317 Questions
What material are nozzles usually constructed of in steam turbines?
Monel metal
What is the primary purpose of the convergent nozzle design in steam turbines?
Achieve specific exit pressure
How does the convergent-divergent nozzle achieve the required steam velocity in a steam turbine?
Through turbulence at the nozzle exit
What role do the stationary nozzles play in a simple impulse turbine?
They increase steam velocity
What happens if the exit pressure is less than the critical pressure in a convergent nozzle?
It produces eddy currents
What is the narrowest part of the convergent-divergent nozzle called?
Throat
What is the purpose of the nozzle in an impulse turbine?
To decrease the pressure of the steam and increase its velocity
What is the function of the buckets in an impulse turbine?
To convert the kinetic energy of the steam into mechanical energy
What produces an impulse force on the blade in an impulse turbine?
The change in the steam's direction
What are the two main disadvantages of a simple impulse turbine?
Extremely large centrifugal forces and large friction losses
How does the steam leave the nozzle in an impulse turbine?
In a high-speed jet
What causes the rotor of an impulse turbine to rotate?
The momentum transfer from the steam to the blades
What is the primary function of the nozzles in an impulse turbine?
To increase the pressure of the steam
In an impulse turbine, what is the role of the turbine blades?
To transfer momentum from the high-speed jet to produce impulse force
What is a significant disadvantage of a simple impulse turbine design due to high rotational speeds?
Excessive friction losses
Which component of an impulse turbine occupies the entire circumference of the rotor 'wheel'?
Buckets
In an impulse turbine, what is the impact of the steam's kinetic energy conversion by the buckets?
It converts into mechanical energy for rotor rotation
What is a significant issue associated with high velocity steam in a simple impulse turbine?
Large friction losses
What is the primary benefit of achieving the critical pressure in a convergent nozzle?
Preventing eddy currents from forming
What is the main difference between convergent and convergent-divergent nozzles?
Pressure drop requirements
What is the purpose of the steam chest in a steam turbine?
To direct steam to the nozzles
What happens to the steam volume as it passes through the divergent section of a convergent-divergent nozzle?
It increases
What is the relationship between the critical pressure and the inlet pressure in a convergent nozzle?
0.577:1
What is the primary purpose of the nozzle in a simple impulse turbine?
To accelerate the steam to high velocity
What is the distinguishing feature of a reaction turbine as described in the text?
Pressure drop across the moving blades
What problem arises from the pressure drops in a reaction turbine according to the text?
Leakage of steam around the tips of the blades
How is the blade shape of reaction blades different from impulse blades?
Reaction blades have a convex trailing edge becoming straight
What is required to prevent steam leakage around the edges of the blades in a reaction turbine?
Keeping blade clearances to a minimum
Why must an arrangement be made to balance the unbalanced thrust on the rotor of a reaction turbine?
Due to the pressure drop across the moving blades
What characteristic distinguishes reaction blades from impulse blades as per the text?
Entrance angle of almost 90°
What is the primary difference between impulse and reaction turbines?
Impulse turbines rely solely on the kinetic energy of the fluid, while reaction turbines rely on both kinetic and pressure energy.
What causes the container to move in the reaction effect demonstration?
The escape of steam through the opening creates an unbalanced pressure on the container walls.
What principle is the rotating wheel in Figure 7 based on?
Newton's Third Law of Motion
How does the steam expand in a reaction turbine?
The steam expands when it is forced through the stationary blades.
What is the primary function of the moving blades in a reaction turbine?
To receive an impulse from the steam.
What causes the steam to escape through the opening in the reaction effect demonstration?
The steam is pushed out of the opening due to the pressure difference inside and outside the container.
What is the distinguishing feature of a reaction turbine?
Pressure drop across moving blades
What must be kept to a minimum because of the tendency of steam to leak around the edges and tips of blades in a reaction turbine design?
Blade clearances
What causes an unbalanced thrust on the rotor in a reaction turbine, requiring balancing arrangements?
Pressure drop across the moving blades
What happens to the steam pressure and velocity across the moving blades in a reaction turbine?
Steam pressure decreases, velocity increases
What distinguishes reaction blades from impulse blades based on the description provided in the text?
Pressure drop across the blades
What type of blade edge do reaction blades have in comparison to impulse blades?
Rounded leading edge
What is the reaction force that causes a container to move in the reaction effect demonstration?
Steam pressure force
How does the principle of reaction causing rotation apply to a rotating wheel in the context of the text?
Pressure forces
What is the primary function of stationary blades in a reaction turbine?
Acting as nozzles
Which component of a reaction turbine receives an impulse from the steam?
Moving blades
What is the main cause of the wheel rotating around the center in a reaction turbine?
Reaction forces from escaping steam
In a reaction turbine, what is the purpose of the moving blades with the same shape as the nozzles?
Steam impulse reception
What is the primary reason for using multiple stages in an impulse turbine?
To reduce the steam and blade velocity
What is the effect of high steam velocities on the nozzles and blading?
High friction losses
What is the blade velocity required for maximum efficiency in a single-stage impulse turbine?
550 m/s
What is the purpose of partitions or diaphragms in a pressure-compounded impulse turbine?
To separate the moving blades from each other
What is the advantage of using multiple stages in an impulse turbine?
Reduced steam and blade velocity
What would be the result of using a single stage in an impulse turbine?
