55593080 electrical hand book

8/6/2019 55593080 Electrical Hand Book

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FOR TRAINING PURPOSE ONLY

1

TRAINING OFFICE

ELECTRICAL

Principle

WKL-1/ BAKHEET AL MAMARI


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AIM

ELECTRICAL PRINCIPLE is addressed to all the people dealing/working with

electrical equipments, for rating and engineering officers, it is a practical guide

to electrical theory for any one who needs to learn or improve in his

understanding of electrical principles. The manual/book incorporates the basic

theories and techniques of what conceits good and competent electrical

workings.

Divided into sections the manual/book deals with electrical theory, principles,

and examples, in short, is covers every aspect of present day electrical

principles. Every section offers readers, safety, theory, diagrams, and

directions of appeal and dependence of simplicity.

A careful study of ELECTRICAL PRINCIPLE should enable you to understand

theories, behind electricity. It will be excellent guide book in skills of all

electrical aspect that make positive difference in your life.


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CHAPTER (1)

1-1 Health and safety at work

It is the duty of each individual at work to ensure his own safety and

safety of others. Dangerous situations should be brought to the attention of an

Officer or Senior Rating to take action to remove/reduce the hazards. In

particular the following safety rules should be observed:-

1. Workshop machinery is dangerous. Only authorized personnel are to

use workshop machines. Do not temper with any machine or appliance

especially (electrical).

2. Goggles are to be worn when using grinding machines, lathes, saws

and battery work.

3. Do not stand beneath anything being lifted.

4. Do not look at welding taking place without wearing welding

goggles/shields.

5. Do not remove safety guards from machines.

6. Do not assume the power supply is (Turned off) from any electrical

appliances, check it.

7. Lifting appliances and overhead cranes are only to be operated by the

authorized personnel.

8. If a fire extinguisher is used do not put it back in its stowage until it is

recharged.

9. Protective or safety clothing is to be worn and correct procedures

followed when working with battery acids or chemical agents.

10.Heavy-duty boots, hard hats and ear defenders are to be worn in

designated areas.

11.Correct handling procedures must be observed during switching

ON/OFF equipment.

12.When moving heavy items or equipment proper slinging must be

provided. If in doubt, consult a qualified slinger or Boson especially

when working aloft.

13.Beware of overhead cranes when in operation.


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14.Access on to the ship lift restricted to personnel who operating or

concerned with a vessel on the lift.

Action in Event of Electric Shock:-

When a person is found in a collapsed condition and it is suspected that he

or she has electric shock, the following actions/precautions must be

taken:-

a) Remove power immediately.

b) Remove casualty as quick as possible catching from his/her clothes.

c) Check his breathing, if not, and then start artificial respiration.

d) If pulse not present, start external heart massage giving alternately, five

heart compressions one lungs inflation.

e) Continue treatment until successful or taken over by expert medical

person.

f) Avoid further injury to the casualty.

Working on LIVE AND DEAD equipments

Always keep in mind that 30 Volts dc and 21 Volts ac can be dangerous.

So live terminal should not be touched. It is frequently assumed 24 Volts

dc is safe. However, the 24 Volts coming from TRU may faulty in the line,

so 440 Volts can cause short circuit due to fault.

So, unless the voltage has been personally measured with respect to earth

and found to be less than 30 Volts dc or 21 Volts ac, especially if your skin

is not dry.


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Dead Equipment

When working on dead equipment, make sure fuses remove first, and then

start work. Where large capacitors are fitted to equipment on which work is

to be done, they are to be discharged to earth before the work is started.

Capacitors hold their charge for some time. Check that they are fully

discharged before assuming that the equipment is dead.

Live Equipment

The following precautionary measures are to be taken when working on

live equipments:-

1) Inform to your senior proceed as.

2) Take a trained man with you for help in case of accident.

3) Avoid direct contact with any circuit and or component which may be

live.

4) Make sure no direct contact is made with any earthed metal eg.

Equipment casing or chassis, bulkhead, handrail, drawer handle etc.

5) If possible work with one hand and other in your pocket.

6) Use insulated tools, ensuring that tools are dry.

7) Stand on approved insulated deck covering, if in doubt use a rubber

mat.

8) Take care that tools or test equipment do not cause a short circuit.

9) Wear rubber gloves and check them before use.


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Electrical Shock Dynamics

Shock is the passage of electrical energy

through the human body. The primary factors

affecting an electrical shock's severity are the

path along which the current travels, the

amount of current, and the duration of

exposure to the current.

Electric Shock

An electric shock is caused to the human body by passing an electric

current through it. Two conditions are necessary before a person will

receive a shock:-

a) A potential difference.

b) A complete circuit.

The basic causes of electric shock are-

a) Equipment failure.

b) Human failure.

c) A combination of both.

Simple examples of the above a and b is as:-

1) Casing of a kettle becoming live.

2) Touching a live terminal.


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RADHAZ AND ALOFT

1- RADHAZ:- Radio transmissions can cause hazards by

inducing voltages in such things as wires , stays and riggings which

causing the ignition of certain armament stores and highly inflammable

liquid fuels. It can also do irreparable damage to internal organs, eyes,

as well as causing electric burns to the skin. (Ref BR 2924).

2- ALOFT:- It is defined as all masts, funnels and ship

superstructure to which aerials are secured or which can be excited by

neighbouring aerials.

3. Precaution for working aloft:-

Before commencing work on a mast or funnel

consideration should be given to prevailing weather conditions,

navigation and propulsion requirements and the physical

condition of the man preparing to carry out the work and his

attendant.

a) Clothing and foot wear: - These should be in good condition,

correctly worn and closely adjusted. Coins, Keys etc. should not

be carried in unsealed pockets.

b) Safety Line: - Should be securely attached to the safety harness,

passed over a suitable support and tended at deck level by a

reliable rating. The free end should always be taken twice

around a suitable securing point at deck level and the loose end

retained in the hand of the attendant.

c) Safety harness: - Should be in good repair, correctly worn and

closely adjusted.


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d) Isolate Hazardous equipment:- Depending on the location of the

work to be done radar and radio equipment must be shut down,

Sirens should be switched off. Engine should not be started.

Safety valves lifted.

e) Tools and equipment: - Should be secure to the person working

aloft by short lanyards as well as being placed in a pocket. A thin

line may be used to supply and retrieve tools.

g) Attendant: - The life of the person working aloft may well

depend upon the attentiveness of the attendant. The attendant

must pay particular attention to keeping the safety line suitable

adjusted and ready for immediate use if required. The attendant

must also be constantly looking for possible dangers or risks to

the person working aloft.

Note: - When berthed alongside another ship it may be necessary to

take similar precautions on the adjacent craft depending on its

closeness.

