Governors Flashcards
True or false: Governors are mechanisms used to control and maintain the speed of a prime mover.
True
With governors, it is very important to verify that the overspeed trip functions correctly and that the fuel or steam supply does not pass by the trip valve. How is this done on small steam turbines?
By manually tripping the overspeed system and partially opening the supply valve.
If any steam or air passes by the trip valve, the overspeed trip may need adjustments or the trip valve and seat may need repair.
How would a governor shut off an engine in an overspeed situation?
By shutting the air inlet to the intake manifold.
True or false: Do not attempt to run up a prime mover without having a functional emergency trip system.
True
When placing a new governor into service, typically the only requirement for the millwright is to fill the governor reservoir with the proper oil and adjust the speed at initial start up. What is the recommendation for the speed setting at start up?
Set the speed lower than required, and increase as needed.
True or false: Typically, governors can be serviced in-house.
False
Some less complex mechanical governors can be serviced in-house, but most require being sent back to the OEM for servicing.
How can the operating speed be adjusted on simple mechanical governors?
By adjusting spring tension
The speed setting can be adjusted by varying the compressive force on the spring.
What are three things that should be checked on mechanical governors during a prime mover overhaul?
- Knife edges and pivot points are in good condition
- Sliding parts are not binding or sticking when moving
- Anti-friction bearings have no wear
This is for a prime mover overhaul ⟶ a governor overhaul should be completed by the OEM.
What does dirt or sludge in the housing of a governor usually indicate?
That it is time to dismantle and governor and perform a thorough cleaning and inspection.
In mechanical-hydraulic governors, large quantities of oil are continually circulated through the hydraulic side of the governor system. What issues can be caused by dirt and grit in the system?
Sticky relays, valves, or servo rams.
When should governors be overhauled (2 things)?
- During an engine or turbine overhaul
- Anytime there is contaimination in the hydraulic system
What are four things that should be done/checked when dismantling a governor and inspecting it for wear or damage?
- Replace all gaskets and seals
- Check linkages for smooth operation
- Clean and check all lines and passageways for blockages
- Flush all parts with the correct hydraulic oil
Some of the seals may break down in the presence of wrong oils.
What are six items that should be completed during routine preventative maintenance of a governor?
- Lubricate all linkages
- Replace worn parts
- Check all clearances
- Inspect the throttle valve
- Clean and inspect the trip valve
- Replace valve stem packing as needed
________ automatically control the speed of a prime mover under varying load conditions
Governors
What are three functions that a governor performs when automatically controlling the speed of a primer mover?
- Maintain the selected speed
- Limit the slow and fast speeds
- Shut down the prime mover if it over speeds
Identify the detection, transmission, and correction of this basic law mower governor:
Detection → vane
Transmission → the linkage
Correction → throttle valve
At start up, what would be the position of the fuel admission valve (steam admission valve, throttle valve, etc.) when controlled by a governor?
Fully open
The valve would be fully open
True or false: Governors operate on the principle of two opposing forces acting against each other.
True
These forces could be springs vs. airflow, etc.
True or false: Governors are fully open at start.
True
What three components are common to all types of automatic governor control?
- Detection
- Transmission
- Correction
All governors must include these three components.
True or false: Most governors on spark ignition engines allow an engine to fire steadily regardless of load, while varying the fuel to air ratio, either by speeding up or slowing down the engine.
True
What valve does the governor in a spark ignition engine actuate to control the speed?
The throttle valve
This valve is located in the intake passage between the carburetor and the manifold and controls the air-fuel mixture entering the engine.
What causes the diaphragm of a governor in a spark ignition engine to move?
Vacuum
Airflow into the engine ↑ = Vacuum ↑
When it comes to governors, what is the detection component of the governor?
This is what detects a change in the operating conditions of the prime mover
It is not the change itself (RPM, vacuum, airflow, etc.) rather what detects this change (diaphragm, flyweights, spring, etc.).
Is Brett gay?
a) He’s too grabby to be otherwise
b) It seems likely
b) It seems likely
This is to see if anyone is even doing these cards.
What are the two most common types of throttle valve governors?
- Vacuum (automatic)
- Flyweights (centrifugal)
These most commonly find use in engines.
