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1. NEETS MOD 5 (Intro To Motors And Generators)
2. NSTM Chap 300, Electrical Plant General
3. Electricians Mate
ReferencesReferences
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Enabling Objectives:
1. RETRIEVE or RECOGNIZE information concerning AC andDC generators.
2. RECOGNIZE information pertaining to the construction andcomponents of AC and DC generators.
3. RECOGNIZE the information pertaining to the basicoperation of generators.
4. RECOGNIZE information pertaining to the procedures usedto PERFORM basic generator maintenance.
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Enabling Objectives:
5. CALCULATE values of frequency, number of poles, RPMs,
and line/phase values in wye/delta connections.
6. RETRIEVE OR RECOGNIZE information pertaining to theeffects of changing operating values on generator
performance.
7. CONSTRUCT and TROUBLESHOOT an AC generator.
8. APPLY the safety precautions associated with the use of
test equipment on generators in accordance with NAVY
SAFETY PRECAUTIONS FOR AFLOAT FORCES
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1. AC GENERATOR THEORY
a. A Generator is a machine that converts MECHANICALenergy into ELECTRICAL energy.
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AC Generator Theory (cond)
b. The same magneticinduction generator that
was used to develop an
AC voltage in unit 11.5
(AC waveforms) contains
the basic components ofall magnetic induction
generators.
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AC Generator Theory (cond)
c. Three factors necessary to create voltage through magneticinduction, given by the formula:
1. A Magnetic Field (I )
2. A Conductor (K)
3. Relative motion between the two (N)
E = K I N
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AC Generator Theory (cond)
d. Recall that as a single loop conductor rotates within a magnetic
field, an AC voltage is induced into the conductor.
1. AC voltage will be delivered to the load through an
assembly of slip rings and brushes
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AC Generator Theory (cond)
e. As long as the 3 necessary elements required to producevoltage are present, voltage will be produced regardless of
the arrangement of the elements.
1. A single loop conductor moving within a magnetic fieldwill produce voltage.
2. A magnet, or magnetic field, moving WITHIN a single
loop conductor will produce voltage as well. This method isthe most common arrangement to produce voltage.
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2. AC GENERATOR COMPONENTS
a. The 2 basic parts of induction generators are the fieldwinding and the armature winding.
1. Field Winding- produces the magnetic field, or main field
flux.
2. Armature Winding- where voltage is induced into the
windings or conductors. Supplies power to the load.
3. For relative motion to take place between the conductor
(armature) and field, all generators must have 2 mechanical
parts. A rotor and a stator.
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AC Generator Components (cond)
a. The Rotor is the part that rotates/revolves, and is centered
inside the generator.b. The Stator is the part that remains stationary.
c. In a DC Generator the armature winding is always wound
in the rotor. In AC generators (alternators) the armature may
be either the rotor or stator.
Rotor Stator
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AC Generator Components (cond)
4. Types of Rotor:
a. There are 2 types of rotors used in alternators. Theyare called Salient Pole and Cylindrical/Turbine Driven.
1. Salient Pole Rotor
laminated with protruding
pole pieces on which the
windings are housed.
Low speed rotor, used at
speeds of1200 RPMs or
below.
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Salient Pole Rotor
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AC Generator Components (cond)
2. Cylindrical/Turbine Driven Rotor windings firmlyembedded in slots. High speed rotor, used at speeds of1200
RPMs or greater.
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Cylindrical/Turbine Driven Rotor
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Generator Rotors
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AC Generator Components (cond)
8. Bearings - Both ends of the shaft.Provides ease of rotation and reducesfriction.
7. End Bells Houses the bearings and aligns the rotor shaft.
6. Core Material - Consists of steel laminations slotted to housethe windings. Designed to concentrate lines of flux.
5. Frame Houses and supports other stator components.
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9. Slip Rings and Brushes Serve as sliding contact to provide
a path for current.
a. The slip rings are metal rings, usually steel or brass,
connected to the ends of the rotor conductors. Insulated fromthe rotor and each other.
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Brush TensionDevice/Spring
Brushes
Slipring
Brush holder
b. The brushes serve as a sliding contact to transfer power.They are usually made of carbon and are sturdy enough tocarry current, but are soft enough so as not to damage the sliprings.