Excessively high rotational speed and centrifugal forces
What causes the steam to slow down after passing through the moving blades in a pressure-compounded impulse turbine?
Friction losses
What is the main difference between a pressure-compounded impulse turbine and a velocity-compounded impulse turbine?
The pressure drop across the turbine stages
What is the main advantage of a pressure-velocity compounded impulse turbine?
Reduced rotational speeds
How does the steam expand in a velocity-compounded impulse turbine?
In stages, with increasing velocity
What causes the steam to change direction in a velocity-compounded impulse turbine?
Stationary blades between rotating blades
What is the main difference between a simple impulse turbine and a pressure-compounded impulse turbine?
Number of stages
What is the primary function of the sets of blades in a pressure-compounded impulse turbine?
Decrease steam velocity
What is a common issue associated with high rotational speeds in simple impulse turbines?
Increased centrifugal forces
What is the role of the moving blades in a reaction turbine compared to an impulse turbine?
Moving blades in reaction turbines decrease steam pressure
What causes the unbalanced thrust on the rotor of a reaction turbine?
Uneven steam pressure on the moving blades
What is the advantage of employing multiple stages in a pressure-compounded turbine?
Improved efficiency by reducing centrifugal forces
In a velocity-compounded impulse turbine, what is the primary function of the stationary blades between the rotating blades?
To redirect the steam with minimal loss of velocity
What is the main purpose of pressure-velocity compounding in turbines that employ this method?
To reduce both steam pressure and velocity in stages
In a velocity-compounded impulse turbine, how does the speed of the rotating blades compare to a single-stage impulse turbine?
One half the speed
What characteristic distinguishes a velocity-compounded turbine from a simple impulse turbine in terms of managing steam velocity?
Reduction of steam velocity in stages
What does the arrangement of one velocity-compounded stage followed by four pressure-compounded stages on very large impulse turbines aim to achieve?
Gradual reduction of pressure across all stages
What role do the stationary blades play in each set of blades of a pressure-velocity compounded turbine?
To redirect the steam with minimal velocity loss
In a pressure-compounded turbine, why is it advantageous to decrease the centrifugal forces?
To reduce the wear and tear on the blades
How does the pressure-velocity profile differ between a pressure-compounded and a velocity-compounded turbine?
There is a minimal pressure drop in the nozzle stages of a pressure-compounded turbine
What effect does decreasing steam velocity have on the design of the rotating blades in a velocity-compounded turbine?
The rotating blades must be geometrically progressive
Why is pressure-velocity compounding beneficial in steam turbines that require low rotational speeds?
To utilize high steam pressures effectively
What method of staging in impulse turbines reduces the steam and blade velocities by causing the steam pressure to drop in two or more stages?
Pressure Compounding
Which of the following is a significant issue associated with using high velocity steam in a simple impulse turbine?
All of the above
Why is it important to keep the blade velocity as close as possible to half of the steam inlet velocity in an impulse turbine?
To increase the efficiency of steam-to-blade energy transfer
What is the purpose of the nozzles in an impulse turbine?
Increase the steam velocity
Which feature distinguishes reaction blades from impulse blades based on the description provided?
Reaction blades change the pressure of steam
Why are the moving blades separated by partitions or diaphragms in pressure-compounded impulse turbines?
To allow nozzles to be set for each stage
In a single flow turbine, how does the steam flow in relation to the turbine shaft?
In one direction only
What is the advantage of a double flow turbine design?
Eliminates end thrust due to pressure differential
Which type of turbine design aims to eliminate end thrust?
Double flow
What type of turbine design helps to counteract the pressure differential across blades?
Velocity-compounded
What is a distinctive feature of a double flow turbine?
Steam flows in two directions relative to the turbine shaft
Which combination is used to describe a large turbine that is both pressure-velocity compounded and double flow?
Pressure-velocity compounded, double flow
What distinguishes extraction turbines from other types of turbines?
They provide steam at a specific pressure for process or heating purposes
What is one distinguishing feature of a double extraction turbine?
It has two extraction points at two different pressures
Which type of turbine takes steam from a high-pressure source and reduces it to a lower pressure?
Topping turbine
What does the term 'Compounded Turbines' refer to?
The arrangement of two separate turbines where the exhaust of one becomes the inlet of the other
What is a common feature of cross compounded turbines?
They have reducing gears to increase RPM
What is the distinguishing feature of tandem compound turbines?
LP and HP turbines are coupled together on separate loads
What is the primary concern addressed by reheat turbines?
Danger of steam condensation in the HP turbine
Why is compounding used in relatively large turbine systems?
High RPM of a single turbine is not feasible
Which of the following is a common application of a topping turbine?
Supplying lower pressure steam while driving an electrical generator
What makes tandem-compound turbines suitable for very large turbine units?
They combine the power of LP and HP turbines to a single load
What type of turbine is used primarily in process plants and receives steam from a higher pressure header and exhausts directly into a lower pressure header?
Non-condensing turbine
What type of turbine is used when maximum power is required from a limited amount of available steam?
Condensing turbine
What type of turbine allows some flexibility in turbine load capability, with extra steam being added if the load demands more power from the turbine?
Mixed pressure condensing turbine
What type of turbine is used when there is no process use for the exhaust steam and/or maximum power is required from a limited amount of available steam?
Condensing turbine
What turbine type is used when the exhaust steam from the turbine can be used for process or heating purposes?
Non-condensing turbine
What type of turbine is used when steam is removed from the turbine at some intermediate point or points between the inlet and the exhaust?
