Information about Induction Motor
Induction Motor (IM) is one kind of AC motor where power is supplied to the rotating device by induction. An electric motor converts electrical power to mechanical power in its rotor (rotating part). There are several ways to supply power to the rotating part of the motor. In a DC Motor this power is supplied to the armature directly from a DC source. But in an AC motor this power is induced in the rotating device. An induction motor can be called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives.
Induction motors are now the preferred choice for industrial motors due to their rugged construction, lack of brushes (See DC Motors) and -- thanks to modern power electronics -- the ability to control the speed of the motor.
The Induction motor does not have any supply onto the rotor, instead a secondary current is induced onto the rotor. Conductors in the rotor induce a current as the rotating magnetic field created by the stator windings sweep past them much in the same way as in a transformer. This current in the rotor conductors will therefore induce a magnetic field which will be attracted to the rotating magnetic field in the stator and the rotor will turn. For this to happen though the speed of the rotor and the speed of the rotating magnetic field in the stator must be different, otherwise the rotor conductors won't 'see' a moving magnetic field and no current will be induced. If this happens the rotor slows slightly until a current is reinduced and the rotor will continue as before. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It is unitless and is a ratio of the speed of the rotor over the speed of the rotating field. Due to this an Induction motor is sometimes referred to as an asynchronous machine. The relationship between frequency(f), no of pole pairs(p) and synchronous speed(n) is given by f = p*n.
from this relationship
Speed of rotating field (n) = f/P (revs.s-1)
Where f is the supply frequency and P is the number of pole pairs.
Speed of Rotor = n(1-S) (rev.s-1)
Where S is the slip.
The motor's phase type is one of two types:
A drawing of an Induction motor can be seen here [1]
There are various techniques to produce a desired frequency available today, the most widely used of which is called PWM (Pulse Width Modulation). This takes a DC signal and cuts it into pulses at varying frequencies, when this is supplied to the inductor windings they smooth the signal which therefore gives an average over that time period. For example, if a 100 V DC signal was cut equally on and off then the average seen by the winding would be 50 V. If it was now cut so that it was on for a third of the time that it is off then the average would be 25 V etc. By changing the mark-space ratio, otherwise known as the duty cycle, a sine wave can be produced at whatever frequency (Motor speed) is required.
The general term for a power electronic device that controls the speed as well as other parameters is called an 'Inverter'. A typical unit will take the mains AC supply, rectify and smooth it into a "Link" DC voltage and then using the method described above will convert this into the desired AC waveform.
Because the Induction motor has no brushes and is now easy to control, many older DC motors are being replaced with Induction motors and accompanying circuitry in industrial applications.
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The stator is the stationary part of an electric motor or alternator.
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Induction motors are now the preferred choice for industrial motors due to their rugged construction, lack of brushes (See DC Motors) and -- thanks to modern power electronics -- the ability to control the speed of the motor.
Basic Operation & Comparison to a Synchronous Motor
The basic difference between a sychronous AC motor and an Induction motor is that in the former a current is supplied onto the rotor. This then creates a magnetic field which, through magnetic attraction, links to the rotating magnetic field in the stator which in turn causes the rotor to turn. It is called synchronous because at steady state the speed of the rotor is the same as the speed of the rotating magnetic field in the stator.The Induction motor does not have any supply onto the rotor, instead a secondary current is induced onto the rotor. Conductors in the rotor induce a current as the rotating magnetic field created by the stator windings sweep past them much in the same way as in a transformer. This current in the rotor conductors will therefore induce a magnetic field which will be attracted to the rotating magnetic field in the stator and the rotor will turn. For this to happen though the speed of the rotor and the speed of the rotating magnetic field in the stator must be different, otherwise the rotor conductors won't 'see' a moving magnetic field and no current will be induced. If this happens the rotor slows slightly until a current is reinduced and the rotor will continue as before. This difference between the speed of the rotor and speed of the rotating magnetic field in the stator is called slip. It is unitless and is a ratio of the speed of the rotor over the speed of the rotating field. Due to this an Induction motor is sometimes referred to as an asynchronous machine. The relationship between frequency(f), no of pole pairs(p) and synchronous speed(n) is given by f = p*n.
from this relationship
Speed of rotating field (n) = f/P (revs.s-1)
Where f is the supply frequency and P is the number of pole pairs.
