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Millwright 4th yr. RTS > Steam Turbines > Flashcards

Steam Turbines Flashcards

1
Q

In many cases, why impulse turbines has a few nozzles are located in only one half of the casing because?

A

No sealing is required

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2
Q

The total energy available from the steam is due to its:

  1. heat
  2. weight
  3. pressure and
  4. velocity - is called
A

Enthalpy of the team

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3
Q

What makes the changes the pressure to velocity in one step and using the same shape as rotor blades, except they are held stationary..

A

The impulse nozzles

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4
Q

Which system that control the steam admission valves can reach 2500 psi?

A

Jacking oil system and hydraulic system

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5
Q

What type of blades that gas turbines used?

A

Reaction profile

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6
Q

Steam leak detection

Advanced and simple leak detection tools are

A 
Advanced tools:
- infrared thermography
-ultrasonic acoustic equipment
Simple tools:
-stick with a rag
- a piece of cardboard
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7
Q

A steam turbine is a type of external or internal combustion engine

A

External combustion engine

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8
Q

For every action, there is an equal and opposite reaction

A

Newton’s third law

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9
Q

On what type of turbine blade the velocity increases pressure drops

A

Reaction blades

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10
Q

What type of turbine’s blades that

  • no change in steam pressure but loss/decrease steam velocity
  • minimal axial thrust due to symmetrical design
  • the energy transferred to the rotating blade is due only to change in direction, giving the wheel an impulse
  • run at higher speeds coz they utilizing the energy in few stages (converts kinetic energy in mechanical energy)
A

Impulse blades sometimes called a “bucket”

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11
Q

What is called rows of fixed or reversing flow guide blades attached to the casing are set between the rows of moving blades

A

Re-directional blades also called reversing blades

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12
Q

What type of turbine blades that are not symmetrical and their tips are not parallel to the shaft and space between the blades is smaller at the exit side, this causes the steam pressure drops and velocity increases?

A

Reaction blades

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13
Q

In reaction turbine, the press drop across moving blades develops an ______ on the rotor

A

unbalanced axial thrust

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14
Q

In reaction turbine
1 the absolute velocity rises in the _____ blades and drops in the ______ blades
- why velocity drop in the moving blades

A
  • fixed blade, moving blades

- because they are imparting energy to the moving wheel

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15
Q

The turbine blades are attached to the rotor by several methods, the most common attachment is the…

A

dovetail or the fir tree method

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16
Q

Low pressure blades has a ____ profile

This gives the blade a partial _____ profile near the base and a _______ profile near the tip

A
  • twisted profile

- impulse profile near the base - and a reaction profile near the tip

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17
Q

When the blades get very large, shrouding is not used, but for added strength and stiffness _____ is used?

A

wire lacing

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18
Q

In reaction turbine, these ____ with ____ are located between each row of rotating blades

A

diaphragms with nozzles

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19
Q

In reaction turbines, the turbine blades get ____ in each successive stage in order to accommodate the steam expansion throughout the turbine

A

longer

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20
Q

-How to determine impulse
steam turbine staging?
- and how many casing

A
  • by each totating wheel as one stage

- only one casing

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21
Q
  • How to determine reaction steam turbine staging?

- How many casing, cylinder or section?

A
  • by a ring of nozzles and the associated rotor wheel with moving blades
  • often more than one casing, cylinder or section
    This section are:
  • high pressure section - HP
  • intermediate pressure section - IP
  • low pressure section - LP
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22
Q

Steam Chest
- the steam chest comes from the boiler or the supply line to the steam admission valve and then to the steam chest. The steam chest bolts to the steam end of the turbine casing which is the strongest part of the turbine. The steam chest has a strainer “WITCH’S HAT” to keep particle from entering the turbine

A

-

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23
Q

When steam goes through any reaction type nozzles

  • steam pressure decreases
  • steam velocity increases
  • steam volume increases
A

-

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24
Q

The reaction turbine is inefficient at higher pressure due to?

A

Leakage past the blade tips

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25
Q

This turbine is good for varying loads, for using high pressure steam and for using all the energy in the steam..

A

A combination impulse/reaction turbine

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26
Q

Condensing steam turbines are more efficient that non-condensing turbines due to?

