An887, ac induction motor fundamentals microchip technology. The electrical frequency used, typically 60 hz or 50 hz. 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. This difference in speed between rotor and stator fields is called slip and is measured in %. When the load on induction motor increases its speed decreases. The synchronous induction motor provides constant speed, large starting torque, low starting current and power factor correction.
A synchronous motor is one in which the rotor normally rotates at the same speed as the revolving field in the machine. The magnetic field created in the stator rotates at a synchronous speed ns. N s a b a s s n s s n b s s n s a b n s supplyf s s. How to calculate synchronous speed and slip of ac induction. 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. Therefore, relational expression of the synchronous speed. At one time nonselfstarting motors without the induction motor cup were manufactured. The induction motor cup outside of the bar magnet fits outside and over the tabs for selfstarting. It is logical that the least expensive, lowest maintenance type motor should be used most often.
Therefore, relational expression of the synchronous speed n s and the stator frequency f s can be written as. A segmentalrotor synchronous reluctance motor is used in a variable speed drive with currentregulated pwm control. It is the speed at which the electromotive force is produced by the alternating machine. Introduction to synchronous motor the engineering projects. Jan 11, 2019 nonexcited synchronous motors have steel rotors. The synchronous motor doesnt rely on induction current for working. This test is represented with an equivalent circuit in figure 1. The speed of induction motor is changed from both stator and rotor side. When the stator is fed with two or three phase ac supply, a rotating magnetic field rmf is produced. Introduction constant speed motors motors synchronous motors. The induction motor cannot run at synchronous speed because the slip is never zero in an induction motor. The rotor needs to be rotated at a speed near to the synchronous speed during starting.
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. Induction motors have been traditionally used as constant speed motors supplied by the ac power source. 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. Pdf difference between induction motor and synchronous motor. Speed of the synchronous motor is controlled by the frequency of the applied current. Induction motors do not run at synchronous speed, they are generally fixed speed motors. 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. Speed control of 3phase induction motor microchip technology. 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. 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. Synchronous induction motor electrical engineering. Record all nameplate information for the induction motor. Fundamental wave model of lineoperated induction machine. Oct, 2016 the difference between these two speeds is called slip and is usually given as a percentage of the synchronous speed.
The direction of rotation of a synchronous motor can be reversed by reversing. If done so, the rotor poles get magnetically coupled with the rotating stator poles, and thus the rotor starts rotating at the synchronous speed. 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. The operating speed of a synchronous speed is where n rotor speed, rps f n rps p. 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. Introduction constant speed motors motors synchronous. Calculate i the synchronous speed ii the rotor speed, when slip. Synchronous and induction motors synchronous motor applications learning objectives 1490 electrical technology 38. There are two basic reasons for the use of singlephase motors rather than 3phase motors. To reduce the speed beyond the gear ratio in the table, attach a decimal gearhead of gear ratio 10. 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.
The rotating magnetic field produced in the stator will create flux in the rotor, hence causing the rotor to rotate. The speed of the motor, starting and operation, the efficiency of both the motors, its cost, usage, and applications. In these motors, unlike induction motor, multiphase ac electromagnets are present on the stator, which produces a rotating magnetic field. 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. In that case, the permissible torques are as follows. Learn more about working of a synchronous motor here. Depending on motor design, the actual mechanical speed may be equivalent synchronous motor or slightly smaller asynchronous motor. 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. 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. Whereas a synchronous motors ns at the same rate as the stator field, an induction. Synchronous speed is directly proportional to the ratio of supply frequency and number of poles in the motor.
As you might guess, a synchronous motor has a rotor that rotates at the same rate as the synchronous speed. Synchronous motor always runs at a speed equal to its synchronous speed. The synchronous speed is given by the usual relation n s 120 f p. In this article, i will share the introduction to synchronous motor with you guys. But the rotor turns at the same speed and in synch with the stator rotating magnetic field. In operation, the rotor is magnetized with the required magnetic poles in a manner analogous to that of an induction motor. Squirrel cage induction motor is generally operating at a constant speed. The rotor poles connect to each other and move at the same speed hence the name synchronous motor. The synchronous speed is given by the relation shown below. Due to the lag between the flux current in the rotor. Rotating speed rpm power mw synchronous motors synchronous motors are best suited for very high power at lower speeds. A segmentalrotor synchronous reluctance motor is used in a variablespeed drive with currentregulated pwm control. Synchronous speed an overview sciencedirect topics. You should also make a dc measurement of stator winding linetoline resistance using a dmm.
Synchronous motor multiple choice questions mcq and answers. A 3 phase induction motor can be used for different applications with various speed and load requirements. Free download induction motor seminar ppt, pdf report. Synchronous speed is equal to 120 times the frequency fac, divided by the number of motor poles p. In other words, rotor rotates at the synchronous speed unlike induction motor, which we have discussed in introduction to induction motor. The synchronous motor either run at synchronous speed or it will not run at all.