Earth and short circuits:-

Earth Potential:-

The earth (and hence the sea) is at a potential of zero volts. Items

connected to the earth (or the sea) e.g. Circuit wiring and electrical

components are said to be earthed or are at earth potential:-

b) This means that there is no difference of potential between the

item and earth. (A ships hull being immersed in the sea, is at earth

potential and therefore at zero volts).

c) If the casing of an item of electrical equipment is earthed

therefore, it is impossible for a person standing on earth to get an


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electric shock by touching that casing. This applies even if a fault

occurs in the equipment, which allows a current carrying conductor to

touch the casing.

Earthing of equipment:-

a) The earthing of equipment casings by heavy gauge conductors safeguard

against Electric shock.

b) If due to a fault a naked line touched to the body of equipment then

current would flow through the casing to ground / ships hull or Sea.

c) Because of the very low resistance of the earthing conductor the casing will

be at almost zero volts and a person touching it would not receive a shock.

d) Where the earthing conductor not fitted, the casing would be at the

potential of the circuit and anyone touching it, now would receive a shock.

This is because; the only current path to earth would then be through the body

of the person.


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3- Portable Equipment:-

Following safety precautions must be taken for check

earth casing of equipment on board ships.

a) Only approved test equipment to be used when testing an

equipment or fuse panel. Test lamp, made-up tester and many

cheaper civilian test instruments are dangerous.

b) All metal cased portable appliances must be fitted with a three

pin plug.

c) The total earth lead continuity resistance between plug and case

must not exceed 0.25 Ohms.

d) The continuity resistance of the earth lead on an extension cable

should not exceed 0.5 ohms.

e) The continuity resistance of the earth lead on an fixed

equipment should not exceed 0.1 ohms.

f) An earth bonding straps must be wide and thick in order to

have zero resistance.

g) Equipment fuses never to be up-rated which is hazard.

4. Fitted Equipment:-

Fitted equipment those which are not portable and have

permanently wired- in cables are often seated on resilient mounting in

order.

a) To protect the machine against ships vibration or shock from

underwater explosion.

b) To prevent machine vibration radiating from the hull in to Sea

water.


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5. Safety for Earth Bonding:-

a) There should be no paint, rust, grease or dirt between the

equipment and the hull.

b) It must secure from metal to metal.

c) It must be sufficiently long to avoid taking a strain when the

resilient mounts flex.

d) If found to be damaged an earth bonding strap must be replaced

by a new one as Soon as possible.

e) Fuses are fitted to protect the supply system firstly and the

equipment secondly. The fuse value can be calculated by the

formula.

125

X Normal full load.

100

The fuse rating is always 25 % above the circuit.

Q-1 If a motor of 2 HP taking current 5 amps at normal load. Find the

fuse rate which should be fitted in 440 volts D.B?

125 25

X 5 = = 6.25 amps.

100 4


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Electrical safety work practices

The electrical safety work practices applied by personnel in the environment

and around the equipment is the third element in hazard identification.

Become familiar with the Electrical Safety Manual.

Read and follow standard operating procedures.

Become familiar with lockout/tagout procedures.

Understand the required qualifications of personnel working on the

equipment.

Wear required Personal Protective Equipment (PPE).

Do not wear loose chains or metal of any kind; this includes watches,

rings, or earrings.


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)2(CHAPTER

Static Electricity, Magnetism & Atom principle

Static electricity

It was discovered centuries ago that certain types of materials would

mysteriously attract one another after being rubbed together.

Fig2.1 producing static electricity by friction

It was also noted that when a piece of ROD rubbed with FUR, Fig2.1 the twomaterials would attract one another. When two pieces of matter rubbed

together, electrons can be wiped off one material onto the other. If a material

is good conductor, it is difficult to obtain a detectable charge on either, since

equalizing currents can flow easily between the conducting materials. These

current equalize the charges almost as fast as they are created; a static

charge is more easily created between no conducting materials. When a hard

rubbed rubber rod is rubbed with fur, the rod will accumulate electrons given

up by the fur, since both materials are poor conductors, very little equalizing

current can flow, and an electrostatic charge builds up. When charge

becomes great enough, current will flow regardless of the poor conductivity of

the materials. These currents will cause visible sparks and produce a cracking

sound.


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MAGNETISM

Fig2.2 Magnet

In order to properly understand the principles of electricity, it is necessary to

study magnetism Fig2.2 and the effects of magnetism on electricalequipments. Magnetism and electricity are so closely related that the study of

either subject would be incomplete without at least a basic knowledge of the

other.

Much of today's modern electrical and electronic equipment could not function

without magnetism. Electrical motors use magnets to convert electrical energy

into mechanical motion; generators use magnets to convert mechanical

motion into electrical energy.


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Magnetic Materials

Magnetism is generally defined as that property of a material which enables it

to attract pieces of iron. A material possessing this property known as a

MAGNET. Materials that are attracted by a magnet, such as iron, steel, nickel,

have the ability to become magnetized. These are called magnetic materials.

Materials, such as paper, wood, glass, or tin, which are not attracted by

magnets, are considered nonmagnetic.

Ferromagnetic Materials

The most important group of materials connected with electricity and

electronics are the ferromagnetic materials. Ferromagnetic materials are

those which are relatively easy to magnetize, such as iron, steel and alloy.

Artificial Magnets

Magnets produced from magnetic materials are called ARTIFICIAL

MAGNETS. Artificial magnets are usually classified as PERMANENT or

TEMPORARY, depending on their ability to retain magnetic properties after

the magnetizing force has been removed. Magnets made from steel and

certain alloys which retain a great deal of their magnetism, are called

PERMANRNT MAGNETS. These materials are difficult to magnetize because

of the opposition offered to the magnetic lines of force as the lines of force try

to distribute themselves throughout the material.

The opposition that a material offers to the magnetic lines of force is called

RELUCTANCE. All permanent magnets are produced from materials having a

high reluctance.

A materials with a low reluctance, such as soft iron is easy to magnetize but

will retain only a small part of its magnetism once the magnetizing force is

removed. Materials of this type that easy lose most of their magnetic strength

are called TEMPORARY MAGNETS.

RESIDUAL MAGNETISM. The ability of a material to retain an amount of

residual magnetism is called the RETENTIVITY of the material.


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Magnetic Poles

The magnetic force surrounding a magnet is not uniform. There exists a great

concentration of force at each end of the magnet and a very weak force at the

center. The two ends, which are the regions of concentrated lines of force, are

called the POLES of the magnet. Magnets have two magnetic poles and both

poles have equal magnetic strength.

Magnetic Fields

The space surrounding a magnet where magnetic forces act is known as the

magnetic field.

Lines of Force

The further describe and work with magnet phenomena, lines are used to

represent the force existing in the area surrounding a magnet these lines,

called MAGNETIC LINES OF FORCE Fig2.3.

Fig2.3 Magnetic lines of force

The characteristics of magnetic lines of force can be described as following:

1. Magnetic lines of force are continuous and will always form closed loops.

2. Magnetic lines of force will never cross one another.

3. Parallel magnetic lines of force traveling in the same direction repel one

another.

