Steam Turbines B Flashcards
1
Q
This component of a steam turbine is used to control the speed of the turbine automatically under varying load conditions.
A
The govenor
This controls the steam admission valve.
2
Q
This steam turbine component is used to quickly closed the steam admission valves in case of sudden removal of the load to the generator.
A
Acceleration governors
These are often found on turbines in power generation stations.
3
Q
This steam turbine component consists of a spring-loaded bolt (or weight) with a slightly off centre of gravity, which moves outwards depending on the speed of the turbine.
A
A mechanical overspeed trip.
The centrifugal forces causes by excess speed cause the tripping mechanism to be thrown out into making contact with the overspeed trip mechanism.
4
Q
What are the two purposes of the nut or shoulder in a mechanical or mechanical/hydraulic overspeed trip?
A
- Provides a stop for the bolt in the tripped position.
- Tripping speed adjustment.
5
Q
What causes a mechanical or mechanical/hydraulic overspeed trip?
A
The centrifugal forces (speed) causes the trip mechanism to be thrown outward into making contact with the overspeed trip mechanism.
6
Q
When an overspeed condition is observed in a mechanical or mechanical/hydraulic overspeed trips, what happens after the overspeed trip mechanism has been activated?
A
The main stop valve is closed.
7
Q
Where are mechanical or mechanical/hydraulic overspeed trip mechanisms mounted on steam turbines?
A
Attached to the main shaft (in someway).
There must be some way for the mechanism to sense the speed of the turbine.
8
Q
- Once an overspeed trip has been activated on a steam turbine, and the stop valve is closed, what valve opens?
- Why is this?
A
- The blowdown valve.
- To relieve pressue back into the condenser.
9
Q
What component of a mechanical or mechanical/hydraulic overspeed trip holds the tripping lever in position?
A
A spring
10
Q
True or false: Some turbines have two or more overspeed devices that act as a backup in case one system fails.
A
True
An overspeed condition, if left unchecked, will result in destruction of the turbine.
11
Q
What is a normal speed trip setting for overspeed trip mechanisms?
A
110% to 115% of operating speed
12
Q
This type of overspeed trip mechanism uses a trip pin which opens a valve that opens a line to dump the oil in a hydraulic system, with the loss of pressure resulting in the spring loaded steam valves closing.
A
Hydraulic overspeed trip mechanisms
These are seen in larger turbines.
13
Q
True or false: Turbine overspeed trips will automatically reset once the speed has reduced to a specific setpoint.
A
False
Overspeed trips must be manually reset.
14
Q
What are three things things that must be repaired and adjusted on a turbine overspeed trip mechanism?
A
- Tripping speed.
- Ensure the trip linkage is operative.
- Main stop valve seats are in good condition.
15
Q
How often does the overspeed trip mechanism on a steam turbine need to be tested (two reasons)?
A
- After any maintenance.
- As per the OEM.
16
Q
What are two things that keep an overspeed trip (stop) valve assembly closed?
A
- The spring tension.
- The steam pressure on the top of the valve.
17
Q
Where is the main stop valve of a steam turbine located?
A
In the steam chest.
Upstream from the SAV and directly connected to the steam inlet.
18
Q
True or false: In a steam turbine, when the overspeed trip activates, it closes the stop valves and stops the flow of steam to the turbine.
A
True
19
Q
True or false: Rigid coupling = solid coupling.
A
True
20
Q
True or false: When using solid couplings, for maximum power transfer and minimum shear stress, the bolts must fit in the holes wihtout clearance.
A
True
For high speed turbines, these bolts will be labelled for specific locations in order to keep the flange balance correct.
21
Q
On steam turbines, this component is located in the lower parts of the turbine casings and steam chest and are opened in order to ensure that there is no water in the turbine at start-up.
A
Casing drains
22
Q
When starting a steam turbine, how long should the casing drains be left open?
A
Until the temperature of the steam turbine is the same as the steam tempeature.
