19671394 governor basics
TRANSCRIPT
Power Systems Universityg Governing Basics
Slide 1
Governing Basics
Objective: To gain an understanding of control fundamentals.
Power Systems Universityg Governing Basics
Slide 2
Safety Information
The engine, turbine or other type of prime mover should be equipped with an overspeed shutdown device, that operates independent of the prime mover control device to protect against runaway or damage to the prime mover with possible personal injury or loss of life should the mechanical-hydraulic governor or electric control, the actuator, fuel control, the driving mechanism, the linkage, or the control device fail.
WARNING!
Power Systems Universityg Governing Basics
Slide 3
What is a Governor ???Governor Definition: a: An attachment to a machine for automatic control or limitation of speed. b: A device giving automatic control (as of pressure or temperature). A governor is a device which controls the energy source to a prime mover to control it for a specific purpose.Basic governors sense speed and sometimes load of a prime mover and adjust the energy source to maintain the desired parameter.Advanced governors are often referred to as Control Systems.
Power Systems Universityg Governing Basics
Slide 4
Why do we need Governors ?
Prime movers must be controlled to do useful work. Common control parameters include:
SpeedLoad (torque or MW)PressureTemperatureValve PositionSpeed DerivativePressure DerivativeAny parameter that can be converted into a 4-20 milliamp signal.
Power Systems Universityg Governing Basics
Slide 9
Prime Mover Introduction
Power Systems Universityg Governing Basics
Slide 10
Prime Mover Introduction
Prime Mover Definition: An initial source of motive power (as a waterwheel, turbine, or engine) designed to receive and modify force and motion as supplied by some natural source and apply them to drive machinery.Before we can understand what a governor is or how a governor works, here is a quick introduction of the prime movers that use governors.
Power Systems Universityg Governing Basics
Slide 11
Basic Control Loop
WoodwardControlSystem
PrimeMover
Load
Exhaust
MeteringValve
Actuator
EnergySource
Power Systems Universityg Governing Basics
Slide 12
Basic Control Loop
A basic prime mover control loop consists of the following pieces:
Energy/Fuel Source - Steam, Diesel, Gas, Water...Fuel Metering Valve - Gas Valve, Steam Valve, Gate Valve, Injector...Load - Generator, Compressor, Propeller...Control System - Governor, Electronic Control System and Actuator.
Power Systems Universityg Governing Basics
Slide 15
Example of a Gas Turbine
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Slide 16
Example of a Gas TurbineA simple gas turbine is comprised of three main sections; a compressor, a combustion assembly and a power turbine.Air is drawn in the front of the turbine and compressed. The compressed air is then mixed with fuel, and burned. The control system governs the amount of fuel being burned.The resulting hot gas expands and is forced through the power turbine creating horsepower or work.The power turbine section is connected to the load.There are many other types of gas turbines; Aero Derivative, 2-Shaft, 3-Shaft ...
Power Systems Universityg Governing Basics
Slide 19
DESIRED SPEED
ACTUAL SPEED
Speed Control: Constant Load
The driver of the car is the control or governor.The speed limit sign is the desired speed setting.The speedometer senses actual speed.The driver compares desired speed to actual speed, If they are the same, fuel is held steady.If desired speed and actual speed are different, the fuel setting is adjusted by the driver to make actual speed equal desired speed.Fuel is held steady until a speed or load change occurs.
Power Systems Universityg Governing Basics
Slide 20
IncreaseFuel
SPEEDLIMIT60
Speed Control: Increased LoadThe car starts up the hill, load increases, speed decreases.The actual speed is less than desired speed.Driver increases the fuel to increase the speed, which returns the actual speed to the desired speed.Before the actual speed reaches the desired speed, the driver reduces the fuel to prevent overshoot of speed. This is called Compensation and is adjusted to match the response time of the prime mover.It takes more fuel to pick up load than to maintain load.
Power Systems Universityg Governing Basics
Slide 21
Speed Control: Decreased Load
The car starts down the hill, load decreases, speed increases.Actual speed is greater than desired speed.Driver decreases fuel to decrease speed, which returns the actual speed to desired speed.Before the actual speed reaches the desired speed, the driver
increases the fuel to prevent undershoot of speed. This is called Compensation and is adjusted to match the response time of the prime mover.
