Electric motors, operating principle, DC motors or AC

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Electric motors

An electric motor is a device that converts electrical energy into mechanical energy transformation reverse mechanical energy into electrical energy, is made of an electric generator principle There are significant differences between the two types of electric machines, the same device can perform both roles different situations



Working principle of electric motor

Most electric motors run on electromagnetic forces acting on a conductor of electricity but also found in field engines magneticExista electrostatic Coulomb force and built on piezoelectric motors





Using electric engine

Built in a wide range of power, electric motors are used in many applications: the engine for electronic parts (hard disk, printer) to very high power electric drives (pumps, locomotives, cranes)





Classification of electric motor

Motors can be classified by type of electric current through them: DC motors and AC motors Depending on the number of phases in which electric motors work engines may be single-or multi-phase motors





DC electric motors

Depending on the type of excitation is divided into three categories:

Electric motors derivation
Electric motors series
Electric motors mixed
AC electric motors
Asynchronous electric motors
Synchronous motors




Regardless of the type of electric motor, it is made of two parts: stator and rotor stator is fixed to the engine, generally outside, including housing, food terminals, armature ferromagnetic stator and rotor winding is moving part of the engine, placed The interior is typically composed of a rotor shaft and armature that supports the rotor winding between stator and rotor there is a portion of air called air gap which allows movement from statorGrosimea rotor air gap is an important indicator of engine performance







DC electric motor

DC electric motor was invented in 1873 by Zénobe Gramme generator by connecting a DC generator to a similar way, could see the car spun, making conversion of electric energy absorbed by the generator



The electric motor has a stator current magnetic poles and coils that create magnetic field concentrated polar excitation the electric motor axle is located a collector current through the winding reverses the rotor excitation so that the magnetic field to exert a constant force to the rotor



Current-carrying rotor windings will have one or more pairs of equivalent rotor magnetic poles moving magnetic field excitation until rotor pole stator poles align right opposite the same time, the collector currents reverses polarity rotor so the rotor is reversed and rotor movement will continue until the next alignment of the magnetic poles

Low power for electric drives and media, or for shareholders does not require variable magnetic field excitation, stator windings are used instead of permanent magnets





Electric motor speed is proportional to the applied voltage and inversely proportional to the rotor winding magnetic field excitation is adjusted by varying engine speed electric motor voltage applied to the nominal value of voltage and higher speeds are obtained by weakening the field excitation voltage Both methods aim variable that can be achieved using a DC generator (Ward-Leonard group) through resistors in circuit or inserierea of ​​using power electronics (controlled rectifiers, choppers)





Torque developed by the electric motor is directly proportional to rotor current through the magnetic field excitation and speed control by field weakening is, therefore, to reduce engine torque electric motors developed by the same current series excitation winding and winding passes through the rotor From this account can be read two electric motors series features: for low engine loads, the couple depends on the square of the electric current absorbed, the electric motor should not be allowed to run unloaded for that in this case the amount of electric current intensity is very low absorbed and thus the excitation field is reduced, leading to packing machine to self-destruction DC motors with series excitation electric traction is used in urban and rail transport (trams, locomotives)





Changing the rotation is done either by changing the voltage polarity, either by changing the magnetic field direction of the electric motor excitation range by changing the voltage polarity change is made sense of both size and direction of rotation remains unchanged Therefore, the electric motor series can be used in AC, where the voltage polarity is reversed once during a period Such a universal electric motor is called motor home and is used in low power applications and high-speed rotation (vacuum cleaner, mixer)





AC electric motor

AC electric motors operate on the principle of rotating magnetic field This principle was identified by Nikola Tesla in 1882 next year designed a two-phase induction motor, creating electric cars running on the rotating magnetic field then transmission systemsAC were used to generate effective transmission distance and power, marking the second industrial revolution Another important point in the history of AC motor was invented by Michael von Dobrowlsky Dolivo-1890 rotor in squirrel cage





Three-phase induction electric motor

Three-phase induction electric motor (or three-phase asynchronous motor) is the electric motor used in electric drives and high average power induction motor stator is composed of ferromagnetic stator armature winding is placed on three-phase stator rotor needed to produce the rotating magnetic field is formed of ferromagnetic rotor armature winding rotor which is placed



Through electromagnetic induction rotating magnetic field will induce a voltage in the rotor winding voltage This creates an electric current through the winding and on those winding acts as an electromagnetic force put in motion in terms of rotor rotating magnetic field is called asynchronous electric motor for the rotor speed is always less than the speed rotating magnetic field, known as speed of synchronism If rotor speed would be equal to the speed of synchronism there would occur the phenomenon of electromagnetic induction, did not induce currents in the rotor would and would not develop motor couple





