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FUNDAMENTAL ELECTRICAL THEORYFUNDAMENTAL ELECTRICAL THEORY

INTRODUCTION - Electricity and its distribution is indispensable to the successful operationof modern vessels. To begin to comprehend complex electrical systems, one must firstunderstand the fundamental concepts of electrical theory. This chapter will examine basicelectrical terms, definitions, and concepts. In addition, the generation of alternating current and

the transformation of chemical energy into electrical energy will be discussed.

Like steam, electricity transports energy. Steam carries the thermal energy produced in the ship's boilers to the turbines, where the energy is expended in doing work. Electric current carries theelectrical energy produced by the generators to the electric motors and other electricalcomponents, where the energy is expended in doing work and performing other useful functions.

ELECTRICAL TERMS -Current - Current is defined as the flow of electric charges (electrons) through a conductor or circuit per increment of time. The unit of current, called the ampere (I), specifies the rate atwhich the electric charges are flowing. In other words, the amperage of a circuit is a measure of the number of charged particles passing a point each second. (Electrical current is analogous tothe rate of flow of water through a pipe.)

Electromotive Force (emf) - Before an electric current can flow through a wire, there must be asource of electric "pressure," just as there must be a pump to build up water pressure beforewater will flow through a pipe. Electric pressure (E) is known as electromotive force (emf,

potential difference, or voltage (V). Generators and batteries are the most common sources of voltage. Increased voltage in a circuit increases the current flow, just as increased pressure onwater in a pipe increases water flow.

Resistance (R) - Electrical resistance is an electrical circuit's opposition to the flow of currentthrough it. The unit of measure of resistance is the ohm ().

Conductor - All materials will conduct electricity, but at varying resistances. Some metals suchas silver, copper, aluminum, and iron, for instance, offer little resistance to current flow andtherefore are called good conductors.

Insulator: Some substances among them wood, paper, porcelain rubber, iron, and plastics-offer ahigh resistance to current flow, and are called insulators. Electric circuits throughout a ship aremade of copper wires covered with rubber or some other good insulator. The wire offers littleresistance to current flow and thus acts as the conductor, while the insulation keeps the currentfrom passing to the steel structure of the ship.

Direct Current (DC) - When a current flow is unidirectional and of constant magnitude, it iscalled direct current (DC). Batteries, for example, produce only direct current. See Figure 1.

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FIGURE 1 DIRECT CURRENT

Alternating Current (AC) - In an AC circuit, the magnitude and direction of current flow are periodically changing. If these changes were plotted, they would describe a sine curve (Figure 2).Starting from zero, the current builds up to a maximum in one direction, then falls back to zeroand builds up to a maximum in the other direction, and then returns to zero ready to start thesequence again. Each such current sequence, is called a cycle. The frequency of an AC circuit isthe number of such cycles per second. The unit of frequency measurement is the hertz (Hz):where 1 Hz = 1 cycle/sec. The most common shipboard electrical frequency is 60 Hz.

FIGURE 2 ALTERNATING CURRENT

ELECTRICAL RELATIONSHIPS - In the early part of the nineteenth century, G. S. Ohm proved by experiment that relationship exists among current, voltage, and resistance. This classicrelationship is called Ohm's Law and is stated as follows:

The current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance. This fundamental law of electricity is expressed by the following equation:

E = IR

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Where E = voltage in voltsI = current in amperesR = resistance in ohms

By definition, power (P) is the rate at which work is done. In an electrical circuit, power is

expressed as follows:

P = PR = EI

Where power has the unit of measure called the watt (W).

ELECTROMAGNETIC INDUCTION - In 1831, in England, one of the most importantdiscoveries in electricity and magnetism was made by Michael Faraday. Faraday's experimentsshowed that an emf (electromotive force) is induced in a conductor if a bar magnet passes by theconductor. This happens because the motion of the magnet relative to the conductor causes themagnet's magnetic lines of flux (electromagnetic force) to be cut.

Suppose that the experiment shown in Figure 3 is performed. When the north pole of the magnetenters the coil, the galvanometer (G) registers a current in one direction. If the magnet is then

pulled back, the galvanometer will register a current in the opposite direction. It follows that the production of a voltage by electromagnetic induction requires a magnetic field, a conductor, andrelative motion of the two. Note that when the conductor is moved through a magnetic field tocut the magnetic lines of flux (see Figure 3); a voltage is also induced in the conductor. As

before, if the conductor is connected to a voltmeter or galvanometer, the voltage is measured bya deflection on the meter. If the conductor is moved in the opposite direction through the field,the voltage will cause the needle to be deflected in the opposite direction because of the reverseddirection of the induced current flow. Thus the same result occurs whether the conductor is heldstationary and the magnetic field is moved relative to it, or vice versa.

The voltage developed in the conductor by electromagnetic induction is known as an inducedemf, and the resulting current is called induced current. The induced emf exists only so long asthere is relative motion between the conductor and the magnetic field. There is a definiterelationship between the direction of flux, the direction of motion of the conductor, and thedirection of the induced emf. When two of these directions are known, the third can bedetermined. The magnitude of the induced current can be increased by increasing the strength of the magnetic field, by increasing the velocity of the motion of the magnetic field and theconductor relative to each other, or by positioning the magnetic field and the conductor so that agreater number of magnetic lines of flux are cut by the conductor.

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FIGURE 3 ELECTROMAGNETIC INDUCTION

FIGURE 4 - ELECTROMAGNET.

