The motor which works on the principle of electromagnetic induction is known as the induction motor. When we connect the primary winding, or the stator to a 3 phase ac source, it establishes rotating magnetic field which rotates at the synchronous speed. 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. How is a rotating magnetic field is produced in a three phase. Production of rotating magnetic fields in polyphase a. The three phase squirrel cage ac induction motor is the most widely used 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. Working principle of an induction motor the motor which works on the principle of electromagnetic induction is known as the induction motor. Stator frame it is the outer most part of the three phase induction motor. This rotating field induces currents in the rotor by electromagnetic induction. How is a rotating magnetic field is produced in a three.
Concept of rotating magnetic field electrical concepts. We can note variation of the induced current in squirrel cage bars. The rotating magnetic field is produced by the threephase current of the stator in the actual threephase induction motor. Figure 44, views ac show the individual windings for each phase. Ideally, the rotation changes direction at a constant angular rate. The rotor will constantly be turning to align its magnetic field with that of the stator field. It can be replaced by permanent magnets in a permanent magnet synchronous motor. An induction motors rotor can be either wound type or squirrelcage type. This field is such that its poles do no remain in a fixed position o. In three phase induction motors such a rotating magnetic field is produced by supplying currents to a set of three stationary windings, with the help of three phase a. The magnetic rotating field rmf is the basis for the threephase motors whether synchronous or asynchronous induction motors. Describe the production of a rotating magnetic field.
Working principle of a single phase induction motor javatpoint. This induces an electric field in a coil or squirrel cage to drive a rotor. In a motor, on the other hand, the rotational motional voltage generated in the armature opposes the applied voltage. Threephase rotating fields the threephase induction motor also operates on the principle of a rotating magnetic field. A 3phase induction motor uses current delivered in three phases in a sequence into the coils of a stator to create a rotating magnetic field.
These are also called as asynchronous motors, because an induction motor always runs at a speed lower than synchronous speed. What is the operating principle of a 3 phase induction motor. 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. Using a 60 hz power supply, this process will repeat 60 times per second. Thus, the description of the rotating magnetic field given thus far applies to both motor and generator action in ac machines. The rotating magnetic field the basic idea of an electric motor is to generate two magnetic fields. Working principle of an induction motor circuit globe. This magnetomechanical attraction creates a force which will drive the rotor to follow the rotating magnetic field in a synchronous manner. Pdf the study of influence of a rotating magnetic field. Nov 27, 2019 working of three phase induction motor production of rotating magnetic field. Production of a rotating magnetic field the stator of an induction motor consists of a number of overlapping windings offset by an electrical angle of 120. Rotating magnetic field eidept, srmcem, lucknow 1 2 introduction rotating magnetic field can be defined as field or flux having constant amplitude but whose axis rotates in a plane at a certain speed. How is rotating magnetic field produced in a synchronous. The three phase induction motors are simple in construction, rugged, low cost and easy to maintain.
The difference between the stator synchronous speed and rotor speeds is called the slip. A rotating magnetic field is a very interesting concept. The study of influence of a rotating magnetic field on mixing efficiency article pdf available in chemical engineering and processing 112 december 2016 with 300 reads how we measure reads. Speed is important to the rotating magnetic field of an ac motor. Dec 05, 2014 the working of an induction motor a 3phase ac current passing through a stator winding produces a rotating magnetic field. Three phase induction motor concept of rotating magnetic field. May 15, 2018 in this article, we will try to understand the theory behind the production of rotating magnetic field. May 09, 2017 the magnetic rotating field rmf is the basis for the threephase motors whether synchronous or asynchronous induction motors. The production of rotating magnetic field in 3 phase supply is very interesting.
The difference in speed between rotor, the synchronous speed and the rotating magnetic field is. Nonuniform magnetic field produces a nonuniform torque which makes. However, the concept of rotating magnetic field and its production can be taught as an independent topic without reference to any. Permanent magnet rotating in a space produces a rotating magnetic field. The rotor bars and endrings are reminiscent of the rotating cages used in bygone days to exercise small rodents or rather to amuse their human captors. A magnetic field in a stator can be made to rotate electrically, around and around. Consider a wheel which can rotate and is fixed on an axle. Nov 29, 2017 three phase induction motor concept of rotating magnetic field.
Production of rotating magnetic field in polyphase stator. Because both the rotor and stator iron surfaces are smooth apart from the regular slotting, and are separated by a small air gap, the flux produced by the stator windings crosses the air gap radially. In this article, we will try to understand the theory behind the production of rotating magnetic field. Sensorless field oriented control of 3phase induction. When we apply a threephase supply to a threephase distributed winding of a rotating machine, a rotating magnetic field is produced which rotates in synchronous speed. P number of poles for more details about rotating magnetic field, read production of rotating magnetic field this rotating field passes through the air gap and cuts the rotor conductors, which are stationary. The induction motor rotates due to the rotating magnetic field in 3 phase induction motor, which is produced by the stator winding in the air gap between in the stator and the rotor. The rotation of the magnetic field in an induction motor has the advantage that no electrical connections need to be made to the rotor. When a 3phase winding is energized from a 3phase supply, a rotating magnetic field is produced. The direction of the rotating magnetic field in synchronous machines is always from the axis of the leading phase of the three phase winding towards the lagging phase of the winding.
