The torque produced by three phase induction motor depends upon the following three factors. Rotor induction motor an overview sciencedirect topics. Induction motors can greatly exceed both their rated torque and current when not at 100% speed. The value of slip in induction motor is can never be zero. Threephase induction motor torquespeed characteristics. Variable voltage variable frequency vf control theory. By default, the block sets the simulation type parameter to continuous to use a continuous sample time during simulation. The national electrical manufacturers association nema provides design letters to indicate the torque, slip, and starting characteristics of threephase induction motors they are as follows. This document is highly rated by electrical engineering ee students and has been viewed 50 times. The block uses the threephase input voltages to regulate the individual phase currents, allowing control of the motor torque or speed. The induction motor block implements a threephase induction motor.
From the above relation it is seen that, when slip s increases the torque, t also increases. Torque ratios in three phase induction motor mcqs with ans. This includes motoring mode, generating mode and braking mode for 0 torque slip characteristics of three phase induction motor. The torque produced by three phase induction motor depends upon the following three factors firstly the magnitude of rotor current, secondly the flux which interact with the rotor of three phase induction motor and is responsible for producing emf in the rotor part of induction motor, lastly the power factor of rotor of the three phase induction motor. Types of starters in three phase induction motor mcqs. This document is highly rated by mechanical engineering students and has been viewed 435 times. Pdf thermal performance analysis of induction motor. Induction motor theory jerry bednarczyk, pe course content introduction the ac induction motor is well suited to applications requiring constant speed operation. Succinctly divided in 14 chapters, the book delves into important concepts of the subject which include armature reaction and commutation. For the immediate value of the slip, the graph changes from one form to the other. There are two basic reasons for the use of singlephase motors rather than 3phase motors. Torque slip characteristics of three phase induction motor. Torque equation of three phase induction motor electrical4u. Due to arrangement of the stator coils and 3 phase supply applied to them, resultant magnetic field inside the motor is a vector constantly rotatin.
Torque slip characteristics of induction machine pull out torque, breakdown torque, motoring mode, generating mode, breaking mode of induction motors, electric motor torque curve torque. When the rotor resistance is increased, so is the slip for maximum torque, and the stable operating slip range of the. This characteristic is very useful for the stability analysis of the machine. Motor performance standard nema designs of various torque characteristics to meet different application loads nema design starting torque starting current breakdown torque full load slip typical sine wave applications a normal high high low mach. For reason of economy, most houses, offices and also rural areas are supplied with single phase a. Uniqueness of torquespeed characteristics of an induction. Design a is a generalpurpose design used for industrial motors. The book principles of electrical machines book by vk mehta and rohit mehta is an ideal text for students who look to gain a current and clear understanding of the subject as all theories and concepts are explained with lucidity and clarity. Pdf principles of electrical machines book by vk mehta. Further increases in load on the motor causes, the slip to increase still more.
Torque slip characteristics of induction motor electrical4u. Tools, fans b normal normal normal normal general industrial c high normal normal normal loaded. The motoring region of the induction machine torque speed curve is the region of greatest interest. When a motor starts to rotate the slip is 100 % and the motor current is at maximum. The number of torque changes based on a given speed of the load. Apr 09, 2020 torque slip speed characteristics of induction motor im electrical engineering ee notes edurev is made by best teachers of electrical engineering ee. Free download pdf of electric motors and drives by austin hughes, free download ebook of electric motor and drives, free download textbook of electric motors and drives, free download engineering book of electric drive and control, electric drive and control pdf free download. When the load exceeds the synchronous pull out torque, the machine looses synchronism and runs as an induction motor with fluctuation in torque and slip. Torqueslip characteristic stability analysis for induction motor. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. The typical base speed of the four pole induction motor varies between 1420 and 1480 rpm at 50. This includes motoring mode, generating mode and braking mode for. As we know, the slip speed is the difference between the synchronous and rotor speed of the induction motor. Torque slip characteristics in three phase induction motor.
Induction motor interview questions and answers pdf free download for electrical engineering students. The rotor reactance at stand still x 2 remains constant. Torque slip characteristic of an induction motor the torque slip characteristic is represented by a rectangular hyperbola. Ppt induction motor powerpoint presentation free to. However, the slip at which the maximum torque occurs changes with rotor resistance. The actual fullload slip of a particular motor is dependant on the motor design. If the rotor speed is less than the synchronous speed n s, the machine acts as a motor. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Apr 20, 2020 torque slip speed characteristics of induction motor im threephase induction motor mechanical engineering notes edurev is made by best teachers of mechanical engineering.