Speed control of induction motor detailed explanation. The low speed torque capability is compared with those of an induction motor, a. Additionally, the synchronous motor does not rely on current induction to produce the rotors magnetic field. The lowspeed torque capability is compared with those of an induction motor, a. For reason of economy, most houses, offices and also rural areas are supplied with single phase a. The rotor in an induction motor can not turn at the synchronous speed. Induction motor seminar ppt, pdf report study mafia. So in this article, we will discuss the total concept of what is synchronous speed, what is slip in induction motor, etc. Equation 3 states that induction motor synchronous speed is directly.
Pdf variable speed induction starting synchronous motor driving. The slip of an ac motor is a key factor and is necessary to produce torque. A 3phase synchronous motor as shown in the figure below generates an electrically rotating field in the stator. 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. 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. In a motor, synchronous speed is the speed at which the magnetic field rotates. Synchronous motor is the type of motor in which the rotating speed of rotor is same as the rotating speed of magnetic field.
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. 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. Synchronous motor multiple choice questions and answers. The speed of a synchronous motor can be calculated as. Now the question is arise, why slip is never zero in an induction motor. 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.
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. However, recently, it has been increasingly used as variable speed motors driven by an inverter. Speed of an induction motor the magnetic field created in the stator rotates at a synchronous speed n s. An induction motors rotor can be either wound type or squirrelcage type.
The difference between these two speeds is called slip and is usually given as a percentage of the synchronous speed. Difference between synchronous and induction motor. If the load increased the speed of the induction motor decreases. The speed control of three phase induction motor from stator side are further classified as. Difference between synchronous motor and induction motor. Considerable over lap exists to allow a choice, but the induction motor usually has the price advantage in the overlap area. 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. 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 speed of a synchronous motor is determined by the following formula. 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. The basic idea of an electric motor is to generate two magnetic fields. 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.
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. An induction motor can therefore be made without electrical connections to the rotor. Synchronous speed is nothing but the speed of rotation of magnetic field produced by the stator of induction motor. Pdf the applications of induction motors in various fields are. 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. The rotor will constantly be turning to align its magnetic field with that of the stator field. Reluctance motors have approximately one third the hp rating they would have as. Synchronous motors will run at synchronous speed in accordance with the formula. Whereas a synchronous motor s ns at the same rate as the stator field, an induction.
Speed control of three phase induction motor electrical4u. In this we are going to see the main difference between synchronous motor and induction motors. The relationship to calculate the ss of an induction motor is. The 3phase set of currents, each of equal magnitude and with a phase. Synchronous motors and induction motors are the most widely used types of ac motor. The ss is a function of the frequency of the power source and the number of poles pole pairs in the motor. In a synchronous electric motor, the rotation of the shaft is synchronized with the frequency of the supply current. 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. Synchronous speed the synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. The speed of the rotor magnetic field in an induction motor lags slightly behind the synchronous speed of the changing stator magnetic field. The synchronous speed for an electric induction motor is determined by.
Induction motor always operates at lagging power factor. The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. Stator poles rotate at the synchronous speed ns when fed with a three phase supply. Differences between synchronous motor and induction motor. Abdelwanis and others published variable speed induction starting synchronous motor driving centrifugal.
Induction motor induction motor always run less than synchronous speed. Cage induction machines institut fur elektrische energiewandlung. Mar 17, 2017 induction motor induction motor always run less than synchronous speed. Why induction motor cannot run at synchronous speed slip.
A synchronous motor has a special rotor construction that lets it rotate at the same speed that is, in synchronization with the stator field. Whats the difference between asynchronous and synchronous. Synchronous motor multiple choice questions mcq and. Difference between induction and synchronous motor is explained with the help of various factors, like the type of excitation used for the machine. The induction motor always runs at speed less than its synchronous speed. In industries mechanical loads should not only be driven but should also be driven at desired speed. The synchronous motor rotor also has a squirrelcage winding, known as an amortisseur winding, which produces torque for motor starting. Machine will rotate at almost a synchronous speed, which makes slip nearly zero. Slip rings and brushes are used to conduct current to the rotor.
Difference between induction motor and synchronous motor. What is the meaning of synchronous speed in motors. The splitphase motor is also known as an induction startinduction run motor. 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 does not require any extra dc excitation source. Generally, it is known as the asynchronous motor because its running speed is less than its synchronous speed. The speed is calculated by dividing the motors synchronous speed 60 hz. The above equation 1 shows that the rotor speed n bears a constant relationship with. This formula is used to calculate speed of rotating magnetic fieldrmf or synchronous speednsof induction motorz f represents. 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.
400 1207 1526 432 997 747 468 344 479 799 1301 469 246 779 78 26 660 587 1323 1663 109 508 744 384 1658 462 207 433 558 360 832 591 1197 594 540