Identify the detection, transmission, and correction of the following vacuum governor:
Detection → diaphragm
Transmission → linkage
Correction → Throttle valve
The diaphragm detects the change in vacuum due to an increase air flow into the engine.
What does a governor on a diesel engine change to regulate the speed of the engine?
The amount of fuel injected into the cylinders.
This usually adjusts the fuel rail, which rotates the plunger in the pumps.
Identify the sensing component of the following centrifugal mechanical governor:
Sensing → spring and flyweights
Sensing = detection
What would happen in a mechanical centrifugal governor if the spring were to break?
The governor would close, resulting in a slowing of the prime mover
What are the two independent speed control functions provided by governors on steam turbines?
- Operating the SAV (speed control)
- Over speed control
True or false: With a governor, a hydraulic cylinder controlling fuel flow belongs to the correction component of the governor.
False
This would be in the transmission component section.
The only things that will be found in the correction component section are things like throttle valves, SAVs, etc.
True or false: The overspeed trip mechanism must be verified as working before setting a new governors speed setting.
True
What are the two opposing forces that sense speed in a mechanical-hydraulic governor?
Spring pressure and centrifugal force
What is the angle formed between the flyweights and toes in a flyweight governor?
90º
What causes the spring to compress on the overspeed trip pin assembly?
Centrifugal force
What are the two opposing forces that sense speed in a diaphragm type governor?
Spring force and air (vacuum) pressure
What is the correction component of a governor on a steam turbine?
The SAV
Identify the detection, transmission, and correction components of the following mechanical-hydraulic governor:
Detection ⟶ the ballhead
Transmission ⟶ pilot valve/hydraulic fluid/spring
Correction ⟶ SAV
With gas turbines, the governors must control both the fuel flow as well as the acceleration and deceleration rates. Why is this?
Gas turbines do not respond well to quick changes in throttle position due to the inertia of the rotor.
If the governor controlled just fuel flow, if fuel flow was decreased too rapidly, it would result in a a too lean air-fuel mixture, and if increased too rapidly, would result in a too rich air-fuel mixture.
What are four parameters that must be monitored by a gas turbine governor?
- actuator position
- turbine rpm
- compressor air inlet temperature and pressure
- combustor or compressor discharge pressure
What is an isochronous governor?
A governor that maintains an exact, constant speed without any fluctuation.
Which type of governor would be selected if an exact, constant speed without any fluctuation was required?
An isochronous governor
This type of governor controls driver speed at any settings between a minimum and maximum speed, while still holding the driver at a steady speed.
A variable speed governor
What is the main difference between an isochronous governor and a variable speed governor?
The speed setting on a variable speed governor can be adjusted.
Once adjusted, a variable speed governor will hold the driver at a steady speed.
With a variable speed governor using flyweights to sense the speed, how is the speed selection adjusted?
By changing the force on the spring that opposes the centrifugal force on the flyweights.
This is usually done with a screw or lever that either reduces or increases the spring tension.
This type of governor is used to prevent overspeeding of the driver.
A speed-limiting control governor
These are common on diesel tractor-trailer units.
True or false: A speed-limiting governor will shut down the unit if it overspeeds.
False
A speed limiting governor does not shut down the unit if it overspeed, instead only limits the speed to a miximum.
What is the main use of pressure regulating governors?
To ensure constant pumping pressure on pipelines
When the pump runs faster, the pipeline pressure increases.
What are three ways that a pressure regulating control governor can sense pressure from the process?
- piston
- diaphragm
- bellows
How would the speed be adjusted on the following pressure regulating governor?
By varying the orifice size of the needle valve
This would allow more pressure to be bled off, resulting in less reaching the the fuel control device.
What are the two opposing forces in a pressure regulating governor?
Spring tension vs. process pressure
What would be the detection, transmission, and correction component in the following pressure regulating governor?
Detection ⟶ bellows
Transmission ⟶ rod between bellows and valve
Correction ⟶ fuel control device
This type of governor is used in electric power generating plants where a stable frequency must be maintained, regardless of wide and often rapid changes in load.
Electric load sensing governors
This adjusts the fuel to the generator to keep it at the same speed.
If the question says load, answer load, if it says speed, answer with speed.
This type of governor reacts to engine speed by measuring the frequency of the electric current produced by the generator.
Electric speed sensing governors
This adjusts fuel to the generator to keep it at the same speed.
