Governors Flashcards
The main purpose of a governor is to
control speed
A governor is meant to do one of three things
maintain the selected speed limit the slow and fast speeds shut down the prime mover if it overspeeds
governing system to be working properly it must perform a series of steps in the proper order. The correct order of these steps is
detection, transmission, correction
On a diesel engine governing system, an increase in engine speed will cause the governor to
react by restricting fuel flow
Which type of governor will maintain a constant speed without change?
isochronous
If a governor causes an engine to speed up and slow down repeatedly, the condition is known as
hunting
__________ is a governor characteristic that prevents hunting.
stability
Reducing the friction in a simple mechanical governor helps to correct a problem known as
dead band
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.
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
On start-up, before steam is admitted into the turbine, what position do the flyweights have?
They are held in close to the shaft.
In an overspeed situation, what does the governor react to do on a steam turbine?
totally shut off the flow of steam
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
The simplest means of supplying stability to a mechanical-hydraulic governor is to add
speed droop.
Hydraulic governors sense a change in __________ to make the speed governing system work
pressure
An increase in shaft speed of the prime mover will cause the hydraulic pump to __________.
increase the flow
The pressure at which the amplifier valve will open is controlled by
compression of the accelerator control spring.
What part of the system controls the final movement of the fuel control rod?
servo piston
What is the purpose of the orifice in the amplifier piston?
to cause a flow decrease
One of the major advantages of an electronic governing system is:
easily adapted to remote operation.
The reversible electric motor is much faster than the hydraulic servo. True or False
False
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.
A decrease in speed on a permanent magnet generator will cause the solenoid to:
be pushed out of the coil by spring force
Why is it common to have more than one magnetic pickup on a large steam turbine?
- If just one pickup quits working, the turbine will continue to run as long as there is a speed signal coming from the remaining pickups.
Regulating the speed or load of a prime mover to keep it within normal operating limits is the purpose of the:
governor system.
It is desirable to set the overspeed trip to operate at __________ above normal maximum operating speed.
10% - 15%.
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 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 10 000 rpm.
The main areas of concern for routine maintenance of mechanical governors are
keeping the mechanical governor clean, well lubricated and properly adjusted.
Sludge in the housing of a mechanical governor would be an indication of:
It is time for a thorough cleaning and inspection.
What kind of problems would be caused by dirt and grit in a hydraulic system?
sticky relays, valves and servo rams, along with leaky seals
When should the oil in a hydraulic governing system be changed?
whenever there is any change in oil quality
What is considered good recommended practice for storing spare governor parts for long periods of time?
Fill the parts with oil, if possible. If not possible, use desiccants to prevent oxidation and sludge build-up.
What is a governor?
- a device that will automatically control the speed of a prime mover under varying conditions of load
What three things can a governor do?
- maintain the selected speed, limit the slow and fast speeds, shut down the prime mover if it overspeeds
What three components should a governing system include?
- a speed-sensing device, a means to transmit this information, some type of device to operate the throttle (actuator)
Why won’t a simple flat vane governor like a lawn mower governor work in a steam turbine?
- because of the governing accuracy needed
What is the governor’s purpose?
- limit maximum engine speed, control idle speed to prevent stalling, supply enough fuel to be able to start the engine, supply additional fuel while the engine is running to prevent lugging, shut down the engine if it overspeeds
What are the two most common types of throttle valve governors?
- automatic or vacuum, and centrifugal
In a diesel engine what does the governor do to meter more or less fuel?
- It adjusts the fuel rack.
On a steam turbine what does the operating speed control or governor actuate?
- It will actuate the steam valves to speed up or slow down the turbine.
Load-limiting governors keep a constant engine speed while __________________ to the capacity of the engine.
- limiting the load
- Load control governors maintain the speed setting by ________________________ in such a manner that the amount of load applied to the driver is the correct predetermined amount for each speed range.
- adjusting the load-limiting device
- Isochronous is another term for __________________________________________.
- constant speed governing
- How does the variable speed closely resemble the constant speed governor?
- It closely resembles the constant speed or isochronous governor in that it holds the driver at a steady speed.
- The difference with the variable speed governor is that it can be __________ by the operator to maintain any __________.
- adjusted, selected speed
- Most variable speed governors use centrifugal __________, and the speed adjustment comes from changing the force on the __________ that opposes the centrifugal force of the flyweights.
- flyweights, spring
- What is the purpose of the speed-limiting governor?
