Lecture 6 three phase induction motors cairo university. Torque formula for induction motor your electrical guide. Enter your email below to receive free informative articles on. Torque speed characteristics of induction motor electrical academia. Next, the torqueslip characteristic of the proposed motor is compared with the induction motor of the conventional structure, which has the same size. They are based on the fact that the induction motor torque at a given slip varies as the square of the voltage. A stator winding is placed in the stator of induction motor and the three phase supply is given to it. Torque slip characteristics of induction machine pull out torque, breakdown torque, motoring mode, generating mode, breaking mode of induction motors. Speed torque characteristics of 3 phase induction motor duration. Pdf uniqueness of torquespeed characteristics of an induction. When a motor starts to rotate the slip is 100 % and the motor current is at maximum. For many induction motors, the average torque drops a bit as it accelerates and then rises to a peak value of torque. Based on type of phase supply three phase induction motor self starting in nature single phase induction motor not self starting other squirrelcage induction motor slip ring induction motor.
The stator is the stationary coils in the motor where the current is produced to create the. The rotational speed n of an induction motor, and thus the slip, depends on the operating point, which depends on a load torque requirement so, for a motor, if torque is higher, speed is lower. Torque slip characteristic of an induction motor low. In this paper, we propose a hightorquedensity axial gap induction motor with toroidal winding. Induction motor aim to obtain the torquespeed characteristics tn r of a three phase squirrel cage induction motor using 1.
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. Torqueslip characteristics of three phase induction motor presented by aniket raj 2. Determination of the torquespeed characteristic of induction motor. Basic principle of operation of threephase induction machine. We can derive an equation from the equivalent circuit that allows the calculation of the torque for a. This document is highly rated by mechanical engineering students and. The magnetization current im flowing in the motors equivalent circuit fig. When the rotor reaches the rated speed, the reactances of both the cages are almost negligible because of low slip figure 2. It is a detailed article on the induction motor torque speed characteristics i have explained every point related to an induction motor.
Slip in electrical induction motors engineering toolbox. Where, t is the torque produced by the induction motor. Torque equation of three phase induction motor electrical4u. Torque speed characteristic of an induction motor torque speed characteristic is the curve plotted between the torque and the speed of the induction motor. 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. As its name indicates stator is a stationary part of induction motor. Hence the stable operating region of the motor lies for the slip values, s0, and that corresponds to maximum torque. The torqueslip behavior of the singlephase induction motor under variable frequency operation provides insights to possible scalar control laws for optimizing performance at all speeds. Torqueslip characteristics in three phase induction motor as the induction motor is located from no load to full load, its speed decreases hence slip increases.
Figure illustrates the torque slip characteristics of an induction motor for the rated voltage. Tools, fans b normal normal normal normal general industrial c high normal normal normal loaded. Induction motor speed torque characteristics typically, when a nema design b induction motor is started acrosstheline, an inrush current of 600 to 800% fla occurs, corresponding to the starting torque point. Torque slip characteristics of induction motor your. Torquespeed characteristics of three phase squirrel cage. 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 characteristics of three phase induction motor the. The torqueslip curve and speedtorque characteristic of an induction motor. E 1 we know that transformation ratio k is defined as the ratio of secondary voltage rotor voltage to that of primary voltage stator. Slip torque characteristics of an induction motor my. Torque slip characteristic of an induction motor the torque slip characteristic is represented by a rectangular hyperbola.
Induction motors are widely used in various industrial applications with different torquespeed characteristics. The motoring region of the induction machine torquespeed curve is the region of greatest interest. Fullload slip varies from less than 1 % in high hp motors to more than 56 % in minor hp motors. Torque slip characteristics of 3 phase induction motor youtube. The synchronous speed of the motor is given by equation 1. The torque developed by an asynchronous induction motor varies when the motor accelerates from zero to maximum operating speed. Record all nameplate information for the induction motor. 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.
Pdf speed drive based on torqueslip characteristic of. We can derive an equation from the equivalent circuit that allows the calculation of the torque for a given value of slip. Machines principle of operation of 3phase induction motor torque, slips characteristics speed control methods singlephase induction motor starting methods. This torque is called pull out or break down or stalling torque. The first ac commutatorfree threephase induction motors were. Figure 1 showed a plot of induction motor torque vs speed from zero to synchronous speed. First, the structure and design criteria of the proposed motor are described. 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.
The speed of the induction motor is characterized by the term known as the slip. Free acceleration characteristics, a rotor speed, b torque, c phase a current d phase b. Torque slip characteristics of 3 phase induction motor. This is seen that for a fixed value of slip, torque is equal to proportional to the square of voltage. The load on the motor has not changed, and with the external applied, or load, torque now greater than the developed torque, the motor slows down. Figure 1 induction motor torquespeed characteristic curves. For a distinctive induction motor, the pullout torque on the curve will be two hundred % of the evaluated torque at full load of the motor, and the starting torque of motor will be one fifty %. Threephase induction motor torquespeed characteristics. Torqueslip characteristics, induction motors, assignment help. An induction motor is often selected based on its linear torque speed under a changing mechanical load. For an induction motor to run steadily, it is essential that its torque should balance the applied load automaticallyas the load applied to the shaft of a motor is increased, the torque developed by the motor must go up in proportion. Torqueslip characteristics in three phase induction motor.