Power Systems Universityg Governing Basics
Slide 23
Closing the Loop
Actual Speedor Load
ControlOf TheEnergy
Desired Speed or Load Reference
Power Systems Universityg Governing Basics
Slide 24
Closing the Loop
The governor functions the same as the car driver.It automatically changes the Fuel Flow to maintain the desired speed or load.Closed Loop Definition: When used as an automatic control system for operation or process in which feedback in a closed path or group of paths to maintain output at a desired level.If parameter(s) of the loop change, it will effect the entire loop and fuel will automatically be corrected to maintain the desiredsetpoint.
Power Systems Universityg Governing Basics
Slide 25
Early Mechanical Governor
Early Mechanical Governor
Power Systems Universityg Governing Basics
Slide 26
Force Balance
1000 lb
F(d)F(a)
1000 lb
DesiredSpeedForce
ActualSpeedForce
DecreaseFuel
IncreaseFuel
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Slide 27
Force Balance
In the governor, Actual Speed and the Desired Speed are converted to a force that represents their respective actions.These forces must be balanced in order to maintain the speed/load constant.If they are not balanced, the governor will increase or decrease fuel until they are balanced.
Power Systems Universityg Governing Basics
Slide 28
Simple Flyweight System
F(a) = Actual Measure of the Centrifugal force = Actual Speed.F(d) = Actual measure of the compressed speeder spring = Desired Speed.F(a) = F(d) for a balanced system.In other words, when the force of the compressed speeder spring equals the centrifugal force, the system is in equilibrium.The forces are summed together in a thrust bearing.
Simple Flyweight System
Power Systems Universityg Governing Basics
Slide 29
Thrust Bearing
Pilot Valve Plunger
Pilot Valve Bushing
Control Land
Control Port
Flyweights and Pilot Valve
IncreaseFuel
Sump
HighPressureOil
IncreaseFuel
Sump
HighPressureOil
PilotValve
ControlLand
SpeedAdjust Output
Servo
Oil Pump
Power Systems Universityg Governing Basics
Slide 30
Pilot Valve Bushing and Porting
RoundHoleSlot
PilotValvePlunger
PlungerandBushing
Pilot Valve Bushings are cut differently to compensate for different size prime movers and prime mover responses.Pilot Valve Bushings are cut with holes or slots.Very tight tolerances are required on both the pilot valves and pilot valve bushings for exact controlling.
Power Systems Universityg Governing Basics
Slide 31
Unstable Governor
Time
SPEE
D
LoadAdded
Prime MoverAcceleration Actual
Speed
Prime MoverDeceleration
DesiredSpeedSetpoint
IncreaseFuel
Sump
HighPressureOil
IncreaseFuel
Sump
HighPressureOil
PilotValve
ControlLand
SpeedAdjust Output
Servo
Oil Pump
As load is added, speed decreases. Fuel is added, increasing speed until speed equals speed setpoint.Due to the acceleration and lag time of the prime mover, speed overshoots thus decreasing the fuel.Speed decreases until speed equals speed setpoint.Due to the deceleration and lag time of the prime mover, speed undershoots thus decreasing the fuel.Process is repeated remaining unstable or in some conditions becoming more and more unstable.
Unstable Governor
Power Systems Universityg Governing Basics
Slide 32
Droop Governor
A droop governor allows the feedback arm to increase or decrease the force on the speeder spring, thus increasing or decreasing the speed reference with a change in load (fuel demand) or speed.
