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Absorber: A material that readily absorbs
photons to generate charge carriers (free electrons or holes).
Absorbers: Dark-colored objects that soak up
heat in solar collectors.
Absorption coefficient: The factor by which
photons are absorbed as they travel a unit distance through a material.
Acceptor: A dopant material, such as boron,
which has fewer outer shell electrons than required in an otherwise
balanced crystal structure, providing a hole, which can accept a free
electron.
Accessible: (As applied to wiring methods)
Capable of being removed or exposed without damaging the building
structure or finish, or not permanently closed in by the structure or
finish of the building.
Accessible: (as applied to equipment) Admitting
close approach: not guarded by locked doors, elevation, or other effective
means. (see Accessible, Readily)
Accessible, Readily: (Readily Accessible)
Capable of being reached quickly for operation, renewal, or inspections,
without requiring those to whom ready access is requisite to climb over or
remove obstacles or to resort to portable ladders, chairs, etc.
Actinide: an element with atomic number of 89
(actinium) or above.
Activation product: A radioactive isotope of an
element (e.g., in the steel of a reactor core) which has been created by
neutron bombardment.
Active solar heater: A solar water or
space-heating system that moves heated air or water using pumps or fans.
Affected employee: An employee whose job
requires him or her to operate or use a machine or equipment on which
servicing or maintenance is being performed under lockout or tagout, or
whose job requires him or her to work in an area in which such servicing
or maintenance is being performed.

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Air Circuit Breakers:
These are used to interrupt circuits while current flows through
them. Compressed air is used to quench the arc when the connection
is broken.
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Air mass: The ratio of the
mass of atmosphere in the actual observer-sun path to the mass that would
exist if the observer was at sea level, at standard barometric pressure,
and the sun was directly overhead. Note: (sometimes called air mass
ratio).
Air mass 1.5 (AM1.5) standard reference spectrum:
The solar spectral irradiance distribution (diffuse and direct) incident
at sea level on a sun-facing 37-degree tilted surface. The atmospheric
conditions for AM1.5 are: precipitable water vapor, 14.2 mm; total ozone,
3.4 mm; turbidity (base e, lambda=0.5 mm), 0.27. [ASTM E 892, Table 2]
Alternating current: Electric current in which
the direction of flow is reversed at frequent intervals: usually 100 or
120 times per second (50 or 60 cycles per second or 50//60 Hz).
ALARA: As Low As Reasonably Achievable, economic
and social factors being taken into account. This is the optimization
principle of radiation protection.
Alpha particle: A positively-charged particle
from the nucleus of an atom, emitted during radioactive decay. Alpha
particles are helium nuclei, with 2 protons and 2 neutrons.
Alternative fuels: Solid fuels such as municipal
solid waste (MSW), refuse derived fuel (RDF), biomass, rubber tires, and
other combustibles that are used instead of fossil fuels (gas, oil, or
coal) in a boiler to produce steam for the generation of electrical
energy.
Ambient Temperature: The temperature of the air,
water, or surrounding earth. Conductor ampacity is corrected for changes
in ambient temperature including temperatures below 86°F. The cooling
effect can increase the current carrying capacity of the conductor.
(Review Section 310-10 of the Electrical Code for more understanding)
Ammeter: An electric meter used to measure
current, calibrated in amperes.
Ampacity: The current-carrying capacity of
conductors or equipment, expressed in amperes.
Ampere (A) or amp: The basic SI unit measuring
the quantity of electricity. The unit for the electric current; the flow
of electrons. One amp is 1 coulomb passing in one second. One amp is
produced by an electric force of 1 volt acting across a resistance of 1
ohm.
Ampere-hour (Ah): Quantity of electricity or
measure of charge. (1 Ah = 3600 C [Coulomb])
Amorphous semiconductor: A non-crystalline
semiconductor material that has no long-range order.
Annual solar savings: The annual solar savings
of a solar building is the energy savings attributable to a solar feature
relative to the energy requirements of a non-solar building.
Anthropogenic: Referring to alterations in the
environment due to the presence or activities of humans.
Antireflection coating: A thin coating of a
material, which reduces the light reflection and increases light
transmission, applied to a photovoltaic cell surface.
Armored Cable: A cable provided with a wrapping
of metal, usually steel wires or tapes, primarily for the purpose of
mechanical protection.
Arc-over Voltage: The minimum voltage required
to cause an arc between electrodes separated by a gas or liquid
insulation.
Array: Any number of photovoltaic modules
connected together to provide a single electrical output. Arrays are often
designed to produce significant amounts of electricity.
Atom: A particle of matter which cannot be
broken up by chemical means. Atoms have a nucleus consisting of
positively-charged protons and uncharged neutrons of the same mass. The
positive charges on the protons are balanced by a number of
negatively-charged electrons in motion around the nucleus.
Attendant: An employee assigned to remain
immediately outside the entrance to an enclosed or other space to render
assistance as needed to employees inside the space.
Attenuation: (l) The ratio of the input to
output power levels in a network (transmission line) when it is excited by
a matched source and terminated in a matched load. (2) Power loss in an
electrical system.
Authorized employee: An employee who locks out
or tags out machines or equipment in order to perform servicing or
maintenance on that machine or equipment. An affected employee becomes an
authorized employee when that employee's duties include performing
servicing or maintenance covered under this section.
Automatic circuit re-closer: A self-controlled
device for interrupting and re-closing an alternating current circuit with
a predetermined sequence of opening and re-closing followed by resetting,
hold-closed, or lockout operation.
Autonomous system: A stand-alone Photovoltaic
system that has no back-up generating source. May or may not include
storage batteries.
Availability: Describes the reliability of power
plants. It refers to the number of hours the turbines are available to
produce power divided by the total hours in a year.
Avoided cost: The minimum amount an electric
utility is required to pay an independent power producer, under the PURPA
regulations of 1978, equal to the costs the utility calculates it avoids
in not having to produce that power (usually substantially less than the
retail price charged by the utility for power it sells to customers).
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Background radiation: The naturally-occurring
ionizing radiation which every person is exposed to, arising from the
earth's crust (including radon) and from cosmic radiation.
Balance of system: Represents all components and
costs other than the Photovoltaic modules. It includes design costs, land,
site preparation, system installation, support structures, power
conditioning, operation and maintenance costs, indirect storage, and
related costs.
Band gap: In a semiconductor, the energy
difference between the highest valence band and the lowest conduction
band.
Band gap energy (EG):
The amount of energy (in electron volts) required to free an outer shell
electron from its orbit about the nucleus to a free state and, thus, to
promote it from the valence level to the conduction level.
Band-to-band Auger recombination: Recombination
of an electron and a hole occurring between bands of the same energy in
which no magnetic radiation is emitted.
Bare Conductor: A conductor not covered with
insulating material.
Barricade: A physical obstruction such as tapes,
cones, or A-frame type wood or metal structures intended to provide a
warning about and to limit access to a hazardous area.
Barrier: A physical obstruction which is
intended to prevent contact with energized lines or equipment or to
prevent unauthorized access to a work area.
Barrier energy: The energy given up by an
electron in penetrating the cell barrier; a measure of the electrostatic
potential of the barrier.
Barrier, fire: A continuous membrane, either
vertical or horizontal, such as a wall or floor assembly, that is designed
and constructed with specified fire resistance rating to limit the spread
of fire and that will also restrict the movement of smoke. Such barriers
can have protected openings.
Base load: That part of electricity demand which
is continuous, and does not vary over a 24-hour period. Approximately
equivalent to the minimum daily load.
Base power: Power generated by a utility unit
that operates at a very high capacity factor.
Baseline performance value: Initial values of
short-circuit current, open-circuit voltage, and current at maximum power
measured by the accredited laboratory and corrected to Standard Test
Conditions, used to validate the manufacturer's performance measurements
provided with the qualification modules per IEEE 1262.