23
Q
Which component of a steam turbine will see the highest steam pressures?
A
The steam chest
This is the inlet to the turbine.
24
Q
On a steam turbine, what component contains a strainer (witch’s hat) to keep particles from entering the turbine?
A
The steam chest
25
What effect does having a longer steam turbine have on power?
Length ↑ = power ↑
26
What effect does having a larger ∅ turbine have on power?
Larger ∅ = power ↑
27
What are two opening/closing mechanisms found in steam admission valves?
1. Cam lift.
2. Bar lift.
## Footnote
These valves are arranged to that steam to the turbine can be progressively admitted.
28
True or false: The governor valve to control the speed of a steam turbine is located in the steam chest.
True
## Footnote
The governor valve and SAV are the same valve.
29
What controls the steam admission valves on steam turbines?
The governor
## Footnote
The SAV is sometimes referred to as the governor valve.
30
On a steam turbine, what is a governor valve?
SAV
## Footnote
These valve names are interchagneable.
31
This component of a steam turbine changes the steam to water after it leaves the turbine by direct contact with water or by contact with a heat exchanger surface.
Condenser
32
1. What effect does a condenser have on the backpressure of a steam turbine?
2. Where does the pressure change take place?
1. It reduces it.
2. The final stages of the turbine.
## Footnote
This is due to the vacuum created by the condensing action of the steam into water.
33
What effect does a condesner have on the efficiency of a steam turbine?
Improves it
## Footnote
This is due to the reduction of backpressure in the final stages of the turbine.
34
What effect does a condenser have on the power of a steam turbine?
Increases it
## Footnote
This is due to the reduction of backpressure in the final stages of the turbine.
35
Why are hyrdaulic steam admission valves common?
High pressures are required to move the valves.
## Footnote
This is due to the high pressure steam acting on the valves.
36
What are three common uses for steam after it leaves a turbine?
1. Condesner.
2. Another turbine (lower pressure).
3. Another process (heating the feedwater).
37
True or false: Steam condesners are ususaly shell and tube heat exchangers.
True
## Footnote
These are located after the final stage of the turbine.
38
Where are steam condesners located on steam turbine assemblies?
Separate, and after the final stage of the turbine.
## Footnote
These are usually shell and tube heat exchangers connected to the discharge of a tubine assembly.
39
True or false: In many cases, the axial thrust of steam turbines can almost be eliminated, using dummy pistons or rotor configurations to reduce the burden on the thrust bearing.
True
40
True or false: The impulse section of large steam turbines does not generate much axial thrust, but the reaction part of the turbine process does.
True
## Footnote
This is due to the pressure differential across reaction type blades. → the thrust forces are in the direction away from the nozzle.
41
This component of a steam turbine is part of the rotor with several stepped diameters that the steam pressure in the turbine can push against to counteract thrust.
Dummy piston.
## Footnote
These are also called balance pistons and balance pipes.
42
True or false: On a steam turbine, a balance piston and balance pipe is the same thing as a dummy piston.
True
43
True or false: By using the correct size of a dummy (balance) piston, the trust in a steam turbine is nearly equalized.
True
## Footnote
There will still be a thrust bearing component, due to changing thrust loads at start-up and shut-down.
44
On a steam turbine, what is the purpose of a balance pipe on a dummy (balance) piston?
To allow low pressure steam to act on the backside of the dummy (balance) piston.
## Footnote
The balance piston is located next to the steam inlet to allow for maximum pressure on the dummy piston.
45
Where is a dummy (balance) piston located in a steam turbine?
Near the steam inlet
## Footnote
This allows for maximum steam pressure to act against the thrust forces developed in the turbine.
46
This type of turbine rotor flow arrangement has the steam entering the cylinder in the centre and taking two paths in opposite directions.
Dual flow rotors
| This flow arrangement is limited to low pressures (LP) sections.