Rotation of the electric induction motor is reversed by changing the rotation of the rotating field This is achieved by changing the two phases together



Electric induction motor rotor cage is cheaper and more reliable than electric induction motor rotor winding it for the brushes wear out and maintenance also induction electric motor with squirrel cage collector and has all the disadvantages that come with this noise, sparks, electromagnetic pollution, reduced reliability and therefore costly maintenance DC motors have been used over time in electrical variable speed drives because the electric motor speed can be changed easily by changing the supply voltage but , with the development of power electronics and in particular the development of renewable power with variable frequency, the trend is the replacement of electric motors dc electric motor with squirrel cage induction









Single phase induction electric motor

If the phase voltage system is not accessible, like in residential applications, you can use a single phase induction motor electric current phase rotating magnetic field can not produce but produce pulsating magnetic field (fixed in space and time-varying) fieldpulsed magnetic rotor can not start, but if it rotates in a sense, then it will act on a rotational torque in the sense or main problem is thus to obtain a rotating magnetic field is switched on the electric motor and this is done in May many ways





By attaching the stator car at an angle of 90 ° an auxiliary phase in series with a capacitor can get a two-phase system of currents that produce a rotating magnetic field after starting the auxiliary phase disconnects the electric motor through a centrifugal switch rotation the electric motor can be changed by moving the auxiliary phase capacitor in the main phase



Instead of auxiliary phase can use a spiral cage placed on a portion of stator pole rotating field for obtaining electric current induced spiral magnetic flux will oppose the change of winding, so that the amplitude of the magnetic field moves on the surface creating rotating magnetic field pole





Electric actuator asynchronous

The actuator is an asynchronous induction machine with two windings: a control winding excitation winding and two windings are placed at an angle of 90 ° to each other for creating a rotating magnetic field is very high for the rotor resistance to achieveautofranarea cancellation engine control voltage on the winding rotor due to resistance high engine efficiency is low and the engine is used in electrical power drives and small





Three-phase synchronous electric motor

Three-phase synchronous electric motor electric car is that the rotor speed equals speed rotating magnetic field regardless of engine load electricMotoarele synchronous electric drives are used in high power and large up to tens of MW





Synchronous electric motor stator is similar to electric induction motor stator (armature is formed of a ferromagnetic three-phase stator winding and stator) synchronous electric motor rotor is formed of a ferromagnetic armature winding rotor and rotor current there may be two types construction of rotors: pole-pole drowned and drowned the apparent rotor pole is notched out ferromagnetic armature and rotor winding is placed in notch This type of electric motor is usually a pair of poles and running at high speeds (3000 rpm at 50 Hz ) Apparently has armature rotor pole as a hub feromagentica polygonal cores are placed on the rotor poles and polar coils instead concentrated in some situations can be used concentrated coil polar permanent magnet synchronous electric motor pole Apparently has a large number of poles and operating at lower speeds the rotor winding access is through a ring-like brush electric induction motor pole synchronous motors can couple the apparent even in the absence of excitation current, the electric motor is the reaction that is based on the torque without winding excitation without permanent magnets





Winding rotor (excitation) traveled to DC electric motor creates a magnetic field fixed to the rotor This field "adhered" to the stator and rotor rotating magnetic field rotates synchronously with this inertia, the rotor magnetic field has no time to stick to the rotating magnetic field and synchronous motor can not start by connecting directly to the network are three main methods for starting synchronous motors:

starting in asynchronous - the soles is provided a polar rotor cage is similar cage induction motor and the engine starts delectric on the same principle as the induction motor
start variable frequency - is possible only when a power supply is available with variable frequency or variable frequency converter To have frequency is slow, so speed rotating field have started small enough to allow for the rotor to "stick" of rotating magnetic field
start with an auxiliary motor - resulting in an auxiliary motor requires a synchronous motor connected to the network when the engine reaches a speed close to the synchronism speed auxiliary engine is decoupled synchronous motor accelerates a little longer to reach the synchronism speed and continue to rotate synchronously with rotating magnetic field




Phase synchronous electric motor

It is usually done as reactive synchronous electric motor with permanent magnets on the rotor or without Like induction phase electric motors, electric motors require a single-phase synchronous rotating magnetic field can be obtained either by using an auxiliary phase and capacitor are using spiral cage on poles statoriciSe shareholders generally used in electrical power systems as low as recording and playback of sound and image





Electric stepper motor

The electric motor is a stepper type synchronous electric motor pole apparent both valves control the appearance of a signal on one of the poles of stator rotor moves until its poles will line up opposite stator poles in front of this type of rotor rotation will be practically the pole in the pole, hence the name of the electric motor electric stepper motor control is electronic and can get well-known displacement of the engine control program according to the step motors are used where high precision is required (hard disk, copy)