Bleeder turbine
What type of turbine can have extra steam added if the load demands more power from the turbine?
Mixed pressure condensing turbine
What type of turbine is used when there is no process use for the exhaust steam?
Condensing turbine
What type of turbine exhausts steam into a condenser where the steam is then condensed by cooling, and the condensate is usually returned to the boiler as feed water?
Condensing turbine
What type of turbine uses additional steam added to the turbine part way between the inlet and exhaust, allowing some flexibility in turbine load capability, with extra steam being added if the load demands more power from the turbine?
Mixed pressure condensing turbine
What is a key advantage of a double flow turbine design compared to a single flow design?
It eliminates the need for end thrust due to pressure differential across blades.
What is the primary difference between extraction and bleeder turbines?
Bleeder turbines have the option for steam extraction for process use, while extraction turbines do not.
What distinguishes a topping turbine from a bottoming turbine?
Topping turbines are mostly used for electrical power generation, while bottoming turbines are used for industrial process heating.
How does pressure-velocity compounding in a turbine improve efficiency?
By allowing steam to expand in multiple stages before exiting the turbine.
What is the primary purpose of a reheat turbine?
To overcome thermal stresses during high-temperature operation.
What is a significant disadvantage of a single flow turbine design?
It lacks the ability to counteract end thrust due to pressure differential across blades.
What type of turbine is primarily used when the exhaust steam can be utilized for process or heating purposes?
Non-Condensing (Back Pressure) Turbine
In which turbine type is steam removed at some intermediate point between the inlet and the exhaust?
Bleeder Turbine
What is the application of a turbine that allows for flexibility in turbine load capability by adding extra steam when the load demands more power?
Mixed Pressure Condensing Turbine
What turbine design helps to counteract the pressure differential across blades?
Pressure-compounded impulse turbine
What is the purpose of the nozzle in an impulse turbine?
To increase the velocity of steam
What type of blade edge do reaction blades have when compared to impulse blades?
Sharper and curved
What is the role of the moving blades in a reaction turbine compared to an impulse turbine?
To create a reaction force
Which type of turbine is typically used in gas turbine combined cycle power plants to extract maximum heat?
Mixed Pressure Condensing Turbine
How does the principle of reaction causing rotation apply to a rotating wheel in the context of the text?
By accelerating the steam as it passes over the blades
What causes the unbalanced thrust on the rotor of a reaction turbine?
Pressure differences between inlet and outlet
What is the main purpose of a topping turbine?
To take steam from a high-pressure header and reduce it to a lower pressure
What distinguishes compounded turbines from other types of turbines?
The arrangement of two separate turbines in series
What is the primary difference between cross-compounding and tandem compounding?
In tandem compounding, the shafts of the LP and HP turbines are coupled together
What is the risk of condensation in a turbine that leads to the use of reheat turbines?
When the steam temperature leaving the HP section is close to the saturation temperature
What is the purpose of using a topping turbine when old, low-pressure boilers are replaced with new high-pressure boilers?
To provide lower pressure steam
What type of turbine is used primarily when there is no process use for the exhaust steam?
Condensing turbine
What distinguishes cross-compounded turbines from tandem compounded turbines in terms of speed?
Cross-compounded turbines operate at a higher RPM than tandem compounded turbines
What type of turbine is used when maximum power is required from a limited amount of available steam?
Condensing turbine
What is the main difference between impulse and reaction turbines?
Impulse turbines change the kinetic energy of the steam, while reaction turbines change the static energy
What is the purpose of the stationary blades in a reaction turbine?
To direct the steam onto the moving blades
Why are shaft seals necessary on steam turbines?
To prevent steam leakage where the shafts extend through the casings
Which material is commonly used for the sealing rings in a labyrinth seal?
Brass
What does a garter spring do in the context of carbon ring seals?
Holds the segments together by force
What is the purpose of the keyway in the carbon ring seal?
To prevent the rings from rotating with the shaft
Why are labyrinth seals preferred for sealing in large turbines?
To provide better sealing and less rubbing surface
What is the purpose of the springs in the labyrinth seals as shown in Figure 25?
To hold the stationary labyrinths against the shaft
Which factor determines the number of labyrinth sections used when the pressure drop is excessive?
Pressure drop across a turbine section
What is the function of steam pockets between labyrinth sections?
To carry leakage steam away from the seal
Why is gland seal steam used in condensing turbines?
To ensure air cannot leak into the condenser
How do labyrinth seals contribute to reducing steam leakage in turbine casings?
By forming sharp edges with minimal clearances to the shaft
What role does the impeller play in a water seal for a turbine?
The impeller rotates and throws out water to create a leak-proof water barrier
What is the primary purpose of a labyrinth seal in a steam turbine?
To stop air infiltration and allow a vacuum to be established
What is the main difference between 'straight' and 'stepped' labyrinth designs?
Stepped labyrinths have grooves in the rotating shaft
Why is gland steam necessary during turbine startup?
To prevent air infiltration and establish a vacuum before the water seal can operate properly
What type of labyrinth packing is used to reduce water and steam leakage?
Labyrinth packing attached to the casing
What is the primary function of the casing in a water seal for a turbine?
To hold water for the impeller to rotate in and create a leak-proof water barrier
What is the primary function of the turbine casing?
To contain the nozzles, stationary blade diaphragms, bearing cases, and external components
What is the most common design of turbine casing?
