Download AVOP-ELEKTRO-SKA-006

Tutorial: Mechanic - electrician
Topic:
Basics of electrical engineering
the 2nd. Year
Three-phase current
Prepared by: Škarka Miloš
Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002
je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.
An inductive (asynchronous) machine is a
rotary electric machine where it‘s magnetic
circuit is divided by the small gap into two
parts: the stator and the rotor. Both parts
have a winding. One winding (usually on the
stator) is connected to the source of the
alternating current and the other (usually on
the rotor) is connected on short distance and
current in it comes from the electromagnetic
induction which is similar to the transformer.
That's why we call it an inductive machine.
The three-phase inductive motor is
simple, reliable in operation and it doesn‘t
require
any
special
service
or
maintenance. It is being manufactured in
wide range of performance: from a few
watts up to 20MW with a very wide
rotation range from tens of rotations per
minute up to 100 000 rot/min. According
to the design of a motor we distinguish:
a) motors with the armature on the short
b)
motors with the binder armature
Function principle
The rotary field created by the stator has a higher speed
than rotor revs. The basis of asynchronous motor
function is a creation of the rotary magnetic field, which
comes from the alternating current passing through the
winding of the stator. This magnetic field induce the
voltage in the rotor and a formed current cause the
power for rotating the rotor. Rotary field revs are
determined by the frequency of the powering voltage
taken from the network and by the number of poles in
the three-phase motor.
Where f is the frequency of the current and p is the
number of pole pairs in the stator
terminal casing
ventilator
terminal
metal bundle of the stator
stator winding
bearing
shaft
metal bundle
of the rotor
short circuit circle
The motor with the armature on the short has
the rotor winding made of bars, which are at
the end connected on the short by conductive
circles. The magnetic circuit is composed of
metals to minimize losses caused by turbulent
currents.
The binder armature – Except of the bundle of
rotor metals there are even collecting circlets on
the shaft. In rebates of metals there is a threephase rotor winding made of insulated conductors
connected to the star, rarely to the triangle. The
winding of the rotor is connected to three
collecting circlets, which can be also connected to
active resistors used for the engine start.
Armature with circlets
Brushes on the collector
Stator winding
Consist of three coils rotated by 120° powered by the
three-phase current. This creates rotary magnetic field.
There are two ways how to
connect the asynchronous motor
Terminal of the asynchronnous motor connected to the
star and to the triangle.
In case of the connection to the star the
voltage on coils is 230V
In case of the connection to the triangle the
voltage on coils is 400V
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Main parts of the asynchronous motor
The difference between the armature on the
short and the binder armature
Describe the picture
What is the voltage on coils?
Picture 1
Picture 2
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Wikipedia.cz
http://www.myinfo.sk
http://referaty-seminarky.cz
http://fei1.vsb.cz