lesson 1: steam turbine operation and control with mechanical governor
Summary
TLDRThis module delves into steam turbine operation and control, focusing on adjusting turbine speed and output. It explains that power output is controlled by modulating steam flow through admission valves. The script describes various valve arrangements, highlighting the benefits of multiple control valves for reducing throttling losses. It also introduces hydraulic control systems, mechanical governors, and their role in sensing turbine speed and adjusting control valves. The discussion includes governor set points, speeder gear adjustments, and their impact on turbine operation, promising more on the governor's effect on the electric power system in subsequent modules.
Takeaways
- 🔧 The principle of steam turbine control is to adjust the power output by varying the steam flow through the turbine.
- 💧 Turbine steam flow is controlled by adjusting admission valves or control valves, which can be a single valve or multiple valves in sequence.
- 🚀 In large turbines, multiple control valves are used to reduce throttling losses compared to using a single large control valve.
- 📍 Steam chests can be located above, below, or on either side of the turbine shell, with multiple control valves in each chest.
- 🛠 A stop valve is typically fitted at the entrance to each steam chest, remaining open during normal operation while control valves modulate steam flow.
- 📊 The opening of control valves is determined by the position of the operating lever, which is adjusted by the power cylinder of the hydraulic control gear.
- 🔄 A mechanical governor senses turbine speed and adjusts the control valve through a hydraulic servo mechanism in response to changes in speed.
- ⚙️ The governor's set point can be adjusted manually or remotely using a speeder gear, which affects steam flow and generator output when the turbine is on load.
- 🔄 A double relay type of pilot valve is often used in large turbines with multiple control valves to manage the significant power requirements.
- 🔧 The centrifugal governor is driven directly from the turbine shaft and adjusts the control valve through a pilot relay, influenced by the centrifugal force on weights.
Q & A
What is the primary method for controlling steam turbine output?
-The primary method for controlling steam turbine output is by adjusting the amount of steam admitted to the turbine through the turbine admission valves or control valves.
How does increasing the power output of a steam turbine relate to the steam flow?
-To increase the power output of a steam turbine, more steam must be passed through it, which is achieved by opening the control valves wider to allow more steam flow.
What is the purpose of having multiple control valves in a steam turbine arrangement?
-Multiple control valves are used to reduce throttling losses by opening them in sequence according to the turbine load, ensuring that only one valve is throttling steam at a time while the others are either fully open or closed.
Why are steam chests often positioned above and below the turbine shell in large turbines?
-In large turbines, steam chests are positioned above and below the shell, or on either side, to facilitate the use of multiple control valves and to manage the steam flow more effectively across the turbine.
What is the role of the stop valve in the steam chest during normal operation?
-During normal operation, the stop valve in the steam chest remains in the wide open position, allowing the steam chest to be charged with steam directly from the boiler while the control valves modulate the steam flow.
How does the hydraulic control system adjust the position of the control valves in a steam turbine?
-The hydraulic control system uses a power cylinder that is adjusted by the position of the operating lever, which in turn is controlled by the power cylinder of the hydraulic control gear, to open and close the control valves.
What is the function of a mechanical governor in a steam turbine control system?
-A mechanical governor senses turbine speed and adjusts the control valve through a hydraulic servo mechanism to maintain a constant speed by modulating the steam flow into the turbine.
How does the centrifugal governor respond to changes in turbine speed?
-The centrifugal governor responds to changes in turbine speed by moving the centrifugal weights inwards or outwards, which in turn lowers or lifts the pilot valve, allowing more or less high-pressure oil to enter the power cylinder and adjust the steam control valve.
What is the purpose of the speeder gear in adjusting the governor set point?
-The speeder gear allows for manual or remote adjustment of the governor set point, which influences the speed of the turbine when not synchronized to the power system or the steam flow when synchronized, maintaining constant generator output.
What is the significance of the double relay type of pilot valve in large turbines?
-In large turbines with multiple control valves, a double relay type of pilot valve is used to manage the significant amount of power required from the power cylinder, ensuring efficient and precise control of the control valves.
Outlines
🔧 Steam Turbine Operation and Control
This paragraph introduces the basics of steam turbine operation and control, focusing on how turbine speed and output are adjusted. The principle behind turbine control is straightforward: to increase power output, more steam is passed through the turbine, and to decrease it, less steam is admitted. The control valves, also known as admission valves, regulate steam flow into the turbine. In simple arrangements, a single control valve is used, but in more complex systems, multiple valves are employed, opening sequentially to manage steam flow efficiently. The hydraulic control system adjusts these valves based on the turbine's load. The paragraph also explains the use of a mechanical governor to sense turbine speed, which, through a series of mechanical and hydraulic actions, modulates the control valves to maintain the desired speed. The governor's set point can be adjusted manually or remotely using a speeder gear, which influences steam flow and, consequently, turbine speed and power output.
🛠 Governor and Control System Adjustments
This paragraph delves deeper into the governor mechanism, which is crucial for controlling the steam turbine. It describes a mechanical centrifugal governor that is connected directly to the turbine shaft and adjusts the control valve through a hydraulic servo mechanism. The governor's set point, which determines the turbine's speed, can be manually adjusted or controlled remotely using a speeder gear. When the turbine is not synchronized with the power system, adjustments to the governor's set point will change the turbine's speed. However, when synchronized, adjustments to the speeder gear primarily affect steam flow rather than generator speed, maintaining a constant output. The paragraph also hints at the discussion of different types of governors and their impact on the electric power system, which will be elaborated in the next module.
