This curve is called the torque speed characteristic curve. The equation of the torque is given as shown below. Its value is at least twice the fullload value when the motor. The proposed fea technique it is known that the determination of the torqueslip characteristic at constant current can be performed by means. And the variation of the slip obtained with the variation of speed. There is a linear relationship between the d current and the torque of the machine for a. A motordriven system consists of several components. An induction motors rotor can be either wound type or squirrelcage type. Induction motor torque speed characteristics youtube. The impactthatvoltage variations have on ac induction motorperformance austin h. Record all nameplate information for the induction motor.
Performance characteristics of induction motor under vf speed control. Figure 1 showed a plot of induction motor torque vs speed from zero to synchronous speed. Twenty ways to optimize energy efficiency in the use of induction motors electric motors convert electrical energy into mechanical energy. This characteristic is very useful for the stability analysis of the machine. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip. Torqueslip speed characteristics of induction motor nptel. Analytical approach to determine speedtorque curve of induction.
Induction motor, speedtorque curve, induction machine 1. The slip is defined as the ratio of the difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Three phase squire cage induction motor, fully enclosed. In this paper, the magnetic field distribution in the slip state was analyzed by using frequency response analysis with the jmagdesigner ver. Variable voltage variable frequency vf control theory. Figure illustrates the torque slip characteristics of an induction motor for the rated voltage.
The impactthatvoltage variations have on ac induction. At zero rotor speed relaxed condition, a unity slip is produced. Communities more files in the power electronics control community. The motoring operation of im is typically in the region of 0 influence of rotor parameters we saw earlier that the rotor resistance and reactance inxuenced the shape of the torquespeed curve. Mar 12, 2020 torqueslip speed characteristics of induction motor im threephase induction motor mechanical engineering notes edurev is made by best teachers of mechanical engineering. Torqueslip characteristic stability analysis for induction motor. The slip is defined as the ratio of difference of synchronous speed and actual rotor. This is seen that for a fixed value of slip, torque is equal to proportional to the square of voltage. 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. Torque slip characteristics electric motor electrical impedance. The rotor reactance at stand still x 2 remains constant. 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.
Torque slip characteristics of three phase induction motor. The magnetization current im flowing in the motor s equivalent circuit fig. Torquespeed characteristics of three phase squirrel cage induction motor aim to obtain the torquespeed characteristics tn r of a three phase squirrel cage induction motor using 1. It is very interesting to study the nature of torqueslip characteristics. As we have already discussed the torque of the induction motor in the topic torque equation of an induction motor. Variations in the voltage will l1ave a significant impact on the motor starting torque. Thus we see there two factors that reduce torque in ac induction motors. When the speed varies the slip vary and in contrast the torque will also var y. What are the torqueslip characteristics of a 3phase. Torque slip characteristics is the graphical relationship between the torque and slip of an induction machine. Torque slip characteristic of squirrel cage induction. Torque slip characteristics of induction motor also known as torquespeed characteristics provide us with the information about the variation of torque with the slip.
Why the rotor slots are slightly skewed in squirrel cage im. 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. Induction motor torque speed characteristics sumit maitra. For the immediate value of the slip, the graph changes from one form to the other. This file calculates the equivalent circuit of a three phase induction motor from the data of open circuit test and blocked rotor test. The curve obtained by plotting torque against slip from s 1 at start to s 0 at synchronous speed is called torque slip characteristics of the induction motor.
Create scripts with code, output, and formatted text in a single executable document. 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. What is the relation between torque, slip, and speed in. This maximum torque in an induction motor is calledpulloutor breakdowntorque. This energy is then used to drive a fan, a compressor, a pump or another rotating or oscillating part. Torque speed characteristics of induction motor slip. It is quite cumbersome to control an induction motor im because of its poor dynamic response in comparison to the dc motor drives. Induction motor torquespeed characteristics figure 6. It also calculates the thevenin equivalent circuit parameters, maximum torque induced, starting torque and slip for maximum power or torque. The magnetization current im flowing in the motors equivalent circuit fig. Sketch and explain the torque slip characteristics of the 3pahse cage and slip ring induction motors. Induction motor starting can be analyzed using electrical, mechanical, and thermal models which. 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.