## Footnote
This arrangement results in axial thrust in both directions, that very nearly cancels out.
47
What is the main advantage of dual flow rotors in steam turbines?
Almost no axial thrust
| This flow arrangement is limited to low pressures (LP) sections.
## Footnote
The dual flow arrangement results in opposing thrust loads that result in almost no axial thrust in the turbine.
48
What type of steam turbine rotor arrangement has an hourglass shaped casing?
A dual flow rotor arrangement
| This flow arrangement is limited to low pressures (LP) sections.
49
This type of steam turbine rotor flow arrangement has two of the rotors in a compound turbine flow in opposite directions.
Opposite flow designs
| This flow arrangment is used for high pressure (HP) sections.
50
Which of the following steam turbine flow arrangement would result in better axial thrust control:
1. Dual flow rotors.
2. Opposite flow desings.
Dual flow rotors
| Dual flow rotors are limited to low pressures (LP) sections.
## Footnote
Opposite flow designs do reduce the axial thrust created by the rotor blades, but not as well as dual flow rotors.
51
What dictates the complexity of the fuel system used in boilers?
The type of fuel used
## Footnote
Coal requires more equipment to burn vs. something like natural gas.
52
This component is used to move the condensate from a steam turbine condenser back into the boiler, all while withstanding and overcoming the high pressures in the boiler.
Boiler feed pumps
## Footnote
This is what supplies the water to the boiler.
53
Where must non-condesning steam turbines have relief valves?
Between the turbine and the turbine isolation shut-off valve.
## Footnote
This is to reduce the possibility of turbine explosion if the isolation shut-off valve is closed or the case is over-pressured.
54
Where must condensing steam turbines have relief valves?
Located in the low pressure section.
55
What are two types of pressure relief valves that can be used for overpressurization protection on the low-pressure section of a condensing turbine?
1. atmospheric relief valve
2. rupture disk
56
This steam turbine safety device is a pre-bulged membrane made of various metals.
A rupture disk
57
What are two ways to provide enough cooling to a steam turbine condenser in order for it to reject enough heat from the steam continually?
1. A large body of water (lake, river, pond)
2. Cooling towers.
## Footnote
When a large body of water is not avaiable, cooling towers are used.
58
When cooling a steam turbine condenser, what effect does cooler cooling water have on the efficiency of the turbine?
Cooler water = efficiency ↑
| This is due to lower backpressure in the turbine.
## Footnote
When cooler water is used in the condenser, it is more effective at condensing the exhaust steam, which leads to a lower pressure in the condenser (since the steam condenses more efficiently at lower temperatures).
59
When cooling a steam turbine condenser, what effect does warmer water have on the efficiency of the turbine?
Warmer water = efficiency ↓
| This is due to higher backpressure in the turbine.
## Footnote
The primary effect of using warmer cooling water in the condenser is that it reduces the condenser's ability to condense the exhaust steam effectively. As a result, the exhaust steam from the turbine remains at a higher temperature and pressure, which increases the back pressure on the turbine.
60
_____ _____ is the pressure that the turbine must overcome when exhausting steam, and it directly affects the turbine’s performance.
Back pressure
61
How are small electrical generators cooled?
Air-cooled
62
How are large electrical generators cooled?
With hydrogen
## Footnote
Hydrogen cooled generators are very effective.
63
This steam turbine component enables the slow rotation of the turbine rotors while there is no steam flowing through the machine.
Turning gear (barring gears)
## Footnote
This is used to remove any bow in the rotor due to sag.
64
What are two things that barring gears are used for when starting up a steam turbine?
1. Remove any bow in the turbine caused by rotor sag.
2. To ensure the turbine heats up evenly*.
| This is done by slowly rotating the turbine assembly.
## Footnote
*Heat applied to a trubine rises, which results in the top of the turbine heating up quicker than the bottom of the turbine.
65
True or false: On a steam turbine, a barring gear is the same thing as a turning gear.
