Dcp 702 Electrical Theory Web
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Transcript of Dcp 702 Electrical Theory Web
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Fundamental ElectricalFundamental ElectricalTheoryTheory
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ObjectivesObjectives Basic electrical theory including ohm's lawBasic electrical theory including ohm's law
and its derivationsand its derivations Generator theoryGenerator theory
Generator construction and controlGenerator construction and control
mechanisms including prime movers andmechanisms including prime movers andpower ratingspower ratings
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ObjectivesObjectives Fundamentals of electric motor theoryFundamentals of electric motor theory
including construction, power rating, usage,including construction, power rating, usage,
and control mechanisms.and control mechanisms.
Compare the uses for AC and DCCompare the uses for AC and DC
electric power and their transmissionelectric power and their transmission
methods.methods.
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References
References
INEINE, Chapter 16,, Chapter 16, pp. 307 pp. 307--318318
PNEPNE, Chapter 20,, Chapter 20, pp. 20pp. 20--11 -- 2020--2020
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DefinitionsDefinitions
Current (I):Current (I): flow of electric charges per unit time or flowflow of electric charges per unit time or flow
rate, measured in amperes or amps (A)rate, measured in amperes or amps (A)
Electromotive Force (emf) (E):Electromotive Force (emf) (E): a potential difference ora potential difference or
electric pressure which drives the flow of charges,electric pressure which drives the flow of charges,measured in volts (V)measured in volts (V)
Resistance (R):Resistance (R): an electrical circuits opposition to currentan electrical circuits opposition to current
flow, measured in ohms (flow, measured in ohms (;;))
Conductor:Conductor: a material which offers little resistance toa material which offers little resistance tocurrent flow, e.g. silver, copper, iron, etccurrent flow, e.g. silver, copper, iron, etc
Insulator:Insulator: a material which offers high resistance to currenta material which offers high resistance to current
flow, e.g. wood, paper, plastic, etc...flow, e.g. wood, paper, plastic, etc...
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ELECTRICAL THEORYELECTRICAL THEORY
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Direct Current (DC)Direct Current (DC)
Current flow is unidirectional and ofCurrent flow is unidirectional and of
constant magnitude (Batteries)constant magnitude (Batteries)
Ohms Law: current in a circuit is directlyOhms Law: current in a circuit is directlyproportional to the applied voltage andproportional to the applied voltage and
inversely proportional to the circuitinversely proportional to the circuit
resistanceresistance
E = I RE = I R
P = I E = IP = I E = I22 RR (W)
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Basic CircuitBasic Circuit
PropertiesProperties Electrons flow (Electrons flow (--) to (+)) to (+)
Kirchoffs Law of VoltagesKirchoffs Law of Voltages
Sum of all voltages in a complete ckt is zeroSum of all voltages in a complete ckt is zero Choose arbitrary current flowChoose arbitrary current flow
If current encounters (+) terminal 1st, then (+)If current encounters (+) terminal 1st, then (+)
voltagevoltage
Voltage drops preceded by (Voltage drops preceded by (--) sign if in the) sign if in the
same direction as electron flowsame direction as electron flow
Sum of current into and out of a node isSum of current into and out of a node is
always zero and constantalways zero and constant
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Basic CircuitBasic Circuit
PropertiesProperties SeriesSeries
Current is constant (flowrate)Current is constant (flowrate)
Voltage drops across each resistor (pressure)Voltage drops across each resistor (pressure)
R = RR = R11 + R+ R22 + R+ R33 + etc+ etc
ParallelParallel
Voltage drop constantVoltage drop constant
IIinin = I= I11 + I+ I22 + I+ I33 +etc+etc
1/R = 1/ R1/R = 1/ R11 + 1/R+ 1/R22 + 1/R+ 1/R33 + etc+ etc
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Example Problem #1Example Problem #1Determine VDetermine V11, V, V22, V, V33, V, V44, and I., and I.
V1
V2
V4
V3
I
90V
+-
20;5;10;10;
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Example Problem #2Example Problem #2Determine IDetermine I11, I, I22, I, I33, I, I44 and total circuitand total circuit
resistance.resistance.
