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4th Year Millwright > Steam Turbines > Flashcards

Steam Turbines Flashcards

1
Q

What is the preferred prime mover in an explosive environment?

A

The steam turbine

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2
Q

What is the purpose of a sentinel valve on a steam turbine?

A

It makes noise (whistles) to warn of overpressure in the turbine

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3
Q

Steam leaks on a turbine may be invisible and are a serious hazard. What methods can be used to detect potential leaks?

A

Leak detection tools such as thermography, ultrasonic, and a simple stick with a rag attached

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4
Q

What condition should the turbine be in when conducting an inspection and test of the overspeed trip?

A

unloaded

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5
Q

What type of engine is a steam turbine?

A

external combustion

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6
Q

What are the two types of turbine blading?

A

Impulse and Reaction

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7
Q

Which type of blading does not produce a pressure drop across it and why?

A

Impulse blading does not produce a pressure drop because there is no change of space between the entry and the exit through the blading

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8
Q

Where does the pressure drop occur in a velocity compounding impulse turbine?

A

The pressure drop occurs at the nozzles before the first set of moving blades.

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9
Q

What happens to the steam as it passes through reaction blading and why?

A

Reaction blading is not symmetrical and the space between the blades is smaller at the exit side. This causes a pressure drop and velocity increase through the blades.

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10
Q

What would a reaction turbine often have to allow it to be shorter in size and increase efficiency?

A

A velocity compounded impulse section at the inlet end of the machine.

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11
Q

Which type of steam turbine produces the most thrust?

A

a condensing turbine

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12
Q

Why does the clearance between the blades and the casing need to be kept to a minimum?

A

To prevent the steam from leaking around the periphery of the blades instead of passing through them

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13
Q

What could the potential centrifugal forces on large, low pressure blades be on just a single blade?

A

Over 200 tons

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14
Q

What is used to attach a turbine rotor blade to its shrouding?

A

a tenon

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15
Q

What is used to add strength and stiffness to the blades sometimes with the shroud, or without the shroud on very large blades?

A

wire lacing

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16
Q

What are the two most common methods of attaching turbine blades to a rotor?

A

the dovetail and fir tree method

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17
Q

What is the speed called at which a rotor becomes unstable and begins to vibrate violently?

A

critical speed

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18
Q

In reaction turbines, why do the turbine blades get longer in each successive stage?

A

to accommodate the steam expansion throughout the turbine

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19
Q

What are the 3 sections that may be connected together to form a very large reaction turbine?

A

HP (high-pressure), IP (intermediate-pressure), and LP (low-pressure) sections

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20
Q

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

A

combination impulse/reaction turbine

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21
Q

What turbine has several sections which are connected to each other at their shafts in a series?

A

tandem compound turbines

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22
Q

Which turbine has multiple turbines with parallel shafts?

A

cross compound turbines

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23
Q

Where is the highest point of pressure in a steam turbine?

A

the steam chest

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24
Q

What are the nozzles in a steam turbine?

A

Stationary blades or orifices the direct steam toward the blades and change high pressure from the boiler into high velocity at the nozzle

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25
Q

What is the SAV, and what controls it?

A

The Steam Admission Valve admits steam to the nozzles and is controlled by the governor

26
Q

Where is the thrust bearing on a steam turbine normally located?

A

at the steam inlet end

27
Q

What type of shaft seals are used on small turbines?

A

carbon seals

28
Q

What type of shaft seals are used on larger turbines?

A

labyrinth seals

29
Q

How are carbon rings installed?

A

according to match marks with the marks (dots) toward the pressure

30
Q

Which seal operates on the principle of pressure drops each time the steam accelerates past a knife edge restriction?

A

labyrinth seals

31
Q

What value is given to a turbine blade to ensure proper rotor assembly?

A

moment weight

32
Q

What is lagging?

A

Insulation used to minimise heat loss and protect against hot parts of the machine in a steam turbine.

