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Millwrong > Steam Turbines B > Flashcards

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.

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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.

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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.

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4
Q

What are the two purposes of the nut or shoulder in a mechanical or mechanical/hydraulic overspeed trip?

A
  1. Provides a stop for the bolt in the tripped position.
  2. Tripping speed adjustment.
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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.

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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.

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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.

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8
Q
  1. Once an overspeed trip has been activated on a steam turbine, and the stop valve is closed, what valve opens?
  2. Why is this?
A
  1. The blowdown valve.
  2. To relieve pressue back into the condenser.
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9
Q

What component of a mechanical or mechanical/hydraulic overspeed trip holds the tripping lever in position?

A

A spring

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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.

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11
Q

What is a normal speed trip setting for overspeed trip mechanisms?

A

110% to 115% of operating speed

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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.

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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.

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14
Q

What are three things things that must be repaired and adjusted on a turbine overspeed trip mechanism?

A
  1. Tripping speed.
  2. Ensure the trip linkage is operative.
  3. Main stop valve seats are in good condition.
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15
Q

How often does the overspeed trip mechanism on a steam turbine need to be tested (two reasons)?

A
  1. After any maintenance.
  2. As per the OEM.
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16
Q

What are two things that keep an overspeed trip (stop) valve assembly closed?

A
  1. The spring tension.
  2. The steam pressure on the top of the valve.
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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.

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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

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19
Q

True or false: Rigid coupling = solid coupling.

A

True

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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.

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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

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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.

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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.

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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

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25
Q

What effect does having a longer steam turbine have on power?

A

Length ↑ = power ↑

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26
Q

What effect does having a larger ∅ turbine have on power?

A

Larger ∅ = power ↑

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27
Q

What are two opening/closing mechanisms found in steam admission valves?

A
  1. Cam lift.
  2. Bar lift.

These valves are arranged to that steam to the turbine can be progressively admitted.

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28
Q

True or false: The governor valve to control the speed of a steam turbine is located in the steam chest.

A

True

The governor valve and SAV are the same valve.

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29
Q

What controls the steam admission valves on steam turbines?

A

The governor

The SAV is sometimes referred to as the governor valve.

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30
Q

On a steam turbine, what is a governor valve?

A

SAV

These valve names are interchagneable.

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31
Q

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.

A

Condenser

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32
Q
  1. What effect does a condenser have on the backpressure of a steam turbine?
  2. Where does the pressure change take place?
A
  1. It reduces it.
  2. The final stages of the turbine.

This is due to the vacuum created by the condensing action of the steam into water.

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33
Q

What effect does a condesner have on the efficiency of a steam turbine?

A

Improves it

This is due to the reduction of backpressure in the final stages of the turbine.

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34
Q

What effect does a condenser have on the power of a steam turbine?

A

Increases it

This is due to the reduction of backpressure in the final stages of the turbine.

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35
Q

Why are hyrdaulic steam admission valves common?

A

High pressures are required to move the valves.

This is due to the high pressure steam acting on the valves.

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36
Q

What are three common uses for steam after it leaves a turbine?

A
  1. Condesner.
  2. Another turbine (lower pressure).
  3. Another process (heating the feedwater).
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37
Q

True or false: Steam condesners are ususaly shell and tube heat exchangers.

A

True

These are located after the final stage of the turbine.

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38
Q

Where are steam condesners located on steam turbine assemblies?

A

Separate, and after the final stage of the turbine.

These are usually shell and tube heat exchangers connected to the discharge of a tubine assembly.

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39
Q

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.

A

True

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40
Q

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.

A

True

This is due to the pressure differential across reaction type blades. → the thrust forces are in the direction away from the nozzle.

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41
Q

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.

A

Dummy piston.

These are also called balance pistons and balance pipes.

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42
Q

True or false: On a steam turbine, a balance piston and balance pipe is the same thing as a dummy piston.

A

True

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43
Q

True or false: By using the correct size of a dummy (balance) piston, the trust in a steam turbine is nearly equalized.

A

True

There will still be a thrust bearing component, due to changing thrust loads at start-up and shut-down.

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44
Q

On a steam turbine, what is the purpose of a balance pipe on a dummy (balance) piston?

A

To allow low pressure steam to act on the backside of the dummy (balance) piston.

