Universal motors are generic ac motors that are operated on both alternate current and direct current sources. To understand how these motors operate, a knowledge of the basic theory of operation of ac motors is necessary. 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. An electrical motor is an electromechanical device which converts electrical energy into mechanical energy. Mechanical energy what is an electric motor an electric motor is a device converting electrical energy into mechanical energy usually a torque. The dc can be considered a particular case of the general ac, with frequency equal to zero. Synchronous and asynchronous alternating current motors theacmsare simplier instructure andmore economicthandcms. This electric motor control circuit training software is quite detailed. Mostafa elshahed objectives learn a brief history of the electrical power systems construction. Ac motors are used worldwide in many applications to transform electrical energy into mechanical energy. Modelling and control of a hydraulic servo system motor basics. The smaller physical size and lower initial cost of a vfd system are additional advantages.
Brushless motors overview there are different types of brushless motors. To explain the details of why this is so, a bit of background knowledge about ac. Ac waveform and ac circuit theory ac sinusoidal waveforms are created by rotating a coil within a magnetic field and alternating voltages and currents form the basis of ac theory direct current or d. The two most widely used types of ac motors are induction motors and synchronous motors. An engineering guide to ac and dc motor designs and operation. Module 6 dc motors this module describes the types of dc motors and includes discussions of speed control, applications, and load characteristics.
Induction motors in practice what controls the speed of an ac motor. The frequency of an alternated circuit is measured by the number of times the. Synchronous ac motors operate with zero slip, which is what primarily distinguishes them from induction motors. The rotor magnetic field may be produced by permanent magnets, reluctance. We not only talk about different type of motors but we also see how different motors work under different conditions. The types of motors can be classified by the performance, usage environmental condition, applications, etc.
Other types of variable speed control do not afford this possibility. Ac motors are electric motors driven by alternating current ac. Basic ac theory i i direct current dc alternating current ac i i figure 1. Simple and rugged design, lowcost, low maintenance and direct connection to an ac power source are the main advantages of ac induction motors.
Although servo motors are not a specific class of motor, they are intended and designed to use in motion control applications which require high accuracy positioning, quick reversing and exceptional performance. Ac induction motors how ac motors work explain that stuff. The rotor and stator are each connected from a different power supply, this gives another degree of freedom for controlling the motor over the shunt. Doehdbk10192 june 1992 doe fundamentals handbook electrical science volume 3 of 4 u. Ac induction motors are the most common motors used in industrial motion control systems, as well as in main powered home appliances. Ac motors ac motors are used worldwide in many applications to transform electrical energy into mechanical energy. Ac induction motor speed control so what can we do to control the speed of an ac induction motor. Ac is used to deliver power to houses, office buildings, etc. Ac motor theory this worksheet and all related files are. Solenoids, timers, sensors, relays, troubleshooting, even an introduction to plcs is included. Introduction to ac motors ac motors electronics textbook. And, the stepper motor, a digital version of the motor, is driven by alternating current square waves, again, generated by solidstate circuitry.
Also ac series motor is a modified dc series motor what does this mean. The principle of an ac motor is that electric current is applied to electromagnets, creating a rotating magnetic field to convert electrical energy to rotation mechanical energy. Motors, generators, and transformers are similar in that their basic principle of operation involves induction. An887, ac induction motor fundamentals microchip technology. Target motor theory 3phase ac motor control with vhz speed closed loop, rev. Before we discuss these modifications, here it is essential to discuss what is the need and where do we need to do modifications. There are many types of ac motors, but this course focuses on threephase induction motors, the most common type of motor used in industrial applications. As a result, the voltage level also reverses along with the current. Principle of operation universal motors a universal motor is a singlephase series motor, which is able to run on either alternating current ac or direct current dc and the characteristics are similar for both ac and dc. Principle of ac servo motor 3 design of motor 2 stator stator is composed of the core and winding which generates torque. Motor speed relationship the synchronous speed of an ac motor is the speed of the rotating magnetic field set up by the stator winding synchronous speed rpm 120 x frequency divided by the number of poles.
