UNIVERSITY OF PORT HARCOURT

FACULTY OF ENGINEERING

DEPARTMENT OF MECHANICAL ENGINEERING

A

PRACTICAL REPORT

ON

ELECTRIC MOTORS, FANS AND BLOWERS

IN

MECHANICAL ENGINEERING LABORATORY III

(MEG 551.1)

SUBMITTED BY

OVIE OLORI

(GROUP 5)

U2008/3025307

COURSE SUPERVISOR: MR OBI

8TH, APRIL 2013

ACKNOWLEDGEMENT

Every achievement no matter how small is a product of several input,

collective efforts and commitments. Through this medium, I acknowledge the

efforts of my friends for giving me insights and helping hand in pursuing my

research. May God bless them.

TABLE OF CONTENT

Title page...............................................................................................................i

Acknowledgement...............................................................................................iii

Table of content...................................................................................................iii

CHAPTER ONE

1.1 Introduction....................................................................................................1

1.2 Electric motor.................................................................................................2

1.3 History of electric motor................................................................................3

1.4 Classification or types of motor....................................................................

1.5 Operating principles of electric motor...........................................................

1.6 How does an electric motor work?................................................................

1.7 Components of an electric motor..................................................................

CHAPTER TWO

2.1 Efficiency of electric motor..........................................................................

2.2 Calculation of electric motor efficiency........................................................

2.3 Energy losses................................................................................................

2.4 Tips for efficient motor operation...........................................................

CHAPTER THREE

3.1 Troubleshooting an electric motor................................................................

3.2 Steps in rewinding an electric motor......................................................

3.3 Tips & warnings.....................................................................................

CHAPTER FOUR

4.1 What are fans and blowers....................................................................

4.2 Differences between fans and blowers................................................

4.3 Classification of fans and blowers.......................................................

4.3.1 Fan types...............................................................................................

4.3.2 Blower types..........................................................................................

4.4 Common fan/blower problems..................................................................

CHAPTER FIVE

5.1 Conclusion....................................................................................................

CHAPTER ONE

1.1 INTRODUCTION

Electric motors, both ac motors and dc motors, come in many shapes and

sizes. Some are standardized electric motors for general-purpose applications.

Other electric motors are intended for specific tasks. In any case, electric motors

should be selected to satisfy the dynamic requirements of the machines on

which they are applied without exceeding rated electric motor temperature as

there are a multitude of motors to choose from. Each has its own unique

characteristics, making one motor type a better choice for an application than

another.

1.2 ELECTRIC MOTOR

An electric motor is an electric machine that converts electrical energy into

mechanical energy (kinetic energy). The mechanical energy is used to rotate

pump impeller, fan, blower, drive compressors and lift materials. In normal

motoring mode, most electric motors operate through the interaction between an

electric motor’s magnetic field and winding currents to generate force within

the motor, electric motors can be found in a variety of appliances including

industrial fans, blowers, machine tools, house hold appliance etc. The largest of

electric motors are used for ship propulsion, pipeline compression and pumped-

storage applications with ratings approaching a megawatt. Electric motors may

be classified by electric power source type, internal construction, application,

type of motion output etc

Fig. 1.1: Diagram of an electric motor

1.3 HISTORY OF ELECTRIC MOTOR

In the year 1821 British scientist Michael Faraday explained the

conversion of electrical energy into mechanical energy by placing a current

carrying conductor in a magnetic field which resulted in the rotation of the

conductor due to torque produced by the mutual action of electric current and

field. Based on his principal the most primitive of machines a D.C.(direct

current) machine was designed by another British scientist William Sturgeon in

the year 1832. But his model was overly expensive and wasn’t used for any

practical purpose. Later in the year 1886 the first electrical motor was invented

by scientist Frank Julian Sprague. That was capable of rotating at a constant

speed under a varied range of load, and thus derived motoring action.

1.4 CLASSIFICATION OR TYPES OF MOTORS

Motors are categorized in a number of types based on the input supply,

construction and principle of operation. Most motors described in the guide spin

on an axis, but there are also specialty motors that move linearly. All motors are

either alternating current (AC) or direct current (DC), but a few can operate on

both. The following lists the most common motors in use today. Each motor

type has unique characteristics that make it suitable to particular applications.

INDEX

1. DC motor

2. Synchronous motor

3. 3 phase induction motor

4. 1 phase induction motor

5. Special types of motor

Among the four basic classification of motors mentioned above the DC

motor as the name suggests, is the only one that is driven by direct current. It’s

the most primitive version of the electric motor where rotating torque is

produced due to flow of electric current through the conductor inside a magnetic

field.