True
66
What are barring turning gears used for when a steam turbine is shut down (idle, not ungergoing maintenance)?
Rotation of the rotor to prevent sag.
| This allows the turbine to be started much quicker.
## Footnote
Jacking oil must be pumped to the bearings when the barring gear is running.
67
True or false: The turning gear system on many turbines is engaged automatically when the turbine slows to a pre-set speed.
True
68
What is a common oil supply pressure seen in large steam turbines?
40 psi
69
What are three things that lubrication oil must do to the main bearings on a steam turbine?
1. Lubricate
2. Carry away heat
3. Remove moisture from steam leakage
70
What are two components of a steam turbine that need to be lubricated?
1. Bearings
2. Speed governor
71
What type of lubrication system is used on small steam turbines?
Oil ring and splash lubrication.
72
What are two characteristics required for lubrication oil used in steam turbines?
1. Must readily separate from water.
2. Good oxidization resistance.
73
On steam turbines a significant amount of excess lubrication is pumped to the bearing. Why is this?
To cool the bearings.
## Footnote
Due to the high temperature of the steam, without this lubrication the bearings would fail.
74
The purpose of this steam turbine lubrication system is to lift the rotors off the bearings and supply an oil film for the shaft to ride on before any shaft rotation occurs.
Jacking oil system
75
On a steam turbine, when is the jacking oil system turned on?
Before there is any rotation in the turbine rotor.
## Footnote
It is usually left on until the turbine reaches 50 to 60 rpm.
76
What does a deviation from normal running conditions usually indicate on a steam turbine?
Buildup or wear on the nozzles or blades.
77
What could be an indication of some form of internal damage in a steam turbine?
A sudden change in pressures or data that cannot be attributed to changes in inlet steam or extraction conditions.
78
In steam turbines, it is not uncommon to have progressive buildup of deposits on the blades and nozzles. What causes this?
Minerals in the water.
## Footnote
Even though the water is highly treated (one of the major costs), the erosion of metallic parts contributes to mineral deposits throughout the turbine over time.
79
What are the two main methods used to removed deposits from the surfaces of a steam turbines?
1. Shut down, disassemble and manually removing them.
2. Shut down, resulting in flaking off due to temperature changes (running vs. shutdown).
## Footnote
Both of these methods require the turbine to be shutdown, the second one doesn't require the turbine to be dismantled.
80
What are three manual cleaning methods used to clean steam turbine components?
1. Manual buffing and scraping
2. blasting with walnut shells
3. blasting with high pressure (HP) dry ice
81
True or false: Each steam turbine has a specific procedure and method that must be followed when removing bolts.
True
## Footnote
Often the bolts must be hydraulicly stretched or heated in order to remove them.
82
Where is the overspeed trip pin located on a steam turbine?
In the rotor shaft.
## Footnote
Mechanical overspeed trips need to be connected to the rotor shaft in some way to be able to sense the speed.
83
What valve is actuated by the overspeed trip pin and linkages?
The stop valve
84
What effect would there be on the pressure difference between the inlet and outlet of a condesning turbine if the cooling water temeprature was lowered?
The difference in pressure between the steam inlet and exhaust will increase.
## Footnote
This is because the steam will condense more efficiently, resulting in a lower pressure in the condenser.
85
What effect would there be on the pressure difference between the inlet and outlet of a condesning turbine if the cooling water temperature was increased?
The pressure difference would decrease.
## Footnote
This is beacuse the steam will condense less efficiently, resulting in a higher pressure in the condenser.
86
What device controls the position of progressive steam admission valves?
A governor linked to a set of cams or a bar.
## Footnote
The cams or bar are dependant on the type of valve mechanism is being used in the SAV.
87
What type of steam turbine requires a relief valve between the turbine and the exhaust isolation valve?
Back pressure turbines
| These are also called non-condensing turbines.
## Footnote
It must be located here in order to prevent overpressure due to the isolation valve being shut.
