Electric motors are broadly classified into two different categories: DC (Direct Current) and AC (Alternating. Current). Within these categories are numerous types. current (dc) motor or generator, the induction motor or generator, and a number . As it will be shown later, alternators operate with both alternating (ac) and. For motor applications, engineers have several options at their disposal. Typically, engineers can choose between direct-current (DC) or alternating- current (AC).
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Types of Electric Motors. Electric Motors. DC Motors. Other Motors h. AC Motors. Shunt motor. Separately Excited. Induction motor. Stepper motor. Brushless DC. Direction of rotation versus the polarities of the armature and field currents. DC and AC operation of a universal motor. Improving AC operation by adding a. Principles and Working of DC and AC A magnetic field is produced when a direct current is applied to . This is the principle on which the dc motor works.
Both single phase and three phase supply are used Only single phase supply is used Number of terminals There are 3 input terminals RYB. There are two input terminals Positive and negative Carbon brushes There are carbon brushes in the DC Motor Applications Suitable for large and industrial applications DC motor is used in small and domestic applications Starting AC Motor are not self starting. It requires some external starting equipments DC Motor are self starting Position of Armature The Armature is stationary and the magnetic field rotates Armature rotates while the magnetic field remains stationary. In an AC Motor, an alternating current passes through the coils. When an alternating current is passed on the electromagnets is a magnetic field is generated. Stationary parts consist of the electromagnets. The magnetic field which is created changes constantly.
The back emf of the motor, plus the voltage drop across the winding internal resistance and brushes, must equal the voltage at the brushes. This provides the fundamental mechanism of speed regulation in a DC motor. If the mechanical load increases, the motor slows down; a lower back emf results, and more current is drawn from the supply. This increased current provides the additional torque to balance the new load.
In AC machines, it is sometimes useful to consider a back emf source within the machine; as an example, this is of particular concern for close speed regulation of induction motors on VFDs. Motor losses are mainly due to resistive losses in windings, core losses and mechanical losses in bearings, and aerodynamic losses, particularly where cooling fans are present, also occur. Losses also occur in commutation, mechanical commutators spark, and electronic commutators and also dissipate heat.
To calculate a motor's efficiency, the mechanical output power is divided by the electrical input power:. It is possible to derive analytically the point of maximum efficiency. Various regulatory authorities in many countries have introduced and implemented legislation to encourage the manufacture and use of higher-efficiency electric motors. Eric Laithwaite  proposed a metric to determine the 'goodness' of an electric motor: From this, he showed that the most efficient motors are likely to have relatively large magnetic poles.
However, the equation only directly relates to non PM motors. All the electromagnetic motors, and that includes the types mentioned here derive the torque from the vector product of the interacting fields.
For calculating the torque it is necessary to know the fields in the air gap. Once these have been established by mathematical analysis using FEA or other tools the torque may be calculated as the integral of all the vectors of force multiplied by the radius of each vector.
The current flowing in the winding is producing the fields and for a motor using a magnetic material the field is not linearly proportional to the current. This makes the calculation difficult but a computer can do the many calculations needed.
Once this is done a figure relating the current to the torque can be used as a useful parameter for motor selection. The maximum torque for a motor will depend on the maximum current although this will usually be only usable until thermal considerations take precedence.
When optimally designed within a given core saturation constraint and for a given active current i. Some applications require bursts of torque beyond the maximum operating torque, such as short bursts of torque to accelerate an electric vehicle from standstill. Always limited by magnetic core saturation or safe operating temperature rise and voltage, the capacity for torque bursts beyond the maximum operating torque differs significantly between categories of electric motors or generators.
Capacity for bursts of torque should not be confused with field weakening capability. Field weakening allows an electric machine to operate beyond the designed frequency of excitation. Field weakening is done when the maximum speed cannot be reached by increasing the applied voltage. This applies to only motors with current controlled fields and therefore cannot be achieved with permanent magnet motors.
Electric machines without a transformer circuit topology, such as that of WRSMs or PMSMs, cannot realize bursts of torque higher than the maximum designed torque without saturating the magnetic core and rendering any increase in current as useless. Furthermore, the permanent magnet assembly of PMSMs can be irreparably damaged, if bursts of torque exceeding the maximum operating torque rating are attempted. Electric machines with a transformer circuit topology, such as induction machines, induction doubly-fed electric machines, and induction or synchronous wound-rotor doubly-fed WRDF machines, exhibit very high bursts of torque because the emf-induced active current on either side of the transformer oppose each other and thus contribute nothing to the transformer coupled magnetic core flux density, which would otherwise lead to core saturation.
Electric machines that rely on induction or asynchronous principles short-circuit one port of the transformer circuit and as a result, the reactive impedance of the transformer circuit becomes dominant as slip increases, which limits the magnitude of active i.