The balance piston is located next to the steam inlet to allow for maximum pressure on the dummy piston.

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45
Q

Where is a dummy (balance) piston located in a steam turbine?

A

Near the steam inlet

This allows for maximum steam pressure to act against the thrust forces developed in the turbine.

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46
Q

This type of turbine rotor flow arrangement has the steam entering the cylinder in the centre and taking two paths in opposite directions.

A

Dual flow rotors

This flow arrangement is limited to low pressures (LP) sections.

This arrangement results in axial thrust in both directions, that very nearly cancels out.

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47
Q

What is the main advantage of dual flow rotors in steam turbines?

A

Almost no axial thrust

This flow arrangement is limited to low pressures (LP) sections.

The dual flow arrangement results in opposing thrust loads that result in almost no axial thrust in the turbine.

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48
Q

What type of steam turbine rotor arrangement has an hourglass shaped casing?

A

A dual flow rotor arrangement

This flow arrangement is limited to low pressures (LP) sections.

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49
Q

This type of steam turbine rotor flow arrangement has two of the rotors in a compound turbine flow in opposite directions.

A

Opposite flow designs

This flow arrangment is used for high pressure (HP) sections.

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50
Q

Which of the following steam turbine flow arrangement would result in better axial thrust control:
1. Dual flow rotors.
2. Opposite flow desings.

A

Dual flow rotors

Dual flow rotors are limited to low pressures (LP) sections.

Opposite flow designs do reduce the axial thrust created by the rotor blades, but not as well as dual flow rotors.

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51
Q

What dictates the complexity of the fuel system used in boilers?

A

The type of fuel used

Coal requires more equipment to burn vs. something like natural gas.

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52
Q

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.

A

Boiler feed pumps

This is what supplies the water to the boiler.

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53
Q

Where must non-condesning steam turbines have relief valves?

A

Between the turbine and the turbine isolation shut-off valve.

This is to reduce the possibility of turbine explosion if the isolation shut-off valve is closed or the case is over-pressured.

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54
Q

Where must condensing steam turbines have relief valves?

A

Located in the low pressure section.

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55
Q

What are two types of pressure relief valves that can be used for overpressurization protection on the low-pressure section of a condensing turbine?

A
  1. atmospheric relief valve
  2. rupture disk
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56
Q

This steam turbine safety device is a pre-bulged membrane made of various metals.

A

A rupture disk

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57
Q

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?

A
  1. A large body of water (lake, river, pond)
  2. Cooling towers.

When a large body of water is not avaiable, cooling towers are used.

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58
Q

When cooling a steam turbine condenser, what effect does cooler cooling water have on the efficiency of the turbine?

A

Cooler water = efficiency ↑

This is due to lower backpressure in the turbine.

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).

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59
Q

When cooling a steam turbine condenser, what effect does warmer water have on the efficiency of the turbine?

A

Warmer water = efficiency ↓

This is due to higher backpressure in the turbine.

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.

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60
Q

_____ _____ is the pressure that the turbine must overcome when exhausting steam, and it directly affects the turbine’s performance.

A

Back pressure

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61
Q

How are small electrical generators cooled?

A

Air-cooled

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62
Q

How are large electrical generators cooled?

A

With hydrogen

Hydrogen cooled generators are very effective.

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63
Q

This steam turbine component enables the slow rotation of the turbine rotors while there is no steam flowing through the machine.

A

Turning gear (barring gears)

This is used to remove any bow in the rotor due to sag.

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64
Q

What are two things that barring gears are used for when starting up a steam turbine?

A
  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.

*Heat applied to a trubine rises, which results in the top of the turbine heating up quicker than the bottom of the turbine.

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65
Q

True or false: On a steam turbine, a barring gear is the same thing as a turning gear.

A

True

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66
Q

What are barring turning gears used for when a steam turbine is shut down (idle, not ungergoing maintenance)?

A

Rotation of the rotor to prevent sag.

This allows the turbine to be started much quicker.

Jacking oil must be pumped to the bearings when the barring gear is running.

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67
Q

True or false: The turning gear system on many turbines is engaged automatically when the turbine slows to a pre-set speed.

A

True

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68
Q

What is a common oil supply pressure seen in large steam turbines?

A

40 psi

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69
Q

What are three things that lubrication oil must do to the main bearings on a steam turbine?