- Speed-limiting governors are used to prevent overspeeding of the driver.
- The main use for pressure regulating governors is on ________________________ to ensure a constant pumping pressure.
- pipeline pumps
- Why are electric load sensing governors used in electric power generating plants?
- They are used where an absolute stable frequency must be maintained regardless of wide and often rapid changes in load
- The response again and again of repeated action (too fast, too slow, too fast, too slow) is known as?
hunting
governor characteristic that requires a specific decrease in speed before the governor tries to give an increase in throttle? is known as
- Speed droop
the change in speed that the driver must make before the governor makes a corrective action? known as
- Dead band
- The early mechanical flyball governor uses what force to overcome the resistance of gravity?
- centrifugal
- If the flyballs are shown at their outermost position, at what speed is the shaft going?
- high speed
- What is the major difference between a pure mechanical and a mechanical-hydraulic governor?
- The mechanical-hydraulic governor involves the addition of a separate hydraulic system to supply the extra force needed to operate larger valves and linkages.
- What is the purpose of the emergency trip mechanism on the governor?
- The emergency trip mechanism will shut the turbine down in an overspeed situation.
- How is the variable speed operation of a hydraulic governor obtained?
- by changing the size of this restriction (opening or closing the needle valve)
- What is the purpose of the high and low-pressure relief valves?
- control the fluid pressure on either side of the servo piston and keep it within operating limits
- What is the major advantage of electronics being used in any governing systems?
- the speed and accuracy with which the system can perform variations in fuel delivery
- What is the purpose of each of the following governing system three functions: the sensors: the system controller (computer): the actuator:
- Detects speed and/or load. Transmits and processes sensor inputs and generates an output signal for the actuator. Moves the fuel metering control to change fuel delivery
- Why is it common to have three magnetic pickups to sense speed?
- The controller can read all the signals and make adjustments according to all of the readings, the advantage being that if one pickup quits working, the machine will continue to run as long as there is a speed signal coming in from both of the remaining pickups. The pickups can be removed from service (1 at a time), while the turbine is running to perform maintenance and calibration checks.
- What two conditions could cause a turbine to overspeed?
- If the load were suddenly removed from an operating turbine, there is a possibility that the governor would not react quickly enough and the turbine could overspeed until it flies apart due to increased centrifugal forces. Any failure of the governor, linkages, or fuel control system could result in this runaway condition, which in turn, could cause turbine or engine damage, or in extreme cases, personal injury or loss of life.
- At what speed should the overspeed governor be set to trip?
- Set the overspeed trip to operate at about 10% to 15% above the normal maximum speed that the engine or turbine will reach under normal operating conditions.
- What should you do to check the operation of the overspeed trip?
- To ensure that it is working properly, test the overspeed trip at regular intervals by purposely allowing the turbine to overspeed under controlled test conditions.
- In an overspeed situation __________ moves out, due to centrifugal force, and hits the trip latch.
- the trip pin
- Why do electronic overspeed trips find their market niche with high-speed turbines?
- Mechanical governors become unreliable at speeds of 10 000 rpm and above
- State three main concerns with simple mechanical governors?
- They must be kept clean, well-lubricated, and in proper adjustment.
- Describe careful measurements in regards to adjusting nuts and spring lengths.
- Measure to ensure accurate relocation of adjusting nuts and installed spring length.
- Describe backlash setting.
- If the governor is driven through a set of bevel gears, the gear position should be checked and marked or recorded. Backlash should be checked at the designated temperature as it can change between hot and cold readings.
- Describe how the condition of the oil affects relays, valves, and servo rams.
- The oil must be kept free of dust, grit and other contaminants to prevent wearing of the close tolerances needed in hydraulic systems to control the oil flow. Dirt and grit in the system can also cause sticky relays, valves or servo rams.
- How often should a governor system be overhauled and how long can a governor system be expected to last?
- Overhaul should occur any time there is contamination in the hydraulic system. To keep the governing system operating at peak performance the governor should be overhauled whenever the engine or turbine is down for a major overhaul. A governing system with proper maintenance and overhauls can last indefinitely.
- Describe setting the mechanical trip pin.
- Loosening off the locknut and turning the adjusting nut either in or out to give more or less compression on the spring will change the speed that centrifugal force will throw the pin out. This is usually accomplished by trial and error by making a change to the setting and then running the turbine into overspeed and recording the trip operating speed. This test should be done at least twice and it should operate at the same speed each time within a small tolerance