Still, bursts of torque that are two to three times higher than the maximum design torque are realizable. The brushless wound-rotor synchronous doubly-fed BWRSDF machine is the only electric machine with a truly dual ported transformer circuit topology i.
If a precision means were available to instantaneously control torque angle and slip for synchronous operation during motoring or generating while simultaneously providing brushless power to the rotor winding set, the active current of the BWRSDF machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable.
Torque bursts greater than eight times operating torque have been calculated. The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation.
Despite the high coercivity of neodymium or samarium-cobalt permanent magnets, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets.
Continuous torque density relates to method of cooling and permissible period of operation before destruction by overheating of windings or permanent magnet damage. Other sources state that various e-machine topologies have differing torque density. One source shows the following: Torque density is approximately four times greater for electric motors which are liquid cooled, as compared to those which are air cooled.
Another source notes that permanent-magnet synchronous machines of up to 1 MW have considerably higher torque density than induction machines. The continuous power density is determined by the product of the continuous torque density and the constant torque speed range of the electric machine.
The latter source, which can be responsible for the "whining noise" of electric motors, is called electromagnetically-excited acoustic noise. An electrostatic motor is based on the attraction and repulsion of electric charge.
Usually, electrostatic motors are the dual of conventional coil-based motors. They typically require a high-voltage power supply, although very small motors employ lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion, and require high current at low voltages. In the s, the first electrostatic motors were developed by Benjamin Franklin and Andrew Gordon.
Today, the electrostatic motor finds frequent use in micro-electro-mechanical systems MEMS where their drive voltages are below volts, and where moving, charged plates are far easier to fabricate than coils and iron cores. Also, the molecular machinery that runs living cells is often based on linear and rotary electrostatic motors. A piezoelectric motor or piezo motor is a type of electric motor based upon the change in shape of a piezoelectric material when an electric field is applied.
Piezoelectric motors make use of the converse piezoelectric effect whereby the material produces acoustic or ultrasonic vibrations to produce linear or rotary motion. An electrically powered spacecraft propulsion system uses electric motor technology to propel spacecraft in outer space, most systems being based on electrically powering propellant to high speed, with some systems being based on electrodynamic tethers principles of propulsion to the magnetosphere.
From Wikipedia, the free encyclopedia. For other kinds of motors, see Motor disambiguation.
For a railroad engine, see Electric locomotive. Main article: History of the electric motor. Rotor electric. Commutator electric. DC motor. Brushed DC electric motor. Permanent-magnet electric motor. Brushless DC electric motor. Switched reluctance motor. Universal motor. AC motor. Induction motor. Torque motor. Synchronous motor. Doubly-fed electric machine. Servo motor. Stepper motor. Linear motor.
This section needs expansion. You can help by adding to it. March Electromotive force. Goodness factor. This section only describes one highly specialized aspect of its associated subject. Please help improve this article by adding more general information. The talk page may contain suggestions. Main articles: Electrostatic motor , Piezoelectric motor , and Electrically powered spacecraft propulsion. Electronics portal Energy portal Electric motors portal.
Single-phase — straight and compensated series motors, railway motor; three-phase — various repulsion motor types, brush-shifting series motor, brush-shifting polyphase shunt or Schrage motor, Fynn-Weichsel motor.
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In universal motors the stator and rotor of a brushed DC motor are both wound and supplied from an external source, with the torque being a function of the rotor current times the stator current so reversing the current in both rotor and stator does not reverse the rotation. Universal motors can run on AC as well as DC provided the frequency is not so high that the inductive reactance of the stator winding and eddy current losses become problems.
Nearly all universal motors are series-wound because their stators have relatively few turns, minimizing inductance.
Universal motors are compact, have high starting torque and can be varied in speed over a wide range with relatively simple controls such as rheostats and PWM choppers. Compared with induction motors, universal motors do have some drawbacks inherent to their brushes and commutators: relatively high levels of electrical and acoustic noise, low reliability and more frequent required maintenance.
Universal motors are widely used in small home appliances and hand power tools. Until the s they dominated electric traction electric, including diesel-electric railway and road vehicles ; many traction power networks still use special low frequencies such as Still widely used, universal traction motors have been increasingly displaced by polyphase AC induction and permanent magnet motors with variable-frequency drives made possible by modern power semiconductor devices.
Main article: Repulsion motor Repulsion motors are wound-rotor single-phase AC motors that are a type of induction motor.
In a repulsion motor, the armature brushes are shorted together rather than connected in series with the field, as is done with universal motors. By transformer action, the stator induces currents in the rotor, which create torque by repulsion instead of attraction as in other motors. Several types of repulsion motors have been manufactured, but the repulsion-start induction-run RS-IR motor has been used most frequently. The RS-IR motor has a centrifugal switch that shorts all segments of the commutator so that the motor operates as an induction motor once it is close to full speed.
