Chapter 69- Steam Turbines Flashcards
A steam turbine is considered
A prime mover
Where does a steam turbine derive its power?
Extracts energy from steam in order to do work and produce useful energy
Define an impulse turbine
If the entire steam pressure drop takes place in stationary nozzle
Imparts a force on the moveable blades
Define a reaction turbine
If the steam pressure drops in passing through moving blades as well as stationary nozzles or blades.
On an impulse turbine are the blades in constant contact with steam?
No only a portion of the blades are in contact at any given time
Impulse turbines the nozzles preform what function on the steam
Pressure is reduced and velocity is increased in the steam
An impulse rotor with a single rotor is called
A single stage impulse rotor
Multi staged impulse turbines were developed to
Make full use of the steam energy
High rotational speed in an impulse turbine
Will cause damage to the blades due to excessive centrifugal force
There are two types of impulse turbine compounding
Velocity compounding and pressure compounding
In an impulse turbine the steam pressure
Drops quickly
In a reaction turbine steam pressure
The pressure drops gradually
Define bearings
The bearings have a split sleeve and oil ring, with a precision bored high grade Babbitt lubrication is done by oil rings that are rotated by the shaft
Define Glands
The gland consists of several adjacently mounted segmental carbon rings, each maintained in close contact with the shaft by a garter spring and each located in its own independent groove this prevents steam leakage in the wheel shaft
What are blades
All blades are durable, rolled and drawn stainless steel,securely held in machined slots in the wheel ring by drive screws
In multi stage turbines what happens to the rotors?
They get bigger
What are the different types of impulse turbines
Pressure compounding
Velocity compounding
Pressure and velocity compounding
Single stage
How do you balance pressure in a steam turbine?
With a dummy piston
Turbine speed is controlled by the
Governor
Main cause of excessive speeds in turbines
Sudden loss of load
Two types of over speed trips
Mechanical and electronic
Mechanical overspeed trip
The extended weight, by centrifugal force, moves a lever which releases a spring that opens the control valve reducing speed dramatically
An overspeed trip usually trips at about
10-15% over the rated speed
Hand speed control
Located on the governor with a normal range of 10% over and 50% below the rated speed
An advantage of the steam turbine regarding lubrication
Bearings are located the high temperature steam zone, so it can deliver oil free condensate or exhaust steam
Large steam turbines can run at lower speeds because of
Compounding
Rotors often have segmental carbon ring sealing glands which are held in place by
Garter springs
A steam turbine should trip or shut down when normal operating speed is exceeded by
10-15%
Condensing turbines
Will have a vacuum in the last row of rotating blades
In a reaction turbine the velocity increase takes place in
Rotating blades, and stationary blades
The stationary passage of reaction turbines are the
Fixed blades
Blades or _________ form the rotor flow passages in impulse turbines
Buckets
The shrouding which connects the tips of the steam turbine blading serves to
Confine steam to the blades
Turbine overspeed trip
Will close the steam stop valve to the turbine
Turbine lubrication oil during use has these characteristics dealing with maintenance
Can be contaminated with water
Must be cooled
Can be used for the turbine governor
Must be filtered
Shaft sealing of steam turbines is done with
Water sealed glands
Carbon rings
Labyrinth seals when temperatures and pressure of the steam is high
The purpose of turbine glands is to prevent
Steam escaping from the turbine
Shaft sealing in high output turbines is done with
Labyrinth seals
Steam turbine governors
Regulate the speed of the turbine automatically
The great majority of turbine governors are of the ________ type
Mechanical centrifugal type
The hand wheel used to adjust the turbine speed on the governor is known as the
Speeder
When the steam pressure drop occurs in only the stationary members or components of a turbine, the turbine is known as an
Impulse unit
A large reaction turbine will have
Steam pressure dropping through moving and stationary sections
Turbine speed can be fine tuned with a device which will be limited to about 10% over the rated speed. This device is the
Hand speed control
Turbine thrust bearings are fixed to the casing and prevent ________ movement of the shaft
Axial
Shaft sealing carbon glands are
Self lubricating
Impulse turbines have these distinct characteristics
Have velocity increase through the nozzles
Blades have a angle of inlet same as the outlet
Could have more than one set of blades
May not require a thrust bearing
The principles of the impulse turbine is that the
Steam pressure is reduced through stationary nozzles
High velocity steam will impinge upon the blades
Steam pressure will drop across the blades
The steam turbine that has a pressure drop across varying sets of blades is a
Reaction turbine
In an impulse turbine, all of the steam pressure drop takes place in the
Stationary nozzle
In a reaction turbine the steam pressure in passing through moving blades, as well as stationary nozzles or blades
Drops
Journal bearings do (2)
- prevent radial movement of the shaft
* support the shaft with in the turbine
Sentinel valves do
Relieves high pressure on the exhaust side of the casing
What is turbine blading?
A combination of impulse and reaction rotors
Exhaust steam from a condensing steam turbine _____than the exhaust from a steam engine
Has more moisture
Which turbine uses a condenser
A turbine exhausting to a vacuum
A shrouding installed on the blading of a steam turbine serves to
Confine the steam to the blades
Turbine over speed trip (3)
- prevents exceeding max speed
- will close the steam stop valve
- should be tested before turbine is placed in services
Turbine trust bearings are fixed to the casing and prevent axial movement of the spindle by contacting a component on the shaft known as
Collar
Steam engines that has a pressure drop across every set of blades
Reaction
