In this article you will learn what AC motors, consider their device, the principle of action, range of applications.It should be noted that today in the industry for more than 95 percent of all used engines accounted for asynchronous machines.They have received widespread due to the fact that they have high reliability, they can serve for a long time due to its maintainability.
The principle of induction motors
To understand how the motor can conduct a little experiment.Of course, you will need to have a special tool.Install the magnet in the shape of a horseshoe so that it was set in motion by the handle.As you know, the magnet has two poles.Between them is necessary to arrange the cylinder is made of copper.With the expectation that it may freely rotate around its axis.Now the experiment itself.Begin to spin the magnet, this creates a field that moves.Inside the copper cylinder begin to arise eddy currents that counteract the field magnet.
As a result, a copper cylinder starts to rotate in the direction in which the moving permanent magnet.And its speed is slightly lower.The reason for this - with equal speed power line no longer intersect with the field magnet.The magnetic field rotates synchronously.But the speed of movement of the magnet Nonsynchronous.And if a little cut definition is asynchronous.Hence the name of the electric machine - induction motor.If the rough, then the circuit of the AC motor is approximately the same as in the above experiment.Only the magnetic field created by the stator winding.
DC motors
They differ somewhat from the AC induction motors.Firstly, there has one or two stator windings.Secondly, a method for changing the rotational speed of the rotor is somewhat different.But the direction of rotation of the rotor changes polarity (for asynchronous machines are reversed-phase mains).Change speed of the rotor of the DC motor can, if increase or decrease the voltage supplied to the stator winding.
DC motor can not work without the excitation winding, which is located on the rotor.The transfer voltage is done by the brush assembly.It is the most unreliable element design.The brushes are made of graphite, eventually erased, leading to failure of the motor, it needs repair.Note that the electric DC and AC have the same elements, but their structures differ considerably.
design motor
Like any other non-static electric machine, induction motor consists of two main parts - the rotor and stator.The first element fixed on it are placed three windings are connected in a certain pattern.The rotor is movable, its design called "squirrel cage".The reason for this name is that the internal structure is very similar to the wheel with the protein.
last, of course, not the motor.Centering the rotor is made with two covers mounted on the stator.They are the bearings that facilitate rotation.On the back of the motor impeller set.With the help of an electrical machine cooling is carried out.Stator made ribs that improve the heat transfer.Thus AC motors operate in a normal thermal regime.
stator induction motor
It should be noted that the stator poles of modern asynchronous motors unexpressed.Simply put, the entire inside surface is perfectly smooth.In order to reduce eddy current losses, the core is collected from very thin sheets of steel.These sheets are very close contact with each other and then fixed in the case of steel.The stator has grooves for laying the windings.
windings made of copper wire.Connecting them is in a "star" or "delta".In the upper part of the body has a small plate, fully insulated.There are terminals for connection of the windings and connections.And you can connect the winding using jumpers installed in the panel.The device is an AC motor allows you to quickly carry out its connections in the desired pattern.
rotor induction motor
about him was too little is said.He looks like a squirrel cage.The rotor design is assembled from thin steel sheets like the stator.The winding is the rotor slots, but it can be of several types.It all depends on whether or phase squirrel cage.The most common latest designs.Thick copper rods are placed in the grooves without insulating material.At both ends of these rods are connected with copper rings.Sometimes, instead of the "squirrel cage" used alloy rotors.
But there is AC motors with slip-ring motors.They are used much less often, mainly for electric motors that have a very large capacity.The second case, in which you must use in the wound rotor motors - the creation of a lot of effort at the time of launch.However, for this you need to use a special dimmer.
Ways to run induction motor
Start AC induction motor is simple, you just have to connect the stator windings in three-phase network.A connection using magnetic contactors.Thanks to them, you can virtually automate the start.Even the reverse can be done without too much difficulty.But in some cases it is necessary to reduce the tension which is applied to the stator windings.
is produced through the use of connection diagrams of the "triangle".This launch is produced when the winding connected in a "star".With increasing speed, the maximum value of the winding must be switched to the scheme "triangle".Thus there is a reduction in current consumption is approximately three times.But be aware that not every stator can function properly when connected on a "triangle".
speed control
in industry and everyday life are becoming increasingly popular frequency converters.With their help, you can flick of the wrist to change the rotational speed of the rotor.It should be noted that AC motors are used with frequency inverters in most mechanisms.It allows for fine adjustment drive, with no need to use magnetic actuators.All controls are connected to the terminals of the frequency inverter.Settings allow you to change the acceleration of the rotor of the motor, it stops, while the minimum and maximum speed as well as many other safety features.
Conclusion Now that you know how the work of the AC motor.Even studied the design of the most popular of the induction motor.It is the cheapest of all, that on the market.In addition, for normal operation there is no need to use different auxiliary devices.In particular, rheostats.And only such an addition, as the frequency converter is able to facilitate the operation of the induction motor, greatly expand its capabilities.