Volume 3 of 4 module 7 basic ac theory this module describes the basic concepts of alternating current ac electrical circuits and discusses the associated terminology. Ac motors ac motor theory ac motor theory ac motors are widely used to drive machinery for a wide variety of applications. In fact, ac and dc motor designs are very similar to their generator counterparts identical for the sake of this tutorial, the ac motor being dependent upon the reversing magnetic. Why is one called synchronous and the other called induction. This article will serve as a comprehensive guide for articles related to ac and dc motors. The basic idea of an electric motor is to generate two magnetic fields. In theory, a single vfd has the capability to control multiple motors. Basic ac electrical generators 1 introduction faradays law.
Alternating current ac alternating current describes the flow of charge that changes direction periodically. Ac alternating current reverses poles of electromagnetic coil 120 times per sec 60hz coils wound into the stator of the motor create rotating magnetic field magnetic field passing through the conductors of the rotor induces current to flow induced current produces magnetic field around rotor conductors which creates magnet. Single phase induction motor, theory of operation double revolving field theory, equivalent circuit, determination of parameters methods of starting, split phase starting. The theory used in the work was collected by studying literature on how electrical motors work, and by simplifying the. Also, the heat is largely produced by internal elements of the dc motor, so most dc motors have a fan to reduce temperature.
Ac and dc motor designs and operations are explained in this article. It is therefore used in starter motors of cars and elevator motors p. In general, the induction motor is cheaper and easier to maintain compared to other alternatives. Fundamentals of alternating current 3 figure 121 sinusoidal wave values. The premise for motor operation is that if you can create a rotating magnetic field in the stator of the motor. There are many types of ac motors, but this course focuses on threephase ac induction motors, the most common type of motor used in industrial applications. Induction motor theory jerry bednarczyk, pe course content introduction the ac induction motor is well suited to applications requiring constant speed operation. In an ac induction motor, one set of electromagnets is. Synchronous ac motors use a permanent magnet rotor, while induction motors use an electromagnet rotor. The induction motor is made up of the stator, or stationary windings, and the rotor. Its operation is based on the principle that when a current carrying conductor is placed in a.
Synchronous motors are occasionally used as traction motors. Singlephase twophase threephase the presentation will describe the basics of the threephase brushless motor because it is the most common version. Various types of ac induction motors are available in the market. Describe how a squirrel cage motor is built, and classify it as either an induction motor or a synchronous motor. The theoretical speed of the rotor in an induction motor depends on the frequency of. An induction motors rotor can be either wound type or squirrelcage type. Question 1 electromechanical watthour meters use an aluminum disk that is spun by an electric 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. Dc motors although ac motors are used in most of the cases, dc motors have many applications and used for multipurpose applications. Other motors that are included are 1phase induction motors, permanent synchronous motors and synchronous reluctance motors. The most significant feature of universal ac motors is their constant high rotary speed often measured in thousands of rounds per minute, which makes them useful in a wide range of applications like railway traction mechanisms, highpower engineering and commercial drill machines. To generate a constant drag on the disk necessary to limit its rotational speed, a strong magnet is placed in such a way that its lines of magnetic flux pass perpendicularly through the.
Ac series motor principle, types, characteristics and. Singlephase ac induction motors a common singlephase motor is the shadedpole motor, which is used in devices requiring low torque, such as electric fans or other small household appliances. In the case of common ac that is used throughout most of the united states, the current flow changes direction 120 times every second. The ac induction motor is the most used electrical motor in industrial applications worldwide. The motor driven by the inverter is a mainly threephase squirrelcage motor, and the motor. Wound rotor motors also can develop high starting torque at standstill while maintaining low inrush. Though few ac motors today bear any resemblance to dc motors, these problems had to be solved before ac motors of any type could be properly designed. Most 9lead motors can be operated on 208v, but the running current increases by about 10%, and the. In ac motors, the input alternating current creates a. In most cases, the considerations can be extended to the other types.
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. Three phase ac motor theory motors have been described as a transformer with a rotating secondary. The inverter converts dc power to ac power at required frequency and amplitude. They have only one moving part, the rotor, which makes them lowcost, quiet, longlasting, and relatively trouble free. An ac motor of this type may be part of a pump or fan or. It is logical that the least expensive, lowest maintenance type motor should be used most often. An introduction to electric motors stmicroelectronics.
