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Electric Motors and Generators
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To view this presentation, you'll need to allow Flash. Click to allow Flash After you enable Flash, refresh this page and the presentation should play. View by Category Toggle navigation. Products Sold on our sister site CrystalGraphics. Title: Electric Motors and Generators. Tags: electric generators motors. Latest Highest Rated. What is the required rotation speed? A four-pole alternator has two pole pairs.
Therefore the output frequency is twice the rotation speed. This is equivalent to 30? This is the basis of an AC generator A commutator can be used to produce a DC generator The magnetic field in an electrical machine is normally produced electrically using field coils DC motors are often similar in form to DC generators Some forms of AC generator can also be used as motors The most widely used form of AC motor is the induction motor.
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Electromagnetic Induction and AC Generators
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Discover everything Scribd has to offer, including books and audiobooks from major publishers. Start Free Trial Cancel anytime. Ppt Dc Motor. Uploaded by ptarwatkar Date uploaded Jul 17, Did you find this document useful? Is this content inappropriate? Report this Document. Description: Basic operation of DC Motor. Flag for inappropriate content. Download Now. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Harisismail Meladhil.
Abir Lovesick.Schematics and operation of different types of motor DC motors Motors and generators Alternators Back emf 'Universal' motors Build a simple motor AC motors synchronous and stepper motors Induction motors Squirrel cage motors Three phase induction motors Linear motors Homopolar motors and generators separate page.
For example, the animation at right has just one loop of wire, no bearings and a very simple geometry. Real motors use the same principles, but their geometry is usually complicated.
If you already understand the basic principles of the various types of motors, you may want to go straight to the more complex and subtle cases described in How real electric motors workby Prof John Storey. DC motors A simple DC motor has a coil of wire that can rotate in a magnetic field. The current in the coil is supplied via two brushes that make moving contact with a split ring. The coil lies in a steady magnetic field. The forces exerted on the current-carrying wires create a torque on the coil.
The two forces shown here are equal and opposite, but they are displaced vertically, so they exert a torque. The forces on the other two sides of the coil act along the same line and so exert no torque. Some use the right hand, some the left. That is the origin of the diagram shown here. The coil can also be considered as a magnetic dipole, or a little electromagnet, as indicated by the arrow SN: curl the fingers of your right hand in the direction of the current, and your thumb is the North pole.
In the sketch at right, the electromagnet formed by the coil of the rotor is represented as a permanent magnet, and the same torque North attracts South is seen to be that acting to align the central magnet. Throughout, we use blue for the North pole and red for the South. This is just a convention to make the orientation clear: there is no difference in the material at either end of the magnet, and they are usually not painted a different colour.
Note the effect of the brushes on the split ring. When the plane of the rotating coil reaches horizontal, the brushes will break contact not much is lost, because this is the point of zero torque anyway — the forces act inwards.
The angular momentum of the coil carries it past this break point and the current then flows in the opposite direction, which reverses the magnetic dipole. So, after passing the break point, the rotor continues to turn anticlockwise and starts to align in the opposite direction. In the following text, I shall largely use the 'torque on a magnet' picture, but be aware that the use of brushes or of AC current can cause the poles of the electromagnet in question to swap position when the current changes direction.Introduction : Introduction In this lecture we consider various forms of rotating electrical machines These can be divided into: generators — which convert mechanical energy into electrical energy motors — which convert electrical energy into mechanical energy Both types operate through the interaction between a magnetic field and a set of windings PowerPoint Presentation : Therefore this arrangement produces a sinusoidal output as shown below.
PowerPoint Presentation : Wires connected to the rotating coil would get twisted Therefore we use circular slip rings with sliding contacts called brushes.
A Simple DC Generator : A Simple DC Generator The alternating signal from the earlier AC generator could be converted to DC using a rectifier A more efficient approach is to replace the two slip rings with a single split slip ring called a commutator this is arranged so that connections to the coil are reversed as the voltage from the coil changes polarity hence the voltage across the brushes is of a single polarity adding additional coils produces a more constant output PowerPoint Presentation : The ripple can be further reduced by the use of a cylindrical iron core and by shaping the pole pieces this produces an approximately uniform field in the narrow air gap the arrangement of coils and core is known as the armature.
