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state different applications of capacitor start single phase induction motor


In many flow control applications, a mechanical throttling device is used to limit the flow. This "shades" portion of the pole, causing the state different applications of capacitor start single phase induction mark walden dating coach motor field in the ringed area to lag the field in the unringed portion. In principle, you could partially strip the wires in such a way that current would be zero in one half cycle. This requires the measure- ment of the rotor position and the stator current. Groups of large, specially constructed, low-inductance high-voltage capacitors capacitor banks are used to supply huge pulses of current for many pulsed power applications. As long as there is enough torque to overcome the load placed on the motor, internal friction etc. Loudspeakers as microphones In the picture above, you can see that a cardboard diaphragm the loudspeaker cone is connected to a coil of wire in a magnetic warum verheiratete frauen flirten field. Porcelain was used in the first ceramic capacitors. Plus, thermal protection is difficult because the high locked-rotor current relative to running current makes it tricky to find a protector with trip time fast enough prevent start-winding burnout. The equivalent series resistance ESR is the amount of internal series resistance one would add to a perfect capacitor to model this. For V power service, a common connection of the windings is called the T connection. In this method, the sinusoidal weighted values are stored in the PICmicro microcontroller and are made available at the output port at user defined intervals. It is always advisable to use the dissipative mean resistor to limit the energy returning to the DC link by dissipating a substantial portion in the resistor. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery. Brushes introduce losses plus arcing and ozone production. In some cases, decreasing the current is the aim of the exercise. Leakage is equivalent to a resistor in parallel with the capacitor. High-voltage capacitors are stored with the terminals shortedas protection from potentially dangerous state different applications of capacitor start single phase induction motor due to dielectric absorption or from transient voltages the capacitor may pick up from static charges or passing weather events. When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. Sometimes they fail with a circuit when next operated. Among other things, this means it operates at lower temperature than other single-phase motor types of comparable horsepower. To start the motor, a secondary "start" winding has a series non-polarized starting capacitor to introduce a lead in the sinusoidal current. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device.


State different applications of capacitor start single phase induction motor Induction motor - Wikipedia

In those instances in which three-phase electric motors are not available or cannot be used state different applications of capacitor start single phase induction motor of the power supply, the following types of single-phase motors are recommended for industrial and commercial applications: With starting winding we connect a capacitor so the current flowing in the capacitor i. Comparison of this performance with the performance shown in Table 1. A centrifugal switch S C is also connected in the circuit. Advantages and Disadvantages of Shaded Pole Motor The advantages state different applications of capacitor start single phase induction motor shaded pole induction motor are Very economical and reliable. So these motors are used in fans, blowers, centrifugal pumps, washing machine, grinder, lathes, air conditioning fans, etc. It has a start-type capacitor in series with the auxiliary winding like the capacitor-start motor for high starting torque. The features of the capacitor start and PSC methods can be combined with this method. Some of the characteristics of Capacitor start single phase induction motor are given below. The typical of integral-horsepower, two-value capacitor motors is shown in Table 1. The capacitor start motor has a cage rotor and has two windings on the stator. This allows higher cycle rates and reliable thermal protection. Induction Motor Characteristics Electric Motor. The speed reversal is also difficult and expensive as it requires another set of copper rings. Hi Yunus As per your requirement we have related articles so please follow the below links https: A permanent split capacitor PSC motor, Figure 3, has neither a starting switch, nor a capacitor strictly for starting. How well do you know your tools and platforms? This type of capacitor motor usually has a tapped winding and a high-resistance rotor. Capacitor start capacitor run induction motor two value capacitor method. single phase induction motor is not self starting? This current in copper band produces its own flux. The figure below shows the connection diagram of a State different applications of capacitor start single phase induction motor Start Motor. When the armature of a d. A current sensor in the is used to limit current drawn by the motor because in a few cases such as failure of the bearing, pump defect or any other reason, the current drawn by the motor exceeds its normal rated current. The Capacitor start motor can be reversed by first bringing the motor to rest condition and then reversing the connections of one of the windings.


Reversing single phase induction motors

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VFD also known as VVVF (variable voltage variable frequency) Drives or AC Inverter drives for 3 phase electric induction motors.