Rest all are A.C. electrical motors, and are driven by alternating current, for e.g.

the synchronous motor, which always runs at synchronous speed. Here the rotor

is an electro – magnet which is magnetically locked with stator rotating

magnetic field and rotates with it. The speed of these machines are varied by

varying the frequency (f) and number of poles (P), as Ns = 120 f/P.

In another type of AC motor where rotating magnetic field cuts the rotor

conductors, hence circulating current induced in these short circuited rotor

conductors. Due to interaction of the magnetic field and these circulating

currents the rotor starts rotates and continues its rotation. This is induction

motor which is also known as asynchronous motor runs at a speed lesser than

synchronous speed, and the rotating torque, and speed is governed by varying

the slip which gives the difference between synchronous speed Ns , and rotor

speed Nr,

It runs governing the principal of EMF induction due to varying flux density,

hence the name induction machine comes. Single phase induction motor like a 3

phase, runs by the principal of emf induction due to flux, but the only difference

is, it runs on single phase supply and its starting methods are governed by two

well established theories, namely the Double Revolving field theory and the

Cross field theory.

Apart from the four basic types of motor mentioned above, there are several

types Of special electrical motors like Linear Induction motor(LIM),Stepper

motor, Servo motor etc with special features that has been developed according

to the needs of the industry or for a particular gadget like the use of hysteresis

motor in hand watches because of its compactness.

1.5 OPERATING PRINCIPLES OF ELECTRIC MOTOR

Before we can examine the function of a drive, we must understand the basic

operation of the motor. It is used to convert the electrical energy, supplied by

the controller, to mechanical energy to move the load. There are really two

types of motors, AC and DC. The basic principles are alike for both. Magnetism

is the basis for all electric motor operation. It produces the force required to run

the motor.

Fig. 1.2: Force on a conductor in a magnetic field

Electric motors derive their turning motion from the interaction of two magnetic

fields. Electric motors consist of a housing together with two or more pole shoes

in which an armature is placed. The rotating motion is achieved by magnetising

the armature, as well as the pole shoes. The armature starts turning due to the

interaction of the forces created by the magnetic fields. This works as follows.

There is a magnetic field around a current-carrying conductor (wire). If the

direction of the current is away from us, the magnetic lines of force will flow to

the right, If the direction of the current is towards us, the magnetic lines of force

will flow to the left

1.6 HOW DOES AN ELECTRIC MOTOR WORK?

When the coil is powered, a magnetic field is generated around the armature.

The left side of the armature is pushed away from the left magnet and drawn

towards the right, causing rotation.

Fig. 1.3: Electric motor operation

When the coil turns through 900, the brushes lose contact with the commutator

and the current stops flowing through the coil.

However the coil keeps turning because of its own momentum.

Now when the coil turns through 1800, the sides get interchanged. As a result

the commutator ring C1 is now in contact with brush B2 and commutator ring C2

is in contact with brush B1. Therefore, the current continues to flow in the same

direction.

1.7 COMPONENTS OF AN ELECTRIC MOTOR

An electric motor has six parts:

Fig. 1.4: Parts of an electric motor

I. ARMATURE OR ROTOR: The armature supports the coil and can help

make the electromagnet stronger. This makes the motor more efficient.

II. COMMUTATOR: A commutator is used to reverse the direction of flow of

current. Commutator is a copper ring split into two parts C1 and C2. The split

rings are insulated from each other and mounted on the axle of the motor..

III. 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

IV. AXLE: The axle holds the armature and the commutator

V. PERMANENT MAGNET: Inside the cover of any electric motor there

are 2 kinds of magnets:

- One does not move and is called the "stator".

- On some kinds of electric motors the stator can be a permanent magnet

and on others it can be an electromagnet.

The other kind of magnet is called the "rotor" because it rotates inside the stator.

Fig. 1.5: Stator and armature

VI. 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.

CHAPTER TWO

2.1 EFFICIENCY OF ELECTRIC MOTOR:

Electrical motor efficiency is the ratio between the shaft output power -

and the electrical input power. The efficiency of the motor increases by:

I. Increasing the number of turns in the coil

II. Increasing the strength of the current

III. Increasing the area of cross-section of the soil

IV. Increasing the strength of the radial magnetic field.

Factors that influence efficiency includes age, temperature, capacity,

speed, rewinding, type and load.

2.2 CALCULATION OF ELECTRIC MOTOR EFFICIENCY

If power output is measured in horsepower (hp), efficiency can be

expressed as:

ηm = Pout 746 / Pin          

where

ηm = motor efficiency

Pout = shaft power out (horsepower, hp)

Pin = electric power in to the motor (Watt, W)

2.3 ENERGY LOSSES

Motors loose energy when serving a load and this includes:

I. PRIMARY AND SECONDARY RESISTANCE LOSSES: The electrical

power lost in the primary rotor and secondary stator winding resistance are also

called copper losses. The copper loss varies with the load in proportion to the

current squared - and can be expressed as

Pcl = R I2                

where

Pcl = stator winding - copper loss (W)

R = resistance (Ω)

I = current (Amp

II. IRON LOSSES: These losses are the result of magnetic energy dissipated

when the motors magnetic field is applied to the stator core.