Horizontally-split casing
What is the purpose of the center line support in a horizontally-split casing?
To allow the casing to expand and contract evenly while maintaining alignment
Why are the walls of the turbine casing made of relatively thick metal?
To withstand high pressures and temperatures
What happens to the wall thickness of the turbine casing towards the LP end of the turbine?
It becomes gradually thinner
What is a significant consideration in the design of turbine casings?
Resisting distortion under high pressure and temperature conditions
What is the primary purpose of the sentinel valve in a steam turbine?
To warn the operator that casing pressure is abnormally high
What is the main advantage of using double casings in high-pressure steam turbines?
Reduced thermal stresses on casings and flanges
What is the purpose of machining grooves in the casing for impulse turbines?
To contain the diaphragms
What is the maximum allowable wetness in the exhaust steam of modern turbines?
14%
What is the purpose of dowel pins in casing joints?
To secure exact alignment of the flange joint and bolt holes
Why are high-pressure casings made of cast alloy steel?
Because it can withstand temperatures above about 550°C
What is the purpose of boring mills in casing construction?
To machine the inside of the casing
What is the primary purpose of casing drainage?
To allow free water to drain to the condenser
What is the purpose of steam flowing through channels in the flanges or axially drilled holes in high-pressure casings?
To overcome the problem of distortion and leakage
What is the primary role of the flanges in high-pressure casings?
To withstand high pressure and temperature
What is the primary function of the horizontally split casing in a turbine?
Facilitate assembly and inspection
Why are turbine casings made of relatively thick metal?
To withstand high pressures and temperatures
What design aspect must the turbine casing take into consideration regarding blade clearances?
Expanding during operation
How does the horizontally split casing support turbine alignment?
By allowing even expansion and contraction
What is the role of the turbine casing in relation to start-up and shutdown procedures?
Resisting distortion
Why is the wall thickness of the turbine casing sometimes made gradually thinner towards the exhaust end of the turbine?
To improve blade clearances
What is the primary function of a garter spring in a carbon ring seal?
Hold the carbon rings together axially
Why are carbon rings generally limited to shafts less than 150 mm in diameter?
To reduce the wear caused by heat generated as the rings ride on the shaft
In a labyrinth seal, what is the purpose of having the rings tapered toward the outer periphery?
To provide a sharp sealing edge
Why are labyrinth seals commonly used in large turbines?
To mitigate steam leakage and maintain turbine efficiency
Why are labyrinth seals beneficial for ensuring turbine efficiency?
To minimize the rubbing surface if the shaft is eccentric
What happens to the leakage steam when multiple labyrinth sections are used in a turbine?
It is discharged to an external location to maintain seal efficiency
Why are small hard-to-pass clearances preferred in labyrinth seal designs?
To minimize rubbing and wear on the rings
What is the material commonly used for the rings in labyrinth seals?
Brass
Why are springs included in the design of labyrinth seals as shown in Figure 25?
To hold the labyrinth rings against the shaft
What is the main difference between carbon rings and labyrinth seals as sealing methods in steam turbines?
Method to prevent steam leaks
What is the primary function of the impeller in a water seal for a turbine?
To spin and throw out water, creating a leak-proof barrier
What is the distinguishing feature of stepped labyrinths in comparison to straight labyrinths?
Stepped labyrinths have longer sealing rings that fit into grooves
What is the main purpose of using clean, cool condensate for water seals in turbines?
To minimize contamination and maintain barrier integrity
What role does the spring play in labyrinth seals, as shown in Figure 25?
To push the sealing rings against the shaft
What is the primary difference between the leakage prevention mechanisms in carbon rings, labyrinth seals, and water seals?
Carbon rings and labyrinth seals permit some leakage, while water seals allow none
What effect does the addition of grooves in the rotating shaft have on the performance of labyrinth seals?
It creates an even more difficult path for escaping steam
Which type of casing flange design is used to minimize thermal stresses in high-pressure casings?
Flange heating by steam
What is the purpose of the sentinel valve in a steam turbine?
To warn the operator of abnormally high casing pressure
Which type of turbine is used for applications with no process use for the exhaust steam and requires maximum power from a limited amount of available steam?
Velocity-compounded impulse turbine
What is the main difference between convergent and convergent-divergent nozzles in a steam turbine?
The difference in their expansion process
What is the primary purpose of a horizontally-split casing in a steam turbine?
To facilitate easy removal and installation of turbine components
Which type of turbine is used to allow flexibility in turbine load capability by adding extra steam if the load demands more power?
Velocity-compounded turbine with multiple stages
What is the main purpose of using a topping turbine when old, low-pressure boilers are replaced with new high-pressure boilers?
To allow for a better match between the steam conditions and the turbine
Which type of turbine is used when maximum power is required from a limited amount of available low-pressure steam?
Velocity-compounded impulse turbine
What component of a reaction turbine receives an impulse from the steam, allowing it to rotate?
The rotating blades
What material are the sealing strips in a reaction turbine typically made of?
Chrome-iron alloy
What is the purpose of the radial fins on the rotating blades in a reaction turbine?
To minimize leakage between the blade tips and the casing
What type of blades are designed with a knife-edge seals in a reaction turbine?
The stationary blades
What is the function of the locks or serrations in a reaction turbine?
To prevent the movement of the stationary blades
What component is used to hold the sealing strips in their respective grooves in a reaction turbine?
