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Transcript
Disclaimer
• This training presentation is provided as a reference for
preparing for the PJM Certification Exam.
• Note that the following information may not reflect
current PJM rules and operating procedures.
• For current training material, please visit:
http://pjm.com/training/training-material.aspx
PJM©2014
Generation Unit Basics
Interconnection Training Program
State & Member Training
PJM©2010
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Agenda
• Provide an overview of:
– Generators
• Describe the types:
–
–
–
–
–
–
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Fossil Steam generating units
Nuclear generating units
Hydroelectric generating units
Combustion turbines
Combined Cycle Power Plants (CCPP)
Wind Power
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Generating Unit Basics
Generating Theory
Part 1
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Generators
•
•
•
•
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Basic Operating Principles
A.C. Generator Components
Generator Rotational Speed
Generator Characteristics
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Basic Operating Principles
• Electromagnetic Induction is the principle used by a generator
to convert mechanical energy into electrical energy
• Induction is further defined as producing a current and an emf
in a circuit by changing a magnetic field around the circuit
• For this to happen, three things are needed:
- A magnetic field
- A current-carrying conductor
- A relative motion between the two
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Basic Operating Principles
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Basic Operating Principles
• Generators use mechanical energy from the prime mover to
turn the generator’s rotor (field) inside the generator’s stator
(armature)
• The turning of the rotor’s magnetic field sets up the main airgap flux inducing a voltage in the stator windings
• The stator’s output to the system is a three-phase alternating
current since the direction of the magnetic field changes in
relation to the windings as the rotor turns 360 degrees
• One rotation is equal to a complete cycle of power
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Basic Operating Principles
• Output voltage of the generator is controlled by changing the
strength of the magnetic field of the rotor.
• This is accomplished by changing the direct current or
excitation current that is supplied to the rotor
• The field excitation is supplied by the exciter
• When real power is constant, the real power output of a
generator is equal to the real power demand.
• Steady-state equilibrium is defined as the mechanical torque
input being equal to the electrical torque output of the
generator
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Basic Operating Principles
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Basic Operating Principles
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Basic Operating Principles
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Review
• A D.C. voltage is applied to the rotor
• Rotor is an electromagnet placed inside the stator
• The rotor rotates within the stator providing relative motion
between the magnetic field and the armature windings
• A.C. voltage is induced in the stator
• The stator voltage is the output voltage at the terminals of the
generator
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Basic Operating Principles
• How is the output voltage determined?
– Strength of the magnetic field
– Number and length of turns of conductors
– Magnitude of relative motion or rotational speed between the
rotor and stator
• Control of excitation voltage is the primary means of
controlling the generator output voltage
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A rotating field is more common
because it’s a low voltage, low
power circuit
It is considerably more difficult to
conduct the higher AC voltage and
power through a set of collector
rings and brushes
A.C. Generator Components
• Rotating Magnetic Field
• Series of Stationary
Conductors
• Source of D.C. Voltage
(Exciter)
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A.C. Generator Components
• Synchronous Machine: an AC machine that under steady-state
conditions operates at a constant speed and a constant
frequency
• Main features include:
- Rotor supplied with a DC field
- Three-phase stator or armature
- Prime mover or turbine
- Controllable DC source or exciter
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A.C. Generator Components: Rotor
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A.C. Generator Components: Rotor
• The basic function of the rotor is to produce a magnetic field
of the size and shape necessary to induce the desired output
voltage in the stator
• The rotating field is required to produce a given number of
lines of magnetic flux which is obtained by: Ampere-turns
• Ampere-turns is the product of the number of turns in the
rotor winding and the current in the winding
• The rotor body forms the path of the magnetic lines for part
of the circuit, and the stator core and air gap provide the
return path for the flux
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A.C. Generator Components: Rotor
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A.C. Generator Components: Rotor
• Generator rotors are made of solid steel forgings with slots cut
along the length for the copper windings
• Insulated winding bars are wedged into the slots and
connected at each end of the rotor and are arranged to act as
one continuous wire to develop the magnetic field
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A.C. Generator Components: Rotor
• Two types of rotors:
- Cylindrical and salient-pole
• Salient-pole rotors are used in low-speed machines with
separate field coils primarily for hydroelectric
• Cylindrical rotors are used in high-speed machines that uses a
slotted integral forging
• Rotor design constraints include:
- Temperature
- Mechanical force
- Electrical insulation
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A.C. Generator Components: Rotor
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A.C. Generator Components: Rotor
• Temperature:
- Ampere-turn requirements for the field increase
with an increase in rating, which entails a
combined increase in heating in the coil
•
Mechanical force:
- Ampere-turn requirements for the field increase
with an increase in rating causing a higher
centrifugal load
• Electrical insulation:
- In older units, slot insulation is a primary thermal barrier
and as current increases, becomes a greater obstacle
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A.C. Generator Components: Rotor
Advantage:
Air gap between the stator
and rotor can be adjusted
so that the magnetic flux
can be sinusoidal
including the waveform
Disadvantage:
Because of its weak
structure it is not suitable
for high-speed generation
It is also expensive
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A.C. Generator Components: Rotor
Advantage:
Cheaper than a salient-pole
Because of its symmetrical
shape, dynamic balance can
be obtained making it
perfect for high-speed
application
Disadvantage:
Air gap is uniform,
generated voltage is
polygonal giving way to the
susceptibility of harmonics
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Rotating Magnetic Field
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Rotating Magnetic Field
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A.C. Generator Components: Rotor
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A.C. Generator Components: Stator
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A.C. Generator Components: Stator
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A.C. Generator Components: Stator
• The stator is the stationary part of the generator that is
comprised of a series of stationary windings or armature coils
and the core
• Basic function of the stator core is to provide a return path for
the lines of magnetic flux, and support the
coils of the stator winding
• The stator core is made of soft iron to provide the magnetic
field path with a high permeability
• The iron is laminated to reduce eddy currents (opposing field)
and hysteresis (power losses)
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A.C. Generator Components: Stator
• In the stator, three phase windings are installed 120 degrees
apart
• Each phase winding is made up of several conductors
connected together at each end of the stator and grouped
into “poles”
• Electromagnetic forces acting on the generator components
are of significant importance steady-state running conditions,
as well as transient or fault conditions
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A.C. Generator Components: Stator
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A.C. Generator Components: Stator
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A.C. Generator Configuration
Two-Pole Generators:
• In a two-pole generator, there are three armature winding coils
installed in the stator
• North and south poles of the rotor are 1800 apart
Four-Pole Generators:
• In a four-pole generator, there are six armature winding coils
installed in the stator
• North and south poles of the rotor are 900 apart
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Generator Rotational Speed
• A generator which is connected to the grid has a constant
speed which is dictated by grid frequency
• Doubling the magnets in the rotor and doubling the windings
in the stator ensures that the magnetic field rotates at half
speed
• When doubling the poles in the stator, the magnets in the
rotor must also be doubled
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Generator Rotational Speed
• Most steam and gas turbines drive two-pole or four-pole
(nuclear) generators with a cylindrical rotor
• Four-pole is a repetition of a two-pole generator
• Since there is a total four pole reversal for every rotor
revolution, the four-pole machine speed is one-half the speed
of a two-pole machine for the same voltage output
• Hydroelectric turbines run more slowly, driving a salient-pole
generator with more than four poles
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Generator Rotational Speed
Frequency = (# Pole Pairs)(RPM)/60
Example: 2 poles
60 Hz = (1 Pole Pair)(3600 RPM)/60
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Generator Rotational Speed
Frequency = (# Pole Pairs)(RPM)/60
Example: 4 poles
60 Hz = (2 Pole Pair)(1800 RPM)/60
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Generator Rotational Speed
Synchronous Generator Speeds (RPM)
Pole Number
2
4
6
8
10
12
16
20
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50 Hz Speed
3000
1500
1000
750
600
500
375
300
40
60 Hz Speed
3600
1800
1200
900
720
600
450
360
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Generator Rotational Speed
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Generator Rotational Speed – 2 Pole
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Generator Rotational Speed – 4 Pole
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A.C. Generator Components: Stator
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A.C. Generator Components: Exciter
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A.C. Generator Components: Exciter
• The function of the excitation system is to provide direct
current for the generator rotor/field windings through slip
rings/brushless to produce the magnetic field
• Maintains generator voltage, controls var flow, and assists in
maintaining power system stability by modifying the field
current based on changes in terminal voltage
• During load changes or disturbances on the system, the
exciter must respond, sometimes rapidly, to maintain the
proper voltage at the generator terminals
• Utilizes “negative” feedback; as terminal voltage increases,
field current decreases
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A.C. Generator Components: Exciter
• Excitation System has three fundamental components:
- Exciter: provides field current for the synchronous generator
- Automatic Voltage Regulator: couples the terminal voltage to the
input of the main exciter
- Amplifier: increases the power of the regulating signal to that
required by the exciter
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A.C. Generator Components: Exciter
• Basic types of excitation systems:
- Rotating DC commutator: uses a DC generator mounted on the
shaft of the synchronous generator to supply field current
- Slow in response
- Requires high maintenance and brushes
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A.C. Generator Components: Exciter
• Basic types of excitation systems:
- AC Alternator: uses an AC alternator with AC to DC rectification to
excitation to the field winding
- Brushless
- Inverted alternator where the field winding is on the stator, and the
armature windings are on the rotor
- Rectification occurs by feeding the alternator output through a
thyristor-controlled bridge
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A.C. Generator Components: Exciter
• Basic types of excitation systems:
- Static system: composed entirely of solid-state circuitry
- Uses a potential and/or a supplied by the synchronous generator
terminals
- Rectified DC output is fed to the field windings via slip rings and
brushes
- Less expensive than AC Alternators, and the additional maintenance
of the slip rings and brushes is outweighed in that the system does
not have a rotating device.