4. Magnetic lines of force tend to shorten themselves.

5. Magnetic lines of force pass through all materials.

6. Magnetic lines of force always enter or leave a magnetic material at right

angles to the surface.


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Voltage Produced by Magnetism

Magnets or magnetic devices are used for thousands of different jobs.

One of the most useful and widely employed applications of magnets is in the

production of vast quantities of electric power from mechanical sources. The

mechanical power may provided by a number of different sources, such as

gasoline or diesel engines, and water or steam turbines.

There are three fundamental conditions which must exist before a voltage can

be produced by magnetism:-

1) There must be a CONDUCTOR in which the voltage will be produced.

2) There must be a MAGNETIC FIELD in the conductor's vicinity.

3) There must be RELATIVE MOTION between the field and conductor.

In accordance with these conditions, when a conductors MOVE ACROSS a

magnetic field so as to cut the lines of force, electrons WITH THE

CONDUCTOR are propelled in one direction or another. An electric force, or

voltage, created Fig2.4.

Fig2.4 Voltage produced by magnetism

In fig2.4 view A, the conductor is moving TOWARD the front of the page and

the electrons move from left to right. The movement of the electrons occurs

because of the magnetically induced emf acting on the electrons in the

copper. The right-hand end becomes negative, and the left-hand end positive.

The conductor is stopped at view B, motion is eliminated and there is no

longer an induced emf. Consequently, there is no longer any difference in


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potential between the two ends of the wire. The conductor at view C is moving

away from the front of the page. An induced emf is again created. However,

note carefully that the REVERSAL OF MOTION has caused a REVERSAL OF

DIRECTION in the induced emf. If a path for electron flow is provided between

the ends of the conductor, electrons will leave the negative end and flow to

the positive end. This condition showing in part view D. Electron flow continue

as long as the emf exists.

Matter

Matter is defined as any thing that occupies space and has weight.

Examples of matter are air, water, clothing, and even our own bodies.

An Element is substance which cannot be reduced to a simpler substance by

chemical means. Examples of elements Iron, gold, silver, copper, and

Oxygen. When two or more chemically combined, the resulting substance is

called COMPOUND. A compound is a chemical combination of elements

which can be separated by chemical. Examples of common compounds are

water which consists of hydrogen and oxygen, and table salt, which consists

of sodium and chlorine.

Molecules

A MOLECULE is a chemical combination of two or more atoms.

In a compound the molecule is the smallest particle that has all the

characteristics of the compound.

Consider water, for example. Water is matter, since it occupies space and has

weight. Depending on the temperature, it may exist as a liquid (Water), a solid

(Ice), or gas (Steam).


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Fig2.5 Atom

Atom

Molecules are made up of smaller particles called ATOMS Fig2.5. An atom is

the smallest particle of an element that retains the characteristics of that

element.

The atoms of one element, however, differ from the atoms of all other

elements. The atoms of each element are made up of ELECTRON.

PROTONS, and, in most cases, NEUTRONS.

The electrons, protons, and neutrons of one element are identical to those of

any other element. The reason that there are different kinds of elements is

that the number and the arrangement of electrons and protons within the atom

are different for the different elements.

of electricity.negative chargeis considered to be a smallelectronThe

The proton has a positive charge of electricity equal and opposite to the

charge of the electron. The electron and proton each have the same quantityof charge, although the mass of the proton is approximately 1837 times that

of the electron. In some atoms there exists a neutral particle called a neutron.

nohas a mass approximately equal to that of a proton, but it hasneutronThe

electrical charge.

In fig2.6 shows one hydrogen and one helium atom. Each has a relatively

simple structure. The hydrogen atom has only one proton in the nucleus with

one electron rotating about it. The helium atom is a little more complex.


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It has a nucleus made up of two protons and two neutrons, with two electrons

rotating about the nucleus.

Fig 2.6 Structures o simple atoms

Elements are classified numerically according to the complexity of their atoms.

The atomic number of an atom is determined by the number of protons in its

nucleus. In a neutral state, an atom contains an equal number of protons and

electrons.

Shells and sub shells

The difference between the atoms, insofar as their chemical activity and

stability are concerned, is dependant upon the number and position of the

electrons included within the atom. The electrons reside in groups of orbits

called shells. These shells are elliptically shaped and are assumed to be

located at fixed intervals. Thus, the shells are arranged in steps that

correspond to fixed energy levels. The shells and the number of electrons

required to fill them. Principle specifies that each shell will contain a

maximum of 2n electrons, where n corresponds to the shell number starting

with the one closest to the nucleus. The second shell, for example, would

contain 2(2) or 8 electrons when full.


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The shells are also given letter designations, as pictured in Fig2.7 starting

with the shell closest to the nucleus and progressing outward, the shells are

labeled K, L, M, N, O, P, and Q, respectively. The shells are considered to be

full, or complete, when they contain the following quantities of electrons: 2 in

the K shell, 8 in the L shell, 18 in the M shell, and so on, in accordance with

the exclusion principle. Each of these shells is a major shell and can be

divided into sub shells, of which there are 4, labeled s, p, d, and f.

The sub shells are limited as to the number of electrons which they can

contain. Thus, the s sub shell is complete when it contains 2 electrons, the p

10 and f 14.

Fig 2.7 Shell designation


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CONDUCTORS, SEMICONDUCTORS, AND INSULATORS

As a means of all elements of which matter is made may be placed into one of

three categories: CONDUCTORS, SEMICONDUCTORS, and INSULATORS,

depending on their ability to conduct an electric current. Conductors are

elements which conduct electricity very readily; Insulators have an extremely

high resistance to the flow of electricity. All matters between these two

extremes may be called Semiconductors.

The electron theory states that all matter is composed of atoms and the atoms

are composed of smaller particles called proton, electrons, and neutrons.

The electrons orbit the nucleus which contains the protons and neutrons. It is

the Valence electrons that we are most concerned with in electricity.

These are the electrons which are easiest to break loose from their parent

atom. Normally, conductors have three or less valence electrons; insulators

have five or more valence electrons; and semiconductors usually have four

valence electrons.

Some metals are better conductors of electricity than others. Silver, copper,

gold, and aluminum are materials with many free electrons and make good

conductors. Silver is the best conductors, followed by copper, gold, and

aluminum. Copper is used more often than silver because of cost. Aluminum

is used where weight is a major consideration, such as in high-tension power

lines, with long spans between supports. Gold is used where oxidation or

corrosion is a consideration and good conductivity is required.


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Chapter (3)

Batteries

Introduction:-

Batteries are commonly used as an independent power source for emergencylighting, alarm systems, low distribution systems, communication systems,damage control flood lamps and torches etc.

Battery Terminology:-

The following terminology relates to batteries:-(1) Cell A cell a device which produces electrical energy by chemical

action.

(2) Primary cell A primary cell is one in which the electrochemical is notreversible.