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AC Generator Components (cond)
c. The brushes are held against the slip rings by a brush
holder assembly that positions the brushes and appliespressure to ensure good connection.
9. Exciter device that supplies/provides DC potential to start or
maintain the main field flux. May be a separate DCgenerator or a rectifier circuit powered from the generator
itself.
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10. Prime Mover- machine that supplies the mechanical force
(motion) that turns the rotor of the generator.
a. Steam/Gas Turbine - because of the high operating
speed of turbines, the generators are not connected directlyto the turbine shaft, but are instead connected through
reduction gears. Generator speed range from 900 to 1800
RPMs. In rare instance: 3600 RPMs.
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2. Gas/Diesel Engine - engine is directly coupled to the
generator and operates at 600-1800 RPMs.
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3. Electric Motor directly coupled with a generator.
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3. AC GENERATORS TYPES
a. Rotating Armature, Stationary Field Generator (RASF)
1. Output voltage is taken from the armature windingsthrough slip rings and brushes.
2. Limiting factor as to the amount of power supplied: thecurrent carrying capacity (size) of the brushes.
3. Seldom used as Ships Service Generator because of its
low power capability. Used only for light loads.
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b. Rotating Field, Stationary Armature Generator (RFSA)
1. Output voltage is taken from the armature windings.
2. Limiting factor as to the amount of power provided isthe size of the armature windings.
3. Most commonly used type because of its high power
capability.
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RASFRevolving Armature, Stationary Field
Magnetic Field StatorRotor output voltage
RFSARevolving Field, Stationary Armature
Magnetic Field Rotor
Stator Windings output voltage
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4. AC SINGLE PHASE ROTATING-FIELD GENERATOR
a. Generating a single phase EMF.
1. Voltage is induced into the armature due to flux of thefield cutting conductors of armature.
2. Minimum or zero voltage is induced when the field polesare positioned at an equal distance between armaturepoles. (Conductors are in parallel with the magnetic field).
3. Maximum voltage is induced when the field poles arealigned with the armature poles (conductors areperpendicular to the field).
4. One complete turn produces one complete sine wave or
one cycle. (commonly referred to as Hertz).
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Generating a single phase EMF (cond)
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Generating a single phase EMF (cond)
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Single Phase AC Generator
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Single Phase AC Generator
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Single Phase AC Generator
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Single Phase AC Generator
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Single Phase AC Generator
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b. Operation of the AC three Phase Rotating-Field Generator
1. Three phase generators are more commonly used than
single phase generators because of some major advantages.
a. Three phase generators deliver more power than single
phase generators of the same physical size.
b. More efficient use of armature space is possible when
using three phase generators.
2. The armature of a three phase generator consists of 3
single phase windings: Phase A, Phase B, and Phase C.
a. The windings are equally spaced 120 electrical degrees
apart on the armature core.
b. The Field is still DC, requiring only 2 slip rings and
brushes to provide excitation.
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c. Generating a 3 Phase EMF
1. Induced voltages in each phase are equal in magnitude
but 120 electrical degrees apart.
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2. When one induced voltage is maximum, the other two
induced voltages are at 50% of maximum BUT of opposite
polarity (direction).
B
100%
A&C50%
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3. The algebraic sum of all 3 induced voltages is equal to
zero.
Example:
C = 100 Volts
A = -50 Volts
B = -50 Volts
Zero(0) Volts
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d. Three phase Armature Connections: The methods of
connecting the 3 single phase armatures to produce a 3
phase generator are basically SERIES (wye) and
PARALLEL (delta).
(1) Terms:
a. LINE VOLTAGE (E) voltage present at output
terminals of a generator.b. PHASE VOLTAGE (e) voltage induced in each
individual phase of the generator.
(2) WYE connection: connected to form a commonjunction, giving characteristics of a SERIES circuit. The
remaining three leads are connected directly to the bus to
supply power to the load.
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S
S
S
S Start
F - Finish
F
a. Two phases are connected in series between any twoa. Two phases are connected in series between any twooutput terminals; therefore, since current is common in seriesoutput terminals; therefore, since current is common in seriescircuits, the Line current is equal to the Phase current.circuits, the Line current is equal to the Phase current.