A
  1. Lubricate
  2. Carry away heat
  3. Remove moisture from steam leakage
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70
Q

What are two components of a steam turbine that need to be lubricated?

A
  1. Bearings
  2. Speed governor
71
Q

What type of lubrication system is used on small steam turbines?

A

Oil ring and splash lubrication.

72
Q

What are two characteristics required for lubrication oil used in steam turbines?

A
  1. Must readily separate from water.
  2. Good oxidization resistance.
73
Q

On steam turbines a significant amount of excess lubrication is pumped to the bearing. Why is this?

A

To cool the bearings.

Due to the high temperature of the steam, without this lubrication the bearings would fail.

74
Q

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.

A

Jacking oil system

75
Q

On a steam turbine, when is the jacking oil system turned on?

A

Before there is any rotation in the turbine rotor.

It is usually left on until the turbine reaches 50 to 60 rpm.

76
Q

What does a deviation from normal running conditions usually indicate on a steam turbine?

A

Buildup or wear on the nozzles or blades.

77
Q

What could be an indication of some form of internal damage in a steam turbine?

A

A sudden change in pressures or data that cannot be attributed to changes in inlet steam or extraction conditions.

78
Q

In steam turbines, it is not uncommon to have progressive buildup of deposits on the blades and nozzles. What causes this?

A

Minerals in the water.

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
Q

What are the two main methods used to removed deposits from the surfaces of a steam turbines?

A
  1. Shut down, disassemble and manually removing them.
  2. Shut down, resulting in flaking off due to temperature changes (running vs. shutdown).

Both of these methods require the turbine to be shutdown, the second one doesn’t require the turbine to be dismantled.

80
Q

What are three manual cleaning methods used to clean steam turbine components?

A
  1. Manual buffing and scraping
  2. blasting with walnut shells
  3. blasting with high pressure (HP) dry ice
81
Q

True or false: Each steam turbine has a specific procedure and method that must be followed when removing bolts.

A

True

Often the bolts must be hydraulicly stretched or heated in order to remove them.

82
Q

Where is the overspeed trip pin located on a steam turbine?

A

In the rotor shaft.

Mechanical overspeed trips need to be connected to the rotor shaft in some way to be able to sense the speed.

83
Q

What valve is actuated by the overspeed trip pin and linkages?

A

The stop valve

84
Q

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?

A

The difference in pressure between the steam inlet and exhaust will increase.

This is because the steam will condense more efficiently, resulting in a lower pressure in the condenser.

85
Q

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?

A

The pressure difference would decrease.

This is beacuse the steam will condense less efficiently, resulting in a higher pressure in the condenser.

86
Q

What device controls the position of progressive steam admission valves?

A

A governor linked to a set of cams or a bar.

The cams or bar are dependant on the type of valve mechanism is being used in the SAV.

87
Q

What type of steam turbine requires a relief valve between the turbine and the exhaust isolation valve?

A

Back pressure turbines

These are also called non-condensing turbines.

It must be located here in order to prevent overpressure due to the isolation valve being shut.

88
Q

When lifting the covers of steam turbines, the lift should be rigged to provide two-way levelling. Why is this?

A

If the top cover is not removed evenly, the diaphragms may contact the rotor blades.

This coud potentially cause damage to the steam turbine.

89
Q

When lifting a cover off of a steam turbine, how should the cover initially be lifted?

A

With jacking bolts

This ensures that the lift is starting clean and level.

90
Q

When installing a steam turbine cover, what type of joining compound is often placed on the flat machined joints.

A

Boiled linseed oil

91
Q

What are four common scenarios where a steam turbine overspeed trip mechanism must be tested?

A
  1. After maintenance of the trip mechanism.
  2. After a major overhaul.
  3. After any major overspeed incident.
  4. As per OEM recommendations.
92
Q

What steam turbine system design is used to reduce thrust forces on the turbine rotors of high pressure turbines?

A

Opposite flow arrangement

93
Q

What device in a steam turbine ensures a lower pressure on one side of the dummy piston?

A

A balance pipe

94
Q

What metals are used to make the alloy babbitt that is used in bearings?

A

Lead and tin

These two comprise the majority of the babbitt, with other metals added in for certain wear characteristics.