(3) Secondary cell A secondary cell is one in which the electrochemicalaction is reversible.

(4) Battery A battery is an assembly of two or more cells connectedtogether and provided with external terminals.

(5) Positive electrode The positive plate of an electrolytic cell whichelectrons leave a system.

(6) Negative electrode The negative plate of an electrolytic cell bywhich electrons enter a system.

(7) Electrolyte An electrolyte is a substance the conducts electricitybecause of its a ability to change its chemical state.

(8) Capacity The capacity of a battery is expression of the quantity ofelectricity it can deliver before the end point voltage is reached.

Capacity is normally expressed in terms of the (Ah) at temperature of20 degrees c. e.g. a cell having a capacity of (10Ah) will supply 1Ampere for 10 hours.

(9) An example of a primary cell is the dry cell (e.g. a torch battery) itconsists of a zinc case electrode (Negative plate) a carbon rodsolution of a ammonium chloride in paste form, the (electrolyte). A tarpaper washer is located at the base of the rod to prevent it fromcoming into contact with the zinc case. At the top, the case containslayers of saw dust, sand and pitch, which hold the carbon rod inposition and prevent electrolyte leakage. The max voltage that aprimary cell can supply is 1.5v.( Primary cell Fig3.1and 3.2)


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Fig 3.1 different types of primary batteries

The combination of electrodes and electrolyte used in the primary cell resultsin one of the electrodes gradually eroding until eventually dissolving in the

electrolyte.The secondary cell uses a combination of electrodes and electrolyte thatmerely suffer a chemical change during the production of current and can berestored to their original condition by passing current from an external sourcethrough the cell in the reverse direction.Lead Acid BatteriesFig 3.4:-

The solution in a lead-acid cell contains sulfuric acid (H2SO4) in water.In water, sulfuric acid molecules dissociate into positively charged hydrogenions (H+) and negatively charged sulfate ions (SO4). Since hydrogen ionscarry only one positive charge and sulfate ions carry two negative charges,

Tarpaper

washer

Positive platecarbon rod

Sawdust

Sand

Pitch

Electrolyte(Ammonium

Chloride in Pasteform)

Negative plate

Zinc case

Brass

Terminal

The primary Cell

Fig 3.2


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the electrically neutral solution contains twice as many hydrogen ions assulfate ions.The cells negative electrode is spongy form of lead metal, housed in a non-reactive lead-alloy lattice. The cells positive electrode is lead dioxide, alsohoused in a protective lead-alloy lattice.

Let us start at the lead dioxide electrode; we will assume that two electronsarrive at the lead dioxide electrode. They are picked up by a lead dioxidemolecule, which reacts with four hydrogen ions and a sulfate ion to produce alead sulfate molecule and two water molecules. The lead sulfate moleculeconsists of a positively charged lead ion and a negatively charged sulfate ion,but its not soluble in water-the two ions bind together so strongly that watermolecules cant separate them and carry them about in solution. The leadsulfate clings to the lead dioxide electrode as a solid.

Fig 3.4 lead- acid Battery


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Fig3.5 Hydrometer

Fig3.6 lead-acid battery process

Measurement of Specific Gravity (Fig3.5):-

The specific gravity (or relative density) of an electrolyte is an indication of thestate of charge of the cell. Specific gravity is defined as the ratio of the massof a given volume of a substance to the mass of an equal volume of water at atemperature of 4 degrees c. the specific gravity of a fully charged cell ranges

between 1215 and 1300, the nominal figure being 1250. Specific gravity ismeasured by an instrument called (a hydrometerfig3. 5).

The process

Lead Acid Battery

Lead Lead Dioxide

pbO2

-

-

pb Pb++So4 -- -

H2O

H2o

+HH

Pb++ So4--

+

A lead-acid cellIs powered byElectrochemicalReaction betweenLead, and leadDioxide, and between

Sulfuric acid, whichCreate lead sulfateAnd water. LeadDioxide molecule(PbO2) picks up twoElectrons from the lLead dioxideElectrode and reactsWith four hydrogenIons (H++) in theSolution to formA lead


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The Method used to measure specific gravity is as following:

(1) Ensure that the hydrometer is clean and that the float moves freely inthe float guide.

(2) Record the electrolyte temperature.(3) Ensure that the hydrometer is at approximately the same temperature

as the electrolyte.(4) Squeeze the rubber bulb of the hydrometer.(5) Insert the hydrometer tube into the electrolyte.(6) Draw electrolyte into the barrel of the hydrometer by releasing the

rubber bulb.(7) Hold the hydrometer so that the surface of the electrolyte is at eye

level.(8) Ensure that no electrolyte is split and that the sample is returned to the

cell from which it was drawn.

(9) Rinse the hydrometer with pure distilled water.

Safety precautions when servicing lead acid batteries:

(1) Do not smoke or expose naked lights near any battery on a charge.(2) Display (No smoking or Naked Lights).(3) Ensue that the ventilation fans are running.(4) Wear full protective clothing:-

a-Apron.b-Gauntlets, PVC.c-Knee boots, rubber.d-Goggles, rubber.

(5) Mix electrolyte only as instructed.(6) Do not allow batteries on charge to gas excessively.(7) Ensure that temperature limits are not exceeded.(8) Avoid touching any exposed terminals.(9) Keep all electrical connections tight.

Ensure that terminals are not accidentally short circuited by tools orlinks.

(10) Use insulated tools.

Mixing the electrolyte

(1) Carry out general safety precautions listed in page 6 from 1 to 5.(2) When mixing always add acid to water, not water to acid. the acid

should be poured on to the water slowly and with care, because heat isgenerated as the liquids meet.

(3) Mix the electrolyte as following:(a) Pour the required volume of water.(b) Pour most of the required volume of acid slowly into the water

stirring continuously.


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(c) Check the specific gravity of the electrolyte with a hydrometermaking temp correction to the reading.

(d) Adjust the specific gravity of the electrolyte by adding more acid.(e) Allow the electrolyte to cool to 27 degrees c before use.(f)Rinse all receptacles and utensils before stowage.

(4) After mixing, the volume of electrolyte will always be slightly less thanthe sum of the separate volumes of acid and water.

Preparations for charging Batteries

(1) Remove and collect all vent caps.(2) Top-up all cells as necessary.(3) Check that the charging supply is switched off.(4) Use spring clips to the battery for all battery connections.(5) Ensure that all temporary leads are sound and all connections are

secure.

(6) Connect the positive terminal of the charging supply to the positiveterminal of the battery. And the negative terminal to the negativeterminal.

(7) Check the charging supply is set to give min current or a voltage notexceeding 2.3 volts per cell.

(8) Switch ON the charging supply.(9) Adjust the charging supply as detailed for the relevant type of charge.