The scope of the IEEE Transactions on Industry Applications includes all scope items of the IEEE Industry Applications Society, that is, the advancement of the theory.

4 Understanding AC induction, permanent magnet and servo motor technologies: OPERATION, CAPABILITIES AND CAVEATS LEESON Electric FHP Series (fractional.

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.

I am wondering if possible to add a speed control to a single phase motor, similar to how a VFD is commonly used to control a 3-phase motor. I have a benchtop disc.
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The are made self starting by providing an additional flux by some additional means. Now depending upon these additional means the single phase induction motors are classified as:

  1. Split phase induction motor.
  2. Capacitor start motor.
  3. Capacitor start run (two value capacitor method).
  4. Permanent split capacitor (PSC) motor.
  5. Shaded pole induction motor.

Split Phase Induction Motor

In addition to the main winding or running winding, the stator of single phase induction motor carries another winding called auxiliary winding or starting winding. A centrifugal switch is connected in series with auxiliary winding. The purpose of this switch is to disconnect the auxiliary winding from the main circuit when the motor attains a speed up to 75 to 80% of the synchronous speed. We know that the running winding is inductive in nature. Our aim is to create the phase difference between the two winding and this is possible if the starting winding carries high. Let us say

Irun is the flowing through the main or running winding, Istart is the current flowing in starting winding, and VT is the supply voltage. split phase induction motor

We know that for highly resistive winding the current is almost in phase with the and for highly inductive winding the current lag behind the voltage by large angle. The starting winding is highly resistive so, the current flowing in the starting winding lags behind the applied voltage by very small angle and the running winding is highly inductive in nature so, the current flowing in running winding lags behind applied voltage by large angle. The resultant of these two current is IT. The resultant of these two current produce rotating which rotates in one direction. In split phase induction motor the starting and main current get splitted from each other by some angle so this motor got its name as split phase induction motor.

Applications of Split Phase Induction Motor

Split phase induction motors have low starting current and moderate starting torque. So these motors are used in fans, blowers, centrifugal pumps, washing machine, grinder, lathes, air conditioning fans, etc. These motors are available in the size ranging from 1 / 20 to 1 / 2 KW.

Capacitor Start IM and Capacitor Start Capacitor Run IM

capacitor start run induction motor The working principle and construction of Capacitor start inductor motors and capacitor start capacitor run induction motors are almost the same. We already know that single phase induction motor is not self starting because the magnetic field produced is not rotating type. In order to produce rotating magnetic field there must be some phase difference. In case of split phase induction motor we use resistance for creating phase difference but here we use capacitor for this purpose. We are familiar with this fact that the flowing through the capacitor leads the voltage. So, in capacitor start inductor motor and capacitor start capacitor run induction motor we are using two winding, the main winding and the starting winding. With starting winding we connect a capacitor so the current flowing in the capacitor i.e Ist leads the applied voltage by some angle, φst.

The running winding is inductive in nature so, the current flowing in running winding lags behind applied voltage by an angle, φm. Now there occur large phase angle differences between these two currents which produce an resultant current, I and this will produce a rotating magnetic field. Since the torque produced by these motors depends upon the phase angle difference, which is almost 90o. So, these motors produce very high starting torque. In case of capacitor start induction motor, the centrifugal switch is provided so as to disconnect the starting winding when the motor attains a speed up to 75 to 80% of the synchronous speed but in case of capacitor start capacitors run induction motor there is no centrifugal switch so, the >capacitor remains in the circuit and helps to improve the and the running conditions of single phase induction motor.

Application of Capacitor Start IM and Capacitor Start Capacitor Run IM

These motors have high starting torque hence they are used in conveyors, grinder, air conditioners, compressor, etc. They are available up to 6 KW.

Permanent Split Capacitor (PSC) Motor

It has a cage rotor and stator. Stator has two windings – main and auxiliary winding. It has only one capacitor in series with starting winding. It has no starting switch. Advantages and Applications No centrifugal switch is needed. It has higher efficiency and pull out torque. It finds applications in fans and blowers in heaters and air conditioners. It is also used to drive office machinery.

