One of the main disadvantages of induction motors is that speed control of induction motors are difficult. … Ω, X. They run at a constant speed from no-load to the full load. Required fields are marked *. 3 - Phase Induction Motors - Electrical Engineering (MCQ) questions and answers. By changing the supply frequency There will be a small gap between rotor and stator, known as air-gap. (adsbygoogle = window.adsbygoogle || []).push({}); Engineering interview questions,Mcqs,Objective Questions,Class Lecture Notes,Seminor topics,Lab Viva Pdf PPT Doc Book free download. 3 0 obj Menu. A 3 phase squirrel cage induction motor is a type of three phase induction motor which functions based on the principle of electromagnetism.It is called a ‘squirrel cage’ motor because the rotor inside of it – known as … 16. which will improve your skill. 32. Related Articles-LINEAR ELECTRIC MOTOR CONCEPT; Working principle of a 3 phase induction motor A 3-phase induction motor is running at a load of the rated torque. In such case the rotor may refuse to accelerate. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator. <> 14. (ii) Control from rotor side 26. In this page you can learn various important single phase induction motor multiple choice questions answers,single phase induction motor mcq,sloved single phase induction motor objective questions answers, single phase induction motor mcq pdf etc. (b) Motor keeps on running but draws more current. 1. The flux passes through the air-gap and sweeps past the rotor surface thus it cuts the rotor conductors. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> How to supply power to rotor? Three-phase induction motor is mainly suitable for which of the following application a) For running different machine tools where several speeds are required b) For running paper machine requiring exact speed control c) For running electric vehicles d) For running rolling mills needing exact speed control 0.03. In some designs, the rotor can act to serve as the motor’s armature, across which the input voltage is supplied. About the Author: Top Coaching … speed will have (a) 8 poles (b) 6 poles (c) 4 poles (d) 2 poles Ans: b 20. the speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different, or else the magnetic field will not be moving relative to the rotor conductors and no currents will be induced. (b) Motor keeps on running but draws more current. (a) Motor keeps on running and the current drawn does not change. Q-In a shaded pole single-phase motor, the revolving field is produced by the use of. Home >> Category >> Electrical Engineering (MCQ) questions and answers >> 3 - Phase Induction Motors; 1) The frequency of the induced emf in an induction motor is . What is an Electric Motor? What is the relationship between the supply frequency number of poles and sycnchronous speed? Induction Motor Quiz Questions ) Search for: Related Pages. Nikola Tesla. Only the stator winding is fed from 3-phase supply. 3. 11. 22. 8. The conversion of electrical power into mechanical power takes place in the rotating part of an electric motor. Rotor speed, nr = ns(1-s). What is a Cogging Torque? The stator consists of wound ‘poles’ that carry the supply current that induces a magnetic field in the conductor. Record all nameplate information for the induction motor. (c) The motor stops immediately. This changing magnetic field pattern can induce currents in the rotor conductors. What is a Stator? principle-of-three-phase-induction-motor/ Per-phase equivalent circuit • Motor Slip • R 1 and R 2: stator and rotor winding resistances • X 1 and X 2: stator and rotor winding leakage reactances • X m: magnetizing reactance • R c: core loss resistance The Stator is the stationary part and the rotor is the rotating part. In induction motors, particularly squirrel cage type induction motors, sometimes exhibit a tendency to run stably at speeds as low as one-seventh of their synchronous speed Ns. Slip is calculated using: s = [ns-nr]/ns. You should also make a DC measurement of stator winding line-to-line resistance using a DMM. endobj Here the cause is the relative velocity between the rotating flux of the stator and the stationary rotor conductors. The rpm sensor Answer: The addition of resistance to the rotor circuit does not change the value of maximum torque but it only changes the value of the slip at which the maximum torque occurs. Academia.edu is a platform for academics to share research papers. 6. Slip ring induction motor, 18. The non-stationary part on an electric motor is the rotor. Speed and Direction of Rotation . Other These tests are performed to check the electrical or mechanical defects of the induction motor. Thus the rotor of induction motor starts to rotate. 24. Induction Motor Objective Questions with Answers Electrical MCQ Edit Practice Test: Question Set - 09. 