Discharging

Consider a battery in the fully charged state; the a active materials arelead(pb) and lead peroxide (Pbo2) at the negative and positive platesrespectively, and the electrolyte diluted sulfuric acid (H2SO4), is at itsmaximum specific gravity. When a load is connected across the batteryterminals, a discharge current flows and chemical action takes place withineach cell.At the negative plate lead is ionized and each positive lead ion combineswith a negative sulfate ion from the electrolyte to form lead sulfate onthe plate. Thus, the active material of the negative plate will contain adecreasing lead contents and increasing lead sulfate content. This

chemical reaction releases electrons from the active material which flowthrough the load to the positive plate.

At the positive plate the positive lead ions combine with the negativesulfate ions from the electrolyte to form lead sulfate on the plate; at thesame time oxygen is released into the electrolyte. Thus the activematerial on the positive plate will contain a decreasing lead peroxidecontent and increasing lead sulfate content.

In the electrolyte the sulfate ion combine with the lead in the positiveand negative plates to form lead sulfate. At the same time, positive

hydrogen ion combine with the oxygen ions (released from the positiveplate) to form water. Thus, the acid content of the electrolyte will


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decrease and the water content increase, reducing the specific gravity ofthe electrolyte.During battery discharge, the active material on both positive andnegative plates has been converted to lead sulfate and the electrolyte isat its lowest specific gravity.

Charging

Once the active materials have been converted to lead sulfate and thespecific gravity has been reduced by the formation of water, thebattery can be charged by passing a current through it in the oppositedirection to the discharge current. The electrolyte separates intopositive hydrogen ions and negative sulfate ions.At the negative plate the lead sulfate is re-converted into lead and thesulfate ions combine with the hydrogen ions in the electrolyte to formsulfuric acid. Thus the active material in the negative plate will contain

an increasing lead content and decreasing lead sulfate content.At the positive plate, the waterformed during discharge separates into itselements ofoxygen and hydrogen and combines with the lead sulfateon the plate and the sulfate ions in the electrolyte. The chemical actionswhich take place result in the production of lead peroxide and sulfuricacid. Thus, the active material in the positive plate will contain anincreasing lead peroxide content and a decreasing lead sulfatecontents. Electrons are released from the active material which flowthrough the generator to the negative plate.

In the electrolyte the acid content will increase and the water willdecrease.During charging, the active material on the positive and negative plateshas reformed to lead peroxide and lead respectively and the electrolyte isonce more at its highest specific gravity.


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Chapter (4)

Generator

A generator is a machine that converts mechanical energy into electrical

energy.

The principle is explained as following:-

Whenever a conductor is moved with in a magnetic field in such away that the

conductor cuts across magnetic lines of flux, voltage is generated in the

conductor. The amount of voltage generated depends on the following:-

(1) The strength of the magnetic field.

(2) The angle at which the conductor cuts the magnetic field.

(3) The speed at which the conductor is moved.

(4) The length of the conductor within the magnetic field.

The polarity of the voltage depends on the direction of the magnetic lines of

flux and the direction of movement of the conductor. To determine the

direction of current in a given situation, the LEFT-HAND RULE FOR

GENERATORS is used. Fig 4.1

Fig4.1left hand rule for generator


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This rule is explained in the following manner:-

Point your thumb in the direction the conductor is being moved.

Point your forefinger in the direction of magnetic flux (from north to south).

Point your middle finger in the direction of current flow.

Fig4.2 the elementary generator

Basic generating principles are most easily explained through the use of the

elementary ac generator. An elementary generatorFig4.2 consists of a wire

loop placed so that it can be rotated in a stationary magnetic field. This will

produce an induced emf in the loop. Sliding contacts (brushes) connect the

loop to an external circuit load in order to pick up or use the induced emf. The

pole pieces (marked N and S) provide the magnetic field. The loop of wire that

rotates through the field is called the ARMATURE. The ends of the armature

loop are connected to rings called SLIP RINGS. They rotate with the

armature. The brushes, usually made of carbon, with wires attached to them,

ride against the rings. The generated voltage appears across these brushes.


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Fig4. 3 Output voltages during one revolution

The generator produces a voltage in the following mannerFig4.3

The armature loop is rotated in a clockwise direction. The initial or starting

point is shown at position A. At (00) the armature loop is perpendicular to the

magnetic field. The instant the conductors are moving parallel to the magnetic

field, they do not cut any lines of flux. Therefore, no emf is induced in the

conductors, and the meter at position A indicates Zero. As the armature

rotates from position A (00) to position B (900) the conductors cut through

more and more lines of flux, at a continually increasing angle. At 900 they are

cutting through a maximum number of lines of flux and at maximum angle.

The result is that between 00 and 900 the induced emf in the conductors builds

up from zero to a maximum value. Observe that from 00 to 900 the black

conductor cuts DOWN through the field. At the same time the white conductor

cuts up through the field. The induced emfs in the conductors are series-

adding. This means the resultant voltage across the brushes is the sum of the

two induced voltages. The meter at position B reads maximum value. As the

armature loop continues rotating from 900 (position B) to 1800 (position C), the

conductors which were cutting through a maximum number of lines of flux at

position B now cut through fewer lines.


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They are again moving parallel to the magnetic field at position C. They no

longer cut through any lines of flux. As the armature rotates from 900 to 1800,

the induced voltage will decrease to zero in the same manner that t increased

during the rotation from 00 to 1800, the meter again reads zero. From 00 to

1800 the conductors of the armature loop have been moving in the same

direction through the magnetic field. Therefore, the polarity of the induced

voltage has remained the same. This is shown by points A through C on the

graph. As the loop rotates beyond 1800 (position C), through 2700 (position

D), and back to the initial or starting point (position A), the direction of the

cutting action of the conductors through the magnetic field reverses. Now the

black conductor cuts UP through the field while the white conductor cuts

DOWN through the field.

As a result, the polarity of the induced voltage reverses. Following the

sequence shown by graph points C,D, and back to A, the voltage will be in the

direction opposite to that shown from points, A,B, and C.

Electromagnetic Poles

Nearly all practical generators use electromagnetic poles instead of the

permanent magnets used in our elementary generator. The electromagnetic

field poles consist of coils of insulated copper wire on soft iron cores, as

shown in Fig 4.4.

Fig4. 4 Four pole generator (without armature)


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Armature losses

In dc generators, as in most electrical devices, certain forces act to decrease

the efficiency. These forces, as they affect the armature, are considered as

losses and may be defined as follows:

1. I2R, or copper loss in the winding. The power lost in the form of heat in

the armature winding of generator.

2. Eddy current loss in the core. The current that are induced in the

generator armature core.

3. Hysteresis loss (a sort of magnetic friction).

Classification of Generators

Self-excited generators are classed according to the type of field

connection they use. There are three general types of field connections:-

1) Series-wound Generator

In the series-wound generator, shown in fig4.5 the field windings are

connected in series with the armature. Current that flows in the armature

flows through the external circuit and through the field windings.

A series-wound generator uses very low resistance field coils, which

consist of a few turns of large diameter wire.

