERSED phase sequence the SLIP BECOMES 2-s.

Discussion

105.	If the three phase supply is fed to the rotor and it is running at its normal operating conditions. Then the synchronous speed can be defined as speed at which?(a) stator magnetic field rotates(b) rotor magnetic field rotates(c) rotor rotates(d) flux is set up in the rotorThis question was posed to me during an online exam.The origin of the question is Rotor EMF, Current and Power in section Induction Machines of Electrical Machines
Answer» The CORRECT answer is (B) rotor magnetic field rotates For EXPLANATION: If it is fed from rotor then the SYNCHRONOUS SPEED is also w.r.t. rotor.

Discussion

106.	The mmf produced by the current of the three phase induction motor _________(a) is standstill with respect to stator mmf(b) rotates at the speed of rotor in air gap(c) rotates at slip speed with respect to stator mmf(d) rotates at synchronous speed with respect to rotorThe question was asked by my college professor while I was bunking the class.The question is from Rotor EMF, Current and Power topic in division Induction Machines of Electrical Machines
Answer» Correct option is (a) is STANDSTILL with RESPECT to stator MMF Easy explanation: The mmf produced will ALSO be at synchronous speed and it will be stationary with respect to stator mmf which itself rotates at synchronous speed.

Discussion

107.	If the three phase supply is fed to the stator and it is running at its normal operating conditions. Then the synchronous speed can be defined as speed at which?(a) stator magnetic field rotates(b) rotor magnetic field rotates(c) rotor rotates(d) flux is set up in the rotorI got this question in class test.I would like to ask this question from Rotor EMF, Current and Power in division Induction Machines of Electrical Machines
Answer» CORRECT option is (a) stator magnetic FIELD rotates The best I can explain: If it is fed from stator then the synchronous speed is ALSO w.r.t. stator.

Discussion

108.	The voltage actually used to set up the working flux in the three phase induction motor is _________(a) equal to applied voltage(b) less than applied voltage(c) more than applied voltage(d) equal to rotor induced emf.This question was addressed to me at a job interview.I want to ask this question from Rotor EMF, Current and Power in division Induction Machines of Electrical Machines
Answer» Correct ANSWER is (a) equal to applied voltage Easy explanation: The actual working FLUX REQUIREMENT is met by the applied voltage and it is same as the applied voltage to it.

Discussion

109.	The rotor of the induction motor must never run at synchronous speed because then the relative speed between the rotating flux and rotor will be _________(a) zero and hence torque will be zero(b) zero, and torque will be maximum(c) maximum and hence, torque will be zero(d) maximum, and torque will also be zeroI got this question in a national level competition.This key question is from Rotor EMF, Current and Power topic in section Induction Machines of Electrical Machines
Answer» CORRECT option is (a) zero and HENCE torque will be zero The best EXPLANATION: At synchronous SPEED the slip will be zero and so the torque.

Discussion

110.	Two of the supply terminals to a three phase induction motor gets interchanges while regular scheduling work. When the machine is switched on, then it will _________(a) rotate in opposite direction(b) rotate in same direction(c) not start(d) get heated and winding will burnThe question was asked during an interview.This intriguing question originated from Rotor EMF, Current and Power in portion Induction Machines of Electrical Machines
Answer» The correct answer is (a) rotate in opposite direction To EXPLAIN I would say: As the supply phase SEQUENCE is REVERSED, the machine’s developed emf will also be reversed.

Discussion

111.	In an induction motor, when the number of stator slots is equal to an integral multiple of rotor slots?(a) machine will fail to start(b) machine will get heated(c) high starting torque will be achieved(d) discontinuity in torque slip characteristicI had been asked this question in class test.This intriguing question comes from Rotor EMF, Current and Power topic in section Induction Machines of Electrical Machines
Answer» Correct CHOICE is (a) machine will FAIL to START Explanation: Machine fails to start as the STATOR slots and rotor slots become EQUAL.

Discussion

112.	Rotor leakage reactance for a three phase slip ring induction motor with slip ‘s’ is?(a) s(x2)(b) (x2)/s(c) x2(d) (x2)(s^2)I had been asked this question by my school principal while I was bunking the class.My question is from Rotor EMF, Current and Power topic in portion Induction Machines of Electrical Machines
Answer» RIGHT ANSWER is (a) s(X2) To ELABORATE: It is s*x2.

