For reason of economy, most houses, offices and also rural areas are supplied with single phase a. What are the torqueslip characteristics of a 3phase. 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. This may be achieved by converting a singlephase supply into twophase supply through the use of an additional winding. Schrage motor operation principle and characteristics of. The single phase induction motor resembles, threephase, squirrelcage motor except that, single phase induction motor has no starting torque and some special arrangement have to be made to make it as self starting.
Torquespeed characteristics of three phase squirrel cage. Slip of a power induction motor is 2 to 3% when the motor is operated under the rated load. Running characteristics of induction motors the stators magnetic field of an induction motor revolves at the synchronous speed. The rotors magnetic field caused by this current interacts with the stators field to produce torque on the rotor. As the load is accelerated to the fullload torque point, the current decreases to 100% fullload current at 100% fullload torque. Succinctly divided in 14 chapters, the book delves into important concepts of the subject which include armature reaction and commutation. The torque slip characteristics of three phase induction motor is shown in figure a. Induction motor torquespeed characteristics figure 6. Schrage motor is essentially a combination of wound rotor induction motor and frequency convertor. There are two basic reasons for the use of singlephase motors rather than 3phase motors. The characteristics of an induction motor, the speed, current, starting torque, maximum torque, the motor losses and efficiency can all be determined from an analysis of the equivalent circuit. The above value becomes somewhat larger with small singlephase motors. After going through this module, students will be able to 1. Torque slip characteristic of an induction motor low.
Before going to the operation and characteristics of splitphase induction motor we should first understand why single phase induction motor is not selfstarting to make a singlephase induction motor selfstarting, we should somehow produce a rotating magnetic field. Thus we see there two factors that reduce torque in ac induction motors. The smoothness of the torque is important for traction applications ands the torque ripple should. This includes motoring mode, generating mode and braking mode for 0 characteristics of an induction motor, the speed, current, starting torque, maximum torque, the motor losses and efficiency can all be determined from an analysis of the equivalent circuit.
The typical base speed of the four pole induction motor varies between 1420 and 1480 rpm at 50. The importance of torqueslip characteristic in understanding motor operation is heighlighted. Torque slip characteristics of induction motor full guide. We have seen the speed torque characteristic of the machine. Ee8353 question bank electrical drives and controls. The equivalent circuits derived in the preceding section can be used to predict the performance characteristics of the induction machine. If the external controller is set at zero resistance, the motor operates almost exactly the same as the squirrelcage motor, since the rotor is shortcircuited.
This torque is called pull out or break down or stalling torque. For the immediate value of the slip, the graph changes from one form to the other. Torqueslip characteristics in three phase induction motor. Single phase induction motor double revolving field theory the threephase induction motor starting torque inversely depends on the slip this implies that a small positive slip 0. When the speed varies the slip vary and in contrast the torque will also var y. 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. Variable voltage variable frequency vf control theory. Torque slip characteristics of induction motor electrical4u. 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.
The actual fullload slip of a particular motor is dependant on the motor design. Tools, fans b normal normal normal normal general industrial c high normal normal normal loaded. 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. 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. The slip increases with the load and is normally expressed as a percentage of the synchronous speed. The rotor is separated from the stator by a small airgap which ranges from 0. Typically, the fullload slip for the squirrel cage induction motor is less than 5%. A typical design b induction motor torquespeed characteristic is as shown in figure 81, along with pertinent characteristics from table 81 labeled. This feature is one of the advantages of the hysteresis motor in contrast to a reluctance motor which must snap its load into synchronism from the induction motor torque speed character istic.
Torqueslip speed characteristics of induction motor nptel. As we have already discussed the torque of the induction motor in the topic torque equation of an induction motor. 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 speed characteristic of an induction motor torque speed characteristic is the curve plotted between the torque and the speed of the induction motor. In this paper, the magnetic field distribution in the slip state was analyzed by using frequency response analysis with the jmagdesigner ver. Torque slip characteristics of induction motor also known as torquespeed characteristics provide us with the information about the variation of torque with the slip.
The motoring region of the induction machine torquespeed curve is the region of greatest interest. Their torquespeed characteristics are the most important. The slip is defined as the ratio of difference of synchronous speed to the speed at any mechanical load to. From the above relation it is seen that, when slip s increases the torque, t also increases. The starting torque and speed characteristics of the cage induction motor of basic standard design are shown in. Since the configuration of the rotor slot has a great. Study on analysis of torqueslip characteristics of axial. The slip is defined as the ratio of difference of synchronous speed and actual rotor. Slip torque characteristics of an induction motor my. You should also make a dc measurement of stator winding linetoline resistance using a dmm. 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. Operating characteristics of a woundrotor slipring. Variation of torque and stator current with slip 3192014. Pdf principles of electrical machines book by vk mehta.
