19671394 Governor Basics

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Power Systems University

Governing Basics

Governing Basics

Objective: To gain an understanding of control fundamentals.

Slide 1

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Governing Basics

Safety Information WARNING! 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. Slide 2

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Governing Basics

What is a Governor ??? z

z

z

z

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 3

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Why do we need Governors ? Prime movers must be controlled to do useful work. Common control parameters include: z z z z z z z z

Speed Load (torque or MW) Pressure Temperature Valve Position Speed Derivative Pressure Derivative Any parameter that can be converted into a 4-20 milliamp signal. Slide 4

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Prime Mover Introduction

Slide 9

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Governing Basics

Prime Mover Introduction z

z

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 10

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Basic Control Loop Woodward Control System

Actuator Energy Source

Metering Valve

Prime Mover

Load

Exhaust Slide 11

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Basic Control Loop zA

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 12

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Example of a Gas Turbine

Slide 15

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Example of a Gas Turbine z z

z z z

A 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, 2Shaft, 3-Shaft ...

Slide 16

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Speed Control: Constant Load DESIRED SPEED ACTUAL The driver of the car is the SPEED control or governor. z The speed limit sign is the desired speed setting. z The speedometer senses actual speed. z The driver compares desired speed to actual speed, If they are the same, fuel is held steady. z If desired speed and actual speed are different, the fuel setting is adjusted by the driver to make actual speed equal desired speed. z Fuel is held steady until a speed or load change occurs.

z

Slide 19

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Speed Control: Increased Load SPEED LIMIT

60 The car starts up the hill, load increases, speed Increase Fuel decreases. z The actual speed is less than desired speed. z Driver increases the fuel to increase the speed, which returns the actual speed to the desired speed. z 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. z It takes more fuel to pick up load than to maintain load. Slide 20

z

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Speed Control: Decreased Load The car starts down the hill, load decreases, speed increases. z Actual speed is greater than desired speed. z Driver decreases fuel to decrease speed, which returns the actual speed to desired speed. z 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. z

Slide 21

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Closing the Loop

Actual Speed or Load

Control Of The Energy

Desired Speed or Load Reference Slide 23

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Closing the Loop The governor functions the same as the car driver. z It automatically changes the Fuel Flow to maintain the desired speed or load. z 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. z If parameter(s) of the loop change, it will effect the entire loop and fuel will automatically be corrected to maintain the desired setpoint. z

Slide 24

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Early Mechanical Governor

Early Mechanical Governor

Slide 25

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Force Balance Desired Speed Force

Actual Speed Force F(a)

F(d)

1000 lb

1000 lb

Increase Fuel

Decrease Fuel

Slide 26

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Force Balance In the governor, Actual Speed and the Desired Speed are converted to a force that represents their respective actions. z These forces must be balanced in order to maintain the speed/load constant. z If they are not balanced, the governor will increase or decrease fuel until they are balanced. z

Slide 27

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Simple Flyweight System

Simple Flyweight System

z z z z z

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. Slide 28

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Flyweights and Pilot Valve Thrust Bearing

Speed Adjust

Pilot Valve Plunger Control Land

Control Port

Pilot Valve Bushing

Output Servo

Pilot Valve High Pressure Oil Control Land Oil Pump

Increase Fuel

Sump

Slide 29

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Pilot Valve Bushing and Porting Pilot Valve Bushings are cut differently to compensate for different size prime movers and prime mover responses. z Pilot Valve Bushings are cut with holes or slots. z Very tight tolerances are required on both the pilot valves and pilot valve bushings for exact controlling. z

Round Hole

Slot

Pilot Valve Plunger

Plunger and Bushing

Slide 30

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Unstable Governor

z

z z

z

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.

Speed Adjust

Output Servo

Pilot Valve High Pressure Oil Control Land Oil Pump

Increase Fuel

Sump Unstable Governor

Prime Mover Acceleration

Actual Speed

Load Added

SPEED

z

Time

Prime Mover Deceleration

Desired Speed Setpoint Slide 31

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Droop Governor Feedback Arm

Droop Governor

Output Servo

High Pressure Oil Increase Fuel Sump

Speed Setpoint

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.

Load Added

Load Removed

Time

Slide 32

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Droop Curve Droop Definition: A decrease in desired speed setpoint for an increase in load or output servo position (feedback).

