The synchronous motor doesnt rely on induction current for working. The speed of a synchronous motor is determined by the following formula. The basic idea of an electric motor is to generate two magnetic fields. Speed of an induction motor the magnetic field created in the stator rotates at a synchronous speed n s. Abdelwanis and others published variable speed induction starting synchronous motor driving centrifugal. Jan 11, 2019 nonexcited synchronous motors have steel rotors. Synchronous speed the synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. In a motor, synchronous speed is the speed at which the magnetic field rotates.
So in this article, we will discuss the total concept of what is synchronous speed, what is slip in induction motor, etc. For reason of economy, most houses, offices and also rural areas are supplied with single phase a. Induction motor always operates at lagging power factor. Machine will rotate at almost a synchronous speed, which makes slip nearly zero. The synchronous motor rotor also has a squirrelcage winding, known as an amortisseur winding, which produces torque for motor starting. Squirrel cage induction motor is generally operating at a constant speed. In this we are going to see the main difference between synchronous motor and induction motors. 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. Difference between induction motor and synchronous motor. Synchronous motors and induction motors are the most widely used types of ac motor.
The rotor needs to be rotated at a speed near to the synchronous speed during starting. Singlephase induction motor threephase induction motor singlephase induction motor there are probably more singlephase ac induction motors in use today than the total of all the other types put together. Reluctance motors have approximately one third the hp rating they would have as. If the load increased the speed of the induction motor decreases. Cage induction machines institut fur elektrische energiewandlung. When the load on induction motor increases its speed decreases. An induction motor can therefore be made without electrical connections to the rotor. In this article, i will share the introduction to synchronous motor with you guys. What is the meaning of synchronous speed in motors. An induction motor can be defined as the ac electric motor device in which a power source fed by the alternating current with the help of a primary winding. Why induction motor cannot run at synchronous speed slip. Principle of operation of induction motor in both induction and synchronous motors, the ac power supplied to the motor s stator creates a magnetic field that rotates in time with the ac oscillations. Speed control of induction motor detailed explanation. The speed of a synchronous motor can be calculated as.
Synchronous speed is nothing but the speed of rotation of magnetic field produced by the stator of induction motor. Free download induction motor seminar ppt, pdf report. Pdf variable speed induction starting synchronous motor driving. Depending on motor design, the actual mechanical speed may be equivalent synchronous motor or slightly smaller asynchronous motor.
Synchronous motor multiple choice questions and answers. Difference between induction and synchronous motor is explained with the help of various factors, like the type of excitation used for the machine. Speed of the synchronous motor is controlled by the frequency of the applied current. A segmentalrotor synchronous reluctance motor is used in a variable speed drive with currentregulated pwm control. The speed of the motor, starting and operation, the efficiency of both the motors, its cost, usage, and applications. Principle of operation of induction motor in both induction and synchronous motors, the ac power supplied to the motors stator creates a magnetic field that rotates in time with the ac oscillations. Synchronous induction motor electrical engineering. The lowspeed torque capability is compared with those of an induction motor, a. This formula is used to calculate speed of rotating magnetic fieldrmf or synchronous speednsof induction motorz f represents. Synchronous motor multiple choice questions mcq and. The rotor will constantly be turning to align its magnetic field with that of the stator field. A segmentalrotor synchronous reluctance motor is used in a variablespeed drive with currentregulated pwm control.
A 3phase synchronous motor as shown in the figure below generates an electrically rotating field in the stator. To reduce the speed beyond the gear ratio in the table, attach a decimal gearhead of gear ratio 10. The synchronous speed is given by the relation shown below. Synchronous motor multiple choice questions mcq and answers.
Synchronous speed is directly proportinal to frequency,similar ti induction motors constant flux operation below base speed is achiecved by operating the synchronous motor with constant v f ratio. In these motors, unlike induction motor, multiphase ac electromagnets are present on the stator, which produces a rotating magnetic field. The induction motor cannot run at synchronous speed because the slip is never zero in an induction motor. There are two basic reasons for the use of singlephase motors rather than 3phase motors. In fact, a given synchronous machine may be used, at least theoretically, as an alternator, when driven mechanically or as a motor, when driven electrically, just as in the case of d. The magnetic field created in the stator rotates at a synchronous speed ns. In that case, the permissible torques are as follows. Synchronous speed is equal to 120 times the frequency fac, divided by the number of motor poles p. The speed is calculated by dividing the motors synchronous speed 60 hz. Mar 17, 2017 induction motor induction motor always run less than synchronous speed. The synchronous speed of the induction motor is controlled by changing the stator frequency because it rotates synchronously with the rotating magnetic field rotating at the frequency of the power source.