Pdf speed drive based on torqueslip characteristic of the. Speed torque characteristics of 3 phase induction motor duration. And the variation of the slip obtained with the variation of speed. Torque speed characteristics of induction motor slip. 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. 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. State the condition at which the starting toque developed in a slipring induction motor is maximum. The induction motor torque varies from zero to full load torque as the slip varies. Record all nameplate information for the induction motor.
A 3 phase induction motor has two main parts i stator and ii rotor. Figure 81 shows the motor output torque as a function of shaft speed with full rated voltage applied to the motor. However, the slip at which the maximum torque occurs changes with rotor resistance. An induction motors rotor can be either wound type or squirrelcage type. Draw the mechanical or speed torque characteristics of all type of dc motors. The maximum torque developed in an induction motor is called the pull out torque or the breakdown torque. This characteristic is very useful for the stability analysis of the machine. This includes motoring mode, generating mode and braking mode for. An887, ac induction motor fundamentals microchip technology. Torque slip characteristic of an induction motor the torque slip characteristic is represented by a rectangular hyperbola. An induction motor can therefore be made without electrical connections to the rotor. 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.
Torqueslip characteristic stability analysis for induction motor. The important performance characteristics in the steady state are the efficiency, power factor, current, starting torque, maximum or pullout torque. Torque slip characteristics of induction machine pull out torque, breakdown torque, motoring mode, generating mode, breaking mode of induction motors. Torque slip characteristics of induction motor your. B running characteristics of induction motors the stators. Various methods of speed control 3phase induction motor. 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. Torque slip characteristics of 3 phase induction motor.
Induction motors are widely used in various industrial applications with different torquespeed characteristics. Analytical approach to determine speedtorque curve of induction. Speed control of three phase induction motor electrical. Torque figure two the motor therefore develops constant torque right up to syn chronous speed, as shown in the ideal speed torque, figure 2. 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 magnetization current im flowing in the motors equivalent circuit fig. Torque slip characteristics of three phase induction motor. In this chapter, we shall focus our attention on the construction, working and characteristics of commonly used singlephase motors.
The equation of the torque is given as shown below. 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. 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. Further increases in load on the motor causes, the slip to increase still more. Unlike induction motor the primary winding of schrage motor is on the rotor. Split phase induction motor operation and characteristics. The rotor reactance at stand still x 2 remains constant. Torque slip characteristics is the graphical relationship between the torque and slip of an induction machine.
Schrage motor can be treated as an inverted poly phase induction motor. Ee8353 question bank electrical drives and controls 7. Induction motor, speedtorque curve, induction machine 1. Lastly, the expression of maximum torque developed and the slip speed at which it occurs, are derived. Thus, it passes through the point of maximum torque when r 2 sx 20. The speed of the induction motor is characterized by the term known as the slip. The slip at full load typically varies from about 6% for small motors to 2% for large motors.
Three phase supply is given to the primary with the help of 3 slip rings. Torque formula for induction motor your electrical guide. The behaviour of motor can be easily judged by sketching a curve obtained by plotting torque produced against slip of induction motor. The torque will attain a maximum value, at s r 2 x 2. 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. Vfd supplied induction motor torquespeed curve with voltage and frequency variation and constant vhz ratio. The speed control of three phase induction motor is done by stator voltage control. The torquespeed curve of the typical threephase induction motor is shown in figure 11. 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. The torque slip curve for an induction motor gives us the information about the variation of torque with the slip.
From comparison between this graph and the above characteristics of dc motors, you will find the following characteristic of induction motors. A 3 phase induction motor can be used for different applications with various speed and load requirements. The slip is defined as the ratio of the difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. The maximum value of the torque developed by an induction motor is independent of rotor resistance r 2. This paper presents load characteristics of a threephase induction motor model core calculated. The slip is defined as the ratio of difference of synchronous speed and actual rotor speed to the synchronous speed of the machine. Torquespeed characteristic of a capacitorstart capacitorrun motor. The output torque of the three phase induction motor is directly proportional to square of supply voltage for a given slip. Characteristics of induction motors nidec corporation. As this field is cut by the short circuited rotor winding, current is induced in the rotor circuit. Home operating characteristics of a woundrotor slipring induction motor fig. Performance characteristics of three phase induction motor.
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