Revision as of 13:36, 16 June 2010 by ***** (***** | *****)
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.
The load factor is the amount of
power used divided by the amount of power that is available if the
to be used continuously. Unlike technologies relying on costly fuel
the 'fuel' for hydropower generation is free and therefore the plant
more cost effective if run for a high percentage of the time. If the
only used for domestic lighting in the evenings then the plant factor
very low. If the turbine provides power for rural industry during the
meets domestic demand during the evening, and maybe pumps water for
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
taken into account during the planning stage. Many schemes use a 'dump'
(in conjunction with an electronic load controller - see below), which
effectively a low priority energy demand that can accept surplus energy
excess is produced e.g. water heating, storage heaters or storage
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
convert the kinetic energy of a jet of water in air into movement by
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,
angular as well as linear momentum of the water is converted into shaft
the pressure of water leaving the runner is reduced to atmospheric or
Load control governors
Water turbines, like petrol or
diesel engines, will vary in speed as load is applied or relieved.
such a great problem with machinery which uses direct shaft power, this
variation will seriously affect both frequency and voltage output from a
generator. Traditionally, complex hydraulic or mechanical speed
altered flow as the load varied, but more recently an electronic load
controller (ELC) has been developed which has increased the simplicity
reliability of modern micro-hydro sets. The ELC prevents speed
continuously adding or subtracting an artificial load, so that in
turbine is working permanently under full load. A further benefit is
ELC has no moving parts, is very reliable and virtually maintenance
advent of electronic load control has allowed the introduction of simple and efficient, multi-jet turbines, no longer burdened by expensive hydraulic governors.
Load- or Flow- controller ensure that the power output does not exceed the power demand (e.g. 230V, 50 Hz).
If flow of water in a MHP-station is constant the energy output of a turbine/generator is constant as well. Power demand is usually fluctuating over the time (e.g. day/night). If supply is higher than demand, excess energy must be diverted / dumped. Alternatively the water flow can be reduced which results also in less power output.
In case of more power demand than supply the controller cuts of the of single users (clusters) in order to keep voltage and frequency constant.
Load controller are placed between generator output and the consumer line.
Electronic circuit, which keeps output power constant in Frequency- and Voltage- parameters.
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).
usually electrical heaters in water or air. If energy demand is temporarily low the excess energy is converted into heat.
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)