Time
Spee
d Se
tpoi
nt LoadAdded
LoadRemoved
IncreaseFuel
Sump
HighPressureOil
IncreaseFuel
OutputServo
Feedback Arm
HighPressureOil
Droop Governor
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Slide 33
Droop CurveDroop Definition: A decrease in desired speed setpoint for an increase in load or output servo position (feedback). 0% 100%50%LOAD
Power Systems Universityg Governing Basics
Slide 34
Droop Calculation
X 100% Droop No Load Speed - Full Load SpeedRated Speed
=
3780 RPM 63 Hz(no load speed)
3600 RPM 60 Hz (full load speed)(rated speed)
3600 RPM - 3420 RPM3600 RPM
= 5% DroopX 100
3780 RPM - 3600 RPM3600 RPM
= 5% DroopX 100
0% LOAD 100%
Generator Set Loaded to Utility Bus or Other Generator Sets
LOAD 100%Mechanical Load or Gen. set loaded by a Load Bank
0 %3420 RPM (full load speed)
3600 RPM (no load speed)(rated speed)
Example of 5% Droop
Power Systems Universityg Governing Basics
Slide 35
105 RPM63 Hz
(no load speed)
0% LOAD 100%
100 RPM60 Hz
(full load speed)&
(rated speed)
100 RPM - 95 RPM100 RPM
Example of5% DROOP
GEN SETLoaded to Utility Bus
95 RPM(full load speed)
LOAD 100%
100 RPM(no load speed)
(rated speed)
Example of5% Droop
Mechanical Load
= 5% DROOP
X 100
105 RPM - 100 RPM100 RPM
= 5% DROOP
X 100
Droop Calculation
0 %
Power Systems Universityg Governing Basics
Slide 36
Droop Calculation
(60 Hz) 100%
(60.6 Hz) 101%
(61.2 Hz) 102%
(61.8 Hz) 103%
(62.4 Hz) 104%
(63 Hz) 105%
(59.4 Hz) 99%
Speed /Speed Setpoint
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Wicket Gate Position / Load
5% Droop Curve
Actual Speed“Fixed” When Tied
Large system
Intersection of Droop CurveAnd Actual Speed Determines
Wicket Gate Position / Load
Power Systems Universityg Governing Basics
Slide 37
Droop Calculation
(60 Hz) 100%
(60.6 Hz) 101%
(61.2 Hz) 102%
(61.8 Hz) 103%
(62.4 Hz) 104%
(63 Hz) 105%
(59.4 Hz) 99%
Speed /Speed Setpoint
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Wicket Gate Position / Load
Intersection of Droop CurveAnd Actual Speed DeterminesWicket Gate Position / Load
Lower Speed SetpointBy 2.5%
(Shifts Droop Curve)
Power Systems Universityg Governing Basics
Slide 38
Droop Calculation
(60 Hz) 100%
(60.6 Hz) 101%
(61.2 Hz) 102%
(61.8 Hz) 103%
(62.4 Hz) 104%
(63 Hz) 105%
(59.4 Hz) 99%
Speed /Speed Setpoint
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Wicket Gate Position / Load
Intersection of Droop CurveAnd Actual Speed DeterminesWicket Gate Position / Load
Increase Speed SetpointBy 1% to 103.5%
Load IncreasesBy 20%
Power Systems Universityg Governing Basics
Slide 39
Droop Calculation
(60 Hz) 100%
(60.6 Hz) 101%
(61.2 Hz) 102%
(61.8 Hz) 103%
(62.4 Hz) 104%
(63 Hz) 105%
(59.4 Hz) 99%
Speed /Speed Setpoint
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Wicket Gate Position / Load
If System Frequency Shifts,Load Will Shift According
To Droop Curve Intersection
Power Systems Universityg Governing Basics
Slide 40
Droop Calculation
(60 Hz) 100%
(60.6 Hz) 101%
(61.2 Hz) 102%
(61.8 Hz) 103%
(62.4 Hz) 104%
(63 Hz) 105%
(59.4 Hz) 99%
Speed /Speed Setpoint
0% 10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Wicket Gate Position / Load
5% Droop Curve2% Droop Curve
Power Systems Universityg Governing Basics
Slide 41
Dashpot Compensated Governor
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Slide 42
Dashpot Compensated Governor
The dashpot compensated governor was the first governor designed to be an isochronous governor.
