# Glossary

Alternating current (AC)
A continuous electric current that periodically reverses direction, usually sinusoidal.

Ampere
The ampere is a measure of the current, or the amount of electric charge passing a point per unit time.

Average annual energy production
The total energy generated annually by a power station, on average over a period of time of full operation or since the start of full operation, measured in kilowatt-hours (GWh).

Banki-Michel Turbine
Also known as a Crossflow Turbine or an Ossberger turbine. Well suited to medium head sites with a variable flow.

Capacity (electric)
The maximum volume of power that can be produced or delivered under specified conditions by a generator or system, usually expressed in kilowatts (kW).

Capacity factor
Ratio of average generation to the capacity rating of an electric generating unit for a specific period, expressed as a percentage.

Cavitation
Noise or vibration causing damage to the turbine blades as a results of bubbles that form in the water as it goes through the turbine which causes a loss in capacity, head loss, efficiency loss, and the cavity or bubble collapses when they pass into higher regions of pressure.

Connection
The physical junction (e.g., transmission lines, transformers, switch gear, etc.) between two electric systems permitting the transfer of electric energy.

Current
The flow of electricity through a conductor, measured in Amperes.

Direct current (DC)
Electric current which flows in one direction.

Distribution (electrical)
The system of lines, transformers and switches that connect the transmission network and customer load. The circulation of electricity to ultimate use points such as homes and businesses.

Draught tube
A water conduit, which can be straight or curved depending upon the turbine installation, that maintains a column of water from the turbine outlet and the downstream water level.

Efficiency
A percentage obtained by dividing the actual power or energy by the theoretical power or energy. It represents how well the hydropower plant converts the energy of the water into electrical energy.

Flow
Volume of water, expressed cubic meters per second, passing a point in a given amount of time.

Vertical change in elevation, expressed in meters or feet, between the head water level and the tail water level.

Generation
The process of producing electric energy.

Green Energy
Electricity generation considered to be less intrusive environmentally than traditional generation.

Grid
A synchronized transmission network that delivers electricity from generating stations to local distributors and other large users at high voltage.

The water level above the powerhouse.

Installed capacity
The measure of a power station’s electric generating capacity at full production, usually measured in megawatts (MW).

Intake
The entrance to a turbine unit at a hydroelectric dam.

Kilowatt (kW)
A unit of electrical power equal to one thousand watts.

Kilowatt-hour (kWh)
The unit of electrical energy equivalent to one kilowatt of power used for one hour. One kilowatt-hour is equal to 1,000 watt-hours, equivalent to the energy consumed by a 100-watt light bulb burning for 10 hours. An average household will use 800 to 1300 kWh per month.

Head of 20 meters or less.

Megawatt (MW)
A unit of electrical production capacity. One million watts or one thousand kilowatts.

Megawatt-hour (MWh)
One million watt-hours of electric energy. A unit of electrical energy which equals one megawatt of power used for one hour.

Micro-hydro
Scale of hydro power plant 50 kw or less. A size plant capable of powering one or two homes.

Pelton Wheel
A runner type that looks like spoons connected to a central shaft. It is best suited for high head sites.

Penstock
A closed conduit or pipe for conducting water to the powerhouse.

Power Purchase Agreement (PPA)
A long-term off-take contract from a large customer to buy the electricity generated by a power plant; it governs the terms of supply and purchase price.

Powerhouse
The building housing the turbine, generator and electrical control equipment.

Renewable resource
A power source that is continuously or cyclically renewed by nature, i.e. solar, wind, hydroelectric, geothermal, biomass or similar sources of energy.

Pumped Storage
A hydroelectric scheme consisting of two reservoirs with a significant difference in elevation that uses surplus off-peak electrical energy to pump large volumes of water to the high elevation reservoir for later use when there is a high peak time demand.

Run-of-the-River
Hydroelectric projects without large reservoirs that divert a portion of the river flow for power generation.

Runner
The rotating part of the turbine that converts the energy of falling water into mechanical energy.

Scroll case
A spiral-shaped steel intake guiding the flow into the wicket gates located just prior to the runner of a Francis turbine.

Single Phase
Refers to the distribution of AC current using a system in which all the voltages of the supply vary in unison.

Small hydro
Projects with a capacity to produce 30 MW or less

Tailrace
The channel that carries water away from a dam.

Tailwater
The water downstream of the powerhouse.

Three Phase
Refers to an AC supply that consists of three AC voltages 120° out of phase with each other.

Turbine
A device in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

Head of 3 meters or less. Traditionally these sites were harnessed with waterwheels and most industrial mill sites would be classified as ‘ultra low head’.

Volt
The International System unit of electric potential and electromotive force, equal to the difference of electric potential between two points on a conducting wire carrying a constant current of one ampere when the power dissipated between the points is one watt.

Voltage
Electromotive force or potential difference, usually expressed in volts.

Watt
A unit of power equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm.

Watt-hour
The basic unit of measurement for consumption of electric energy; equal to the wattage multiplied by the time in hours; the quantity of electrical energy used or produced when one watt is used for one hour.

Wicket gates
Adjustable elements that control the flow of water to the turbine passage.