Download 1- A resistor is a device. It adds resistance to a circuit . BY

UNIT 7
THE ELECTRIC MOTOR
Vocabulary:


The induction motor
Relays
Grammar and functions:


Instructions: purpose and method
Describing machine operation
TRANSLATION: THE DC MOTOR
An electric motor is a machine for CONVERTING (CONVERT) electrical energy INTO
mechanical energy. Motors can be designed to run ON direct (DC) or ALTERNATING (AC)
current. The most important parts of DC motors are the rotor, the stator and the brush.
The rotor is the moving part. It contains an armature, WHICH is a set of wire loops
(WHICH/THAT ARE) WOUND (WIND) on a steel core. When current is FED (FEED) to the
armature, these windings produce a magnetic field. The armature and core are mounted ON a
shaft which runs on bearings. It provides a means OF transmitting power from the motor.
The rotor also contains a commutator. This consists OF a number of copper segments insulated
FROM one another. The armature windings are connected TO/WITH these segments. Carbon
brushes are HELD (HOLD) in contact with the commutator BY (MEANS OF) springs. These
brushes allow current TO PASS (PASS) to the armature windings. AS/(WHEN) (A MEDIDA
QUE) the rotor turns, the commutator acts AS a switch making the current in the armature
alternate.
(work/behave
)
LIKE,
act
AS
The stator DOES NOT MOVE/ KEEPS STILL (NO SE MUEVE). It consists OF magnetic and
electrical conductors. The magnetic circuit is MADE (MAKE) up of the frame and the poles.
Wound AROUND the poles are the field coils. THESE (ESTOS) form the stator’s electrical
circuit.
The field coils and the poles are attached. THE LATTER (Estos) …
Aquéllos
THE FORMER
When current is FED (FEED) to them, a magnetic field is SET (SET) up/established/produced
in the stator.
The motor operates ON the principle that when a current-carrying conductor is placed INTO
/(NEAR/NEXT TO) a magnetic field, a force is produced ON the conductor. The interaction of
the forces produced IN the magnetic field of the rotor and the stator MAKES THE ROTOR
TURN/(rotate) – CAUSES THE ROTOR TO TURN (HACE QUE EL ROTOR GIRE)
The forces produced in the magnetic field of the rotor… MAKE
MAKE IT HAPPEN (it is made to happen)
PERMIT IT TO HAPPEN
CAUSE IT TO HAPPEN
STOP IT FROM HAPPENING
LET
PREVENT IT FROM HAPPENING
IT HAPPEN (it is let to happen)
ENABLE IT TO HAPPEN
AVOID IT FROM HAPPENING
ALLOW IT TO HAPPEN
KEEP IT FROM HAPPENING
VIDEO: How an electric motor works
1- What is an electric motor? ……………………………………..
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
2- Which devices are operated by electric motors? …………………………………..
3- All electric motors that produce …………………….. work in the same way ………
…………………………………………… (used to drive ……………………….)
4- An electric motor works like this:
Current flows …………………. to a block of graphite ……………………….
The brush transmits …………..
The commutator consists …………………………….
The commutator is connected to ……………
Current flows from ………………………
Current then flows …………….
The electromagnets are made of ………………………..
This flow of current through the magnet’s coil produces …………………
The field has ……………………….
The current in the armature …………………..
The direction of the motion depends …………….
The split ring of the commutator interacts …………..
Thus the loop in the output shaft continues ……………………………….
Source: http://www.youtube.com/watch?v=Q2mShGuG4RY&feature=related
VOCABULARY
A: Read the definitions and label the diagram
Coil
The coil is made of copper wire - because it is such an excellent
conductor. It is wound onto an armature. The coil becomes an
electromagnet when a current flows through it.
Armature
The armature supports the coil and can help make the electromagnet
stronger. This makes the motor more efficient.
Permanent magnets
There are two permanent magnets. They produce a steady magentic field
so that the coil will turn when a current flows in it.
Some motors have electromagnets instead of permanent magnets. These
are made from more coils of copper wire.
Commutator
Each end of the coil is connected to one of the two halves of the
commutator. The commutator swaps the contacts over every half turn.