Permanent magnets are not the only means by which a magnetic field can be generated and infact permanent magnets provide too small a magnetic field to induce sufficient current for

practical applications. The most common method of magnetic field generation is by the use of anelectromagnet. The electromagnet (illustrated in Figure 4) consists of coil of wire wrapped

around a ferrous metal core. Direct current is passed through the wire and a magnetic field is produced. The magnitude of field (B) is determined by the number of turns of wire (N) and themagnitude of the direct current (I DC):

B = (constant) NIDC

The machine used to convert mechanical energy into electrical energy is called a generator. Agenerator comprises the essentials of Faraday's Law: a conductor, a magnetic field, and a relativemotion. In its simplest form it consists of a magnet (either a permanent one or an electromagnet),

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a coil of conducting wire that rotates between the distinct poles of the magnet, and brush contacts(slip-rings) on the wire coil so that a connection can be made between the coil and an externalcircuit, as shown in Figure 5.

The generator is one of the most useful and widely employed applications of magnetic induction.It results in the production of vast quantities of electric power from mechanical sources. The

sources of mechanical energy may be provided by a number of different prime movers, includinggasoline engines, diesel engines, water turbines, steam turbines, and gas turbines.

FIGURE 5 A SIMPLE GENERATOR

ALTERNATING CURRENT (AC) GENERATORS - Most electrical power used on boardvessels is generated by alternating current (AC) generators. AC generators are constructed inmany different sizes, depending on their intended use. For example, any one of the severalgenerators at Boulder Dam can produce millions of watts, while generators used on aircraft may

produce only a few thousand watts. Regardless of size, all generators operate on the same basic principle: a magnetic field cutting through conductors (or conductors passing through a magnetic

field). All generators have two distinct sets of conductors: a group of conductors in which theoutput voltage is induced, and a second group of conductors through which direct current is passed to produce the electromagnetic field. The conductors in which the output voltage isinduced are called the armature windings (armature). The conductors used to produce theelectromagnetic field are called the field windings (field).

For voltage to be induced there must be motion of the armature and the field relative to eachother. To provide this motion, generators are constructed of two major mechanical assemblies:the stator and the rotor. The stator is the stationary housing of the generator, and the rotor rotates,

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inside the stator. The rotor is driven by the prime mover; thus motion of the stator and the rotor relative to each other is produced. Two variations in the construction of AC generators are usedtoday; the only difference between them is the ways the armature and the field are arranged withrespect to the stator and the rotor.

REVOLVING ARMATURE - In the revolving-armature AC generator, the stator provides a

stationary electromagnetic field and the rotor acts as the armature revolving in the field. As thearmature cuts the lines of magnetic flux, current is induced in the conductors of the armature.The current is transferred out of the rotor through sliding contacts (slip-rings and brushes). SeeFigure 6.

The revolving-armature AC generator is seldom used, because of the requirement to transmit theoutput power through sliding contacts. These contacts are subject to sparking and frictional wear and may arc over at high output voltages. Consequently, this generator is limited to low-power,low-voltage applications.

FIGURE 6 REVOLVING-ARMATURE AC GENERATOR

REVOLVING FIELD - The revolving field AC generator is the most widely used type. It passes a small direct current, from a separate source, through the field windings on the rotor (bymeans of slip-rings and brushes) to produce an electromagnetic field of fixed polarity on therotor (similar to a rotating bar magnet). The magnetic lines of flux from this rotating magneticfield extend outward from the rotor and cut the armature windings mounted in the surroundingstator. As the rotor turns, an alternating current is induced in the armature, because magneticfields of first one polarity and then the other move through the armature windings. (See Figure 7)Since the output power is taken from stationary armature windings, the output may be connectedthrough fixed terminals. This is advantageous, because there are no sliding contacts in the outputcircuit and the whole circuit is continuously insulated. This minimizes the danger of arc-over.Slip-rings and brushes are used on the rotor to supply the small amounts of direct current to the

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field. Slip-rings and brushes are adequate for this purpose, because the power level in the field ismuch lower than in the armature circuit.

In order to maintain a constant 60 Hz output frequency from a rotating field generator, the speedof rotation of the field must be kept constant. As shown in Figure 7, when the polarity of themagnetic field reverses, the direction of induced current flow also reverses (convention has it

that the North Pole produces positive current flow). A constant-speed governor is used on the prime mover to maintain the rpm of the rotor (thus the field) at a constant speed, regardless of the load on the generator. The required speed of rotation is the speed necessary to produce outputAC power at 60 Hz.

The only practical way to regulate the voltage output of a constant-speed AC generator is tocontrol the strength of the rotating magnetic field. The strength of the electromagnetic field may

be varied by changing the amount of direct current flowing through the field windings. Thusvoltage in an AC generator is regulated by varying the field current (I DC). This allows a relativelylarge AC voltage to be controlled by a much smaller direct current.

FIGURE 7 REVOLVING-FIELD AC GENERATOR

VOLTAGE PRODUCED BY CHEMICAL ACTION - Chemical energy is transformed intoelectrical energy within the cells of a battery. On naval ships electricity from this source supplies

power for emergency lighting (with dry-cell batteries) and the starting of small engines (withwet-cell batteries).

The most common dry-cell battery consists of a cylindrical zinc container, a carbon electrodeand an electrolyte of ammonium chloride and water in paste form. The zinc container is thenegative electrode of the cell; it is lined with a non-conducting material to insulate it from theelectrolyte. When a circuit is formed, the current flows from the negative zinc electrode to the

positive carbon electrode.

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In a common wet-cell storage battery, the electrodes and the electrolyte are altered by thechemical action that takes place when the cell delivers current. Such a battery may be restored toits original condition by forcing an electric current through it in the direction opposite to that of discharge.

The most common wet-cell storage battery in use is the lead-acid battery, having an emf of 2.2

volts per cell. In the fully charged state, the positive plates are lead peroxide, and the negative plates are lead immersed in a diluted sulfuric-acid electrolyte. See Figure 8.

FIGURE 8 - WET -CELL BATTERY.