DC generators

If the rotor spins between two stationary magnetic poles, the rotor current flow in one direction during a half rotation and the other during the other half to produce a constant shift in a single direction of current from such device, it is necessary to provide a means by which the current results have the same meaning throughout the rotations In older machines this is achieved by means of collector plates, a metal ring split in half, mounted on the rotor shaft two halves are isolated and are fixed across the coil of metal or carbon brushes are held on collector plates that rotate while, connecting electric wire coil to the outer While spinning rotor, each brush in contact alternately with collector plates, changing their position when the current in the coil reverses The external circuit is connected to the generator is supplied with a DC current generators are usually used for low voltage to avoid sparks between brushes and pads resulting in high voltage greatest potential generally obtained by such generators is 1,500 volts in some newer machines this reversal is made using high-power electronic devices such as diode rectifiers such



Modern generators use cylindrical rotors which usually consist of a large number of coils placed longitudinally in special places and connected to pads collected in a winding that is a small number of places, the current product will increase and decrease depending on the magnetic field passing a winding rotor which consists of several segments and a circular rotor circuit permanently connected almost constantly since the longitudinal winding always moving through an area with intense magnetic fields from the field of modern generators are usually four or more layers, to increase size and strength for magnetic field smaller poles are sometimes added to compensate for distortions caused by the effect of the magnetic flux of the rotor magnetic



DC motors

In general, are similar in construction with DC generators They can actually be described as generating "work backwards" When current passes through a rotor motorelectric, it generated a magnetic field which generates the electromagnetic force, and resulting rotor action rotates the brushes and collector plates is exactly the same as the generator rotor rotation induces a voltage in the rotor winding induced voltage is opposite The external voltage applied while the electric motor rotor rotates faster, resulting voltage is almost equal to that induced current is small, and the electric motor speed remains constant as long as the electric motor does not operate any task, or the engine does not perform mechanical work other than that made for spinning rotor when the rotor is applied load, voltage will be reduced and a higher current can pass through the rotor The electric motor is able to receive more power from the power you feed, and thus perform more mechanical work



Since the rotation speed control current to pass through the rotor, special mechanisms should be used for starting DC motors when rotor is at rest, he actually has no resistance, and if normal voltage is applied, current will pass a large which could damage the motor carbon brushes or for preventing such accidents electricMijloacele common is the use of series of resistance at first, with the rotor, for the current limit until the engine begins to develop an electric current electric motor sufficiently Along the catch speed, strength is gradually reduced, either manually or automatically



The speed with which an electric motor with DC function, depends on the strength of the magnetic field acting on the rotor and the rotor current The more powerful magnetic field, much less its rotation rate is needed to create a need for a secondary current applied current counter this reason speed DC motors can be controlled by varying the current field







Electricity

Circuit: Any closed port, through which electricity can flow in a circuit containing a simple battery, a switch and a light bulb when the switch is closed, current flows from conventional battery positive terminal to the negative, the switch and bulb , making it shine, current continues through the battery



Electric voltage

Electric voltage is what causes the electrons to move along the circuit It is produced by a potential difference (V) A simple source, as is a battery has two terminals, one positive and the other negative, there is a difference between them potential when two terminals are connected through a circuit, a current arises from the point with higher potential, the potential to lower a potential difference may produce even greater penetration of an insulator, causing current to pass through it A phenomenon of this type occurs when pulsed





Volt

A volt (symbol V) is the unit of electric voltage or potential difference name was given after the name of the Italian scientist Alessandro Volta, who invented the electric battery volt is the potential difference between two points in a conductor a current of one ampere when the power dissipation of this is a watt



AC

The first public electricity supply occurred in late 1800 have different voltage electrical energy, is distributed in the form of current (DC) or alternative current (AC) AC If there is no standard for the frequency at which changes its meaning As the use of electricity created, it became evident that there benefits from standardization voltages Besides energy transfer from one area to another, would have been easier and build power plants can and simplified



Once the generators have chosen and most organizations have adopted a standard of electricity, or install network cables for the elctricitatea generated in an area of ​​the country can be used anywhere else

This national network of cables made more reliable energy distribution elevtrice If a generator is damaged, the current can be taken from another region and if the application create the network can be connected generators

Electricity is distributed in the form of alternative current voltage Since we changed it to be easy with a transformer - a simple, reliable and efficient



In elemental form, an electric transformer consists of two separate coils wrapped around the same iron core when a voltage is applied to one coil alternative, called the primary coil, it creates a variable field induces a voltage in the middle of this alternative in the other coil called secondary