88
When lifting the covers of steam turbines, the lift should be rigged to provide two-way levelling. Why is this?
If the top cover is not removed evenly, the diaphragms may contact the rotor blades.
## Footnote
This coud potentially cause damage to the steam turbine.
89
When lifting a cover off of a steam turbine, how should the cover initially be lifted?
With jacking bolts
## Footnote
This ensures that the lift is starting clean and level.
90
When installing a steam turbine cover, what type of joining compound is often placed on the flat machined joints.
Boiled linseed oil
91
What are four common scenarios where a steam turbine overspeed trip mechanism must be tested?
1. After maintenance of the trip mechanism.
2. After a major overhaul.
3. After any major overspeed incident.
4. As per OEM recommendations.
92
What steam turbine system design is used to reduce thrust forces on the turbine rotors of high pressure turbines?
Opposite flow arrangement
93
What device in a steam turbine ensures a lower pressure on one side of the dummy piston?
A balance pipe
94
What metals are used to make the alloy babbitt that is used in bearings?
Lead and tin
## Footnote
These two comprise the majority of the babbitt, with other metals added in for certain wear characteristics.
95
What type of bearing is used to control the large thrust loads on a reaction type steam turbine?
Tilting pad thrust bearings
96
What items are used to measure the rotor to diaphragm labyrinth seal clearances on a reaction type steam turbine?
Lead wire and blade micrometer
97
Which method of cylinder bolt installation and preloading does not require heating or turning the fastener while it is loaded?
Hydraulic stretch
98
How are steam turbine casings designed so axial thermal expansion does not affect the foundation?
With dove tail connections to the sole plates
99
How is proper contact of a plain bearing adjusted?
By scraping the surface
| Minimum contact percentage is 85% of the loaded zone.
100
Journal bearings on a typical steam turbine are mounted in turbine pedestals. What does this allow?
Adjustment of the bearing height and position.
| Through the addition or subtraction of shims under the bearing seat pads
101
On steam turbines, what is a turbine pedestal?
An adjustable pedestal that houses the plain journal bearings.
## Footnote
These pedestals allow shims to be added or subtracted in order to adjust the height and positon of the bearing.
102
A typical babbitted journal bearing has about ____ inch clearnace per inch of shaft diameter.
0.001"
103
What effect does the oil viscosity have on a steam turbine?
Proper viscosity keeps the turbine stable.
## Footnote
This is why it is critical to keep the temperature of the oil cool and consistent.
104
How is rotor axial position set on a steam turbine?
With shims at the thrust bearing.
105
On steam turbines, what are the two functions of thrust bearings?
1. Keep the rotor in a specified position.
2. Absorb any remaining axial thrust on the rotor.
106
On tandem-compound turbine arrangements with solid couplings, how many thrust bearings are required to control axial movement of all coupled rotors?
One thrust bearing for all turbine sections.
## Footnote
If multiple thrust bearings are used in a configuration with rigid couplings, the axial load distribution between the bearings becomes uneven, resulting in uneven loading on certain bearings whch will result in premature failure.
107
On a tandem-compound turbine arrangement with flexible couplings, how many thrust bearings are required to control axial movement of all coupled rotors?
On thrust bearing per turbine section.
108
True or false: Each piece of equipment that connects to the turbine (generator) has its own thrust control.
True
## Footnote
While they may only have one thrust bearing for the entire assembly, each section will have to have some sort of thrust control (dummy piston, dual flow arrangement, etc.).
109
True or false: Turbines with reaction blades cannot depend on a thrust bearing alone to counter the axial thrust generated within the turbine.
True
## Footnote
Some other method of thrust contorl is required (dummy piston, opposite flow arrangement, etc.).
110
What is the purpose of dovetail guides in the cylinder (housing) of a steam turbine?
To allow for thermal expansion and contraction of the casing.
| These are the same things as keyways.