The caulking strips
What is the purpose of the labyrinth seal in a reaction turbine?
To prevent the leakage of steam across the blade tips
What is the primary function of the discs in a disc rotor?
To attach the moving blades in an impulse turbine
What is the purpose of the machined groove on the outer circumference of each disc?
To attach the moving blades
Why are there suitable clearances left between the hubs of the discs?
To allow for disc expansion along the line of the shaft
What is the advantage of producing disc rotors as a single, solid forging?
It reduces the number of moving parts
Why are the discs shrunk or keyed onto the shaft?
To securely attach the discs to the shaft
What is the purpose of the central section of each disc, also known as the hub?
To be shrunk or keyed onto the shaft
What is the primary reason for using a drum rotor design in reaction turbines?
To eliminate surface areas that could cause thrust
What is the purpose of shrouding in an impulse turbine?
To strengthen the assembly and stabilize the ends of the blades
How are the nozzles attached to the diaphragm in an impulse turbine?
By rivets and screws
What is the purpose of sealing in an impulse turbine?
To direct the steam flow and ensure best efficiency
What type of design is typically used for large, high-pressure rotors?
Solid, forged and machined disc rotor
Why is a solid, forged and machined disc rotor design expensive?
Due to the machining process that wastes about 50% of the initial forging
What is the purpose of the drum end cover with shaft in a hollow drum rotor design?
To install with a shrink fit and then weld in place
What is the advantage of the welded drum rotor design shown in Figure 30?
Greater resistance to centrifugal forces
What is the purpose of the diaphragm in an impulse turbine?
To mount the stationary blades or nozzles
What is the purpose of the machined groove on the outer circumference of each disc on a disc rotor?
To attach the blades
Why are suitable clearances left between the hubs of the discs in a disc rotor?
To allow for disc expansion
How is the wider, central section of each disc (the hub) attached to the shaft in a disc rotor?
Shrunk or keyed onto the shaft
What distinguishes impulse turbines from reaction turbines regarding pressure drop?
No pressure drop occurs across the moving blades in impulse turbines
In a disc rotor with individually mounted discs, what is the purpose of the 'steps' machined onto the shaft?
To accommodate the discs with different diameters
Why is there no axial thrust on the turbine shaft in impulse turbines with disc rotors?
No pressure drop across the individual discs
What is the primary purpose of the radial fins on the rotating blades in a reaction turbine?
To minimize leakage between the blade tips and the casing
What material is commonly used for the sealing strips in reaction turbines?
Chrome-iron alloy
What is the purpose of the locking strip on one side of the root in a drum type rotor?
To tighten the blades solidly in the grooves
What is the effect of the pressure differential across the blades in a reaction turbine?
It causes steam leakage across the blade tips
What is the purpose of the knife-edge seals in a reaction turbine?
To minimize steam leakage between the rotating and stationary blades
What type of design is used for the sealing strips in reaction turbines?
Knife edge design
What is the primary purpose of the shrouding in an impulse turbine?
To strengthen the assembly and stabilize the ends of the blades
What is the advantage of using a drum rotor design in reaction turbines?
It eliminates surface areas that could cause thrust
How are the nozzles secured in the diaphragm in an impulse turbine?
By rivets and screws
What is the purpose of the diaphragm in an impulse turbine?
To attach the stationary blades
Why is the center opening of the disc made slightly smaller than the shaft diameter?
To allow for uneven expansion between the shaft and the discs
What is the purpose of machining the main part of the drum in a hollow drum rotor design?
To ensure good balance and reduce weight
What is the advantage of using a solid, forged and machined disc rotor design?
It creates a strong, fully balanced rotor
Why are labyrinth seals used in reaction turbines?
To seal the steam flow
What is the purpose of the drum end cover with shaft in a hollow drum rotor design?
To provide additional support to the rotor shaft
What is the primary reason for using a double flow turbine design?
To reduce the end thrust on the turbine rotor
What is a common method for counteracting thrust in turbines?
Using thrust bearings, dummy pistons, and thrust adjusting gear
What is the main purpose of a thrust bearing in a turbine?
To keep the rotor in an exact position in the casing and absorb any axial thrust
What is a characteristic of a reaction turbine?
There is a considerable pressure drop across each row of moving blades
What is the function of the radial fins on the rotating blades in a reaction turbine?
To improve the efficiency of the turbine by reducing the leakage steam
What is a common application of a topping turbine?
When old, low-pressure boilers are replaced with new high-pressure boilers
What type of bearing is used when tandem compound turbines are joined together by a solid, non-flexible coupling?
Simple thrust bearing
What is the function of the dummy piston in a reaction turbine?
To balance the thrust force by exerting a force in the opposite direction
What is the purpose of the labyrinth seals around the circumference of the piston?
To prevent steam leakage
Which type of bearing uses a number of tilting pads attached to a stationary plate?
Kingsbury thrust bearing
What is the primary advantage of a dummy piston in a reaction turbine?
It helps maintain the balance condition at all turbine loads
What is the function of the thrust adjusting gear in a reaction turbine?
To maintain the relative position of stationary and rotating blades
What is the main difference between pressure-compounded impulse turbines and velocity-compounded impulse turbines?
The number of stages of expansion the steam goes through
What is the primary function of the impeller in a water seal for a turbine?
To facilitate the flow of cooling water
What is the primary difference between extraction and bleeder turbines?
