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School of Terrestrial Wind Energy

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Glossary: Wind Energy Conversion Systems

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Aerodynamic control: the use of a propeller's design (i.e., shape, size, structure and material) and it's properties in varying velocities of wind to act as an overspeed protection for a wind generator.

Ampere: unit of measurement of current.

Alternator: an electric generator for producing alternating current.

Alternating current: current flowing in one direction and then in the other.

Ampere-hour: a unit quantity of electricity equal to the quantity carried past any point of a circuit in one hour by a steady current of one ampere.

Anemometer: an instrument for measuring and indicating the force or speed of the wind.

Armature: a drum-like cylinder composed of a multitude of thin sheets of steel and wrapped with wires which are made to pass through a magnetic field and produce electricity in a generator.


Battery: an electricity producing device which converts a chemical action between two electrodes and the electrolyte in which they are immersed into electron flow.

Battery bank: a group of batteries which stores excess electrical energy for later use.

Blade tip spoilers: overspeed protection device: a general mechanical protuberance attached to the tip of a propeller used in high velocity wind to increase drag and slow propeller rotation.

Brushes: box shaped bits of carbon which rest against the commutator or contact the slip-rings to transmit the generated electricity onto where it can be used.

Brushless exciter: a small ac generator with a rotating armature and a stationary field mounted on the main shaft of a generator.


Centrifugal blade pitching: an overspeed protection system: a spring and weight mechanism attached to propellers changing the angle, or pitch of the blade in higher than rated velocity winds.

Charge: to lay or put a load on or in: to restore the active materials (in storage battery) by the passage of a direct current through in the opposite direction of that of the discharge.

Closed circuit: current flowing in a complete path from the power source, through the conductor to the load and back to the source.

Commutator: a ring of the copper wire endings from the surface of the armature. When the armature turns, the commutator is contacted by brushes which slide over it and transmit the generated electricity on to be used.

Conductor: any material which permits the free flow of electrons, or which facilitates such flow.

Constant frequency: a regular and consistent number of alternations per second of an alternating current (standard is 60/minute).

Controls: a mechanism used to regulate or guide the operation of a wind generator, i.e., (voltage, frequency, shutdown, utility connect and disconnect, ac or dc mode).

Coriolis force: an apparent force that as a result of the earth ' s rotation deflects moving objects (as projectiles or air currents) to the right in the northern hemisphere and to the left in the southern hemisphere.

Cyclical variation: excess ac ripple in rectified dc current.


Darrieus: a vertical axis wind system invented by G. M. Darrieus of France in l925 (often referred to as the "eggbeater" because of the rotor shape).

Diodes: a rectifier that consists of a semiconducting crystal with two terminals and that is analogous in use to an electron tube diode.

Direct current: current which flows in one direction only.

Discharge: to relieve of a charge, the conversion of the chemical energy of a battery into electrical energy.

Downwind: a wind system which has it's propellers facing out of the wind, (i.e., the wind hits the propeller from behind).

Dynamic braking: the machine acts as an electrically overloaded generator, dissipating the stored and kinetic energy of rotation either as heat in a braking resistor or in a direct short circuit on the generator.


Electrically actuated tail control: a small servo-motor control folds the tail horizontally to turn the generator out of the wind.

Electricity: the flow of electrons through a conductor.

Electrodes: conductors used to establish electrical contact with a nonmetallic part of a circuit.

Electrolyte: a nonmetallic electric conductor in which current is carried by the movement of ions.

Electrolysis: the producing of chemical changes by passage of an electric current through an electrolyte.

Electromagnet: a magnet which has been given increased magnetic properties by passing a conductor (wires, in which a current is flowing), through its magnetic field.

Electrons: invisible, negatively charged particles which orbit the nucleus of an atom.

Equalization charge: a charge to batteries which equalizes the charge on all cells and brings them back to 100% readiness.


