“Induction (Asynchronous) Machines”
Submitted by:
Cruz, Levin
Gonzalez, Miguel Ernesto Luis
Soriano, Abigail C.
Submitted to:
Engr. Enrique Manzano
I. Introduction (All) (this includes single phase and three phase)
An Asynchronous motor, is an AC electric motor that uses
electromagnetic induction from the magnetic field of the stator winding in
order for the electric current present in the rotor to produce torque.
An induction motor is also classified as an Asynchronous motor due to
the fact that its operating speed is slightly less than that of a synchronous
speed.
The three phase induction machine is the most widely used rotating
machine in industry. Induction machines are almost always operated as
motors due to their undesirable characteristics as a generator. Single-phase
induction motors are also very commonplace, being used for most household
applications requiring motor.
The induction motor gets its name from the manner in which it
operates. An external AC current is provided to the stator windings of an
induction motor but no external current is provided to the rotor windings.
The AC currents that results in the rotor of an induction motor are the result
of induction(Faraday’s law). A machine is classified as a synchronous machine
if its operating speed is directly proportional to the frequency of the electrical
system.
II. How it Works (Abi) (single phase and three phase)
In a three-phase induction motor, three-phase voltages are applied to
the stator windings. This results in balanced three phase currents flowing in
the stator windings; based on the geometry of the stator coils and the
resulting currents, a rotating magnetomotive force(mmf) is produced by the
stator in the rotor. In an induction motor, the stator is the field winding and
the rotor is the armature. The rotation speed of the stator mmf is dependent
on the number of poles (P) in the stator winding. The number of poles is
always an even number since the magnetic poles always occur in pairs. The
stator mmf rotates at a rate of 2/P revolutions per period. The speed of the
stator mmf rotation is defined as the synchronous speed (ns). The rotating
stator mmf is applied through the air gap between the stator and the rotor.
There are two types of rotors used in induction motors.
Rotor Types
1. Squirrel-cage rotor - conducting bars that are electrically connected at
both ends of the rotor by end rings.
2. Wound rotor - polyphase windings connected to slip rings at both ends
of the rotor.
Both rotor types are contained in slots in a laminated core which is mounted
on the motor shaft.
The conductors of the rotor experience the rotating mmf of the stator. The
orientation of the rotor conductors relative to the rotating stator mmf
produce an electromotive force along the conductor. These forces on the
conductors set the rotor in motion.
III. Characteristics (Levin) (single phase and three phase)
Characteristic of Induction Motor
The classifications of the induction motor are single-phase motor and
three-phase motor.
For a single-phase induction motor, it is not possible to reverse the
direction of rotation within a short time during operation caused by the
inertia torque exerting against the direction the motor is supposed to changed
to. In order to do this, stop the motor first and then change the direction of the
rotation. This will prevent damaging the motor.
The three-phase induction motor has simpler connection, higher
efficiency and reliability than the single-phase motor caused by the direct
power source of the three-phase.
- It is possible for the motor for continuous rated operation
- It is designed to be used in single direction only
- The number of rated revolution of the motor varies depending on the
load imposed on it.
IV. Applications (Migz) (single phase and three phase)
Since induction machines have undesirable characteristics as a generator, it is
most often operated as a motor. Also, the speed of an induction motor is
nearly constant. The speed typically varies by only a few percent going from
no load to rated load.
Since single-phase induction motors are very common place, they are often
used for household appliances that requires a motor. Such as electric fans.
Three-phase induction motors on the other hand are mostly used in industrial
drives due to it being able to carry out their function for many years with
reduced maintenance and adapt themselves to different performances
according to the requirements.
They are used in lifting systems, transporting systems such as conveyors,
ventilation and air conditioning installations, and as pumps and compressors.
V. References
- http://www.ece.msstate.edu/~donohoe/ece3183asynchronous_synchr
onous_machines.pdf
- http://www.nidec.com/en-NA/technology/motor/basic/00027/
- http://www.kocomotion.de/fileadmin/pages/10_PRODUKTE/GGM/Dat
enblaetter/K9Ix40Nx.pdf (characteristic lang)
- http://www04.abb.com/global/seitp/seitp202.nsf/0/41cbf93732b796
63c125761f00500f5f/$file/Vol.7.pdf (three phase application)
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