The voltage output increases as the load circuit starts drawing more

current. Under low-load current conditions, the current that flows in the

load and through the generator is small. Since small current means that a

small magnetic field is set up by the field poles, only a small voltage is

induced in the armature. If the resistance of the load decreases, the load

current increases. Under this condition, more current flows through the

field. This increases the magnetic field and increases the output voltage.

A series-wound dc generator has the characteristic that out put voltage

varies with load current.


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To Load Generator Series

Circuit Output Field

Armature

Fig 4.5 Series-wound generator

2) Shunt-Wound Generator

In a shunt-wound generator, like the one shown in Fig6, the field coils

consist of many turns of small wire. They are connected in parallel with the

load. In other words, they are connected across the output voltage of the

armature.

Shunt Field

Generator output

Armature

Fig4.6 Shunt-wound generator

Current in the field windings of a shunt-wound generator is independent of the

load current (Currents in parallel branches are independent of each other).

Since field current, and therefore field strength, is not affected by load current,

the output voltage remains more nearly constant than does the output voltage

of the series-wound generator.


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The output voltage in a dc shunt-wound generator varies inversely as load

current varies. The output voltage decreases as load current increases

because the voltage drop across the armature resistance increases (V=IR).

In a series-wound generator, output voltage varies directly with load current.

In the shunt-wound generator, output voltage varies inversely with load current.

3) Compound-Wound Generators

Compound-wound generators have a series-field winding in addition to a

shunt-field winding, as showing in fig4.7

Series Field

Shunt Field

GeneratorOutput

Armature

Fig4.7 Compound -wound generator

The shunt and series windings are wound on the same pole pieces.

In the compound-wound generator when load current increases, the armature

voltage decreases just as in the shunt-wound generator. This causes the

voltage applied to the shunt-field winding to decrease, which results in a

decrease in the magnetic field. This same increase in load current, since it

flows through the series winding, causes an increase in the magnetic field

Produced by that winding. By proportional the two fields so that the decrease

in the shunt field is just compensated by the increase in the series field, the

output voltage remains constant. This is shown in Fig4.8, which shows thevoltage characteristics of the series-, and compound-wound generators. As

you can see, by proportioning the effects of the two fields (series and shunt),

A compound-wound generator provides a constant output voltage under

varying load conditions.


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Output Voltage Out put Voltage

Load Current Load Current Load Current

C. Compound-Wound B. Series-Wound A. Shunt-Wound

DC Generator DC Generator DC Generator

Fig4.8 Voltage output characteristics of the series-, shunt-, and compound-wound dc generators.

Generator Construction

Fig4.9 views A through E, shows the components parts of dc generators.

Fig4.9 Components of a dc generator


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AC GENERATORS

Regardless of size, all electrical generators, whether dc or ac, depend upon

the principle of magnetic induction. An emf is induced in a coil as a result of

(1) a coil cutting through a magnetic field, or (2) a magnetic field cutting

Through a coil. As long as there is relative motion between a conductor and a

magnetic field is called the field. That part in which the voltage is induced is

called the armature. For relative motion to take place between the conductor

and the magnetic field, all generators must have two mechanical parts-a rotor

and a stator. The rotor is the part that rotates; the stator is the part that

remains stationary. In a dc generator, the armature is always the rotor. In

alternators, the armature may be either the rotor or stator.

Fig4.11 Types of ac generators


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Rotating-Armature Al ternators

The rotating-armature alternator is similar in construction to the dc generator

in that the armature rotates in a stationary magnetic field as show in Fig4.11

view A. in the dc generator, the emf generated in the armature windings is

converted from ac to dc by means of commutator. In the alternator, the

generated ac is brought to the load unchanged by means of slip rings. The

rotating armature is found only in alternators of low power rating and generally

is not used to supply electric power in large quantities.

The rotating-field alternator has a stationary armature winding and a rotating-

field winding as shows in Fig4.11 view B the advantage of having a stationary

armature winding is that the generated voltage can be connected directly to

the load. A rotating armature requires slip rings and brushes to conduct the

current from the armature to the load. The stationary armature, or stator, of

this type of alternator holds the windings that are cut by the rotating magnetic

field. The voltage generated in the armature as a result of this cutting action is

the ac power that will be applied to the load. The stators of all rotating-field

alternators are about the same. The stator consists of a laminated iron core

with the armature windings embedded in this core as shown in Fig4.12 the

core is secured to the stator frame.

Fig4.12 Stationary armature windings


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Generator Operation

Fig4.13

Fig4.13 showed an engine supplies the power to turn shaft (1). Exciter

armature (2) and main fields (4) attached to shaft (1). As shaft (1) turns,

exciter armature (2) and related components generate DC. This DC is

supplied to main field (4) and creates a magnetic field around the poles of

main field (4). As main field (4) turns with shaft (1), the magnetic field also

rotates and induced an AC voltage into stationary main armature (3). Main

armature (3) is a coil with many turns of wire, and the current that flows

through it flows to the load.

The exciter supplies DC to main field (4). The load (terminal) voltage is

controlled by varying the small current to exciter armature (2). There are two

methods for excitation used on SR4 Generators; conventional self-excited

(SE) to satisfy most applications, or an optional permanent magnet pilot

exciter (PMPE) which allows the generator to better sustain an overload for a

short duration. Self-excited generators receive the power for excitation from

the generator armature (the generator output).


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Fig4.13a RFA

Fig4.13a showed when the engine starts turning rotating field assembly

(RFA); the residual magnetism in exciter field (L1) causes a small amount of

AC voltage to be generated in exciter armature (L2). This induced voltage in

(L2) causes an AC to flow. This AC flows through the three-phase full wave

bridge rectifier circuit (CR1 thru CR6). DC then flows through main field (L3).

The flow of DC through main field (L3) creates a magnetic field, which adds to

the existing residual magnetism of main field (L3). As main field (L3) rotates,

an AC voltage is induced into main armature (L4) which appears as a three-

phase AC voltage at output terminals T0, T1, T2, and T3. The voltage

regulator taps the AC output through wires 20, 22, and 24. During startup, this

tapped output is sensed by the voltage regulator as a low voltage output

condition. Therefore the voltage regulator output to exciter field (L1) is

increased so that the generator output will continue to increase up to the rated

voltage. The amount of current that flows through the exciter directly affects

the generator output voltage. The function of the voltage regulator is to keep

the generator output voltage constant with changing loads. The voltage

regulator controls the DC voltage that is supplied to the exciter and therefore,

the generator output voltage. The voltage regulator senses and uses the

generator output voltage at wires 20, 22, and 24. The voltage regulator thensupplies a controlled DC voltage to the exciter through wires (F1) and (F2).


