Hydro Power and Related Technology
Hydro turbines can be categorized by the water head levels, namely high, medium,
and low levels. These levels have a direct correlation with the size of turbines. Low water
head requires a large turbine, where as high water head requires a small one when compared
at the same production capacity. The main reason for differentiating the design of hydro
turbines operating at different head levels is the rotation speed of the power generator.
The turbines have to be designed accordingly to have a corresponding rotational speed to
that of the generator. Small hydropower can be divided into 3 sizes according to their
production capacities, namely small hydropower with 1-30 MW capacity, mini hydropower
with 200 kW - 1 MW capacity, and micro hydropower with capacity less than 200 kW.
Moreover, hydro turbines can be divided into 2 types according to the nature of
their operation, namely impulse turbine and reaction turbine.
1. Impulse turbine, or pelton turbine, changes the kinetic energy of hydropower into
potential energy when the turbine rotates. Pelton or Turgo turbines have single or multiple
nozzles to help increase water speed. This type of turbine operates under air pressure while
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the blades was not totally submerged after water hit the blades and down to the exit
underneath. There are 3 main kinds of impulse turbines.
Pelton Turbine consists of wheels with buckets at the rim. Water flows through
nozzle and causing the wheel to rotate with high-speed water making water flow down
underneath the wheel.
Turgo turbine operates similarly to the Pelton turbine. However, the water that flows
through nozzle is designed to impact with the wheel with a specific impact angle (around
20 ํ). Water flows in from one side of the turbine and flows out in the other side.
Cross flow (or Banki) turbine consists of runners similar to a squirrel cage turbines.
Water comes through a nozzle above the turbines and impact with the upper part of the
turbine and subsequently the lower part before flowing out below.
2. Reaction turbine comes in both horizontal and vertical axis. In theory, reaction turbine
relies on the difference of pressure on the runners for rotation. At the rear of the turbine,
there is a diffuser tube called draft tube designed for water flow in order to increase the
static pressure in the exit area of the turbine where pressure is low. This type of turbine is
more complicated to be designed than the impulse ones, in terms of both the shape and
the draft tube. Nevertheless, this kind of turbine is suitable for low head water and is very
popular in research and development. Reaction turbines can be divided into 2 main types.
Propeller-type turbine operates similarly to ship propellers only in the other way
round. Fixed guide vane is the key equipment which control the flow direction, installed
in front of the turbines. The adjustable turbine runners are called Kaplan. The mechanism
for angle adjusting and the angle of the guide vane have high cost, only suitable for large
turbines. However, angle adjustment of turbines can help increase efficiency of water flow
in general. Francis turbine is a turbine applied from the propeller turbine by controlling
water flow within its range towards the turbine, and flow out along the turbine’s axis.
The runner is located in the middle of a snail-shaped casing with a guide vane that helps
adjust impact angle.
Kinetic energy turbine, or free flow turbine, can produce electricity from kinetic
energy, such as flowing water. This is different from using potential energy that exists due to
the difference in head levels. It is suitable to be used in rivers, canals, tides or ocean currents.
Kinetic energy system can be used with the water flow channels without the need to use
tubes to control the flow. It does not need large structure and can be used with bridge-type
structures.
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Power generator of a hydro power plant is similar to that of other type of power plants.
The most popular types of generator are (1) synchronous generator, (2) induction generator,
and (3) permanent magnet generator.
Synchronous generator is suitable for stand-alone power plants which requires an
automatic control of water quantity used for power generation per demand through a control
equipment called governor. As for induction generator, it is suitable for grid-connected
power plants. The generator operates alongside programmable logic controller which controls
the operation of the hydro turbine. Permanent magnet generator is also suitable for
grid-connected power plants. This kind of generator gains an increasing popularity. It is
suitable for low-head hydro turbine as it is able to generate electricity at various rotational
speeds. It also requires an inverter to adjust the electricity frequency to be at 50 Hz.
Other equipment necessary for a generator include controller box, transformer, and
switchyard. The technologies related to electricity generation with hydro