Brushes
The brushes press on the commutator. They keep contact with the
commutator even though it is spinning round. The current flows in and out
of the motor through the brushes.
Steel frame
The frame made of magnetic material links the two permanent magnets
and, in effect, makes them into a single horseshoe shaped magnet.
Commercial motors often use a horseshoe magnet
B: Look at the descriptions below. Each one describes a part of an electric
motor. Choose from the list at the bottom.
Provides a steady magnetic field.
Automatically reverses the current in the coil.
Becomes an electromagnet when a current flows.
Feeds the current into or out of the motor.
Supports the coil and can strengthen the magnetic field.
commutator,
brushes,
coil,
armature,
magnets
C: Choose the correct alternative to complete the sentence:
An efficient motor transfers A LITTLE / SOME /MOST of the THERMAL / ELECTRICAL /
CHEMICAL / KINETIC energy to THERMAL / ELECTRICAL / CHEMICAL / KINETIC energy.
Copper wire is used for the BRUSH / COIL / COMUTATOR / ARMATURE of motors because of
its low CONDUCTANCE/ RESISTANCE / DENSITY / CAPACITY
Source: http://resources.schoolscience.co.uk/cda/14-16/physics/copch3pg1.html
D: Find the definitions corresponding to these terms
motor
primary winding
AC motor
shaft
coil
yoke
alternating current (AC)
secondary winding
armature
brush
stator
core
direct current (DC)
winding
air gaps
commutator
torque
rotor
1-The standard power supply available from local electric utility companies. It changes its
direction of flow (cycles)
2- A motor operating on current that flows in either direction. There are two general types:
induction and synchronous.
3- The space between the rotating (rotor) and stationary (stator) member in an electric motor
4 The portion of the magnetic structure of a DC motor which rotates
5 Current conducting material in a DC motor, usually graphite, or a combination of graphite and
other materials. The brush forms an electrical connection between the armature and the power
source
6 they carry and produce the magnetic field when the current passes through them.
7 A cylindrical device mounted on the armature shaft and consisting of a number of copper
segments arranged around the shaft (insulated from it and each other). It provides the means to
transmit the electrical current to the moving armature through the brushes
8 The iron portion of the stator and rotor made up of cylindrical laminated electric steel
9 A current that flows only in one direction in an electric circuit.
10 A device that takes electrical energy and converts it into mechanical energy to turn a shaft.
11 The winding of a motor, transformer or other electrical device which is connected to the
power source
12 The rotating component of an induction AC motor. It is typically constructed of a laminated,
cylindrical iron core with slots of cast-aluminum conductors. Short-circuiting end rings complete
the "squirrel cage," which rotates when the moving magnetic field induces current in the shorted
conductors.
13 Winding which is not connected to the power source, but which carries current induced in it
through its magnetic linkage with the primary winding
14 Cylindrical rod or axle of the motor
15 That part of an induction motor's magnetic structure which does not rotate. It usually contains
the primary winding. It is made up of laminations with a large hole in the center in which the
rotor can turn; there are slots in which the windings for the coils are inserted.
16 Turning force delivered by a motor shaft, usually expressed in inch-pounds
17 Typically refers to the process of wrapping coils of copper wire around a core, usually of
steel
18 A bent crosspiece connecting two other parts
Source: http://www.reliance.com/prodserv/motgen/b9652new/b9652.htm
COMPLETE THE PARAGRAPH
One word has been omitted from each sentence. Try to figure it out
Basic AC Motor Operation
An AC motor has two basic electrical parts: a "stator" and a "rotor" as shown
in the figure. The stator is the stationary electrical component consists
of a group of individual electro-magnets arranged in such way that
form a hollow cylinder, with one pole of each magnet facing toward the center of the group. The
stator is stationary part of the motor whereas the
rotor is the rotating electrical component also consists of a group of
electro-magnets arranged around cylinder, with the poles facing toward the stator poles. The
rotor located inside the stator and is mounted on the
motor's shaft. The objective of these motor components is make the rotor
rotate which in turn cause the motor shaft rotate. This rotation will occur
because the magnetic phenomenon that unlike magnetic poles attract
each and like poles repel. If we progressively change the polarity of the
stator poles that their combined magnetic field rotates, then the rotor will
follow and rotate with the magnetic field of the stator.
