19671394 governor basics

Power Systems Universityg Governing Basics

Slide 1

Governing Basics

Objective: To gain an understanding of control fundamentals.


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!


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.


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.


Slide 9

Prime Mover Introduction


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.


Slide 11

Basic Control Loop

WoodwardControlSystem

PrimeMover

Load

Exhaust

MeteringValve

Actuator

EnergySource


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.


Slide 15

Example of a Gas Turbine


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 ...


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.


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.


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.


Slide 23

Closing the Loop

Actual Speedor Load

ControlOf TheEnergy

Desired Speed or Load Reference


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.


Slide 25

Early Mechanical Governor

Early Mechanical Governor


Slide 26

Force Balance

1000 lb

F(d)F(a)

1000 lb

DesiredSpeedForce

ActualSpeedForce

DecreaseFuel

IncreaseFuel


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.


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


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


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.


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


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


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


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


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 %


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



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%


0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Intersection of Droop CurveAnd Actual Speed DeterminesWicket Gate Position / Load

Lower Speed SetpointBy 2.5%

(Shifts Droop Curve)


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%


0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Intersection of Droop CurveAnd Actual Speed DeterminesWicket Gate Position / Load

Increase Speed SetpointBy 1% to 103.5%

Load IncreasesBy 20%


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%


0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


If System Frequency Shifts,Load Will Shift According

To Droop Curve Intersection


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%


0% 10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


5% Droop Curve2% Droop Curve


Slide 41

Dashpot Compensated Governor


Slide 42

Dashpot Compensated Governor

The dashpot compensated governor was the first governor designed to be an isochronous governor.


Slide 43

ISOCHRONOUS(ISO+CHRONOS = SAME +TIME)

CONSTANT SPEEDNo change in speed setting

with an change in load

Isochronous Definition


Slide 44

Isochronous Curve

0% 100%50%LOAD LOAD

Spee

d /

Spee

d Se

tpoi

nt


Slide 45

Pressure Compensated Governor


Slide 46

Pressure Compensated Governor Response

Spee

d /

Spee

d Se

tpoi

nt


Slide 47

Electronic Governor Basics


Slide 48

Review of Basic Governor Elements

Speed SensorSpeed ReferenceSumming PointStabilizing MethodHydraulic Pressure SourceOutput ServoControlling Amplifier


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.


Slide 50

Proportional ActuatorLevel Adjustment

IncreaseFuel

Coil

Coil

To SumpControl Port

Control Oil

High Pressure

Control Land

PermanentMagnet

CenteringScrew

+

_

Demand

From Governor


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


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.


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


Slide 54

MPU Generated Waveforms


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.


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)


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.


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


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


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.


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


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.

+

-


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


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.


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


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


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.


Slide 69

Example of Temperature Limiting LSS


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.


Slide 71

Example LSS


Slide 72



Slide 73

Example of HSS


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.


Slide 75

Example HSS


Slide 76



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


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


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.


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.


Slide 81

PID Tutorial


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.


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.


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.


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.


Slide 86

PID Tutorial

TIME

SPEE

D

GAINADJUSTMENT

COMPENSATIONADJUSTMENT

RESETADJUSTMENT


Slide 87

“Text Book” Dynamic Response


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.


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

19671394 governor basics

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