Derivation of the expression for the gross torque developed as a function of slip speed of induction motor sketch the above characteristics of torqueslip speed, explaining the various features derive the expression of maximum torque and the slip speed at which it occurs. The full load torque occurs at different slips when the voltage is varied. The equation of the torque is given as shown below. The maximum torque developed in an induction motor is called the pull out torque or the breakdown torque. The torquespeed characteristic is required in order to predict behavior of induction machines in electrical motor drives 1. The torquespeed curve is linear between no load and full load. An887, ac induction motor fundamentals microchip technology. Torque speed characteristics of induction motor slip. Torqueslip speed characteristics of induction motor im.
This renders the speed control of induction motors feasible over a limited range by supply voltage variation. An induction motors rotor can be either wound type or squirrelcage type. For this test, a dc generator, or dynamometer, is connected to the induction motor so. Torque slip characteristics of induction motor also known as torquespeed characteristics provide us with the information about the variation of torque with the slip. Torque slip characteristics is the graphical relationship between the torque and slip of an induction machine. All ac motors have the same basic components, a stator and rotor. In the general case, the higher the starting torque the greater the full load slip. As we have already discussed the torque of the induction motor in the topic torque equation of an induction motor. The torque slip curve for an induction motor gives us the information. 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. Pdf this letter states and proves a uniqueness theorem for the torquespeed. Thus, it passes through the point of maximum torque when r 2 sx 20. The induction motor torquespeed characteristic gives information. Determination of the torquespeed characteristic of.
This curve is called the torque speed characteristic curve. Torque slip characteristics of induction motor full guide. The equivalent circuit per phase of im, gross torque developed, torque slip. Torqueslip speed characteristics of induction motor nptel. As the load is accelerated to the fullload torque point, the current decreases to 100% fullload current at 100% fullload torque. From the above relation it is seen that, when slip s increases the torque, t also increases.
Since the configuration of the rotor slot has a great. Typical torque speed characteristics of induction motor when supplied from variable voltage at rated frequency are given in fig. 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. When the speed varies the slip vary and in contrast the torque will also vary.
Dynamometer housing is made free to rotate and connected to the weight. The torqueslip curve and speedtorque characteristic of. You should also make a dc measurement of stator winding linetoline resistance using a dmm. What is the relationship between the supply frequency number of poles and sycnchronous speed. Induction motor the starting torque is low, typically 100% to 175% of the rated torque.
This characteristic is very useful for the stability analysis of the machine. This curve is called the torquespeed characteristic curve. Also, electromagnetic torque for this region of operation of induction motor is positive as clear from the characteristics and equation 1. Torque slip characteristics of three phase induction motor. Variable voltage variable frequency vf control theory an induction motor compared to a dc motor has some major advantages such as. Finally, we show an optimized torque density for the proposed motor. But in ac motors the rotor receives electric power, not by conduction but by induction. Typically, an electric motor has at three rated torques. The slip increases increasing the rate at which the stator flux cuts the rotor conductors. This application note discusses the basics of an ac. There is a maximum possible torque that the motor cannot exceed. Ac induction motors are one of the most common types of motors used in a variety of applications due to the fact that they run off of ac voltage which is readily available at every outlet. May 09, 2020 torqueslip speed characteristics of induction motor im threephase induction motor mechanical engineering notes edurev is made by best teachers of mechanical engineering. The curve below shows the torque speed characteristic.
A high starting torque is more important for application or machines. Squirrel cage induction motors are very widely used in both fixedspeed and. At the maximum torque, the speed of the rotor is expressed by the equation shown below. The locked rotor torque or starting torque is the torque an electrical motor develops when starting at zero speed. For the immediate value of the slip, the graph changes from one form to the other. In fact, an induction motor can be treated as a rotating transformer i. To draw the torque slip characteristics of induction motor three phase following points are considered at synchronous speed n s. In this range, the rotor reactance is much smaller than the rotor resistance, so the rotor current, magnetic field, and induced torque varies linearly with slip. 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. Number of poles, frequencies and synchronous induction motor speed.
An induction motor or asynchronous motor is an ac electric motor in which the electric current. The maximum generated torque ranges from 250% to 350% of the rated torque see figure9 for torquespeed curve. The rotor of the slip ring induction motor is also cylindrical or constructed of lamination. The slip is defined as the ratio of difference of synchronous speed and actual rotor. The speed of the motor comes to zero, when the slip reaches to 1. From here we can say that these motors are not self starting unlike the case of three phase induction. What are the torqueslip characteristics of a 3phase. Ss 120 x f p 120 x 60 8 900 rpm rotor speed motor slip is known, equation 2. That is why such motors are known as induction motors. Full load torque formula for induction motor is as follows starting torque formula for induction motor the starting torque of a motor is that torque which is produce by it at start. The slip for maximum torque is independent of voltage. As the slip is less than 1, this means that the speed of rotor is less than synchronous speed and the rotor is rotating in the direction of rotating magnetic field. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. The equivalent circuit per phase of im, gross torque developed, torqueslip.
The developed torque decreases due to reduced rotor current. And the variation of the slip obtained with the variation of speed. Operating characteristics of a woundrotor slipring. Study on analysis of torqueslip characteristics of axial gap. When the speed varies the slip vary and in contrast the torque will also var y. Starting torque, from stopped, running torque at rated rpm and hp output, stall torque, when prevented from running with power applied. The load test traces the linear torque speed characteristic as the mechanical load changes. The torque will attain a maximum value, at s r 2 x 2. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Torque slip characteristics of induction motor electrical4u. This includes motoring mode, generating mode and braking mode for. Study on analysis of torqueslip characteristics of axial. Torque vs speed characteristics of induction motor torque slip characteristics of three phase induction motor electrical machines 2.
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