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Batteries:
These are used in the substation control house as a backup to
power the control systems in case of a power blackout.
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Battery energy storage:
The three main applications for battery energy storage systems include
spinning reserve at generating stations, load leveling at substations, and
peak shaving on the customer side of the meter. Battery storage has also
been suggested for holding down air emissions at the power plant by
shifting the time of day of the emission or shifting the location of
emissions.
Bayonet Coupling: A quick coupling device for
plug and receptacle connectors, accomplished by rotation of a cam
operating device designed to bring the connector halves together.
Becquerel: The SI unit of intrinsic
radioactivity in a material. One Bq measures one disintegration per second
and is thus the activity of a quantity of radioactive material which
averages one decay per second. (In practice, GBq or TBq are the common
units.)
Beryllium Copper (BeCu): A relatively expensive
contact material with properties superior to brass and phosphor bronze. It
is recommended for contact applications requiring repeated extraction and
reinsertion because of its resistance to fatigue at high operating
temperatures.
Beta particle: A particle emitted from an atom
during radioactive decay. Beta particles may be either electrons (with
negative charge) or positrons.
BIPV (Building-Integrated Photovoltaic): A term
for the design and integration of Photovoltaic into the building envelope,
typically replacing conventional building materials. This integration may
be in vertical facades, replacing view glass, spandrel glass, or other
facade material; into semitransparent skylight systems; into roofing
systems, replacing traditional roofing materials; into shading
"eyebrows" over windows; or other building envelope systems.
Biological shield: A mass of absorbing material
(e.g., thick concrete walls) placed around a reactor or radioactive
material to reduce the radiation (especially neutrons and gamma rays
respectively) to a level safe for humans.
Blocking diode: A diode used to restrict or
block reverse current from flowing backward through a module. [UL 1703]
Alternatively, diode connected in series to a Photovoltaic string; it
protects its modules from a reverse power flow and, thus, against the risk
of thermal destruction of solar cells.
Boiling water reactor (BWR): A common type of
light water reactor (LWR), where water is allowed to boil in the core thus
generating steam directly in the reactor vessel. (cf PWR)
Bonding Jumper: A bare or insulated conductor
used to ensure the required electrical conductivity between metal parts
required to be electrically connected. Frequently used from a bonding
bushing to the service equipment enclosure to provide a path around
concentric knockouts in an enclosure wall - also used to bond one raceway
to another.
Boron (B): A chemical element, atomic number 5,
semi-metallic in nature, used as a dopant to make p-semiconductor layers.
Boule: A sausage-shaped synthetic single-crystal
mass grown in a special furnace, pulled and turned at a rate necessary to
maintain the single-crystal structure during growth.
Breakdown Voltage: The voltage at which an
insulator or dielectric ruptures, or at which ionization and conduction
take place in a gas or vapor.
Breed: To form fissile nuclei, usually as a
result of neutron capture, possibly followed by radioactive decay.
Breeder reactor: see Fast Breeder Reactor and
Fast Neutron Reactor.
British thermal unit (Btu): The amount of heat
energy required to raise the temperature of one pound of water from 60
degrees F to 61 degrees F at one atmosphere pressure.
Burnable poison: A neutron absorber included in
the fuel which progressively disappears and compensates for the loss of
reactivity as the fuel is consumed. Gadolinium is commonly used.
Burnup: Measure of thermal energy released by
nuclear fuel relative to its mass, typically Gigawatt days per tonne (GWd/tU).
Bushing: An insulating structure, including a
through conductor or providing a passageway for such a conductor, with
provision for mounting on a barrier, conducting or otherwise, for the
purposes of insulating the conductor from the barrier and conducting
current from one side of the barrier to the other.