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Fig 4.13b

Fig4.13b showed when the voltage regulator senses a decrease in output

voltage; it will increase the DC voltage at wires (F1) and (F2). This increases

the DC flow through exciter field (L1), therefore (L1) magnetic field increases

the AC voltage induced in exciter armature (L2). This increased AC voltage

from exciter armature (L2) causes more AC to flow. The AC is then rectified toDC by the three-phase full wave bridge rectifier circuit, which consists of

rectifiers (CR1-CR6). The increased DC output from the bridge rectifier is

carried to main field coils (L3) by conductors, which are routed through a

passage in the generator shaft. Increased current through main field coils (L3)

increases the magnetic field of the generator. The increased magnetic field

induces a large AC voltage into main armature (L4). Therefore the three-

phase AC voltage at terminals T0. T1, T2 and T3 increases until the voltage

regulator no longer senses a decreased output voltage.

When the voltage regulator senses an increase in output voltage, it will

decrease the DC voltage to the exciter. This decrease will flow on through the

generator output voltage.

Residual magnetism is necessary for start-up of the self-excited generator.

The main field coils are wound on magnetic steel that retains a small amount

of magnetism after shutdown.


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Al ternator characteristics and limitations

Al ternators are rated according to the voltage they are designed to produce

and the maximum current they are capable of providing. The maximum

current that can be supplied by an alternator depends upon the maximum

heating loss that can be sustained in the armature. This heating loss (which is

an I2R power loss) acts to heat the conductors, and if excessive, destroys the

insulation.

Single-phase al ternators

A generator that produces a single, continuously alternating voltage is known

as a SINGLE PHASE alternator. This term is used in ac generator when the

windings are at 180 degree apart from each other. The stator (armature)

windings are connected in series. The individual voltage, therefore, add to

produce a single-phase ac voltage. Fig4.14

Fig4.14 Single-phase alternator

Fig4.14 shows a basic alternator with its single-phase output voltage.

Single-phase alternators are found in many applications. They are most often

used when the loads being driven are relatively light. The reason for this will

be more apparent as we get into multiphase alternators.

Power that is used in homes, shops, and ships, to operate portable tools andsmall applications is single-phase power.


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Two Phase Al ternator

Fig 4.15 shows two-pole, two-phase alternator. The windings of two phases

are connected 90 degree apart from each other.

Fig415 Two Phase alternator

The outputs of each phase 900 apart, with A leading B. there will always be

900 between the phases this is by design. The stator windings consist of two

single-phase windings separated from each other each winding is made up of

two windings that are connected in series so that their voltages add. The rotor

is identical to that used in the single-phase alternator. In the left hand

schematic, the rotor poles are opposite all windings of phase A. Therefore, the

voltage induced in phase A is maximum, and the voltage induced in phase B

is zero. As the rotor continues rotating counterclockwise, it moves away from

the A windings and approaches the B windings. As a result, the voltage

induced in phase a decrease from its maximum value, and the voltage

induced in phase B increases from Zero. In the right-hand schematic, the rotor

poles are opposite the windings of phase B. Now the voltage induced in


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phase B is maximum, whereas the voltage induced in phase A has dropped to

Zero.

Three Phase Alternator

The three-phase alternator, as the name implies, has three single-phase

windings spaced such that the voltage induced in any one phase is displaced

by 1200 from the other two. A schematic diagram of a three-phase stator

shows in Fig4.16.

Fig4.16 Three phase alternator connection

View A, shows all the windings of each phase lumped together as one

winding. The rotor is omitted for simplicity. The voltage waveforms generated

across each phase are drawn on a graph, phase-displaced 1200 from each

other. The three phase alternator as shown in this schematic is made up of

three-single-phase alternators whose generated voltages are out of phase by

1200. The three phases are independent of each other.

The neutral connection is brought out to a terminal when a single-phase load

must be supplied. Single-phase voltage is available to A, neutral to B, and

neutral to C. In three-phase, Y connected alternator, the total voltage, or line

voltage, across any two of the three line leads is the vector sum of the

individual phase voltages. Each line voltage is 1.73 times one of the phase


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voltages. Because the windings from only one path for current flow between

phases, the line and phase currents are the same (equal).

Three-Phase Connections

The stator coils of three-phase alternators may be joined together in either

wye or delta connections, as shown in Fig4.17 with these connections only

three wires come out of the alternator. This allows convenient connection to

three-phase motors or power distribution transformers.

Fig417Three-phase alternator or transformer connections

A three-phase transformer may be made up of three, single-phase

transformers connected in delta, wye, or a combination of both.

Frequency

The output frequency of alternator voltage depends upon the speed of rotation

of the rotor and the number of poles. The faster the speed, the higher the

frequency. The lower the speed, the lower the frequency. The more poles

there are on the rotor, the higher the frequency is for a given speed.

For a given frequency, the more pairs of poles there are, the lower the speed

of rotation. The frequency of any ac generator in hertz (Hz), which is the

number of cycles per second, is related to the number of poles and the speed

of rotation, as expressed by the equation


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F=NP/120

Where P is the number of poles, N is the sped of rotation in revolutions per

minute (rpm), and 120 is a constant to allow for the conversion of minutes to

seconds and from poles to pairs of poles. For example, a 2-pole, 3600-rpm

alternator has a frequency of 60 Hz; determined as follows:

23600/120 = 60Hz

POWER FACTOR

Power factor affects every operation with a 3-phase AC electrical supply to

some degree or other. Power factor is a measure of how efficiently electrical

power is consumed. The ideal power factor is unity, or one. Any thing less

than one, (or 100% efficiency), means that extra power is required to achieve

the actual task at hand. This extra power is known as Reactive Power, which

unfortunately is necessary to provide a magnetizing effect required by motors

and other inductive loads to perform their desired function. Reactive Power

can also be interpreted as wattles, magnetizing or wasted power and extra

burden on the electricity supply.

Power Factor correction is the term given to a technology that has been used

since the turn of the 20th century to restore power factor to as close to unity as

is economically viable. This is normally achieved by the addition of capacitors

to the electrical network which provide or compensate for the Reactive Power

demand of the inductive load, and thus reduce the burden on the supply.

Benefits of Power Factor Correction

Below are just some of the benefits that can be achieved by applying the

correct power factor correction:

Power consumption reduced.

Electricity bills reduced.

Electricity energy efficiency improved.

Extra KVA availability from the existing supply.

Transformer & distribution equipment I2R losses reduced.

Minimized voltage drop in long cables.


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How is power factor caused?

Most electrical equipment such as motors, compressors, welding sets and

even fluorescent lighting, create what's known as an inductive load on the

supply. An inductive load requires a magnetic field to operate, and in creating

such a magnetic field causes the current to lag the voltage ( ie. The current is

not in phase with the voltage).

Power factor correction is the process of compensating for the Lagging

current by applying a Leading current in the form of capacitors. This way

power factor is adjusted closer to unity and energy waste is minimized.

Power Factor Explained

AC power supplies comprise three main components:

Active power: The real, usable power measured in KW.

Reactive power: The part of the supply that creates the inductive load,

measured in KVAr (kilo-volt-amperes- reactive).