A
  • less back pressure (steam is now cooling water state) and recycled condensate
  • vacuum created in the condenser
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27
Q

On small turbines, the rotor has wheels or discs that are shrunk and keyed to the shaft and have impulse bucket or blade mounted around its circumference

A

-

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28
Q

On large turbines, rotor disc are machined as part of the shaft with grooves around its circumference for mounting the blades in position

A

-

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29
Q

Which valve controls the position of the steam admission valve to control the speed

A

governor valve

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30
Q

Which valve admits steam to the nozzles?

A

“Steam admission valves”

The governor adjust the position of the steam admission valve to regulate turbine speed

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31
Q

What valve is a warning device blows off and make a whistling sound (small turbines) in excess pressure?

A

sentinel valve

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32
Q

Which valve shuts off all steam to the turbine in the event of an overspeed situation?

A

“stop valve”

  • this spring loaded valve is activated mechanically or by releasing hydraulic fluid that overcomes the spring load which hold the valve open in normal postition
33
Q
  • Bearing on small turbines may be?

- Many larger turbines use bearings that have..

A
  • either plain bearings or anti-friction bearings
  • self-aligning spherical seats, the spherical seats allow the bearing to tilt according to the sag of the shaft spherical seats also help maintain shaft contact during thermal growth movement
34
Q
  • What types of bearing used on small impulse turbines that develop little axial thrust?
  • What types of bearings used on larger turbines, especially those that use reaction blades, the turbine shaft usually has a thrust collar.
A
  • a deep grooved ball bearings
  • a set of tilting pad bearings acts on the thrusts collar, usually located at the steam inlet end. Tilting pad bearings also called kingburry thrust bearings
35
Q

The shaft seal prevent leakage

  • Types of seals use on small turbines
  • and on larger turbines
A
  • small turbines used “carbon seals”
    assemble carbon ring according to the match marks and install them with the marks (dots) toward the pressure
  • larger turbines used “labyrinth seals”
36
Q

How labyrinth seals works?

A

They operate on the principle of pressure dropping each time the steam accelerates past the knife edge restriction. Axial shaft position is critical to the survival of these seals.

37
Q
  • What types of seals will be used if the thermal growth exceeds the capability of labyrinth seals?
  • And its operating principle
A
  • Annulus seals

- the principle is the same as a labyrinth, but axial movement is not a factor

38
Q

What type of seals use for very high pressures or when sealing a vacuum on the condenser end of a large turbine

A
  • by using a series of labyrinth seals with steam pocket, (steam seals) where steam is either introduced or bled off between the sets of labyrinth seals
39
Q

Regular maintenance
Most failures occur because of some type of lubrication issue. Over speed conditions cause the majority of catastrophic failures; monitoring lube oil is a small investment when you consider it’s importance

A

-

40
Q

Shaft couplings

  • are often integral on large turbines
  • removable on smaller units
  • coupling bolts are typically marked for each specific location due to fit and balance
A

-

41
Q

Condensing turbines
In the condenser - the latent heat of the steam transfer to the cooling water in the condenser. This creates a low pressure (vacuum in the condenser. The lack of back pressure and the turbulence in the last set of turbine blades increase turbine efficiency. Condensing steam turbines are more efficient that non-condensing turbines

A

-

42
Q

Extraction control valve
Reasons for extraction steam
- used to feed water heating
- to avoid wet steam in the later stages of the turbine
- regulates flow to the remainder of the turbine in an effort to maintain constant back pressure at the extraction point of the preceding section.

A

-

43
Q

In reaction turbines, the turbine blades get longer in each successive stage in order to accommodate the steam expansion throughout the turbine

A

-

44
Q

Reaction Turbine
The blade must be made strong enough to withstand:
- high temperatures
-stresses from heavy, often pulsating
- team loads
There is also the stress due to centrifugal force for large LP blades, the centrifugal force on a single blade may exceed 200 tons

A

-

45
Q

2 places has to be seals

  1. case
  2. shroud of the blade
A

-

46
Q

What types of seals are used on reaction turbines to increase efficiency? Specific location - casing to the tip of blade?