If the question says load, answer load, if it says speed, answer with speed.
With electric load sensing and electric speed sensing governors, what electrical parameter are the governors trying to maintain?
Frequency
Both increase or decrease the speed of the prime mover to keep the frequency stabl at 60Hz.
What is happening what a governor is said to be “hunting”?
Where a governor causes an engine to speed up and slow down repeatedly
This governor characteristic requires a specific decrease or increase in speed before the governor tries to change the throttle valve.
Speed droop
This helps to reduce hunting
This governor characteristic is the variation in governor rotating speed from a no load to a full load setting, without the governor making a throttle adjustment.
Speed droop
This is usually expressed as a percentage of rated speed.
When it comes to governors, what is stability?
The opposite of hunting
The governor is maintaining a very stable speed.
Reducing the friction in a simple mechanical governor helps to correct dead band. Why is that?
Friction in the governor’s moving parts can dampen the governor’s responsiveness, causing delays in speed correction.
This results in the governor overcorrecting, which can lead to hunting.
Referring to a simple gravity-type flyball governor, once the force of gravity equals the centrifugal force of the flyballs, what happens to the throttle valve?
The fuel setting will not change
Once the forces are equalized, the throttle valve will change.
What are the opposing forces in a simple gravity-type flyball governor?
Gravity and centrifugal force
Referring to the more modern flyweight type of mechanical governor, what counterbalances the centrifugal force of the flyweights when the system is balanced?
compression on the speeder spring
Referring to a simple mechanical-hydraulic governor, what do the mechanical flyweights control directly in order to be capable of adjusting the speed?
spool valve
What are the toes of a modern day flyweight governor?
The component of the flywheel the converts the motion from centrifugal force acting on the flyweights into axial movement of the speed rod
How do the toes in modern flyweight governors transfer their rotation to the non-rotating speed spring?
Through an anti-friction bearing
What are the opposing forces in the following flyweight governor:
Centrifugal force vs. speeder spring
Why is it not a good idea to completely reduce the friction in a modern day flyweight governor?
It would result in hunting
The speeder spring and flyweight tend to oscillate like a pendulum after a speed change, and without any friction to stop this, it would appear that further speed corrections needed to be made when they didn’t ⟶ think vertical plumb bob in a bucket of oil
On a flyweight governor:
1. What holds the flyweights out?
2. What holds the flyweights in?
- centrifugal force
- spring tension
When these two forces are balanced, the control rod stops moving and delivery of steam/fuel to the prime mover stabilizes.
When a flyweight governor is used on a diesel system, what component does the governor control to limit fuel into the engine?
the fuel rack
This supplies the fuel to the injector pumps
What are the two main advantages of centrifugal governors?
- Simplicity
- Ruggedness*
*This makes it suitable for many applications
What are the three main disadvantages of a centrifugal governor?
- A large change in speed is required to change valve position
- They are comparatively insensitve
- There is a dead band area due the friction and clearances in the linkage
How can the force exterted by a flyweight governor be increased?
By increasing the size of the governor
This is practical to a certain size, which is where hydraulic governors come into play.
In mechanical centrifugal governors, anti-friction bearings have been installed at all joints to decrease friction along with mechanical oscillators to keep the system moving slightly. Why is it good for the governor linkage to always be moving?
To substitute static friction with kinetic friction
It takes much less force to change the direction of something already in motion (vs. something at rest). This results in the linkage being more sensitive to changes in the governor.
This type of governor uses a mechanical flyweight connected to a separate hydraulic system to supply the extra force needed to operate larger valves and linkages.
A mechanical-hydraulic governor
These can be used to operate multiple steam inlet valves on large turbines as well as govern diesel engines.
What does the mechanical flyweight in a mechanical-hydraulic governor control?
A pilot valve
This is turn controls the flow of oil from a separate hydraulic system into a simple reciprocating piston (servo piston).
- What does the pilot valve control on a mechanical-hyrdaulic governor?
- What does this activate?
- The flow of oil in the separate hydraulic system.
- The hydraulic oil activates servo piston (reciprocating piston) and servo spring, which activate the throttle valves
On the following mechanical-hydraulic governor, what is the detection, transmission, and correction?