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Bus Support Insulators:
These are porcelain or fiberglass insulators that serve to isolate
the bus bar switches and other support structures and to prevent
leakage current from flowing through the structure. These
insulators are similar in function of other insulators used in
substations and transmission poles and towers.
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Bypass diode: A diode
connected across one or more solar cells in a photovoltaic module such
that the diode will conduct if the cell(s) become reverse biased. [UL
1703] Alternatively, diode connected anti-parallel across a part of the
solar cells of a Photovoltaic module. It protects these solar cells from
thermal destruction in case of total or partial shading of individual
solar cells while other cells are exposed to full light.
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Cable: A conductor with insulation, or a
stranded conductor with or without insulation and other coverings
(single-conductor cable), or a combination of conductors insulated from
one another (multiple-conductor cable).
Cable Assembly: A cable with plugs or connectors
on each end.
Cable sheath: A conductive protective covering
applied to cables. Note: A cable sheath may consist of multiple layers of
which one or more is conductive.
Cadmium (Cd): A chemical element, atomic number
48, used in making certain types of solar cells and batteries.
Cadmium telluride (CdTe): A polycrystalline
thin-film photovoltaic material.
Calandria: (in a CANDU reactor) a cylindrical
reactor vessel which contains the heavy water moderator. It is penetrated
from end to end by hundreds of calandria tubes which accommodate the
pressure tubes containing the fuel and coolant.
CANDU: Canadian deuterium uranium reactor,
moderated and (usually) cooled by heavy water.
Capacitance: That property of a system of
conductors and dielectrics that permits the storage of electricity when
potential difference exists between the conductors. Its value is expressed
as the ratio of quantity of electricity to a potential difference. A
capacitance value is always positive.

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Capacitor Bank:
An array of capacitors connected into a circuit. Capacitors are
used to control voltages supplied to the customer by eliminating
the voltage drop in the system caused by inductive reactive loads.
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Capacity factor: The
amount of energy that the system produces at a particular site as a
percentage of the total amount that it would produce if it operated at
rated capacity during the entire year. For example, the capacity factor
for a wind farm ranges from 20% to 35%. Thirty-five percent is close to
the technology potential.
Cathodic protection: A method of preventing
oxidation (rusting) of exposed metal structures, such as bridges and
pipelines, by imposing between the structure and the ground a small
electrical voltage that opposes the flow of electrons and that is greater
than the voltage present during oxidation.
Cell: The basic unit of a photovoltaic system.
Cell barrier: A very thin region of static
electric charge along the interface of the positive and negative layers in
a photovoltaic cell. The barrier inhibits the movement of electrons from
one layer to the other, so that higher-energy electrons from one side
diffuse preferentially through it in one direction, creating a current and
thus a voltage across the cell. Also called depletion zone, cell junction,
or space charge.
Cell junction: The area of immediate contact
between two layers (positive and negative) of a photovoltaic cell. The
junction lies at the center of the cell barrier or depletion zone.
Central power: The generation of electricity in
large power plants with distribution through a network of transmission
lines (grid) for sale to a number of users. Opposite of distributed power.
Chain reaction: A reaction that stimulates its
own repetition, in particular where the neutrons originating from nuclear
fission cause an ongoing series of fission reactions.
Charge carrier: A free and mobile conduction
electron or hole in a semiconductor.
Chemical vapor deposition (CVD): A method of
depositing thin semiconductor films. With this method, a substrate is
exposed to one or more vaporized compounds, one or more of which contain
desirable constituents. A chemical reaction is initiated, at or near the
substrate surface, to produce the desired material that will condense on
the substrate.
Chlorofluorocarbon: A family of chemicals
composed primarily of carbon, hydrogen, chlorine, and fluorine whose
principal applications are that of refrigerants and industrial cleansers
and whose principal drawback is the tendency to destroy the Earth's
protective ozone layer.
Circuit: A conductor or system of conductors
through which an electric current is intended to flow.

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Circuit Switchers:
Circuit switchers a a set of switches for redirecting current in a
substation. Circuit switchers provide equipment protection for
transformers, lines, cables, and capacitor banks. They also are
used to energize and deenergize capacitor banks and other
circuits.
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Cladding: The metal tubes
containing oxide fuel pellets in a reactor core.
Clearance (between objects): The clear distance
between two objects measured surface to surface.
Clearance (for work): Authorization to perform
specified work or permission to enter a restricted area.
Cleavage of lateral epitaxial films for transfer
(CLEFT): A process for making inexpensive GaAs photovoltaic cells
in which a thin film of GaAs is grown atop a thick, single-crystal GaAs
(or other suitable material) substrate and then is cleaved from the
substrate and incorporated into a cell, allowing the substrate to be
reused to grow more thin-film GaAs.
Closed Entry Contact: A female contact designed
to prevent the entry of a pin or probing device having a cross-sectional
dimension (diameter) greater than the mating pin.
Coal: A black, solid fossil fuel found in the
Earth. Coal is often burned to make electricity.
Coaxial Cable: A high-band width cable
consisting of two concentric cylindrical conductors with a common axis
that is used for high-speed data communication and video signals.
Cogeneration: The process in which fuel is used
to produce heat for a boiler-steam turbine or gas for a turbine. The
turbine drives a generator that produces electricity, with the excess heat
used for process steam.
Combined collector: A photovoltaic device or
module that provides useful heat energy in addition to electricity.
Compact fluorescent lights: Lights that use a
lot less energy than regular light bulbs. We can use compact fluorescent
lights for reading lights and ceiling lights.
Component Lead: The solid or stranded wire or
formed conductor that extends from a component and serves as a readily
formable mechanical or electrical connection or both.
Compressed-air energy storage (CAES): CAES
plants use off-peak electrical energy to compress air into underground
storage reservoirs for storage until times of peak or intermediate
electricity demand. Wind power offers a good opportunity for charging CAES
storage. The storage is typically underground in natural aquifers,
depleted oil or gas fields, mined salt caverns, or excavated or natural
rock caverns. To generate power, the compressed air is first heated by gas
burners, then passed through a turbine.
Concentrator: A Photovoltaic module that uses
optical elements to increase the amount of sunlight incident on a
Photovoltaic cell.
Concentrating: arrays must track the sun and use
only the direct sunlight because the diffuse portion cannot be focused
onto the Photovoltaic cells.
Concentrate: See Uranium oxide concentrate (U3O8).
Concentrator (module, array, or collector): An
arrangement of photovoltaic cells that includes a lens to concentrate
sunlight onto small-area cells. Concentrators can increase the power flux
of sunlight hundreds of times.
Concentricity: In a wire or cable, the
measurement of the location of the center of the conductor with respect to
the geometric center of the surrounding insulation.