Shaded Pole Single Phase Induction Motors

shaded pole single phase induction motor The stator of the shaded pole single phase induction motor has salient or projected poles. These poles are shaded by copper band or ring which is inductive in nature. The poles are divided into two unequal halves. The smaller portion carries the copper band and is called as shaded portion of the pole.

ACTION: When a single phase supply is given to the stator of shaded pole induction motor an alternating flux is produced. This change of flux induces emf in the shaded coil. Since this shaded portion is short circuited, the current is produced in it in such a direction to oppose the main. The flux in shaded pole lags behind the flux in the unshaded pole. The phase difference between these two fluxes produces resultant rotating flux. We know that the stator winding current is alternating in nature and so is the flux produced by the stator current. In order to clearly understand the working of shaded pole induction motor consider three regions-

  1. When the flux changes its value from zero to nearly maximum positive value.
  2. When the flux remains almost constant at its maximum value.
  3. When the flux decreases from maximum positive value to zero.
REGION 1: When the flux changes its value from zero to nearly maximum positive value – In this region the rate of rise of flux and hence current is very high. According to whenever there is change in flux emf gets induced. Since the copper band is short circuit the current starts flowing in the copper band due to this induced emf. This current in copper band produces its own flux. Now according to the direction of this current in copper band is such that it opposes its own cause i.e rise in current. So the shaded ring flux opposes the main flux, which leads to the crowding of flux in non shaded part of stator and the flux weaken in shaded part. This non uniform distribution of flux causes magnetic axis to shift in the middle of the non shaded part.

REGION 2: When the flux remains almost constant at its maximum value- In this region the rate of rise of current and hence flux remains almost constant. Hence there is very little induced emf in the shaded portion. The flux produced by this induced emf has no effect on the main flux and hence distribution of flux remains uniform and the magnetic axis lies at the center of the pole.

REGION 3: When the flux decreases from maximum positive value to zero - In this region the rate of decrease in the flux and hence current is very high. According to whenever there is change in flux emf gets induced. Since the copper band is short circuit the current starts flowing in the copper band due to this induced emf. This current in copper band produces its own flux. Now according to the direction of the current in copper band is such that it opposes its own cause i.e decrease in current. So the shaded ring flux aids the main flux, which leads to the crowding of flux in shaded part of stator and the flux weaken in non shaded part. This non uniform distribution of flux causes magnetic axis to shift in the middle of the shaded part of the pole. This shifting of magnetic axis continues for negative cycle also and leads to the production of rotating magnetic field. The direction of this field is from non shaded part of the pole to the shaded part of the pole.

Advantages and Disadvantages of Shaded Pole Motor

The advantages of shaded pole induction motor are
  1. Very economical and reliable.
  2. Construction is simple and robust because there is no centrifugal switch.
The disadvantages of shaded pole induction motor are
  1. Low power factor.
  2. The starting torque is very poor.
  3. The efficiency is very low as, the copper losses are high due to presence of copper band.
  4. The speed reversal is also difficult and expensive as it requires another set of copper rings.

Applications of Shaded Pole Motor

Applications of Shaded pole motors induction motor are- Due to their low starting torques and reasonable cost these motors are mostly employed in small instruments, hair dryers, toys, record players, small fans, electric clocks etc. These motors are usually available in a range of 1/300 to 1/20 KW.
Three-phase totally enclosed fan-cooled () induction motor with end cover on the left, and without end cover to show cooling fan. In TEFC motors, interior heat losses are dissipated indirectly through enclosure fins, mostly by forced air convection.
Cutaway view through stator of induction motor, showing rotor with internal air circulation vanes. Many such motors have a symmetric armature, and the frame may be reversed to place the electrical connection box (not shown) on the opposite side.

An induction motor or asynchronous motor is an in which the in the needed to produce torque is obtained by from the of the winding. An induction motor can therefore be made without electrical connections to the rotor. An induction motor's rotor can be either or

induction motors are widely used as industrial drives because they are rugged, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with (VFDs) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque fan, pump and compressor load applications. Squirrel cage induction motors are very widely used in both fixed-speed and (VFD) applications.

Contents

History[]

A model of Tesla's first induction motor, in Tesla Museum, Belgrade
Squirrel cage rotor construction, showing only the center three laminations

In 1824, the French physicist formulated the existence of, termed. By manually turning switches on and off, Walter Baily demonstrated this in 1879, effectively the first primitive induction motor.

