HYDROPOWER Basics
Glossary of Terms
Alternating current (AC)
Electric current that reverses direction many times per second.
Ampere
A measure of electric current (similar to describing water volume in cubic feet per
second).
Ancillary services
Operations provided by hydroelectric plants that ensure stable electricity delivery and
optimize transmission system efficiency.
Cavitation
Noise or vibration causing damage to the turbine blades as a result of bubbles that form
in the water as it goes through the turbine. Cavitation causes capacity loss, head loss,
efficiency loss.
Conductor
Material, such as wire or cable, used to carry electricity. This term can also be used in
reference to a pipeline that carries water.
Consumption
End use of energy and energy sources, such as electricity, and is typically measured in
kilowatt-hours.
Current
The flow of electrons in an electrical conductor - measured in amperes.
Dam
A barrier constructed to store or divert water for different purposes, including electricity
production. Typically made of earth, rock, or concrete.
Direct current (DC)
Electric current that flows in one direction.
Distribution
A process of moving power at lower voltages from substations to customers.
Draft tube
A water conduit that maintains a column of water from the turbine outlet to the
downstream water level, which can be straight or curved depending upon the turbine
installation.
Efficiency
A percentage obtained by dividing the actual power or energy by the theoretical
maximum power or energy available. It represents how well the hydropower plant
converts the potential energy of the water into electrical energy.
Electric energy
Power delivered over a period of time; commonly measured in kilowatt-hours (kWh) or
megawatt-hours (MWh).
HYDROPOWER Basics
Glossary of Terms
Electric power
Rate of electric energy delivery; also a measure of a power plant’s generating capacity or
installed capacity; the basic measures are the kilowatt (kW) and megawatt (MW).
Environmental assessments
Planning and decision-making tool used by industry and regulators to identify the
environmental impacts and costs of proposed energy projects, and potential solutions.
Fish ladder
A series of pools arranged like steps that allow fish to pass upstream over a dam.
Flow
Volume of water, expressed as cubic feet (or cubic meters) per second.
Flow management
Management of hydroelectricity operations to control downstream water flows and their
effects.
Generating capacity
A power plant’s ability to produce a specific amount of electricity at a specific moment in
time; measured in kilowatts or megawatts - also known as “installed capacity” or
“nameplate capacity”.
Generation
The process of converting different forms of energy — thermal, mechanical, chemical, or
nuclear, into electricity.
Gigawatt (GW)
A measure of electric power; the equivalent of 1,000 megawatts or 1 million kilowatts.
Gigawatt-hours (GWh)
A measure of electric energy; the equivalent of 1,000 megawatt-hours or 1 million
kilowatt-hours.
Grid
A regional or nation-wide network of high-voltage transmission lines.
Head
The vertical change in elevation expressed in either feet or meters, between the
reservoir (“head water”) level and the downstream river (“tailwater”) level.
Headwater
The water level above the powerhouse or at the upstream face of a dam.
HYDROPOWER Basics
Glossary of Terms
Hydropower (“Hydro”)
The process of generating electricity by capturing the potential energy of falling water through
the use of a water wheel (turbine) to mechanically spin rotating magnets which create electrical
current that can be distributed to users by transmission lines.
Large Hydropower: Although definitions vary, the U.S. Department of Energy (DOE)
defines large hydropower as facilities that have a capacity of more than 30 megawatts.
Small Hydropower: The DOE defines small hydropower as facilities that have a
capacity of 100 kilowatts to 30 megawatts.
Micro Hydropower: A micro hydropower plant has a capacity of up to 100 kilowatts. A
small or micro-hydroelectric power system can produce enough electricity for a home,
farm, ranch, or village.
Hydrologic Cycle
The natural process by which water evaporates,
primarily from the oceans as energy from the
sun and wind is absorbed. Water vapor in the
form of clouds is transported by winds to higher
atmospheric levels and over land where water
condenses and falls as precipitation (rain &
snow). The cycle continues when water then
runs off the land into rivers, and back to the
oceans where the cycle repeats.
Installed capacity
The amount of power that can be generated at a given moment by a power plant.
Usually measured in kilowatts (kW) or megawatts (MW) – NOTE: actual generation is
measured in kilowatt-hours or megawatt-hours.
Intake
The entrance to a turbine unit at a hydroelectric dam.
Kilowatt
A measure of electric power; the equivalent of 1000 watts.
Kilowatt-hour (kWh)
A measure of electric energy; the equivalent of 1,000 watt-hours (e.g. if you burn ten
100-watt light bulbs for one hour, they will use one kilowatt-hour of electricity) – NOTE:
residential customers are usually charged for electricity based on a rate of cents per
kilowatt-hour.