I1
75V
+-
I4
I3
I2
20;
30;
20;
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Navy Generators
Navy Generators
GeneratorGenerator-- machine used to convertmachine used to convert
mechanical energy into electrical energy.mechanical energy into electrical energy.
Generator is comprised of the essentialGenerator is comprised of the essential
elements of Faradays Law to produceelements of Faradays Law to produce
electrical powerelectrical power
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Induction of VoltageInduction of Voltage
(Faraday)(Faraday) ThreeThree thingsthings mustmust bebe presentpresent inin orderorder toto
produceproduce electricalelectrical currentcurrent::
MagneticMagnetic fieldfield
ConductorConductor
RelativeRelative motionmotion
ConductorConductor cutscuts lineslines ofof magneticmagnetic flux,flux, aavoltagevoltage isis inducedinduced inin thethe conductorconductor
Direction/SpeedDirection/Speed importantimportant
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ElectromagneticElectromagnetic
InductionInduction
MAGNET
RELATIVE MOTION
COIL (CONDUCTOR)
VOLTMETER
INDUCED CURRENT
INDUCED CURRENT
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Direction ofInduced emfDirection ofInduced emf
B
MOTION OF
CONDUCTOR
INDUCED
CURRENT
N S
LEFT HAND
GENERATOR RULE(electron flow)
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Generator PartsGenerator Parts Prime moverPrime mover: mechanical work which turns the rotor, may: mechanical work which turns the rotor, may
be a steam turbine, gas turbine, diesel engine...be a steam turbine, gas turbine, diesel engine...
Armature windingsArmature windings: the conductor in which the output: the conductor in which the output
voltage is inducedvoltage is induced
Field windingsField windings: the conductors used to produce the: the conductors used to produce theelectromagnetic field (needs a DC power supply), theelectromagnetic field (needs a DC power supply), the
magnetmagnet
Stator Stator: stationary housing of the generator, contains the: stationary housing of the generator, contains the
magnet (field windings)magnet (field windings)
Rotor Rotor: rotates inside the stator, moved by a prime mover: rotates inside the stator, moved by a prime mover
(steam turbine, gas turbine, diesel), contains the(steam turbine, gas turbine, diesel), contains the
conductor (armature windings)conductor (armature windings)
PolesPoles: one set of armature windings is called a pole in the: one set of armature windings is called a pole in the
generatorgenerator
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DC GeneratorDC Generator
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ElectroElectro--MagnetMagnet
BBEE (N x I)(N x I)
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D
C MotorsD
C Motors Similar in construction to DC generatorsSimilar in construction to DC generators
A DC generator may be made to act as a DCA DC generator may be made to act as a DC
motor by applying a suitable voltage across itsmotor by applying a suitable voltage across itsoutput terminals (a DC motor acts as a DCoutput terminals (a DC motor acts as a DC
generator operating in reverse)generator operating in reverse)
Operates based on the principle that a currentOperates based on the principle that a current
carrying conductor placed in, and at right anglescarrying conductor placed in, and at right anglesto, a magnetic field tends to move in a directionto, a magnetic field tends to move in a direction
perpendicular to the magnetic lines of force (rightperpendicular to the magnetic lines of force (right--
hand rule)hand rule)
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AC PowerAC Power
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Alternating CurrentAlternating Current
(AC) Theory(AC) Theory
ACAC-- The magnitude and direction ofThe magnitude and direction of
current flow in an AC circuit willcurrent flow in an AC circuit willchange periodically (called a cycle).change periodically (called a cycle).
The frequency (Hz) of an AC circuit isThe frequency (Hz) of an AC circuit is
the number of cycles per second.the number of cycles per second.