The first commutator-free two phase AC induction motor was invented by Hungarian engineer ; he used the two phase motor to propel his invention, the.

The first AC three-phase induction motors were independently invented by and, a working motor model having been demonstrated by the former in 1885 and by the latter in 1887. Tesla applied for in October and November 1887 and was granted some of these patents in May 1888. In April 1888, the Royal Academy of Science of Turin published Ferraris's research on his AC polyphase motor detailing the foundations of motor operation. In May 1888 Tesla presented the technical paper A New System for Alternating Current Motors and Transformers to the (AIEE) describing three four-stator-pole motor types: one with a four-pole rotor forming a non-self-starting, another with a wound rotor forming a self-starting induction motor, and the third a true with separately excited DC supply to rotor winding.

, who was developing an system at that time, licensed Tesla’s patents in 1888 and purchased a US patent option on Ferraris' induction motor concept. Tesla was also employed for one year as a consultant. Westinghouse employee was assigned to assist Tesla and later took over development of the induction motor at Westinghouse. Steadfast in his promotion of three-phase development, invented the cage-rotor induction motor in 1889 and the three-limb transformer in 1890. Furthermore, he claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work. Although Westinghouse achieved its first practical induction motor in 1892 and developed a line of polyphase 60 induction motors in 1893, these early Westinghouse motors were with wound rotors until developed a rotating bar winding rotor.

The (GE) began developing three-phase induction motors in 1891. By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the squirrel-cage rotor. was the first to bring out the full significance of (using j to represent the square root of minus one) to designate the 90º operator in analysis of AC problems. GE's greatly developed application of AC complex quantities including an analysis model now commonly known as the induction motor.

Induction motor improvements flowing from these inventions and innovations were such that a 100- induction motor currently has the same mounting dimensions as a 7.5-horsepower motor in 1897.

Principle of operation[]

A three-phase power supply provides a rotating magnetic field in an induction motor
Inherent slip - unequal rotation frequency of stator field and the rotor

In both induction and, the AC power supplied to the motor's creates a that rotates in synchronism with the AC oscillations. 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. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short-circuited or closed through an external impedance. The rotating induces currents in the windings of the rotor; in a manner similar to currents induced in a 's secondary winding(s).

The induced currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. Due to, the direction of the magnetic field created will be such as to oppose the change in current through the rotor windings. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied mechanical load on the rotation of the rotor. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slightly slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5% to 5.0% for standard Design B torque curve induction motors. The induction motor's essential character is that it is created solely by induction instead of being separately excited as in synchronous or DC machines or being self-magnetized as in.

For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field ( n s {\displaystyle n_{s}} ); otherwise the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating field is called "slip". Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as "asynchronous motors".

An induction motor can be used as an, or it can be unrolled to form a which can directly generate linear motion.

Synchronous speed[]

An AC motor's synchronous speed, n s {\displaystyle n_{s}} , is the rotation rate of the stator's magnetic field,

n s = 2 f p {\displaystyle n_{s}={2f \over {p}}} ,

where f {\displaystyle f} is the motor supply's frequency, where p {\displaystyle p} is the number of magnetic poles and where n s {\displaystyle n_{s}} and f {\displaystyle f} have identical units. For f {\displaystyle f} in unit and n s {\displaystyle n_{s}} in, the formula becomes

n s = 2 f p ⋅ ( 60   s m i n ) = 120 f p ⋅ ( s m i n ) {\displaystyle n_{s}={2f \over {p}}\cdot \left({\frac {60\ \mathrm {s} }{\mathrm {min} }}\right)={120f \over {p}}\cdot \left({\frac {\mathrm {s} }{\mathrm {min} }}\right)} .

For example, for a four-pole three-phase motor, p {\displaystyle p} = 4 and n s = 120 f 4 {\displaystyle n_{s}={120f \over {4}}} = 1,500  and 1,800 , RPM synchronous speed, respectively, for 50 Hz and 60 Hz supply systems.

The two figures at right and left above each illustrate a 2-pole 3-phase machine consisting of three pole-pairs with each pole set 60º apart.