I = iI = i
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b. Line voltage (E) is equal to 1.73 x phase voltage (e)b. Line voltage (E) is equal to 1.73 x phase voltage (e)
E = 1.73eE = 1.73ec.c. Line voltage can also be found by VERTORIALLY addingLine voltage can also be found by VERTORIALLY adding
the Phase voltages together.the Phase voltages together.
d. Being a series circuit, if a phase winding opens, thatd. Being a series circuit, if a phase winding opens, thatphase will be lost and one line connection will bephase will be lost and one line connection will beavailable.available.
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A Phase
B Phase
C Phase
WYEConnection
N S
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DELTA Connection
S Start
F - Finish
A
B
C
AF
CF
BF
Cs
As
Bs
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a. Voltage is common in a parallel circuit, therefore line voltage
and phase voltages are equal.
b. Line current (I) is equal to 1.73 x phase current (i) due to the
phase current being 120 electrical degrees out of phase with
each other.
E = e
I=1.73ic. Line current can also be found by VECTORIALLY adding the
Phase currents together.
d. The type of connection used on a particular generator is
generally selected by the manufacturer to obtain the
required operating characteristics and to ensure ease and
simplicity of manufacture and repair in the most economical
way possible.
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H. GENERATOR LOSSES
1. Power Loss Anything that produces heat in the generator
and reduces its efficiency. More power is applied than is
being extracted.
2. Efficiency ratio of output to input power
Pout
Pin%Efficiency =%Efficiency = X 100X 100
3. Friction Losses wind & bearing friction in the rotor to slow
down requiring more power from prime mover.
4. Three Types of Core Losses:a. Hysteresis molecular friction caused by shifting
domains in the core material. To minimize, use low
reluctance material. Example: soft iron, silicon steel.
(Reluctance low opposition to magnetic lines of flux)
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b. Eddy Currents circulating current in the core material.
Reduced by using thin sheets of core material calledlaminations.
c. Copper Losses (I2
R) losses due to resistive properties
of a wire as current flows through it. Reduced by using
less wire as possible.
3 Types of Core Losses: (cond)
5 A t R ti th di t ti f th i fi ld fl
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5. Armature Reaction the distortion of the main field flux
caused by the interaction of the main field and armature field.
a. It is compensated by increasing the DC excitation to the
main field windings.b. The greater the load on the generator or armature
current, the greater the Armature Reaction.
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c. Flemings Left Hand Rule:
1. Thumb1. Thumb motionmotion of conductorof conductor2. Index finger2. Index finger direction of magneticdirection of magnetic fluxflux3. Middle finger3. Middle finger direction ofdirection of currentcurrent
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Exercise 1:
N S NSN S. X .X X
What is the direction
of the rotor?
What side is the
North and Southpole?
What is the direction
of current?
.
6 Motor Action the development of a force that opposes the
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6. Motor Action the development of a force that opposes the
speed of the prime mover. It is base on the principle that
when a current carrying conductor is placed in a magnetic
field, that conductor will tend to move at right angles to that
field.
6 Motor Action (cond)
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6. Motor Action (con d)
No load = No current flow
6 Motor Action (cond)
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6. Motor Action (con d)
a. As the Armature pole approaches the main field pole, an
interaction between the 2 fluxes causes thearmature flux to build up (increase) on the main
field. Both fluxes opposes each other and will
cause the rotor to stop if the rotor were moving too
slowly.
b. To compensate for this loss, increase the speed of the
prime mover.
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I. GENERATOR RATINGS
1. Generators are rated by its ability to dissipate heat generated
by its power losses (i.e. Heat)
2. AC generators are generally rated by the Apparent Power (AP)it can deliver to a load and is measured in Volt-Amp/Kilo-Volt-
Amp.
E x I x 1.73
1000Apparent Power = = KVA
Generator Ratings (cond)
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Generator Ratings (cond)
3. True Power (TP) power that is actually used or consumed by
the resistive load and is measured in KW (Kilowatt). It isDEPENDENT upon the power factor of the load.