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Alternating CurrentAlternating Current
(AC)(AC) Current is constantly changing in magnitudeCurrent is constantly changing in magnitude
and direction at regular intervalsand direction at regular intervals
Current is a function of time and usuallyCurrent is a function of time and usually
varies as a sine functionvaries as a sine function
I
t
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Two Types of AC GeneratorsTwo Types of AC Generators
Revolving armatureRevolving armature
rotor is an armature (conductor) which is rotating insiderotor is an armature (conductor) which is rotating inside
a stationary electromagnetic fielda stationary electromagnetic field
seldom used since output power must be transmittedseldom used since output power must be transmittedthrough slipthrough slip--rings and brushesrings and brushes
Revolving fieldRevolving field
dc current is supplied to the rotor which makes adc current is supplied to the rotor which makes a
rotating electromagnetic field (revolving magnet) insiderotating electromagnetic field (revolving magnet) insidethe stator, stator becomes the armature (conductor) ontothe stator, stator becomes the armature (conductor) onto
which electrical current is induced.which electrical current is induced.
more practical since the current required to supply amore practical since the current required to supply a
field is much smaller & there is reduced sparking andfield is much smaller & there is reduced sparking and
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Generator PartsGenerator Parts Prime moverPrime mover: mechanical work which turns the rotor, may: mechanical work which turns the rotor, may
be a steam turbine, gas turbine, diesel engine...be a steam turbine, gas turbine, diesel engine...
Armature windingsArmature windings: the conductor in which the output: the conductor in which the output
voltage is inducedvoltage is induced
Field windingsField windings: the conductors used to produce the: the conductors used to produce theelectromagnetic field (needs a DC power supply)electromagnetic field (needs a DC power supply)
Stator Stator: stationary housing of the generator: stationary housing of the generator
Rotor Rotor: rotates inside the stator, moved by a prime mover: rotates inside the stator, moved by a prime mover
(steam turbine, gas turbine, diesel)(steam turbine, gas turbine, diesel) Sliding contacts (slipSliding contacts (slip--rings and brushes)rings and brushes): used to conduct: used to conduct
the field or armature current to and from the rotorthe field or armature current to and from the rotor
CommutatorCommutator -- maintains output current in one directionmaintains output current in one direction
(DC generators)(DC generators)
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Revolving ArmatureRevolving Armature
(Low Power/Voltage)(Low Power/Voltage)
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Revolving FieldRevolving Field
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Most electrical equipment in the UnitedMost electrical equipment in the United
States operates on 60 Hz AC electricalStates operates on 60 Hz AC electricalpower (many foreign countries use 50 Hz)power (many foreign countries use 50 Hz)
How fast must a 2How fast must a 2--pole generator bepole generator be
rotating to produce a 60 Hz output?rotating to produce a 60 Hz output?
N x P = 120 x fN x P = 120 x f
NN -- rpm Prpm P -- poles f poles f -- frequency (Hz)frequency (Hz)
Relationship BetweenRelationship Between
Generator Speed andGenerator Speed andFrequencyFrequency
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Classifying ACClassifying AC
GeneratorsGenerators Number of phasesNumber of phases: most shipboard electrical: most shipboard electricalpower is 3 phase, this is more reliable plus loss ofpower is 3 phase, this is more reliable plus loss of
one phase will not cause a loss of equipmentone phase will not cause a loss of equipment
operabilityoperability FrequencyFrequency: most shipboard electrical power is 60: most shipboard electrical power is 60
Hz, some electronic equipment operate at 400 HzHz, some electronic equipment operate at 400 Hz
or higheror higher
VoltageVoltage: usually 450 V, smaller appliances use: usually 450 V, smaller appliances use
120 V120 V
PowerratingPowerrating: measured in kW, most shipboard: measured in kW, most shipboard
generators are 2,000generators are 2,000 -- 3,000 kW3,000 kW
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ThreeThree--Phase ElectricalPhase Electrical
PowerPower Uses three sets of armature windings to produceUses three sets of armature windings to produce
three separate outputsthree separate outputs
Armature windings are physically separated 120Armature windings are physically separated 120oo
from each other, and therefore, each phase is 120from each other, and therefore, each phase is 120oo
apart from anotherapart from another
More power may be generated by a generator of aMore power may be generated by a generator of a
given size and weightgiven size and weight
Provides continuous power to electrical equipmentProvides continuous power to electrical equipment
even if one phase is damagedeven if one phase is damaged
