Steam Turbines Flashcards
What is a sentinel valve?
A high pressure warning device on small turbines
What is Newton’s third law?
For every action, there is an equal and opposite reaction
What is Bernoulli’s principle?
When a gas or liquid passes through a restriction the pressure drops and the velocity increases. When the fluid or gas leaves the restriction the velocity drops and the pressure increases.
What are the two turbine blades and what shape is each?
Reaction blades, they look like a airplane wing
Impulse blades, that are symmetrical
What is the purpose of an impulse nozzle?
To change the pressure to velocity in one step.
Is there a change in steam pressure across an impulse blade?
No there is zero change in steam pressure across the blade when the steam passes through it. The blade spacing is the same between entry and exit.
What happens to the velocity on the impulse stationary blade?
It stays a constant because it is just redirecting the steam into the next moveable blade
How does a reaction blade work?
The steam pressure drops across both the fixed and the moving blades while the absolute velocity rises in the fixed blades and drops in the moving blades.
The velocity drop in the moving blades are because they are imparting energy to the moving wheel.
Do impulse blades require sealing between the blades?
No because there is no pressure difference
What are the most common ways of turbine blade attachment?
Dovetail and fir tree method
What happens when steam goes through any reaction type nozzle?
Steam pressure decreases
Steam velocity increases
Steam volume increases
How can staging of a turbine be determined?
By the number of rotating rows of blades in the turbine or by the number of pressure drops across the turbine
What is a combination impulse/reaction
turbine best for?
Good for varying loads
Using high pressure steam and
Using all the energy in the steam
What area of a turbine has the highest pressure?
The steam chest
How are carbon rings installed?
With the dots towards the pressure
When thermal growth exceeds the capability of labyrinth seals, what seal is used?
Annulus seals that consist of knife edges fitting close to a journal-like section of the shaft.
How does a labyrinth seal operate?
The principle of pressure dropping each time the steam accelerates past the knife-edge restriction.
How is moment weight calculated?
The weight of the blade multiplied by the radial distance to the centre of gravity of each blade.
What are the stationary blades in a reaction type turbine housed in?
The diaphragm
Where are diaphragms located on a reaction type turbine?
The diaphragms with nozzles are located between each row of rotating blades.
In a reaction turbine what are the he stationary blades also known as?
Nozzles
What is the purpose of the governor?
Used to control the turbine automatically under varying load conditions
How is an over speed device reset?
Manually
What should the overspeed trip setting be?
10-15% higher then maximum running speed
What are the 2 different ways to move a steam admission valve?
Either by use of a cam lift or bar lift
What is a steam condensers purpose?
To change steam back to water after it leaves the turbine so it can be recycled back to the boiler
What is a dummy (Balance) piston?
A part of the rotor with several stepped diameters that the steam pressure in the turbine can push against to counteract thrust
What is the purpose of the boiler feed pump?
To move the condensate from the condenser back into the boiler
What is a Turning Gear?
Barring gear
Enables the slow rotation of the rotors while there is no steam flowing through the machine. This is to minimize the effects or rotor sag
How much oil psi do large turbines use?
About 40 psi
What is jacking oil?
It is used to lift the rotor off the bearings and supply an oil film for the shaft before any rotation occurs
What speed is the jacking oil typically left on until?
50-60 rpm because this is when an oil wedge begins to form
What blading is better for higher pressure?
Impulse because the reaction blades seals can’t handle the higher pressures