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Concrete Foundations:
A platform made of concrete that provides a solid stable support
for large equipment. Concrete foundations or pads are laid for all
large equipment, support structures, and control buildings in a
substation.
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Conductance: The
reciprocal of resistance. It is the ratio of current passing through a
material to the potential difference at its ends.
Conduction band; Conduction level: Energy level
at which electrons are not bound to (orbiting) a specific atomic nucleus
but are free to wander among the atoms. An energy band in which electrons
can move freely in a solid, producing a net transport of charge.
Conductivity: The ability of a material to
conduct electric current. It is expressed in terms of the current per unit
of applied voltage. It is the reciprocal of resistivity.
Conductor: A wire or combination of wires not
insulated from one another, suitable for carrying electric current.

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Conduits:
Conduits are hollow tubes running from manhole to manhole in an
underground transmission or distribution system.
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Connection: That part of a
circuit that has negligible impedance and that joins components, devices,
etc., together.
Connector: A device providing electrical
connection/disconnections. It consists of a mating plug and receptacle.
Various types of connectors include DIP, card edge, two-piece,
hermaphroditic and wire-wrapping configurations. Multiple contact
connectors join two or more conductors with others in one mechanical
assembly.
Connector Discontinuity: An ohmic change in
contact resistance.
Connector Insert: For connectors with metal
shells, the insert holds contacts in proper arrangement while electrically
insulating them from each other and from the shell.
Connector Shell: The case that encloses the
connector insert and contact assembly. Shells of mating connectors can
protect projecting contacts and provide proper alignment.
Constant-speed wind turbines: Turbines that
operate at a constant rotor revolutions per minute (RPM) and are optimized
for energy capture at a given rotor diameter at a particular speed in the
wind power curve.
Contact, Female: A contact located in an insert
or body in such a manner that the mating contact is inserted into the
unit. It is similar in function to a socket contact.
Contact, Male: A contact located in an insert or
body in such a manner that the mating portion extends into the female
contact. It is similar in function to a pin contact.
Contact Plating: Plated-on metal applied to the
base contact metal to provide the required contact resistance and/or wear
resistance.
Contact Resistance: Maximum permitted electrical
resistance of pin and socket contacts when assembled in a connector under
typical service use.
Contact Retainer: A device either on the contact
or in the insert to retain the contact.
Contact Size: Defines the largest size wire that
can be used with the specific contact. By specification dimensioning, it
also defines the diameter of the engagement end of the pin.
Contact resistance: The resistance between
metallic contacts and the semiconductor.
Continuity: The state of being whole, unbroken.
Continuous Load: A load where the maximum
current is expected to continue for three hours or more. Rating of the
branch circuit protection device shall not be less tan 125% of the
continuous load.

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Control House:
The substation control house contains switchboard panels,
batteries, battery chargers, supervisory control, power-line
carrier, meters, and relays. The control house provides all
weather protection and security for the control equipment. It is
also called a doghouse.
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Control Panels:
Control panels contain meters, control switches and recorders
located in the control building, also called a doghouse. These are
used to control the substation equipment, to send power from one
circuit to another or to open or shut down circuits when needed.
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Control rods: Devices to
absorb neutrons so that the chain reaction in a reactor core may be slowed
or stopped by inserting them further, or accelerated by withdrawing them.

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Control Wires:
Control wires are installed connecting the control house control
panels to all the equipment in the substation. A typical
substation control house contains several thousand feet of conduit
and miles of control wire.
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Conversion: Chemical
process turning U3O8 into UF6 preparatory
to enrichment.
Conversion efficiency (cell or module): The
ratio of the electric energy produced by a photovoltaic device (under
one-sun conditions) to the energy from sunlight incident upon the cell.

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Converter Stations:
Converter stations are located at the terminals of a DC
transmission line. Converter stations change alternating current
into direct current and invert direct current to alternating
current.
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Coolant: The liquid or gas
used to transfer heat from the reactor core to the steam generators or
directly to the turbines.
Copper indium diselenide (CuInSe2, or CIS):
A polycrystalline thin-film photovoltaic material (sometimes incorporating
gallium (CIGS) and/or sulfur).
Core: The central part of a nuclear reactor
containing the fuel elements and control devices.

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Coupling Capacitors:
Coupling capacitors are used to transmit communication signals to
transmission lines. Some are used to measure the voltage in
transmission lines.
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Critical mass: The
smallest mass of fissile material that will support a self-sustaining
chain reaction under specified conditions.
Criticality: Condition of being able to sustain
a nuclear chain reaction.
Current at maximum power (Imp): The current at
which maximum power is available from a module. [UL 1703]