Additionally, the synchronous motor does not rely on current induction to produce the rotors magnetic field. Nov 03, 2019 synchronous speed is the speed of rotation of the magnetic field in a rotary machine, and it depends upon the frequency and number poles of the machine. Induction motor seminar ppt, pdf report study mafia. Calculate i the synchronous speed ii the rotor speed, when slip. Synchronous motor always runs at a speed equal to its synchronous speed. Synchronous motors are rotating the speed of the rotating magnetic field, the speed is constant, it has only one speed which means the speed if the motor always synchronized with supply frequency. Actually the motor starts as an induction motor and after it has reached its maximum speed as an induction motor, the reluctance torque pulls its rotor into step with the revolving field, motor now runs as synchronous motor by virtue of its saliency. Synchronous motors will run at synchronous speed in accordance with the formula. Induction motor does not require any extra dc excitation source. The above equation 1 shows that the rotor speed n bears a constant relationship with.
Differences between synchronous motor and induction motor. Synchronous and asynchronous synchronousspeedof an ac motor the speed of the rotating magnetic field is referred to as the synchronous speed ns of the motor. If done so, the rotor poles get magnetically coupled with the rotating stator poles, and thus the rotor starts rotating at the synchronous speed. 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. Synchronous motor is the type of motor in which the rotating speed of rotor is same as the rotating speed of magnetic field. When the stator is fed with two or three phase ac supply, a rotating magnetic field rmf is produced. A 3 phase induction motor can be used for different applications with various speed and load requirements.
Due to the lag between the flux current in the rotor. Introduction constant speed motors motors synchronous motors. Synchronous speed the speed with which the stator magnetic field rotates, which will determine the speed of the rotor, is called the synchronous speed ss. This test is represented with an equivalent circuit in figure 1. The induction motor, on the other hand, requires slip to induce current in the rotor winding, which means that the rotor must rotate slightly slower than the ac current alternations. It is logical that the least expensive, lowest maintenance type motor should be used most often. Synchronous speed is directly proportional to the ratio of supply frequency and number of poles in the motor. In both induction and synchronous motors, the ac power supplied to the motor s stator creates a magnetic field that rotates in synchronism with the ac oscillations. The induction motor always runs at speed less than its synchronous speed. Stator poles rotate at the synchronous speed ns when fed with a three phase supply. Considerable over lap exists to allow a choice, but the induction motor usually has the price advantage in the overlap area. This difference in speed between rotor and stator fields is called slip and is measured in %.
Whereas a synchronous motors ns at the same rate as the stator field, an induction. The stator is similar to that of an induction machine consisting of a cylindrical iron frame with windings, usually threephase, located in slots around the inner periphery. Induction motors have been traditionally used as constant speed motors supplied by the ac power source. The direction of rotation of a synchronous motor can be reversed by reversing. But the rotor turns at the same speed and in synch with the stator rotating magnetic field. At one time nonselfstarting motors without the induction motor cup were manufactured. The difference between these two speeds is called slip and is usually given as a percentage of the synchronous speed. The operating speed of a synchronous speed is where n rotor speed, rps f n rps p. Slip rings and brushes are used to conduct current to the rotor. The speed of the rotor magnetic field in an induction motor lags slightly behind the synchronous speed of the changing stator magnetic field. The rotor in an induction motor can not turn at the synchronous speed.
The synchronous speed is given by the usual relation n s 120 f p. In industries mechanical loads should not only be driven but should also be driven at desired speed. Equation 3 states that induction motor synchronous speed is directly. Therefore, relational expression of the synchronous speed n s and the stator frequency f s can be written as. The low speed torque capability is compared with those of an induction motor, a. An887, ac induction motor fundamentals microchip technology. Rotating speed rpm power mw synchronous motors synchronous motors are best suited for very high power at lower speeds. As we know the speed of induction motor, torque of induction motor, so, the speed of induction motor can be changed by changing synchronous speed or by changing the slip of induction motor and then parameter r2 and x2 are changed then torque remain constant and change in slip is affected in speed control. Whats the difference between asynchronous and synchronous.