Drive mode use in conjunction with performance testtorquespeed characteristics motor. It is usually designed for fixedspeed operation, larger ratings having such features as deep rotor bars to limit direct on line dol starting currents. This document is highly rated by mechanical engineering students and. The designer can vary both of these parameters, and we will explore the pros and cons of the various alternatives. Slip torque characteristics of an induction motor my. Load torque will depend on the type of load be it a pump or fan etc. Nema states when the line voltages applied to a polyphase induction motor are not equal. The maximum torque developed in an induction motor is called the pull out torque or the breakdown torque. Equivalent circuit of an induction motor and torque speed. The induction machine operates between zero speed slip 1 and synchronous speed slip 0. Thus, it passes through the point of maximum torque when r 2 sx 20. Torquespeed characteristics of three phase squirrel cage. Torque slip characteristics of induction machine pull out torque, breakdown torque, motoring mode, generating mode, breaking mode of induction motors. Since there is no slip ring in squirral cages we cannot connect resistor bank.
Torqueslip speed characteristics of induction motor im. It helps to make the motor run quietly by reducing magnetic hum and ii. Characteristics of induction motors nidec corporation. It is very interesting to study the nature of torque slip characteristics. This includes motoring mode, generating mode and braking mode for. We can derive an equation from the equivalent circuit that allows the calculation of the torque for a given value of slip. From the above relation it is seen that, when slip s increases the torque, t also increases. 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. Simulink model of three phase induction motor file. The speed of an ac motor depends on the frequency of the input power and the number of poles for which the motor is wound. Torque slip characteristic of an induction motor low. To limit the mathematics the discussion will be mainly qualitative, but it. Speed torque characteristics of 3 phase induction motor duration. As the load is accelerated to the fullload torque point, the current decreases to 100% fullload current at 100% fullload torque.
An induction motor can therefore be made without electrical connections to the rotor. The usual operating area for a motor is the speed between 90 and 100% so the torque increasing from 0 to 1 times full load torque fl. When a motor is designed in such a way that impedance of the aluminum. It finally plots torque speed characteristics of induction motor.
Torque slip characteristics free download as powerpoint presentation. From above equation greater the slip greater will be the induced e. The induction motor torque varies from zero to full load torque as the slip varies. We have seen that for a constant supply voltage, e 2 is also constant. You should also make a dc measurement of stator winding linetoline resistance using a dmm. This torque is called pull out or break down or stalling torque. Torque slip characteristics of induction motor full guide. Twenty ways to optimize energy efficiency in the use of.
From comparison between this graph and the above characteristics of dc motors, you will find the following characteristic of induction motors. Performance characteristics of three phase induction motor. Changing external resistance bank can change maximum torque point over slip. This characteristic, shown in figure 4, will be useful in. Torque slip characteristics of induction motor your. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Introduction to motor starting analysis ced engineering. Their torquespeed characteristics are the most important. 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. The curve obtained by plotting torque against slip from s 1 at start to s 0 at synchronous speed is called torqueslip characteristics of the induction motor. 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 important performance characteristics in the steady state are the efficiency, power factor, current, starting torque, maximum or pullout torque. Design of direct torque controller of induction motor dtc. Torque is the turning force through a radius with the units nm in the sisystem and the units lb ft in the imperial system the torque developed by an asynchronous induction motor varies when the motor accelerates from zero to maximum operating speed. However, the slip at which the maximum torque occurs changes with rotor resistance. The rotor bars are not parallel to the shaft but slightly skewed for the following purposes, i.
The torque will attain a maximum value, at s r 2 x 2. Torqueslip characteristics 2 2 2 2 1 2 r sx k sr t r iii as slip increases beyond fullload slip for increasing load of the motor, the torque increases and becomes maximum ats r 2x 2. Torque slip characteristics of induction motor electrical4u. The speed of the induction motor is characterized by the term known as the slip. Further increases in load on the motor causes, the slip to increase still more. Satisfactory efficiency and reasonable power factor.
Torqueslip characteristics, induction motors, assignment help. At synchronous rotor speed, a nil slip is obtained and hence no torque is produced. This simplest form of ac induction motor or asynchronous motor is the basic, universal workhorse of industry. Torqueslip characteristics in three phase induction motor. Pdf performance characteristics of induction motor under. However, these control method only valid for wound type rotor induction machine. The equivalent circuits derived in the preceding section can be used to predict the performance characteristics of the induction machine. Study on analysis of torqueslip characteristics of axial. Induction motor torque speed characteristics figure 6. The maximum value of the torque developed by an induction motor is independent of rotor resistance r 2. 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.
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