Control valve or distribution valve or relay valve Centrifugal governor or pendulum Rotating guide vanes Regulating lever, regulating rod and regulating ring Gear pump is used here as oil pump in the oil pressure governor. Gear pump will be driven by the power obtained from the turbine shaft. Centrifugal governor or pendulum will be connected with the turbine main shaft with the help of belt or gear. Piping arrangements will connect the oil sump with the control valve and control valve to servomotor or relay cylinder. Rotating guide vanes control the flow rate of water flowing to turbine.
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Characteristics of Water Turbines 2. Governing of Water Turbines 3. Characteristics of Water Turbines: 1. Head: Reaction turbines of various types can be used for operating heads up to m and Pelton turbines are used for operating heads above m. Specific Speed. Turbine Setting: A Pelton wheel is always set at a higher level than the highest tailrace level usually 2 m above while a Francis turbine runner is placed at a level very near or below the lowest tailrace level.
The generator coupled to the turbine must be capable of withstanding the full runaway speed of turbine under permissible head. From the curves drawn, it can be concluded that the Kaplan and Pelton turbines perform well at part loads but Francis and Propeller turbines do not. Governing of Water Turbines: In order to have electrical output of constant frequency it is necessary to maintain speed of the alternator driven by the turbine constant.
This is achieved by controlling the flow of water entering the turbine by the automatic adjustment of guide vanes in case of reaction turbines and of the nozzle needle in the case of impulse turbines. Such an operation of speed regulation is called the governing, and it is attained automatically by means of a governor. In case of impulse turbine the governor also operates the auxiliary relief valves or jet deflectors.
With the movement of deflector plate out of the path of water jets, the needles slowly reduces the flow of water so as to keep the output of the turbine constant at the level of new load.
The regulators close as fast as the guide vanes open and vice versa. The governor should be quite sensitive to variations in the shaft speed and should be rapid in action but not so rapid as to cause water hammer in the penstock. The governing systems for the modern hydraulic turbines have a regulating time of seconds. Control valve or relay valve to supply fluid under pressure to the power cylinder servomotor in order to actuate the turbine control mechanism.
The use of control valve and servomotor is to amplify the small force created by the flyballs. The restoring mechanism or follow-up linkage to hold the servomotor in required fixed position when the turbine output and load demand are equalised. The fluid pressure supply required for the action of servomotor. The flyballs may be belt driven, as shown in Fig.
The piston moves to the left and closes the nozzle with the help of a spear in the case of Pelton wheels and adjusts the guide vanes in the case of reaction turbines. In case of increase of load on the generator, the speed of the turbine will decrease and the reverse action would take place. The restoring or follow up linkage resets the relay; pilot or control valve after the servomotor piston has adjusted the water control mechanism. In case of Pelton wheel a combined spear and deflector regulation is employed in order to avoid water hammer in the penstock.
In the mean time, the spear has been adjusted to the new position of equilibrium and the deflector plate is moved out of the path of water nozzle. For very high head i. Reaction turbines are not suitable for such high heads as due to high velocity of water, there will be rapid wear and friction losses. For medium heads i. For low heads i. In case of considerable variations in head and load, Kaplan turbine gives improved efficiency as compared to the fixed blade propeller turbine.
For example, for a head of m either of the Pelton or Francis turbines can be used. Similarly for a head of 30 m, either of the Kaplan or Francis turbine can be employed.
It is a general practice to select a runner of higher specific speed. A runner of high specific speed will generate more power for the same head resulting in small size of the turbo-alternator and the power house. For larger output but at low head, a runner of high specific speed is used to keep the size of the turbo-alternator and power house smaller and economical. For high head and even with medium output plants, even a low specific speed runner will attain high rotational speed and a high specific speed runner need not be selected.
Characteristics of Water Turbines 2. Governing of Water Turbines 3. Characteristics of Water Turbines: 1. Head: Reaction turbines of various types can be used for operating heads up to m and Pelton turbines are used for operating heads above m.
EXPLAIN GOVERNING OF REACTION TURBINE
Nakora The crest of spillway is kept at full reservoir level. Left hand end of the main lever lowers down, 4. This governinf gives better performance since the force required for operation of Francis turbine guide vanes is much more compared to Pelton turbine. The process of providing any arrangement which will keep the speed constant and will regulate the rate of flow as per variation in load. Hydropower Engineering — ppt video online download The piston in the control valve moves upward in the cy binder, 5.