A
  • blade seals
  • the blade seals maybe of radial or axial design and are often part of the shroud. The seal clearances are kept as small as possible.
47
Q

The weight of the blade multiplied by the radial distances to the center of gravity of each blade.

A
  • moment weight

- if the moment weight is perfectly balance, this minimizes the amount of balancing required

48
Q

In turbines power operation,
What type of controls, when the turbines running of a sudden removal of the load to the generator? Or running during high acceleration?

A
  • acceleration governor

- the governor closes the admission valve only during high acceleration

49
Q

Must be tested after doing any maintenance on the trip system and after any major overhauls

  • safety feature is used to shut
  • steam off to the turbine in an over speed situation?
  • over speed trips must be manually reset if they are tripped
A
  • over speed trip
  • speed trip settings usually 110% ti 115% of operating speed
  • when disassembling the over speed trip mechanism, count the number of turns required to remove the spring. This makes assembly easier because you get close to the correct tripping speed
50
Q

Remove Flange nuts:
Most turbines have a row of casing bolts, nuts and studs to hold the thick flanges of the turbine together.
Procedure and method for removing the bolts:
-hydraulically stretched bolts that have to be stretched before you unscrew the nuts
-many large bolts are hollowed so they can be heated internally with electric heating element or hot air. When the stud heated, the nut can be removed.

A

Many of the smaller bolts can be undone using torque multiplier or hammer wrenches

51
Q

Casing drain are in the lower parts with the turbine casing and steam chest.
Must be opened and checked for water - before start-up and after shut down

A

-

52
Q
  • When the over speed trip activates, it closes the ____ and stop the flow of steam to the turbine.
  • and where this valve mounted?
A
  • stop valves

- mounted in the steam system before the steam chest

53
Q

Impulse section of the large turbines does not generate much thrust, but the reaction part of the turbine does.
Thrust control methods:
1. dummy (balance) piston and balance pipe
2. rotor configuration to reduce the burden on the thrust bearing

A

-

54
Q

A _____is a part of the rotor with several stepped diameters that the steam pressure in the turbine can push against to counteract the thrust.

A

a dummy (balance) piston and balance pipe

55
Q

Thrust control methods by rotor configuration:

  1. dual flow rotors
  2. opposite flow designs
A

-

56
Q

The thrust control method are arranged so that the steam enters the cylinder at the center and takes 2 paths in opposite direction and how to identify them?

A
  • dual flow rotors
  • identified them by their “hourglass shape”
  • control of axial thrust
57
Q

A major auxiliary component that move the condensate from the condenser back into the boiler. They must be able to withstand and overcome the higher pressure in the boiler.

A

” boiler feed pumps”

58
Q

Relief valves for non-condensing turbines.
Must have a relief valve between the turbine and the turbine discharge isolation shut-off valve to reduce the possibility of turbine explosion if the isolation shut-off valve is closed or the case is over pressure

A

Relief valve or rupture disc for condensing turbines

- have an atmosphere relief valve or a rupture disc located in the low pressure section

59
Q

Generator cooling

  • small generators are air cooled
  • larger generators are cooled with hydrogen, very effective
A

-

60
Q

Turning Gear ( barring gear)

  • features and
  • mounting location - usually the drive is in the bottom half of the pedestal or some on the coupling spacer has gear teeth on it so it is used as a point of contact
A
  • enables the slow rotation of the turbine rotors while there is no steam flowing
  • speed can be varied anywhere from 1 to 60 rpm
  • used to rotate rotor slowly long before start-up so that any bow in the rotor due to sag can be removed before started
  • to allow evenly heating
61
Q

Lubrication

  • large turbines use pressured lubrication provides a large volume at about 40 psi
  • small turbines use an oil ring lubricating system
A

-

62
Q

Jacking Oil

  • supplies oil at pressures of several hundred to a few thousand PSI
  • purpose to lift the rotors off the bearing and supply oil film for the shaft to ride on before any shaft rotation occurs
A

The jacking oil is applied before the start-up of the turning gear and at very slow rotor speeds. The jacking oil is left on until about 50 to 60 rpm

63
Q

Turbine top casing

When the cover is to be installed later, what a jointing compound may be used?

A
  • often boiled linseed oil
64
Q

Type of recording system during inspection/overhauling?