When a circuit is formed, the chemical action between the ionized electrolyte and dissimilar metal plates converts chemical energy to electrical energy. As the storage battery discharges thesulfuric acid is depleted by being gradually converted to water and both positive and negative

plates are converted to lead sulfate. This chemical reaction is represented by the followingequation, the reversibility of which depends on the addition of electrical energy during thecharging cycle:

Discharging

Pb + PbO 2 + 2H 2SO 4 2PbSO4 + 2H20

Charging

The capacity of a battery is measured in ampere-hours. The capacity is equal to the product of the current (in amperes) and the time (in hours) during which the battery supplies this current toa given load. The capacity depends upon many factors, the most important of which are (1) thearea of the plates in contact with the electrolyte (liquid acid) in the battery, (2) the quantity and

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specific gravity of the electrolyte, (3) the general condition of the battery, and (4) the finallimiting voltage. Large wet cell batteries of the lead-acid type are used to provide emergency

power on nuclear submarines.

MISCELLANEOUS ELECTRICAL DEVICES - Two of the most common electrical devicesfound on board a ship are transformers and rectifiers.

Transformers - A transformer is a device without moving parts that transfers energy from onecircuit to another by electromagnetic induction. The energy is transferred without a change infrequency, but usually with changes in voltage and current. A step-up transformer receiveselectrical energy at one voltage and delivers it at a higher voltage; a step-down transformer receives electrical energy at one voltage and delivers it at a lower voltage. Since a transformer neither increases nor decreases the electrical energy in the circuit, an increase in voltage resultsin a decrease in amperage, and vice versa. A typical transformer has two windings, which areelectrically insulated from each other and mounted on opposite sides of a ring made of aferromagnetic material. This ring is called the core. The winding that receives the energy fromthe AC source is called the primary winding, and the winding that delivers the energy to the load

is called the secondary winding. See Figure 9. In a step-up transformer, the primary winding hasfewer turns of wire than the secondary, and in a step-down transformer the primary winding hasmore turns of wire than the secondary.

FIGURE 9 SIMPLE TRANSFORMER

Since a transformer operates on electromagnetic-induction principles, all of the followingelements must be present: a conductor, a magnetic field, and relative motion. The secondarywindings satisfy the first condition, and the current through the primary windings satisfies thesecond. But if the transformer has no moving parts, how can relative motion be obtained? Theanswer: through the use of alternating current. As the current constantly fluctuates from zero to a

positive maximum to zero to a negative maximum, the magnetic flux constantly reverses. Thisreversing of the lines of force provides the relative motion between field and conductor. For obvious reasons, transformers cant be used for direct current, since there is no reversal of current flow in direct current.

Rectifying Devices - A rectifying device converts alternating current into direct current. It isdesigned so that it has a very small resistance to current flow in one direction and a very largeresistance to current flow in the opposite direction. This allows the device to act as a conductor

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for the positive half of the AC cycle and as an insulator for the negative half of the cycle. Figure10 shows the output of a rectifying device with an AC input. The output of this circuit isessentially DC power. Rectifying devices themselves are semi-conductor devices commonlycalled diodes or rectifiers.

FIGURE 10 - OUTPUT OF SIMPLE RECTIFYING DEVIC E.

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ELECTRICAL BASICS

ELECTRICAL HAZARDS - Probability - More deaths aboard Navy ships occur fromelectrical shock than from any other accidents.

WHAT IS ELECTRICAL SHOCK? - It is the flow of electrical current through the body,

causing damage to the body.

FACTORS INVOLVED A. How much current and for how long.B. Where in the body the current flows; nerve contact and voltage.C. If a 60 cycle current pass from hand to hand, or hand to foot.

1. .001 AMP perceptible (1MA)2. .01(10MA) intense enough to prevent voluntary control of muscles (you cant let go).3. .1 AMP (100MA), fatal of it lasts for more than 1 second.

1. SHOCK PREVENTION

a. Stay away from shock hazard area whenever possibly. b. Do not work on live circuits unless absolutely necessary. (Assume live circuit).c. When working on live equipment use only one hand. Watch out for long hair, neck

jewelry etc.d. Work with a buddy if possible. Let someone know where you are and what you are

doing.e. Work on a rubber mat and wear rubber gloves.f. Report / repair all hazards immediatelyg. Have a safety training programh. Use common sensei. Make sure metal cased protable tools (hand drills etc) are electrically grounded (plugs &

receptiables)i. 3 prong plug

ii. check the power cord for frayed or cracked insulation j. Do NOT touch someone who is on contact with live wires

i. Turn of power sourceii. Use dry wood pole/chair or any non-conducting object to remove

victom from wires (or wires from victim)k. Learn CPR l. Do provide safety checks (meggur test of insulation)

2. CAUSES OF ELECTRICAL SHOCK

a. Failure to observe common sense precautions b. Failure to observe posted safety precautions.c. Use of unauthorized equipment or unauthorized modifications to equipment (jumping

out interlocks, use of man-killersd. Failure to routinely check equipment test and electrical equipment and other equipment.

(Look for frayed insulation).

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WHEN WORKING ON LIVE ELECTRICAL EQUIPMENT (GET PERMISSIONFIRST)

A. Make sure person working is not grounded: wear rubber soles and gloves. Check solesof shoes and gloves for cracks and dirt. Even thick dry paper is a good insulator.

B. Dont wear watches, rings or any jewelry etc. NO metal chains.C. Dry clothing and shoes must be worn

D. Good illumination is critical.E. Use non-conducting, wrenches and tools, (tape with electrical tape), keep clean and dry.F. Wear rubber glovesG. Work with one hand.H. Be sure that connections test leads will not come looseI. Tag-out equipmentJ. Never use extension light without a guard.

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DEFINITIONS

AMBIENT TEMPERATURE - The temperature of the surrounding area or space.