0%

LOAD

50%

100%

Slide 33

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Droop Calculation % Droop =

No Load Speed - Full Load Speed Rated Speed

X 100

Example of 5% Droop 3600 RPM - 3420 RPM X 100 = 5% Droop 3600 RPM

3600 RPM (no load speed) (rated speed)

3420 RPM (full load speed)

0%

LOAD

100%

Mechanical Load or Gen. set loaded by a Load Bank

3780 RPM 63 Hz (no load speed)

3780 RPM - 3600 RPM X 100 = 5% Droop 3600 RPM

3600 RPM 60 Hz (full load speed) (rated speed)

0%

LOAD

100%

Generator Set Loaded to Utility Bus or Other Generator Sets

Slide 34

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Droop Calculation Example of 5% Droop 100 RPM (no load speed) (rated speed)

Mechanical Load

95 RPM (full load speed)

100 RPM - 95 RPM 100 RPM = 5% DROOP

0%

LOAD

100%

105 RPM 63 Hz (no load speed)

X 100

Example of 5% DROOP

100 RPM 60 Hz (full load speed) & (rated speed)

GEN SET Loaded to Utility Bus

0%

LOAD

100%

105 RPM - 100 RPM 100 RPM

X 100

= 5% DROOP Slide 35

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Governing Basics


Droop Calculation

Speed / Speed Setpoint (63 Hz) 105%

5% Droop Curve

(62.4 Hz) 104%

Intersection of Droop Curve And Actual Speed Determines Wicket Gate Position / Load

(61.8 Hz) 103% (61.2 Hz) 102% (60.6 Hz) 101% (60 Hz) 100%

Wicket Gate Position / Load

100%

90%

80%

70%

60%

50%

40%

30%

10%

20%

Actual Speed “Fixed” When Tied Large system

99%

0%

(59.4 Hz)

Slide 36

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Droop Calculation


Lower Speed Setpoint By 2.5% (Shifts Droop Curve)

(62.4 Hz) 104% (61.8 Hz) 103%


(61.2 Hz) 102% (60.6 Hz) 101% (60 Hz) 100%


100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

99%

0%

(59.4 Hz)

Slide 37

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Droop Calculation


Increase Speed Setpoint By 1% to 103.5%

(62.4 Hz) 104%


(61.8 Hz) 103% (61.2 Hz) 102% (60.6 Hz) 101% (60 Hz) 100% 99%


100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

Load Increases By 20% 0%

(59.4 Hz)

Slide 38

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Droop Calculation

Speed / Speed Setpoint (63 Hz) 105% (62.4 Hz) 104%

If System Frequency Shifts, Load Will Shift According To Droop Curve Intersection

(61.8 Hz) 103% (61.2 Hz) 102% (60.6 Hz) 101% (60 Hz) 100%


100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

99%

0%

(59.4 Hz)

Slide 39

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Droop Calculation


5%

(62.4 Hz) 104% (61.8 Hz) 103%

Dro op C urve

2% Droop

(61.2 Hz) 102%

C ur v e

(60.6 Hz) 101% (60 Hz) 100%


100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

99%

0%

(59.4 Hz)

Slide 40

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Dashpot Compensated Governor

Slide 41

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Dashpot Compensated Governor z

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

Slide 42

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Isochronous Definition

ISOCHRONOUS (ISO+CHRONOS = SAME +TIME) CONSTANT SPEED No change in speed setting with an change in load

Slide 43

Isochronous Curve Speed / Speed Setpoint

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0%

LOAD

50%

LOAD

100%

Slide 44

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Pressure Compensated Governor

Slide 45

Governing Basics

Pressure Compensated Governor Response

Speed / Speed Setpoint

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Slide 46

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Electronic Governor Basics

Slide 47

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Review of Basic Governor Elements z z z z z z z

Speed Sensor Speed Reference Summing Point Stabilizing Method Hydraulic Pressure Source Output Servo Controlling Amplifier

Slide 48

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Actuators z

z z

z

z

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 49

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Proportional Actuator Level Adjustment

Centering Screw

Increase Fuel

Coil

+ Demand From Governor

_

Coil Permanent Magnet High Pressure Control Oil

Control Land

Control Port To Sump

Slide 50

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Integrating Actuator Null Current Adjustment Centering Springs

LVDT Excitation

LVDT Feedback

Centering Screw Increase Fuel

Demand

+

From Governor

-

(-)

N

N

S

S

Magnet High Pressure Oil CL Control Land

Coil CL

Coil Power Servo Control Pressure Control Port

To Sump Slide 51

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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 52

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Magnetic Pick-Up’s Magnetic Lines of Force 1.5 V RMS Minimum

Gap Jam Nut s

MPU Bracket mpu

Ferrous Gear

s

Coil Permanent Magnet

S

Pole Piece

The voltage amplitude output is dependent on the air gap of the MPU. A decrease in air gap equals an increase in voltage. z MPU voltage must be >1.5 V RMS, at the lowest control speed. z