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A.C. Generator Components: Exciter
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A.C. Generator Components: Exciter
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Governor Characteristics
• Governors control generator shaft speed.
• Adjust generation for small changes in load.
• Operate by adjusting the input to the prime
mover.
-Steam flow for fossil
-Water flow for hydro
-Fuel flow for combustion turbine
• Amount of governor control varies according to plant design.
• Equivalent to a car’s cruise control
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Governor Characteristics
• The Watt centrifugal governor was the mechanical means for
governor control
- Used weights that moved radially as rotational speed
increased that pneumatically operated a servo-motor
- Electrohydraulic governing has replaced the
mechanical governor because of:
- High response speed
- Low deadband
- Accuracy in speed and load control
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Governor Characteristics
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Governor
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Governor Characteristics
Mechanical style of
governor
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Governor Characteristics
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• Load
– Rate of frequency decline from
points A to C is slowed by “load
rejection.”
• Generators
– Generator governor action halts the
decline in frequency and causes the
“knee” of the excursion, and brings
the frequency back to point B from
point C.
It is important to note that frequency will not recover from point B to 60 Hz until the
deficient control area replaces the amount of lost generation.
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Governor Droop
• Adding a droop characteristic to a governor forces generators
to respond to frequency disturbances in proportion to their
size.
• Droop settings enable many generators to operate in parallel
while all are on governor control and not compete with one
another for load changes.
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Generators - Droop
• Droop (continued)
– Now imagine if there was a feature added to the cruise control
such that any change in speed and subsequent signal to the
cruise control, would be weighted based on the car’s engine
capacity (droop)
• Example:
– If more load were added to the trailer, both car A and car B
would assume more load, however, (because of this new droop
feature) the signal from the cruise control (governor) would be
based on the engine sizes of the two cars.
– Load changes could be more evenly shared between cars
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Generators - Droop
• Droop
– Using the “cruise control” analogy, consider two cars coupled by
a chain to a heavy trailer.
– If the cruise controls (governors) on each car are not exactly
identical there would be instability in how they each carried the
load.
– One car would assume more load from the trailer, and one car
would slow down.
– There would be constant racing and runback in the engines of
both cars.
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Governor Droop
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Generators/Cruise Control
• Think about the previous analogy of the two cars on cruise
control….
• When a generator synchronizes to the system
– It couples itself to hundreds of other machines rotating at the
same electrical speed.
– Each of these generators have this “droop” feature added to
their governor
– They will all respond in proportion to their size whenever there
is a disturbance, or load-resource mismatch.
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Generators - Deadband
• Deadband
– An additional feature displayed by generators.
– Deadband is the amount of frequency change a governor must
“see” before it starts to respond.
– Deadband was really a natural feature of the earliest governors
caused by friction and gear lash (looseness or slop in the gear
mechanism)
– Deadband serves a useful purpose by preventing governors
from continuously “hunting” as frequency varies ever so slightly
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Generator Characteristics
• Generator limitation factors
– Power capability of the prime mover
– Heating of generator components (I2R losses)
– Necessity to maintain a strong enough magnetic field to transfer
power from the rotor to the generator output
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Generator Characteristics
• Heating of generator components
– Heat generated within the armature windings is directly related
to the magnitude of the armature current
– Heat generated in the rotor is directly related to the magnitude
of the field current
– Heat dissipated by the generator is limited by the cooling system
design
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Generator Characteristics
• Magnetic field strength
– Controlled by excitation voltage
– If excitation voltage is lowered:
• Voltage induced in A.C. windings is lowered
• More VARS absorbed by generator from system
• Undervoltage can cause overcurrent conditions in the stator
and lead to armature or stator heating
– Capability curves provide Max/Min limits
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Generator Characteristics
• Relay protection:
- Stator short circuits
- Grounded field (unbalanced air-gap fluxes; vibration)
- Loss of excitation (loss of synchronization)
- Unbalanced phase currents (overheating of the rotor)
- Motoring or reverse power (overheating of turbine)
- Loss of synchronism (system electrical center)
- Abnormal frequency (turbine/generator damage)
- Overexcitation (hot spots and saturation of generator/
transformer)
- External faults (uncleared faults)
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Power Factor
MVA =
MW2 + MVAR2
MVA = 100.2
Power Factor is the ratio
of Real Power to
Apparent Power:
PF = P/S
AC Power is made up of
three components:
- Reactive Power (Q)
- Real Power (P)
- Apparent Power (S)
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Generator Capability Curve
• The steady-state capability of a generator as it is influenced by
the power factor is divided into three major components on
the curve
• Region A-B: Zero power factor lagging to rated power factor
- Generator is over-excited
- Field current is at rated value
- Capability limitation is field overheating
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Generator Capability Curve
• Region B-C: Rated power factor lagging through unity to 0.95
power factor leading
- Capability limitation is dependent on the stator
current
- Maximum nameplate stator amperes should not
be exceeded
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Nameplate Data
•
Main Generator “Nameplate” Characteristic Data
•
Rated Output
•
496,000 kVA
•
Rated Voltage
•
22,000 v
•
Rated Stator Current
•
13,017 amps
•
Rated Field Current
•
3,017 amps
•
Power Factor
•
0.9
•
Poles
•
2
•
Phases
•
3
•
Electrical Connection
•
Wye
•
Rated Speed
•
3,600 RPM
•
Rated Frequency
•
60 Hz
•
Rated Hydrogen Pressure
•
48 psig
•
Rated Hydrogen Purity
•
97%
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Generator Capability Curve
• Region C-D: leading power factor operation
- Excessive heating in the stator end-iron due to
flux leakage from the core
- Capability limitation is end-iron heating
- This is also an underexcitation region and
capability is further reduced by the voltage
squared during reduced terminal voltage
operation
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MVAR Flow & Voltage
VAR / Voltage Relation
• MVARs flow “downhill” based on voltage
• Flow from high per unit voltage to low per unit voltage
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MVAR Flow & Voltage
VAR / Voltage Relation
• MVAR flow between buses is determined by magnitude
difference between bus voltages
• Voltage magnitude difference is driving for MVAR flow
• The greater the voltage drop or rise between 2 locations – the
greater the MVAR flow
V1
V2
X
Bus 1
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Bus 2
V1 (V1 - V2)
VARs =
X
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MW Flow & Power Angle
Power-Angle Relation
• MW flow between buses is determined by phase angle
difference between voltages at the buses
• Phase angle difference between voltages is called Power
Angle which is represented by the symbol
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MW Flow & Power Angle
Power Angle
P
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Power Angle
•
Rotor Angle
on transmission system is similar to rotor angle
– aka: Load angle or Torque angle
• No load
– Field pole of rotor lined up with stator field (in
phase)
– =0
• Load added
– Rotor advances with respect to stator
– MW flow out of machine
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MW Flow & Power Angle
Rotor Angle
MW
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Generator Synchronizing
• In order to synchronize properly, three different voltage
variables must be monitored:
- Voltage magnitudes
- Frequency of the voltages
- Phase angle difference between the voltages
• If voltage magnitudes are not matched, Mvar will rise
suddenly when the breaker is closed
• If frequencies are not matched, a sudden change in MW flow
will occur when the breaker is closed
• Most important, if phase angle difference is not minimized,
MW flow will increase when the breaker is closed
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Generator Synchronizing
• System is modeled as an infinite bus
• With the unit output breakers open, the generator is operated
at slightly above system frequency
• Excitation is adjusted for equal voltage magnitudes on either
side of the output breakers
• The phase angle difference between the unit and system is
monitored through the use of a synchroscope
• When the phase angle is small and heading towards zero, the
output breakers are closed pulling the generator in step with
the system
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Generator Synchronizing
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Generator Synchronizing
Voltage
Frequency
Phase Angle
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Generator Synchronizing
• Reference (Running) voltage: Bus voltage
• Incoming voltage: Generator voltage
• Clockwise motion: Generator frequency is greater than bus
frequency
• Once synchronized, excitation system can be put into
automatic voltage regulation, and speed governor can be put
in automatic generation control
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Four-Part Process
Basic Energy Conversion
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Generating Unit’s Principles of Operation
Energy Conversion Process
Chemical Energy (Fuel)
to
Thermal Energy (Steam)
to
Mechanical Energy (Work)
to
Electrical Energy (Generator)
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Principles of Operation
• Four Phases - Steam/Water Cycle
– Generation (Boiler)
• Changes chemical energy of fuel to thermal energy of steam
and water in boiler
– Expansion (Turbine)
• Changes potential energy to kinetic energy
• Nozzle changes pressure to velocity
• Thermal energy to mechanical energy.