Power Systems Universityg Governing Basics
Slide 43
ISOCHRONOUS(ISO+CHRONOS = SAME +TIME)
CONSTANT SPEEDNo change in speed setting
with an change in load
Isochronous Definition
Power Systems Universityg Governing Basics
Slide 44
Isochronous Curve
0% 100%50%LOAD LOAD
Spee
d /
Spee
d Se
tpoi
nt
Power Systems Universityg Governing Basics
Slide 45
Pressure Compensated Governor
Power Systems Universityg Governing Basics
Slide 46
Pressure Compensated Governor Response
Spee
d /
Spee
d Se
tpoi
nt
Power Systems Universityg Governing Basics
Slide 47
Electronic Governor Basics
Power Systems Universityg Governing Basics
Slide 48
Review of Basic Governor Elements
Speed SensorSpeed ReferenceSumming PointStabilizing MethodHydraulic Pressure SourceOutput ServoControlling Amplifier
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Slide 49
Actuators
The part of an electronic governing system that converts the electrical output signal of the electronics into a mechanical movement which positions the throttle, steam valve, fuel metering valve etc.An ACTUATOR is a hydraulic, or pneumatic, or electrical device
that converts an electrical signal to a mechanical position.A SERVOMOTOR is a hydraulic cylinder assembly controlled by a pilot valve and usually directly connected to the prime mover's energy-medium control (fuel valve, steam valve, etc.).Woodward electro-hydraulic actuators usually convert 20 -160 milliamps to zero to ~45 degrees of rotation, or zero to one inch, depending on the actuator. Other manufacturers (Valtec, Vickers, Fisher, etc.) convert 4-20 milliamps to zero to full stroke.
Power Systems Universityg Governing Basics
Slide 50
Proportional ActuatorLevel Adjustment
IncreaseFuel
Coil
Coil
To SumpControl Port
Control Oil
High Pressure
Control Land
PermanentMagnet
CenteringScrew
+
_
Demand
From Governor
Power Systems Universityg Governing Basics
Slide 51
Integrating Actuator
Magnet
Control Land Control Port
Coil
Coil
CenteringScrew
CenteringSprings
IncreaseFuel
Null CurrentAdjustment
CL
CL
To Sump
Control PressurePower Servo
S
N
S
N
High Pressure Oil(-)
LVDTExcitation
LVDT Feedback
+
-
Demand
From Governor
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Slide 52
Speed Sensing • Speed of the prime mover is
sensed using Magnetic Pickups (MPU).
• An MPU generates a frequency signal that is directly proportional to the speed of the prime mover.
• Single pole, alternating current, electric generator.
• Single magnet, attached to a pole piece which is wrapped with multiple layers of copper wire.
• The ferrous gear teeth and the magnet creates a path for the magnetic lines of force.• Making and breaking of the flux lines induces an alternating voltage into the coil around the
pole piece.• Each pulse is represented by a gear tooth passing by the Magnetic Pick-up.• The Impedance of a Magnetic Pick-up is approximately 220 ohms.
Power Systems Universityg Governing Basics
Slide 53
Magnetic Pick-Up’s
s s S
1.5 V Minimum
RMS
Ferrous Gear
Coil Pole PieceMPU BracketPermanentMagnet
Magnetic Lines of Force
Gap
Jam Nut
The voltage amplitude output is dependent on the air gap of the MPU. A decrease in air gap equals an increase in voltage.MPU voltage must be >1.5 V RMS, at the lowest control speed.
mpu
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Slide 54
MPU Generated Waveforms
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Slide 55
MPU Generated WaveformsThe output waveform of the MPU depends on the following items:
Speed of the gear and number of teeth.The air gap between the pole piece and the gear tooth.The dimensions of the MPU and the type of gear.The impedance connected across the output coil.
MPU Advances per turn:16 Threads Per Inch = 0.0625 inch.18 Threads Per Inch = 0.0550 inch.20 Threads Per Inch = 0.0500 inch.24 Threads Per Inch = 0.0415 inch.28 Threads Per Inch = 0.0357 inch.