A

as- found and as-left measurements

65
Q

Types of bearings on each end of the turbine rotors

A
  • radial load journal bearing
    the journal bearing surface is made of a soft, multi metal composition known as BABBIT
  • one thrust bearing
66
Q

Journal bearings

  • mounting location
  • is it height adjustable
  • typical babbitted journal bearings clearance
A
  • mounted in the turbine pedestal
  • are adjustable by addition or subtraction of shims
  • clearance about 0.001/in of shaft O
67
Q

Oil Viscosity

  • acceptable range oil viscosity entering the bearings occurs when the oil temperature is between
  • exits the bearing at about
A
  • 105F to 140F (41C to 60C)

- 130F to 160F (54C to 71C)

68
Q
  • How many thrust bearings on a tandem compound turbine are joined together with solid couplings?
  • What type of bearings need if flexible couplings are used?
A
  • only one thrust bearing is used to control axial movement of all couples rotors
  • each rotor assembly needs a thrust bearing
69
Q

The hot gases are directed toward the turbine rotor blades which has…

A
  • high velocity
  • high temperature
  • and lower pressure
70
Q

Turbine shaft arrangement
Parallel shaft arrangement
Can be found on?

A

cross compound turbines

71
Q

Steam turbines - the blades getting bigger or longer at the end of compressor
Gas turbines - the blades getting smaller at the end of compressor

A

-

72
Q

Thrust bearing

  • Controlling the axial thrust is an aspect in larger reaction turbines. The shaft of the turbine has a thrust bearing collar that is either an integral part of the shaft or is attached to the shaft for thrust control
  • There is also a set of fitting pad bearings that push on the thrust collar
  • The rotor axial position is set with shims at the thrust bearing location in the turbine housing
A

-

73
Q

Diaphragm, seals and packing installation

  • A laser unit, piano wire or a dummy shaft cn be used to determine clearance
  • All diaphragm positioning is referenced to this turbine centerline using bearing centers.
  • Diaphragms have shims or crush pins installed for alignment and fitting
  • One method for checking rotor to labyrinth seal clearance is by using lead wire
A

Gap measured by lead wire, lead wire crushed down and tools used in measuring lead wire crushed is “ blade micrometer”

74
Q

Rotor Installation

  • When you install the rotor, check the clearance between the blades and casing, blades and diaphragms and rotor shaft and labyrinth seals. You do this by taping lead wire to the blades and seals.
  • You must measure all blade and seal markings.
A

-

75
Q

Top Casing Installation
- Lead wire has to be placed in the 1st half of casing and then lower down the top casing. The top casing has to be removed to measure the lead wire indicating the clearance at the top of the rotor (seals and blades)

A

-

76
Q

Bolt Stretch Method

  • You must measure the bolts before and after they are tightened to ensure the correct amount of stretch. The larger and longer bolts have holes drilled lengthwise in the bolt to measure the stretch from the inside
  • if you can’t measure the bolt stretch, you have to make calculation by determining the force on the wrench and the length of the wrench handle or by calculating the amount of stretch for every turn of the nut
A

-

77
Q

Grouting

  1. The top of the foundation should have steel sole plates installed. These steel plates have 2” - 3” thick steel plates
  2. The initial parts installed are the bearing pedestal and the bottom halves of the cylinder. These are installed with keyways and guides often dovetail shape for superior, that allow turbine casing to expand in length and width
A

-

78
Q

Bearing Installation

  • The bearing position and alignment can be adjusted by adding or removing shims from several positions (pads) under the bearing.
  • Some turbines use a bridge gauge designed to indicate main bearing wear as referenced by a lowering of the shaft or a lateral movement of the shaft
  • The bridge gauge is used to determine when to schedule maintenance of the turbine journal bearings
A

-

79
Q

Many turbine rotor blades have a shroud attached to the end of the blade. The shrouding on blading is riveted in section over a tenon and acts to..

  • maintain blade spacing around the wheel
  • reduce leakage past the blades and the steam through the blades
  • strengthen the whole blade assembly
A
  • reduce blade vibration and stress by changing the natural frequency of the blades

Millwright 4th yr. RTS (15 decks)

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