## Footnote
These dovetails/keyways should be lubricated.
111
True or false: Diaphragms in steam compressors have a specified clearance above, below and on each side of the rotor.
True
## Footnote
This is to reduce steam leakage.
112
What are three ways to verify/determine the clearance of the diaphragms on steam turbines?
1. Laser unit
2. Paino wire
3. Dummy shafts
## Footnote
All diaphragms are references to the turbine bearing centrelines.
113
What is the reference point for all diaphragms in steam turbines?
The bearing centreline.
114
On steam turbines, ________ have shims or crush pins installed for alignment and fitting.
diaphragms
115
True or false: In a steam turbine, the split line in a diaphragm has to maintain a steam-tight seal so the halves are installed with a slight protrustion to assure good sealing.
True
| This protrusion acts the same was as bearing crush.
116
What three things must the diaphragm clearance on steam turbines account for?
1. Shaft sag
2. Clearances between components
3. Thermal growth within the casing
117
On large steam turbines, brass or stainless steel segments that are spring loaded are placed in the diaphragm to create a very small clearance between the seal and the shaft. Why is this?
To allow the sealing segments to be pushed back in the case of accidental contact with the shaft.
## Footnote
This can be caused by a bowed shaft or an uneven thermal expansion at startup.
118
What are two reasons that a steam turbine shaft may come into contact with the spring loaded sealing segments in the diaphragm?
1. Bowed shaft (sitting idle for too long)
2. Uneven thermal growth at startup
| Both of these issues arise at startup.
119
How should labyrinth seal clearance be checked between the diaphragm and turbine rotors in a steam turbine?
With lead wire and a blade micrometer.
120
How should steam turbine rotors be temporarily stored?
In a cradle that supports the ends of the shaft.
| Ensure that the flooring can bear the weight of the turbine and cradle.
121
When installing a rotor into a steam turbine, what three measurements must be taken?
1. Between blades and casing
2. Between blades and diaphragms
3. Between rotor shaft and labyrinth seals
| This is usually done by taping lead wire to the blades and seals.
122
When installing a rotor into a steam turbine, how would the clearance between the blades and casing be verified?
By taping lead wire to the rotor blade and then measuring it with a blade micrometer.
## Footnote
This goes for the measurements between blades and diaphragms as well as the measurements between the rotor shaft and labyrinth seals.
123
What type of shaft seal would be used on large steam turbines with high surface speeds?
Labyrinth seals
124
What type of labyrinth seal can be replaced without having to remove the rotor of a steam turbine?
J strips
125
How are J strips secured to the shaft of a steam turbine?
A wire is pushed into the groove and peened so that it cannot slide out
## Footnote
The strips are then machined to the correct diameter.
126
When installing J strips, once the strip has been installed into place and peened, what last step must be taken?
Machining the strip to the correct diameter
127
Which component of a steam turbine requires the use of a set of guide pins to ensure that no accidental contact is made when being removed?
The top casing
128
True or false: When installing the top casing of a steam turbine, the top casing holes must be centred around the guide pins and the cover must be kept level.
True
## Footnote
Failure to do so can result in serious damage to the turbine rotor assembly and stationary blades.
129
How is the tension of the fasteners that hold the top and bottom half of a turbine casing together determined?
With bolt stretch
## Footnote
This is the most accurate way to tensioning fasteners.
130
1. This method of cylinder bolt installation and preloading requires large bolts with hollowed cores.
2. What is the hollow core for?
1. Thermal elongation
2. An electric heating element can be placed in the core for even heating of the fastener
131
True or false: When installing and preloading cylinder bolts with thermal elongation, a gas flame can be used to heat the fasteners up.
True; but there should be no contact between the fastener and the flame
## Footnote
Direct contact with the flame could damage the material of the bolt.
132
How are smaller bolts tensioned and preloaded on steam turbines?
With a torque multiplier turning the bolt a certain number of degrees of rotation.
| This is similar to the torque turn method.