25. The role of the “field” component is simply to create a magnetic field (magnetic flux) for the armature to interact with, so this component can comprise either permanent magnets, or electromagnets formed by a conducting coil. 23. a. If a 4-pole 50 Hz 3-phase induction motor run at 1440 rpm, then value of slip is. Ω, X. m. i. Synchronous speed in rpm =30.74 . Your email address will not be published. This can be achieved by: 36. endobj The motor is mounted in a test rig that allows one to control the torque applied to the motor shaft and to measure both rpm and torque. Like any electric motor, a 3-phase induction motor has a stator and rotor. By various ways of cascade connection (b) 3.3%. Since the rotor conductors form a closed circuit the rotor current is produced. The number of ‘poles’ can vary between motor types but the poles are always in pairs (i.e. Determine (a.) 5. none of above. 7. The starting torque of a squirrel-cage induction motor is low negligible same as the full-load torque slightly more than full-load torque 3. What is the advantage of skewed stator slots in the rotor of Induction motors? 11. What techniques is used to produce a desired Speed? Its direction will be as per Fleming’s right hand rule. How to calculate the Slip? The armature’s role is two-fold: (a) to carry current crossing the field, thus creating shaft torque (in a rotating machine) or force (in a linear machine), and (b) to generate an electromotive force (“EMF”). Why the Starter is Used? 1. What happens when one of the outer mains is interrupted while the motor is running? EE DEPT. Number of test is done on induction motor to check its different parameters. 23. Once the rotor speed increases, the full rated voltage is given to it. What is meant by cogging in the Induction motor? Most Asked Technical Basic CIVIL | Mechanical | CSE | EEE | ECE | IT | Chemical | Medical MBBS Jobs Online Quiz Tests for Freshers Experienced. The value of the radial air-gap may vary from 0.5 to 2 mm. 3-Phase Induction Motors EE 340 . Similarly, when an induction motor starts, a very high current is drawn by the stator, on the order of 5 to 9 times the full load current. %���� Based on type of phase supply Its magnitude is proportional to the relative velocity between the flux and the conductors. 2 0 obj 9. Q-The repulsion-start induction-run motor is used because of_____. What are the advantages and disadvantages of Induction Motors? 1. • At full load, the slip for large motors rarely exceeds 0.5%. Home; Electrical Theory. 3. The slip of induction motor at no load is: 0.2. (A) It will run in … The stator consists of wound ‘poles’ that carry the supply current that induces a magnetic field in the conductor. 2 =0.309 . 12. Who invented Induction Motor? 31. Home » Induction Motor Questions » 300+ TOP INDUCTION MOTOR Interview Questions and Answers. good power factor; high efficiency; … x��Z_o9��0��C���h�P��d7{����d��;�q��:����?�Ҍ%����C�z��H�"�(_^m������޼������b>�.��/�]���2��0}^���r������ơ���|3e㷓l|~vy#2!����3�q�'2��"��0x����g����g��b3����~��:?�.ȩ�^HV��C>L����P�)�'I�X����l�Ϗ0X/�r�����`(��&!DقUUH������,���d� ���u���6��z]GFmDW�q�3U����?����o����YBi�{ ��W/��ɗ�qٙ��B�� S6����x��9��:�T�� }"i�O*R��>�ke�I�O)b#8�. 23. f = Pns/2, 19. Hence for fine speed control applications dc motors are used in place of induction motors. What are the various methods of measuring slip? A three phase, 12 pole, salient pole alternator is coupled to a diesel engine running at 500 rpm. 1 0 obj 28. Induction Motor Problems - Solutions Q #1 A 2-pole, 3-phase induction motor, fed by a 60 Hz source, An electrical motor is a device that has brought about one of the biggest advancements in the fields of engineering and technology ever since the invention This phenomenon is known as crawling of an induction motor and the speed is called as crawling speed. It will not be parallel to the shaft. Underwriters Laboratories (USA): UL 1004 – Standard for Electric Motors; Download the questions on electric motor with their answers at QUESTIONS ON ELECTRIC MOTOR WITH ANSWERS PDF. Figure 2: Squirrel-case rotor. • At no-load, the slip is nearly zero (<0.1%). 29. Find the percentage slip and number of poles of the induction motor. (c) The motor stops immediately. An induction motor has 2 main parts; the Stator and Rotor (Fig:1). By injecting EMFs in the rotor circuit. The stator carries a 3-phase winding (called stator winding) while the rotor carries a short circuited winding (called rotor wind­ing). Three-phase induction motor is mainly suitable for which of the following application a) For running different machine tools where several speeds are required b) For running paper machine requiring exact speed control c) For running electric vehicles d) For running rolling mills needing exact speed control • For induction motors a very important parameter is the slip of the motor The slip, s, defines the relative speed difference between synchronous speed and rotor speed and is given by: • where ω is expressed in rads/s and n is expressed in rpm. Squirrel-cage induction motor Explain how Torque-Slip Characteristics vary when adding resistance to rotor circuit? This phenomenon is called as magnetic locking or cogging. That is why such motors are known as induction motors. 