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Current Transformers:
Current transformers can be used to supply information for
measuring power flows and the electrical inputs for the operation
of protective relays associated with the transmission and
distribution circuits or for power transformers.
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Cycle life: Number of
discharge-charge cycles that a battery can tolerate under specified
conditions before it fails to meet specified criteria as to performance
(e.g., capacity decreases to 80-percent of the nominal capacity).
Czochralski process: A method of growing large
size, high quality semiconductor crystal by slowly lifting a seed crystal
from a molten bath of the material under careful cooling conditions.
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Dangling bonds: A chemical bond associated with
an atom on the surface layer of a crystal. The bond does not join with
another atom of the crystal, but extends in the direction of exterior of
the surface.
dc to DC converter: Electronic circuit to
convert DC voltages (e.g., Photovoltaic module voltage) into other levels
(e.g., load voltage). Can be part of a maximum power point tracker (MPPT).
Decay: Disintegration of atomic nuclei resulting
in the emission of alpha or beta particles (usually with gamma radiation).
Also the exponential decrease in radioactivity of a material as nuclear
disintegrations take place and more stable nuclei are formed.
Decommissioning: Removal of a facility (e.g.,
reactor) from service, also the subsequent actions of safe storage,
dismantling and making the site available for unrestricted use.
De-energized: Free from any electrical
connection to a source of potential difference and from electric charge;
not having a potential different from that of the earth. Note: The term is
used only with reference to current-carrying parts, which are sometimes
energized (alive).
Deep discharge: Discharging a battery to
20-percent or less of its full charge.
Deflagration: Propagation of a combustion zone
through a fuel-oxidizer mixture at a rate that is less than the speed of
sound in the un-reacted medium and capable of producing a significant
increase in pressure.
Demand Factor: For an electrical system or
feeder circuit, this is a ratio of the amount of connected load (in kva or
amperes) that will be operating at the same time to the total amount of
connected load on the circuit. An 80% demand factor, for instance,
indicates that only 80% of the connected load on a circuit will ever be
operating at the same time. Conductor capacity can be based on that amount
of load.
Dendrite: A slender threadlike spike of pure
crystalline material, such as silicon.
Dendritic web technique: A method for making
sheets of polycrystalline silicon in which silicon dendrites are slowly
withdrawn from a melt of silicon whereupon a web of silicon forms between
the dendrites and solidifies as it rises from the melt and cools.
Depletion zone: Same as cell barrier. The term
derives from the fact that this microscopically thin region is depleted of
charge carriers (free electrons and holes).
Depleted uranium: Uranium having less than the
natural 0.7% U-235. As a by-product of enrichment in the fuel cycle it
generally has 0.25-0.30% U-235, the rest being U-238. Can be blended with
highly-enriched uranium (e.g., from weapons) to make reactor fuel.
Designated employee (designated person): An
employee (or person) who is designated by the employer to perform specific
duties under the terms of this section and who is knowledgeable in the
construction and operation of the equipment and the hazards involved.
Detachment: The locating of a combustible
particulate solid process in the open air or in a separate building.
Deuterium: "Heavy hydrogen", a stable
isotope having one proton and one neutron in the nucleus. It occurs in
nature as 1 atom to 6500 atoms of normal hydrogen, (Hydrogen atoms contain
one proton and no neutrons).
Diallyl Phthalate (DAP): A thermosetting plastic
that offers outstanding dimensional stability and resistance to most
chemicals and chemical compounds. It is used in the production of
connector housings.
Dielectric: (l) Any insulating medium that
intervenes between two conductors. (2) A material that, having the
property required to establish an electric field, is recoverable in whole
or in part as electric energy.
Dielectric Constant: That property of a
dielectric that determines the electrostatic energy stored per unit volume
for a unit potential gradient. Permittivity is the preferred term.
Dielectric Strength: The maximum voltage that a
dielectric material can withstand, under specified conditions, without
rupturing. It is usually expressed as volts/unit thickness. Also called
Disruptive Gradient or Electric Strength.
Dielectric Withstanding Voltage: Maximum
potential gradient that a dielectric material can withstand without
failure.
Diffuse insulation: Sunlight received indirectly
as a result of scattering due to clouds, fog, haze, dust, or other
obstructions in the atmosphere. Opposite of direct insulation.
Diffusion furnace: Furnace used to make
junctions in semiconductors by diffusing dopant atoms into the surface of
the material.
Diffusion length: The mean distance a free
electron or hole moves before recombining with another hole or electron.
Direct current (dc): Electric current in which
electrons flow in one direction only. Opposite of alternating current.
Direct gain: In direct-gain buildings, sunlight
directly enters the home through the windows and is absorbed and stored in
massive floors or walls. These buildings are elongated in the east-west
direction, and most of their windows are on the south side. The area
devoted to south windows varies throughout the country. It could be as
much as 20% of the floor area in sunny cold climates, where advanced
glazings or moveable insulation are recommended to prevent heat loss at
night. These buildings have high insulation levels and added thermal mass
for heat storage.
Direct insulation: Sunlight falling directly
upon a collector. Opposite of diffuse insulation.
Discharge rate: The rate, usually expressed in
amperes or time, at which electrical current is taken from the battery.

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Disconnect Switches:
Disconnect switches or circuit breakers are used to isolate
equipment or to redirect current in a substation.
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Distributed power: Generic
term for any power supply located near the point where the power is used.
Opposite of central power. See 'stand-alone'; 'remote site.'
Distributed systems: Systems that are installed
at or near the location where the electricity is used, as opposed to
central systems that supply electricity to grids. A residential
photovoltaic system is a distributed system.

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Distribution Bus:
A distribution bus is a steel structure array of switches used to
route power out of a substation.
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Distribution Feeder
Circuits: These are the connections between the output
terminals of a distribution substation and the input terminals of
primary circuits. The distribution feeder circuit conductors leave
the substation from a circuit breaker or circuit recloser via
underground cables, called substation exit cables.
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Distribution
Transformers: Distribution transformers reduce the
voltage of the primary circuit to the voltage required by
customers.
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DOD: 'Depth of Discharge,'
from 100-percent state of charge (SOC), in a battery or battery system.
Donor: An n-type dopant that puts an additional
electron into an energy level very near the conduction band; this electron
is easily exited into the conduction band where it increases the
electrical conductivity over than of an undoped semiconductor.
Donor level: The level that donates conduction
electrons to the system.
Dopant: A chemical element (impurity) added in
small amounts to an otherwise pure semiconductor material to modify the
electrical properties of the material. An n-dopant introduces more
electrons. A p-dopant creates electron vacancies (holes).
Doping: The addition of dopants to a
semiconductor.