ALTERNATING CURRENT (AC) - Produced by alternators. The frequency of AlternatingCurrent is its number of cycles per second, (i.e., the number of times per second the current

changes direction and the returns to its original direction). Cycles are now called Hertz (hz).

AMPERE - Unit of electrical flow. It is commonly called an Amp.

CAPACITANCE - The tendency of electrical circuits to resist a change in voltage, and is produced by capacitors. Across a capacitor Alternating Current (AC) leads voltage by a 90* phase angle.

DIRECT CURRENT (DC) - Flows in one direction only. It is produced by batteries and DCgenerators.

DRIP PROOF - Enclosures that protect from falling liquid.

ELECTROMAGNET - Is produced when DC current passes through an electrical coil woundaround a soft iron core.

EXPLOSION PROOF - Electrical equipment can be made this way, which means it is builtstrong enough to contain an explosion and keep it from spreading outside its enclosure.

GROUND - An electrical connection between the circuit and the frame, housing or other pathsto the earth.

GROUNDED CIRCUITS - Some electrical systems are designed to use the hull of the ship (or body of the car) as part of the circuit.

HORSEPOWER - .746 watts of electrical power equals one.

INDUCTANCE - The tendency of electrical circuits to resist a change in current. It is producedin coils conducting Alternating Current (AC) and results in a counter ElectroMotive Force(EMF). Across a coil AC voltage leads current by a 90 phase angle.

OHMS - Units for measuring electrical resistance.

OPEN - A break in a circuit. It may be accidental when the circuit burns out, or intentional aswhen a switch is turned off.

RECTIFIER - A device that changes Alternating Current (AC) into Direct Current (DC).

SHORT CIRCUIT - An accidental path of low resistance which results in high current.

TORQUE - Force applied in a twisting (i.e., rotary) direction.

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VOLT - Unit of electrical force (or in a manner of speaking, pressure).

WATT - Unit of electrical power. One thousand (1.000) watts make one kilowatt (KW).

WET OR DAMP LOCATIONS - Machinery spaces and the galley, are considered wet or damp locations for shipboard electrical installation.

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BASIC ELECTRICAL INTRODUCTION / SHIPBOARD CIRCUITS.

- What is electricity? - It is a form of energy/power.

- Electrical sources are generators powered by diesel, steam/gas turbine or batteries

Electrical Sources Convert one form of energy to electrical energy. Electrical power (watts or kilowatts (kw) is both voltage and current together at the same time.

1. Generator takes in mechanical power from the diesel - Amount of mechanical power the generator takes is just enough to power the load replacement.

Generators also are rated byPower: 1000 kw (1250 kva)Voltage: 460 VoltsFrequency: 60 cycles (hz)

Current (amperage) 160 amps for a 1000 kw generator

Temperature can get to 105 - 220 C. Water boils at 100 C. To convert 220 C to F use thefollowing formula:

F =5

9x 220 = 32 428

F =5

9(C +32 ) C =

9

5(F - 32)

- Temperature rating is MOST important!- Keep all equipment cool, clean, lubed and well ventilated.

If generator is rated at 1000kw, 480, 60hz It may put out between 0kw to 1000kw (whatever theload demands: but it must always be 480v and 60 hz)Another electrical power source is the chemical battery (cell) limited (small compared togenerators) energy source.

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1. Dry cell - 1.5 V, 9V - Limited energy supply, use and dispose2. Storage batteries - Have more energy in them than do simple dry cells and can be

recharged. To be recharged means to replace the used up energy.Storage battery types -a. Alkaline Battery: flat plate nickel-cadium,

b. Lead Acid: many types and designs (hydro-cloric used) danger of freezing and

explosion.

Alkaline last longer than lead-acid.

Uses of storage cells:Emergency lighting (general and engine room)Emergency steeringStarting emergency generatorsUsed in life boatsBells, whistlesDistress call Apparatus

TelephonesFire detection

3. Batteries are rated by voltage level and Ampere-hour. Voltage rating for storage batteries (lead acid) is 12 volts

Be careful of polarity connections

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ELECTRICAL LOADS 1. Electrical motors are a type of electrical load (the largestloads!)

Motors are rated by:

Power - Horse power - 3HP, 100HP up to 1000HP- 1HP = 746 Watts- 746 Watts is the same as 12.4, 60-watt light bulb- 100HP is the same as 1240, 60-watt light bulbs!

Speed - RPM (revolutions per minute) - For a/c motors typically between 900 RPM and 3600RPM

Torque - a twisting force.

PH.P. =

F L B H P R P M n f t l b ==

2 9 2

1 8 0 05 2 5 2()1 0 0(

5 2 5 2)()(

100HP Motor @1800RPM

Voltage and Frequency for a/c motors typically 440v and 60hz for motors larger than 2 or 3horse power; 110v and 60hz for smaller motors.

B. Another type of load is lighting.- There are both interior and exterior lights.- Lights typically use 120v, 60hz sources, but ship generators @ 480v. So a transformer

is needed to change voltage level from 480v to 120v.- Light load centers are feed electrical power via transformers and switch boards.- Illuminate passageways, work centers and living spaces etc.- Above deck / weather deck lighting

1. Running lights

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2. Underway ops lighting- Red lighting

ELECTRICAL POWER AND DISTRIBUTION VIA CABLES AND SWITCHBOARDS.

A. Cables : these are conductors at electrical currents and power they are of copper and can be

solid (single strand) or multi-strand conductor.

Conductors are sized by their diameter:

Area = d

d is given in circular mil (c.m.).001 inch = 1 c.m.

inch = .250 inch = 250 c.m.

The larger the diameter, the more current and power the cable can carry. Wire and cables aresized (numbered) according to a table known as the American Wire Gage (AWG).