Apparent power: The resultant of the other two components, measured in

KVA (kilo-volt-amperes).

The power factor of a supply can be expressed in two ways:

1. Power factor = Active power (KW) / Apparent power (KVA)

2. the cosine of the angle between Apparent Power and Active Power is

expressed as the power factor (cos)


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Capacitive KVAr (Leading)

Active powerKW

Inductive KVAr (Lagging)

Apparent Power KVA

Fig4.17.1

Fig 4.17.1 shows the phasor relationship between active, reactive and

apparent power:-

o Inductive KVAr lags the KW by 90.

o Apparent Power (KVA) is the phasor sum of +KVAr (lag).

o Power Factor is the cosine of angle .

Understanding Power Factor

A good analogy to help appreciate the affect of power factor on an electrical

network is to imagine a person running in the direction A to

As shown in Fig4.17.2 below. The energy required certainly depends uponthe load that the person is carrying (weight) and the distance covered, but the

gradient of the running surface also influences the effort that is needed.

A Fig4.17.2 B


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When the running surface is flat, then angle is 00.

Cosine (00) = 1.00

Or efficiency = 100%

In other words, 100% of the energy burned is being used to move the

running form A to B.

But if the running surface is uphill as shown in Fig4.17.3 say at 300 to the

horizontal, then:

Cosine (300) = 0.87.

Or power factor = 0.87

Or efficiency = 87%

In other words, only 87% of the energy burned is being used to move the

runner in the horizontal direction of B, and so extra energy will be required

to achieve the same objective.

A B

Fig4.17.3

Example

A 100KW motor operates at a given power factor of 0.8 lagging. The total or

apparent power required by the motor is actually 100Kw / 0.8 = 125KVA By

improving the power factor of the load to close to unity, say 0.95, then the total

power drawn from the supply will be reduced to 105KVA (100KW / 0.95) A

total power reduction of 20KVA or an overall energy saving of 16%.


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The Hidden cost

Electrical networks with a poor power factor draw more power than is strictly

required, forcing electricity generators to increase output.

This extra power means extra generating costs which are subsequently

passed on to the industrial consumer in one form or another. However, due to

the wide variation in the way that industrial/commercial electricity tariffs are

presented, these extra costs or penalties for inefficient use of electricity are

not always readily apparent and sometimes only a power factor survey at the

main incoming electricity supply will determine the presence of a poor power

factor.


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A.C MOTORS

Introduction

Motor:-

It is a machine which converts electrical energy in to mechanical energy.

Most of the power-generating systems shore and afloat, produce ac. For this

reason a majority of the motors used throughout the Navy are designed to

operate on ac. There are other advantages in the use of ac motors besides

the wide availability of ac power. In general, ac motors cost less than dc

motors.

Some types of ac motors do not use brushes and commutators. This

eliminates many problems of maintenance and wear. It also eliminates the

problem of dangerous sparking.

An ac motors is well suited for constant-speed applications. This is because

its speed is determined by the frequency of the ac voltage applied to the

motor terminals.

Industry builds ac motors in different sizes, shapes, and ratings for many

different types of jobs. These motors are designed for use with either

polyphase or single-phase power systems.

LENZS LAW

When an electromagnetic force is applied in a conductor (stator), it produces a

current in that conductor and due to changing of current; it induces an other

current in the other conductor (rotor), which always opposes the main field

(stator). So there a torque produces and that is in opposite direction of the

main field.

PRINCIPLE OF INDUCTION MOTOR:-

The stator magnetic field rotates clockwise, cutting the loop as it does so. By

Faradays law this will induce a current in the loop, the direction of which is

given by Flemings Right Hand Rule.


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SYNCHRONOUS MOTORS

Basically it is an induction motor, but these motors are used where a constant

speed is required with the load changes. It has a strong power factor

(normally it is called unit power factor), having two fields one stator field

winding its input supply is 440v 60Hz 3phase and the other is rotor field

winding having 115v DC supply though slip rings. Fig4.18

Initially it is started as an induction motor with normal 440v and when it

reaches up to normal speed then applied a DC voltage on rotor winding

through slip rings. These voltages strengthening the rotor field and lock it

electrically at one speed. It is used in heavy load and with continuous run

such as propulsion of ships etc.

Stator Field

440v 60Hz 3

L1

L2

L3

Rotor Field

115 DC Supply

+ ve

-ve

Fig4.18 synchronous motor


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INDUCTION MOTOR

There are many types of induction motors,

Single phase AC motor

It has two windings connected 900 apart each other. One winding is called

start and other called running winding. One winding is directly connected with

power supply while the other winding is connected to the power supply via a

capacitor connected in series. Fig4.19

Capacitor gives a phase advance to split phase in both windings. So it

produces a torque to start the motor. These are used in portable fans, and

ceiling fans etc. These motors work on 115v, 220v 60Hz single phase supply.

Start Winding

L1

L2 C

Running Winding

Fig4.19 Single phase AC motor

THREE PHASE AC MOTOR Fig4.19.1

It has three windings, are connected in 1200 apart from each other. Normally

the three phase AC motors are Star/Delta Fig4.19.2 connected with 440v, 3

60Hz and mostly the star connected motors are used on ships. These motorsare used as pumps motors, compressor motors; purifier motors and for

exhaust / supply fans etc.


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L1

L2

L3

Fig4.19.1 Three phase motor (Star connection)

L1 L2 L3

Fig4.19.2 Delta Connection

Important Electrical Terms

Insulation:-

The material which protects the leakage of current through a conductor which

is layered on conductor strain.

Continuity:-

If there is no breakage in a wire or conductor checked by AVO or Bridge

Megger giving Zero reading is called continuity.

Phase Balance:-

If resistance of all three windings of generator or motor having equal value

checked by AVO or Bridge megger is called phase balance.


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Single phasing effect:-

When one phase of a three phase motor is open or missing and two phases

are present there, it is called a single phasing effect. Due to this effect the

motor will burn.

Causes of single phase

1) One fuse blown.

2) Loose connection.

3) Unbalance line voltage.

4) One phase earthed.

Causes of motor burning

1- Due to dripping of water over the motors body.

2- Due to hard bearing.

3- Due to hard pump or fan impeller or any type of heavy load.

4- Due to single phasing effect.

5- Draw a heavy current due to short circuit in the body winding or in terminal

box.

6- Due to body deteriorated or life expired.

7- Due to low insulation of windings.

8- Due to loose connections.

Do not attempt to start the motor, if the motor fails to start twice, find out the

fault and then start the motor.


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References

1. Engineering standing order.2. RQB term one book.

3. www.howstuffworks.com4. www.howthingsworks.com5. http://en.wikipedia.org/wiki/Battery_(electricity)
http://www.howstuffworks.com/http://www.howthingsworks.com/http://www.howthingsworks.com/http://www.howstuffworks.com/

55593080 electrical hand book

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