- Detection ⟶ ballhead speed/speed droop linkage
- Transmission ⟶ pilot valve/hydraulic fluid/servo piston/servo spring
- Correction ⟶ The throttle valve
What is the main downside to a simple mechanical-hydraulic governor?
It is always hunting
The only equilibrium position is when the valve is fully closed ⟶ this is where oil is neither being admitted or released from the servo.
The simplest means of supplying stability to a mechanical-hydraulic governor is to add:
a speed droop
True or false: A simple mechanical flyweight governor that operates the throttle directly has a speed droop, since the only means of increasing the throttle is for the flyweights to move inward, which requires a decrease in speed.
True
This is due to the dead band caused by the friction and clearances in the linkage.
- How is a speed droop added to a mechanical-hydraulic governor?
- How does it work?
- By adding a mechanical linkage between the servo (which controls the throttle) and the governor speed setting
- When the servo moves, it also moves the lever, which reduces the speeder spring pressure, allowing the flyweights to move outward, which moves the pilot valve up and reduces flow to the servo piston
This essentially allows the governor to reduce fuel to the engine without needing the corresponding reduction in speed, as the movement of the servo piston closes the pilot valve instead of the a change from the flyweights.
What type of governor would be used in power generation applications that require a very exact singular speed?
An isochronous governor
The speed is constant regardless of load.
Hydraulic governors sense a change in ____________ to make the speed governing system work.
pressure
This pressure is usually supplied from a shaft mounted gear pump.
An increase in shaft speed of the prime mover will cause the hydraulic pump to
increase the flow
Since the pump is tied to the shaft speed, the pump output will be proportional to the shaft speed.
How is variable speed operation of a pure hydraulic governor achieved?
By changing the size of the restriction of a needle valve
This allows pressure acting on the throttle valve to be reduced or increased depending on how much is bled off.
On the following hydraulic governor, what is the detection, transmission, and correction?
Detection ⟶ dead-end bellows
Transmission ⟶ the linkage
Correction ⟶ throttle valve
With a variable hydraulic governor, opening the needle valve causes a(n) 1.________ (increase/decrease) in speed while closing the needle valve causes a(n) 2.________ (increase/decrease) in speed.
- increase
- decrease
This higher the pressure in the governor, the more the hydraulic pressure acts against the throttle valve, closing it ⟶ remember that governors start fully open.
The purpose of this component of a hydraulic governor is to strengthen the relatively weak pressure signal from the pump so that it is more easily measured.
The amplifier chamber
In a hydraulic governor, the pressure at which the amplifier valve will open is controlled by:
compression of the accelerator control spring
What part of a hydraulic governors system controls the final movement of the fuel control rod?
servo piston
On a hydraulic governor, what is the purpose of the orifice in the amplifier piston?
to cause a pressure increase
What is a major advantage of using electronics in any governing system?
The speed and accuracy with which the system can perfrom can perform variations in fuel delivery
What is a major advantage of an electrohydraulic governor?
It is easily adaptable to complex control requirements (better safety, sensing and process measurements).
What are the detection, transmission, and correction of an electronic governing system?
- Detection ⟶ sensors detect speed and/or load
- Transmission ⟶ system controller transmits sensor inputs and outputs signals for the actuator
- Correction ⟶ actuators move the fuel metering control
Sensors in electrohydraulic systems can be almost any speed sensing device, including AC and DC tachometers, speedometers, gear tooth counters, vibrating reeds and stroboscopes.
When a simple electric solenoid is energized, what will happen to the soft iron core?
It will be pulled into the coil by magnetic force.
The greater the current to the coil, the greater the magnetic attraction and the fruther the iron core will move into the coil.
A decrease in speed on a permanent magnet generator will cause the solenoid to:
be pushed out of the coil by spring force.
The decrease in speed will reduce the current to the coil, reducing the magnetic force pulling the iron core into the solenoid.
What component usually operates the pilot valve which then controls the flow of hydraulic pressure to activate the fuel control valve in an electrohydraulic governor?
A solenoid
This can receive current flow directly from an AC or DC tachometer or from a magnetic pickup.
Why is it common to have three magnetic pickups to sense speed on an electrohydraulic governor (2 reasons)?
- Redundency ⟶ if one fails, the system will still have sensing
- Maintenance ⟶ one can be calibrated/repaired without having to take the system offline
With an electrohydraulic governor with three magnetic pickups for speed sensing, how many pickups can fail before the system shuts down?
