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Generators & Power Distribution
Glossary
Generators
-- Power
Distribution
Alternating Current (AC) — A
current which reverses in regularly recurring intervals of time
and which
has alternative positive and negative values, and occurring a specified
number of times per second. (See frequency.)
Ampere (Amp) — The
unit of electric current flow. One ampere will flow when one volt
is applied across a resistance
of one ohm. (Amp Chart)
Automatic Voltage Regulator (AVR)
- an electronic device used to maintain and control the output voltage
of an A.C. generator. It consits of three circuits; input,
sensing and output.
Auto-Start
- the ability to start a generator and have it produce power without
the assistance of an operator. This is usually accomplished
by using an automatic transfer switch.
Capacitance — The property of a circuit
or body that permits it to store an electrical charge equal to
the
accumulated charge
divided by the voltage. Capacitance is expressed in farads.
Circuit — A complete or partial path over
which electric current may flow.
Circuit Breaker — A mechanical switching
device capable of making, carrying, and breaking currents under
normal conditions.
Also making, carrying for a specific time, and automatically breaking
currents under specified abnormal circuit conditions, such as those
of short circuit. Circuit breakers have an ampere trip rating for
normal overload protection and a maximum magnetic ampere interrupting
capacity (AIC) for short circuit protection.
Commercial Power — The
term applied to power furnished by an electric power utility.
Conductor — A
wire, cable, or bus bar designed for the passage of electrical
current.
Contactor — An electro-mechanical device
operated by an electric coil; it allows automatic or
remote operation to repeatedly
establish or interrupt an electrical power circuit.
Contacts — Devices
for making and breaking electrical circuits, which are a part of
all electrical switching
devices.
Current (I) — The amount of electricity
flowing in a circuit, measured in amperes.
Cycle — A given length of time (see Alternating
Current). In the U.S., most electric current is 60 cycle (60 Hz).
Delta Connection — A common three-phase
connection shaped schematically like the Greek delta.
The end of one phase is connected to the beginning of the next
phase, or vice
versa.
Dielectric — Insulating material, such as
air or glass, that has a high resistance to the conductance of
electric current;
a
non-conductor.
Direct Current (DC) — An electric current
flowing in one direction.
Distribution Panel — A device that
provides multiple power outlets from a 208V 3-phase or 240V single-phase
power source for
operating power tools, work lights, and other electrical equipment.
Efficiency Factor (EFF) — Output
power to input power ratio in an electric motor.
Electric Utilities — All
enterprises engaged in the production and/or distribution of
electricity for use by
the public.
Electronic Govenor - Used
to maintain the rotational speed of an engine. An electronic governor
is considered isochronous. Because of the precision of the electronic
referenced used, they are capable of maintaining a pre-set frequency
from no load to full load.
Electromotive Force (E) — The
force or electric pressure that causes or tends to cause a
current to
flow in a circuit,
equivalent
to the potential difference between the terminals and commonly
measured in volts.
Emergency (Stand-by) Power
- An
independent reserve source of electric power that provides
stand-by electric
power upon failure or outage of normal power source.
Frequency — The number of complete
cycles of an alternating voltage or current per unit of time,
usually
expressed in cycles per second or Hertz (Hz).
Full Load Current (Amps) — The
greatest current that a motor or other device is designed to carry
under
specific conditions: when rated voltage is applied at rated
frequency with rated horsepower. Any additional current is an overload.
Fuse — An over-current protective device
that consists of a conductor that melts and breaks when current
exceeds rated value beyond a predetermined time.
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Fuseable Disconnect Switch — A switching
device that provides a safe way to distribute power for operating
electrical equipment.
Generator — A machine that converts
mechanical energy into electrical energy/power.
Generator Receptacle — A contact device
installed for the connection of a plug and flexible cord to
supply emergency power from a portable generator or other alternate
source of power. Receptacles are rated in voltage, amps, number
of wires, and by enclosure type.
Ground — A connection, either intentional
or accidental, between an electric circuit and the earth or
some conducting body serving in place of the earth.
Ground Fault Circuit Interrupter (GFCI) — A
receptacle with a built in circuit that will detect leakage
current to ground on the load side of the device. When the
GFCI detects
leakage current to ground, it will interrupt power to the load
side of the device, preventing a hazardous ground fault condition.
GFCI receptacles must conform to UL Standard 943 Class A requirements,
and their use is required by the National Electric Code NFPA-70
in a variety of indoor and outdoor locations.
Grounded Neutral — The common neutral
conductor of an electrical system, which is intentionally connected
to ground to provide a current carrying path for the line to
neutral load devices.
Grounding Conductor — The conductor
that is used to establish a ground and that connects equipment,
a
device, a wiring system, or another conductor (usually the
neutral conductor) with the grounding electrode.
Hertz (Hz) — A unit of frequency equal
to one cycle per second.
Horsepower (HP) — The amount of energy
required to lift 33,000 lbs., one foot, in one minute. The
electrical equivalent of one horsepower is 745.6 watts.
Impedance — A characteristic of an electric
circuit that determines its hindrance to the flow of electricity.