Basic electrical components of an AC motor.
INSTRUCTIONS
When giving instructions the IMPERATIVE tense is generally used. However, SHOULD
is often used to give impersonal instructions to operators, etc. on the correct method of
doing something.
Instructions usually consist of:
- The instruction itself (IMPERATIVE or SHOULD)
- The result (PURPOSE)
- The way of carrying out the instructions (METHOD)
Expressing purpose
TO
SO AS TO
IN ORDER TO
+ INFINITIVE
FOR THE PURPOSE OF
WITH THE AIM OF
WITH THE OBJECTIVE OF
+ GERUND
SO THAT
+ CLAUSE
Expressing method
BY
+ GERUND
BY MEANS OF
WITH
WITH THE HELP/AID/ASSISTANCE OF
+ NOUN
EXERCISE
Match the parAgraphs with the pictures:
MAKE YOUR OWN ELECTRIC MOTOR
Fig 1
Fig 3
Fig 2
Fig. 4
Fig 5
The motor is simply a battery, a magnet, and a small coil of wire you make yourself
A: Fig. 4
We start by winding the armature, the part of the motor that moves. To make the armature nice
and round, we wind it on a cylindrical coil form, such as a small battery. Don't try to be neat, a
little randomness will help the bundle keep its shape better.
B: Fig. 5
Now carefully pull the coil off of the form by holding the wire so that it doesn't spring out of
shape.To make the coil hold its shape permanently, wrap each free end of the wire around the
coil a couple of times, making sure that the new binding turns are exactly opposite each other,
so as to allow the coil to turn easily on the axis formed by the two free ends of wire, like a
wheel.
C: Fig. 2
Hold the coil at the edge of a table in order to keep it staight (not flat on the table), with one of
the free wire ends lying flat on the table. With a sharp knife, remove the top half of the insulation
from the free wire end. Be careful to leave the bottom half of the wire with the insulation intact.
The top half of the wire will be shiny bare copper, and the bottom half will be the color of the
insulation. Do the same thing to the other free wire end, making sure that the shiny bare copper
side is facing up on both wire ends
D: Fig. 3
The next step is to make the axle supports. In order to make the supports, take a stiff piece of
bare wire (copper or brass will work, as will a straightened paper clip) and bend it around a
small nail to make a loop in the middle. Do the same to another wire, so you have two supports.
E: Fig. 1
Attach the support wires securely to the battery holder by winding the free ends several times
through the small holes in the plastic at each end. Bend the support wires so the rings are just
far enough apart for the armature to spin freely. Bend them apart a little and insert the armature
into both rings, then bend them back so that they are close to the coil, but not touching it. Insert
the battery into the holder. Place the magnet on top of the battery holder just underneath the
coil.
Note that there is a strip of paper stuck in between the battery and the electrical contact in the
holder. This is the on/off switch. Remove the paper to allow electricity to flow into the motor, and
replace the paper in order to stop the motor.
Source: http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p009.shtml
READING COMPREHENSION: RELAYS
RELAYS
Electromagnetism is the basis on which most electrical devices, like electric motors, electric
bells or relays, work. Let´s see how relays work.
A relay is normally used to open or close another
circuit.
The relay shown on the diagram is used to open or
close a high voltage circuit. The system consists of two
parts: the contacts of the high voltage circuit,
operated(6) by a spring-loaded armature, and the low
voltage electromagnetic circuit.
The electro-magnet is made up of(7) a horseshoe
magnet with two coils(8) wound around the ends of the
piece of iron. These coils are connected to each other
and to a battery by leads. A switch controls the current
flow in the low voltage circuit.
The relay works like this: when the switch is closed,
the current flows through the coils magnetizing the
electromagnet so that the armature is attracted to it; on
moving, this(9) closes the contacts of the high voltage circuit allowing the current to flow
through it(10); when the switch is opened, the armature is pulled back to its original position by
the spring, opening the contacts.