The process use of the exhaust steam
What type of flange design is used to minimize thermal stresses in high-pressure casings of steam turbines?
Convergent nozzle design
What is the primary purpose of a thrust bearing in a turbine?
To absorb any axial thrust on the rotor
In a double flow turbine design, what happens to the steam admitted midway along the turbine casing?
It flows axially towards each end of the turbine
Why is the thrust in reaction turbines more severe than in impulse turbines?
Because of the high pressure drop across each row of moving blades
What is the benefit of placing the thrust bearing at the steam inlet end of a turbine?
It ensures the shaft is free to expand in one direction
What is the purpose of opposing rows of blading in a double flow turbine design?
To cancel the opposing thrusts created in each half of the turbine
What is the primary purpose of counteracting thrust in a turbine?
To prevent the moving and stationary parts from contacting each other
What is the primary purpose of the dummy piston in a reaction turbine?
To balance the thrust force
What type of bearing is used in impulse turbines where thrust is minimal?
Sleeve bearing with radial Babbitt faces
Why are labyrinth seals used around the circumference of the dummy piston?
To prevent steam leakage
What is the purpose of the thrust adjusting gear in a reaction turbine?
To control the axial position of the shaft
How does the Kingsbury thrust bearing handle the axial thrust and radial load?
Using multiple tilting pads
What is the primary purpose of the axial seals in a reaction turbine?
To prevent damage or excessive wear
What is the purpose of the balance pipe connected to the dummy piston?
To balance the thrust force
What type of bearing is used in reaction turbines that require more substantial designs?
Kingsbury thrust bearing
Why are grooves fitted on the thrust surfaces of the bearing in an impulse turbine?
To permit more efficient distribution of lubricating oil
Which type of turbine is used when a large demand for lower pressure steam exists?
A straight, non-condensing turbine
What is the primary characteristic of a double extraction turbine?
It is rated at 3955 kW and 3600 r/min
What type of turbine is primarily used when there is no process use for the exhaust steam?
A velocity-compounded impulse turbine
What is the primary function of the governing system in a straight, non-condensing turbine?
To control the turbine's steam output
What is a common application for a straight, non-condensing turbine?
When there is a large demand for lower pressure steam
How is the steam output of a straight, non-condensing turbine controlled?
By controlling the process steam pressure
What is the speed range of the General Electric Company mechanical drive turbines?
1000 rpm to 6500 rpm
What is the purpose of the row of stationary blades between the two rows of moving blades in Figure 39?
To direct the steam flow
What is the power rating of the 28 cm blade wheel diameter turbine shown in Figure 40?
90 kW
What type of turbine is shown in Figure 41?
Velocity-compounded impulse turbine
What is the function of the Anti-Friction Thrust Bearing in Figure 41?
To absorb the thrust
What is the purpose of the Governor Lubrication system in Figure 41?
To lubricate the moving parts
What is the main purpose of the stationary blades in the mechanical drive turbine illustrated in Figure 39?
To reverse the direction of the steam flow
What distinguishes the mechanical shaft governor from the oil reservoirs in the mechanical drive turbine components list?
Control over turbine speed
In the small industrial mechanical drive turbine manufactured by Skinner Engine Co., Dean Hill Turbine Division, what is the significance of the blade wheel diameter being 28 cm?
It determines the power output of the turbine
What distinguishes metric fasteners from labyrinth-type bearing case seals in the mechanical drive turbine illustrated in Figure 39?
Size and material composition
What feature differentiates the Skinner Engine Co., Dean Hill Turbine Division turbines from General Electric Company turbines?
The steam pressure and temperature requirements
What is the primary function of governor coupling in a mechanical drive turbine?
To aid in the control of turbine speed based on load variations
What is the primary purpose of the turbine shown in Figure 43?
To provide process steam to nearby industries
What happens when the steam demand drops in the system with the turbine shown in Figure 43?
The turbine reduces its output accordingly
What is the primary advantage of the design shown in Figure 43?
It can provide process steam at a lower pressure
What is the rating of the turbine shown in Figure 42?
3955 kW and 3600 r/min
What type of turbine is shown in Figure 42?
Double extraction turbine
How many impulse wheels are used in the turbine shown in Figure 42?
Two
What is the primary purpose of helical gears in a speed reduction gearbox?
To mesh more easily and smoothly
Why are gears sometimes cut in a 'double helical' or 'V' pattern in situations with potential excessive thrust?
To eliminate thrust
In a speed reduction gearbox, when might a double-reduction gear be used?
When a very large speed reduction is needed
How many speed reduction steps are there in a single-reduction gear system?
One
What design feature helps reduce gear noise and vibration in a speed reduction gearbox?
Helical gears
What is the function of a pipe supplying oil mist to gears in a speed reduction gearbox?
To reduce gear noise and vibration
What is the purpose of a reduction gear set in steam turbines?
To decrease the speed at the driven shaft
In a reduction gear set, what role does the pinion gear play?
It has fewer teeth than the driven gear
How does the ratio of gear teeth affect the rotational speeds of a reduction gear set?
The lower the ratio, the higher the driven shaft speed
Where are reduction gear sets typically housed in medium and large-sized steam turbines?
In an oil tight casing separate from the turbine
In a reduction gear set, what is the purpose of the larger gear attached to the output shaft?
To reduce the speed at the driven shaft
What is the effect of having the turbine shaft and the driven shaft rotate at the same speed in a reduction gear set?