Discussion

113.	The rotor winding for 3-phase slip ring induction motor having delta connected stator must be connected in _________(a) star(b) delta(c) tertiary(d) any of the mentionedI got this question by my college professor while I was bunking the class.The query is from Rotor Frequency topic in section Induction Machines of Electrical Machines
Answer» Correct ANSWER is (a) STAR Easiest explanation: We should use star CONNECTED resistors as the initial requirement is low RESISTANCE for HIGH starting torque.

Discussion

114.	The squirrel cage induction motor of 6-pole can be used as ________ induction motor.(a) any number of poles(b) 6 pole(c) 6 or 12 pole(d) integral number of 4 polesThis question was posed to me in a job interview.The question is from Rotor Frequency topic in division Induction Machines of Electrical Machines
Answer» The CORRECT OPTION is (a) any number of POLES For EXPLANATION I would SAY: The poles in a squirrel cage induction motor can be adjusted.

Discussion

115.	In a three phase slip ring induction motor, brushes are connected to _________(a) external star connected resistors(b) dc supply(c) 3-phase ac supply(d) any of the mentionedThis question was addressed to me in an interview.Question is from Rotor Frequency topic in chapter Induction Machines of Electrical Machines
Answer» The correct ANSWER is (a) EXTERNAL STAR connected resistors Best explanation: The rotor external resistances must E connected in star and at the external end of the rotor.

Discussion

116.	The rotor of th 3-phase induction motor rotates in the same direction as that of stator field. This can be explained by _________(a) Newton’s laws of motion(b) Farady’s laws of electromagnetic induction(c) Lenz’s law(d) Fleming’s right hand ruleI have been asked this question in exam.Question is from Rotor Frequency topic in section Induction Machines of Electrical Machines
Answer» CORRECT choice is (a) Newton’s LAWS of motion Easiest explanation: Newtons’s LAW EXPLAINS the over all behaviour of the inertia involved in the MACHINE and a unidirectional torque generated.

Discussion

117.	The 3-phase induction motor with rotor circuit open will _________(a) not run(b) run normally(c) get over heated(d) make noiseI got this question during a job interview.Enquiry is from Rotor Frequency topic in section Induction Machines of Electrical Machines
Answer» RIGHT ANSWER is (a) not run For explanation I would say: It will not run because there will not be any closed PATH for the FLUX in rotor CIRCUIT of the machine to generate emf.

Discussion

118.	For a 4-pole, 3-phase induction motor the rotor speed found is 2100 rpm at 50 Hz. Then the phase sequence of the emf generated will be?(a) acb(b) abc(c) no emf will be induced(d) cbaThis question was addressed to me in an online quiz.The above asked question is from Rotor Frequency in division Induction Machines of Electrical Machines
Answer» Correct ANSWER is (a) acb The best EXPLANATION: Stator field will be running at the speed of 600 RPM ANTICLOCKWISE wrt to rotor. So the phase sequence GENERATED at the slip rings is reversed.

Discussion

119.	Stator flux induces emf in the rotor conductors _________(a) magnitude depending on the load(b) rotating at synchronous speed around stator(c) constant in magnitude(d) none of the mentionedThe question was asked in an online interview.The origin of the question is Rotor Frequency in division Induction Machines of Electrical Machines
Answer»

Discussion

120.	A 4-pole, 3-phase slip ring induction motor is used as a frequency changer. Its stator is excited from 3-phase, 50 Hz supply. A load requiring 3-phase, 20 Hz supply is connected to the star-connected rotor through three slip-rings of SRIM. At what two speeds the prime mover should drive the rotor of this SRIM?(a) 900 rpm(b) 600 rpm(c) 1500 rpm(d) 0I have been asked this question during an interview for a job.The query is from Rotor Frequency topic in chapter Induction Machines of Electrical Machines
Answer» Right ANSWER is (a) 900 rpm Explanation: NS = 1500 rpm. Speed of the rotor field with RESPECT to rotor structure = 120 * f2/P = 120*20/4 = 600 rpm Nr = 1500-600 = 900 rpm.