HYDROPOWER Basics
Glossary of Terms
Load
The total amount of electricity on a specific power system required to meet customer
demand at any moment.
Base Load Plant – Plant operates at maximum output at all times to provide maximum
energy into the grid used to meet some or all of a given region's continuous energy
demand.
Load Following Plant (“Intermediate Peaking”) – A plant that operates at variable
power output setting to meeting the changing energy demand of customers, usually slow
moving changes such as from night periods to day periods.
Dispatchable Power (“Fast Peaking”) – Dispatchable generation refers to sources of
electricity that can be dispatched at the request of power grid operators; that is,
generating plants that can be quickly turned on or off, or can adjust their power output
on demand.
HYDROPOWER Basics
Glossary of Terms
Megawatt (MW)
A measure of bulk power; the equivalent of 1,000 kilowatts or 1 million watts; the unit is
generally used to describe the output of a generator.
Megawatt-hour (MWh)
A measure of electric energy; the equivalent of 1,000 kilowatt-hours or 1 million watthours – NOTE: Megawatt-hours are determined by a hydropower plant’s capacity and
how long the plant is running (e.g. a 1,000-megawatt power plant running at full power
for one hour produces 1,000 megawatt-hours (MWhs) of electricity; and if that plant runs
all day, it produces 24,000 MWhs).
Penstock
A closed conduit or pipe for conducting water to the powerhouse.
Power
In electricity transmission, current delivered at a given voltage is measured in watts or
kilowatts.
Powerhouse
The physical structure of an electric generating facility.
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 turbine.
Spill
The release of water from a dam or hydropower project without passing it through the
powerhouse – NOTE: Typically a situation to be avoided as water “spilled” is lost powergeneration revenue.
Spillway
The structure or portion of a larger structure that is used to release excess water over or
around a dam.
HYDROPOWER Basics
Glossary of Terms
Stratification
A variation in temperature and quality of deep water as surficial water is warmed by the
sun fostering biologic growth while colder, oxygen-depleted water sinks to lower levels.
Substation
An electrical facility where the voltage of incoming and outgoing circuits is changed and
controlled.
Supersaturation
Change in water quality that occurs when turbulent water passing over a spillway absorbs
and entrains free air. This process increases nitrogen levels in the water – NOTE: fish
exposed to supersaturated water can be injured or killed when the nitrogen gas produces
bubbles in their bloodstream. This effect is called “gas bubble disease” and is similar to
“the bends” that can occur in human divers.
Sustainable
Ecosystem condition in which biodiversity, renewability and resource productivity are
maintained over time.
Sustainable development
Development that meets the needs of the present without compromising the ability of
future generations to meet their own needs (as defined by United Nations World
Commission on Environment and Development).
Tailrace
The downstream channel that carries water away from a dam or powerhouse.
Tailwater
The water level downstream of the powerhouse or dam.
Terawatt
A measure of electric power, the equivalent of 1,000 gigawatts or 1 billion kilowatts; the
unit is generally used to describe generating capacity at national or international levels.
Terawatt-hour
A measure of electric energy; the equivalent of 1,000 gigawatt-hour or 1 billion kilowatthours.
Transformer
An electromagnetic device for changing alternating current (AC) electricity to higher or
lower voltages.
Transmission
The process of moving electric power at high voltages from the generation facility to local
communities.
Turbidity
Muddy or unclear water quality caused by suspended sediments.
HYDROPOWER Basics
Glossary of Terms
Turbine
A rotary engine that converts the energy of a moving stream of water, steam or gas into
mechanical energy.
TURBINE TERMS:
Generator
An arrangement of magnets spinning
inside a coil of wire to produce
electricity.
Rotor
The moving part of an electric
generator – NOTE: the rotor's outer
surface is covered with
electromagnets and as the rotor turns
inside the stator, the electrons in the
copper windings "vibrate" such that
their movement generates an electric
current.
Stator
The stator is the stationary part of an
electric generator – NOTE: the stator
is comprised of a series of vertically
oriented copper coils nestled in the
slots of an iron core so that as the
rotor spins its magnetic field induces
a current in the stator's windings
thereby generating electricity.
Wicket gates
Adjustable elements that control the flow of water from the scroll case into the
turbine passage.
Voltage
A measure of the electric pressure that pushes electric current through a circuit (just as
pressure causes water to flow in a pipe); measured in volts or kilovolts.
Watershed
Area draining into a stream or river.
Watt
A measure of electric power; standard light bulbs are rated at 25, 40, 60 or 100 watts.