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Duct Runs: Ducts
are hollow tubes running from manhole to manhole inside a conduit
in an underground system. They are of various sizes usually from 2
to 6 inches in diameter.
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Dustproof: Constructed
or protected so that dust will not interfere with its successful
operation.
Dusttight: Constructed so that dust will not
enter the enclosing case under specified test conditions.
Duty, continuous: A service requirement that
demands operation at a substantially constant load for an indefinitely
long time.
Duty, intermittent: A service requirement that
demands operation for alternate intervals of load and no load, load and
rest, or load, no load, and rest.
Duty, periodic: A type of intermittent duty in
which the load conditions regularly reoccur.
Duty, short time: A requirement of service that
demands operations at a substantially constant load for a short and
definitely specified time.
Duty, varying: A requirement of of service that
demands operation at loads, and for intervals of time, both of which may
be subject to wide variation.
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Edge-defined film-fed growth (EFG): A method for
making sheets of polycrystalline silicon in which molten silicon is drawn
upward by capillary action through a mold.
Elastomer: A material that at room temperature
stretches under low stress to at least twice its length and snaps back to
original length upon release of stress.
Electric circuit: Path followed by electrons
from a power source (generator or battery) through an external line
(including devices that use the electricity) and returning through another
line to the source.
Electric current: A flow of electrons;
electricity.
Electrical grid: An integrated system of
electricity distribution, usually covering a large area.
Electric line truck: A truck used to transport
personnel, tools, and material for electric supply line work.
Electric Strength: The maximum potential
gradient that a material can withstand without rupture. Also called
Dielectric Strength and Disruptive Gradient.
Electric supply: Conductors used to transmit
electric energy and their necessary supporting or containing structures.
Signal lines of more than 400 volts are always supply lines within this
section, and those of less than 400 volts are considered as supply lines,
if so run and operated throughout.
Electric supply equipment: Equipment that
produces, modifies, regulates, controls, or safeguards a supply of
electric energy.
Electric utility: An organization responsible
for the installation, operation, or maintenance of an electric supply
system.
Electrodeposition: Electrolytic process in which
a metal is deposited at the cathode from a solution of its ions.
Electrolyte: A liquid conductor of electricity.
Electron volt: An energy unit equal to the
energy an electron acquires when it passes through a potential difference
of one volt; it is equal to 1.602 x 10-19 volt.
Element: A chemical substance that cannot be
divided into simple substances by chemical means; atomic species with same
number of protons.
Emc: Electromagnetic compatibility.
Emi: Electromagnetic interference.
Enclosed space: A working space, such as a
manhole, vault, tunnel, or shaft, that has a limited means of egress or
entry, that is designed for periodic employee entry under normal operating
conditions, and that under normal conditions does not contain a hazardous
atmosphere, but that may contain a hazardous atmosphere under abnormal
conditions.
Note: Spaces that are enclosed but not designed for employee entry
under normal operating conditions are not considered to be enclosed
spaces for the purposes of this definition. Similarly, spaces that are
enclosed and that are expected to contain a hazardous atmosphere are not
considered to be enclosed spaces for the purposes of this definition.
Such spaces meet the definition of permit spaces in 1910.146, and entry
into them must be performed in accordance with that standard.
Energized (alive, live): Electrically
connected to a source of potential difference, or electrically charged so
as to have a potential significantly different from that of earth in the
vicinity.
Energy audit: A survey that shows how much
energy you use in your house or apartment. It will help you find ways to
use less energy.
Energy contribution potential: Recombination
occurring in the emitter region of a photovoltaic cell.
Energy density: The ratio of energy available
from a battery to its volume (Wh/1) or mass (Wh/kg).
Energy isolating device: A physical device that
prevents the transmission or release of energy, including, but not limited
to, the following: a manually operated electric circuit breaker, a
disconnect switch, a manually operated switch, a slide gate, a slip blind,
a line valve, blocks, and any similar device with a visible indication of
the position of the device. (Push buttons, selector switches, and other
control-circuit-type devices are not energy isolating devices.)
Energy levels: The energy represented by an
electron in the band model of a substance.
Energy source: Any electrical, mechanical,
hydraulic, pneumatic, chemical, nuclear, thermal, or other energy source
that could cause injury to personnel.
Enriched uranium: Uranium in which the
proportion of U-235 (to U-238) has been increased above the natural 0.7%.
Reactor-grade uranium is usually enriched to about 3.5% U-235,
weapons-grade uranium is more than 90% U-235.
Enrichment: Physical process of increasing the
proportion of U-235 to U-238.
Environment: All the natural and living things
around us. The earth, air, weather, plants, and animals all make up our
environment.
Epitaxial growth: The growth of one crystal on
the surface of another crystal. The growth of the deposited crystal is
oriented by the lattice structure of the original crystal.
Equipotential zone:
A zone of equal potential used to protect workers from hazardous step and
touch potentials.
Extrinsic semiconductor: The product of doping a
pure semiconductor.
Explosionproof: Designed and constructed to
withstand and internal explosion without creating an external explosion or
fire.
Exposed: Not isolated or guarded.
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Fast breeder reactor (FBR): A fast neutron
reactor configured to produce more fissile material than it consumes,
using fertile material such as depleted uranium in a blanket around the
core.
Fast neutron reactor: A reactor with little or
no moderator and hence utilizing fast neutrons. It normally burns
plutonium while producing fissile isotopes in fertile material such as
depleted uranium (or thorium).
Feeder: A circuit, such as conductors in conduit
or a busway run, which carries a large block of power from the service
equipment to a sub-feeder panel or a branch circuit panel or to some point
at which the block power is broken into smaller circuits.
Fermi level: Energy level at which the
probability of finding an electron is one-half. In a metal, the Fermi
level is very near the top of the filled levels in the partially filled
valance band. In a semiconductor, the Fermi level is in the band gap.
Fertile (of an isotope): Capable of becoming
fissile, by capturing neutrons, possibly followed by radioactive decay;
e.g., U-238, Pu-240.
Fill factor: The ratio of a photovoltaic cell's
actual power to its power if both current and voltage were at their maxima.
A key characteristic in evaluating cell performance.
Fire Barrier Wall: A wall separating buildings
or subdividing a building to prevent the spread of fire and having a fire
resistance rating and structural stability.
Fire loading: The amount of combustibles present
in a given area, expressed in Btu/ft2 (kJ/m2).
Fire point: The lowest temperature at which a
liquid in an open container will give off sufficient vapors to burn once
ignited. It generally is slightly above the flash point.
Fire protection rating: The time, in minutes or
hours, that materials and assemblies used as opening protection have
withstood a fire exposure as established in accordance with test
procedures of NFPA 252, Standard Methods of Fire
Tests of Door Assemblies, and NFPA 257, Standard on Fire Test for Window
and Glass Block assemblies, as applicable.
Fissile (of an isotope): Capable of capturing a
slow (thermal) neutron and undergoing nuclear fission, e.g., U-235, U-233,
Pu-239.
Fissionable (of an isotope): Capable of
undergoing fission: If fissile, by slow neutrons; if fertile, by fast
neutrons.
Fission: The splitting of a heavy nucleus into
two, accompanied by the release of a relatively large amount of energy and
usually one or more neutrons. It may be spontaneous but usually is due to
a nucleus absorbing a neutron and thus becoming unstable.
Fission products: Daughter nuclei resulting
either from the fission of heavy elements such as uranium, or the
radioactive decay of those primary daughters. Usually highly radioactive.
Flammable liquid: Any liquid having a flash
point below 100°F (37.8°C) and having a vapor pressure not exceeding an
absolute pressure of 40 psi (276 kPa) at 100°F (37.8°C).
Flat-plate photovoltaic module: An arrangement
of photovoltaic cells mounted on a rigid flat surface with the cells
exposed freely to incoming sunlight.
Flat-plate Photovoltaic: Refers to a
Photovoltaic array or module that consists of non-concentrating elements.
Flat-plate arrays and modules use direct and diffuse sunlight, but if the
array is fixed in position, some portion of the direct sunlight is lost
because of oblique sun-angles in relation to the array.
Float charge: Float charge is the voltage
required to counteract the self-discharge of the battery at a certain
temperature.
Float life: Number of years that a battery can
keep its stated capacity when it is kept at float charge (see float
charge).
Float-zone process: A method of growing a
large-size, high-quality crystal whereby coils heat a polycrystalline
ingot placed atop a single-crystal seed. As the coils are slowly raised
the molten interface beneath the coils becomes single crystal.
Fossil fuel: A fuel based on carbon presumed to
be originally from living matter, e.g., coal, oil, gas. Burned with oxygen
to yield energy, used in a boiler to produce steam for the generation of
electrical energy.
Fresnel lens: An optical device that focuses
light like a magnifying glass; concentric rings are faced at slightly
different angles so that light falling on any ring is focused to the same
point. Fresnel lenses are flat rather than thick in the center and can be
stamped out in a mold.