Discussion

121.	A properly shunted center zero galvanometer is connected in the rotor circuit of a 6-pole, 50 hz wound rotor induction motor. If the makes 90 complete oscillations in one minute, the rotor speed is?(a) 1000 rpm(b) 970 rpm(c) 950 rpm(d) 930 rpmI got this question during an interview.My query is from Rotor Frequency in division Induction Machines of Electrical Machines
Answer» Correct ANSWER is (b) 970 RPM The BEST I can EXPLAIN: Rotor frequency= s*f1 = 90/60 = 1.5 Hz. s = 1.5/50 = 0.03 rotor SPEED = 1000(1-0.03) = 970 rpm.

Discussion

122.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Speed of the rotor field w.r.t. stator field is?(a) zero(b) 150 rad/s(c) 6.28 rad/s(d) 145 rad/sThis question was posed to me in examination.I'm obligated to ask this question of Rotor Frequency topic in division Induction Machines of Electrical Machines
Answer» Correct answer is (a) zero Best explanation: As both the rotor FIELD and stator FILE rotate at synchronous SPEED, the RELATIVE speed between them is zero.

Discussion

123.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Speed of the stator field revolving rotor structure is?(a) 157 rad/s(b) 150 rad/s(c) 6.28 rad/s(d) 145 rad/sThis question was addressed to me in an online quiz.The origin of the question is Rotor Frequency in division Induction Machines of Electrical Machines
Answer» Right CHOICE is (C) 6.28 rad/s For EXPLANATION I would say: Speed of the STATOR field REVOLVING rotor structure = 1550-1440 = 60 rpm = 6.28 rad/s.

Discussion

124.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Speed of the rotor field w.r.t. rotor structure is?(a) 157 rad/s(b) 150 rad/s(c) 6.28 rad/s(d) 145 rad/sI have been asked this question during an interview.The query is from Rotor Frequency topic in chapter Induction Machines of Electrical Machines
Answer» CORRECT option is (c) 6.28 rad/s The best I can explain: Speed of the rotor FIELD w.r.t. rotor structure= 120rotor frequency/Poles = 1202/4 = 60 RPM = 6.28 rad/s.

Discussion

125.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Speed of the stator filed with respect to stator structure is?(a) 157 rad/s(b) 150 rad/s(c) 6.28 rad/s(d) 145 rad/sThe question was posed to me in semester exam.My query is from Rotor Frequency topic in portion Induction Machines of Electrical Machines
Answer» RIGHT OPTION is (a) 157 rad/s Easy explanation: SPEED of the stator filed with respect to stator STRUCTURE = Ns = 1500 rpm = 157 rad/s.

Discussion

126.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. The full load slip will be?(a) 4%(b) 5%(c) 2.4%(d) 3%This question was posed to me by my college professor while I was bunking the class.My question is from Rotor Frequency topic in chapter Induction Machines of Electrical Machines
Answer» CORRECT ANSWER is (a) 4% To ELABORATE: s = 1500-1440/1500 = 4%.

Discussion

127.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. The number of poles of this motor is?(a) 4(b) 6(c) 5(d) 2The question was asked during an interview for a job.This interesting question is from Rotor Frequency in section Induction Machines of Electrical Machines
Answer» Correct CHOICE is (a) 4 Easy explanation: P = 120f/N = 120*50/1440 = 4(1/6). The NUMBER of the poles should be whole number and must be even. So number of poles must be 4.

Discussion

128.	A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Rotor frequency is?(a) 2 Hz(b) 50 Hz(c) 52 Hz(d) 58 HzI have been asked this question in homework.My question comes from Rotor Frequency topic in division Induction Machines of Electrical Machines
Answer» Right choice is (a) 2 Hz For explanation I WOULD SAY: s = 0.04, rotor frequency = sf = 0.0450 = 2 Hz.

Discussion

129.	For a 4 pole three phase induction motor having synchronous speed of 1500 rpm is operating at 1450rpm. The frequency of the induced emf in rotor is?(a) 100 Hz(b) 50 Hz(c) 150 Hz(d) 0 HzThe question was posed to me in class test.The origin of the question is Rotor Frequency topic in section Induction Machines of Electrical Machines
Answer» CORRECT option is (a) 100 HZ The explanation is: The INDUCED frequency will be f = P(Ns-Nr)/2. f = 4(1500-1450)/2 = 100 Hz.