Slide 53

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MPU Generated Waveforms

Slide 54

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MPU Generated Waveforms z

The 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.

z

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 55

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MPU Frequency Calculation MPU 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 56

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Proximity Probes

z

z

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 57

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Hydraulic-Mechanical vs. Electrical HydraulicMechanical

Electrical Analog

Digital

z

Speed Sensing

Fly Weights

Magnetic Pick Up or Proximity Probe

Magnetic Pick Up or Proximity Probe

z

Speed Setting

Speeder Spring

Speed Potentiometer

Software Ramp Block

z

Summing of Forces

Thrust Bearing

Summing Amplifier

Software Add Block

Software PID Block

z

Stability

Needle Valve

Reset Capacitor/Potentiometer

z

Gain

Buffer Springs

Gain Potentiometer

Software PID Block

z

Reaction to Error Signal

Pilot Valve Porting

PID Amplifier

Software PID Block Slide 58

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Speed Control Summing Junction Speed Reference or Desired Set - Point Error Output To Amplifier

Other Inputs (Load Sensor) (Synchronizer) (Droop Signal) (Etc.)

PID Feedback

Output To Actuator

PID

Actual Speed

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 59

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Summing Point z z z

z z

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 60

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Analog Electronic Speed Control Desired Speed +DC Volts

PID Feedback

Error Signal

PID

Summing Junction Actuator Actual Speed - D.C. Volts

Prime Mover Frequency to Voltage Converter

Generator

Magnetic Pickup AC Sine Wave Slide 61

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Digital Control System Block Diagram Setpoint (+)

PID Feedback Summing Junction

+ +

Error Signal

-

Adjustable Dynamics and Amplification

Output To Fuel Valve

-

PID

Actual (-)

The Thesetpoint setpointisisthe theonly onlyparameter parameteraccessible accessibleininthe theclosed closedloop loop system. system. The Thecontrol controlwill willforce forcethe theactual actualparameter parameterto tomatch matchthe the setpoint setpointby byactuating actuatingthe thefuel fuelvalve. valve. Slide 62

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Closed Loop Speed Control Speed Reference

Feedback

Generator

Servomotors Valve

Droop (Gate Position) Prime Mover

D.C. Volts

ZVPU Interface Module

15V 0V

Pulse Train

Zero Velocity Pickups Slide 63

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Closed Loop Speed Control z z z z

Actual 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 64

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Mechanical / Electrical Governor Comparison Pivot Points

Speeder Spring

Needle Valve

Electrical

Gain Reset

Rated Speed Pot

Mechanical

Generator

Summing Point

Error Signal

Servomotors Valve

Prime Mover Thrust Bearing

Flyweights

ZVPU Interface Module

Zero Velocity Pickups Pilot Valve Porting

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Slide 66

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HSS - LSS LSS Speed Control Temperature Control Accel Control High Limit

HSS

Output To Actuator

Decel Control Low Limit

Slide 67

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HSS - LSS z z z z

LSS = 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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Example of Temperature Limiting LSS

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Example of LSS z z z

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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Example LSS

Slide 71

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Example of HSS

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Example of HSS z z z

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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Example HSS

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What is a PID ? If you don’t understand the following equation / algorithm, then continue on. OUTPUT = Kc

1 e(t) + I

d e(t) e(t) dt + D dt

e=error, Kc = gain, I = integral, and D = derivative settings

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PID Tutorial z

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. Speed Reference or Desired Set - Point

Other Inputs (Load Sensor) (Synchronizer) (Etc.)

Error Output To Amplifier

Actual Speed

Feedback

PID

Output To Actuator

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PID Tutorial PID stands for Proportional, Integral, and Derivative. z A PID amplifier is used to calculate an appropriate response to the output based on changes to the input. z Controllers use PID’s to eliminate the need for continuous operator attention. z

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PID Tutorial z z

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.

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PID Tutorial

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PID Tutorial z z

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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PID Tutorial z z

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 setpoint.

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PID Tutorial z z

z

Reset - 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.

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PID Tutorial z z

z z

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 85

Governing Basics

PID Tutorial RESET ADJUSTMENT

SPEED

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GAIN ADJUSTMENT

COMPENSATION ADJUSTMENT

TIME Slide 86

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“Text Book” Dynamic Response

Slide 87

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“Text Book” Dynamic Response z

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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Governor Assumptions • Consistent fuel quality

Steam pressure, gas pressure, BTU value, etc.

•

Control of valves

•

Linkage

•

Linearity

•

Consistent machine geometry No change in dynamic response

Valves must be calibrated for zero to 100 percent travel Smooth travel No lost motion Linear flow for zero to 100 percent travel Power output linear with valve position

Slide 89

19671394 Governor Basics

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