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Principles of Operation
• Four Phases - Steam/Water Cycle
– Condensation (Condensate System)
• Changes steam to water removing latent heat
• Recover condensate
• Largest efficiency loss: 1035 BTU/Lb
– Feedwater (Feedwater System)
• Increases energy, both thermal (temperature) and potential
(pressure) of water returning to the boiler, including the
economizer
• 1% gain in efficiency for every 100 F rise
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Generating Unit Basics
Fossil Generation
Part 2
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Principles of Operation
• Coal / Oil / Gas Steam Plants
– Provide about 76.9% of the PJM area generation
– Power output is as low as 15-20 MW or as high as 1,300 MW
– Rate of change of power is several MW/min. on older units, and
10-20 MW/min. for newer units
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Principles of Operation
• Fossil steam plants can use coal, oil, gas
• Each fuel requires a unique set of components to control the
reaction that produces heat, and handle the by-products of
the reaction
• These factors place limitations on the operating capabilities of
the plant
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Fossil Generation
• Boiler is defined simply as a closed vessel in which water is
heated, steam generated, and superheated under pressure by
the application of additional heat
• Basic functions of a boiler:
- Pressure containment
- Heat transfer
- Steam separation
• Two types of boilers:
- Subcritical (drum type)
- Supercritical
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Fossil Generation
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Fossil Generation
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Principles of Operation
• Drum Type Boiler Components
–
–
–
–
–
–
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Economizer
Steam Drum
Downcomers
Mud Drum
Superheater (3% efficiency gain/1000 F inc)
Reheater (4%-5% gain/1000 F inc)
- Lower pressure/same heat
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Principles of Operation
• Economizer: Improve boiler efficiency by extracting heat from the
flue gases and transferring it to the feedwater
• Steam Drum: Separate the water from the steam generated in the
furnace walls
• Downcomers: Return path for the feedwater back to the boiler;
located away from main heat source
• Mud Drum: Fed from downcomers; collection point for sentiment
and impurities
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Principles of Operation
• Superheater: Increases cycle efficiency by adding heat to raise
the steam temperature above its saturation point; located in
the flue gas path
- Radiant: Direct radiation from the furnace
- Convection: Absorb heat from hot gases
• Reheater: Adds energy to the steam that has been partially
used by the turbine
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Principles of Operation
• Furnace Air System
– Air Heaters
• Used to transfer heat from stack flue gases to
the combustion and primary air
– Forced Draft Fans
• Used to maintain windbox and secondary air pressure to
accelerate combustion
– Induced Draft Fans
• Used to maintain a negative furnace pressure
• Always larger than FD due to combustion gas
expansion
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Air Heater
Air Inlet
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Steam Turbine
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Steam Turbine
• Steam Turbine: Form of heat engine with the function of
converting thermal energy into a rotating mechanical energy
• Turbine is made up of four fundamental components
- Rotor: carries the blades or buckets
- Stationary part
- Nozzles: flow passages for the steam
- Foundation: support for the stationary and
rotor parts
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Steam Turbine
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Steam Turbine
• Two steps are required to convert the thermal energy of the
steam into useful work:
- Thermal energy of the steam is converted into
kinetic energy by expanding the steam in
stationary nozzles or in moving blades
- Thermal energy is converted into work when
the steam passes through the moving blades
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Steam Turbine
• Turbine Stages
– High Pressure Turbine (HP)
• Supplied by Main Steam (Suphtr. outlet)
• Exhausts to boiler Reheater
– Intermediate Pressure Turbine (IP)
• Supplied by Reheat Steam (Reheater Outlet)
• Exhausts to Low Pressure Turbine
– Low Pressure Turbine (LP)
• Supplied by IP Turbine exhaust
• Exhausts to Condenser
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Steam Turbine
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Steam Turbine
• Each turbine stage consists of stationary blades (nozzle) and
the rotating blades (buckets)
• Nozzles convert the potential energy of the steam into kinetic
energy directing the flow into the rotating blades
• The buckets convert the kinetic energy into forces, caused by
the pressure drop, into rotation
• Limitations on blades:
- Erosion due to moisture (Low pressure)
- Solid particle erosion
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Steam Turbine - Blading
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Steam Turbine
• Auxiliary Turbine Equipment
- Bearings:
- Thrust axially locate the turbine shaft
- Journal support the weight of the shaft
- Shaft seals: series of ridges and grooves around
the housing to reduce steam leakage
- Turning gear: slowly rotates the turbine, after
shutdown to prevent bowing of the shaft and to
even out temperature distribution
- Vibration detection: measures the movement of
the shafts in their bearings
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Steam Turbine - Bearings
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Steam Turbine – Turning Gear
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Principles of Operation
• Operating Limitations:
- Eccentricity: shaft out of concentric round
- Differential expansion: rotor and turbine casing
heat up and expand at different rates
- Bearing vibration limits
- Critical speed: harmonics due to natural
resonance
- Back pressure limitation: fatigue cracks and
harmonics on low pressure blades
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Principles of Operation
• Operating Limitations:
- Bearing material: temperature limitations
- Bearing oil: temperature limitations
- Babbitt material: temperature limit
- Rotor prewarming
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Principles of Operation
• Turbine Trips:
- Low bearing oil pressure
- Thrust bearing wear detection
- Low vacuum
- Bearing vibration/bearing metal temperature
- Low steam temperature
- Differential expansion
- Reverse power
- High heater level
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Principles Of Operations
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Condensate System
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Condenser
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Principles of Operation
• Condensate System
– Condenser: converts the exhaust steam into water
after it leaves the last stage of the turbine
– Hotwell: receptacle where water is collected from
the condenser
– Hotwell Make-up / Draw-off valves: distilled or
demineralized water to compensate for losses or
excesses to or from the condensate storage tank
- Controlled by the deareator level
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Principles of Operation
• Condensate System
- Demineralizers: condensate purification
- Condensate Pumps
- Low Pressure Feedwater Heaters: condensate is pumped to be
preheated before entering the deareator
- Deareator: open heater where condensate passes and is mixed
with steam to increase temperature and remove noncondensible gases (mainly oxygen)
- Provides water to the suction side of the
Boiler Feed Pump
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Condensate System – Feedwater Heater
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Condensate System – Feedwater Heater
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Condensate System - Deaerator
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Principles of Operation
• Feedwater System
– Boiler Feed Pump: supplies water to the boiler and has to
overcome boiler pressure, friction in the heaters, piping, and
economizer
– High Pressure Feedwater Heaters (Boiler feed pump pressure):
preheats the feedwater before entering the boiler
– Economizer: serves as a feedwater heater effecting economy by
extracting heat from the flue gases
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Feedwater System – Boiler Feed Pump
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Feedwater System – Boiler Feed Pump
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Principles of Operation
• Miscellaneous Systems
– Gland sealing: enable the turbine to be sealed where the shaft
exits the casing (air out, steam in)
– Hydrogen Cooling System: cooling water coils in the generator
to cool the hydrogen gas
– Hydrogen Seal Oil System: seals the generator where the shaft
exits the casing keeping the hydrogen in
– Cooling Water (Lube oil, hydrogen, seal oil, service water, and
stator oil)
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Principles of Operation
• Miscellaneous Systems:
- Circulating Water: primarily provides the cooling
water for the condenser
- Turbine Lube Oil: free of foreign material and
moisture supplied at proper temperature, pressure,
and quantity
- Fire Protection
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Principles of Operation
• Miscellaneous Systems
– Bottom Ash (slag): course, granular, incombustible by-products
collected from the bottom of the boiler
– Fly ash: fine-grained, powdery particulate that is found in flue
gas
– Fuel Systems: Oil, Gas, Coal
– Service Air: for deslagging and any pnuematic needs within the
plant
– Control Air: used on pneumatic applications where moisture
cannot be tolerated such as instrumentation and control
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Principles of Operation
• Miscellaneous Systems
- Demineralization: purification of condensate for
boiler
- Waste Water Treatment:
- Station Battery (Lube oil, cooling water, turning gear)
- Scrubber Facilities: traps pollutants and sulfur that is produced
from burning coal and natural gas from escaping into the air
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Principles of Operation
• Super Critical Boiler (Once Thru): the boiler feed pump
supplies the pressure for the cycle
• Once proper pressure is obtained, heat is applied, and water
is directly converted to steam without going through the
boiling process
–
–
–
–
–
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Does not have a boiler drum
No recirculation process
Consists of many circuits of superheaters
Operates in excess of 3206.2 psia / 705.4 F
Requires a Start-up system (By-pass)
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Principles of Operation
• Supercritical boilers cannot use the drum design because
there is no distinct water/steam phase transition above the
critical pressure
• Boiler is operated at supercritical pressures (~3200) as
compared to the subcritical (~2400)
• Increased efficiency: 1.5% to 2% gain using a supercritical as
opposed to a subcritical for same output
• More efficient in certain MW ranges
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Principles of Operation
• The form of steam turbine employed with supercritical
conditions is the same as that for subcritical cycles, although
temperatures and pressures are higher
- Stronger materials for rotor forgings, casings,
steam lines, and valves
- Ferritic materials are being replaced by nickelbased superalloys
- Special alloys on the last stages of blading
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Principles of Operation
• Start-Up System:
- Before steam can be supplied to the turbine, the boiler must
be brought up from a virtual cold condition to supercritical
temperature and pressure
- Provides minimum flow through the pressurized parts of the
boiler matching the steam temperature and pressure to the
initial metal temperature of the turbine for shorter roll times
- Provides a steam source for deaeration and also a means of
heat recovery during start-up
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Principles of Operation
Limitations:
• Temperature limit on the furnace water wall caused by increases in
pressure and final steam temperatures
• Corrosion of superheater and reheater tubes caused by the
increase in steam temperatures
• Airheater thermal efficiency is compromised because an increase in
feedwater temperature to the boiler leads to a rise in airheater gas
inlet temperature
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Principles of Operation
• Super Critical Boilers
– Advantages
• Greater efficiency (45%)
• Faster response to changing load
• Reduced fuel costs due to thermal efficiency
• Low emissions (CO2, NOx, SOx)
– Disadvantages
• Long start-up time
• Expensive to build (greater press. / temp.)