Discussion

130.	Slip is defined as _________ (Ns as the synchronous speed and Nr is the rotor speed)(a) Ns-Nr/Ns(b) Ns-Nr/Nr(c) Nr-Ns/Ns(d) Ns-NrThe question was asked during a job interview.Origin of the question is Rotor Frequency topic in division Induction Machines of Electrical Machines
Answer» Right choice is (a) Ns-Nr/Ns Best explanation: Slip is the ratio of the relative SPEED of between the STATOR MMF and the ROTOR speed to the SYNCHRONOUS speed of the machine.

Discussion

131.	Starting torque induced in a three phase induction motor in a direction of rotating magnetic field depends on _________(a) number of poles squared(b) inverse of number of poles(c) number of poles(d) number of number poles cubicThis question was posed to me in unit test.My doubt is from Flux and MMF Phasors and Waves in Induction Motors topic in section Induction Machines of Electrical Machines
Answer» The CORRECT CHOICE is (a) NUMBER of POLES squared Explanation: T = (pi/8).(P^2) φ (F^2)COS(θ).

Discussion

132.	The external resistance can be inserted in rotor circuit of _________(a) wound rotor induction motor(b) slip ring induction motor(c) wound rotor as slip ring induction motor(d) neither of motorsI have been asked this question by my college director while I was bunking the class.This interesting question is from Flux and MMF Phasors and Waves in Induction Motors topic in section Induction Machines of Electrical Machines
Answer» The correct CHOICE is (a) wound rotor INDUCTION motor To elaborate: External RESISTANCE can be inserted only in the wound rotor as does not get shorted as like squirrel CAGE motor.

Discussion

133.	For a 6-pole three phase squirrel cage induction motor has flux density wave of four poless, then the rotor induced poles will be?(a) 4(b) 6(c) 2(d) 10This question was posed to me during an interview.This intriguing question comes from Flux and MMF Phasors and Waves in Induction Motors in chapter Induction Machines of Electrical Machines
Answer» RIGHT ANSWER is (a) 4 Easiest EXPLANATION: For a squirrel-cage induction MOTOR the rotor will have the induced POLES will be same as flux density poles which are induced inside the machine while working.

Discussion

134.	In an induction motor, the stator is also known as _________ and the rotor as __________(a) field winding, armature winding(b) armature winding, field winding(c) armature winding, compensating winding(d) armature winding, interpole windingI have been asked this question in final exam.Question is taken from Flux and MMF Phasors and Waves in Induction Motors topic in section Induction Machines of Electrical Machines
Answer» The correct option is (a) field winding, armature winding To EXPLAIN I would say: In an INDUCTION motor, the stator is ALSO KNOWN as field winding, and the ROTOR as armature winding.

Discussion

135.	For a slip ring induction motor having leakage impedance of (1+j), the maximum generated emf would be attained at _________(a) 135°(b) 45°(c) -45°(d) 0°The question was asked by my school teacher while I was bunking the class.The question is from Flux and MMF Phasors and Waves in Induction Motors topic in section Induction Machines of Electrical Machines
Answer» Right choice is (a) 135° Best explanation: Due to LEAKAGE reactance there will be a LAGGING of ANGLE θ in the excitation VOLTAGE with the main FLUX. So the maximum is attained at 90°+θ.

Discussion

136.	For the three phase induction motor having leakage impedance, the maximum generated emf would be attained at an angle of θ having a purely resistive load is?(a) 90 + θ(b) θ(c) 90 – θ(d) -θThe question was posed to me in a national level competition.My question is based upon Flux and MMF Phasors and Waves in Induction Motors in section Induction Machines of Electrical Machines
Answer» Right CHOICE is (a) 90 + θ To ELABORATE: Due to leakage REACTANCE there will be a LAGGING of angle θ in the EXCITATION voltage with the main flux. So the maximum is attained at 90°+θ.

