Throughout the weeks the
lesson that I found the most interesting was week 7 where Mo explained the
differences between AC/DC motors. The reason I found this so interesting was
I’ve liked and enjoyed being around vehicles all my life.
Taking components apart
to the last piece is one of my favorite things to do, this is because I like to
find out how everything works together and why it’s constructed the way it is.
Nikola Tesla was the
first person to invent and construct the first induction motor. This was back
in 1887. Nikola first began to experiment in 1888. He owed his own experimental
shop in New York. Nikola Tesla was born in Croatia on the 10th July
1856. He immigrated to the United States of America in the early 1880’s.
Frank Julian Sprague was
the first person to invent the first practical DC Motor. This motor worked was
a non-sparking motor that worked under variable loads without the change of
speed. Frank Julian Sprague was born one year later than Nikola Tesla. Unlike
Nikola Tesla, Frank Julian Sprague was born in the United States of America
where he attended the United States Naval Academy where he was very successful
in mathematics which led him to graduate 7th out of 30+ other
AC MOTOR- Induction Motor
Most homes, factories
and offices are supplies alternating current which has a frequency of around
The induction motor has two
main parts the stator which is stationary and the rotor which rotates. The
stator is a three-coil winding and three-phase AC power input is supplied to it.
The winding passes through the holes of the stator these holes are made by
stacking quite thin permeable steel laminations; these laminations are usually
inside cast iron or a steel frame. When a three-phase current passes through
the windings it creates a rotating magnetic field. The turning speed of the
magnetic field is known as the synchronous speed. According to Faradays law because
the magnetic field is varying an EMF will be induced in the loop.
An EMF will produce a current
in the loop, according to Lorentz law when an electromagnetic field is produced
on the loop this will cause the loop to begin to rotate. This same sort of
process happens inside a three-phase, squirrel cage, induction motor.
The three-phase AC current
passing through the stator produces a rotating magnetic field. Current will be
induced in the base of the squirrel cage, which is shorted by the end-rings.
This will cause the motor to commence to rotate. This is the reason why this
type of motor is called the induction motor because electricity is induced on
the rotor with avail of electromagnetic induction rather than a direct
connection. The avail such electromagnetic induction insulated iron core
laminas are placed inside the rotor.
Tiny sizes of iron ascertain that Eddy current losses are
kept as low as possible. The induction motor has a quite big advantage as it is
self-starting. Induction motors rule both the domestic and industrial worlds. An
induction motor does not require a permanent magnet. They do not even require
brushes, commutator rings not even a position sensor unlike a dc motor. The
speed of an induction motor can be controlled by changing the input power.
A DC MOTOR speed can be
changed by changing the supply voltage or by changing the field winding
current. A DC MOTOR uses power directly from the battery.
In a DC Motor the stator
provides a constant magnetic field, and the armature which is a simple coil is
connected to a DC power supply through a pair of commutator rings. When the
current flows through the coil an electromagnetic force is induced on it
according to the Lorentz law.
This means that the
coil will begin to rotate. As the coil rotates the commutator rings that are
connected to the DC power supply have opposite polarity. This results that on
the left side of the coil the electricity will always flow away, and on the
right side the electricity will always flow towards. This ensures that the
torque action is also in the same direction throughout the motion, this means
that the coil will continue to rotate. But if you look at the coil action
closely you will notice that as the coil is nearly vertical to the magnetic
flux the torque action is approximately zero.
This result is irregular motion of the motor
that’s if you chose to run this sort of dc motor. On the other hand to overcome
this problem more loops are added to the motor with a separate commutator pair.
With this sort of arrangement as the first loop is perpendicular to the
magnetic flux, the second loop will be connected to the power source so the
motor force is always present in the system. The more loops you add to the
motor the smoother the motor rotation.