Slip[]

Typical torque curve as a function of slip, represented as "g" here

Slip, s {\displaystyle s} , is defined as the difference between synchronous speed and operating speed, at the same frequency, expressed in rpm, or in percentage or ratio of synchronous speed. Thus

s = n s − n r n s {\displaystyle s={\frac {n_{s}-n_{r}}{n_{s}}}\,}

where n s {\displaystyle n_{s}} is stator electrical speed, n r {\displaystyle n_{r}} is rotor mechanical speed. Slip, which varies from zero at synchronous speed and 1 when the rotor is at rest, determines the motor's torque. Since the short-circuited rotor windings have small resistance, even a small slip induces a large current in the rotor and produces significant torque. At full rated load, slip varies from more than 5% for small or special purpose motors to less than 1% for large motors. These speed variations can cause load-sharing problems when differently sized motors are mechanically connected. Various methods are available to reduce slip, VFDs often offering the best solution.

Torque[]

See also:

Standard torque[]

Speed-torque curves for four induction motor types: A) Single-phase, B) Polyphase cage, C) Polyphase cage deep bar, D) Polyphase double cage
Typical speed-torque curve for NEMA Design B Motor

The typical speed-torque relationship of a standard NEMA Design B polyphase induction motor is as shown in the curve at right. Suitable for most low performance loads such as centrifugal pumps and fans, Design B motors are constrained by the following typical torque ranges:

  • Breakdown torque (peak torque), 175-300% of rated torque
  • Locked-rotor torque (torque at 100% slip), 75-275% of rated torque
  • Pull-up torque, 65-190% of rated torque.

Over a motor's normal load range, the torque's slope is approximately linear or proportional to slip because the value of rotor resistance divided by slip, R r ′ / s {\displaystyle R_{r}^{'}/s} , dominates torque in linear manner. As load increases above rated load, stator and rotor leakage reactance factors gradually become more significant in relation to R r ′ / s {\displaystyle R_{r}^{'}/s} such that torque gradually curves towards breakdown torque. As the load torque increases beyond breakdown torque the motor stalls.

Starting[]

See also:

There are three basic types of competing small induction motors: single-phase, split-phase and shaded-pole types and small polyphase motors.

In two-pole single-phase motors, the torque goes to zero at 100% slip (zero speed), so these require datingsite voor lager opgeleiden alterations to the stator such as to provide starting torque. A single phase induction motor requires separate starting circuitry to provide a rotating field to the motor. The normal running windings within such a single-phase motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction.

In certain smaller single-phase motors, starting is done by means of a shaded pole with a copper wire turn around part of the pole. The current induced in this turn lags behind the supply current, creating a delayed magnetic field around the shaded part of the pole face. This imparts sufficient rotational field energy to start the motor. These motors are typically used in applications such as desk fans and record players, as the required starting torque is low, and the low efficiency is tolerable relative to the reduced cost of the motor and starting method compared to other AC motor designs.

Larger single phase motors are and have a second stator winding fed with out-of-phase current; such currents may be created by feeding the winding through a capacitor or having it receive different values of inductance and resistance from the main winding. In capacitor-start designs, the second winding is disconnected once the motor is up to speed, usually either by a centrifugal switch acting on weights on the motor shaft or a which heats up and increases its resistance, reducing the current through the second winding to an insignificant level. The capacitor-run designs keep the second winding on when running, improving torque. A resistance start design uses a starter inserted in series with the startup winding, creating reactance.

Self-starting polyphase induction motors produce torque even at standstill. Available squirrel cage induction motor starting methods include direct-on-line starting, reduced-voltage reactor or auto-transformer starting, star-delta starting or, increasingly, new solid-state soft assemblies and, of course, VFDs.

Polyphase motors have rotor bars shaped to give different speed-torque characteristics. The current distribution within the rotor bars varies depending on the frequency of the induced current. At standstill, the rotor current is the same frequency as the stator current, and tends to travel at the outermost parts of the cage rotor bars (by ). The different bar shapes can give usefully different speed-torque characteristics as well as some control over the inrush current at startup.

Although polyphase motors are inherently self-starting, their starting and pull-up torque design limits must be high enough to overcome actual load conditions.