Mindmap
Keywords
💡Turbine Construction
💡Turbine Speed
💡Control Valves
💡Throttling Losses
💡Hydraulic Control System
💡Mechanical Governor
💡Centrifugal Weights
💡Power Cylinder
💡Steam Chest
💡Speeder Gear
Highlights
The principle of turbine control is to adjust steam flow to increase or decrease power output.
Turbine steam flow is controlled by adjusting admission valves or control valves.
In simple arrangements, one control valve regulates steam flow into the turbine.
Multiple control valves are used in most turbines to reduce throttling losses.
Control valves open in sequence according to the position of the cross-arm.
Large machines often have two steam chests, one above and one below the turbine shell.
Each steam chest in large machines has multiple control valves.
Stop valves are fitted at the entrance to each steam chest and remain open during normal operation.
The opening of control valves is determined by the position of the operating lever, adjusted by the hydraulic control gear.
A mechanical governor senses turbine speed and adjusts the control valve through a hydraulic servo mechanism.
Centrifugal weights in the governor move in response to changes in turbine speed.
The governor's set point can be adjusted by manipulating the compression on the spring.
Adjustments to the governor setpoint can be made manually or via a remote speeder gear.
When the turbine is on load, adjustments to the speeder gear affect steam flow but not generator speed.
The governor's effect on the electric power system will be discussed in the next module.
Different types of governors are used on various machines for turbine control.
Transcripts
[Music]
in the previous module we looked at the
main features of turbine construction
and the essential support systems now
it's time for us to turn our attention
to steam turbine operation and control
and we'll begin by looking at the means
of adjusting the turbine speed or
turbine output the principle of turbine
control is very simple if we need to
increase the power output of the turbine
we have to pass more steam through the
turbine conversely in order to decrease
power output it is necessary to decrease
the amount of steam admitted to the
turbine turbine steam flow is controlled
by adjusting the turbine admission
valves or control valves as they are
often called in the most simple
arrangement shown here we have one
control valve which depending on its
setting allows more or less steam to
flow into the turbine from the steam
chest when the turbine stop valve is
open the steam chest is charged with
steam directly from the boiler in most
turbines multiple control valves are
used as shown here in this particular
arrangement the steam chest is located
above the high-pressure end of the
turbine shell we can see here eight
valves and these are opened in sequence
according to the position of the
cross-arm which is itself adjusted by
the hydraulic control system these
control valves are set in such a manner
that only one valve at a time is
actually throttling steam while the
others are either fully open or closed
depending on the actual load the result
is that the throttling losses are
smaller than in the case where only one
large control valve is used in large
machines say greater than 100 megawatts
it is more common to have to steam
chests one above and one below the shell
or located one on either side of the
turbine in this case multiple control
valves are located in each steam chest
with steam lines connect
to the turbine shell at the
high-pressure end in most arrangements
of this type a stop valve is fitted at
the entrance to each steam chest during
normal operation the stop valve remains
in the wide open position while the
control valves are modulated to adjust
steam flow the actual opening of the
control valves is determined by the
position of the operating lever and this
in turn is adjusted by the power
cylinder of the hydraulic control gear
this schematic shows us a simplified
version of a hydraulic control scheme in
this particular arrangement a mechanical
governor is used to sense turbine speed
other types of Governors are also used
as we'll see in a moment in this
configuration a change of turbine speed
causes the centrifugal weights to move
for example a decrease in speed causes
the centrifugal weights to move inwards
and lower the pilot valve this in turn
allows more high pressure oil to enter
the power cylinder and raise the piston
against the compression spring this
movement of the power piston opens the
steam control valve and allows more
steam to enter the turbine which causes
its speed to increase also known as the
power piston Rises the reset lever lifts
the pilot valve back into the neutral
position again on large turbines with
multiple control valves a considerable
amount of power is required from the
power cylinder in this case its usual to
employ a double relay type of pilot
valve in this arrangement we have high
pressure oil above and below the piston
now when the position of the governor
spindle changes say for an increase in
speed the pilot valve lifts and allows
high pressure oil to flow into the space
above the power piston at the same time
the pilot valve exposes the space below
the piston to the oil drain and returns
the oil to the tank the high pressure
above the piston pushes it downward and
consequently moves the control valve in
the close direction at the same time it
also moved the reset lever to bring the
pilot valve back to neutral position so
prevented further movement of the
control valve now let's take a closer
look at the governor itself this
mechanical type centrifugal governor is
driven directly from the turbine shaft
through a gear drive as speed increases
the weights fly outward due to
centrifugal force and lift the sleeve
against the compression spring the
sleeve itself is connected to the pilot
relay which in turn adjusts the control
valve through the hydraulic servo
mechanism we can adjust the set point of
the governor by adjusting the
compression on the spring the adjusting
nut moves up or down on the cording to
rotation of the screw thread this action
can be performed manually at the turbine
or as is more usual well from a remote
position by operation of a small motor
drive known as the speeder gear this
name derives from the fact that when the
turbine generator is not synchronized to
the power system any adjustment of the
governor setpoint
will indeed alter the speed of the
turbine however when the turbine is on
load and the generator is synchronized
to other machines any adjustment of the
speeder year produces an imperceptible
change in generator speed instead this
action causes a change in steam flow
through the turbine with the constant in
generator output but we'll be talking
more about characteristics of the
governor and its effect on the electric
power system in the next module
another type of governor used on many
machines is
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