Generally, it is known as the asynchronous motor because its running speed is less than its synchronous speed. It is the speed at which the electromotive force is produced by the alternating machine. The rotating magnetic field produced in the stator will create flux in the rotor, hence causing the rotor to rotate. Starting a synchronous motor a synchronous motor can not start by itself the motor is equipped with a squirrel case winding so as to start as an induction motor during starting, the dc field winding is short circuited when the motor has accelerated close to synchronous speed, the dc excitation is then applied to produce the. Fundamental wave model of lineoperated induction machine. Where, e 2 is the rotor emf n s is the synchronous speed r 2 is the rotor resistance x 2 is the rotor inductive reactance. In other words, rotor rotates at the synchronous speed unlike induction motor, which we have discussed in introduction to induction motor. Pdf difference between induction motor and synchronous motor. The synchronous speed for an electric induction motor is determined by. The splitphase motor is also known as an induction startinduction run motor. Introduction to synchronous motor the engineering projects. In operation, the rotor is magnetized with the required magnetic poles in a manner analogous to that of an induction motor. A synchronous motor is one in which the rotor normally rotates at the same speed as the revolving field in the machine. A synchronous motor has a special rotor construction that lets it rotate at the same speed that is, in synchronization with the stator field.
You should also make a dc measurement of stator winding linetoline resistance using a dmm. N s a b a s s n s s n b s s n s a b n s supplyf s s. As you might guess, a synchronous motor has a rotor that rotates at the same rate as the synchronous speed. The speed of induction motor is changed from both stator and rotor side. The slip of an ac motor is a key factor and is necessary to produce torque. Speed control of 3phase induction motor microchip technology. Here rotor is of a permanent magnet which gets synced with the rotating magnetic field and rotates in synchronous to the frequency of current applied to it. The speed control of three phase induction motor from stator side are further classified as.
The relationship to calculate the ss of an induction motor is. This type of motor starts and comes up near synchronous speed as an induction motor, then pulls into synchronism and runs at synchronous speed as a reluctance motor. The electrical frequency used, typically 60 hz or 50 hz. Synchronous and induction motors synchronous motor applications learning objectives 1490 electrical technology 38. In this page you can learn various important synchronous motor multiple choice questions answers, synchronous motor mcq,sloved synchronous motor objective questions answers, synchronous motor mcq pdf etc. Therefore, relational expression of the synchronous speed. However, recently, it has been increasingly used as variable speed motors driven by an inverter. Whereas a synchronous motor s rotor turns at the same rate as the stator field, an induction motor s rotor rotates at a somewhat slower speed than the stator field. The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. An induction motor is an ac electric motor in which the electric current in the rotor is produced by electromagnetic induction from the magnetic field of the stator winding. The synchronous motor either run at synchronous speed or it will not run at all. Difference between induction motor and synchronous motor difference between induction and synchronous motor is explained with the help of various factors, like the type of excitation used for the machine.
The 3phase set of currents, each of equal magnitude and with a phase. Pdf the applications of induction motors in various fields are. The induction motor cup outside of the bar magnet fits outside and over the tabs for selfstarting. The synchronous induction motor provides constant speed, large starting torque, low starting current and power factor correction. Synchronous speed an overview sciencedirect topics. Dec 17, 2019 where, e 2 is the rotor emf n s is the synchronous speed r 2 is the rotor resistance x 2 is the rotor inductive reactance. Now the question is arise, why slip is never zero in an induction motor. An induction motors rotor can be either wound type or squirrelcage type.
Oct, 2016 the difference between these two speeds is called slip and is usually given as a percentage of the synchronous speed. Induction motor induction motor always run less than synchronous speed. Difference between synchronous and induction motor. Induction motors do not run at synchronous speed, they are generally fixed speed motors. Introduction constant speed motors motors synchronous. The rotor poles connect to each other and move at the same speed hence the name synchronous motor.
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