In wound rotor motors, rotor circuit connection through slip rings to external resistances allows change of speed-torque characteristics for acceleration control and speed control purposes.

Speed control[]

Resistance
Typical speed-torque curves for different motor input frequencies as for example used with

Before the development of semiconductor, it was difficult to vary the frequency, and cage induction motors were mainly used in fixed speed applications. Applications such as electric overhead cranes used DC drives or wound rotor motors (WRIM) with for rotor circuit connection to variable external resistance allowing considerable range of speed control. However, resistor losses associated with low speed operation of WRIMs is a major cost disadvantage, especially for constant loads. Large slip ring motor drives, termed slip energy recovery systems, some still in use, recover energy from the rotor circuit, rectify it, and return it to the power system using a VFD.

Cascade

The speed of a pair of slip-ring motors can be controlled by a cascade connection, or concatenation. The rotor of one motor is connected to the stator of the other. If the two motors are also mechanically connected, they will run at half speed. This system was once widely used in three-phase AC railway locomotives, such as.

Variable-frequency drive

Main article:

In many industrial variable-speed applications, DC and WRIM drives are being displaced by VFD-fed cage induction motors. The most common efficient way to control asynchronous motor speed of many loads is with VFDs. Barriers to adoption of VFDs due to cost and reliability considerations have been reduced considerably over the past three decades such that it is estimated that drive technology is adopted in as many as 30-40% of all newly installed motors.

Construction[]

Typical winding pattern for a three-phase (U, V, W), four-pole motor. Note the interleaving of the pole windings and the resulting.

The stator of an induction motor consists of poles carrying supply current to induce a magnetic field that penetrates the rotor. To optimize the distribution of the magnetic field, windings are distributed in slots around the stator, with the magnetic field having the same number of north and south poles. Induction motors are most commonly run on single-phase or three-phase power, but two-phase motors exist; in theory, induction motors can have any number of phases. Many single-phase motors having two windings can be viewed as two-phase motors, since a capacitor is used to generate a second power phase 90° from the single-phase supply and feeds it to the second motor winding. Single-phase motors require some mechanism to produce a rotating field on startup. Cage induction motor rotor's conductor bars are typically skewed to avoid magnetic locking.

Standardized NEMA & IEC motor frame sizes throughout the industry result in interchangeable dimensions for shaft, foot mounting, general aspects as well as certain motor flange aspect. Since an open, drip proof (ODP) motor design allows a free air exchange from outside to the inner stator windings, this style of motor tends to be slightly more efficient because the windings are cooler. At a given power rating, lower speed requires a larger frame.

Rotation reversal[]

The method of changing the direction of rotation of an induction motor depends on whether it is a three-phase or single-phase machine. In the case of three-phase, reversal is straightforwardly implemented by swapping connection of any two phase conductors.

In a single-phase split-phase motor, reversal is achieved by changing the connection between the primary winding and the start circuit. Some single-phase split-phase motors that are designed for specific applications may have the connection between the primary winding and the start circuit connected internally so that the rotation cannot be changed. Also, single-phase shaded-pole motors have a fixed rotation, and the direction cannot be changed except by disassembly of the motor and reversing the stator to face opposite relative to the original rotor direction.

Power factor[]

The of induction motors varies with load, typically from around 0.85 or 0.90 at full load to as low as about 0.20 at no-load, due to stator and rotor leakage and magnetizing reactances. Power factor can be improved by connecting capacitors either on an individual motor basis or, by preference, on a common bus covering several motors. For economic and other considerations, power systems are rarely power factor corrected to unity power factor. Power capacitor application with harmonic currents requires power system analysis to avoid harmonic resonance between capacitors and transformer and circuit reactances. Common bus power factor correction is recommended to minimize resonant risk and to simplify power system analysis.

Efficiency[]

(See also ) Full load motor efficiency varies from about 85% to 97%, related motor losses being broken down roughly as follows:

  • Friction and, 5–15%
  • Iron or, 15–25%
  • Stator losses, 25–40%
  • Rotor losses, 15–25%
  • Stray load losses, 10–20%.

Various regulatory authorities in many countries have introduced and implemented legislation to encourage the manufacture and use of higher efficiency electric motors. There is existing and forthcoming legislation regarding the future mandatory use of premium-efficiency induction-type motors in defined equipment. For more information, see:.