Some of these motors also lift the brushes out of contact with source voltage regulation. Repulsion motors were developed before suitable motor starting capacitors were available, and few repulsion motors are sold as of Exterior rotor[ edit ] Where speed stability is important, some AC motors such as some Papst motors have the stator on the inside and the rotor on the outside to optimize inertia and cooling.
Sliding rotor motor[ edit ] AC Motor with sliding rotors A conical rotor brake motor incorporates the brake as an integral part of the conical sliding rotor. When the motor is at rest, a spring acts on the sliding rotor and forces the brake ring against the brake cap in the motor, holding the rotor stationary.
When the motor is energized, its magnetic field generates both an axial and a radial component. The axial component overcomes the spring force, releasing the brake; while the radial component causes the rotor to turn. There is no additional brake control required.
The high starting torque and low inertia of the conical rotor brake motor has proven to be ideal for the demands of high cycle dynamic drives in applications since the motor was invented, designed and introduced over 50 years ago. This type of motor configuration was first introduced in the USA in Single-speed or two speed motors are designed for coupling to gear motor system gearboxes.
Conical rotor brake motors are also used to power micro speed drives. Motors of this type can also be found on overhead cranes and hoists. The micro speed unit combines two motors and an intermediate gear reducer.
These are used for applications where extreme mechanical positioning accuracy and high cycling capability are needed. The intermediate gearbox allows a range of ratios, and motors of different speeds can be combined to produce high ratios between high and low speed. Electronically commutated motor[ edit ] Main article: Brushless DC electric motor Electronically commutated EC motors are electric motors powered by direct-current DC electricity and having electronic commutation systems, rather than mechanical commutators and brushes.
The current-to-torque and frequency-to-speed relationships of BLDC motors are linear. The graphical representation of these quantities showed a much simpler relationship where a linear, directly proportional, inversely proportional or a curved nature of the graph is shown.
Output power increased proportional with the load current showing a linear relationship. Output voltage vs speed shows a directly proportional increase, as the speed increases so does the voltage.
These results can be explained by the motion of the rotor which causes a flux to be produced and this varies with speed. This is represented on the graph as speed increases so does the output voltage. The biggest disadvantage of a separately DC generator is that we require an external source of excitation. So to sum up the field current increases as the voltage increases and this is subsequently caused by speed increase.
The output power is dependent on load current which increases as the current does. The load current is dependent on the resistance so as the resistance is varied e. DC shunt and series motors differ in the practical world.
Some common uses of the shunt motor are machine shop lathes, and industry process lines and this is where speed and control is critical and since the shunt motor has a better control of speed it is preferred over the series motor for this job. A common use of the series motor includes a crane hoist meaning a heavy load will be manipulated.
The series motor provides a high torque and this is enough torque required for moving large loads whereas the shunt motor has a low start torque making it unsuitable for this use. A train is probably the best example that is widely used around the world and it has traction motors that series motors providing the required torque and power to shift the large amounts of mass.
Experiment 3 which focused on the three phase squirrel cage, deals with 2 types of circuits which are the star and delta connected motors. In this experiment the control was torque and with small increments of 0. The speed decreases with torque linearly and the line current increases steadily with torque.
The efficiency also increases with torque. In the delta connected motor experiment, the speed decreases as the torque increases and this is seen to be linearly. Current increases as the torque increases and the efficiency increases with torque but the increase in efficiency is steeper than the increase in current and this can be seen on the graph.
So it can be seen that in both star and delta experiments, the same outcome is observed that: The speed decreases as torque increases.
The line current increases as the torque increases. The efficiency increases as the torque increases. The experiment helped me understand how different connections affect the way an AC motor is operating. It also allowed me to use torque as an independent variable and understand practically and mentally how this affects the speed, line current and efficiency showing that the overall efficiency and gradient for the delta experiment turned out to be higher showing me that it is slightly better than star connection.
Towards the end of the experiments the correlation between torque and some of the other vector or scalar quantities that are in place such as speed. Seeing the difference between star and delta setup for induction motor; in a star setup induction motor, when the torque is increased the speed decreased more rapidly compared to that of a delta induction motor. From the graph showing three sets of data of speed vs.
A difference in the 2 setups star and delta was that the mains of the mains voltage where the star connection had an initial voltage of V compared to the V of the delta connection where they both used a three phase setup.
Some aspects of this experiment were made easier due to its own cause. For example the use of a computer using some of its components like the fan to cool it down is due to motors.
The use of excel in this experiment helped a lot as it was the main platform that the data was stored on and it also helped to do the calculation much faster than it would have taken on a calculator or other methods.
One of the problems I had during the experiment was the power factor as my research brought me to use the wrong methods of obtaining it and getting the wrong results and these are as follows below: Voltmeter readings set to approximately the same to provide a balanced load as an imbalanced load.
The bars of the cage rotor will be cut by this rotating magnetic flux so that a current will be induced in them. Download pdf. Remember me on this computer.