Power Plant Engineering

352 POWER PLANT ENGINEERING

where V = velocity of flow in m/s,

p = pressure in N/m^2 ,

ρ = density of water kg/m^3

and H = the height of the level of water above some datum level.

Theoretical power available from water = WQH, watts

where Q = water flow in cumecs

and H = net head available in m.

= Total head minus the frictional losses.

If the turbine has an efficiency ηt, then the B.P. at turbine shaft

= W.Q.H.ηt watts

It the efficiency of the electric generator is ηg, then the effective power at switch board

= W.Q.H.ηt.ηg watts ...(11.2)

In the above calculations, the following relations can be used to calculate the discharge.

1 cusecs = 1.3 sq.mile, ft. per year.

i.e. one foot of water over an area of 1.12 sq mile will give a discharge of one cusecs throughout

the year, assuming the run off as 100%.

11.8 Classification of Hydro-Plant

In hydro-plants, water is collected behind the dam. This reservoir of water may be classified as

either storage or pondage according to the amount of water flow regulation they can exert. The function

of the storage is to impound excess river flow during the rainy season to supplement the low rates of

flow during dry seasons. They can meet the demand of load fluctuations for six months or even for a

year. Pondage involves in storing water during low loads so that this water can be utilized for carrying

the peak loads during the week. They can meet the hourly or weekly fluctuations of load demand. With

poundage, the water level always fluctuates during operations It rises at the time of storing water, falls at

the time ‘off drawing water, remains constant when the load is constant.

The hydro-power plants can be classified as below:

l. Storage plant

(a) High head plants

(b) Low head plants

(c) Medium head plants.

2. Run-of-river power plants
   (a) With pondage
   (b) Without pondage.


3. Pumped storage power Plants.

11.8.1 Storage Plants

These plants are usually base load plants. The hydro-plants cannot be classified directly on
the basis of head alone as there is no clear line of demarcation between a high head and a medium head