AC AND DC MOTORS PDF

adminComment(0)

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.


Ac And Dc Motors Pdf

Author:MADALINE CATANO
Language:English, Japanese, Portuguese
Country:Vanuatu
Genre:Politics & Laws
Pages:544
Published (Last):17.05.2016
ISBN:415-5-18490-661-6
ePub File Size:22.65 MB
PDF File Size:9.14 MB
Distribution:Free* [*Registration Required]
Downloads:38527
Uploaded by: MAVIS

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).

DC electric motors use different motor connections of the field and armature winding to produce different speed and torque regulation.

Unlike AC electric motors, DC electric motor speed can be controlled within the winding by changing the voltage applied to the DC motor armature, or by adjusting the field frame current. Most DC electric motors today are manufactured to be controlled with industrial electronic DC drives. DC electric motors are still used in many applications across the globe such as paper producing machines, and steel mill rolling machines. DC motors are usually seen in applications where the motor speed needs to be externally controlled.

AC motors work best in applications where power performance is sought for extended periods of time.

All DC motors are single phase, but AC motors can be single phase or three phase. In AC motors the armature does not rotate and the magnetic field continuously rotates.

In some applications today, DC electric motors are replaced by combining an AC electric motor with an electronic speed controller, known as variable frequency drives.

DC electric motors are replaced with an AC electric motor and an electronic speed controller because it is a more economical and less expensive solution. DC electric motors have many moving parts that are expensive to replace, and DC electric motor repair is usually more expensive than using a new AC electric motor with an electronic controller.

You can save thousands of dollars by switching from three phase DC to AC motors. AC Motors now own the majority of the market share, driving down costs. AC Variable Frequency Drives such as the ones we sell at our web store give complete control over the speed and power consumption of an AC Motor.

Although many of us have learned how a basic motor works, from simple science books and web pages such as this, many of the motors we use everyday—in everything from factory machines to electric trains—don't actually work that way at all. What the books teach us about are simple direct current DC motors, which have a loop of wire spinning between the poles of a permanent magnet ; in real life, the majority of high-power motors use alternating current AC and work in a completely different way: they're what we call induction motors and they make very ingenious use of a magnetic field that rotates.

Let's take a closer look!

Need A Variable Frequency Drive To Control The Speed / Soft Start Your AC Or DC Motor?

Photo: An everyday AC induction motor with its case and rotor removed, showing the copper windings of the coils that make up the stator the static, non-moving part of the motor. These coils are designed to produce a rotating magnetic field, which turns the rotor the moving part of the motor in the space between them.

How does an ordinary DC motor work? Artwork: A DC electric motor is based on a loop of wire turning around inside the fixed magnetic field produced by a permanent magnet.

The commutator a split ring and brushes carbon contacts to the commutator reverse the electric current every time the wire turns over, which keeps it rotating in the same direction.

The simple motors you see explained in science books are based on a piece of wire bent into a rectangular loop, which is suspended between the poles of a magnet. Physicists would call this a current-carrying conductor sitting in a magnetic field.

What is the difference between an AC motor and a DC motor?

When you hook up a wire like this to a battery , a direct current DC flows through it, producing a temporary magnetic field all around it. This temporary field repels the original field from the permanent magnet, causing the wire to flip over.

Normally the wire would stop at that point and then flip back again, but if we use an ingenious, rotating connection called a commutator, we can make the current reverse every time the wire flips over, and that means the wire will keep rotating in the same direction for as long as the current keeps flowing. That's the essence of the simple DC electric motor, which was conceived in the s by Michael Faraday and turned into a practical invention about a decade later by William Sturgeon.

You'll find more detail in our introductory article on electric motors. Before we move on to AC motors, let's quickly summarize what's going on here.

In a DC motor, the magnet and its magnetic field is fixed in place and forms the outside, static part of the motor the stator , while a coil of wire carrying the electric current forms the rotating part of the motor the rotor.

The magnetic field comes from the stator, which is a permanent magnet, while you feed the electric power to the coil that makes up the rotor. The interaction between the permanent magnetic field of the stator and the temporary magnetic field produced by the rotor is what makes the motor spin. How does an AC motor work? Unlike toys and flashlights, most homes, offices, factories, and other buildings aren't powered by little batteries: they're not supplied with DC current, but with alternating current AC , which reverses its direction about 50 times per second with a frequency of 50 Hz.

If you want to run a motor from your household AC electricity supply, instead of from a DC battery, you need a different design of motor.

In an AC motor, there's a ring of electromagnets arranged around the outside making up the stator , which are designed to produce a rotating magnetic field.

Inside the stator, there's a solid metal axle, a loop of wire, a coil, a squirrel cage made of metal bars and interconnections like the rotating cages people sometimes get to amuse pet mice , or some other freely rotating metal part that can conduct electricity. Unlike in a DC motor, where you send power to the inner rotor, in an AC motor you send power to the outer coils that make up the stator.

The coils are energized in pairs, in sequence, producing a magnetic field that rotates around the outside of the motor. Photo: The stator makes a magnetic field using tightly wound coils of copper wire, which are known as the windings.

DC motors and AC motors: selection and application analysis

When an electric motor wears out, or burns out, one option is to replace it with another motor. Sometimes it's easier to replace the motor windings with new wire—a skilled job called rewinding, which is what is happening here.

How does this rotating field make the motor move? Remember that the rotor, suspended inside the magnetic field, is an electrical conductor. The magnetic field is constantly changing because it's rotating so, according to the laws of electromagnetism Faraday's law , to be precise , the magnetic field produces or induces, to use Faraday's own term an electric current inside the rotor.

If the conductor is a ring or a wire, the current flows around it in a loop. If the conductor is simply a solid piece of metal, eddy currents swirl around it instead. Either way, the induced current produces its own magnetic field and, according to another law of electromagnetism Lenz's law tries to stop whatever it is that causes it—the rotating magnetic field—by rotating as well.

You can think of the rotor frantically trying to "catch up" with the rotating magnetic field in an effort to eliminate the difference in motion between them.

Electromagnetic induction is the key to why a motor like this spins—and that's why it's called an induction motor. How does an AC induction motor work? Here's a little animation to summarize things and hopefully make it all clear: Two pairs of electromagnet coils, shown here in red and blue, are energized in turn by an AC supply not shown, but coming in to the leads on the right.

Electric motor

The two red coils are wired in series and energized together and the two blue coils are wired the same way. Since it's AC, the current in each coil doesn't switch on and off abruptly as this animation suggests , but rises and falls smoothly in the shape of a sine wave: when the red coils are at their most active, the blue coils are completely inactive, and vice-versa.

As the coils are energized, the magnetic field they produce between them induces an electric current in the rotor.

This current produces its own magnetic field that tries to oppose the thing that caused it the magnetic field from the outer coils. The interaction between the two fields causes the rotor to turn. As the magnetic field alternates between the red and blue coils, it effectively rotates around the motor. The rotating magnetic field makes the rotor spin in the same direction and in theory at almost the same speed.A typical drive system is assembled with a electric motor may be several and a sophisticated control system that controls the rotation of the motor shaft.

The design allows zero winding overhang; percent of the windings are active. Since N is directly proportional to the Eb. A common use of the series motor includes a crane hoist meaning a heavy load will be manipulated. Parasitic eddy currents cannot form in the rotor as it is totally ironless, although iron rotors are laminated.

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.

After many other more or less successful attempts with relatively weak rotating and reciprocating apparatus Prussian Moritz von Jacobi created the first real rotating electric motor in May