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WIRE GAUGE

STANDARD SOLID COPPER (american Wire Gauge)

GaugeNumber

Diameter(mile)

Cross Section Ohms per 1,000 ft Ohms permile 25C(=77F)

Poundsper 1,000

ft.Circular

mileSquareinches

25C(=77F)

65C(=149F)

0000 460.0 212,000.0 0.166 0.0500 0.0577 0.264 641.0000 410.0 168,000.0 .132 .0630 .0727 .333 508.0

00 365.0 133,000.0 .105 .0795 .0917 .420 403.00 325.0 106,000.0 .0829 .100 .116 .528 319.01 289.0 83,700.0 .0657 .126 .146 .665 253.02 258.0 66,400.0 .0521 .159 .184 .839 201.03 229.0 52,600.0 .0413 .201 .232 1.061 159.04 204.0 41,700.0 .0328 .253 .292 1.335 126.05 182.0 33,100.0 .0260 .319 .369 1.685 100.06 162.0 26,300.0 .0206 .403 .465 2.13 79.57 144.0 20,800.0 .0164 .508 .586 2.68 63.08 128.0 16,500.0 .0130 .641 .739 3.38 50.09 114.0 13,100.0 .0103 .808 .932 4.27 39.6

10 102.0 10,400.0 .00815 1.02 1.18 5.38 31.411 91.0 8,230.0 .00647 1.28 1.48 6.75 24.912 81.0 6,530.0 .00513 1.62 1.87 8.55 19.813 72.0 5,180.0 .00407 2.04 2.36 10.77 15.714 64.0 4,110.0 .00323 2.58 2.97 13.62 12.415 57.0 3,260.0 .00256 3.25 3.75 17.16 9.8616 51.0 2,580.0 .00203 4.09 4.73 21.6 7.8217 45.0 2,050.0 .00161 5.16 5.96 27.2 6.2018 40.0 1,620.0 .00128 6.51 7.51 34.4 4.9219 36.0 1,290.0 .00101 8.21 9.48 43.3 3.9020 32.0 1,020.0 .000802 10.4 11.9 54.9 3.0921 28.5 810.0 .000636 13.1 15.1 69.4 2.4522 25.3 642.0 .000505 16.5 19.0 87.1 1.94

23 22.6 509.0 .000400 20.8 24.0 109.8 1.5424 20.1 404.0 .000317 26.2 30.2 138.3 1.2225 17.9 320.0 .000252 33.0 38.1 174.1 0.97026 15.9 254.0 .000200 41.6 48.0 220.0 0.76927 14.2 202.0 .000158 52.5 60.6 277.0 0.61028 12.6 160.0 .000126 66.2 76.4 350.0 0.48429 11.3 127.0 .0000995 83.4 96.3 440.0 0.38430 10.0 101.0 .0000789 105.0 121.0 554.0 0.30431 8.9 79.7 .0000626 133.0 153.0 702.0 0.24132 8.0 63.2 .0000496 167.0 193.0 882.0 0.19133 7.1 50.1 .0000394 211.0 243.0 1,114.0 0.15234 6.3 39.8 .0000312 266.0 307.0 1,404.0 0.12035 5.6 31.5 .0000248 335.0 387.0 1,769.0 0.095436 5.0 25.0 .0000196 423.0 488.0 2,230.0 0.075737 4.5 19.8 .0000156 533.0 616.0 2,810.0 0.060038 4.0 15.7 .0000123 673.0 776.0 3,550.0 0.047639 3.5 12.5 .0000098 848.0 979.0 4,480.0 0.037740 3.1 9.9 .0000078 1,070.0 1,230.0 5,650.0 0.0299

Wire and cables are insulated to prevent shorting of electricity. The limit of current dependson cable heating due to carrying current too hot: burn the insulation.

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When conductors carry curretn they heat-up (temperature increases) because the wires have asmall amount of resistance.

heat = (current) 2 x resistance x time*Note Current squared

Heat depends on how much current 2 for how long a time. If insulation gets too hot, it will break

down.

Insulated or resistance - Resistant to leakage currents (check for cracks)

Dielectric strength - Ability to withstand voltage break down (what is it made of and how thick)

Insulation rubber, varnish, plastics, organic metals

B. Switches: Circuit Breakers/fuses1 Circuit breakers connect leads to sources. They act like light switches in the home. But

the also act like fuses in the home as well. So circuit breakers are circuit protectiondevices as well as simple off on switches.

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Circuit breakers are rated by voltage, interrupt capacity and interrupt time. Breakers open tostop currents. These currents can be normal load currents or extremely high fault currentsdue to shorts of grounds. 5000 A or greater in a fraction of a second. Indicative currents are the

worse kind because they create arc.

Fuses also protect against shorts, grounds (faults) and over current conditions.

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TYPICAL FUSES AND SCHEMATIC SYMBOLS

TYPICAL FUSES AND SCHEMATIC SYMBOLS

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ELECTRICAL QUANTITIES - Ohm, Amphere (Amp), Volt and Watt

A. Ohm - Opposition to the flow of electricity. The opposition is called resistance.

Schematic Symbol

Schematic is an electrical circuit diagram made up of electrical symbols.

Therefore temperature is always the enemy of electrical equipment.

- Conductors are to have O (very low)- Insulation re to have very high of resistance.- Check most resistors and conductors with the ohmmeter.- Check very high insulator resistance with a megger.

COLOR COLOR

Black 0 Blue 6Brown 1 Violet 7

Red 2 Grey 8Orange 3 White 9Yellow 4 Gold 5%Green 5 Silver 10%

None 20%

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B. Current - The flow of charges (electrons) (Q)

qe = - 1.6 x 10-19

Coulomb.