## Footnote
No heat is applied with this method.
133
How are larger and longer bolts measured for bolt stretch?
With hole drilled lengthwise through the bolt.
| This allows us to measure bolt stretch from the inside out.
134
What three tools are required to measure bolt stretch from the inside of the bolt?
1. depth micrometer
2. adapter
3. extension rod
135
After installation, how should tightness and bolt stetch be checked periodically?
With high-frequency sound waves
## Footnote
If there is any discrepancy in the time of flight, the previous records can be checked and comapred.
136
When installing bolts with the bolt stretch method with heat, what can happen if the flanges are overheated?
The bolts may be below the required torque
## Footnote
This is due to excessive flange shrinkage after the heat is removed.
137
When checked bolt elongation with high frequency sound waves, what are you measuring?
Time of flight
## Footnote
This is how long it takes for the sound wave to travel to the end of the bolt and then bounce back.
138
True or false: Small steam turbines under 10 megawatts (MW) are shipped completely assembled.
False
| Under 1 megawatt are shiped completely assembled.
139
The foundation of a steam turbine must do what 4 things?
1. Remain in position without settling
2. Operate without excessive vibration
3. Thermally expand without stress
4. Handle dynamic loads*
## Footnote
*These loads are associated with shaft rotation, sudden load changes, and forces exerted due to piping or driven equipment.
140
True or false: The condenser of a steam turbine must be loacted below the final stage of the turbine.
True
## Footnote
The condenser is usually located below the turbine to take advantage of gravity for steam and condensate flow.
141
The foundation of the turbine should be at least ________ times the mass of all the steam turbine assembly.
2.5
## Footnote
This ensures the foundation does not move and helps dampen vibrations.
142
Large steam turbine mount on foundations that have openings in the floor. Why is this?
To mitigate thermal expansion
## Footnote
The hole allows the turbine cylinder to be mounted along the centerline, with the bottom half of the cylinder hanging in the opening.
143
What effect does mounting steam turbines along the cylinder centreline have on thermal expansion of the shaft centreline?
It reduces it
## Footnote
By mounting the cylinders along the centreline, the thermal growth happens both above and below the shaft centreline, reducing the misalignment due to thermal growth.
144
What is used to support a steam turbine when it is set on the bed of the foundation?
| Three items.
1. Sole plates
2. Grout pads
3. Wedge block
145
What would happen to a steam turbine if the rotor wasn’t barred over while the turbine was heating up?
The turbine would heat unevenly, resulting in the top of the turbine heating up quicker than the bottom.
## Footnote
This could result in the top of the turbine overheating by the time the turbine is up the temperature, which could result in it rubbing when started.
146
True or false: When the foundation for a steam turbine is poured, the top of the foundation should have steel sole plates installed
True
147
When installing a larger multi-stage steam turbine assembly, which components are installed first?
The bearing pedestals and the bottom halves of the cylinders.
## Footnote
These components have keyways (dovetails) to allow the casing to expand in length and width.
148
Which large multi-stage steam turbine assemblies are equipped with dovetails or keyways?
1. The bearing pedestals
2. The bottom halves of the cylinders
## Footnote
These allow for thermal expansion of the turbine without distorting the foundation.
149
What is the purpose of dovetails or keyways on the bottom halves of steam turbine cylinders?
To allow longitudinal thermal expansion of the turbine without stressing the foundation.
150
This steam turbine component is located at the end of each casing and is mounted directly to the sole plates.
The bearing pedestals
151
What is the purpose of an alignment key on steam turbine bearing pedestals?
To keep the pedestal and cylinder in alignment.
152
During a steam turbine installation, the tops of the cylinders and pedestals are installed to apply as much weight as possible to the installation. Why is this?
To mimic the weight of the whole turbine in order to reduce cylinder sag.
