HOW DO
ELECTRIC MOTORS WORK?
TITLE: Mr
SURNAME: Zwane
INITIALS: BW
Date given; N/A
Date due: N/A
"Imagination
is more important than knowledge."
"Everything
should be made as simple as possible, but not simpler."
"Equations are
more important to me, because politics is for the present, but an equation is
something for eternity." Page 0
Components of the simple DC electric motor
The
electric motor
The
simple two pole DC electric motor has six parts
Permanent
magnet (field magnet): There are two permanent magnets; they produce a
steady electric field so that the coil will turn when the current flows through
it. Some motors have electromagnets instead of permanent magnets; these are
made from more coils of copper wire.
Steel
former: The former made from magnetic
material links the two permanent magnets and in effects make them to be a
single horseshoe or U shaped magnet. As shown below. [1, 2] 
THE COIL (wire)
The reason that a coil is included is to make an
electro-magnet. The coil is made of a copper wire because it is an excellent
conductor. It is wound onto an armature. The coil becomes an electromagnet when
the current flows through it. [4, 2]
The magnet must be as strong as possible
in order for a machine to be operated. Thus, the type of electro-magnet that
should be built must be made from a large number of turns of wire wrapped
around an iron post. The amount of magnetic field obtained from this type of
magnet is proportional to the number of turns; hence, for greater magnetic
field more turns are needed. The field is also proportional to the amount of
current in the wire. Until a limit called saturation is reached, the field from the magnet
increases as the product of the number of turns (N) and the current (I)
increases. This is often abbreviated as NI, (N times I) where N=the number of turns, and I=the current through the wire.[6,7].The empirical formulae that give
a relationship between N (number of turns),I (current) & V (voltage) : Voltage and Turns in Coil:
Voltage (p) x Turns (s) = Voltage (s) x Turns (p)
or Ep x Ts = Es x Ip
Amperes and Turns in Coil:
Amperes (p) x Turns (p) = Amperes (s) x Turns (s)
or Ip x Tp = Is x Ts
Page 1
COMMUTATOR&BRUSHES
A commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power similarly [3]. As a switch, it has exceptionally long life, considering the number of circuit makes and breaks that occur in normal operation. The contact point where a brush touches the commutator is referred to as the commutating plane.A commutator is a common feature of direct current rotating machines. By reversing the current direction in the moving coil of a motor's armature, a steady rotating force (torque) is produced. Similarly, in a generator, reversing of the coil's connection to the external circuit provides unidirectional (i.e. direct) current to the external circuit
.
To keep the torque on a DC motor from reversing every time the coil
moves through the plane perpendicular to the magnetic field, a split-ring
device called a commutator is used to reverse the current at that point.[7,1] The electrical contacts to the
rotating ring are called "brushes" since copper brush contacts were
used in early motors. Modern motors normally use spring-loaded carbon contacts,
but the name still persist. Brushes
press on the commutator. They keep contacts with commutator even though it is
spinning round. The current flows in and out of the motor through the brushes [4, 2].THE ARMATURE
Armature is the part of an electric generator or motor that contains the main current-carrying winding. The armature usually consists of a coil of copper wire wound around an iron or steel core. The coil and core are placed in a magnetic field produced by one or more permanent magnets or electromagnets. If the armature in a generator or motor is designed to rotate, it is called a rotor; if it is a stationary part, it is called a stator. As the rotor turns, the current in the winding reverses every time the commutator makes half a turn. This reversal of the winding current compensates for the fact that the winding has also rotated half a turn relative to the fixed magnetic field. The current in the winding causes the fixed magnetic field to exert a rotational force (a torque) on the winding, making it turn. As the rotor's field comes close to aligning itself with that of the stator, the commutator switches the rotor's polarity, so the motor is perpetually trying to settle [5].
In a generator, either the armature or the magnet is rotated by an outside force (provided by a steam or water turbine or a gasoline or diesel engine) so that the armature coil cuts the lines of the magnetic field created by the magnet. [6, 7, 8].This action produces an alternating current of electricity in the coil. This alternating current is transferred through slip rings (conducting metallic rings) connected to the ends of the coil to a set of brushes (stationary strips of metal) and conducted from there to the electric circuit where it is to be used. If direct current, instead of alternating current, is desired, a commutator (a ring divided into two insulated segments) is used instead of slip rings. In an induction motor (the most widely used type of electric motor), an alternating electric current is supplied to the motor's electromagnets. The oscillating magnetic field produced by the magnets induces a current in the armature, causing it to rotate [8]. Page 2
THE REFERENCES
1.
Joseph Henry
1797-1878
2.
www.electronics –tutorials.ws/electromagnets
4.
Resources.schoolscience.co.uk- Physics(14-16)
5.
www.swigercoil.com
6.
www.armature.com
7.
science.howstuffworks.com
8.
http//hyperphysics.phy-astr.gsu.edu/hbase
