Hydroelectric Power Generation - Renewable Energy: Technology, Economics and Environment - page 369

maximum power output is not required. This is generally uneconomic and can
hardly be found in industrialised countries these days.
Like large hydroelectric power stations, small hydroelectric power stations can
be operated in isolated or grid operation. They also require the corresponding syn-
chronous or asynchronous generators that feed the grid with generated alternating
current at low-voltage.
Very small hydroelectric power stations are also often used to supply remote
settlements. Nowadays, synchronous generators can be bought for isolated opera-
tion, complete with voltage regulator, and suitable for reactive power generation.
The frequency depends on the turbine speed and is mainly kept at a constant level
by electro-magnetic or electronic frequency regulators.

8.2.5 Energy conversion chain, losses and power curve

Energy conversion chain. A hydroelectric power station consists of the compo-
nents already described (Chapter 8.2.2). An energy transformation chain is caused
by the interaction of these system elements, which is represented schematically in
Fig. 8.15.

Trans-

Trans-

formation

formation Mech.-

Electr.-
electr.
trans-
former
(trans-
former)

of kinetic Mech.-

electr.
trans-
former
(generat.)

of potential mech.

& pressure

energy trans-

former
(trans-
mission)

energy

into kinetic
& pressure
energy

into
mechanical
energy

(penstock)

(turbine)

Grid

Kinetic/
pressure

Kinetic/
potential Mechanical energy Electric energy

energy
of water

energy
of water

along the shaft inside the generator

or the grid

Fig. 8.15 Energy transformation chain for the use of hydropower (mech. mechanical,
electr. electrical, generat. generator; see /8-5/)

Therefore in the intake structure and/or the penstock, the potential and the ki-
netic energy of the water in front of the dam is converted into pressure and kinetic
energy before reaching the turbine. The water then flows through the turbine; here
the water energy is transformed into rotary movement, and thus into mechanical
energy of the runner and the turbine shaft respectively. This kinetic energy is
sometimes transformed to another rotational speed by a transmission and then fed
into the generator where the mechanical rotation is converted into electrical en-
ergy. Afterwards, an additional electrical-electrical transformation can be required