Discussion

137.	In a three phase induction motor of rotor impedance as (0.2+j0.2), rotor current in each phase lags behind the generated emf in that phase to rotor by a power factor angle of _________(a) 45°(b) 135°(c) 90°(d) 0°I had been asked this question by my school principal while I was bunking the class.This interesting question is from Flux and MMF Phasors and Waves in Induction Motors in chapter Induction Machines of Electrical Machines
Answer» CORRECT OPTION is (a) 45° The best explanation: The power factor angle WOULD be ATAN(0.2/0.2) = 45°.

Discussion

138.	In a three phase induction motor, rotor current in each phase lags behind the generated emf in that phase to rotor by a power factor angle of _________(a) atan(r2/x2)(b) atan(x2/r2)(c) atan(x1/r1)(d) atan(r1/x1)I got this question in an online quiz.Question is from Flux and MMF Phasors and Waves in Induction Motors topic in section Induction Machines of Electrical Machines
Answer» Correct ANSWER is (b) ATAN(x2/r2) Explanation: The power FACTOR ANGLE is atan(x2/r2).

Discussion

139.	A three phase induction motor is not self starting.(a) True(b) FalseI got this question during an internship interview.The query is from Flux and MMF Phasors and Waves in Induction Motors topic in chapter Induction Machines of Electrical Machines
Answer» Correct option is (b) False To ELABORATE: A three phase induction motor is self STARTING. Because air gap FLUX and rotor mmf produce electromagnetic torque in the DIRECTION of rotating magnetic field.

Discussion

140.	The starting method for a 3-phase squirrel-cage induction motor which is inferior in view of poor starting torque per ampere of line current drawn is?(a) series-inductor method of starting(b) direct-on-line starting(c) auto-transformer method(d) star-delta methodThis question was posed to me at a job interview.My question is taken from Principle of Operation in portion Induction Machines of Electrical Machines
Answer» Right answer is (a) series-inductor method of STARTING Easiest explanation: DUE to inductor method, REACTANCE INCREASES and the starting TORQUE decreases.

Discussion

141.	If use auto transformer method starting to start an induction motor to replace star-delta method, then the required tapping on the transformer will be _________(a) 57.73%(b) 86.7%(c) 57%(d) 66.66%I had been asked this question at a job interview.I'm obligated to ask this question of Principle of Operation topic in chapter Induction Machines of Electrical Machines
Answer» The CORRECT ANSWER is (a) 57.73% To ELABORATE: K = 1/1.73 = 57.73%.

Discussion

142.	A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. Then the rotor emf E2 and the rotor current I2 are zero at _________(a) Ns(b) 2Ns(c) Zero(d) Slip of 50%I had been asked this question during an online exam.This key question is from Principle of Operation topic in division Induction Machines of Electrical Machines
Answer» RIGHT option is (a) Ns Best EXPLANATION: The rotor EMF and CURRENT are zero at the speed of synchronous speed of the MACHINE.

Discussion

143.	A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is less than stator frequency?(a) It operates as induction motor(b) Emf is induced in rotor(c) Rmf will rotate at synchronous speed(d) All of the mentionedI had been asked this question in my homework.My doubt stems from Principle of Operation in chapter Induction Machines of Electrical Machines
Answer» The CORRECT choice is (d) All of the mentioned To ELABORATE: It will OPERATE as induction MOTOR.

Discussion

144.	A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is greater than stator frequency?(a) Rotor will be driven against rmf(b) Rotor will be driven in direction of rmf(c) No emf will be induced(d) The losses will be maximumThis question was addressed to me in an online quiz.I would like to ask this question from Principle of Operation in section Induction Machines of Electrical Machines
Answer» Right OPTION is (a) Rotor will be driven against RMF Explanation: As the rotor rotates at larger speed than the STATOR, the rmf speed is less than the rotor speed and it tries to rotate in the OPPOSITE direction to rmf.

Discussion

145.	A three phase induction motor is sometimes calles a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is equal to stator frequency?(a) It will not operate(b) It will operate as induction motor only(c) It will operate as induction generator(d) It will operate in braking modeThis question was posed to me at a job interview.This is a very interesting question from Principle of Operation topic in chapter Induction Machines of Electrical Machines
Answer» Right option is (a) It will not operate For EXPLANATION I WOULD say: As the rotor and stator frequencies are EQUAL, there will be no slip and so the ZERO EMF will be produced.