1
The system can still run with one pickup not working.
What is the purpose of the overspeed governor on a prime mover?
To prevent a runaway speed condition from occuring
True or false: Under normal operating conditions, a speed governor can react quickly enough to shut down a turbine if the load was suddenly removed.
False
This is why there is an overspeed governor installed in this type of machine.
True or false: To give the greatest degree of protection, the overspeed governor should be completely independent of the normal governor system.
True
Regulating the speed or load of a prime mover to keep it within normal operating limits is the purpose of the:
the governor
It is desirable to set the overspeed trip to operate at ____ above normal maximum operating speed.
10% to 15%
If the maximum speed is set lower than 10% of normal, that would be the overspeed setting.
A basic overspeed mechanical trip pin is held in the normal running condition by:
spring compression force being greater than the centrifugal force acting on the pin.
A hydraulic overspeed trip is usually activated by:
a mechanically operated trip pin.
Electronic overspeed trips are the system of choice when operating:
turbines above I0,000 rpm.
Mechanical governors are unreliable at speeds over 10,000 rpm
With an overspeed governor, where is the basic trip pin located?
Inside of a hole in a shaft
How does a trip pin in an overspeed governor trigger a shutdown in an overspeed condition?
The spring compression is overcome and thrown out by centrfugal force, triggering the trip pin/trip latch
This will close the stop valve, which is upstream of the SAV in the steam chest.
True or false: Under normal operating conditions, the trip pin is held inside the shaft by trip pin spring.
True
True or false: After an overspeed governor has tripped and slowed down the machine, it will automatically reset at a preset speed.
False
Overspeed governors need to be manually reset.
This type of overspeed governor is with larger systems that require larger valves.
A hydraulic overspeed governor
Hydraulic force is a natural choice due to its ease of control along with its unlimited force, which can move larger valves.
Which type of overspeed governor trip would be selected where problems with mechanical wear could not be tolerated?
An electric overspeed trip
Which type of overspeed governor can be tested and replaced without shutting down the equipment?
An electric overspeed trip
What is the primary application of electronic overspeed trips?
High-speed turbines
At what speed do mechanical governors become unreliable?
10,000 rpm and above
List three advantages of electronic overspeed trips.
- High degree of accuracy and repeatability
- Extremely fast response times
- Can be tested and replaced without shutting down equipment
True or False: Electronic overspeed trips are susceptible to temperature or humidity levels.
False
Fill in the blank: Electronic overspeed trips can store and display _______.
speed
What is a significant mechanical advantage of electronic overspeed trips?
No problems of mechanical wear
What is one maintence requirement that electronic overspeed trips eliminate compared to mechanical systems?
Constant adjustments
How do electronic overspeed trips compare in terms of testing and replacement when compared to mechanical overspeed trips?
Can be tested and replaced without shutting down equipment
What is the response time characteristic of electronic overspeed trips?
Extremely fast
- Many manufacturers recommend that the overspeed trip be tested ____ by overspeeding the turbine under control of the governor.
- How many times should this test be done?
- What precautions need to be taken with the driven machine?
- quarterly
- twice, and within a very small tolerace of the overspeed setting
- it should be uncoupled while the overspeed test is performed
On start-up, before steam is admitted into the turbine, what position do the flyweights on a mechanical governor have?
They are held close to the shaft
A new governor is installed on a turbine. What setting should the speeder spring be set to at the first start?
The minimum setting
What happens to the flyweights in a mechanical governor when the speeder spring compression is increased?
The flyweights move closer to the centre of rotation
What are the two opposing forces that sense the speed of a pump that is controlled by a hydraulic governor?
The fluid pressure from the pump and the compression force on the governor spring
What condition would cause the iron core in the solenoid of a electrohydraulic governor to move out of the coil?
A) An increase in turbine speed
B) A reduction in turbine speed
B) A reduction in turbine speed
Which action in an electronic governor does a gear tooth counter perform?
A) Transmission
B) Detection
C) Correction
B) Detection
A gas turbine has a normal operating speed of 8700 rpm and a maximum speed of 9150 rpm. What is the maximum speed that the overspeed trip should be set to for this turbine?
9150 rpm
