Introduction to electrical motor
An electric motor is a machine that can convert
electrical energy and transform it into mechanical energy. An electric motor has
a coil of wire which creates a magnetic field when the electricity flows
through it. The magnetic field is the region of influence of a magnet. The magnetic
field is shown in figure 1. This is known as electromagnet. In figure 2, a
simple electromagnet is shown. The current is sent through the loop of the wire
that is positioned inside the magnetic field. “When current flows through a magnetic
field, the charges feel a magnetic force on them at 90 degrees to the direction
they’re moving. Because of this, the wire as a whole feels a big force. And
this force causes the loop of wire to move; electrical energy has been changed
into movement.” (Wood, David 2017).
Drawing magnetic field diagram (Unknown Author (2014) Drawing
magnetic field diagram.
Figure 2, Electromagnet (Wood, David 2017).
2. Ceiling fans
A ceiling fan is a mechanical fan that usually
works through electrical power. It is used on the ceiling of any room. In
general, the ceiling fan rotation power is typically slower than other types of
fans such as electric desk fans.
In the figure 3, an illustration of a ceiling
fan is provided. They tend to work on induction motors that convert electrical
energy into mechanical energy. The mechanism of the ceiling fan is that the
capacitor of the fan torques up the electric motor which allows it to run just
after a start. The current reaches the motor and makes its path towards the
coil. The current then conducts through the wire, while the magnetic field is
created, and exerts force in a clockwise movement, which then converts electrical
energy into mechanical energy. From this, the motor coil begins to rotate; the
coils then spin and the fan captures the motion while transferring it to the fan
Figure 3, Ceiling
fan drawing (Jeremy
2.1 Ceiling fan features
There are various features that a ceiling fan
(1) Blade size: It is important to know what blade size would be more
suitable, depending on the room size. In figure 4, it is demonstrated that blades
come in several sizes, and measured by the full blade sweep they produce 30,
42, 44, 46, 50, 52 and 60 inches.
Figure 4, Ideal blade length per room size. (Sawyers,
In figure 5 and 6 you can see the suggested
lengths of drop rod for ceiling fans that have a range from 9 to 13 or more. It
shows in figure 5 the right distance to install a ceiling fan for safety
Sizing and locating a fan (Vandervort, Don 2016).
Suggested lengths of drop rod for ceiling (Vandervort, Don 2016).
7, we can see the rotation rule of blades; a counter clockwise rotation pushes
air downward to a room and will make you feel colder whereas reverse rotation
will draw air upward to circulate hot air.
Figure 7, Which way should a ceiling fan spin. (Alucard 2017).
(2) Material of fan: ceiling fans can be made
from different materials such as wood, plastic or wicker.
Figure 8 shows the
ability of a fan through its control of it speed. In figure 9-11, the 3 type of
speed regulators are provided.
Fan speed regulator (Erlmarli, Khiri and others 2017).
Figure 9, Conventional
fan regulator (Erlmarli,
Khiri and others 2017).
Figure 10, Electronic
fan regulator (Erlmarli,
Khiri and others 2017).
Capacitive type regulator (Erlmarli, Khiri and others 2017).
Fan speed regulator. (Erlmarli, Khiri and others 2017).
For the induction motor, the variable speed
induction motor equation is presented in figure 13-14.
Variable speed induction motor torque equation (Rayner, Robert 2017).
Variable speed induction motors (Rayner, Robert 2017).
Figure 15 shows what is inside a ceiling fan.
Figure 15, inside a
ceiling fan (Sawyers, Harry 2011).
2.2 Ceiling fan motor type
Typically, in a ceiling fan, an AC Motor is used.
It runs in a single-phase with an induction motor assembled in it. The AC motor
has two basic parts: a stator and a rotor, which are shown in figure 16. “The stator
is in the stationary electrical component. It consists of a group of individual
electro-magnets arranged in such a way that they form a hollow cylinder, with
one pole of each magnet facing toward the centre of the group. The rotor is the
rotating electrical component. It also consists of a group of electro-magnets
arranged around a cylinder, with the poles facing toward the stator poles. The
rotor is located inside the stator and is mounted on the AC motor’s shaft.” (AC
Motor Diagrams-Basic Stator and Rotor Operation 2017).
Basic electrical components of an AC motor. (Unknown Author (2017) Basic electrical components of an AC Motor).
an induction motor to be able to work, there is a need to have different speeds
between the rotor and stator fields, as demonstrated in figure 17.
speed differences between rotor and stator fields (Rayner, Robert 2017).
Inductor motors involve rotating magnetic
fields, which move the machinery. Figure 18 shows the different components of
the inductor motor:
1. Wires- they are conductors that carry
electrical current to sets of cooper coils which are called windings.
2. Windings- they are wrapped around steel bars
and are energised windings from an electromagnet, which is called a stator.
3. Stator- the fluctuation polarity creates a
rotating magnetic field in the stator. This field crosses a 0.3 mm gap to
induce current in the lamination of the rotor, which spins around the
4. Rotor- The rotor faces a certain angle; the
stator faces the rotor. The distance between the two, and the geometry of slots
carved into each set of laminations create two out of phase magnetic fields.
