Hydraulic Turbines Flashcards
What are the components of the impulse turbine?
The buckets the stripper the disc or spoked wheel the nozzle body nozzle and needle servomotor base frame and wheel pit liner and water housing * No wicket gates!
When are multiple jets used on one impulse wheel?
2 jets are sometimes used to increase the power on the horizontal shaft will but in most cases they are used on a vertical shaft turbine if they are used.
What factors determine the power available at the nozzle in an impulse turbine ?
Power varies directly with Static head and the quantity of water Can be expressed through power equals quantity of water (ft^3) times static or total head divided by 8.8
Speed regulation in an impulse turbine?
Impulse turbine speed regulation is with denitto valve opening or closing as needed to maintain the electrical load.* It is important that the water hammer pressure be kept within reasonable limits to prevent the penstock from being damaged or ruptured
How to control the penstock pressure on impulse turbine?
During times when a decreased load is required from the generator the amount of water supply to the impulse turbine is reduced by the use of jet deflectors that deflect water from coming in contact with the wheel .* Also comes from auxiliary needle nozzles that move in sequence with the main needle valve the allows excess water to flow beneath the main nozzle, maintaining the flow and pressure through the penstock.
What is the key advantage in reaction or Francis turbines in regards to the diameter of the rotor?
The reaction turbine needs all the runner passages filled completely with water in order to work this factor alone permits a smaller diameter rotor needs be required over an impulse wheel
What are the main parts of a reaction turbine?
The main part of a reaction turbine RD casing, guide vanes or wicked gates, runner, draft tube and guide bearing. The auxiliary parts are the shifting ring, connecting links, servomotor, and pressure regulator. * No stripper
How do you obtain maximum efficiency from wicked gate position?
Wicket gates are also known as movable guide vanes and they regulate the amount of water entering the runner . The wicket gate is now almost universally used maximum efficiency can be obtained with wicked gates open to 80 to 90% of their open position.
What’s a good way to check the Effectiveness of the seal rings on the upper runner of a reaction turbine.
Leakage pasty upper seal can subject the Crown cover to penstock pressure on large butter passages are provided to bleed off this leakage quite often pressure gauges are install the Crown cover or Crown plait the amount of pressure showing on the gate is a good indication of the degree of the effectiveness of the seal ring.
What two key functions does a draft tube serve?
When is to allow the turbine runner to set above the tale water level without losing any of the head thereby creating an unbroken stream of water from headwater to taiwater. The other function is to reduce the velocity of discharge at exit from the draft tube, reducing the final loss of kinetic energy at discharge.Overall effect of the draft tube is to increase the effective head of the turbine.
What is the history in the operating functions of a propeller type turbine?
1st developed in 1919 by doctor Kaplan
1st developed as an adjustable blade type propeller runner, The blades adjusted automatically maintaining the best efficiency 4 wicket gate position and also for variations of head.
Cavitations effect on different materials?
Very hard on cast iron , not as bad on steel plate bronze and stainless steel. Cavitation would be a minor problem for a turbine that operated at constant load with no variation in the effective head.
What are the more common terms for the impulse, the reaction, and a propeller turbine?
The more common names are the pelton wheel, the Francis, and the Kaplan turbine.
What is one form of speed regulation in an impulse turbine?
Some installations provide an auxiliary needle nozzle below the main nozzle to reduce water flow during sudden load changes. As the governor rapidly moves the needle to reduce the flow of water to the buckets, it’s simultaneously opens the auxiliary nozzle which functions to discharge in a jet that completely misses the wheel, thus there is no change in flow through the penstock.
What is specific speed of a turbine?
The speed in revolutions per minute at which a model in question would operate with a runner of such a size as to deliver one horse power under one foot of head.