• Requires a start-up system
• Loss of circulation causes serious boiler damage
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Megawatt Limitations
• Limitations that can restrict scheduled or operating MW
capacity of a generating unit:
–
–
–
–
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Environmental
Fuel
Maintenance
Operating
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Megawatt Limitations
• Environmental
– Maximum allowable water temperature, pH (solubility) and
turbidity (suspended solids) of cooling water return to river or
lake
– Maximum allowable values of substance discharged to the
atmosphere
• Nitric Oxide - NOX
• Sulfur Dioxide - SO2
• Carbon Monoxide – CO
• Carbon Dioxide – CO2
• Particulates - Opacity
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Megawatt Limitations
• pH (solubility): depends on the relative concentration of
hydrogen ions
- A substance is acidic if the positive cations
outnumber the negative anions
- The acidity of cycle water has a great impact on
the corrosion of system components
• Turbidity: suspended solids such as sediment, mud, and dirt
that are in the water
• Dissolved solids: minerals picked up by the water that will
form hard adherent deposits on the internal surfaces of the
boiler (Conductivity meter)
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Megawatt Limitations
• Dissolved Oxygen: entrapped in water, attacking metal parts
including feedwater, condensate, and boiler tubes
• Iron: concentration must be at a certain level in order to raise
temperatures in a supercritical unit
• Silica: found in water as a dissolved solid
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Megawatt Limitations
• Fuel
– Excessive moisture/bad weather
- Coal
- Difficulty unloading
- Buildup in chutes
- Sliding on conveyor belts
- Frozen coal
- Poor quality
- Excessive slagging tendencies
- High ash resistivity
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Megawatt Limitations
• Oil:
- Moisture: deteriorates the performance of oil
increasing the risk of corrosion
- Coking
- Particulate and impurities
• Gas:
- Moisture: when mixed with impurities form a
corrosive mixture
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Fuel Types
• Gas, oil, and coal
• Oil:
- Needs to be prewarmed to pump (150-180o) and to burn
(250-3300)
- Guns need cleaned and maintained regularly
• Coal: crushed or pulverized
- Type of burner
- Pulverized
- Stoker
- Cyclone
• Major problem is flame detection in boiler
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Megawatt Limitations
• Maintenance
– Auxiliary equipment out of service, scheduled or unscheduled
which prevents full output
• Heat Cycles
• Heaters, condensate or boiler feed pumps
• Pulverizers (Mills) or oil pumps, gas
• Fans: ID, FD, or primary air
• Pumps: circulating water
• Fuel
• Ash handling
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Megawatt Limitations
• Operating
–
–
–
–
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Boiler Water Chemistry
Poor equipment thermal performance
High vibration on rotating equipment
High condenser backpressure
• Vacuum leaks
• Dirty condenser waterboxes
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Boiler Water Chemistry
• Scale: hard tube deposits/overheat failure
• Oxygen: causes corrosion in boiler tubes
• Silica (O2): limits operating pressure and can leave deposits on
turbine blades causing imbalances and loss of turbine
efficiency
• Condenser leaks are the main source of impure water
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Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
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Cooling tower
Cooling water pump
Three-phase transmission line
Step-up transformer
Electrical generator
Low pressure steam turbine
Boiler feedwater pump
Surface condenser
Intermediate pressure stage
Steam control valve
High pressure stage
Deaerator
Feedwater heater
Coal conveyor
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
169
Coal hopper
Coal pulverizer
Boiler steam drum
Bottom ash hopper
Superheater
Forced draft fan
Reheater
Combustion air intake
Economizer
Air preheater
Precipitator
Induced draft fan
Flue gas stack
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Generating Unit Basics
Nuclear Generation
Part 3
Nuclear Generation
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Nuclear Generation
•
•
•
•
PJM©2010
Has the greatest potential as an energy source
Provide about 19.1% of the PJM area generation
Power output can be as high as 1,200 MW
The nature of nuclear fuel requires the rate of raising power
be limited to very slow rates at certain times during the 12-24
month fuel cycle of the reactor.
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Nuclear Generation
• Government Control
- Nuclear Regulatory Commission
- Power plants must conform to NRC regulations
- Once a license is received it must be maintained by certain rules
“Tech Specs”
- “Tech Specs” are the laws that describe operational
requirements of plant equipment, and
operating/shutdown limitations on plant equipment
- Violations could result in fines and/or forced plant shutdown
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Nuclear Generation
• In US, Light-Water Reactors are pre-dominant
• Light-water reactors use ordinary water to slow down the fast
neutrons produced in the reaction
• Light-water reactors use enriched uranium, U235
• Two types of light-water reactors:
- Pressurized Water Reactor (PWR)
- Boiling Water Reactor (BWR)
- Both types supply steam at or near saturation at approximately
1000 psi
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PWR/BWR Reactors
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Nuclear Generation
• The Boiling Water Reactor operates essentially the same way
as a fossil-fueled generating plant where a steam/water
mixture is produced within the vessel
• The Pressurized Water Reactor differs from the Boiling Water
Reactor in that the steam is produced in the steam generator
rather than in the reactor vessel
• In the United States, PWR’s outnumber the BWR’s two-thirds
to one-third
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Nuclear Generation
• The fission process or the “splitting apart” of an atom is what
produces heat in a nuclear reactor
• The process occurs when a free neutron enters the nucleus of
a fissionable atom causing the nucleus to become unstable,
vibrate, and split into two at a high rate of speed releasing 2
to three more neutrons
• The kinetic energy of the split is transformed into heat
• The process continues into a chain reaction
• The key is to control the rate of the emitted neutrons and the
nuclear chain reaction
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Nuclear Generation
• Nuclear fission provides ~ 10 million times more energy than
conventional chemical processes
• Conventional light water reactors utilize fuel with an initial
235U concentration enriched to at least 3.5%
• Heat from the reaction has a conversion efficiency of 33%
• Fuel is loaded at 3.5% 235U and replaced once the
concentration has fallen to 1.2%
• A 1 GW light water plant consumes 30 tons of fuel per year in
comparison to 9,000 tons of coal per day for a fossil plant of
the same magnitude
• Pound of highly enriched uranium has the same amount of
energy as 1 million gallons of gasoline
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Nuclear Generation
• Basic Components of a Nuclear Reactor:
- Fuel: pellets of enriched uranium encased in fuel rods that
are bundled in assemblies
- Control Rods: absorb neutrons controlling the rate of the
chain reaction
- Coolant: usually water to carry heat away from the reactor
- Moderator: material used to slow neutrons down
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Control Rod
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Fuel Assembly
• Both PWR’s and BWR’s fuel assemblies consist of the same
major components:
- Fuel rods: approximately 12 feet long containing the ceramic
fuel pellets and are arranged in a square matrix from 17x17
(PWR) to 8x8 (BWR)
- Spacer grids: separate the individual rods providing rigidity of
the assemblies and allowing the coolant to flow freely up
through the assemblies and around the fuel rods
- Upper and lower end fittings: structural elements of the
assemblies; directs flow of coolant through the assemblies
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Fuel Assembly
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Fuel Assembly
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Pressurized Water Reactor
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Pressurized Water Reactor
• Two major systems are used in the conversion:
- Primary system: transfers heat from the fuel to the steam
generator
- Secondary system: steam formed in the steam generator is
transferred to the main turbine generator
• In order for the primary and secondary systems to perform
their functions, there are approximately one hundred support
systems
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PWR Components
• Reactor Vessel: supports and contains the fuel core and
supplies the flow paths for coolant
• Steam Generator: heat exchanger between primary and
secondary systems
• Reactor Coolant Pump: pumps water back to the reactor (2, 3,
or 4 cooling loops)
A 1000-1300 Mw unit would require (4) 6,000-10,000 hp
pumps
• Pressurizer: controls pressure in the cooling system to prevent
boiling in the reactor (2250 psi at 590-600 degrees F). Acts as
a surge tank also.