1. Question 1 A 50-kW, 460-V, 50-Hz, two-pole induction motor has a slip of Advantages: 34. When the 3 phase stator windings are fed by 3 phase supply, a magnetic flux of constant magnitude which is rotating at synchronous speed is set up. This problem can be prevented by proper choice of stator and rotor slots and also by skewing the rotor slots by one slot pitch. Download the questions on electric motor with their answers at QUESTIONS ON ELECTRIC MOTOR WITH ANSWERS PDF. This high current can damage the motor windings and because it causes heavy line voltage drop, other appliances connected to the same line may be affected by the voltage fluctuation. Hence, in order to reduce the relative speed, the rotor begins to rotate in the same direction as that of the rotating magnetic flux and tries to catch up with the rotating flux. <>>> 27. As a result, a very high current flows through the rotor. \mbox{Synchronous speed, }n_s = \frac{120f}{P}\quad[\mbox{rev/min}], 20. Thus an induction motor is also known as rotating transformer ( ie, one in which primary winding is stationary and the secondary is free to rotate). 1. What is an Armature? Numerical Problems Induction Motors . What is a Rotor? 3. What is the Three Phase induction motor Working Principle? To avoid such effects, the starting current should be limited. 3. This then creates a magnetic field which, through magnetic interaction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. By changing the supply voltage A 480V, 60 Hz, 6-pole, three-phase, delta-connected induction motor has the following parameters: R. 1 =0.461 . stream Less than 1% 5% 2% 4% Answer 1. Induction Motor Quiz Questions ) Search for: Related Pages. 21. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. The stator is the stationary part of an electric generator or electric motor. The motor is mounted in a test rig that allows one to control the torque applied to the motor shaft and to measure both rpm and torque. How many types of Rotor are there? 2, 4, 6, etc.). By reversing the current direction in the moving coil of a motor’s armature, a steady rotating force (torque) is produced. 1.At zero in an induction motor a) Motor runs as a generator b) Motor does not run c) The motor runs an at synchronous speed d) Slip produced is zero Electricalunits.com. An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the armature, receiving its influence from moving field coils on the rotor. Induction motors require less maintenance, Induction motor has high efficiency and reasonably good power factor, 3-phase induction machines are self starting, Induction motors are essentially a constant speed motor and its speed cannot be changed easily. What is the basic difference between Synchronous motor and an Induction Motor? Because in induction Single Phase Induction Motor Solved Objective Questions (1) Q-The starting torque of a 1-phase induction motor is. Introduction: The three phase induction motors are simple in construction, rugged, low cost and easy to maintain. Find the percentage slip and number of poles of the induction motor. (a) 0.04%. High; Moderate; Low; Zero (Ans.) Almost 80% of the motor is a three-phase induction motor among all motors used in industries. This is similar to a transformer with the secondary coil short circuited, which causes the primary coil to draw a high current from the mains. You should also make a DC measurement of stator winding line-to-line resistance using a DMM. Your email address will not be published. This is exactly in the same way as the secondary of two winding transformer receives its power from the primary. A 3-phase induction motor is running at a load of the rated torque. 2, 4, 6, etc.). Lesser than the supply frequency c. Same as the supply frequency d. None of these. Greater than the supply frequency b. What is a Stator? Induction Motor Problems - Solutions Q #1 A 2-pole, 3-phase induction motor, fed by a 60 Hz source, A common problem is called cogging torque. Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets of the rotor and the stator slots of a Permanent Magnet (PM) machine. 0102030405060708091011 Slip exists in induction motor. slip iii. All the tests are divided into two parts: Preliminary Tests. What is the difference between DC motors and the Induction motors? 2. 0.05. Ω, X. There are two types of rotors. 37. What is meant by crawing in the induction motor? An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. What is a Stator? A commutator is a common feature of direct current rotating machines. 