Discussion

146.	Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have better full-load power factor?(a) A(b) B(c) Both A and B(d) Neither A nor BThe question was posed to me by my college director while I was bunking the class.Query is from Principle of Operation topic in portion Induction Machines of Electrical Machines
Answer» Right choice is (b) B Explanation: At FULL load CONDITIONS, the excitation current is not very HIGH and so the POWER factor improves.

Discussion

147.	Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have poorer power factor?(a) A(b) B(c) Both A and B(d) Neither A nor BI had been asked this question in class test.This intriguing question originated from Principle of Operation topic in portion Induction Machines of Electrical Machines
Answer» The CORRECT option is (a) A The BEST I can explain: Due to LARGER air gap of motor A, it will need more of exciting current. So the no load angle will increase and power FACTOR will DETERIORATE.

Discussion

148.	Two three phase induction motors A and B are identical in all respects except that motor A has a larger air-gap than motor B. Which motor will have more no load current?(a) A(b) B(c) Both A and B(d) Neither A nor BI have been asked this question in a national level competition.Asked question is from Principle of Operation topic in chapter Induction Machines of Electrical Machines
Answer» The correct answer is (a) A Best explanation: As the air gap of MOTOR A is more, it will REQUIRE more flux to EXCITATION and so the no LOAD CURRENT.

Discussion

149.	The direction of rmf when a three phase supply is given to stator of three phase induction motor is?(a) Zero(b) Ns(c) 2Ns(d) -NsThe question was asked during an interview.This is a very interesting question from Principle of Operation in chapter Induction Machines of Electrical Machines
Answer» RIGHT choice is (b) Ns The best I can explain: There will be rotating magnetic field will be produced causing the EMF to be induced and the current will flow in the ROTOR at a SPEED of synchronous speed.

Discussion

150.	The rotor of 3-phase slip ring induction motor is fed from a 3-phase supply with its stator winding short circuited having rotor rotating clockwise at a speed of Nr, then the _________(a) speed of air gap field w.r.t. stator is Ns-Nr anticlockwise(b) speed of air gap field w.r.t. stator is Ns-Nr clockwise(c) speed of airgap field w.r.t rotor is Ns clockwise(d) speed of airgap field w.r.t. stator is Ns-Nr clockwiseI have been asked this question in final exam.I want to ask this question from Induction Motor as a Transformer topic in section Induction Machines of Electrical Machines
Answer» Correct option is (a) SPEED of air GAP field w.r.t. STATOR is Ns-Nr anticlockwise Explanation: The air gap field of stator = -(Ns-Nr).

Discussion

Explore topic-wise InterviewSolutions in .

The 3-phase induction motor with rotor circuit open will _________(a) not run(b) run normally(c) get over heated(d) make noiseI got this question during a job interview.Enquiry is from Rotor Frequency topic in section Induction Machines of Electrical Machines

A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. The number of poles of this motor is?(a) 4(b) 6(c) 5(d) 2The question was asked during an interview for a job.This interesting question is from Rotor Frequency in section Induction Machines of Electrical Machines

A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. Rotor frequency is?(a) 2 Hz(b) 50 Hz(c) 52 Hz(d) 58 HzI have been asked this question in homework.My question comes from Rotor Frequency topic in division Induction Machines of Electrical Machines

Slip is defined as _________ (Ns as the synchronous speed and Nr is the rotor speed)(a) Ns-Nr/Ns(b) Ns-Nr/Nr(c) Nr-Ns/Ns(d) Ns-NrThe question was asked during a job interview.Origin of the question is Rotor Frequency topic in division Induction Machines of Electrical Machines

A three phase induction motor is not self starting.(a) True(b) FalseI got this question during an internship interview.The query is from Flux and MMF Phasors and Waves in Induction Motors topic in chapter Induction Machines of Electrical Machines

The direction of rmf when a three phase supply is given to stator of three phase induction motor is?(a) Zero(b) Ns(c) 2Ns(d) -NsThe question was asked during an interview.This is a very interesting question from Principle of Operation in chapter Induction Machines of Electrical Machines