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| | == Turbine types == | | == Turbine types == |
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| − | <span><!--{127668415349214}--></span><span>A turbine converts the energy in | + | <span><!--{127668415349214}--></span><span> |
| − | falling water into shaft power. There are various types of turbine which
| + | </span> |
| − | </span>can be categorized in one of several ways. The choice of turbine will depend mainly on the pressure head available and the design flow for the proposed hydropower installation. As shown in table 2 below, turbines are broadly divided into three groups; high, medium and low head, and into two categories: impulse and reaction. | + | |
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| + | <span>A turbine converts the energy in |
| | + | falling water into shaft power. There are various types of turbine which |
| | + | </span>can be categorized in one of several ways. The choice of turbine will depend mainly on the pressure head available and the design flow for the proposed hydropower installation. As shown in table 2 below, turbines are broadly divided into three groups; high, medium and low head, and into two categories: impulse and reaction. <br> |
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| | <span>The difference between impulse and | | <span>The difference between impulse and |
Revision as of 15:58, 18 June 2010
Ballast or dump load
A ballast load is mostly an electrical resistance heater. It's sized to handle the
full generating capacity of the microhydro turbine. They're placed in air or water. If there is more electricity produced then consumed the charge controller uses this excess energy to generate heat.
Other but not common ballast load may be pumping water or ice production.
Load factor
The load factor is the amount of
power used divided by the amount of power that is available if the
turbine were
to be used continuously. Unlike technologies relying on costly fuel
sources,
the 'fuel' for hydropower generation is free and therefore the plant
becomes
more cost effective if run for a high percentage of the time. If the
turbine is
only used for domestic lighting in the evenings then the plant factor
will be
very low. If the turbine provides power for rural industry during the
day,
meets domestic demand during the evening, and maybe pumps water for
irrigation
in the evening, then the plant factor will be high.
It is very important to ensure a
high plant factor if the scheme is to be cost effective and this should
be
taken into account during the planning stage. Many schemes use a 'dump'
load
(in conjunction with an electronic load controller - see below), which
is
effectively a low priority energy demand that can accept surplus energy
when an
excess is produced e.g. water heating, storage heaters or storage
cookers.
Turbine types
Turbine
Runner
|
Head
pressure
|
|
High
|
Medium
|
Low
|
|
Impulse
|
Pelton
Turgo
Multi-jet Pelton
|
Crossflow
Turgo
Multi-jet Pelton
|
Crossflow
|
|
Reaction
|
Francis
Pump-as-turbine (PAT)
|
Propeller
Kaplan
|
|
A turbine converts the energy in
falling water into shaft power. There are various types of turbine which
can be categorized in one of several ways. The choice of turbine will depend mainly on the pressure head available and the design flow for the proposed hydropower installation. As shown in table 2 below, turbines are broadly divided into three groups; high, medium and low head, and into two categories: impulse and reaction.
The difference between impulse and
reaction can be explained simply by stating that the impulse
turbines
convert the kinetic energy of a jet of water in air into movement by
striking
turbine buckets or blades - there is no pressure reduction as the water
pressure is atmospheric on both sides of the impeller. The blades of a reaction
turbine, on the other hand, are totally immersed in the flow of water,
and the
angular as well as linear momentum of the water is converted into shaft
power -
the pressure of water leaving the runner is reduced to atmospheric or
lower.
Controller:
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A Load- or Flow- controller ensures that the power output does not exceed the power demand and power output is stable (e.g. 230V, 50 Hz).
Water turbines, like petrol or
diesel engines, will vary in speed as load is applied
or relieved.
Although not
such a great problem with machinery which uses direct shaft power, this
speed
variation will seriously affect frequency and voltage output from a
generator.
Traditionally, hydraulic or mechanical speed
governors
altered flow as the load varied. Nowadays usually electronic load
controller (ELC) are used. These prevent speed
variations by
continuously adding or subtracting an artificial load (load controller). In that in
effect, the
turbine is working permanently under full load and the ELC diverts excess energy into a dump load, mostly a heater. The traditional kind of equalizing power in and output by controlling the flow is usually also automatised (flow control). Thereby the ELC steers a valve which regulates the amount of water inflowing.
In case of more power demand than supply the controller cuts off single users (clusters) in order to keep voltage and frequency constant for the others (first and second class connections). Load or flow controller are placed between generator output and the consumer line.
Controller Types
Fluctuating energy demand requires a mechanism which either regulates the water input into the turbine (= flow control) or by diverting excess energy from the consumer connection (= ballast load).
For small micro or pico hydropower sites it's sometimes not easy to find the right controller. There is a lower price limit of several 100 USD even for only 1 or 2 kW power. In such cases there may be thought of manual control.
Load control:
The electric load controller (ELC) keeps outgoing Voltage and Frequency stable. Therefore the load on the generator has to be kept stable. The controller adds and subtracts an artificial load (heater) in a way to neutralise the fluctuations on the consumer side.
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Ballast load
usually electrical heaters in water or air. If energy demand is temporarily low the excess energy is converted into heat.
Flow control
regulates the amount of water into the turbine in order to match power output and power demand. Nowadays flow control is done mostly via electronics, which steer a valve
Manual flow control
In very small schemes often all power for lighting and TV is used constantly. Then energy consumption barely alters or does only at certain times. In such cases it can be even practical to train an operator who open / closes a valve manually to stabilise the Voltage. This allows to disclaim a controller, which saves costs and potentially flaws.
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