Hydro Power

Question 1

What is hydroelectric power?

Answer 1

Converting the potential energy of water at elevations above a datum into kinetic energy which is harvested to eventually drive an alternator

Question 2

Give the equation for the maximum power available from a hydroelectric machine?

Answer 2

P = pgQH

Question 3

Identify four devices used to convert the potential and kinetic energy in flowing water into mechanical power. State their optimal operational ranges.

Answer 3

Frances Turbine: H = 1-1000m, Q = 1-1000m3

Propeller: H = 1-10m, Q = 1-1000m3

Pelton Turbine: H = 20-1000m, Q = 0.1-20m3

Cross Flow: H = 1-20m, Q = 0.1-1m3

Question 4

What is the optimal velocity of a water jet relative to the Pelton wheel?

Answer 4

If the wheel is moving at the same speed as the jet then there is no momentum transferred.

If the wheel is stationary, there is a large force but no mechanical power.

Hence there is an optimum. This is where the reflected jet velocity is the is the same as the initial jet velocity. This occurs when the relative velocity of the incident jet is (U-Uc) and that of the reflected jet is -(U-Uc) so the total change in momentum is -2(U-Uc).

F = Mass x Change in Momentum

Question 5

Give the equations for the power of a Pelton wheel.

Answer 5

P = pgQH

P = T x 2pi x RPS