DC Generators or Dynamos : DC Generators or Dynamos Practical DC generators or dynamos can take a number of forms depending on how the magnetic field is produced can use a permanent magnet more often it is generated electrically using field coils current in the field coils can come from an external supply this is known as a separately excited generator but usually the field coils are driven from the generator output this is called a self-excited generator often use multiple poles held in place by a steel tube called the stator PowerPoint Presentation : Field coil excitation sometimes the field coils are connected in series with the armature, sometimes in parallel shunt and sometimes a combination of the two compound these different forms produce slightly different characteristics diagram here shows a shunt-wound generator.
PowerPoint Presentation : DC generator characteristics vary slightly between forms examples shown here are for a shunt-wound generator. AC Generators or Alternators : AC Generators or Alternators Alternators do not require commutation this allows a simpler construction the field coils are made to rotate while the armature windings are stationary Note : the armature windings are those that produce the output thus the large heavy armature windings are in the stator the lighter field coils are mounted on the rotor and direct current is fed to these by a set of slip rings PowerPoint Presentation : Example — see Example What is the required rotation speed?
A four-pole alternator has two pole pairs. Therefore the output frequency is twice the rotation speed. DC Motors : DC Motors When current flows in a conductor it produces a magnetic field about it - as shown in a below when the current-carrying conductor is within an externally generated magnetic field, the fields interact and a force is exerted on the conductor - as in b PowerPoint Presentation : Therefore if a conductor lies within a magnetic field: motion of the conductor produces an electric current an electric current in the conductor will generate motion The reciprocal nature of this relationship means that, for example, the DC generator above will function as a DC motor although machines designed as motors are more efficient in this role Thus the four-pole DC generator shown earlier could equally well be a four-pole DC motor.
PowerPoint Presentation : DC motor characteristics many forms — each with slightly different characteristics again can be permanent magnetor series-woundshunt-wound or compound wound figure below shows a shunt-wound DC motor. AC Motors : AC Motors AC motors can be divided into two main forms: synchronous motors induction motors High-power versions of either type invariably operate from a three-phase supplybut single-phase versions of each are also widely used — particularly in a domestic setting PowerPoint Presentation : Synchronous motors just as a DC generator can be used as a DC motor, so AC generators or alternators can be used as synchronous AC motors three phase motors use three sets of stator coils the rotating magnetic field drags the rotor around with it single phase motors require some starting mechanism torque is only produced when the rotor is in sync with the rotating magnetic field not self-starting — may be configured as an induction motor until its gets up to speed, then becomes a synchronous motor.
PowerPoint Presentation : Induction motors these are perhaps the most important form of AC motor rather than use slip rings to pass current to the field coils in the rotor, current is induced in the rotor by transformer action the stator is similar to that in a synchronous motor the rotor is simply a set of parallel conductors shorted together at either end by two conducting rings.
PowerPoint Presentation : In a three-phase induction motor the three phases produce a rotating magnetic field as in a three-phase synchronous motor a stationary conductor will see a varying magnetic field and this will induce a current current is induced in the field coils in the same way that current is induced in the secondary of a transformer this current turns the rotor into an electromagnet which is dragged around by the rotating magnetic field the rotor always goes slightly slower than the magnetic field — this is the slip of the motor.
PowerPoint Presentation : In single-phase induction motors other techniques must be used to produce the rotating magnetic field various techniques are used leading to various forms of motor such as capacitor motors shaded-pole motors such motors are inexpensive and are widely used in domestic applications.
Key Points : Key Points Electrical machines include both generators and motors Motors can usually function as generators, and vice versa Electrical machines can be divided into AC and DC forms The rotation of a coil in a uniform magnetic field produces a sinusoidal e. This is the basis of an AC generator A commutator can be used to produce a DC generator The magnetic field in an electrical machine is normally produced electrically using field coils DC motors are often similar in form to DC generators Some forms of AC generator can also be used as motors The most widely used form of AC motor is the induction motor.
Take care; there would be a relative space or relative time variation between the magnetic field and the conductor to generate this EMF.
This law directs us to focus on the most important elements of dc generator which are:. And to get a better idea of the construction of Dc generator we will imagine that we have a simple loop Dc generator with only one turn coil and one pair of a magnet. Here they still static and we need a motion; the conductor or the magnetic field must moveand we guess that there is a mechanical input caused a rotation of the coil.
If we again rotate the coil to a next right angle position, the coil will perpendicular the direction of the magnetic field, and there is no change in magnetic field strength, as a result, the current will be zero. Again; when we rotate the coil to a next right position, the coil will parallel the magnetic field direction and a maximum EMF will be induced, but with a reversed current.