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PWR Components
• Reactor vessel houses the reactor core and all associated
support and alignment devices including:
Core Barrel: houses the fuel and supports the fuel assemblies
- Reactor Core
- Upper Internals: sits on top of the fuel and contains the guide
columns to guide the control rods
-
• Steam generator allows the secondary feedwater to absorb
sufficient heat from the reactor coolant to boil and form
steam
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Pressurized Water Reactor
Control
Rods
Reactor
Vessel
Inlet
Outlet
Water flows downward on the
outside of the core barrel to the
bottom of the reactor. The flow
then turns upward in between the
fuel rods from the bottom to the
top of the reactor. The water
leaves the reactor on it way to
the steam generator
Core
Barrel
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PWR Components
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PWR Components
• The Reactor Coolant Pump provides forced primary coolant
flow to remove the heat being generated by the fission
process
• Major components of the RCP
- Motor
- Hydraulic section (impeller and discharge volute)
- Seal package: prevents water from leaking up the containment
shaft into the containment atmosphere
• Horsepower rating is 6,000 to 10,000; approximately
100,000 gallons of coolant per minute per pump
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PWR Components
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PWR Components
• Pressurizer is the component in the reactor coolant system
which provides a means of controlling the system pressure
due to changes in coolant temperature
• Pressurizer operates with a mixture of steam and water in
equilibrium
- Coolant temperature increases, coolant density decreases and the
coolant takes up more space causing steam pressure to increase
- Coolant temperature decreases, coolant density increases and the
coolant will occupy less space causing steam pressure to decrease
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Secondary Systems
• Main Steam System
- Condensate/Feedwater System
•
•
•
•
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Chemical and Volume Control System
Auxiliary Feedwater System/Steam Dump System
Residual Heat Removal System
Emergency Core Cooling Systems
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Secondary Systems
Main Steam System
Condensate/Feedwater System
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Secondary Systems
• Chemical and Volume Control System is a major support
system for the reactor coolant system
- Purifies reactor coolant using filters and demineralizers
- Adds and removes boron
- Maintains the pressurizer level at setpoint
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Secondary Systems
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Chemical and Volume
Control System
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Secondary Systems
• Auxiliary Feedwater System and Steam Dump System work
together to remove heat from fission decay in the reactor
during shutdown to prevent fuel damage
- Auxiliary feedwater system pumps water from the condensate
storage tank to the steam generators producing steam that can be
dumped to the main condenser through the steam dump valves or
directly to the atmosphere if the condenser or steam valves are
not available
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Secondary Systems
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Auxiliary Feedwater System/Steam
Dump System
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Secondary Systems
• Residual Heat Removal System is used when the decay heat is
not sufficient to generate enough steam in the generators to
continue the cool down by removing heat from the core and
transferring it to the environment
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Secondary Systems
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Residual Heat Removal
system
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Secondary Systems
• Emergency Core Cooling Systems
- Provide core cooling to minimize fuel damage for a coolant loss
- Ensure the reactor remains shutdown following the cool down
associated with a main line steam rupture
• Both incidents of coolant loss and a ruptured steam line are contained
through the injection of large quantities of borated water
- Four separate systems (powered from diesel generators)
- High pressure injection system
- Intermediate pressure injection system
- Cold leg accumulators
- Low pressure injection system
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Secondary Systems
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Emergency Core211Cooling Systems
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Pressurized Water Reactor
• Utilizes two to four separate cooling systems
• Reactor water and steam are separate.
• Reactor power is controlled by boron injection in the reactor
coolant
• Moderator is the reactor coolant
• Control rods are inserted from the top
• Water is pressurized to about 2250 psi and heated to
~ 600 degrees F without boiling
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Pressurized Water Reactor
• Advantages:
- Fuel leak in core is isolated
- Very stable due to producing less power as temperatures
increase
- Can be operated with a core containing less material reducing the
chance of the reactor running out of control
- Enriched uranium allows ordinary or light water to be used as a
moderator
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Pressurized Water Reactor
• Disadvantages:
- Coolant water is highly pressurized to remain liquid at high
temperatures requiring high strength piping and a heavy
pressure vessel
- PWR’s cannot be refueled while operating
- High temperature coolant with boric acid is corrosive to carbon
steel limiting the lifetime of the reactor, and adds to the overall
cost for filtering and radiation exposure
- Fuel production costs are increased by use of enriched uranium
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Pressurized Water Reactor
• Disadvantages:
- It is not possible to build a fast breeder reactor with PWR
design
- Reactor produces energy slower at higher temperatures; a
sudden decrease in temperature could increase power
production
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Boiling Water Reactor
PJM©2010
•Primary Containment: includes the suppression chamber, the reactor, and the
recirculation pumps
•Reactor Building: (secondary containment) surrounds primary containment
and serves the same purpose as the PWR’s auxiliary building
•Turbine Building
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Boiling Water Reactor
• Inside a BWR, a steam water mixture is produced when
reactor coolant moves upward through the core
• The major difference in this operation from other nuclear
systems is the steam formation in the core
• Steam is separated from the mixture as it leaves the core and
enters two stages of moisture separation directly exiting to
the main turbine
• Reactor power is controlled by varying the coolant flow
through the reactor core by using the recirculation pumps and
jet pumps
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BWR Components
• Reactor Vessel Assembly includes
- Core Support Structures
- Core Shroud: provides a partition to separate the upward flow of
coolant through the core from the downward recirculation flow
- Moisture Removal Equipment
- Steam separators
- Steam dryers
- Jet Pump Assemblies: accelerating jet pulls in or entrains the
reactor coolant delivering it at an elevated pressure
• Recirculation Pump: same as the reactor coolant pump for a
Pressurized Water Reactor
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Boiling Water Reactor
Steam
Dryers
Water flows downward on the
outside of the core barrel to
the bottom of the reactor. The
flow then turns upward in
between the fuel rods from the
bottom to the top of the
reactor.
Steam is separated at the top
from the water.
Steam
Separators
Shroud
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Systems
•
•
•
•
•
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Reactor Water Cleanup System
Decay Heat Removal
Reactor Core Isolation cooling
Standby Liquid Control System
Emergency Core Cooling Systems
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Systems
• The purpose of the Reactor Water Cleanup System is to
maintain high reactor water quality by removing fission
products, corrosion products, and other soluble and insoluble
impurities
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Systems
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Reactor Water Cleanup
System
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Systems
• Decay Heat Removal works similar to the systems used during
shutdowns for a PWR
• During a reactor shutdown, the core will still continue to
generate decay heat
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Systems
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Decay Heat Removal
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Systems
• Reactor Core Isolation Cooling provides makeup water to the
core for cooling when the main steam lines are isolated and
the normal supply of water to the reactor vessel is lost
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Systems
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Reactor Core Isolation
Cooling
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Systems
• Standby Liquid Control System injects boron (neutron poison)
into the reactor vessel to shutdown the chain reaction,
independent of the control rods, and maintain the reactor
shutdown as the plant is cooled
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Systems
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Standby Liquid Control
System
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Systems
• Emergency Core Cooling Systems provide core cooling under
the loss of coolant accident conditions to limit fuel cladding
damage
- Systems consist of two high pressure and two low pressure
systems
- High pressure system is independent requiring no auxiliary
AC power, plant air systems, or external cooling water
systems. It also works in conjunction with the automatic
depressurization system which opens safety relief valves
- Low pressure system includes the core spray system and the low
pressure residual heat removal system
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Systems
High Pressure Emergency Core
Cooling System
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Low Pressure Emergency Core
Cooling System
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Boiling Water Reactor
• Utilizes one cooling loop
• Reactor water and steam are one and same
• Reactor power is controlled by positioning the control rods
when starting up the reactor and operating up to 70% of rated
power
• Increasing/decreasing water flow through the core is the
normal method for controlling power when operating
between 70% and 100% rated power
• Control rods are inserted from the bottom
• Water is kept at 1000 psi and does not boil until
~ 545 degrees F
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Boiling Water Reactor
• Advantages:
- Reactor vessel and associated components operate at a
lower pressure as compared to a PWR
- Operates at a lower nuclear fuel temperature
- Fewer components; no steam generators or pressurizer vessel
- Fewer pipes, welds, and no steam generator tubes lowering the
risk of a loss of coolant
- Vessel is subject to little irradiation (brittleness)
- Can operate at lower core power density using natural
circulation and can be designed so that recirculation pumps
are eliminated
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Boiling Water Reactor
• Disadvantages:
- Complex design; two-phase fluid flow requiring more in-core
nuclear instrumentation and complex operational calculations
- Larger pressure vessel than PWR, with corresponding cost
- Turbine contamination with fission products requiring shielding
and access control during normal operations
- Control rods are inserted from below for current BWR designs
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Nuclear Systems
• Plant Systems
– There are approximately 80 systems in a nuclear power plant
– Three systems that control and/or limit nuclear plant output
are:
• Control rod drive system
• Reactor coolant system
• Off-gas system
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Nuclear Systems
• Control Rod Drive System: controls reactor power output.
• Reactor Coolant System: removes energy from the core and
transfers it directly (BWR) or indirectly (PWR) to the steam
turbine
• Off-Gas System: Processes air and any non-condensable gases
in the main condenser before being released to the
environment. Condenser vacuum is decreased if gases are not
removed.