A) Label the diagram
B) True OR False statements. Correct THE FALSE ONES
1- When the switch in the low voltage circuit is closed, the high voltage circuit is broken
2- When the contacts in the high voltage circuit are closed, current flows from the low
voltage circuit to the high voltage circuit
3- When the switch in the low voltage corcuit is open, the armature moves towards the
magnet
4- The contacts in the high voltage circuit are controlled by the electromagnet
5- The function of the iron magnet is to open and close the contacts in the high voltage
circuit
6- The armature becomes a magnet when the current flows through the circuit
7- The electricity is used to magnetize the coil
8- When the contacts are closed they act as conductors.
C) Answer the following questions
1- Translate “operated” into Spanish
2- Give a synonym for “made up of”
3- Explain in English: “coils”
4- Give the reference for “this”
5- Give the reference for “it”
VIDEO: ELECTRIC MOTOR
Take notes while you watch the video and write a short summary
Source: http://www.ehow.co.uk/video_4951184_electric-motor-work_.html
GUIDED WRITING EXERCISE
Join the following sentences using the words provided at the end of the
sentences.
1- A resistor is a device. It adds resistance to a circuit . BY WHICH
2- There are two types of resistors. Resistors can be fixed or variable. CLASSIFY
3- Most resistors are made from two materials. Resistance wire and graphite are used.
EITHER … OR
4- A ceramic coating is applied over the winding. The ceramic coating insulates the
winding. IN ORDER TO
5- An induction motor is a type of alternating current motor where power is supplied to
the rotor. The pronciple is electromagnetic induction. BY MEANS OF
6- An electric motor turns. The cause is the magnetic force between the rotor and the
stator. BECAUSE OF
7- Different types of electric motors can be distinguished. The electric current is supplied
to the rotor in different ways. BY HOW
8- In a DC motor, current is provided directly. Electrical contacts or commutaros are
used. BY MEANS OF
9- Normal transformers change the current. For that purpose they use time varying flux.
BY
10-Induction motors differ from transformers. They use rotating magnetic fields. UNLIKE
11- The current in the primary creates an electromotive field. This field interacts with the
electromagnetic field of the secondary. WHICH / THAT OF
12- In a synchronous AC motor the rotating magnetic field of the stator will impose an
electromagnetic torque on the magnetic field of the rotor. The rotor moves around a
shaft. CAUSING
13- At steady state, the speed of the rotor is ………… the speed of the rotating magnetic
field in the stator. SAME
14- The induction motor does not have any permanent magnets; a current is induced in
the rotor. INSTEAD OF
15- The stator windings are arranged around the rotor. They create a rotating magnetic
field. SO AS TO
16- These currents interact with the rotating magnetic field created by the stator. This
causes a rotational motion on the rotor. RESULTING
17- To induce these currents, the speed of the physical rotor must be less than the
speed of the rotating magnetic field in the stator. FOR THESE CURRENTS …
18- Typical induction motors run on single-phase or three-phase power. Two-phase
motors also exist. DESPITE
VIDEO ELECTROMAGNETISMO
I’ve chosen to make this program about _____________________ because they make use of the three
_____________________________ principles that we learnt in this course in the most ingenious manner.
Briefly, what happens in an _____________________________ is this:
- What happens when a varying current is applied to some coils?
____________________________________
- What is the loop of? ______________________
- Why is it freely suspended? ______________________
- What happens when the loop is placed in the varying field? Because
___________________________________________________________
_______________________________________________
- What happens then to the current when it interacts with the field? ____________
- What is the effect of the force? ______________________________________
- What makes the rotating coil move in this arrangement? __________________
_______________________________________________________________
So, that’s in very simple terms what an __________________________ is like.
- What is the first principle of electromagnetism? ________________________
_______________________________________________________
Here I’ve got an ________________________________________ mounted vertically
_____________________________ I can pass a current
- What is the little magnetic compass used for? ______________________
_________________________________________
- Why is the compass at the moment pointing N-S? ___________________
__________________________________________
When I pass a current _______________________________ (I’m switching the current on), what
happens to the compass pointer? ________________________
___________________________________________
As you can see it is pointing along the conference of a circle where the ____________________ is
the centre of the circle.