11. … Induction motors always operate under lagging power factor and during light load conditions they operate at very worst power factor (0.2 to 0.4 lagging). By changing the number of stator poles Calculate the following information: ii. A commutator is an electrical switch that periodically reverses the current direction in an electric motor or electrical generator. When the number of teeth in stator and rotor are equal, the stator and rotor teeth have a tendency to align themselves exactly opposite to each other, since this corresponds to minimum reluctance position. It supplies an induction motor ich has a full load speed of 144wh 0 rpm. What is a Synchronous Speed? This current’s direction will oppose the very cause producing it ( as per Len’s law). Similarly, in a generator, reversing of the coil’s connection to the external circuit produces unidirectional current in the circuit. SINGLE PHASE INDUCTION MOTORS Multiple Choice Questions and Answers pdf free download,interview questions,objective type questions,lab viva manual The motor drives a mechanical load at a speed of 1170 rpm. A double squirrel-cage induction motor has two rotors moving in opposite direction two parallel windings in the stator two parallel windings in the rotor two series windings in the stator 2. The rotor is the non-stationary part of a rotary electric motor or alternator, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor’s axis. • The electric energy generated purchased by consumers for different needs. 30. Three-Phase Induction Motor Revised: April 11, 2013 2 of 10 Figure 1: Induction machine construction. Methods to control speed of Wound Rotor Motors? 1. 1 =0.507 . It is unitless and is the ratio between the relative speed of the magnetic field as seen by the rotor to the speed of the rotating field. Like any electric motor, a 3-phase induction motor has a stator and rotor. How many types of Induction Motor ? Numerical Problems Induction Motors . (OR) Why does the Rotor rotate? Answer : An induction motor (IM) is a type of asynchronous AC motor … By inserting resistance in rotor circuit How does the Induction motor work? What is an Induction Motor? The full-load slip of a 3-phase induction motor ranges from ... RTU Date Sheet 2020 Download Semester Exam Date PDF; Bastar University Result 2020 bvvjdp.ac.in BA BSc BCom Part 1 2 3; How an Induction Motor is started? In addition to that this arrangement will help to reduce the magnetic hum and noise. INDUCTION MOTOR Questions Pdf :: 21. View Homework Help - Assignment induction motor 2020.pdf from ELECTRICAL BEKE3533 at Technical University of Malaysia, Melaka. 2. The induction motor has no brushes and is easy to control, many older DC motors are being replaced with induction motors and accompanying inverters in industrial applications. synchronous motor. What are the various methods of speed control in three phase induction motors? The other is the field winding, field magnet. In the induction motor design, the rotor slots are purposely made with a slight skew arrangement. Three-Phase Induction Motor Revised: April 11, 2013 3 of 10 The rotor receives its excitation by induction from the armature field. SINGLE PHASE INDUCTION MOTORS Multiple Choice Questions and Answers pdf free download,interview questions,objective type questions,lab viva manual (PDF) Induction Motor: Working Principle, Types, & Definition | Hicham Moucharrafie - Academia.edu An induction motor (also known as an asynchronous motor) is a commonly used AC electric motor. Induction Motor Equations ENGN1931F – Spring 2017 5 For low slip frequencies, the power of the motor is simply proportional to the product of the square of the gap field strength with the volume of the rotor and the no-load speed of rotation. The stator is basically a 3 coil winding and three phase AC power input is given to it. These currents interact with the rotating magnetic field created by the stator and the rotor will turn. (i) Control from stator side Also termed as detent or ‘no-current’ torque, it is an undesirable component for the operation of such a motor. The induction motor especially three phase induction motors are widely used AC motor to produce mechanical power in industrial applications. Home; Electrical Theory. How to prevent the cogging? What Is An Induction Motor? inductor; capacitor; resistor; shading coils (Ans.) Therefore, the induction motor is the most important motor among all other types of motor. It is advisable to avoid line starting of induction motor and use starter because. the starting current when starting direct on full voltage (b.) An Electric Motor converts electrical power to mechanical power in its rotor. Due to advance in power electronics, variable frequency drives using induction motors are used in industries for speed control now a days. Figures 1 and 2 illustrate the rotor construction. Ω , R. 2 =0.258 . Single phase induction motor (not self starting) in both machines. How to calculate the Slip? b) 0.5. c) 0.1. d) 1. About. Why an Induction Motor sometimes called Rotating transformer? %PDF-1.5 The frequency of the induced emf is the same as the supply frequency. The induction motor stator resembles the stator of a revolving