Power Systems Universityg Governing Basics
Slide 56
MPU Frequency CalculationMPU Frequency(cycles/sec) = Gear Speed(revolutions/min) x Number of
Teeth 60(sec/min)
OR
Gear Speed(revolutions/min) = MPU Frequency(cycles/sec) x 60(sec/min)Number of Gear Teeth
For a 60 Tooth Gear:
Gear Speed(revolutions/min) = MPU Frequency(cycles/sec)
Power Systems Universityg Governing Basics
Slide 57
Proximity Probes
Proximity Probes or Proximity Switches are active devices usually used where slow rpm or a large air gap is required. This is necessary due to the large runout of the monitored gear and the slow speeds of large engines or turning gears on turbines. These have a slower surface speed which an MPU cannot detect.Proximity probes require an external power supply, usually 24 Vdc to operate.
Power Systems Universityg Governing Basics
Slide 58
Hydraulic-Mechanical vs. Electrical
AnalogHydraulic-Mechanical
Electrical
SpeedSensing
SpeedSetting
Summing ofForces
Stability
Gain
Reaction to Error Signal
DigitalFly Weights
Speeder Spring
Thrust Bearing
Needle Valve
Buffer Springs
Pilot Valve Porting
Magnetic Pick Up orProximity Probe
Speed Potentiometer
Summing Amplifier
Reset Capacitor/Potentiometer
Gain Potentiometer
PID Amplifier
Magnetic Pick Up orProximity Probe
Software Ramp Block
Software Add Block
Software PID Block
Software PID Block
Software PID Block
Power Systems Universityg Governing Basics
Slide 59
Speed Control Summing JunctionSpeed Reference orDesired Set - Point
Actual Speed
Other Inputs(Load Sensor)(Synchronizer)(Droop Signal)
(Etc.)
Error Output
To Amplifier
PID
OutputTo
Actuator
PID Feedback
The Set-point or reference is where you would like the actual measurement to be. Error is defined as the difference between the set-point and actual measurement
Power Systems Universityg Governing Basics
Slide 60
Summing Point
The summing point is where all signals in a control loop add up.The input signals must sum up to zero for precise steady state control.The summing point is electronically the same as the thrust bearing in a hydraulic / mechanical control where all the forces balance to zero.Many parameters can be added into the summing point.The PID block and feedback block represent a special type of amplifier.
Power Systems Universityg Governing Basics
Slide 61
Analog Electronic Speed Control
Generator
Frequencyto
Voltage Converter
AC Sine Wave
Actual Speed- D.C. Volts Prime
Mover
MagneticPickup
Desired Speed +DC Volts
Actuator
PIDError SignalSumming Junction
PID Feedback
Power Systems Universityg Governing Basics
Slide 62
Digital Control System Block Diagram
++
--
Setpoint (+)
Output To
Fuel ValveError Signal
Actual (-)
Adjustable Dynamics and Amplification
PID
PID Feedback
Summing Junction
The setpoint is the only parameter accessible in the closed loopsystem.The control will force the actual parameter to match the setpoint by actuating the fuel valve.
The setpoint is the only parameter accessible in the closed loopsystem.The control will force the actual parameter to match the setpoint by actuating the fuel valve.
+
-
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Slide 63
Feedback
ZVPUInterfaceModule
Pulse Train
D.C. Volts
Speed Reference
Closed Loop Speed Control
Valve
Prime Mover
Generator
Zero VelocityPickups
Servomotors
Droop (Gate Position)
0V
15V
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Slide 64
Closed Loop Speed ControlActual speed is converted to a DC voltage that is proportional to the speed of the prime mover. Speed reference is compared to the actual speed.An error signal is produced if the actual speed voltage and the speed reference are not matched.An increase fuel or decrease fuel signal is then given to the actuator.
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Slide 65
Valve
Prime Mover
Generator
Mechanical / Electrical Governor Comparison
ZVPUInterface Module
Zero VelocityPickups
SpeederSpring
Thrust Bearing
Flyweights
Pilot Valve Porting
SummingPoint Error
Signal
Gain ResetRatedSpeedPot
Pivot Points NeedleValve Mechanical
Electrical
Servomotors
Power Systems Universityg Governing Basics
Slide 66
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Slide 67
HSS - LSS
Speed Control
Temperature Control
Accel Control
High Limit
OutputToActuator
LSS
HSS
Decel Control
Low Limit
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Slide 68
HSS - LSSLSS = Low Signal Select. Whichever input is the lowest, will be sent to the output.HSS = High Signal Select. Whichever input is the highest will be sent to the output.These Hardware or Software algorithms allow different items to be in control as they are needed.Only one input can be in control at any one time.