In a practical motor
the armature loops are fitted inside slots with highly permeable steel layers
this will result in the enhancement of the magnetic flux interaction. Spring
loaded commutator brushes help to keep the contact with the power source. A
permanent magnet is used is smaller DC motors. Most often an electromagnet is
used, the field coil of the electromagnet is powered from the same DC source.
The field coils can be
connected to the rotor windings in two different ways which are in parallel or
in series. The two main differences are that the motor connected in series
wound motor has very high starting torque but once you apply load the speed
will drop drastically. On the other hand the parallel motor also known as the shunt
motor has a low starting torque but when load is applied the speed of the motor
DC Motor Parts
DC MOTOR PARTS
DC MOTOR PARTS
and negative terminals
DC MOTOR ADVATAGES AND DISADVATAGES
One of the main advantages of a brushed DC MOTOR is that it
is easy and very cheap to produce. It is very simply built.
On the other hand it does require a lot of looking after
due to the wear on the brushes.
DC MOTOR ADVATAGES AND DISADVANTAGES
A brushless DC Motor has a big advantage over the brushed
dc motor which is that it is highly efficient and does not require as much
maintenance. It has a higher output power.
The main disadvantage is that it is very expensive to
produce and reproduce. They also require electronic components to control and
INDUCTION MOTOR ADVATAGES AND DISADVATAGES
An ac induction motor is self-starting; this is a good
advantage as it does not need a direct power source. Unlike the brushed dc
motor it does not need as much maintenance to keep it running. It is highly
One of the disadvantages is that you cannot change the
speed of the induction motor as easy as they are pretty much running at one
ac motor advantages and disadvantages
A synchronous ac motor does not require a dc power for the
rotor excitation they also require rotor windings unlike the induction motor as
an induction motor uses a squirrel cage.
Synchronous motors will not start at load the motor has to
have zero load applied to it for the motor to be able to start. The kilowatt power
output costs more to produce rather than an induction motor.
cars- Tesla model S
The powerhouse of the Tesla car is invention by Nikola
Tesla. (For more information about Nikola Tesla you can read the introduction
to this assignment). The Tesla model s is ran by an induction motor which
Nikola Tesla discovered. The induction motor has two main parts the stator and
the rotor. You can find more information on this motor on page 4-5. The rotor is basically a collection of
conducting bars which is short circuited by the end rings. A three phase ac
current in the coil creates a magnetic field. The Tesla model s produces a
four-pole magnetic field. This turning magnetic field induces rotor bars to
make it turn; the induction motor is robust and powerful. The induction motor
speed depends on the frequency of the ac power supply. Just by changing the
frequency you will be able to change the speed of the vehicle road wheels. This
known fact makes car speed very controllable and reliable. The motor speed can
range from zero to 18,000rpm, this is the most sizeable advantage that electric
cars have compared to internal combustion cars.
An internal combustion engine produces usable torque and
power output only within limited speed range. Therefore, connecting the engine
rotation directly to the drive wheel isn’t the best idea. That’s why a
transmission is put in to vary the drive wheel speed, where as an induction
works efficiently at any speed range. Therefore no speed varying transmission
is needed for an electric car.
The power output of an internal combustion engine is always
uneven many accessories are needed to overcome this issue. Where as you will get direct rotational
rotation motion and power output with an induction motor. Many part, components
are simply removed which makes the engine lighter compared to a compared to a
combustion engine. As a result of doing this you will get a higher power to
weight ratio making the vehicle faster lighter and more environmentally
and disadvantages of electric cars
sound- people can’t hear them coming
drive range per charge
In conclusion, I really enjoyed the AC and DC topic, this
is because it got me more inspired to learn more about the different variety of
motors that the previous and the current generation still use; this is because
most of them are so easy to produce and relatively cheap and very reliable.
This subject was very interesting just learning about how motors change and
help today’s world to produce electricity for big and small cities and villages.
This topic didn’t just teach me this but it also taught me that a lot of stuff
look more complicated than they are.