95
Q

What type of bearing is used to control the large thrust loads on a reaction type steam turbine?

A

Tilting pad thrust bearings

96
Q

What items are used to measure the rotor to diaphragm labyrinth seal clearances on a reaction type steam turbine?

A

Lead wire and blade micrometer

97
Q

Which method of cylinder bolt installation and preloading does not require heating or turning the fastener while it is loaded?

A

Hydraulic stretch

98
Q

How are steam turbine casings designed so axial thermal expansion does not affect the foundation?

A

With dove tail connections to the sole plates

99
Q

How is proper contact of a plain bearing adjusted?

A

By scraping the surface

Minimum contact percentage is 85% of the loaded zone.

100
Q

Journal bearings on a typical steam turbine are mounted in turbine pedestals. What does this allow?

A

Adjustment of the bearing height and position.

Through the addition or subtraction of shims under the bearing seat pads

101
Q

On steam turbines, what is a turbine pedestal?

A

An adjustable pedestal that houses the plain journal bearings.

These pedestals allow shims to be added or subtracted in order to adjust the height and positon of the bearing.

102
Q

A typical babbitted journal bearing has about ____ inch clearnace per inch of shaft diameter.

A

0.001”

103
Q

What effect does the oil viscosity have on a steam turbine?

A

Proper viscosity keeps the turbine stable.

This is why it is critical to keep the temperature of the oil cool and consistent.

104
Q

How is rotor axial position set on a steam turbine?

A

With shims at the thrust bearing.

105
Q

On steam turbines, what are the two functions of thrust bearings?

A
  1. Keep the rotor in a specified position.
  2. Absorb any remaining axial thrust on the rotor.
106
Q

On tandem-compound turbine arrangements with solid couplings, how many thrust bearings are required to control axial movement of all coupled rotors?

A

One thrust bearing for all turbine sections.

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
Q

On a tandem-compound turbine arrangement with flexible couplings, how many thrust bearings are required to control axial movement of all coupled rotors?

A

On thrust bearing per turbine section.

108
Q

True or false: Each piece of equipment that connects to the turbine (generator) has its own thrust control.

A

True

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
Q

True or false: Turbines with reaction blades cannot depend on a thrust bearing alone to counter the axial thrust generated within the turbine.

A

True

Some other method of thrust contorl is required (dummy piston, opposite flow arrangement, etc.).

110
Q

What is the purpose of dovetail guides in the cylinder (housing) of a steam turbine?

A

To allow for thermal expansion and contraction of the casing.

These are the same things as keyways.

These dovetails/keyways should be lubricated.

111
Q

True or false: Diaphragms in steam compressors have a specified clearance above, below and on each side of the rotor.

A

True

This is to reduce steam leakage.

112
Q

What are three ways to verify/determine the clearance of the diaphragms on steam turbines?

A
  1. Laser unit
  2. Paino wire
  3. Dummy shafts

All diaphragms are references to the turbine bearing centrelines.

113
Q

What is the reference point for all diaphragms in steam turbines?

A

The bearing centreline.

114
Q

On steam turbines, ________ have shims or crush pins installed for alignment and fitting.

A

diaphragms

115
Q

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.

A

True

This protrusion acts the same was as bearing crush.

116
Q

What three things must the diaphragm clearance on steam turbines account for?

A
  1. Shaft sag
  2. Clearances between components
  3. Thermal growth within the casing
117
Q

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?

A

To allow the sealing segments to be pushed back in the case of accidental contact with the shaft.

This can be caused by a bowed shaft or an uneven thermal expansion at startup.

118
Q

What are two reasons that a steam turbine shaft may come into contact with the spring loaded sealing segments in the diaphragm?

A
  1. Bowed shaft (sitting idle for too long)
  2. Uneven thermal growth at startup

Both of these issues arise at startup.

119
Q

How should labyrinth seal clearance be checked between the diaphragm and turbine rotors in a steam turbine?

A

With lead wire and a blade micrometer.

120
Q

How should steam turbine rotors be temporarily stored?

A

In a cradle that supports the ends of the shaft.

Ensure that the flooring can bear the weight of the turbine and cradle.

121
Q

When installing a rotor into a steam turbine, what three measurements must be taken?

A
  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
Q

When installing a rotor into a steam turbine, how would the clearance between the blades and casing be verified?