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Frequency Changers:
A frequency changer is a motor-generator set that changes power of
an alternating current system from one frequency to one or more
different frequencies, with or without a change in the number of
phases, or in voltage.
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Fuel: Any material that
can be burned to make energy.
Fuel assembly: Structured collection of fuel
rods or elements, the unit of fuel in a reactor.
Fuel cell: A device that converts the energy of
a fuel directly to electricity and heat, without combustion. Because there
is no combustion, fuel cells give off few emissions; because there are no
moving parts, fuel cells are quiet.
Fuel fabrication: Making reactor fuel
assemblies, usually from sintered UO2 pellets which are
inserted into zircalloy tubes, comprising the fuel rods or elements.
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Gallium (Ga): A chemical element, atomic number
31, metallic in nature, used in making certain kinds of solar cells and
semiconductor devices.
Gallium arsenide (GaAs): A crystalline
high-efficiency semiconductor/photovoltaic material.
Gamma rays: High energy electro-magnetic
radiation from the atomic nucleus, virtually identical to X-rays.
Gassing current: Portion of charge current that
goes into electrolytic production of hydrogen and oxygen from the
electrolytic liquid. This current increases with increasing voltage and
temperature.
Gel-type battery: Lead-acid battery in which the
electrolyte is composed of a silica gel matrix.
Genetic mutation: Sudden change in the
chromosomal DNA of an individual gene. It may produce inherited changes in
descendants. Mutation in some organisms can be made more frequent by
irradiation (though this has never been demonstrated in humans).
Gigawatt (GW): One billion watts. One million
kilowatts. One thousand megawatts.
Glazings: Clear materials (such as glass or
plastic) that allow sunlight to pass into solar collectors and solar
buildings, trapping heat inside.
Grain boundaries: The boundaries where
crystallites in a polycrystalline material meet.
Graphite: Crystalline carbon used in very pure
form as a moderator, principally in gas-cooled reactors, but also in
Soviet-designed RBMK reactors.
Gray: The SI unit of absorbed radiation dose,
one joule per kilogram of tissue.
Greenhouse effect: The effect of the Earth's
atmosphere, due to certain gases, in trapping heat from the sun; the
atmosphere acts like a greenhouse.
Greenhouse gases: Gases that trap the heat of
the sun in the Earth's atmosphere, producing the greenhouse effect; the
two major greenhouse gases are water vapor and carbon dioxide; lesser
greenhouse gases include methane, ozone, chlorofluorocarbons, and nitrogen
oxides.
Grid-connected (Photovoltaic system):
A Photovoltaic system in which the Photovoltaic array acts like a central
generating plant, supplying power to the grid.
Grid-interactive (Photovoltaic system):
See 'Grid-connected (Photovoltaic system).'
Ground: A large conducting body (such as the
earth) used as a common return for an electric circuit and as an arbitrary
zero of potential.
Grounded, effectively: Intentionally connected
to earth through a ground connection or connections of sufficiently low
impedance and having sufficient current-carrying capacity to prevent the
buildup of voltages that may result in undue hazards to connect equipment
or to persons.
Grounded Conductor: A system or circuit
conductor that is intentionally grounded, usually gray or white in color.
Grounding Conductor: A conductor used to connect
metal equipment enclosures and/or the system grounded conductor to a
grounding electrode, such as the ground wire run to the water pipe at a
service; also may be a bare or insulated conductor used to ground motor
frames, panel boxes, and other metal equipment enclosures used throughout
electrical systems. In most conduit systems, the conduit is used as the
ground conductor.
Grounding Equipment Conductor: The conductor
used to connect the noncurrent-carrying metal parts of equipment,
raceways, and other enclosures to the system grounded conductor, the
grounding electrode conductor, or both, of the circuit at the service
equipment or at the source of a separately derived system.
Grounding Electrode: The conductor used to
connect the grounding electrode to the equipment grounding conductor, to
the grounded conductor, or to both, of the circuit at the service
equipment or at the source of a separately derived system.