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3 Phase3 Phase
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Three PhaseThree Phase
-1.5000
-1.0000
-0.5000
0.0000
0.5000
1.0000
1.5000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21 22 23 24 25
Sine
Sine + 120
Sine + 240
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AC MotorsAC Motors
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Synchronous MotorSynchronous Motor
Constructed exactly like a generatorConstructed exactly like a generator
In a synchronous motor, the field is on theIn a synchronous motor, the field is on the
statorstator
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Synchronous MotorSynchronous Motor
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Induction MotorInduction Motor
Induction motorInduction motor -- simple, reliable and cheapsimple, reliable and cheap
DifferenceDifference -- the construction of the rotorthe construction of the rotor
Rotating field generated on statorRotating field generated on stator
No slipNo slip--rings or external source of power torings or external source of power to
the rotorthe rotor
Ideal for constant speed, varying torqueIdeal for constant speed, varying torque
applicationsapplications
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Induction MotorInduction Motor
N S
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Other ElectricalOther ElectricalDevicesDevices
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BatteriesBatteries
DryDry--cell batteries: cylindrical zinccell batteries: cylindrical zinc
container, carbon electrode, and ammoniumcontainer, carbon electrode, and ammoniumchloride/water electrolytechloride/water electrolyte
WetWet--cell batteries: leadcell batteries: lead--acid battery is theacid battery is the
most common, can be charged by forciblymost common, can be charged by forcibly
changing the direction of electrical currentchanging the direction of electrical current
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LeadLead--acidBatteryacidBattery
PbPbO2
+ -
H2SO4
Pb + PbO2 + 2H2SO4 2PbSO4 + 2H20pn
Load
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TransformersTransformers
A device that transfers energy by electromagneticA device that transfers energy by electromagnetic
inductioninduction
Primary windings (receive energy from AC source) andPrimary windings (receive energy from AC source) and
secondary windings (delivers energy to the load) (insulatedsecondary windings (delivers energy to the load) (insulated
from each other electrically) are mounted on opposite sidesfrom each other electrically) are mounted on opposite sides
of a ferromagnetic coreof a ferromagnetic core
Used to raise voltage (stepUsed to raise voltage (step--up transformer) or lowerup transformer) or lower
voltage (stepvoltage (step--down transformer)down transformer) Voltage is raised when the primary winding has fewerVoltage is raised when the primary winding has fewer
turns than the secondary winding, and voltage is loweredturns than the secondary winding, and voltage is lowered
when the primary winding has more turns than thewhen the primary winding has more turns than the
secondary windingsecondary winding
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A Simple TransformerA Simple Transformer
CORE
PRIMARY
WINDING
SECONDARY
WINDING
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RectifiersRectifiers
Uses diodes to convert alternating currentUses diodes to convert alternating current
into direct currentinto direct current
Diodes have a small resistance to currentDiodes have a small resistance to current
flow in one direction and a very largeflow in one direction and a very large
resistance to current flow in the oppositeresistance to current flow in the opposite
direction (act as a conductor for half of thedirection (act as a conductor for half of thecycle and as an insulator for the other half)cycle and as an insulator for the other half)
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RectifyingDeviceRectifyingDevice
OutputOutput
t t
I I
INPUT OUTPUT
DIODE
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Voltage KillsVoltage Kills
It is the volume of the current that flowsIt is the volume of the current that flows
that kills.that kills.
0.001 amps = 1 milliamp0.001 amps = 1 milliamp TinglesTingles
0.01 amps = 10 milliamps0.01 amps = 10 milliamps Severe shockSevere shock,,
uncontrolled muscle spasmsuncontrolled muscle spasms
0.1 amps = 100 milliamps0.1 amps = 100 milliamps DEATHDEATH!!
If the current passes through vital organsIf the current passes through vital organs
such as the heart.such as the heart.
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AC vs DCAC vs DC
AC power is easier to generate and requiresAC power is easier to generate and requires
less complex equipment (smaller machines)less complex equipment (smaller machines)
AC energy can be used in transformers toAC energy can be used in transformers to
step up or step down voltages where DCstep up or step down voltages where DC
energy cannotenergy cannot
DC can be stored for reserve use, i.e. theDC can be stored for reserve use, i.e. theships battery!!!ships battery!!!
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SummarySummary