- Why does this happen? ___________________________________________
____________________________________________________________
What is the second principle? ____________________________________________
______________________________________________________________________
_______________________________
I can show you that in another demonstration. Again I’ve got a vertically mounted _____________ but this
time the _____________________________________ so it can respond to a force
__________________________
If I pass a current _____________________________ light comes on but as you can see, at the moment
there is apparently no force ________________________________ and it doesn’t move. But if I put a
______________________________________ so that now the magnetic field is
___________________________ of the magnet, the __________________ is going to move vertically
either up or down
Let’s see ______________________________________________.
- What happens if I switch the current on? ______ _____________________________;
- What happens if I reverse the current? _____________________________________. I can move it
backwards and forwards just by reversing the current.
So, the force is dependent __________________________________and is reversed if
___________________________________________
What happens if I ____________________________________?
I take __________________away and turn it over and you can immediately see that
______________________________________
- In which two situations the direction of the force is reversed?
1. ______________________________________
2. ______________________________________
- Which three magnitudes are at the moment mutually perpendicular?
_____________________, _____________________ and _______________________
Remember the left-hand motor rule
Let’s see if I can adjust the _______________________ so that it’s in the same direction
__________________________ is free to move.
________________________________________________ is in that direction too.
- What happens if I place it in the right position, when I put the current on?
_____________________________________ so there is no force ________________
_____________________________. It is always _______________________________ and it is
also at right angles ______________________________________________
- Which is the second principle? ___________________________________
____________________________________
- And the third principle? ____________________________________________
______________________________________________________________
EXTRA READING
ELECTRIC MOTORS
Modern brushless DC motors are amazing devices that can handle torque reversals instantly. In
fact, they can even generate electricity during those reversals!
Instant reversals of direction, however, aren't physically possible (because of inertia) and aren't
actually what your friend wants anyway. I'll say more about the distinction between torque
reversals and direction reversals in a minute.
In general, a motor has a spinning component called the rotor that is surrounded by a stationary
component called the stator. The simplest brushless DC motor has a rotor that contains
permanent magnets and a stator that consists of electromagnets. The magnetic poles on the
stator and rotor can attract or repel one another, depending on whether they like or opposite
poles—like poles repel; opposite poles attract.
Since the electronics powering the stator's electromagnets can choose which of the stator's
poles are north and which are south, those electronics determine the forces acting on the rotor's
poles and therefore the direction of torque on the rotor. To twist the rotor forward, the
electronics make sure that the stator's poles are always acting to pull or push the rotor's poles in
the forward direction so that the rotor experiences forward torque. To twist the rotor backward,
the electronics reverses all those forces.
Just because you reverse the direction of torque on the rotor doesn't mean that the rotor will
instantly reverse its direction of rotation. The rotor (along with the rider of the scooter) has
inertia and it takes time for the rotor to slow to a stop and then pick up speed in the opposite
direction. More specifically, a torque causes angular acceleration; it doesn't cause angular
velocity. During that reversal process, the rotor is turning in one direction while it is being
twisted in the other direction. The rotor is slowing down and it is losing energy, so where is that
energy going? It's actually going into the electronics which can use this electricity to recharge
the batteries. The "motor" is acting as a "generator" during the slowing half of the reversal!
That brushless DC motors are actually motor/generators makes them fabulous for electric
vehicles of all types. They consume electric power while they are making a vehicle speed up,
but they generate electric power while they are slowing a vehicle down. That's the principle
behind regenerative braking—the vehicle's kinetic energy is used to recharge the batteries
during braking.
With suitable electronics, your friend's electric scooter can take advantage of the elegant
interplay between electric power and mechanical power that brushless DC motors make
possible. Those motors can handle torque reversals easily and they can even save energy in
the process. There are limits, however, to the suddenness of some of the processes because
huge flows of energy necessitate large voltages and powers in the motor/generators and their
electronics. The peak power and voltage ratings of all the devices come into play during the
most abrupt and strenuous changes in the motion of the scooter. If your friend wants to be able
to go from 0 to 60 or from 60 to 0 in the blink of eye, the motor/generators and their electronics
will have to handle big voltages and powers.
Source: http://www.howeverythingworks.org/electric_motors.html