Guide on How to Develop a Small Hydropower Plant
ESHA 2004
GLOSSARY Alternating current (AC): Electric current that reverses its polarity periodically (in contrast to direct current). In Europe the standard cycle frequency is 50 Hz, in N. and S. America 60 Hz. Anadromous fish: Fish (e.g. salmon), which ascend rivers from the sea at certain seasons to spawn. Average Daily Flow: The average daily quantity of water passing a specified gauging station. Base flow: That part of the discharge of a river contributed by groundwater flowing slowly through the soil and emerging into the river through the banks and bed. BFI baseflow index: The proportion of run-off that baseflow contributes. Butterfly Valve: A disc type water control valve, wholly enclosed in a circular pipe that may be opened and closed by an external lever. Often operated by a hydraulic system. Capacitor: A dielectric device, which momentarily absorbs and stores electric energy. Catchment Area: The whole of the land and water surface area contributing to the discharge at a particular point on a watercourse. Cavitation: A hydraulic phenomenon whereby liquid gasifies at low pressure and the vapour bubbles form and collapse virtually instantaneously causing hydraulic shock to the containing structure. This can lead to severe physical damage in some cases. Compensation flow: The minimum flow legally required to be released to the watercourse below an intake, dam or weir, to ensure adequate flow downstream for environmental, abstraction or fisheries purposes. Demand (Electric): The instantaneous requirement for power on an electric system (kW or MW). Demand Charge that portion of the charge for electric supply based upon the customer’s demand characteristics. Direct Current (DC): Electricity that flows continuously in one direction sd contrasted with alternating current.
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