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Nuclear Plant Auxiliaries
• Similarities (Nuclear to Fossil)
- Feedwater system contain the same components, but with less
pumping power required due to the lower feedwater pressure and
low-pressure steam
- Reactor feed pumps are equivalent to boiler feed pumps
• Contrasts
- For fossil, feed pumps are driven by steam; motor drives are
applied to reactor feed pumps
- Nuclear does not require large fan drives or large fuel preparation
drives
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Nuclear Plant Auxiliary Power system
• The basic auxiliary power system of a nuclear facility is very
similar to a fossil plant, except for the engineered safety
features
• ESF systems are intended to ensure safe shutdown of the
reactor under abnormal conditions
• The aux power system must be able to supply power to
redundant drives and loads which provide the safety features
predominantly the core cooling systems
• The power system must provide separate paths to redundant
ESF systems and must have (2) off-site
power sources available after a shutdown is initiated
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Nuclear Limitations
• Equipment Vibration
– Individual component vibration is monitored by a central
computer
– Systems are quickly identified and isolated to prevent damage
from excessive vibration
– A problem area in nuclear plants are the protective relay panels
• Excessive vibration may cause a system or plant shutdown
due to vibration of relays
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Nuclear Limitations
• Power Ascension: 0-100% power increase depends on:
- Amount of testing required during start-up
- After a forced outage, power ascension takes
~ 24 hours
- After a refueling outage, power ascension takes
~ 48 hours
• Fuel Depletion: occurs by the absorption of neutrons and the
fission process
• Reactor core refueling: 1/4 to 1/3 of the fuel bundles are
removed at intervals of 12-18 months
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Nuclear Generation
• Abnormal Operations
– Reactor SCRAM (Safety Control Rod Axe Man)
(Safety Cut Rope Axe Man)
• When all control rods move into the core to shut down the
reactor.
– A SCRAM occurs when a protective device sends a signal
to the control rod drive system.
– Reactor power decreases because the control rod
material absorbs neutrons, thus interrupting the nuclear
chain reaction.
– The cause of a SCRAM must be determined before a unit
is restarted.
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Generating Unit Basics
Hydroelectric Generation
Part 4
Hydroelectric Generation
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Hydroelectric Generation
• Hydro once played a significant role in the electric utility
industry accounting for 30%-40% of the total energy produced
• Currently, hydroelectricity produces about 10% of the
electricity generated in America
• Hydro is regarded as a free source of energy since it uses no
fuel
• Because the water cycle is an endless, constantly recharging
system, hydro power is considered a renewable energy
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Hydroelectric Generation
• Provide about 3.7% of PJM’s energy
• Typical PJM unit output is between 20 and 510 MW
• Two types of hydroelectric generating plants:
- Run-of-River
- Pumped Storage
• Pumped storage facilities operate the same as runof-river with the exception of the motor pump function
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Hydroelectric Generation
• Basic elements of hydroelectricity
- Water at one elevation, and a dam to hold it
there
- Lower elevation location where the water
output can be directed
- Hydraulic turbine connected to a generator
- Penstock to conduct water from the upper level
through the turbine at a lower level
- Controls and auxiliaries (Governor oil pump,
head-gate motors, crane, air compressor)
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Hydroelectric Generation
• Hydro plants capture the kinetic energy of falling water
• Power capacity of a hydro plant is the function of two
variables:
- Flow rate which is expressed in cubic feet per second
(Kinetic energy)
- Hydraulic head: difference vertically between head water and
tail water elevation
(Potential energy)
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Hydroelectric Generation
• A simple formula for approximating electric power production
at a hydroelectric plant is: P = ρhrgk, where
- P is Power in watts,
- ρ is the density of water (~1000 kg/m3),
- h is height in meters,
- r is flow rate in cubic meters per second,
- g is acceleration due to gravity of 9.8 m/s2,
- K is a coefficient of efficiency ranging
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Hydroelectric Generation
• Basic Parts of a Hydroelectric Plant:
- Dam: a reservoir is constructed by building a dam. The dam
will increase the height of the water level and the working
head (potential energy) of the plant
- Trash racks: removes debris from entering the intake gate and
penstock
- Intake gate/Valve house: controls the intake for the flow of
water into the powerhouse. Usually includes the trash racks
and gates and the entrance to a canal, penstock, or directly
to the turbine
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Hydroelectric Generation
• Basic Parts of a Hydroelectric Plant:
- Penstock: pipe between the surge tank and plant that carries
the water from the reservoir to the turbines in the station
- A disilting chamber precedes the penstock to remove larger
size sediment from entering
- Surge tank: to avoid sudden, large pressure increases due to
rapid start of the turbine or valve closing
- Acts as a pressure relief opening to absorb surplus kinetic
energy
- Acts as a balancing reservoir to supply or store additional
water during starting or closing of the gates and valves
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Hydroelectric Generation
• Basic Parts of a Hydroelectric Plant:
- Draft tube: diffuser that regains residual velocity energy of
the water leaving the turbine runner
- Runner: the rotating element of the turbine that converts
hydraulic energy into mechanical energy
- Turbine/Generator: vertical/horizontal machine that is low
speed, and inherent high reactance
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Hydroelectric Generation
- Amortisseur Windings:
- Reduce overvoltage induced in the field caused by
surges/unbalances in the stator
- Reduce overvoltage in the stator caused by unbalanced
faults on the machine
- Reduce generator output oscillations caused by loads
connected through resistance circuits
- Aids in stability reducing rotor oscillations
- Wicket Gates: adjustable vanes that control the amount
of water that can enter the turbine. These are controlled
by the governor by changing the angle of the gates
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Hydroelectric Generation
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Hydroelectric Generation
• Types of Hydraulic Turbines
- Impulse:
- Used in high head plants: needs less water volume
- Low-velocity head is converted into a high-velocity jet and
directed into spoon-shaped buckets
- Energy supplied is kinetic completely
- Runner operate in air; water is at atmospheric pressure
- Efficiency is less than Reaction-type at full load, but better at
partial load
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Hydroelectric Generation
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Hydroelectric Generation
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Hydroelectric Generation
• Advantages of an Impulse turbine:
- Greater tolerance for sand/other particles in the water
- Better access to working parts
- No pressure seals around the shaft
- Easier to fabricate and maintain
- Better part-flow efficiency
• Disadvantage: unsuitable for low-head sites because of low
specific speeds
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Hydroelectric Generation
• Types of Hydraulic Turbines
- Reaction:
- Two types: Francis and propeller (Kaplan)
- Runner is fully immersed in water and
enclosed in a pressure casing
- Pressure differences impose lift forces
causing the runner to rotate
- Low to medium head is converted into
high speed
- Energy supplied is both kinetic and
“pressure head”
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Hydroelectric Generation
Francis
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Hydroelectric Generation
Kaplan Turbine
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Hydroelectric Generation
• Advantages of a Reaction turbine:
- Rotate faster at the same given head and flow
conditions
- Eliminates a speed-increasing drive system
- Simpler maintenance thereby reducing costs
- Higher efficiency
- High running speeds at low heads from a compact
machine
• Disadvantages:
- Require more sophisticated fabrication
- Poor part-flow efficiency characteristics
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Run-of-River
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Run-Of-River
• Low impact method that utilizes the flow of water within the
natural range of the river, requiring little or no impoundment.
• Produce little change in the stream channel or stream flow
• Plants can be designed using large flow rates with low head or
small flow rates with high head
• Hydraulic head is the elevation difference that the water falls
in passing through the plant
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Run-Of-River
• Operating Considerations
• Rainfall in Watershed Area
• River Flow and Forebay/Tailrace Elevation
• Water Quality Impacts
- Dissolved Oxygen
- Higher temperatures
- Decreased food production
- Siltation
- Increased phosphorus and nitrogen
- Decomposition products
• Ice during frigid temperatures
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Run-Of-River
• Advantages:
- Reduced exposure to price volatility
- Minimal construction
- Ecologically sound
- Reliable
- Low operating costs
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Prevents debris from entering
Minimizes pressure surges
or the effects of water
hammer
Penstock
Head:
Vertical change in elevation between the head
water level and the tailwater level.
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Acts like a diffuser.