E x I x 1.73 X PF
1000
True Power = = KW
4. Reactive Power (RP) power that is stored and returned back
to the source by the reactive components and is measured in
KVAR (Kilo-Volt Amp Reactive). It is the vectorial differencebetween KVA and KW.
Reactive Power = KVA2 - KW2
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J. Methods of controlling the terminal output of Generators
1. Conductor (K) increase/decrease the number of turns will
vary the output voltage, but it is neither practical noreconomical.
2. Speed of the Prime mover (N) increase/decrease speed will
vary output voltage, but will also affect the frequency (F) of
the output voltage.3. Strength of the Magnetic Field (I) increase/decrease strength
of magnetic field will vary output voltage. It is the
PREFERRED method. It is accomplished by using a variable
rheostat (VAR) in series with the field windings.
Methods of controlling the terminal output of Generators
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g p
(cond)
4. The field winding receives excitation from an external DC
source (battery, rectifier, DC generator). When the main fieldincreases, the armature windings are cut with greater force
inducing more voltage into the armature.
5. Induced voltage increase, armature current increase and
armature reaction and motor action increase.
Methods of controlling the terminal output of Generators
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g p
(cond)
Adding Load Removing Load
Armature CurrentArmature Reaction
Motor Action
Gen. Output Voltage
Prime Mover
Frequency
VAR
Magnetic Field (I)
Gen. Output Voltage (E)
Methods of controlling the terminal output of Generators
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g p
(cond)
6. Voltage Regulation ability of the generator to maintain a
constant terminal output voltage under varying load condition.
ENL - EFL
EFL% Voltage Regulation =% Voltage Regulation = x 100x 100
a. Voltage control of the AC generator is usually performed
automatically by electronic components and systems, butcan be performed manually. It is controlled by changing
the strength of the magnetic field.
K M th d f t lli th t t f f AC
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1. Factors affecting frequency:
a. Number of poles
b. Speed of rotation most preferred/feasible method
K. Methods of controlling the output frequency of an AC
generator
Frequency (F) =Frequency (F) =P = Number of Poles
N = Speed
2. Formula:
P N
120
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3. Frequency/cycles per second - shows how many North andSouth poles will complete a cycle in 1 second.
4. The standard output frequency of AC generators is 60 cycles
per second, also known as Hertz (Hz).
a Armature Reaction causes Motor Action which slows
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a. Armature Reaction causes Motor Action which slowsdown the primer mover. As the load increases on thegenerator, Armature Reaction and Motor Action increase,slowing the prime mover and lowering the frequency.
b. By increasing the fuel supply to Diesel or Gas Turbineengines, or by increasing the steam flow to Steam Turbines,these prime movers will increase speed of the generator rotor,and return the frequency to the rated value.
L DC G t
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L. DC Generators
DC generators are quickly being replaced with AC generators;
however, some special applications, such as cranes & mine
sweeping systems, require a high amount of DC current.
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DC Generators (cond)
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DC Generators (con d)
3. A DC generator uses a COMMUTATOR in place of SLIP
RINGS. The split slip ring is the commutator which
produces a DC output voltage.
4. COMMUTATION the process of obtaining a DC output
voltage from armature windings that has an AC voltage
induced into it.
DC Generators (cond)
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DC Generators (con d)
Recall the basic RASF generator, but instead of the 2 slip rings,use one slip ring cut in half with the brushes placed opposite
each other.
a. The Split slip ring is the commutator which produces aDC output voltage.
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BASIC DC GENERATOR
b Size of the brushes
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b. Size of the brushes
limiting factor as to the
amount of power
generated by a DCgenerator.
c. Increasing the number of
commutation
segment/armatureconductors provide a
smoother output voltage.
1. High power DC
generator have several
sets of brushes mounted
on the commutator to
increase the amount of
DC current available.
DC Generators (cond)
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DC Generators (con d)
5. The same power losses that affect AC generators, affect DC
generators:
a. Friction loss
b. Eddy current loss
c. Hysteresis loss
d. Copper loss
e. Armature Reaction
f. Motor Action
M Generator Maintenance
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M. Generator Maintenance
1. Majority of generator malfunctions are caused by improper /
lack of preventive maintenance on the brush riggingassembly and slip ring / commutator.