Speed of Rotor = n(1-S) (rev.s-1)
Where S is the slip.
Construction
The stator consists of wound 'poles' that carry the supply current and will induce a magnetic field in the conductor. The number of 'poles' can vary between motor types but are always in pairs (ie 2,4,6 etc). There are two types of rotors:- Squirrel-cage rotor
- Slip ring rotor
The motor's phase type is one of two types:
- Single-phase induction motor
- 3-phase induction motor
A drawing of an Induction motor can be seen here [1]
Speed Control
The rotating speed of the rotor is controlled by the number of pole pairs (number of windings in the stator) and the frequency of the supply voltage. Before the development of cheap power electronics it was difficult to vary the frequency to the motor and therefore the uses for the Induction Motor were limited.There are various techniques to produce a desired frequency available today, the most widely used of which is called PWM (Pulse Width Modulation). This takes a DC signal and cuts it into pulses at varying frequencies, when this is supplied to the inductor windings they smooth the signal which therefore gives an average over that time period. For example, if a 100 V DC signal was cut equally on and off then the average seen by the winding would be 50 V. If it was now cut so that it was on for a third of the time that it is off then the average would be 25 V etc. By changing the mark-space ratio, otherwise known as the duty cycle, a sine wave can be produced at whatever frequency (Motor speed) is required.
The general term for a power electronic device that controls the speed as well as other parameters is called an 'Inverter'. A typical unit will take the mains AC supply, rectify and smooth it into a "Link" DC voltage and then using the method described above will convert this into the desired AC waveform.
Because the Induction motor has no brushes and is now easy to control, many older DC motors are being replaced with Induction motors and accompanying circuitry in industrial applications.
See also
Electric motors | ||
|---|---|---|
| Broad Motor Categories | Synchronous motor • AC motor • DC Motor | ) |
| Conventional Electric Motors | Induction • Brushed DC • Brushless DC • Stepper • Linear • Unipolar • Reluctance | |
| Novel Electric Motors | Ball bearing • Homopolar • Piezoelectric • Ultrasonic • Electrostatic | |
| Motor Controllers | Adjustable-speed drive • Direct Torque Control • Direct on line starter • Electronic speed control • Variable-frequency drive | |
| See also | Barlow's Wheel • Nanomotor • Traction motor • Lynch motor • Mendocino motor • Repulsion motor • Inchworm motor • Booster (electric power) • Brush (electric) | |
An AC motor is an electric motor that is driven by an alternating current. An AC motor consists of two basic parts:
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- An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and;
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For magnetic induction, see .
Electromagnetic induction is the production of voltage across a conductor situated in a changing magnetic field or a conductor moving through a stationary magnetic field...... Click the link for more information.
electric motor converts electrical energy into mechanical energy. The reverse process, that of converting mechanical energy into electrical energy, is accomplished by a generator or dynamo.
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Rotor may refer to:
In engineering:
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In engineering:
- Helicopter rotor, the rotary wing(s) of a rotorcraft such as a helicopter
- Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element called the stator.
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A DC motor is designed to run on DC electric power.
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- The brushed DC motor will generate torque directly from DC power applied to the motor leads, due to its internal commutation.
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Direct current (DC or "continuous current") is the constant flow of electric charge. This is typically in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams.
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An AC motor is an electric motor that is driven by an alternating current. An AC motor consists of two basic parts:
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- An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and;
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This article is about the component in an electric motor. For the component of a compressor, see Axial compressor # Description.