When we use the commutator we deal with an open loop, in the first case the current passes through the coil and brushes segments, and in the next case the current passes reversal in the coil and also in brushes segments but it has the same direction in the load resistance, and the current is unidirectional.
After we deeply recognize working principle of Dc generator and working with commutator it leads us to ask about the construction of dc generator.
DC generator like all other machines consists of:. A stator : which is the stationary part Contains inside:.
Those are the parts of DC generators and we will explain later in details and details of details. After what we know we should deduce that DC generator can classify into many types.
Basic construction and working of a DC Generator.
Each type has its special characteristics, applications, advantages and also triples. And we will also explain intensively. And the most important in DC generator working principle of DC generator which needs a lot of space and high interest.
Follow me constantly to find what pleased you and develop your knowledge, and now we should gather advantages and disadvantages of DC generators. Unfortunately, like all other machines, it has some disadvantages. Posted By samar lashin — 23rd October ' AC motors Induction motor-types of induction motor — parts and principle. Electrical Machines construction of Dc generator full details about DC generator construction.
Author samar lashin.We have seen that when a conductor is moved in a magnetic field or when a magnet is moved near a conductor, a current flows in the conductor. The amount of current depends on:. Figure The greatest flux passes through the conductor when the plane of the conductor is perpendicular to the magnetic field lines as in Figure The number of field lines passing through the conductor decreases, as the conductor rotates until it is parallel to the magnetic field Figure If the emf induced and the current in the conductor were plotted as a function of the angle between the plane of the conductor and the magnetic field for a conductor that has a constant speed of rotation, then the induced emf and current would vary as shown in Figure The current alternates around zero and is known as an alternating current abbreviated AC.
The angle changes as a function of time so the above plots can be mapped onto the time axis as well. This can be stated mathematically as:. Faraday's Law relates induced emf to the rate of change of magnetic flux, which is the product of the magnetic field strength and the cross-sectional area the field lines pass through.
As the closed loop conductor changes orientation with respect to the magnetic field, the amount of magnetic flux through the area of the loop changes and an emf is induced in the conducting loop.
The principle of rotating a conductor in a magnetic field to generate current is used in electrical generators. A generator converts mechanical energy motion into electrical energy. The layout of a simple AC generator is shown in Figure The conductor is formed of a coil of wire, placed inside a magnetic field.
The conductor is manually rotated within the magnetic field. This generates an alternating emf. The alternating current needs to be transmitted from the conductor to the load, which is the system requiring the electrical energy to function. The load and the conductor are connected by a slip ring. A slip ring is a connector which is able to transmit electricity between rotating portions of a machine.
It is made up of a ring and brushes, one of which is stationary with respect to the other. Here, the ring attaches to the conductor and the brushes are attached to the load. Current is generated in the rotating conductor, passes into the slip rings, which rotate against the brushes.
The current is transmitted through the brushes into the load, and the system is thus powered. The direction of the current changes with every half turn of the coil. As one side of the loop moves to the other pole of the magnetic field, the current in the loop changes direction.DC Generator A dc generator is an electrical machine which converts mechanical energy into direct current electricity. This energy conversion is based on the principle of production of dynamically induced emf.
This article outlines basic construction and working of a DC generator. These basic constructional details are also valid for the construction of a DC motor.
Hence, let's call this point as construction of a DC machine instead of just 'construction of a dc generator'. The above figure shows constructional details of a simple 4-pole DC machine.
A DC machine consists of two basic parts; stator and rotor. Basic constructional parts of a DC machine are described below. Yoke: The outer frame of a dc machine is called as yoke. It is made up of cast iron or steel. It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding. Poles and pole shoes: Poles are joined to the yoke with the help of bolts or welding. They carry field winding and pole shoes are fastened to them.
Pole shoes serve two purposes; i they support field coils and ii spread out the flux in air gap uniformly. Field winding: They are usually made of copper. Field coils are former wound and placed on each pole and are connected in series.
They are wound in such a way that, when energized, they form alternate North and South poles. Armature core rotor Armature core: Armature core is the rotor of a dc machine. It is cylindrical in shape with slots to carry armature winding. The armature is built up of thin laminated circular steel disks for reducing eddy current losses. It may be provided with air ducts for the axial air flow for cooling purposes.