Alternating current motors or ac motors are built on the principle that nikola tesla discovered in the late 19th century. These types of motors are known as selfstarting induction motors. Ac alternating current motors are lowcost and highefficiency mechanisms used in large variety of applications. In synchronous ac motors, the rotor turns at exactly the same speed as the rotating magnetic field. The typical 3phase inverter is illustrated in figure 32. Direct vs alternating current distribution systemsthat are far more ef. Jan 06, 2019 ac series motors are also known as the modified dc series motor as their construction is very similar to that of the dc series motor. Overview the acdc motor theory course was specifically developed for electricians and electronic technicians as well as for the multicraft training needs of process and manufacturing facilities. The premise for motor operation is that if you can create a rotating magnetic field in the stator of the motor, it. Pdf dc motor dc motor theory cahtayu cahtayu academia. Many motors are used for various industrial machines to home appliances or bicycle in daily use. If you happen to have a string of blinking christmas lights to use as a prop in illustrating a rotating magnetic field, this would be a good thing to show your students. Ac motors are widely used in industry, primarily due to their high efficiency, and their ability to produce constant torque up to the rated speed.
At maximum speed limit, the current into the motor is minimum in theory it is zero. Iit delhi announcement outlines of the slides in the 1 outlines of the slides in the lectures on 3 lectures on. An induction motor can therefore be made without electrical connections to the rotor. Generating ac ac can be produced using a device called an alternator. The figure above shows the family tree of the ac motors described in this chapter.
The biggest advantage of ac induction motors is their sheer simplicity. Dc motors, by contrast, have a commutator and carbon brushes that wear out and need replacing from time to time. The most common type of ac motor being used throughout the work today is the induction motor. Applications of threephase induction motors of size varying from half a. What is common to all the members of this family is that the basic physical process involved in their operation is the conversion of electromagnetic energy to mechanical energy, and vice versa. Ac drives lead the technical revolution of electric forklifts. The stator is a permanent magnet, so the motor is smaller in size. Differentiate between the various types of generating electric power stations.
Electric motors and controls training electric motors and controls training certificate course software. Ac motors offer a simple design, consisting of a magnetically driven, copper wounded stator and a rotor mechanism. List and describe the more commonly used equipment in an electric substation. What makes the wound rotor motor a unique induction machine is its rotor. Explain how this motor can be operated as either a synchronous motor or a plain induction motor. The handbook includes information on alternating current ac and direct current dc theory, circuits, motors, and generators. Generators, motors, transformers, and solenoids each use the principle of electromagnetism. The field windings of a series motors are connected in series with the armature windings. Moreover, we also discuss about various factors that affect working of these motors and reliable ways to improve.
Ac motors are designed and rated for a certain type of ac power. This course consists of 11 interactive, online lessons that address ac and dc motor theory. Long motor life is ensured with the use of external resistor banks or liquid rheostats that dissipate heat buildup generated during motor startup. The brushless dc motor, actually an ac motor, is replacing the conventional brushed dc motor in many applications. Dc motor principle a machine that converts dc power into mechanical energy is known as dc motor. The theory used in the work was collected by studying literature on how electrical motors work, and by simplifying the explanations to suit the intended reader. A servo motor is one of the widely used variable speed drives in industrial production and process automation and building technology worldwide. In the case of three phase ac alternating current operation, the most widely used motor is a 3 phase induction motor, as this type of motor does not require an additional starting device.
Ac motors are widely used to drive machinery for a wide variety of applications. Ac series motor or the universal motor is an electric motor which operates in either ac or dc power at the same speed and output. The singlephase ac induction motor best fits this description. The use of vfds significantly reduces overall system maintenance. The theoretical speed of the rotor in an induction motor depends on the frequency of the ac supply and the number of coils that make up the. Frequency, as expressed in hertz hz or cycles per second, indicates the frequency of the oscillations of alternating current. Ac motors principle of operation resources for engineers. Objective identify the components of an ac motor and explain their function. The rotor and stator windings are connected in parallel. The concept of the rotating magnetic field is central to ac motor theory, so it is imperative that students grasp this concept before moving on to more advanced concepts.
877 904 1022 1501 1273 1023 1423 566 919 456 1182 238 306 1200 122 1183 643 1004 271 838 753 123 321 622 1121 1102 1167 131 1278 1219 654 561 464 447 389 441