1 Coulomb = 6.28 x 10 28 electrons.

6.28 million, million, million electrons 628 with 28 zeros

Current Flows - Current has direction (usually out of the positive high potential side of thesource) and magnitude (how much).For current to flow, we need:

1. Electrical source of power/energy

2. Conductors provide a complete path and free electrons3. An electrical load that requires electrical power (connects the power to --)

C. Voltage (volt) The electrical push that makes charges more through conductors andresistors (loads). The voltage of a source is an energy (potential energy) difference betweentwo points.

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There is a voltage at the teminals of the sourceNote Voltage does NOT flow or move. Voltage gives energy to charges (current) that

moves.

When high energy current goes into load (resister) it drops energy and creats a voltageacross the R

D. Electrical Power - Electrical power is measured or calculated in watts. For a light bulb P=60 watts

Explain power as the rates of using (transforming) energy.

P =sec

joulestimework

= watts

Work = Force x distanceTry not to confuse them

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High-powered devices are usually larger (have greater surface area) than do low power devices.

Power dissipation heat and temperature

For d/c circuits P=V.I = R

V 2

= I 2 R

Use of a multimeter to measure R, V and Ia. Ohmmeter DMM and S-260 in lab

b. d-c / a-c voltmeter DDM and s-260 in lab CAUTION!c. D-c / a-c Ammeter- clip on and S-260 in lab CAUTION!

TYPICAL MULTIMETER

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ELECTRICAL CIRCUITS & OHM'S LAW The material a conductor is made of will determine whether it is considered a conductor

(i.e., with low resistance) or an insulator (i.e., with high resistance). An example of aconductor is a copper wire. A conductor's resistance to the flow of electricity variesdirectly with its length and its temperature . A conductor's resistance varies inverselywith its cross sectional area . For example, the resistance of a wire with a large cross

section is less than if the % of arc had a smaller cross section. American wire gauge (AWG) tables use the circular mil as the unit of cross sectionalarea. One circular mil is the area inside a circle with a diameter of 1/1000 of an inch.

You can indirectly measure the resistance of a conductor by measuring the voltage dropacross it and the Amperage through it and applying Ohm's Law to calculate its resistance.

Series circuits have all components connected so electricity flows in a straight linethrough all components. In batteries this means the positive (+) pole of one battery, isconnected to the negative (-) pole of the next battery.

In series circuits the voltages and resistances are added while the same current flowsthrough all components.

Parallel circuits have branches. In batteries this means that all positive (+) poles are

connected together and all negative (-) poles are connected together. All circuit components in a parallel circuit have the same voltage across them. Thecurrent through each component is added to give the total circuit current. The totalresistance (R in ohms) is less than the resistance of the lowest component, as follows:

n

n

r r r

Ralsor r r R 1

....11

11....

111

21

1

211 +++

=+++=

A resistor in parallel aids in regulating the voltage output. Ohm's Law explains the relationship between voltage (V), current (I) and resistance (R)

with these formulas:

V = I x R I = V/R R = V/R

which can besummarized,

To use this diagram cover thecharacteristic required - therelationship of the other twois given .

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Apparent power (P) equals voltage times current. P (watts) = I (amps) x V (volts)

Impedance is the name for total electrical resistance and is equal to resistance plusimpedance plus capacitance

BATTERIES Lead-acid batteries are composed of several 2-volt cells connected in series to give their

rated voltage.

You can measure the specific gravity of the sulfuric acid electrolyte with a hydrometer todetermine the charge of a lead-acid battery. (Vocabulary: Electrolyte = the liquid in a battery.)

A fully charged lead-acid battery will have a specific gravity of 1.280 to 1.300. A hydrometer will give an inaccurate reading immediately, after you add water to a

battery.

When charging a battery, you can tell it is fully charged when the electrolyte reaches the proper specific gravity range and does not increase over a period of 1 to 4 hours.

To mix electrolyte for a battery, you should pour sulfuric acid into distilled water in aglass container. It is safer to splash mostly water rather than concentrated sulfuric acidwhen you begin pouring.

A fully charged battery (i.e., one with high specific gravity) freezes at a lower temperature (i.e., has a lower freezing point) then a dead battery.

Battery capacity is rated in ampere - hours (i.e., the amps delivered times the number of hours.)

When salt-water mixes with sulfuric acid it produces a gas that is a respiratory irritant

that can be fatal.

Routine maintenance of lead-acid batteries includes keeping the terminals clean, providing a protective covering for the cable connections and keeping the battery under a trickle charge.

Battery rooms must be ventilated since lead-acid batteries produce hydrogen gas whichis explosive. When charging, remember that hydrogen is a highly explosive gas that risesabove the batteries and may be trapped beneath the overhead.

Local action refers to the loss of an electrical charge over a period of time when a batterynot being used.

Nickel Cadmium batteries contain a potassium hydroxide electrolyte. This type of battery must be tested with a voltmeter.

MOTORS The primary function of an electric motor is to provide torque (i.e., a force that produces

rotation). DC motors provide an easier and a wider range of speed control than AC motors. Some DC motors have smaller field poles located between the main field poles of the

stator (i.e., housing). They are called interpoles (or commutator poles) and reducesparking at the commutator.


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To change the direction of rotation of a DC motor you should either: Reverse the polarity of the field poles or; Reverse the current to the brushes.

However, if you reverse both the polarity and the current, the motor rotation will remainthe same.

A series wound motor has a very high starting torque and is often used as a starter motor

and for other uses that require high torque. The field windings and armature are in seriesin this motor. When not under load, a series wound motor will run away and its speedwill increase until it damages itself.

In a shunt wound motor the field is in parallel with the armature. When you apply a loadto this motor, it tends to slow down slightly.

A compound wound motor has field coils both in parallel and in series with thearmature.

Universal motors operate on both AC and DC. They have brushes and commutators.They are used to power portable tools, small fans and other fractional horsepower applications.