A

By taping lead wire to the rotor blade and then measuring it with a blade micrometer.

This goes for the measurements between blades and diaphragms as well as the measurements between the rotor shaft and labyrinth seals.

123
Q

What type of shaft seal would be used on large steam turbines with high surface speeds?

A

Labyrinth seals

124
Q

What type of labyrinth seal can be replaced without having to remove the rotor of a steam turbine?

A

J strips

125
Q

How are J strips secured to the shaft of a steam turbine?

A

A wire is pushed into the groove and peened so that it cannot slide out

The strips are then machined to the correct diameter.

126
Q

When installing J strips, once the strip has been installed into place and peened, what last step must be taken?

A

Machining the strip to the correct diameter

127
Q

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?

A

The top casing

128
Q

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.

A

True

Failure to do so can result in serious damage to the turbine rotor assembly and stationary blades.

129
Q

How is the tension of the fasteners that hold the top and bottom half of a turbine casing together determined?

A

With bolt stretch

This is the most accurate way to tensioning fasteners.

130
Q
  1. This method of cylinder bolt installation and preloading requires large bolts with hollowed cores.
  2. What is the hollow core for?
A
  1. Thermal elongation
  2. An electric heating element can be placed in the core for even heating of the fastener
131
Q

True or false: When installing and preloading cylinder bolts with thermal elongation, a gas flame can be used to heat the fasteners up.

A

True; but there should be no contact between the fastener and the flame

Direct contact with the flame could damage the material of the bolt.

132
Q

How are smaller bolts tensioned and preloaded on steam turbines?

A

With a torque multiplier turning the bolt a certain number of degrees of rotation.

This is similar to the torque turn method.

No heat is applied with this method.

133
Q

How are larger and longer bolts measured for bolt stretch?

A

With hole drilled lengthwise through the bolt.

This allows us to measure bolt stretch from the inside out.

134
Q

What three tools are required to measure bolt stretch from the inside of the bolt?

A
  1. depth micrometer
  2. adapter
  3. extension rod
135
Q

After installation, how should tightness and bolt stetch be checked periodically?

A

With high-frequency sound waves

If there is any discrepancy in the time of flight, the previous records can be checked and comapred.

136
Q

When installing bolts with the bolt stretch method with heat, what can happen if the flanges are overheated?

A

The bolts may be below the required torque

This is due to excessive flange shrinkage after the heat is removed.

137
Q

When checked bolt elongation with high frequency sound waves, what are you measuring?

A

Time of flight

This is how long it takes for the sound wave to travel to the end of the bolt and then bounce back.

138
Q

True or false: Small steam turbines under 10 megawatts (MW) are shipped completely assembled.

A

False

Under 1 megawatt are shiped completely assembled.

139
Q

The foundation of a steam turbine must do what 4 things?

A
  1. Remain in position without settling
  2. Operate without excessive vibration
  3. Thermally expand without stress
  4. Handle dynamic loads*

*These loads are associated with shaft rotation, sudden load changes, and forces exerted due to piping or driven equipment.

140
Q

True or false: The condenser of a steam turbine must be loacted below the final stage of the turbine.

A

True

The condenser is usually located below the turbine to take advantage of gravity for steam and condensate flow.

141
Q

The foundation of the turbine should be at least ________ times the mass of all the steam turbine assembly.

A

2.5

This ensures the foundation does not move and helps dampen vibrations.

142
Q

Large steam turbine mount on foundations that have openings in the floor. Why is this?

A

To mitigate thermal expansion

The hole allows the turbine cylinder to be mounted along the centerline, with the bottom half of the cylinder hanging in the opening.

143
Q

What effect does mounting steam turbines along the cylinder centreline have on thermal expansion of the shaft centreline?

A

It reduces it

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
Q

What is used to support a steam turbine when it is set on the bed of the foundation?

Three items.

A
  1. Sole plates
  2. Grout pads
  3. Wedge block
145
Q

What would happen to a steam turbine if the rotor wasn’t barred over while the turbine was heating up?

A

The turbine would heat unevenly, resulting in the top of the turbine heating up quicker than the bottom.

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
Q

True or false: When the foundation for a steam turbine is poured, the top of the foundation should have steel sole plates installed

A

True

147
Q

When installing a larger multi-stage steam turbine assembly, which components are installed first?

