Various AC Motor Types

 

Various AC Motor Types

 AC motors can be equipped with variable frequency drives, but the improved speed control comes with reduced power quality.

Types of AC Motors:

AC motors divided into three broad categories:

·         Induction  motor

·         Synchronous motor

·         Linear Motor.

 

 

 1- Induction motor

 Voltage is induced in the rotor, the magnetic field to allow for an induced voltage

 Slip: Torque can only occur if the shading ring has an induce current. It is find by the current in the ring and exist if there’s flux variation. S= (N_syn – N_m)/ N_syn

Synchronous
speed (N_syn), shaded ring speed (N_m), “slip” (s)

Slip control and operation of induction machines.

 s = 0:  rotor run at synchronous speed.

 s = 1:   rotor is stationary.

 S is – ve:  rotor runs at speed > synchronous speed.

 S is +vet:  rotor runs at speed < the synchronous speed.

 Advantages:

·         low-price

·          fractional horsepower to 10 MW

 

The two kinds of inductive motors mentioned above can be divided into the following 2 categories:

 

I. Induction motors with a single phase:

These have a single-phase power source, a caged squirrel rotor, and only one stator winding, and they need a method to start the motor. For applications requiring a maximum of 3 to 4 horsepower.

II - Induction motors with three phases:

Its supply generates the revolving magnetic field. These motors are self-starting, have large power capacities, and can have winding (although 90% do). This motor is thought to make up roughly 70% of all industrial motors. They come in ratings ranging from 1/3 to several hundred horsepower.

2. Synchronous Motor: The rotor attempts to align itself with the spinning magnetic field across the stator. It has a dc motor's rotor and an induction motor's stator. AC motor that runs at a constant speed determined by the system's frequency is called a synchronous motor. Due to its low beginning torque and need for direct current towards excitation, it is well suited for low-load starting applications.

The following are the key distinction between synchronous motors & induction motors:

Huge synchronous machines can be picked over induction motors in ratings larger than a few hundred horsepower because they are frequently better than induction machines. In contrast to an asynchronous motor, synchronous motor is energized by a DC source that is external to the device.

Construction:

It's different from an asynchronous motor because a part of the stator I doesn't cause the flux within the air gap. A synchronous motor's primary parts are following

1.      Stator

It has a housing, circuit often made of steel laminations, and a three-phase coil that generates a rotating field, much like the three-phase coil of an asynchronous motor powered by three-phase AC. The stator generates a revolving magnetic field proportionate to frequency input. Synchronous speed for this motor is determined by the equation shown below.

Ns = 120* frequency / Poles, F = Supply Frequency Frequency

P is the no. of poles.

2. Rotor

Rotor Pole is made from high-strength steel laminations with field winding. Field winding compose of an insulated copper and bonded by a temperature, strength epoxy resin.

3. Stator Frame

The bearing housings may be included in the stator frame, which also holds and supports the remaining components.

Operation:  When the "Stator" winding is activated by a poly-phase (often 3-phase) supply, the motor develops a revolving magnetic field. The permanent magnet-like rotor winding receives DC and generates a field that latches onto the revolving magnetic field and spins with it. The motor is believed to be in synchronization, and a force called torque.

Applications All industrial applications requiring consistent speed can benefit from synchronous motors. As synchronous condensers, improving power factor. 

3. Linear motors

Electric motors, which were sliced in a radial plane and unfolded to create a linear configuration. Linear electric motor that may convert rotating motion using belts. Linear motors lack the luxury of a 360-degree enclosed rotation, they have to either lengthen the primary coil assembly or maintain a short-moving secondary's magnet assembly.

Thus, a linear motor is a power source that has experienced its stator & rotor "unrolled" to produce a linear force down its length instead of a torque (rotation).

Applications: sliding doors, along with several related actuators. 

Vehicle acceleration during crash tests. 

Transportation.

Types: 

There are two primary categories of linear motors:

·         LIM, or a linear induction motor.

·         LSM, or linear synchronous motor.

(1) Linear induction motor

Although it operates on the same fundamental principles as conventional induction motors, the linear inductive motor constitutes an AC asynchronous straight motor often made to produce motion directly in a straight line. 3 phase power supplies are widely used in it.

Operating principles

 The motion of the magnetic field

Conductors in the field on which an oscillating linear magnetic field exerts force. Eddy currents will be created in any conductor placed in this field, whether it be a loop, according to Lenz's law, producing an opposite magnetic field. As the magnetic field moves through the metal, both opposing fields compete and produce motion.

 Final result

A straight induction motor exhibits end effects as opposed to a circular one.

If it has at least two poles, a short secondary behaves almost exactly like a rotary machine, while a short primary causes a drop in thrust at low slip (below roughly 0.3) until it has eight poles or more.

 Levitation

This force is zero at zero slip and tends to increase steadily in both directions as the slip increases.

2. LSM, or linear synchronous motor

A linear synchronous motor, also known as an LSM, is a linear motor where the mechanical motion is synchronized with the magnetic field. In straight stepping or switched resistance motors, the magnetic field is generated through online switched Windings and a series of magnetic poles or an adjustable reluctance ferromagnetic rail.