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Grounding Resistors:
Grounding Resistors are designed to provide added safety to
industrial distribution systems by limiting ground fault current
to reasonable levels.
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Grounding
Transformers: A grounding transformer intended
primarily to provide a neutral point for grounding purposes.
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Ground Fault Circuit Interrupter: A device intended for the
protection of personal that functions to de-energize a circuit or portion
thereof within an established period of time when a current to ground
exceeds some predetermined value that is less than required to operate the
overcurrent protection device of the supply circuit.
Ground Fault Protection of Equipment: A system
intended to provide protection of equipment from damaging line to ground
fault currents by operating to cause a disconnecting means to open all
ungrounded conductors of the faulted circuit. This protection is provided
at current levels less than those required to protect conductors from
damage through the operations of a supply circuit overcurrent device.
Guarded: Covered, fenced, enclosed, or otherwise
protected, by means of suitable covers or casings, barrier rails or
screens, mats, or platforms, designed to minimize the possibility, under
normal conditions, of approach or accidental contact by persons or
objects. Note: Wires which are insulated, but not otherwise protected, are
not considered as guarded.
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Half-life: The period required for half of the
atoms of a particular radioactive isotope to decay and become an isotope
of another element.
Hazardous atmosphere: An atmosphere that may
expose employees to the risk of death, incapacitation, impairment of
ability to self-rescue (that is, escape unaided from an enclosed space),
injury, or acute illness from one or more of the following causes:
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Flammable gas, vapor, or mist in excess of 10 percent of its lower
flammable limit (LFL);
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Airborne combustible dust at a concentration that meets or exceeds
its LFL; Note: This concentration may be approximated as a condition
in which the dust obscures vision at a distance of 5 feet (1.52 m) or
less.
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Atmospheric oxygen concentration below 19.5 percent or above 23.5
percent;
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Atmospheric concentration of any substance for which a dose or a
permissible exposure limit is published and which could result in
employee exposure in excess of its dose or permissible exposure limit;
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Note: An atmospheric concentration of any substance that is
not capable of causing death, incapacitation, impairment of
ability to self-rescue, injury, or acute illness due to its health
effects is not covered by this definition.
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Any other atmospheric condition that is immediately dangerous to
life or health.
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Note: For air contaminants for which OSHA has not determined a
dose or permissible exposure limit, other sources of information,
such as Material Safety Data Sheets that comply with the Hazard
Communication Standard, 1910.1200, published information, and
internal documents can provide guidance in establishing acceptable
atmospheric conditions.
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Heat pump: Like an air
conditioner or refrigerator, a heat pump moves heat from one location to
another. In the cooling mode, heat pumps reduce indoor temperatures in the
summer by transferring heat to the ground. Unlike an air conditioning
unit, however, a heat pump's cycle is reversible. In winter, a heat pump
can extract heat from the ground and transfer it inside. The energy value
of the heat thus moved can be more than three times the cost of the
electricity required to perform the transfer process.
Heavy water: Water containing an elevated
concentration of molecules with deuterium ("heavy hydrogen")
atoms.
Heavy water reactor (HWR): A reactor which uses
heavy water as its moderator, e.g., Canadian CANDU (pressurized HWR or
PHWR).
Heterojunction: A region of electrical contact
between two different semiconductor materials.
High-level wastes: Extremely radioactive fission
products and transuranic elements (usually other than plutonium) in spent
nuclear fuel. They may be separated by reprocessing the spent fuel, or the
spent fuel containing them may be regarded as high-level waste.
Highly (or High)-enriched uranium (HEU): Uranium
enriched to at least 20% U-235. (In weapons it is about 90% U-235.)
High-power tests: Tests in which fault currents,
load currents, magnetizing currents, and line-dropping currents are used
to test equipment, either at the equipment's rated voltage or at lower
voltages.

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High Voltage
Underground Cables: High voltage cables are designed to
carry high voltage current and are constructed in many different
ways, but are usually shielded cables. They are made with a
conductor, conductor-strand shielding, insulation, semi-conducting
insulation shielding, metallic insulation shielding, and a sheath.
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High voltage direct current (HVDC)
converter station: A facility that functions as an electrical
rectifier (ac-dc) to control and transmit power in a high voltage network.
There are two types of HVDC valves: the mercury arc valve and the
present-day technology solid state thyristor valve. Both types of valves
present a fire risk due to high voltage equipment that consists of
oil-filled converter transformers, wall bushings, and capacitors in
addition to various polymeric components.
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