III. STRAY LOSSES: Stray losses are the losses that remains after primary

copper and secondary losses, iron losses and mechanical losses. The largest

contribution to the stray losses is harmonic energies generated when the motor

operates under load. These energies are dissipated as currents in the copper

windings, harmonic flux components in the iron parts, leakage in the laminate

core.

IV. MECHANICAL LOSSES: Mechanical losses includes friction in the

motor bearings and the fan for air cooling.

2.4 TIPS FOR EFFICIENT MOTOR OPERATION

1. Properly lubricate all moving parts

2. Keep motor couplings properly aligned

3. Properly align tension belts while installing the motor

4. Keep bearings clean and lubricated

5. Check proper supply voltage

CHAPTER THREE

3.1 TROUBLESHOOTING AN ELECTRIC MOTOR

Electric motors are normally long lasting and dependable. Motors often

operate for years in dusty and dirty environments. Most motors are normally

mounted out of sight, so they often do not get serviced or inspected regularly.

Many problems can be traced to improper maintenance by the owner. Following

the manufacturer's service instructions will usually ensure that the motor

functions for a long time. In many cases it will simply be easier to replace the

motor if it has any kind of internal problems, especially if it has been running

for years

INSTRUCTIONS

1. Check to see if the motor smells like it is burning. Replace the motor if it

does not run and has an electrical burning odour.

2. Ensure that the motor is receiving input voltage. The cord may be damaged or

the house's circuit breaker may be tripped. Check the fuse on the motor itself if

so equipped and make sure it is serviceable.

3. Check to see if the motor is overheated. Blow the motor with compressed air

to remove accumulated dust, dirt or wood shavings. Allow motor to cool and

then attempt to restart.

4. Loud squeaking or vibration may indicate worn or damaged bearings.

Lubricate the bearings if possible, otherwise replace the motor.

5. Make sure that the device that the motor is turning is not locked up or

damaged. Disconnect the device and see if the motor will run.

6. A motor that tries to run but only hums may indicate a bad starting capacitor.

Examine the capacitor for leaking oil. Replace if capacitor is leaking. If not

leaking, test the capacitor with the procedure listed below in the Resources

section. If unserviceable, replace the starting capacitor.

3.2 STEPS IN REWINDING AN ELECTRIC MOTOR

1. Clean your work surface to make sure it’s free of dirt and dust

2. Remove the motor housing to reveal the armature, stator, and the

windings

3. Document the present configuration by taking notes or photographs. You

may even wish to videotape your deconstruction so that you can precisely

recreate the original winding pattern and connections.

4. Take the wire from the tabs on the brush pads. Bend the tabs gently (and

as little as possible) and completely remove the wire from the tabs before

cutting the coils of the wind.

5. Cut the coils in the wind free from the armature and/or stator. The

easiest place to cut is at the tops of the coils at the top of the armature and/or

stator posts. Count the number of winds in each coil so that you can rebuild the

motor to its original configuration.

6. Check the insulation that lines the actual steel laminate areas of the

stator before you rewind an electric motor. If it’s in good shape, you can put

it back in place before beginning your rewind. You can replace burned or

damaged insulation with similar material or insulating tape.

7. Rewind the armature and/or stator using the same gauge and type of

magnet wire that was on the original motor. If you’re more experienced, you

may wish to upgrade your wire’s quality, substituting a nylon-and-

polyurethane-coated wire for the original enamel-coated wire, for instance.

8. Recreate the exact winding pattern and number of coils around each

winding. Take great care to make each coil tight and precise for the best

performance.

When beginning your first winding, leave the end of the first winding free

but long enough to reach the first tab. The last winding will attach to the

same point.

Crimp all the other windings down as you work to hold the wire in place.

You do the winding with one long wire, so don’t cut anything as you go.

Before you crimp the wire down behind the tabs, use a sharp knife or

sandpaper to remove the insulation from the wire at the point where it

makes contact with the tab. Make sure you only remove as much

insulation as is necessary to create good contact.

9. Connect the end of the last winding and the loose wire you left in the first

winding to the tab where you began.

10. Check to make sure that none of the wires connecting to the tabs are

touching.

11. Reassemble the motor housing.

3.3 TIPS

I. Practice on an old or inexpensive motor before you try working on an

expensive one.

II. A/C motors are the best types for beginners as all of the wiring and windings

are concentrated in the stator. On all A/C stators, whether 2, 4, 6, 8 pole, etc,

every other coil is wound in a different direction.

