The next considerations were concerned with power production available, penstock and channel lengths and the distance to the s

The next considerations were concerned with power production available, penstock and channel lengths

and the distance to the secondary distribution substation.

Site 1 has the greatest power potential and the shortest transmission distance.

Site 2 has the shortest penstock, but the longest channel length and longest transmission distance.

Site 3-b has no channel at all, but a very long penstock.The penstock has by far the greater expense than the channel,

so site 3-b does not seem good compared to site 1, which has penstock of half the length, greater power production potential

and shorter transmission distance.

Site 1 has a slighlty shorter channel and shorter transmission distance than site 2, but a penstock one and half times greater.

However the potential resource is approximately four times greater for site 1, which outweighs the benefits of site 2 in the

power orders being considered .

Site-1 was selected as the most appropriate location for the embedded hydro-electric plant.

Site 1: details of the energy resource are given below.

annual average rainfall: 2148 mm

annual average evaporation and transpiration: 350 mm

catchment area: 6 km²

base flow index (BFI):0,42

Fig.2 shows daily water flow variations in this stream for a typical year.

Fig.2. Daily water flow variations in this stream for a typical year.

Physical Layout

The system will consist of the following components:

- weir

- intake

- channel

- spillways

- settling pond

- penstock

- power house

- turbine

- generator

- step-up transformer

- transmission lines

The proposed layout of the scheme is shown in fig.3.

fig.3.Layout of the scheme is shown in .

Hydraulic Losses and Effective Head

As the water flows from the intake, along the channel and down through the penstock, potential energy is lost.

These losses occur in the form of friction and turbulence losses. The losses in the channel are due to the height

difference through which the channel must fall. Losses in the penstock are caused by friction of water against

water and of water against pipe-wall, and also by turbulence at various points in the pipe. These losses effectively

reduce the head further.

The total head minus the all the losses in head is described as the effective head. This is the value used in the calculation

of the potential energy which the turbine absorbs.

For the case study the calculation of head loss is given here. The values are given below.

channel head loss,

penstock head loss,

effective head,

Turbine Selection

There are various types of hydro-turbines, each with a preferred operating domain in terms of head and flow-rate.

Fig.4 shows the typical operating domain for the three major turbine types - Pelton, Francis and Kaplan.

Fig.4.Typical operating domain for the three major turbine types - Pelton, Francis and Kaplan.

The effective head at the site is 48m, which implies the most appropriate turbine is the Francis (within our capacity range).

Turbine Efficiency

The efficiency of a Francis turbine is a function of percentage of water flow - shown in fig.5.

fig.5.Efficiency of a Francis turbine

The power production of the plant at any given time is expressed as:

eq.1

where is acceleration due to gravity; ,

is density of water, assumed here to be

is overall system efficiency: generation & transmission (see below)

is effective head;

is water flow at any given time

generation efficiences

turbine efficiency, see aboves

generator efficiency, ~ 97% (typically)

gear efficiency, ~ 98% (typically)

transmission efficiencies

transformer efficiency, ~ 98% (typical)