Types of AC motors (1 Viewer)

[porcupinetree]

Ok, so I'm a little confused about this.

9.3.5i says "describe the main features of an AC electric motor"

My teacher says that he suspects that this refers to an induction motor, however both textbooks that I have (Physics in Focus and Excel HSC Physics) state that an "AC motor" is just like a DC motor but with slip rings, and an "AC induction motor" is, well, an induction motor. Excel also mentions some stuff about synchronous motors.

Basically, I'm confused about what type of motor this dot point refers to. Is it referring to an induction motor, or a motor with slip rings that is fed AC current? Or something else? And does this motor have a specific name other than "AC motor" or "AC electric motor"?

Thanks.

 

[astroman]

2.5.1 Describe the main features of an AC motor>>https://www.scribd.com/doc/49281225/5/Motors-and-Generators

The AC induction generator used in large-scale power stations has a very similar structure to an AC induction motor. However, in an AC induction generator, the rotor is an electromagnet powered by a separate DC circuit, and the stator consists of 6 coils. A source of torque is used to rotate the electromagnet at 50 revolutions per second, which causes AC electricity to be generated in the field coils.

There are three types of AC motors- standard AC motors, universal motors and AC induction motors,and they each work differently. A standard AC motor is essentially identical to an AC generator, with astator providing a magnetic field, a rotor that current is passed through, and slip rings connecting therotor to a circuit. In addition, an AC motor usually has a fan to keep the rotor cool, a ferromagneticcore in the rotor to strengthen the magnetic field and it runs at 50 revolutions per second, the sameas the frequency of AC power oscillation (50Hz). A universal motor is similar to a DC motor. It canoperate on an AC or DC supply. Power is fed in, and runs through electromagnetic stators beforeentering a commutator. Each brush is connected to a wire that comprises one of the field coils, andis also connected to one end of a circuit. With a DC source, the commutator switches the currentand the motor operates. With an AC source, although the direction of current being fed into thecommutator is varying, the same variations are fed into the field coils, with the net effect that ACoscillation is cancelled out and the motor runs.

AC induction motors are entirely different. Induction motors have a rotor that is not connected to apower source- instead changing flux is used to induce a current in the rotor. This means that thereis very low friction as the rotor is not actually in contact with the rest of the motor, and it alsomeans there is very little wear and tear. AC induction motors have a more complicated stator withseveral field coil pairs. There are a total of 6 field coils, and each opposite pair is fed one phaseof triple-phase AC power. This sets up a rotating magnetic field inside the stator. The rotor of aninduction motor is generally similar to a squirrel cage (the type that allows pets to run endlessly),with two end rings and aluminium or copper bars linking the end rings to form a cylindrical shape.This cylinder is encased in a laminated iron armature so that the magnetic field passing through therotor cage is intensified. As the field rotates, it induces current in the bars of the squirrel cage. Thiscreates a force in the same direction as the rotation of the magnetic field, from Lenz’s Law. Thesquirrel cage then rotates, ‘chasing’ the changing magnetic field.

Remember- AC motors have a stator, rotor and slip rings. They also use an iron core and usually afan. A universal motor uses a commutator and has a magnetic field generated using field coils. AC induction motors have a stator with 3 pairs of field coils (for a total of 6), and a “squirrel cage” rotor.