Feathering: an overspeed protection which changes the angle or pitch of the blades to slow them in high velocity winds. Frequency: the number of complete alternations per second of an alternating current. Force field: lines of force which tend to pull or push one object or electron from another because of the alignment of their atomic electrons.

Generation component: those sub-elements of a wind system which actually contribute to producing electric power, including the generator or alternator, the tower, the rotor, the controls.

Generator a device which produces large amounts of electricity by repeatedly passing a conductor (wire) or series of conductors (wires) through the magnetic field of a series of magnets.

Generator field the magnetic field of a generator.

Governor an attachment to a machine for automatic control or limitation of speed.

Guyed tower: a tower that is supported with a chain, wire, rope or rod.


Hertz: a unit of frequency equal to one cycle per second.

Horizontal axis a wind generator which has its axis or center around which the rotor revolves, parallel to the earth's surface and the wind flow.

Hydraulic operated by water or other liquid flowing through a pipe, channel or orifice.

Hydraulic blade pitch control blade pitch of angle change operated through the use of hydraulics.

Hydro-electric: production of electricity by water power.

Induction generator consists of an electrical load where the time phase sequence of the current and the voltage is such that the current lags the voltage by some phase angle. This type of load usually has some form of iron or steel core such as a transformer or motor.


Inductive load: an example of the reversibility of electro-mechanical energy conversion. An induction machine either squirrel cage type or wound rotor type is forcibly driven above its synchronous speed at which point it acts as a generator of electrical power into whatever electric system it happens to be connected (assuming that electric system is energized and can supply the necessary excitation current to the induction machine.)

Inverter: a device for converting direct current to alternating current by mechanical or electronic means.

Insulator: a material which hinders or denies the free flow of electrons.

Isobars: an imaginary line or a line on a map or chart connecting or marking places on the surface of the earth where the height of the barometer reduced to sea level is the same either at a given time or for a certain period.


Kilowatt : 1,000 watts.

Kilowatt hours: a unit of work or energy equal to that expended by one kilowatt in one hour.

Lead-acid batteries:

Load: an electrical draw on a generator.

Magnet: any substance which attracts another substance through space by means of a force field.

Magnetic field: invisible lines of force which surround all magnets and which pass from the north pole to the south pole of the magnet.

Magnetism (magnetic force): the effects of a magnet.

Mechanical air spoilers: centrifically actuated plates which moves out at a predetermined speed to increase drag and effectively air brake the propeller.

Motors: generators to which electricity has been supplied by an external source.

Multi-bladed: consisting of more than two blades.


Natural magnet: some metals, usually special kinds of iron ore, such as magnetic ore lodestone, which are capable of exerting large forces of attraction and repulsion on other metals.

Negatively charged: having an excess of electrons.

Neutron: invisible, positively charge particles found within the nucleus of an atom.

Ohm (r): unit of resistance.

Open circuit: disrupted path of current.

Overspeed protection: protection designs which take effect at a predetermined speed for the purpose of protecting the generator from physically flying apart and preventing the possibility of an electrical overload.ß


Parallel circuit: current flows through one or many branches and can take any path.

Permanent magnet: a magnet that retains its magnetism after removal of the magnetizing force.

Photons: energy unit of light.

Positively charged: having a shortage of deficiency of electrons.

Postmill: a windmill with a central deeply imbedded post, having its housing built around the post with the ability to pivot as wind direction shifted.

Primary cell: voltaic (battery) cells which must be discarded, that is, are used up, when the action between the electrodes and electrolyte ends.

Pressure gradient: the change in atmospheric pressure per unit of horizontal distance.

Propeller: a blade that propels, specifically an airscrew propeller.

Protons: invisible, positively charged particles found within the nucleus of an atom.


Rectifiers: devices which permit the flow of electrons in only one direction.

Resistance: low opposition to electron (current) flow.

Resistive load: an electrical load where the time phase sequence of the current and the voltage is such that the current and the voltage are in phase with each other. This type of load is usually made up of a straight current carrying conductor or wire like a light bulb.