A

The bearing pedestals and the bottom halves of the cylinders.

These components have keyways (dovetails) to allow the casing to expand in length and width.

148
Q

Which large multi-stage steam turbine assemblies are equipped with dovetails or keyways?

A
  1. The bearing pedestals
  2. The bottom halves of the cylinders

These allow for thermal expansion of the turbine without distorting the foundation.

149
Q

What is the purpose of dovetails or keyways on the bottom halves of steam turbine cylinders?

A

To allow longitudinal thermal expansion of the turbine without stressing the foundation.

150
Q

This steam turbine component is located at the end of each casing and is mounted directly to the sole plates.

A

The bearing pedestals

151
Q

What is the purpose of an alignment key on steam turbine bearing pedestals?

A

To keep the pedestal and cylinder in alignment.

152
Q

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?

A

To mimic the weight of the whole turbine in order to reduce cylinder sag.

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
Q

What are the two methods used for aligning a steam turbine and which one is more accurate?

A
  1. Paino wire
  2. Laser alignment ⟶ more accurate

The laser alignment also takes less time.

154
Q

When installing the sections of a steam turbine and generator, what needs to be taken into account when aligning the shafts?

A

The sag of the turbine unit needs to be taken into account.

This permits the rotor couplings to mate properly.

155
Q

On steam turbines, what is a bridge gauge?

A

A measuring instrument used to monitor the wear of the main bearings.

It does this by measuring the distance between the bridge and the top of the turbine shaft.

156
Q

True or false: Every bearing pedestal on a steam turbine has a bridge gauge.

A

True

157
Q

What does a larger bridge gauge measurement on a steam turbine indicate?

A

Increased wear on the main bearings.

The larger distance is caused by the bearing wearing, which drops the main turbine shaft away from the bridge gauge.

158
Q

This component of a steam turbine is used to measure main bearing wear.

A

A bridge gauge

It measures main bearing wear by measuring the distance from the bridge to the top of the turbine shaft.

159
Q

When a steam turbine has sat idle for some time, how long will the rotor be barred over before being started up?

A

Until the eccentricity meters indicate the shaft is of acceptable straightness.

This could be for several hours.

160
Q

Why do casing drains need to be open during start-up of a steam turbine?

A

Steam entering the cold turbine condenses into water.

The water drains should be left open until the machine reaches thermal saturation.

161
Q

When starting up a steam turbine, how long should the casing drains be left open?

A

Until the steam turbine reaches thermal saturation

Thermal staturation ⟶ the turbine is the same temperature as the steam.

162
Q

Why is it important to ensure that the thermal growth of a steam turbine at start-up is gradual and equal in all parts?

A

Uneven thermal growth can result in rubbing.

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
Q

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.

A

True

164
Q

Where is the nozzle ring located in a steam turbine?

A

In the steam chest

165
Q

During start-up of a steam turbine, the turbine should first be loaded to about ________% to allow for further thermal expansion.

A

20%

166
Q

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.

A

True

167
Q

What two functions do automatic controls on a steam turbine?

A
  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
Q

On a steam turbine, what is a trip valve exerciser?

A

Allows the overspeed trip mechanism to be verified without shutting down the turbine.

The exerciser can confirm the movement of the trip valve stem without shutting down the turbine.

169
Q

How often should a trip valve exerciser on a steam turbine be checked?

A

Weekly

On large turbines.

170
Q

This steam turbine test requires the turbine to be uncoupled and run on bypass steam until the trip speed has been reached.

A

An overspeed trip check

This test is very dangerous, yet the only way that one can verify an over-speed trip setting.

171
Q

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 ________℉.

A

105℉ to 140℉

172
Q

On steam turbine bridge gauges, main bearing wear is indicated to what references?

A

Either a lowering of the shaft or a lateral movement of the shaft in relation to the bridge.

173
Q

What is a transverse anchor block on a steam turbine assembly.

A

A transverse anchor block in a steam turbine assembly is a structural component designed to anchor and stabilize the turbine casing or shaft.

174
Q

Why are steam admission valves arrenged so that the valves open at different positions?

A

To progressively admit the steam.

This is what allows for the variable control of the steam through the valve.

Millwrong (27 decks)

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