Steinmetz equivalent circuit[]

Many useful motor relationships between time, current, voltage, speed, power factor, and torque can be obtained from analysis of the Steinmetz (also termed T-equivalent circuit or IEEE recommended equivalent circuit), a mathematical model used to describe how an induction motor's electrical input is transformed into useful mechanical energy output. The equivalent circuit is a single-phase representation of a multiphase induction motor that is valid in steady-state balanced-load conditions.

The Steinmetz equivalent circuit is expressed simply in terms of the following components:

  • and ( R s {\displaystyle R_{s}} , X s {\displaystyle X_{s}} ).
  • resistance, leakage reactance, and slip ( R r {\displaystyle R_{r}} , X r {\displaystyle X_{r}} or R r ′ {\displaystyle R_{r}^{'}} , X r ′ {\displaystyle X_{r}^{'}} , and s {\displaystyle s} ).
  • ( X m {\displaystyle X_{m}} ).

Paraphrasing from Alger in Knowlton, an induction motor is simply an electrical transformer the magnetic circuit of which is separated by an air gap between the stator winding and the moving rotor winding. The equivalent circuit can accordingly be shown either with equivalent circuit components of respective windings separated by an ideal transformer or with rotor components referred to the stator side as shown in the following circuit and associated equation and parameter definition tables.

Steinmetz equivalent circuit

The following rule-of-thumb approximations apply to the circuit:

  • Maximum current happens under locked rotor current (LRC) conditions and is somewhat less than V s / X {\displaystyle {V_{s}}/X} , with LRC typically ranging between 6 and 7 times rated current for standard Design B motors.
  • Breakdown torque T m a x {\displaystyle T_{max}} happens when s ≈ R r ′ / X {\displaystyle s\approx {R_{r}^{'}/X}} and I s ≈ 0.7 L R C {\displaystyle I_{s}\approx {0.7}LRC} such that T m a x ≈ K ∗ V s 2 / ( 2 X ) {\displaystyle T_{max}\approx {K*V_{s}^{2}}/(2X)} and thus, with constant voltage input, a low-slip induction motor's percent-rated maximum torque is about half its percent-rated LRC.
  • The relative stator to rotor leakage reactance of standard Design B cage induction motors is
X s X r ′ ≈ 0.4 0.6 {\displaystyle {\frac {X_{s}}{X_{r}^{'}}}\approx {\frac {0.4}{0.6}}} .
  • Neglecting stator resistance, an induction motor's torque curve reduces to the Kloss equation
T e m ≈ 2 T m a x s s m a x + s m a x s {\displaystyle T_{em}\approx {\frac {2T_{max}}{{\frac {s}{s_{max}}}+{\frac {s_{max}}{s}}}}} , where s m a x {\displaystyle s_{max}} is slip at T m a x {\displaystyle T_{max}} .

Linear induction motor[]

Main article:

Linear induction motors, which work on same general principles as rotary induction motors (frequently three-phase), are designed to produce straight line motion. Uses include, linear propulsion,, and pumping.

See also[]

  1. That is, electrical connections requiring, separate-excitation or self-excitation for all or part of the energy transferred from stator to rotor as are found in, and motors.
  2. NEMA MG-1 defines a) breakdown torque as the maximum torque developed by the motor with rated voltage applied at rated frequency without an abrupt drop in speed, b) locked-rotor torque as the minimum torque developed by the motor at rest with rated voltage applied at rated frequency, and c) pull-up torque as the minimum torque developed by the motor during the period of acceleration from rest to the speed at which breakdown torque occurs.

References[]

  1. IEC 60050 (Publication date: 1990-10). Section 411-31: Rotation Machinery - General,
  2. Babbage, C.; Herschel, J. F. W. (Jan 1825).. Philosophical Transactions of the Royal Society. 115 (0): 467–496. :. Retrieved 2 December 2012. 
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Classical sources[]

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Zahra Doe Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.

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Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.
Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.
Zahra Doejune 2, 2017
Morbi gravida, sem non egestas ullamcorper, tellus ante laoreet nisl, id iaculis urna eros vel turpis curabitur.

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