Maintains a water
column between turbine
and downstream
Provides high efficiency
operation by recuperating
kinetic energy
Pump Storage
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Pump Storage
• Uses off-peak electricity to pump water from a lower
reservoir to an upper reservoir
• During periods of high electrical demand, water is released to
generate electricity
• Most modern plants utilize a reversible Francis-type turbine
which operates in one direction of rotation as a pump, and
the opposite direction as a turbine connected to a
synchronous generator/motor driving the pump in one
direction, and generating power in the other direction
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Pump Storage
• Operating Considerations
• Water Quality Impacts
- Thermal Stratification
- Toxic Pollutants
- Eutrophication: loss of nutrients
• Reservoir Sedimentation
• Flood Control and Hazard
• Groundwater level
• Ice Formation
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Pump Storage
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Hydroelectric Generation
• Both Run-Of-River and Pump Storage offer:
- Rapid start-up, shutdown, and loading
- Long life
- Low operating and maintenance costs
- Low outage rates
- Units, when generating, can respond and follow to system load
changes limited only by the speed with which the gate valves can
be operated
- Can be designed to operate as a synchronous condenser for
voltage control when not generating
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Hydroelectric Generation
• Auxiliary Equipment:
- Inlet valve pressure oil system
- Lubricating oil system: turbine/generator bearings
- Hydraulic oil system: turbine governor control
- Cooling water system: used to supply cooling water the generator
air coolers, lube oil coolers, turbine/generator bearings, and
transformers
- Compressed air system: supply compressed air to various turbine
and generator auxiliaries for rotor lifting, generator braking,
charging governor oil systems, control systems, and service air
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Hydroelectric Generation
• Auxiliary Equipment:
- De-watering system: used to dewater the powerhouse in case of
seepage and maintenance
- Used for de-watering the tunnels and penstocks
- Pump water out of the draft tube for maintence
- Service units: small hydraulic turbine/generator used for
station service and as a independent source of power in case
of system separation
- Turbine gland water for shaft packing
- Fire protection
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Hydroelectric Generation
• Safety Considerations:
- Extra flywheel effect is built into the generator dictated by the
hydraulic conditions to prevent excessive rate of rise in speed if
load is suddenly lost
- Both turbine and generator need to be built to stand “runaway”
speed due to the possibility that full load may be lost at a time
when the gate-closing mechanism is inoperative
- “Runaway” speed is defined as turbine speed at full flow, with no
shaft load
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Generating Unit Basics
Combustion Turbine
Part 5
Combustion Turbines
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Combustion Turbines
• Combustion turbines play an important role in utility system
generation planning
• Characteristics that make it attractive include:
- Peaking applications
- Where a exhaust heat recovery system can be used
- Base-load operation
• Combined-cycle units provide most of the advantages of the
simple-cycle peaking plant with the benefit of a good heat
rate; it also requires less cooling water than conventional
fossil and nuclear of the same size
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Simple-Cycle Combustion Turbines
• Operation is similar to a jet engine
• Air is compressed, mixed with fuel in a combustor, to heat the
compressed air
• The turbine extracts the power from the hot air flow
• It is an internal combustion engine employing a continuous
combustion process
• 2/3 of the produced shaft power runs the compressor; 1/3
produces the electric power
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Simple-Cycle Combustion Turbine
• Brayton Cycle: describes the relationship between the space
occupied by the air (volume) and the pressure that its under
(basic thermodynamic cycle)
- Air is compressed increasing the pressure as the volume of
space occupied by the air is reduced
- Air is heated at a constant pressure continuously
- Hot compressed air is allowed to expand reducing the pressure
and temperature while increasing the volume ( power to the
turbine shaft
- Volume and temperature of the air is decreased as heat is
absorbed into the atmosphere
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Simple-Cycle Combustion Turbine
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Combustion Turbine
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Combustion Turbine
• Basic Parts of a Combustion Turbine:
- Starting package: AC motor and a hydraulic torque converter
- Compressor: draws in and compresses the air
- Combustor: adds fuel to heat the compressed air
- Turbine: extracts the power from the hot air flow
- Generator: produces the electric power output
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Combustion Turbines
•
•
•
•
•
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CTs are quick response units.
Can be started, loaded and shutdown remotely.
Typical capacity is 15-180 MW.
Not designed to run on a continuous basis.
CTs make up about 3% of the PJM area generation.
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Combustion Turbines
• CT Advantages
– Automatic- Unmanned (some cases)
– Low initial capital investment
– Turn-key operation (modular construction)
– Self contained unit
– Short delivery time
– Fast starting and fast load pickup
– Governor response units
– Black start capability
– No cooling water required
– Low emission
– Minimum operation and maintenance costs
– Minimum transmission requirements
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Combustion Turbines
• CT Disadvantages
– Fuel operating cost (heat rate)
– Low Efficiency: 25%- 40%
– Thermal stress
• High rate of temperature change
• Short life due to cycling
• High maintenance cost
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Combustion Turbines
• Efficiency can be increased by:
- Regeneration: install a heat exchanger (recuperator) gives 5-6%
efficiency increase and improved part-load applications
- Intercooling: is a heat exchanger that cools the gas during the
compression process
- Reheating: used when turbine has two stages increasing efficiency
by 1-3% by reheating the flow between the two stages
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Simple-Cycle Combustion Turbine
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Combustion Turbine
• Output Limitations:
- Ambient air temperature and density
- High barometer/low temp: air most dense
- Low barometer/high temp: air least dense
- Highest efficiency: cold, dense air
- Cold weather
- Lube oil temperature
- Moisture in fuel
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Combustion Turbines
• Environmental
– Stack Emission (NOx/CO2/CO)
• Temperature 980 - 1000 F.
• High temperature in combustion section accelerates nitric
oxide emission
• Particulate emission – opacity (oil)
– Sound levels
– Combined cycle units require:
• Circulating water source
• Waste water treatment for plant effluent
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Combustion Turbines
• Because turbine combustors operate at a very high
temperature, high levels of NOX are produced
• Common methods for control:
- Water injection to reduce combustion temperature
- Selective Catalytic Reduction is an after-treatment to remove NOX
- Xonon is a combustor that operates below the NOX formation
temperature
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Simple Combined Cycle Unit
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Simple Combined Cycle Unit
• One combustion turbine unit along with an associated
generator
AND
• One Heat Recovery Steam Generator (HRSG) along with it’s
own steam turbine
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Simple Combined Cycle
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Combined Cycle Unit
• Heat Recovery: utilizing the large volume of exhaust that is
high in oxygen content
• Duct Burner: direct-fired gas burner located in the turbine
exhaust stream that boosts the total available thermal energy
• HRSG: heat recovery steam generator utilizes the heat in the
turbine exhaust
• Diverter: used to divert turbine exhaust to the
atmosphere
• The higher the electrical efficiency of the turbine, the lower
the available thermal energy in the exhaust
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Combined Cycle Unit
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Combined Cycle
• The HRSG’s convert heat in the CT exhaust gas to steam for
use in the steam turbine
• CT’s utilizing the HRSG can be operated from 50 to 100% peak
load
• Start-up system (static frequency converter) is used to start
the rotation for light-off of the CT
• Generator acts as a synchronous motor
• The generator’s stator and rotor is supplied by current via a
start-up transformer
• The rotor is supplied by the static excitation system
• The stator is supplied from the SFC
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Combined Cycle Unit
• HRSG incorporates features of conventional fossil-fired boilers
such as:
- Economizer, Evaporator, and Superheater
- Auxiliary systems for the steam turbine portion are similar to
conventional steam plants
- Cooling water must be supplied for the steam turbine’s
condenser
- Operates with a simple feedwater cycle
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Simple Combined Cycle Unit
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Multiple Combined Cycle
• More than one combustion turbine unit along with it’s own
generator
AND
• More than one Heat Recovery Steam Generator (HRSG) along
with one or more steam turbines and generators
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Multiple Combined Cycle
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Combined Cycle and Co-Generation
• Combined Cycle units can be used in conjunction with CoGeneration
• Co-Generation (Distributed Generation)
– A means of generating hot water, and / or high and low pressure
steam and electricity at the same time, from the same energy
source, yielding a highly efficient power plant
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Combined Cycle with Cogeneration
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Why Combined Cycle Plants?
•
•
•
•
•
•
•
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Competition / Future Projections
Plant Conversions / Stagnant
Efficient
Environment
Cheaper / Built Faster
Short Payback Time
Distributed Power Applications
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Competition /Future Projections
• Competition between Generation Companies, IPPs, Merchant
Plants and others to participate in the selling of energy
produced in an efficient manner.
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Thermal Efficiency
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Generation Type
Efficiency
Combustion Turbine
Steam (no reheat)
Steam (reheat)
Combined Cycle
28% - 34%
31% - 35%
36% - 41%
42% - 53%
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Environment
• Gas fired Combined Cycle Unit
– Lower Emissions
•
•
•
•
SO2 and Particulate emissions are negligible
Nox emissions are lower than a conventional coal plant
No production or emission of sludge
No production or emission of ash
– Land Use
• CCPP on the average require five times less land than a coal fired plant
(100 acres versus 500 acres)
– Water Use
• Lower cooling and condensate water consumption
• Condensing steam turbine is only about 35% of output
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Short Payback Time
• High Availability rate of 90%
• CCPP is designed primarily for Peaking and Intermediate or
Mid-Merit use.