The stator has a three phase stationary winding which can be either star connected or delta connected. The n pole of the rotor will move toward the s pole of the magnetic field of the stator, and vice versa. In an induction motor the ladder is closed upon itself to form a squirrelcage fig. Jun 06, 20 the n pole of the rotor will move toward the s pole of the magnetic field of the stator, and vice versa. Understanding the rotating magnetic field by eric p. The following discussion shows how the stator windings can be connected to a threephase ac input and have a resultant magnetic field that rotates. The field is produced by the 3phase currents that flow in the stator windings. For that, we will first imagine one stator of an electric motor where threephase winding is physically distributed in the stator core in such a manner that winding of each phase is separated from other by 120 o in space. Hence the magnetic flux is said to rotate at synchronous speed. There basically 2 types of induction motor depending upon the type. If you have any doubt, please write in comment box. Working principle of a single phase induction motor. When a motor is designed in such a way that impedance of the aluminum conductor of the rotor is reduced, its efficiency is increased in a highspeed range. In fact, an induction motor can be treated as a rotating transformer i.
Synchronous speed means the speed of the rotating magnetic field in the stator. Thus revolving field is a key to the operation of the induction motor. Induction motors are the most commonly used motors in many applications. Rotating magnetic field in 3 phase induction motor your. The electromagnetic induction is the phenomenon in which the electromotive force induces across the electrical conductor when it is placed in a rotating magnetic field. In an induction motor, when ac supply is given to the the stator, magnetic flux is produced which is revolving at synchronous speed. Review dc machines have been studied where a permanent magnetic field is established and a rotor is made to turn, when supplied by dc current a commutator is required to achieve continuous rotation of the dc motor there are 2 common types of dc. The stator and rotor are two essential parts of the motor. Whenever the ac supply is connected to the stator windings, line currents i r, i y, and i b start flowing. These currents produce the rotor magnetic field, which interacts with the stator magnetic field, and produces torque, which is the useful mechanical output of the machine. Rotating magnetic fields the principle of rotating magnetic fields is the key to the operation of most ac motors. A portion of rotating magnetic field in a threephase induction motor. Elemental principles an examination of the rudimentary interaction between inductance coils and field magnets will provide some insight into the principles behind the rotary magnetic field.
The stator of the motor consists of overlapping winding offset by an electrical angle of 120 o. And on the other hand, when designed to have a high impedance, the motor has an increased amount of torque. The speed of the rotating magnetic field is the same as the speed of the alternator that is supplying power to the motor if the two have the same number of poles. P number of poles for more details about rotating magnetic field, read production of rotating magnetic field.
Rotating magnetic field an overview sciencedirect topics. When the primary winding or stator is connected to a 3 phase a. The absence of any means for making direct electrical connection to the rotor underlines the fact that in the induction motor the rotor currents are induced by the airgap weld. Hope the concept of rotating magnetic field and its production in three phase electrical machine like induction motor is clear. Introduction the topic, rotating magnetic field, is taught generally just before the chapter on induction motors is taken up for teaching. Consequently, the rotor cannot reach the synchronous speed. Jan 05, 2016 the rotor bars and endrings are reminiscent of the rotating cages used in bygone days to exercise small rodents or rather to amuse their human captors.
Characteristics of induction motors nidec corporation. Apr 23, 2010 how rotating field is produced in induction motor. When the primary winding or stator is connected to a three phase alternating current supply, it establishes a rotating magnetic field which rotates at a synchronous speed. This rotating field passes through the air gap and cuts the rotor conductors, which are stationary. Working principle of a single phase induction motor production of rotating field. Working principle of a threephase induction motor rotating magnetic speed. On the periphery of the wheel, magnets have been fixedpierced of say n poles from all side.
Working of three phase induction motor production of rotating magnetic field. So rotating magnetic field rotates from axis of 1 to axis of 2 and then to axis of 3 i. The fundamental principle behind the production of the rotary magnetic field serves as the. That is why such motors are known as induction motors. A rotating magnetic field is a magnetic field that has moving polarities in which its opposite poles rotate about a central point or axis. The threephase induction motor also operates on the principle of a rotating magnetic field. The threephase windings of the inner stator are spaced 120 electrical degrees apart.
The working of an induction motor a 3phase ac current passing through a stator winding produces a rotating magnetic field. The rotating magnetic field can be defined as the field or flux having constant amplitude but whose axis is continuously rotating in a plane with a certain speed. This is a key principle in the operation of the alternatingcurrent motor rotating magnetic fields are often utilized for electromechanical applications such as induction motors and. It will now be shown that when threephase windings displaced in space by 120 0, are fed by threephase current displaced in time by 120 0, they produce a resultant magnetic flux which rotates in space as if actual magnetic poles were being rotated mechanically. Consider two winding a and b so displaced that they produce magnetic field 90 apart in space. Consider a simple electromechanical device consisting of a piece of iron with a copper loop. This post will explain you in brief about production of rotating magnetic flux for 2 phase as well as 3 phase supply. Production of rotating magnetic field studyelectrical. Aug 19, 2018 thus, the rotating magnetic field revolves with a speed of 120fp r.
Sensored field oriented control of 3phase induction motors. The rotating stator magnetic field induces currents in the short circuited rotor. Both synchronous and induction types of motors rely on rotating magnetic fields in their stators to cause their rotors to turn. Induction motors derive their name from the way the rotor magnetic field is created. A permanent magnet in such a field will rotate so as to maintain its alignment with the external field. 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. Single phase induction motor double revolving field theory the pulsating filed is divided a forward and reverse rotating field motor is started in the direction of forward rotating field this generates small 5% positive slip reverse rotating field generates a larger 1.
793 448 987 1247 1153 1443 131 107 372 402 825 1390 786 280 1494 391 1163 354 579 20 1225 775 975 1400 1347 1252 123 586 1240 1055 634 303 1255 436 698 871 1420