Test: Hydroelectric Power Plant - 3 - Mechanical Engineering MCQ

Specific speed of multi-jet nozzle turbine

So, the Kaplan turbine.

where,
f is the frequency for power generated in cycles per second.
P is the number of poles for the generator.

Rapid velocity fluctuations occur in pipe line during
1. Sudden opening and closing of valves
2. Start and shut down of a turbine or closure of wicket gates during speed regulation of a turbine.
Due to rapid velocity fluctuations, large magnitude pressure transients are set-up and these excessive pressure may lead to bursting of pipe this phenomenon is known as water hammer. Some arrangement needs to be made to convert the rapid velocity fluctuations into slow velocity fluctuations and for this surge tank is provided just upstream of the power unit in a hydroelectric plant.

In axial flow turbine both inlet and exit of turbine is axial.
If water flows through the runner in the radial direction but leaves in the direction parallel to the axis of rotation of the runner. The turbine is called mixed flow turbine.

A special type of propeller turbine is called Kaplan turbine in which the individual runner blades are Pivoted on the hub so that their inclination may be adjusted automatically rotating about Pivots with the help of a governor servo-mechanism.
In Kaplan turbine, because of the arrangement for automatic variation of inlet blade angle with variation in load, the turbine can be run at max efficiency at ail loads.

Guide vanes are the vanes which are attached to the causing and guides the water to enter into the runner.

It is a diverging tube which is attached at outlet of the runner to carry water from the exit of runner to tail race.
The diverging tube helps to increase the pressure on the account of conversion of kinetic head into pressure head.

Hydraulic Efficiency: It is defined as the ratio of power given by the water to runner of a turbine (runner is a rotating part of a turbine and on the runner vanes are fixed) to the power supplied by the water at the inlet of the turbine.

Pelton wheel: It is high head (1770 m) and low discharge turbine.
Francis turbine: It is medium head (60 - 250 m) and medium discharge turbine.
Kaplan Turbine: It is low head (less than 60 m) and high discharge turbine.

At inlet of reaction turbine water is admitted with high pressure head (above atmospheric pressure) with some kinetic energy. The pressure head of water gradually decreases from inlet to exit. Finally water leaves the runner with low pressure and small kinetic energy to tail race. Quite often, the pressure head of the water at turbine exit fall below the ambient pressure. A draft tube attached to the exit of the turbine, working like a diffuser converts the remaining kinetic energy of water discharged by the runner into the pressure energy so that water is discharged to the tail race with a positive pressure head to avoid cavitation.