• CCPP can also be used as a Base Load unit
• CCPP also has excellent performance responsiveness for
spinning reserve capability
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Advantages/Disadvantages
• Advantages:
– Higher efficiency
– Lower capital investment
– Operational flexibility
– Base, Intermediate or Peaking
– Distributed Power application
– Dual fuel capability
- Natural gas (primary/Low sulfur fuel oil (secondary)
– Technological and Strategic advantages over Steam Power Plants
(STPP)
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Advantages/Disadvantages
• Disadvantages:
- Increased chemistry requirements with more complex plants
- Rapid heating and cooling of critical components
- Emissions to the environment: nitrogen oxides (NOx), sulfur
dioxide (SO2), carbon monoxide (CO), carbon dioxide (CO2), and
opacity
- Availability and cost of fuel
- Poor thermal performance, high vibration, tube leaks, and
ambient conditions
- Auxiliary equipment out of service which prevents unit from
achieving full load
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Generating Unit Basics
Wind Generation
Part 6
Wind Power Generation
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Wind Power Generation
• Wind is a form of solar energy caused by:
- Uneven heating of the atmosphere by the sun
- Irregularities of the earth’s surface
- Rotation of the earth
• Wind flow patterns are modified by:
- Earth’s terrain
- Bodies of water
- Vegetative cover
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Wind Power Generation
• Wind power turns kinetic energy of the wind into mechanical
and electrical power
• Power available in the wind is proportional to the cube of its
speed (Double the speed increases the power by a factor of
eight)
• Wind power depends on elevation and wind speed
• Wind speed increases with altitude and over open areas
• It is considered a free and renewable resource just like
hydroelectricity
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Type of Wind Generators
• Horizontal Axis Wind Turbine (HAWT)
Most commonly used type of wind turbine
• Vertical Axis Wind Turbine (VAWT) – most common
Emerging Technologies and many times smaller capacity and use
• Ducted Wind Turbines (DWT)
Developed decades ago, this design causes the wind speed to increase just before it strikes the
blades, which in turn creates faster revolutions. Normally smaller operations
• Wind power provides more than 2.5% of all electricity
consumption (2010)
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Wind Power Generation
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Wind Turbine Major Parts
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Other type units may have gear
boxes
317
Over the past decade, wind turbine use has increased at more than 25 percent a year
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Tower Components
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Power plants are the largest stationary source of air pollution in the United States
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Wind Generation
• Generator: Induction
- Utilizes the principle of electromagnetic induction
- Requires reactive power for excitation
- Requires the stator to be magnetized from the grid, at least
initially, to produce the rotational magnetic flux
- Generating: Produces electrical power when the rotor is rotated
faster than synchronous frequency causing an opposing rotor flux
to cut the stator coils producing a current in the stator coils
- Motoring: stator flux rotation is faster than rotor rotation creating
opposing rotor flux causing the rotor to drag behind the stator flux
by a value equal to the “slip”
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Induction Generator
• Produces electric power when the shaft of the generator is
rotated faster than the synchronous frequency of the
equivalent induction motor
• Induction generators:
- Produce useful power at varying rotor speeds
- Simpler both mechanically and electrically than other types
of generators
- Do not require brushes or commutators
- Not self-exciting; require external excitation
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Induction Generator
• The rotating magnetic flux from the stator induces currents in
the rotor, which also produces a magnetic field
- If the rotor turns slower than the rate of the rotating flux, the
machine acts like an induction motor
- If the rotor turns faster than the rate of the rotating flux, the
machine acts like an induction generator, producing power at
the synchronous frequency
- In a stand-alone situation, capacitor banks are used to
supply the magnetizing flux until the machine starts
producing power
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Induction Generator
Most Wind Generators use 4 or 6 pole
generators based on cost and size savings
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Wind Power Generation
• Anemometer: measures wind speed transmitting data to the
controller
• Blade: catches the wind causing the blades to “lift” converting
it to rotational shaft energy
• Brake: mechanically, electrically, or hydraulically stops the
rotor in emergencies
• Chopper: used in the rectifier circuit
- Improves the power factor of the overall system
- Controls the level of DC voltage
- Controls the torque of the machine
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Wind Power Generation
• Controller: computer which monitors the turbine conditions
such as overheating and power quality. It also starts the
turbine, yaws it against the wind, and checks the safety
systems
- Starts at wind speeds 8-16 mph
- Shutdown at wind speeds greater than 55 mph
• Gearbox: optimizes the power output by connecting the lowspeed shaft to the high-speed shaft increasing rotational
speeds (30-60 rpm to ~ 1,000 to 1,800 rpm)
Newer “direct-drive” generators operate at lower rotational
speeds without gear boxes (5-11.7 rpm)
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Wind Power Generation
• Inverter: converts incoming DC power into AC power for use
on the Interconnection
• Nacelle: housing atop the tower containing the gear box, lowand high-speed shafts, generator, controller, and brake
• Pitch: blades turned out of the wind to control rotor speed
and keep the unit from turning into too high or low winds to
restrict electrical production
• Rectifier: converts incoming AC power into DC power for
excitation
• Rotor: blade and hub assembly. Power available to the blades
is proportional to the square of the diameter of the rotor
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Wind Power Generation
• Tower: tubular steel, concrete, or steel lattice
• Wind vane: measures wind direction and communicates with
the yaw drive to orient the unit properly with respect to the
wind
• Yaw: Rotation of the unit parallel to the ground to face winds.
Upwind turbines face into the wind; yaw drive keeps the rotor
facing into the wind (Not required on a downwind turbine)
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Wind Power Generation
• Wind turbines are available in a variety of sizes
- Largest has blades that span more than the length of a
football field, stands 20 building stories high, and
produces electric power for ~ 1400 homes
- Smaller machines have rotors between 8 and 25 feet,
standing ~ 30 feet, supplying an all-electric home or
small business up to 50 kW
- Utility-scale turbines range in size from 50 kW to 7.50 MW
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Wind Power Generation
• Advantages:
- Wind is a free, renewable resource
- Clean, non-polluting energy
• Disadvantages:
- Higher initial investment
- 80% equipment, 20% site preparation/installation
- Environmental
- Noise produced by the rotor blades
- Visual impacts
- Avian/bat mortality
- Intermittent wind/remote locations
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Generating Unit Basics
Solar Power Generation
Part 7
Wind Power Generation
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Solar Power Generation
• Solar power is the conversion of sunlight into electricity, either
directly (photovoltaic), or indirectly (concentrated solar power)
- Photovoltaic: solar cells that change sunlight directly into electricity.
Individual solar cells can be grouped into panels and arrays of
panels for a wide range of applications
- Solar Energy Concentrator Systems: generates electricity by using
heat from solar thermal collectors to heat fluid which produces
steam that drives a turbine/generator package.
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Solar Power Generation
• Photovoltaic cell, or solar cell, is a non-mechanical device
usually made from a silicon alloy
- Individual cells, considered to be the basic building block of the
system, vary in size from ½ to 4 inches across
- To increase power output, cells are connected electrically into
modules which are further connected to form an array
- The number of modules in an array depends on the amount of
power output needed
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Solar Power Generation
• Photons, particles of solar energy, are absorbed by the cells
dislodging electrons from the cell material’s atoms causing the
electrons to migrate to the PV cell’s front surface
• The resulting imbalance in charge between the cell’s surfaces
creates a voltage potential similar to a DC battery
• Once a load is connected across the cell’s surfaces, a current
flows completing the circuit
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Solar Power Generation
• Applications of a Photovoltaic Cell:
- First used to power US space satellites
- Small consumer electronics (calculators, watches)
- Provide electricity to pump water, power communications
equipment
- Solar panel installations on residential roofs
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Solar Power Generation
• Advantages of a Photovoltaic Cell:
- Conversion from sunlight to electricity is direct; generators are
unnecessary
- Arrays can be installed quickly and in any size
- Environmental impact is minimal, requiring no water for cooling
and generating no by-products such air or water pollution
- No greenhouse gases
• Disadvantages of a Photovoltaic Cell:
- Photovoltaic cell is dependent on sunlight. Clouds and fog have a
significant effect on its performance
- DC must be converted to AC power requiring inverters
- Most modules have a 10% efficiency
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Solar Power Generation
• Solar Energy Concentrator System:
- Works the same as fossil fuel generation, except that the steam is
produced by heat collected from sunlight and transferred indirectly
to a fluid
- Main types of solar energy concentrator systems:
- Parabolic trough system
- Solar dish/engine system
- Solar power tower
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Solar Power Generation
• Parabolic Trough System:
- The collector utilizes a long parabolic-shaped reflector (mirror) that
focuses the sun’s rays on a receiver pipe located at the focus of
the parabola
- The collector tilts with the sun’s movement from east to west
- Concentration ratio (focus) is 30 to 100 times the sun’s normal
intensity, achieving fluid temperatures over 750 degrees F
- Transfer fluid, usually oil, is heated as it circulates from receiver to
heat exchanger to superheat water into steam for use in a
conventional steam turbine/generator
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Solar Power Generation
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Solar Power Generation
• Solar Dish/Engine System:
- Uses collectors, always pointing straight at the sun, to concentrate
the solar energy at the focal point of the dish
- Concentration ratio (focus) is much higher than a trough system,
typically over 2,000 with a fluid temperature over 1,380 degrees F
- Stirling engine converts heat into mechanical energy by
compressing the working fluid when cold, heating the compressed
fluid, and then expanding the fluid through a turbine or with a
piston to produce work
- Engine is coupled to an electric generator to convert the
mechanical energy into electrical power
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Solar Power Generation
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Solar Power Generation
• Solar Power Tower:
- Generates electricity by focusing concentrated solar energy on a
tower-mounted heat exchanger
- The system uses flat sun-tracking mirrors called heliostats to
reflect and concentrate the solar energy onto a central receiver
tower (concentrated energy can be as much as 1,500 times that
of the energy coming in from the sun)
- Energy losses are minimized as the energy is directly transferred
from the heliostats to a single receiver
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Solar Power Generation
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Solar Power Generation
• Disadvantages of Solar Energy:
- The amount of sunlight at the surface of the earth is not constant.
It depends on location, time of day, time of year, and weather
conditions.
- Because the sun doesn’t deliver that much energy to any one
place at any given time, a large surface area is needed to collect
the energy at a useful rate
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Summary
• Overview
– Generators
– Electrical and governor characteristics
• Plant Principles of Operation
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Steam
Nuclear
Hydro
Combustion Turbines
Combined Cycle Power Plants (CCPP)
Wind Power
Solar Power
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Questions?
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Disclaimer:
PJM has made all efforts possible to accurately document
all information in this presentation. The information seen
here does not supersede the PJM Operating Agreement or
the PJM Tariff both of which can be found by accessing:
http://www.pjm.com/documents/agreements/pjmagreements.aspx
For additional detailed information on any of the topics
discussed, please refer to the appropriate PJM manual
which can be found by accessing:
http://www.pjm.com/documents/manuals.aspx
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