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Slide 69
Example of Temperature Limiting LSS
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Slide 70
Example of LSS
The two inputs on the LSS are speed and temperature.If the temperature input ever exceeds the speed, then the fuel would be limited by temperature.Exhaust Gas Temperature, Compressor Discharge Pressure, Manifold Air Pressure, Lube Oil Temperature, Multiple Speeds, are examples of LSS Inputs.
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Slide 71
Example LSS
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Slide 73
Example of HSS
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Slide 74
Example of HSS
Redundant Magnetic Pickups are often used in control systems.Both inputs to the HSS are the same, yet coming from different MPU’s.If either MPU should fail and the input go to zero, the good MPU will send its output to the summing point.
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Slide 75
Example HSS
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Slide 77
What is a PID ?
If you don’t understand the followingequation / algorithm, then continue on.
e=error, Kc = gain, I = integral, and D = derivative settings
OUTPUT = Kc 1 d e(t)
dt I e(t) + e(t) dt + D
Power Systems Universityg Governing Basics
Slide 78
PID TutorialThe Set-point or reference is where you would like the actual measurement to be. Error is defined as the difference between the set-point and actual measurement.
Speed Reference orDesired Set - Point
Other Inputs(Load Sensor)(Synchronizer)
(Etc.)
Error OutputTo Amplifier Output
ToActuator
Actual Speed
PID
Feedback
Power Systems Universityg Governing Basics
Slide 79
PID Tutorial
PID stands for Proportional, Integral, and Derivative. A PID amplifier is used to calculate an appropriate response to the output based on changes to the input.Controllers use PID’s to eliminate the need for continuous operator attention.
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Slide 80
PID Tutorial
Question: Why are dynamic adjustments necessary in a governor or control system?Answer: Control Systems must be matched to the prime movers, in order for them to operate properly.
Power Systems Universityg Governing Basics
Slide 81
PID Tutorial
Power Systems Universityg Governing Basics
Slide 82
PID Tutorial
The output of a PID controller will change in response to a change in measurement or set-point. PID - Combinations of Proportional, Integral, and Derivative will provide the best type of process control required.
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Slide 83
PID Tutorial
Gain - The gain is the proportional gain term in the PID controller.With Proportional Gain, the control output is proportional to the error in measurement or set-point.
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Slide 84
PID TutorialReset - The reset is the integral term in the PID controller. With integral action, the controls output is proportional to the amount of time the speed error is present.It prevents slow hunting at steady state and controls the time rate at which the speed error returns to zero after a speed or load disturbance.
Power Systems Universityg Governing Basics
Slide 85
PID Tutorial
Compensation - The compensation is the derivative term in the PID controller.With Derivative action, the controls output is proportional to the rate of change of the measurement or error.The controls output is calculated by the rate of change of the measurement with time.Compensation is used to avoid overshoot.
Power Systems Universityg Governing Basics
Slide 86
PID Tutorial
TIME
SPEE
D
GAINADJUSTMENT
COMPENSATIONADJUSTMENT
RESETADJUSTMENT
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Slide 87
“Text Book” Dynamic Response
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Slide 88
“Text Book” Dynamic Response
Characteristics of correctly tuned prime mover:Stable control at no load.Stable control over all load ranges.Minimum overshoot with no ringing or instability.
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Slide 89
Governor Assumptions
•Consistent fuel qualitySteam pressure, gas pressure, BTU value, etc.
• Control of valvesValves must be calibrated for zero to 100 percent travel
• LinkageSmooth travelNo lost motion
• LinearityLinear flow for zero to 100 percent travelPower output linear with valve position
• Consistent machine geometryNo change in dynamic response