The stator is the stationary part of an electric motor or alternator.
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A polyphase system is a means of distributing alternating current electrical power. The most common example is the three-phase power system used for most industrial applications.
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A squirrel cage rotor is the rotating part commonly used in an AC induction motor. An electric motor with a squirrel cage rotor is sometimes called a squirrel cage motor. In overall shape it is a cylinder mounted on a shaft.
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A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels or electrical rotary joints, are commonly found in
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electric motor converts electrical energy into mechanical energy. The reverse process, that of converting mechanical energy into electrical energy, is accomplished by a generator or dynamo.
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A synchronous electric motor is distinguished by its rotor spinning at the same rate as the oscillating field which drives it. Another way of saying this is that it has zero slip under usual operating conditions.
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An AC motor is an electric motor that is driven by an alternating current. An AC motor consists of two basic parts:
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- An outside stationary stator having coils supplied with AC current to produce a rotating magnetic field, and;
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A DC motor is designed to run on DC electric power.
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- The brushed DC motor will generate torque directly from DC power applied to the motor leads, due to its internal commutation.
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Adjustable speed drive (ASD) or variable-speed drive (VSD) describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products.
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Direct torque control is one method used in variable frequency drives to control the torque (and thus finally the speed) of three-phase AC electric motors. This involves calculating an estimate of the motor's magnetic flux and torque based on the measured voltage and current of the
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A direct on line starter, often abbreviated DOL starter, is a widely-used starting method of electric motors. The term is used in electrical engineering and associated with electric motors. There are many types of motor starters, the simplest of which is the DOL starter.
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An electronic speed control or ESC is a device mounted onboard an electrically powered radio control model in order to vary its drive motor's speed, its direction and even to act as a dynamic brake in certain controllers.
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A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive.
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Barlow's Wheel is the name given to an early demonstration of a homopolar motor, designed and built by English mathematician and physicist, Peter Barlow in 1822. An electric current passes through the hub of the wheel to a mercury contact on the rim; this is contained in a small
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nanomotor is a molecular device capable of converting energy into movement and forces on the order of the piconewtons.
A proposed branch of research is the integration of molecular motor proteins found in living cells into molecular motors implanted in artificial devices.
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A proposed branch of research is the integration of molecular motor proteins found in living cells into molecular motors implanted in artificial devices.
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A traction motor is a type of electric motor used to power the driving wheels of a vehicle such as a railroad locomotive, electrical multi-unit train (such as a subway or light rail vehicle train), a tram, or an automobile.
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The Lynch Motor is a unique axial gap permanent magnet brushed DC motor invented by Cedric Lynch, U.S. patent 4823039 amongst others cover the motor and its construction. The motor was then developed in to a production item by Cedric and Trevor Lees in the early 1990's.
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The Mendocino motor is a solar-powered magnetically-levitated motor.
The motor consists of a four-sided rotor block in the middle of a shaft. The rotor block has two sets of windings and a solar cell attached to each side.
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The motor consists of a four-sided rotor block in the middle of a shaft. The rotor block has two sets of windings and a solar cell attached to each side.
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A Repulsion motor is a type of electric motor for use on alternating current. It was formerly used as a traction motor for electric trains but has been superseded by other types of motor and is now only of historical interest.
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The inchworm motor is a device that uses piezoelectric actuators to move a shaft with nanometer precision. The term is a trademark of the patent holder for this scheme, Exfo.
The inchworm motor uses three piezo-actuators connected together.
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The inchworm motor uses three piezo-actuators connected together.
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A Booster was a motor-generator (MG) set used for voltage regulation in direct current (DC) electrical power circuits. The development of alternating current and solid-state devices has rendered it obsolete.
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brushes conduct current between stationary wires and moving parts, most commonly in a rotating shaft. Most importantly, in an electric motor, an alternator or electric generator, the coils of the rotor have to be connected.
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