The rotor spins as it repels the rotating magnetic field induced by the stator.
5. Housing- the illustration in figure 10 shows
the inside of a motor. It is shown that the fan blades attach to the bottom of
the housing. The vents on top cool the motor, as it needs breeze in order to do
Single phase inductor motor of a ceiling fan (Sawyers, Harry 2011).
Electrical characteristics are provided in
figure 19 and 20.
Electrical characteristics part 1 (Rayner,
Electrical characterises part 2 (Rayner,
2.3 Ceiling fan energy and characteristics
Single-phase inductors are simple and reliable
motors that can produce energy up to the unit of 1 KW. The torque characteristics
of a single-phase inductor are similar to the 3 phases. The difference is in
the starting torque because there isn’t any starting torque and capacitive
split phase starting method is applied in this case. At the starting point, a
single-phase supply is divided into two phases at almost 90 degrees out of
phase with each other to be able to get a rotating flux. In the following 21-23, the characteristics of
an induction motor are shown.
Induction motor characteristic (Rayner, Robert 2017).
Induction motor characteristic example, part 1 (Rayner, Robert 2017).
Induction motor characteristic example, part 2 (Rayner, Robert 2017).
Different ceiling fans have different power
outputs. Fans from the size range of 36 inches to 56 inches use 55 to 100
Figures 24 and 25 show the global electricity
Global electricity prices part 1. (Unknown Author (2017) Global Electricity
Global electricity prices part 2 (Unknown Author (2017) Global Electricity
In figure 26, the energy used for a 48-inch
ceiling fan has been calculated, considering that it is being uses for 5 hours
a day at 75 Watts, at the United Kingdom rate of 25 kWh.
Electricity usage of a ceiling fan. (Unknown Author (2017) Electricity usage of a
RPM low-speed fans have speeds of around 40 to 70 rpm per minute; the
medium speed range is from 100 to 115, whereas high speeds hit 180 to 200.
For the single phase start capacitive run
induction motor, it is developed from a low torque operation which has a range
of 0.22 to 0.72N-m, depending on the size of the blade. In Figure 27, the
comparison between different single-phase motors is shown.
Figure 27, Type of motor load. (Erlmarli,
Khiri and others 2017).
In the following figures 28 and 29, the motor
torque output is provided.
Motor torque output part 1 (Rayner, Robert 2017).
Motor torque output part 2 (Rayner, Robert 2017).
2.4 Ceiling fan efficiency
The stator of a single-phase induction motor has
laminated stamping, to be able to reduce current losses on its periphery. When
the stator is given a single-phase AC supply, the magnetic field is produced. The
motor will then be rotated at a speed slightly less than the synchronous speed
of Ns which is given by:
In this equation f = supply voltage frequency,
P= number of poles of the motor.
The single-phase induction motor is very widely
used in home applications as well as industrial, despite the fact that it has a
lower power rating because of the larger quantity and the fact that part of the
total motor electricity consumption goes to this type of motors. Therefore, efficiency
in this motor is usually low. One method for the improvement of efficiency is
the well-known stator voltage control. Although it has very limited saving
capabilities in a limited speed range, it doesn’t have the potential of a
variable frequency supply.
According to the research carried out by Bijan
Zahedi the Maximum Efficiency conditions are shown in figures 30 to 33.
Figure 30, Maximum
efficiency condition part 1 (Zahedi, Bijan 2009).
Maximum efficiency condition part 2 (Zahedi, Bijan 2009).
Maximum efficiency condition part 3 (Zahedi, Bijan 2009).
Maximum efficiency condition part 4 (Zahedi, Bijan 2009).
From these equations given in the figures 31-33,
it is clear that there’s a possibility to achieve the maximum efficiency, following
the conditions. However, the consequence of this is that this procedure is
Figure 34 shows that single-phase motors are
less efficient than three-phase induction motors. A three-phase motor has an
efficiency of about 74 %. On the other hand, the single-phase motor has the
efficiency of about 64 %. The figure below shows that the full load of the
efficiency of the single-phase motor is 64.66 %.
Figure 34, Single phase data (Perez,
The best way to achieve maximum efficiency is by
using the windings current phase as an appropriate electrical control variable.
Through this implementation, there is no need for any mechanical sensor. The
motor slip is controlled by controlling the windings current phase difference.
A VSD with the ability of speed control and efficiency maximising in different
operating points can be designed. According to experimental designs, it shows
that it is superior over the constant V/f control method and shows that it has
had an efficiency improvement of over 18 %.
All in all, ceiling fans are significantly
cheaper than air conditioners, and they help save money and energy. In addition
to that, they also generate warmth as well as cool air. Fan manufacturers
estimate that consumers can save as much as 40% on bills during the season of summer.
Although there’s a variety of ceiling fan models, the cheaper models tend to be
the noisiest, and tend to overheat quicker. However, they are still a popular
choice, as they are used by numerous people. It is a one-time instalment, which
can also be used as a decoration in the room. Although single phase induction
motors are not the most efficient, they are economically friendly and don’t
take up too much power in houses, offices and industries and can function by
single power system. They are reliable, easy to repair and maintain.