To change the direction of rotation of a three-Phase induction (AC) motor switch anytwo of the phase leads to the stator. An induction motor that operates at a fixed frequency can provide several different

speeds only if you reconnect the stator windings (i.e., field windings) to provide adifferent number of poles.

Synchronous speed is the speed of the rotating field. 60 cycle current providesapproximately 3600 RPM in a two pole induction motor. To find the synchronous speedof any induction motor divide the number of poles by 2 and then divide that number into 3600. A four pole motor: 4 2 = 2; 3600 2 = 1800. With a synchronous speed of 1800 RPM the induction motor must turn somewhat slower* to provide the slip to

produce the induction which causes the torque . Depending on the load, most four pole

induction motors actually rotate in the 1720 to 1780 range . (Less a few RPM for slip.) The starting winding on a split-phase induction motor is not designed to carry current

when the motor is running. If the cut-out switch for this winding does not operate (i.e.,fails to open,) the winding will probably burn out.

A capacitor in series with a winding splits the phase and provides a rotating field for starting purposes.

Synchronous motors often have a cage rotor winding which is used to start the motoras if it were an induction motor. After starting, this winding is shorted and the rotor locks into step (i.e., synchronizes) with the rotating field.In a synchronous motor, the DC creates electromagnets on the rotor. Theseelectromagnets electrically lock onto the rotating field produced by the stator.

You can change the speed of a synchronous motor by changing the frequency of thecurrent to the stator and the number of poles in the stator. A dynamic brake is used to slow or stop a DC motor. AC motor name plates contain information on the temperature rise the motor is

designed for.

MOTOR STARTERS AND CONTROLLERS Across-the-line starters provide high starting torque.


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Shading coils reduce vibration and noise (i.e., such as that caused by contact chatter)in starters, controllers and contactors.

Chattering or humming in a circuit breaker, relay or controller may be caused by lowoperating coil voltage or dirt on the faces of the magnets.

A motor surface controller seldom develops a ground since its components are mountedon a non-conducting panel.

Accidentally-welded contacts may prevent a relay from dropping out (i.e., opening)when it loses coil voltage. A low voltage release allows any connected equipment to restart automatically as soon

as you restore the proper voltage.A low voltage protection device must be reset manually when you restore the proper voltage. It is used in places where it is dangerous to have the equipment automatically,re-activate (i.e., re-start), such as on a boiler fuel oil service pump.

Controllers often have electric strip heaters to prevent moisture from condensing inthem.A Run or Start button starts an electric motor. The motor will keep running after yourelease the button . A Jog button will only run a motor when it is held down.

USCG Regulations require that a wiring diagram be posted inside all motor controller doors.

GENERATORS AND ALTERNATORSThe amount of voltage induced (i.e., produced by induction in a rotating machine*) varies with(i.e., depends directly upon) the

o Turns in the armature (i.e., number of conductors in series in the armature'swinding).

o Speed of rotationo Strength of the magnetic field cutting the armature.

(*A machine could be a motor, a generator or an alternator.) Both AC and DC rotating machines produce alternating current in the armature.

In a DC machine the commutator changes the alternating current produced in thearmature to a pulsating DC current. This current is carried off, by the brushes, to anoutside circuit.

An exciter produces the electricity which powers the electromagnets to produce therequired magnetic field. If the exciter fails, the machine will not build up line voltage.

In a rotating field AC machine (which has no brushes), the AC produced in the exciter ischanged into DC by a solid state (i.e., a semi-conductor) rectifier mounted on the exciter armature.

A full wave rectifier requires four diodes. If only one diode is defective (i.e., burned out

or in an open condition), then a rectified half wave will be produced. The most common marine AC machine has a stationary armature (where the electricity

is produced) and a rotating electromagnetic field. The torque to turn an electricity-producing machine (i.e., a generator or an alternator) is

provided by a mechanical prime mover such as a diesel engine or a steam turbine. You can regulate the output voltage of a three phase (AC) generator by changing the

strength of the magnetic field if you change the DC voltage to the field.


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The frequency produced by an AC machine is controlled (i.e., determined) by the speedof rotation of the magnetic poles in relation to the armature windings. To increasefrequency, simply increase the speed of the prime mover.

When paralleling generators and alternators, the machine coming on-line must have aslightly higher voltage so that it picks up some of the load when it is placed on the

board by closing the circuit breaker.

If machines are not in phase (i.e., synchronized) when they are paralleled, severe crosscurrents will occur and may cause damage. The maximum a machine can be out of phase is 180.

Machines operating in parallel are both on line and sharing the load. However, theymust have the same frequency, number of phases and phase rotation to do this. Whenconnected they are electronically locked together

When paralleling, if the synchronizing lamps are dark and the synchroscope is at 12o'clock (i.e., the 0 position), it indicates the on-coming alternator is in phase with thebus.

To place an alternator on line, adjust the on-coming machine's speed until thesynchroscope revolves slowly in the fast direction. Then close the circuit breaker when

the synchroscope is at the 12 o'clock (i.e., 0 position). The on-coming alternator should have slightly higher frequency than the on-line or busfrequency to:

1. Assume its load immediately2. Not float on the line3. Not motorize and activate the reverse power relay.

After closing the circuit breaker to parallel the two machines, you should balance theloads ( kilowatts) between the two machines by adjusting the governor settings,

A darkened ground detector lamp indicates a grounded phase.If you lose a paralleled alternator operating near its rated load, (over 60%) immediatelystrip the board of (i.e., turn off) all non-vital circuits.

If a paralleled machine loses excitation, it will lose its load and tend to overspeed.