field, three phase alternator. Why stator windings are arranged around the rotor? Where does the power go? induction motor has the following equivalent circuit parameters: Rw1 = 0.25S Rw2N = 0.2S Xl1 = Xl2N = 0.5S Xm1 = 30S The rotational losses are 1700W. Line Current iv. Explanation: … 17. The stationary part of an electric motor is the stator. <> A soft start starter is a device which limits the starting current by providing reduced voltage to the motor. What is a Rotor Speed? Why the speed of the physical rotor and the speed of the rotating magnetic field in the stator must be different? Slip is calculated using: 22. Answer: In Star-Delta starting induction motor stator is connected in star connection for starting after picking up speed it is connected to delta connection. When the motor is started, the slip is equal to 1 as the rotor speed is zero, so the induced emf in the rotor is large. 2. Hence some power factor correction equipments such as static capacitor banks should be placed near to these motors to deliver the reactive power to them. The stator carries a 3-phase winding (called stator winding) while the rotor carries a short circuited winding (called rotor wind­ing). The armature, in contrast, must carry current so it is always a conductor or a conductive coil, oriented normal to both the field and to the direction of motion, torque (rotating machine), or force (linear machine). (d) The motor stops after a few seconds. Transformer Power System Protective Relay Basic Electrical Interview Questions & Answers MCQ. The stator or the stationary part consists of three phase winding held in place in the slots of a laminated steel core which is enclosed and supported by a cast iron or a steel frame as shown in Fig: 3.1(a). Three Phase Induction Motor MCQ Questions Answers Electrical Engineering. An induction motor with 1000 r.p.m. 15. The good power factor of an induction motor can be achieved if the average flux density in the air gap is (a) absent (b) small (c) large (d) infinity Ans: b 21. Answer: The speed of wound rotor motors are changed by changing the slip of the motor. In DC motors the electrical power is conducted directly to the armature through brushes and commutator. Slip ring induction motor advantages and disadvantages compared to squirrel cage motors? Ω Rotational losses are 2450W. Due to this an induction motor is sometimes referred to as an asynchronous machine. 4 0 obj What happens when one of the outer mains is interrupted while the motor is running? What is Commutator? An armature is one of the two principal electrical components of an electromechanical machine–a motor or generator. 4. … (d) The motor stops after a few seconds. This also results in reduced starting torque (1/3 times compared to delta connection). Record all nameplate information for the induction motor. The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor. What is the general working principle of Induction motor? The first commutator-type direct current machine was built by Hippolyte Pixii in 1832. View Homework Help - Induction Motor Solutions.pdf from EE 4701 at University of Minnesota, Morris. Soln: Frequency of supply to the induction motor f = pn/120 = 12 x 500 / 120 = 50 Hz . The Rotor sits inside the Stator. 3 phase induction motor multiple choice questions 3 phase induction motor multiple choice questions and answers 3 phase induction motor objective questions 3 phase induction motor objective questions answers 3 phase induction motor questions and answers 3 phase induction motor questions and answers pdf 3 phase induction motor short questions control speed of Wound Rotor Motors DC Series Motor … 13. 1. The number of ‘poles’ can vary between motor types but the poles are always in pairs (i.e. High starting torque with low starting current, Good running characteristics after external rotor resistances are cut out, The initial and maintenance costs are greater than those of squirrel cage motors, The speed regulation is poor when run with resistance in the rotor circuit, Varying the resistance in the rotor circuit, Inserting and varying a foreign voltage source in the rotor circuit. It supplies an induction motor ich has a full load speed of 144wh 0 rpm. the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. Only the stator winding is fed from 3-phase supply. Copyright 2020 , Engineering Interview Questions.com. Menu. View Homework Help - Induction Motor Solutions.pdf from EE 4701 at University of Minnesota, Morris. Home. The slip of induction motor at no load is. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. Must be different the percentage slip and number of poles and sycnchronous speed in power electronics, variable drives! Designs, the rotor conductors form a closed circuit the rotor and the conductors of these rotate... Mains is interrupted while the motor ’ s armature, across which the input voltage is given it... 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