The driven shaft spins slower than the turbine shaft
What is the primary reason for using a double flow turbine in a steam turbine system?
To balance the axial thrust
Which of the following is a common application of a topping turbine?
Turbine driven direct current generators
What is the primary role of the flanges in high-pressure casings?
To prevent leakage of steam
What is the purpose of the labyrinth seal in a reaction turbine?
To prevent leakage of steam
What is the distinguishing feature of a pressure-compounded impulse turbine?
The use of multiple stages
What is the main purpose of using a topping turbine when old, low-pressure boilers are replaced with new high-pressure boilers?
To increase the pressure of the steam
What is the primary purpose of the helical design in gears?
To reduce gear noise and vibration
What is the purpose of the "double helical" or "herringbone" gear pattern?
To eliminate thrust on the gears and shafts
In a double-reduction gear, how many gears and shafts are used?
Three gears and two shafts
What is the direction of rotation of the driven shaft in a situation that requires three gears?
Same as the turbine shaft
What is supplied to the gears at their mesh point in Figure 45?
Oil mist
What is the primary function of the gear reducer in Figure 44?
To decrease the speed of the driven machine
Study Notes
Impulse Turbine Operating Principles
- High-pressure steam expands through a stationary nozzle, dropping pressure and increasing velocity.
- The high-velocity steam is then applied to a properly shaped turbine blade, changing the steam direction and transferring momentum to the blade.
- This produces an impulse force on the blade, causing movement.
- If the blade is attached to the rotor of a turbine with no restriction to movement, the rotor will rotate on its shaft.
Impulse Turbine Nozzles and Buckets
- A turbine has many blades (buckets) attached to the rotor and many nozzles attached to the casing.
- Nozzles supply high-velocity steam to the buckets, which occupy the entire circumference of the rotor wheel.
- Buckets convert the kinetic energy of the steam into mechanical energy, causing the shaft to rotate.
- Two disadvantages of simple impulse turbines are:
- Extremely large centrifugal forces on the buckets due to high rotational speeds.
- Large friction losses due to high velocity of the steam.
Steam Nozzles
- Nozzles are constructed of Monel metal, a nickel-copper alloy with high tensile strength.
- Passages that direct steam to the nozzles are located outside the casing and are referred to as the steam chest.
- There are two nozzle designs for steam turbines:
- Convergent nozzles, used for relatively small pressure drops.
- Convergent-divergent nozzles, used when larger pressure drops are required.
Convergent Nozzles
- The convergent shape of the nozzle causes the steam pressure to drop and the steam velocity to increase.
- In a well-designed convergent nozzle, the pressure should drop to a specific exit pressure, called the "critical pressure", which is 0.577 times the inlet pressure.
Convergent-Divergent Nozzles
- The convergent-divergent nozzle design is used when larger pressure drops are required.
- When properly designed, the pressure at the nozzle throat (the narrowest part of the nozzle) should be at the critical pressure.
- The pressure then continues to drop in the divergent section of the nozzle, and the velocity increases across the entire nozzle.
Impulse Turbine Pressure-Velocity Profile
- The pressure-velocity profile of a simple impulse turbine shows the change in pressure and velocity as the steam passes through the stationary nozzles and then the moving blades.
- The velocity increases sharply in the nozzles.
Reaction Turbine Operating Principles
- The moving blades of a turbine are shaped to expand steam and drop pressure, producing a reaction force on the blades.
- The reaction effect can be illustrated by considering a container filled with high-pressure steam, which will move if there is an unbalanced pressure on the walls.
- In a reaction turbine, steam expands and the pressure drops as it passes through the moving blades, producing a reaction force.
Reaction Blading
- A reaction turbine has rows of stationary blades alternating with rows of moving blades.
- The stationary blades act as nozzles, and the moving blades receive an impulse from the steam and produce a reaction force.
- The steam expands first in the stationary blades, gaining velocity as the pressure drops.
- The steam then enters the moving blades, where the direction of flow is changed, producing a force on the blades.
Reaction Turbine Pressure-Velocity Profile
- The pressure-velocity profile of a reaction turbine shows the change in pressure and velocity as the steam passes through the stationary blades and then the moving blades.
- The steam pressure can be seen to decrease across both the stationary blades and the moving blades.
- The absolute velocity increases in the stationary blades, but decreases in the moving blades.
- The distinguishing feature of the reaction turbine is the pressure drop across the moving blades.
Impulse Turbine Staging
- In an impulse turbine, the steam must transfer all of its kinetic energy to the moving blades, which would require excessively high rotational speeds.
- To avoid this, the steam and blade velocities may be reduced using one or more of the following methods:
- Pressure compounding
- Velocity compounding
- Pressure-velocity compounding
Pressure Compounding
- Pressure compounding reduces steam and blade velocity by causing the steam pressure to drop in two or more stages.
- Two or more impulse stages are used in series, inside a single casing.
- The advantages of pressure-compounded turbines are:
- Increased efficiency
- Reduced centrifugal forces
- Ability to design for a wide range of inlet steam conditions
Velocity Compounding
- Velocity compounding reduces the steam velocity in stages.
- It consists of one set of stationary inlet nozzles, a rotor containing two sets of rotating blades, and a set of stationary blades between the rotating blades.
- The total pressure drop occurs in the stationary inlet nozzles, and the pressure then remains constant across the three sets of blades.