33
Q

What is the principle difference between a condensing turbine and a non-condensing turbine?

A

Condensing turbines exhaust is at lower than atmospheric pressure, non-condensing exhaust is at higher than atmospheric pressure.

34
Q

What are some methods of compensating for thrust produced from pressure drops across blading in certain types of turbines?

A

Dummy piston/balancing drum, opposed flow design, dual flow design, thrust bearing

35
Q

What are 2 methods used to compensate for the effects of thermal change on the shafts of steam turbines?

A

Centerline mounting, and dovetails/keys for casing axial movement

36
Q

Name some of the purposes of blade shrouding

A

Seal, stiffen, dampen vibration, re-direct steam

37
Q

Diaphragms contain fixed blades that act as nozzles, and serve to…

A

re-direct flow, drop pressure and increase velocity

38
Q

Name the three areas that a steam turbine must be sealed

A

tips of blades, rotor and diaphragm, at either end of casing

39
Q

Name 3 types of seals found on steam turbines

A

carbon seals, labyrinth seals, water and steam seals

40
Q

What would be used to lift the upper casing on large steam turbines to prevent damage to the components:

A

spreader bars, levels, guide pins

41
Q

What type of governors do most steam turbines use?

A

Most use mechanical governors, though larger ones will use hydraulic governors.

42
Q

What is used to shut steam off in an overspeed situation?

A

the overspeed trip

43
Q

What is the overspeed trip setting usually?

A

110-115% of operating speed

44
Q

What relieves internal pressure from the turbine after it’s tripped? Where is the pressure sent?

A

the blowdown valve opens to relieve the internal pressure back into the condenser

45
Q

What are casing drains used for and where are they located?

A

Casing drains are located in the lower parts of the turbine casing and steam chest and are opened to check for water before start-up.

46
Q

What does the term “superheated” mean?

A

a vapour that is hotter than its boiling point

47
Q

What may happen to an SAV that operates in a highly restricted position for too long?

A

it may become wire-drawn or steam-cut

48
Q

What end of the turbine would a dummy piston normally be found?

A

HP end

49
Q

Dual flow rotors are used to control axial thrust in some turbines, how are they identified and what section of the turbine would they be found in?

A

Identified by their hourglass shape, found in the LP section

50
Q

What purpose does the turning(barring) gear serve?

A

To remove bow in the rotor due to sag and allow for even heating to the rotor on start-up.

51
Q

Aside from bearing lubrication, what other main function does the lube system on a steam turbine carry out?

A

carry away heat transferred from the steam

52
Q

What are walnut shells used for on a steam turbine?

A

to remove buildup of deposits on blades and nozzles

53
Q

What type of bearing material is commonly used on larger steam turbines, and how much contact should the bearings have on the shaft journal?

A

tin-based Babbitt is commonly used, and the bearing should have 85% contact or more with the shaft journal

54
Q

How much clearance would a typical babbitted journal bearing have?

A

About 0.001” clearance per inch of shaft diameter

55
Q

What is the purpose of the spherical seats in turbine bearings?

A

to accommodate shaft sag when unit is shut down

56
Q

How is the clearance of the thrust bearing set in a larger reaction turbine?

A

shims

57
Q

What is the most accurate method of torquing the bolts on a large steam turbine casing? What is another method?

A

thermal elongation, another method is hydraulically stretching the bolts

58
Q

How large should the foundation of a turbine be relative to the turbine itself?

A

at least 2.5 times the mass of the turbine assembly

59
Q

What are two methods of aligning turbine parts, and which is most accurate?

A

piano wire and laser are two methods, laser is more accurate

60
Q

What gauge can be used to indicate main bearing wear?

A

bridge gauge

61
Q

What type of thrust bearing is normally used in a steam turbine?

A

tilting pad Kingsbury thrust bearing

4th Year Millwright (11 decks)

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