ELECTRICAL INSTRUMENTS A galvanometer measures the flow of very small amounts of electrical current or

voltage. A multi-meter (i.e., a volt-ohm-milliammeter) tests for voltage, current, resistance,

grounds, and continuity (i.e., a continuous circuit with no breaks or opens in the circuit). A multi-meter uses internal batteries to measure for resistance. When measuring for a

resistance, clip the two leads together and calibrate the instrument by adjusting theneedle to 0 ohms with the adjusting knob. If you cannot adjust the zero reading, then youshould replace the internal batteries.

After adjusting a multi-meter to measure resistance, you must select the proper resistancerange or you may damage the meter. If you have no idea what the resistance is start byusing the highest range; then work down to the range where a valid reading falls as nearlyas possible in mid-range.

You must connect an ammeter (i.e., a current measuring device) in series with a circuit tomeasure all the current passing through the current. Most of the current passes through ashunt, which is built into the ammeter to protect the delicate meter mechanism. The shunt


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is designed to carry a large, fixed proportion of the current while the meter is calibratedto read the entire current that passes through the meter mechanism including its built-inshunt.

A megohm is 1,000,000 ohms. A megohmmeter is commonly called a megger. Itmeasures very high resistances and is most commonly used to measure the resistance of wire insulation.

A series of slight kicks downscale by the needle on your megger indicates that current isleaking somewhere along the surface of a wires dirty insulation. When reading an instrument that measures resistance, be sure to note, which end of the

scale is zero and which is the highest reading. Also be careful that you understand theunits you are using. In meggers, one side of the scale is often in thousands of ohms whilethe other end is in megohms (i.e., millions of ohms).

A DC generator is prevented from motorizing by a reverse current relay. An ACgenerator, more properly called an alternator, uses a reverse power relay to protectagainst motorization. The torque for the timing elements of a reverse power relay is

provided by electromagnets. A synchroscope compares the phases of the oncoming machine to the bus (i.e., on-line)

phases. If the synchroscope's needle revolves in the slow direction (i.e.,counterclockwise) it indicates that the oncoming machine has a lower frequency (hencea lower RPM) than the bus frequency

A properly operating synchroscope indicates synchronization when the needle is at the12 o'clock position. Synchronizing lamps indicate synchronization when all lamps aredim or out. If one or more lamps remain lit when the scope is at 12 o'clock, thesynchroscope is either defective or broken.

Ground detection lamps for a grounded phase remain either dim or out when youoperate the test button or switch.

CIRCUIT PROTECTION, POWER DISTRIBUTION AND TRANSFORMERS Fuses and circuit breakers are safety devices that should open when overloaded. Fuses are rated in amps and volts. A fuse blows when its rating in amps is exceeded. A time delay (i.e., delayed action) fuse allows a momentary overload without melting

(i.e., opening) the fuse. Time delay fuses are common in motor circuits. Cartridge fuses have their metal fuse material in a fiber tube. Electrical cables that pass through a watertight boundary (i.e., either a bulkhead or a

deck) must utilize a device to maintain their water-tightness. The device is normally atube, which uses packing in a stuffing box type arrangement.

Accidentally grounding one line of an ungrounded power distribution system will not

cause a system outage, but it may damage some electrical equipment. You may close a shore power circuit breaker only after taking the generators off the bus

(i.e., off-line). Feeder circuits are inputs into distribution panels. Transformers operate on the principle of electromagnetic induction. Electric power is the same on both the primary and secondary side of a transformer.

However, the voltage (V) and the amperage (I) change inversely. A three phase, open-delta connected transformer provides two phase power with line

current equal to phase current


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When replacing a transformer, re-connect the polarity marks the same way as before toensure that the equipment runs as it did before (i.e., that the motors rotate properly, etc.)

Transformers are classed according to how they change the voltage. If the voltage on atransformer's secondary windings is higher than on its primary windings, it is called astep-up transformer. If the secondary voltage is lower than the primary voltage, it is astep-down transformer.

You can determine the ratio of change in voltage by comparing the number of turns onthe transformer's primary windings to the number of turns on the secondary. The changein current is inversely related to this ratio of turns. For example, if the secondary voltageis tripled (i.e., multiplied 3 times), the secondary amperage will be reduced to one-thirdthe amperage of the primary.


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ELECTRICAL SAFETY


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ELECTRICAL TROUBLESHOOTING, MAINTENANCE AND REPAIR

In order to do logical troubleshooting you must first understand and recognize how a piece of equipment normally operates.

Before working on any electrical component you should secure (i.e., open) and tag switchesleading to its power supply.

The preferred way to clean dust and foreign matter from electrical equipment is byvacuum suction.

You should remove dirt encrusted inside electrical equipment with a fiber scraper since this isleast likely to damage electrical components and insulation.

Electrical tape should overlap itself on each turn when wrapping an electrical splice To prevent moisture from damaging electrical apparatus during periods of lay up, place

heat lamps in the housings. Only use rosin flux when you solder electrical wiring. Grounded probes from a water level control switch can cause an auxiliary boiler feed

pump to fail.

Since a capacitor may still hold an electrical charge that can shock you, be sure to short out allcapacitors, even in a de-energized circuit, before you touch them.

If a motor won't start, first check its fuse or circuit breaker. Check fuses on an energized circuit with a voltmeter.

To check a fuse using a voltmeter, place one lead downstream of the fuse you are checking andthe other lead on the load side of a different fuse.

Repair accidental grounds as soon as possible since they damage insulation and maycause outages.

To locate grounds, open (i.e., turn off) switches on the distribution system until the grounddetection lamps indicate there are no grounds (i.e., when the dim light goes on).

An electric motor bearing containing foreign matter may fail in service if you don't clean

it before repacking. It also may fail from misalignment or over-lubrication. Periodically wipe a brushless generator clean with a dry rag. A properly operating DC motor's commutator will be chocolate brown in color.

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