3.3.1 WARNINGS

I. Before you remove the windings, you must understand exactly how the

brushes, windings, and armature interact, or you won’t be able to successfully

complete a rewind project.

II. Only magnet wire is to be used in rewinding a motor. Any other types of

wire (floral, arts and crafts, hanging wire, etc) will not produce any spin in the

motor at all and in fact has the potential to cause electrocution and even send

you to the emergency room

III. Be sure to use the exact same gauge wire that was originally used. Too

heavy a gauge, and the motor will spin slow or not at all.

IV. Do not, under any circumstances, wind the new wire on the bare steel of the

stator/armature posts.

CHAPTER FOUR

4.1 WHAT ARE FANS AND BLOWERS?

Fans and blowers provide air for ventilation and industrial process

requirements. Fans generate a pressure to move air (or gases) against a

resistance caused by ducts, dampers, or other components in a fan system.

4.2 DIFFERENCES BETWEEN FANS AND BLOWERS

Fans and blowers are differentiated by the method used to move the air, and by the system pressure they must operate against. As per American Society of Mechanical Engineers (ASME) the specific ratio - the ratio of the discharge pressure over the suction pressure - is used for defining the fans and blowers.

Equipment Specific Ratio Pressure RiseFans Up to 1.11 1136Blowers 1.11 to 1.20 1136 - 2066

Table 4.1: Differences between fans and blowers

4.3 CLASSIFICATION OF FANS AND BLOWERS Fan and blower selection depends on the volume flow rate, pressure, type of material handled, space limitations, and efficiency.

4.3.1 FAN TYPES I. CENTRIFUGAL FANS: Uses a rotating impeller to move the air stream and are able to produce high pressures, which makes them suitable for harsh operating conditions, such as systems with high temperatures. Centrifugal fans are categorized by their blade shapes.

II. AXIAL FANS: Also known as propeller fans, move the air stream along

the axis of the fan, The way these fans work can be compared to a propeller on

an airplane, the propeller fan makes more noise than the centrifugal fan so it is

normally used where noise is not a factor.

Fig 5.1 & 5.2: Centrifugal fan and axial fan

4.3.2 BLOWER TYPESI. CENTRIFUGAL BLOWERS: Look more like centrifugal pumps than fans. The impeller is typically gear-driven and rotates as fast as 15,000 rpm. Centrifugal blowers typically operate against pressures of 0.35 to 0.70 kg/cm2, but can achieve higher pressures. One characteristic is that airflow tends to drop drastically as system pressure increases.

Fig 4.3: Centrifugal blower

II. POSITIVE DISPLACEMENT BLOWERS: They have rotors, which "trap" air and push it through housing. These blowers provide a constant volume of air even if the system pressure varies. They turn much slower than centrifugal blowers (e.g. 3,600 rpm) and are often belt driven to facilitate speed changes.

4.4 COMMON FAN/ BLOWER PROBLEMS1. Poor performance2. Excessive noise3. Premature component failure4. Vibration

CHAPTER FIVE

5.1 CONCLUSION

All motors have two basic parts: a rotor and a stator. The stator is usually

stationary, and the rotor revolves around it. The stator is a magnet that shapes a

magnetic field. The rotor is a conductor connected to the electric circuit that

interacts with this magnetic field, and in turn produces a magnetic field that acts

on the stator.

Modern motors can be classified into two groups: electromagnetic motors and

magnetic motors. Electromagnetic motors improve in performance as they are

enlarged; magnetic machines improve as they are scaled-down. Electromagnetic

motors include the induction, AC polyphase commutator, AC single-phase

commutator, DC, synchronous, and repulsion motors. The magnetic motors

include the solenoid, relay, reluctance, and hysteresis motors.

An induction motor uses AC and a ring of fixed electromagnets (the stator) to

produce a rotating magnetic field. The moving electromagnetic field causes the

rotor to spin, producing mechanical energy. More than 90% of the world's

motors are of this type. A synchronous motor uses either permanent magnets or

DC-fed electromagnets to produce a magnetic field. Unlike the induction motor,

whose rotor "chases" after the rotating magnetic field, the synchronous motor

has a magnetized rotor. The rotor's magnetic field matches the rotating magnetic

field, resulting in a synchronized mechanical motion that has very little

slippage.

There are two main disadvantages to induction and synchronous motors:

without a variable power supply, they cannot provide efficient speed variation

over a wide range.

REFERENCES

“The development of the electric motor”, http://www.sparkmuseum.com/motors

“Electricity and magnetism” McMillan and Co…http://books.google.ca/books

“Two-phase induction motor”,

http://www.fi.edu/learn/case-files/tesla/motor.html

Wikipedia, the free encyclopedia

www.edisontechcenter.org/electricmotors.html

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