Ripple ac: cyclical variation in rectified dc current.

Rotary inverter: a device having a combination motor generator with a governor which inverts dc to ac.

Rotor: a complete system of blades which supplies all the force driving a wind generator.


Sail wing: a propeller having cloth stretched over a metal wire frame which forms an airfoil section.

Savonius: a vertical axis rotor developed by S. I. Savonius in the 1920's --resembles two halves of a barrel in the letter "s" configuration.

Secondary cell: battery which is capable of being recharged, i.e., where the elements can be restored to their original condition.

Self-supporting tower: a tower which receives its strength from its tapered design and firm anchoring. It needs no guying.

Series circuit: current flow where only one path is available.

Short circuit: current path which bypasses the load.

Slip rings: copper circular pieces which bind a bundle of armature wires together to be contacted by the brushes, or which is used to transmit electricity on if the armature wires are bound together by a single brush.

Smock mill: windmill having wooden, rectangular sloping sides

Sine wave: a wave form that represents periodic oscillations in which the amplitude of displacement at each point is proportional to the sine of the phase angle of the displacement and that is visualized is a sine curve.

Sine wave inverter: a solid state inverter designed with transistors or SCR's which produces a sine wave.

Solar cells: devices which take their energy directly from the sun and produce electricity.


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Solid state electronics: a very general term which has come to indicate, no moving parts and the use of transistors, silicon controlled rectifiers.

Solid state inverter: an inverter designed with transistors or SCR's which has no moving parts.

Solidity ratio: the ratio of blade area to disc area.

Specific gravity: the ratio of the density of a substance to the density of a substance taken as a standard when both densities are obtained by weighing in air.

Static electricity: theoretically, electricity "at rest": this is a misnomer for electricity caused by friction.

Storage capacity: the number of amp hours a battery bank is capable of storing.

Storage component: those sub-elements of a wind system which are used to store excess electricity

Synchronous inverter: a unit which converts dc current to ac while at the same time regulating frequency to that of the power line.


Tail vane deflect: an overspeed protection -- spring loaded tails fold in a horizontal plane to turn the machine out of the wind as the velocity increases.

Temporary magnet: material which has magnetic properties when being brought near a magnetic field, but which loses these properties when the field is removed.

Thermocouple: device which produces electricity when two dissimilar metals are joined and heat is applied to the juncture. Current will flow in wires attached to the ends of the metal pieces, from the negatively charged metal to the positively charged metal.

Three phase generator: a generator which produced ac power in three windings which are 120 electrical degrees apart from each other.

Tip spillage: air sneaking by the tip, creating turbulence.

Tip speed ratio: ratio of the propeller tip speed to the wind speed.

Topography: the configuration of a surface, including its relief and the position of its natural and man-made features.

Torque: a force that produces or tends to produce rotation.

Tower shadow: an occurrence where wind has to pass over the tower before it reaches the generator, i.e., the generator is in the wind shadow of the tower.

Transformers: devices which increase or decrease voltage by electromagnetic induction.


Upwind system: a wind system which has its propellers facing into the wind.

Utility grid: the utility company's network of lines.

Variable frequency: a varying number of complete alternations per second of an alternating current.

Venturie effect: a funneling effect

Vertical axis: a wind system which has its axis of rotation perpendicular to the earth and the wind's flow.

Voltage: (e) - electromotive force: unit of electric pressure.

Voltage regulator: a device or design implementation which regulates the electromotive force (volts).

Voltaic cell: another name for battery. A primary cell named for its inventor Alessandro Volta.


Watt (w): rate of electrical flow.

Watt hours: a unit of work or energy equivalent to the power of one watt operating for one hour.

Wind energy conversion system: a system consisting of sub-components which converts wind energy to electrical energy and having major components: generator rotors, tower and storage system.

Wind generators: generators which get their power from wind turning a permanent magnet around a stationary armature or visa versa.

Windmill: technically, a wind powered machine used to grind grain for flour.

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