## Footnote
This practise takes the sag out of the cylinders; when the two halves of the cylinder are bolted togther, the sag in the bottom half of the cylinder is taken out.
153
What are the two methods used for aligning a steam turbine and which one is more accurate?
1. Paino wire
2. Laser alignment ⟶ more accurate
## Footnote
The laser alignment also takes less time.
154
When installing the sections of a steam turbine and generator, what needs to be taken into account when aligning the shafts?
The sag of the turbine unit needs to be taken into account.
## Footnote
This permits the rotor couplings to mate properly.
155
On steam turbines, what is a bridge gauge?
A measuring instrument used to monitor the wear of the main bearings.
## Footnote
It does this by measuring the distance between the bridge and the top of the turbine shaft.
156
True or false: Every bearing pedestal on a steam turbine has a bridge gauge.
True
157
What does a larger bridge gauge measurement on a steam turbine indicate?
Increased wear on the main bearings.
## Footnote
The larger distance is caused by the bearing wearing, which drops the main turbine shaft away from the bridge gauge.
158
This component of a steam turbine is used to measure main bearing wear.
A bridge gauge
## Footnote
It measures main bearing wear by measuring the distance from the bridge to the top of the turbine shaft.
159
When a steam turbine has sat idle for some time, how long will the rotor be barred over before being started up?
Until the eccentricity meters indicate the shaft is of acceptable straightness.
| This could be for several hours.
160
Why do casing drains need to be open during start-up of a steam turbine?
Steam entering the cold turbine condenses into water.
## Footnote
The water drains should be left open until the machine reaches thermal saturation.
161
When starting up a steam turbine, how long should the casing drains be left open?
Until the steam turbine reaches thermal saturation
## Footnote
Thermal staturation ⟶ the turbine is the same temperature as the steam.
162
Why is it important to ensure that the thermal growth of a steam turbine at start-up is gradual and equal in all parts?
Uneven thermal growth can result in rubbing.
## Footnote
This is also a factor to bar the rotor over during start-up to prevernt the top of the rotor from heating up faster than the bottom.
163
True or false: When starting up a steam turbine, allow 360º arc admission at the steam admission valves as this aids in proper thermal expansion.
True
164
Where is the nozzle ring located in a steam turbine?
In the steam chest
165
During start-up of a steam turbine, the turbine should first be loaded to about ________% to allow for further thermal expansion.
20%
166
True or false: When starting up a steam turbine, the greatest amount of thermal stress is created at the heavier steel section of the casing.
True
167
What two functions do automatic controls on a steam turbine?
1. Minimize the amount of thermal and rotating stress.
2. Bring the turbine up to rated speed and run it with the least amount of stress and damage in emergency and normal situations.
168
On a steam turbine, what is a trip valve exerciser?
Allows the overspeed trip mechanism to be verified without shutting down the turbine.
## Footnote
The exerciser can confirm the movement of the trip valve stem without shutting down the turbine.
169
How often should a trip valve exerciser on a steam turbine be checked?
Weekly
| On large turbines.
170
This steam turbine test requires the turbine to be uncoupled and run on bypass steam until the trip speed has been reached.
An overspeed trip check
## Footnote
This test is very dangerous, yet the only way that one can verify an over-speed trip setting.
171
The oil viscosity to the bearings of steam turbines is importnat to keep the rotor stable. The acceptable range of oil viscosity entering the bearings occurs when the oil temperature is between ________℉ to ________℉.
105℉ to 140℉
172
On steam turbine bridge gauges, main bearing wear is indicated to what references?
Either a lowering of the shaft or a lateral movement of the shaft in relation to the bridge.
173
What is a transverse anchor block on a steam turbine assembly.
A transverse anchor block in a steam turbine assembly is a structural component designed to anchor and stabilize the turbine casing or shaft.
174
Why are steam admission valves arrenged so that the valves open at different positions?
To progressively admit the steam.
## Footnote
This is what allows for the variable control of the steam through the valve.
