Steam Turbines

Question 1

What is the preferred prime mover in an explosive environment?

Answer 1

The steam turbine

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

unloaded

Question 5

What type of engine is a steam turbine?

Answer 5

external combustion

Question 6

What are the two types of turbine blading?

Answer 6

Impulse and Reaction

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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.

Question 10

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

Answer 10

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

Question 11

Which type of steam turbine produces the most thrust?

Answer 11

a condensing turbine

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Over 200 tons

Question 14

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

Answer 14

a tenon

Question 15

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

Answer 15

wire lacing

Question 16

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

Answer 16

the dovetail and fir tree method

Question 17

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

Answer 17

critical speed

Question 18

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

Answer 18

to accommodate the steam expansion throughout the turbine

Question 19

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

Answer 19

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

Question 20

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

Answer 20

combination impulse/reaction turbine

Question 21

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

Answer 21

tandem compound turbines

Question 22

Which turbine has multiple turbines with parallel shafts?

Answer 22

cross compound turbines

Question 23

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

Answer 23

the steam chest

Question 24

What are the nozzles in a steam turbine?

Answer 24

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

Question 25

What is the SAV, and what controls it?

Answer 25

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

Question 26

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

Answer 26

at the steam inlet end

Question 27

What type of shaft seals are used on small turbines?

Answer 27

carbon seals

Question 28

What type of shaft seals are used on larger turbines?

Answer 28

labyrinth seals

Question 29

How are carbon rings installed?

Answer 29

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

Question 30

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

Answer 30

labyrinth seals

Question 31

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

Answer 31

moment weight

Question 32

What is lagging?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

Centerline mounting, and dovetails/keys for casing axial movement

Question 36

Name some of the purposes of blade shrouding

Answer 36

Seal, stiffen, dampen vibration, re-direct steam

Question 37

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

Answer 37

re-direct flow, drop pressure and increase velocity

Question 38

Name the three areas that a steam turbine must be sealed

Answer 38

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

Question 39

Name 3 types of seals found on steam turbines

Answer 39

carbon seals, labyrinth seals, water and steam seals

Question 40

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

Answer 40

spreader bars, levels, guide pins

Question 41

What type of governors do most steam turbines use?

Answer 41

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

Question 42

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

Answer 42

the overspeed trip

Question 43

What is the overspeed trip setting usually?

Answer 43

110-115% of operating speed

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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.

Question 46

What does the term "superheated" mean?

Answer 46

a vapour that is hotter than its boiling point

Question 47

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

Answer 47

it may become wire-drawn or steam-cut

Question 48

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

Answer 48

HP end

Question 49

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?

Answer 49

Identified by their hourglass shape, found in the LP section

Question 50

What purpose does the turning(barring) gear serve?

Answer 50

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

Question 51

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

Answer 51

carry away heat transferred from the steam

Question 52

What are walnut shells used for on a steam turbine?

Answer 52

to remove buildup of deposits on blades and nozzles

Question 53

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

Answer 53

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

Question 54

How much clearance would a typical babbitted journal bearing have?

Answer 54

About 0.001" clearance per inch of shaft diameter

Question 55

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

Answer 55

to accommodate shaft sag when unit is shut down

Question 56

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

Answer 56

shims

Question 57

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

Answer 57

thermal elongation, another method is hydraulically stretching the bolts

Question 58

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

Answer 58

at least 2.5 times the mass of the turbine assembly

Question 59

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

Answer 59

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

Question 60

What gauge can be used to indicate main bearing wear?

Answer 60

bridge gauge

Question 61

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

Answer 61

tilting pad Kingsbury thrust bearing