The starting torque of the motor is slightly larger than its fullload torque, so this motor will start carrying any load that it can supply at full power 4. An induction motor can therefore be made without electrical connections to the rotor. This curve is called the torque speed characteristic curve. The characteristics are drawn with rated voltage and. Number of poles, frequencies and synchronous induction motor speed. The slip is defined as the ratio of difference of synchronous speed and actual rotor. I squirrel cage induction motor iiwound rotor slip ring motor. A 3 phase induction motor can be used for different applications with various speed and load requirements. Typically, the fullload slip for the squirrel cage induction motor is less than 5%. The speed of the induction motor is characterized by the term known as the slip. And on the other hand, when designed to have a high impedance, the motor has an increased amount of torque in a lowspeed range. And the variation of the slip obtained with the variation of speed. The emf induces in the rotor because of the relative motion, or we can say the slip speed of the motor. When a motor is designed in such a way that impedance of the aluminum conductor of the rotor is reduced, its efficiency is increased in a highspeed range.
Torque slip characteristics of induction motor the torque slip curve for an induction motor gives us the information about the variation of torque with the slip. Torque slip characteristics of induction motor full guide. Characteristics of induction motors nidec corporation. Slip torque characteristics of an induction motor stable and unstable region of the slip torque characteristics.
Slip torque characteristics of an induction motor my. Torqueslip speed characteristics of induction motor im. Speed torque characteristics of induction motor from eq. Torquespeed characteristics of three phase squirrel cage. Different types of electrical motors 2 electric motors ac motors synchronous induction squirrel cage slip ring dc motors separately excited self excited series shunt compound 3. Speed torque characteristics of 3 phase induction motor. Torque speed characteristics of three phase squirrel cage induction motor aim to obtain the torque speed characteristics tn r of a three phase squirrel cage induction motor using 1. In an induction motor, torque is equal to the power crossing the air gap divided by the synchronous mechanical speed. An induction motors rotor can be either wound type or squirrelcage type. The slip is defined as the ratio of difference of synchronous speed to the speed at any mechanical load to. The slip is defined as the ratio of the difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Torque slip characteristic of an induction motor low.
The torque will attain a maximum value, at s r 2 x 2. The maximum torque developed in an induction motor is called the pull out torque or the breakdown torque. The most important specification for wound rotor motors is how they operate once powered, and this is visualized through torque speed graphs. Torque slip characteristics of induction motor also known as torque speed characteristics provide us with the information about the variation of torque with the slip. Slip in induction motor is the relative speed between the rotating magnetic flux and rotor expressed in terms of per unit synchronous speed.
Determination of the torquespeed characteristic of. The induction motor is made up of the stator, or stationary windings, and the rotor. This design exhibits normal torques and fullload slip of approximately 3 percent and can be used for many types of industrial. Speed torque characteristics of induction motors figure 2 shows the typical speed torque characteristics of an induction motor. For an induction motor with p polesand f frequency, slip 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. Torque slip characteristics of three phase induction motor presented by aniket raj 2. The rotor circuit resistance has significant impact on starting torque, the speed at which the breakdown torque occurs, and the slip during the normal running operation. We can derive an equation from the equivalent circuit that allows the calculation of the torque for a given value of slip.
Wound rotor induction motors with three rotor slip rings have been used in adjustable speed drives for many years. Thus, it passes through the point of maximum torque when r 2 sx 20. What are the torqueslip characteristics of a 3phase. Free download pdf of electric motors and drives by austin. Derivation of the expression for the gross torque developed as a function of slip speed of induction motor sketch the above characteristics of torque slip speed, explaining the various features derive the expression of maximum torque and the slip speed at which it occurs. The torque speed characteristic is required in order to predict behavior of induction machines in electrical motor drives 1. An843, speed control of 3phase induction motor using. Condition for maximum torque in three phase induction motor. Fullload slip varies from less than 1 % in high hp motors to more than 56 % in minor hp motors. Torque slip characteristics of induction motor your. Torque slip speed characteristics of induction motor im. To see the effect of rotor resistance on torque slip characteristics of induction motor, consider a slip ring induction motor in which additional resistance in the rotor circuit can be introduced through slip rings. Slip in electrical induction motors engineering toolbox. An induction motor or asynchronous motor is an ac electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.
Three phase induction motor questions pdf free download for freshers experienced. In general, the induction motor is cheaper and easier to maintain compared to other alternatives. Consider a 3 phase motor is supplied by 3 phase ac. Figure 1 showed a plot of induction motor torque vs speed from zero to synchronous speed. The characteristics curves for synchronous induction motor operating at full load unity p. Firstly the magnitude of rotor current, secondly the flux which interact with the rotor of three phase induction motor and is responsible for producing emf in the rotor part of induction motor, lastly the power factor of rotor of the three phase induction motor.
This torque is called pull out or break down or stalling torque. Torque speed characteristics of induction motor slip. The maximum value of the torque developed by an induction motor is independent of rotor resistance r 2. Speed and torque behavior of three phase induction motor based on torque equation. When the speed varies the slip vary and in contrast the torque will also var y.
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