- The advantages of velocity compounding are:
- Reduced steam velocity
- Lower rotational speed
- Larger size of the second set of rotating blades
Pressure-Velocity Compounding
- Pressure-velocity compounding reduces both the steam pressure and steam velocity in stages.
- It consists of two or more velocity-compounded sections (stages) in series on the same shaft, within one casing.
- The main advantage of pressure-velocity compounding is that high steam pressures can be utilized to obtain relatively low rotational speeds.
Velocity and Pressure Stages
-
On very large impulse turbines, it is common to employ another arrangement of velocity-pressure compounding, in which a velocity-compounded first stage is followed by several pressure-compounded stages.
-
This arrangement allows for high steam pressures and relatively low rotational speeds.### Impulse Turbine Staging
-
In an impulse turbine, the steam must leave the moving blades at the lowest possible velocity to transfer all its kinetic energy.
-
The lowest velocity occurs when the blade velocity is equal to half the steam inlet velocity to the blades.
-
If the steam expands from inlet pressure to final exhaust pressure in a single stage, the velocity of the steam leaving the nozzles could be about 1100 m/s, requiring excessively high rotational speed.
-
To avoid high centrifugal forces and friction losses, the steam and blade velocities may be reduced using pressure compounding, velocity compounding, or pressure-velocity compounding.
Pressure Compounding
- Pressure compounding reduces steam and blade velocity by causing the steam pressure to drop in two or more stages.
- Two or more impulse stages are used in series, inside a single casing.
- The rows of moving blades are separated by partitions or diaphragms, into which the nozzles are set.
- Advantages of pressure-compounded turbines include increased efficiency, reduced centrifugal forces, and flexibility in design for a wide range of inlet steam conditions.
Velocity Compounding
- Velocity compounding reduces the steam velocity in stages.
- It consists of one set of stationary inlet nozzles, a rotor containing two sets of rotating blades, and a set of stationary blades between the rotating blades.
- The total pressure drop occurs in the stationary inlet nozzles, and the pressure remains constant across the three sets of blades.
- Reducing the steam velocity in two stages results in a lower rotational speed and larger blade size.
Pressure-Velocity Compounding
- Pressure-velocity compounding reduces both steam pressure and velocity in stages.
- It consists of two or more velocity-compounded sections in series on the same shaft, within one casing.
- Advantages of pressure-velocity compounding include the ability to utilize high steam pressures to obtain relatively low rotational speeds.
Turbine Arrangements
- Velocity-compounded first stage followed by pressure-compounded stages is a common arrangement for large impulse turbines.
- This arrangement allows for a large number of stages without excessively large disc or casing diameters.
Turbine Types
- Non-condensing (backpressure) turbines are used when the exhaust steam can be used for process or heating purposes.
- Condensing turbines are used when there is no process use for the exhaust steam and maximum power is required.
- Bleeder turbines are used when steam is removed at some intermediate point between the inlet and exhaust.
- Mixed pressure condensing turbines are used when additional steam is added to the turbine part way between the inlet and exhaust.
Classification of Turbines
- Type of blading: impulse, reaction
- Type of compounding: velocity, pressure, or a combination of both
- Direction of steam flow along the axis: single flow or double flow
- Exhaust condition: condensing, non-condensing
- Steam flows to/from the turbine: extraction, bleeder, reheat, topping, etc.Here are the study notes for the text:
Extraction Turbines
- Used primarily in process plants where steam from the turbine is used at a specific pressure for process or heating purposes
- Controlled amount of steam is extracted at one or more points to provide the required pressure
- Can be condensing (Figure 15, “E”) or non-condensing (Figure 15, “F”)
- Can have a single extraction point (Figure 15, “F”) or two extraction points at different pressures (Figure 15, “E”), known as double extraction turbines
Topping Turbines
- A type of backpressure turbine that takes steam from a high-pressure header and reduces it to a lower pressure for process or turbine use
- Provides lower pressure steam while driving an electrical generator
- Used when old, low-pressure boilers are replaced with new high-pressure boilers, but part of the process still requires the original steam pressure
Compounded Turbines
- Arrangement of two separate turbines where the exhaust steam from one becomes the inlet steam for the other
- Used in large systems where design conditions and demands would prohibit using a single turbine
- Two basic arrangements: cross-compounding and tandem compounding
- Cross-compounding: separate turbines with their own shafts, each driving an electrical generator (Figures 16 and 17)
- Tandem compounding: shafts of LP and HP turbines are coupled together (Figure 18)
Reheat Turbines
- Used in larger turbines to reheat the steam to improve efficiency
- Steam loses heat energy in HP stages, and reheating prevents condensation in LP turbine
- Designs include Figure 14, which shows four different turbine arrangements
Turbine Casing
- Contains nozzles, stationary blade diaphragms, bearing cases, and external components
- Must operate under high pressure and temperature conditions
- Designed to resist distortion and maintain alignment
- Common design is the horizontally-split casing, which facilitates assembly and inspection
Shaft Seals
- Used to prevent steam leakage where shafts extend through the casing
- Types of seals include carbon rings (Figure 24) and labyrinth seals (Figure 25)
- Labyrinth seals are commonly used in large turbines and consist of several rings with small clearances to the shaft
- Water seals (Figure 26) are used when a positive, leak-proof seal is required
Learn about the operating principles of impulse turbines, where high-pressure steam expands through a nozzle, leading to high-speed jet formation. Understand how the impulse force is produced on turbine blades through momentum transfer.
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