2. Brush rigging assemblya. The bottom of the
brush holder should
be between 1/8 1/16 inch from the
surface of the
commutator/slip rings.
1/8-1/16
Generator Maintenance (cond)
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Generator Maintenance (con d)
b. All brush leads should be securely connected to the
brushes and the brush holders. They also should move freely
in their holders but should not vibrate.
c. Replace all brushes that are:
1. Worn or chipped
2. Have damaged leads or pigtails3. Worn 50% of original length/size
4. Metal portion of the brush
is 1/8 inch from contact
with the commutator/sliprings.
Generator Maintenance (cond)
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( )
d. Before replacing brushes clean all carbon and grease off
brush rigging.
e. All brushes should be checked for proper seating beforeputting a generator back in operation.
f. SEATING process of shaping a brush until it fits the
contour (shape) of the commutator / slip ring.
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Generator Maintenance (cond)
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g. Methods of seating the brush:
1. Sandpaper preferred method. Use a fine grade of
sandpaper, about the same width as the slip rings.
Steps:
Generator is secured andtagged out of commission.
Place the sandpaper underthe brush (course sideup). Pull sandpaper underin the direction of rotation.Ensure sandpaper is kepton the surface of slip rings
so as not to round theedges of brushes.Continue process until ittakes the shape of sliprings. Finish by using afiner grade of sandpaper.
Generator Maintenance (cond)
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2. Seating stone made of soft abrasive material. Place
max pressure on brush. Generator MUST be running. After
seating, adjust spring tension.
Generator Maintenance (cond)
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( )
3. Adjust the brush tension by using a scale and a piece of
paper. (Use 2 - 2.5 psi pressure if a MRC or MTM is not
available.)
4. After the brushes
have been seated,
regardless of
which method isused, clean the
inside of the
generator by using
a vacuum cleaner(suction side) or
lint-free rags.
D t
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Dynanometer
Generator Maintenance (cond)
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3. Slip rings / Commutators
a. After 2 weeks ofoperation, an oxide film
which is uniform glaze
brown in color develops
on the surface of the slip
rings / commutator. Thismust NOT be removed.
It prevents excessive
wear of the brushes and
slip rings/commutator.
Generator Maintenance (cond)
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b. If generator cannot be secured, use canvass wiper to clean
the surface of slip ring / commutator.
c. If generator can be secured,
use vacuum cleaner and lint-
free rags. Remove any buildup of grease or carbon dust.
d. If the surface becomes pitted, grooved or scratched, it
causes sparking and excessive brush wear. Notify WCS so
the proper corrective action is taken.
Generator Maintenance (cond)
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4. Using a multi-meter, the resistance between the phases
should be equal or the same.
5. Megger (Meg-Ohm meter) used to measure ground
(insulation) resistance of generator. Readings should be
infinite or at least 1 megohm or stated on PMS card.
N APPLICATION
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N. APPLICATION
Generator Trainer
Set-up for WYE Connection
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Set-up forWYE Connection
Set-up for DELTA Connection
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Set-up forDELTA Connection
General Safety Precautions
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General Safety Precautions
1. Remove all metal or jewelry prior to entering lab.
2. During lab operation the trainee will NOT make or
break electrical connections on energized circuits.
3. Power is to be secured prior to any changes in circuit
configuration.
Review of Objectives:
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Review of Objectives:
This is what you have learned.
1. RETRIEVE or RECOGNIZE information concerning AC andDC generators.
2. RECOGNIZE information pertaining to the construction and
components of AC and DC generators.
3. RECOGNIZE the information pertaining to the basic operation
of generators.
4. RECOGNIZE information pertaining to the procedures used to
PERFORM basic generator maintenance.
Review of Objectives:
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5. CALCULATE values of frequency, number of poles, RPMs,and line/phase values in wye/delta connections.
6. RETRIEVE OR RECOGNIZE information pertaining to the
effects of changing operating values on generatorperformance.
7. CONSTRUCT and TROUBLESHOOT an AC generator.
8. APPLY the safety precautions associated with the use of testequipment on generators in accordance with NAVYSAFETY PRECAUTIONS FOR AFLOAT FORCES
Review of Objectives:
This is what you have learned.
SUMMARY AND REVIEW
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SUMMARY AND REVIEW