The higher the impedance, the lower the current. The unit of
measure is the same as resistance (ohms).
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Inductance — The property of an electric
circuit that causes it to store energy in the form of a magnetic
field and because of which a varying current in a circuit induces
an electromotive force (voltage) in that circuit or a neighboring
circuit.
Kilowatt (kW) — A unit of measure of
electrical power, equal to 1000 watts. Used where larger units
of electrical
power are measured.
Kilovolt-Amperes (kVA) — A rating of
apparent power before being used, such as the rating of a transformer.
Load Bank
- a device that consumes electricity in a controlled manner. It
is used to make a generator set work to produce the power it is
rated for. It does this by running the electricity through resistors
and converting it into heat. The heat is blown off the resistors
by fans.
Load Sharing -
the ability for all generators in a parallel system to share equally
the total load on the system. As the load on the system increases
or decreases, all generators share a proportional part of the load.
Manual Transfer Switch — A switch designed
to disconnect the load from one power source and reconnect
it to another source, while at no time allowing both sources
to
be connected to the load simultaneously.
Megohm — A unit of resistance equal
to one million ohms.
NEC — The National Electrical Code,
which is the standard of the National Board of Fire Underwriters
for
electric wiring and apparatus, as recommended by the National
Fire Protection Association.
NEMA — National Electrical Manufacturers
Association, a non-profit trade association supported by the
manufacturers of electrical apparatus and supplies. NEMA promulgates
standards to facilitate understanding between manufacturers
and users of electrical products.
Neutral — The point common to all phases
of a polyphase circuit, conductor to that point, or return
conductor in a single phase circuit. The neutral in most systems
is grounded
at or near point of service entrance only and becomes the grounded
neutral.
Ohm — Unit of electrical resistance.
One volt will cause a current of one ampere to flow through
a resistance of one ohm.
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Ohm’s Law — The
rate of the flow of the current is equal to the electromotive force
divided by the resistance. The three basic Ohm’s law formulas
are:
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Amperes = Volts ÷ Ohms
Ohms = Volts ÷ Amperes
Volts = Amperes x Ohms |
Overload Protection — The
effect of a device operative on excessive current, but not necessarily
on short circuit, to cause and maintain the interruption of current
flow to the device being governed.
Parallel Circuit — An electrical circuit that
has more than one path though which electrons may flow.
Paralleling
- the process of connecting two or more generators together electrically.
Paralleling is for several reasons; to increase the capacity
of an exiting system, or if the size and weight do not allow the
use of one large unit or to allow non-interruption of the supply
when serving is required.
Peak Shaving
- the process of reducing the power demand on a power system.
Pin and
Sleeve — A receptacle with cylindrical
sleeve-type contacts.
Power
Factor (PF) — The
ratio of true power to volt-amperes in an alternating current
circuit. Power factor is expressed in a percent of unity either
lagging for inductive loads or leading for capacitive loads.
Resistive loads produce a unity power factor.
Reactance — The
component of impedance that does not dissipate energy. Inductive
reactance stores magnetic energy and hinders the flow of alternating
current. Capacitive reactance stores electric energy.
Relay — An
electric device that is designed to interpret input conditions
in a prescribed manner and, after specified conditions are met,
to respond and cause contact operation or similar abrupt changes
in associated electric control circuits.
Resistance (R) — The
non-reactive opposition that a device or material offers to the
flow of direct or alternating current. Usually measured in ohms.
The larger the resistance the lower the current for a given source
(driving) voltage.
Resistive Load Bank — A
device that provides temporary electrical loads for field testing
power sources such as generators and uninterruptible power supplies.
Series Circuit — Electrical
circuit with only one path though which electrons may flow.
Single-Phase Circuit — A
circuit that differs in phase by 180°. Single-phase circuits
have two conductors, one of which may be a neutral or three conductors,
and one of which is neutral.
Stand-by Power — See
Emergency Power.
Star Connection — A
three-phase connection, so called because, schematically, the joint
of the “Y” points looks like a star (same as a “Y” or “Wye” connection).
Starting Amps — The
maximum current drawn by a motor during the starting period.
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Step-Down Transformer — A
transformer that provides one or more electrical outlets at reduced
voltage and current from the main power source.
Surge Arrestor — A
protective device for limiting surge voltages on equipment by discharging
or bypassing surge current; it prevents continued flow of follow
current to ground, and is capable of repeating these functions
as specified.
Switch — A
device for making, breaking, or changing connections in a circuit.
Terminal Block — An
insulating base equipped with terminals for connecting wires.
Three-Phase Circuit — A
combination of circuits energized by alternating electromotive
sources that differ in phase by one third of a cycle, that is,
120°. A three-phase circuit may be three wire or four wire
with the fourth wire being connected to the neutral point of the
circuit that may be grounded.
Transfer Switch
- used to monitor incoming system voltage and frequency. Any
interruption in the voltage or frequency will cause the connection
to the incoming system and load to be disconnected. This happens
when a set of auxiliary contacts are made which will start up an
emergency power generator. When the generator voltage and
frequency are present, the connection to the load and generator
is made. The reverse occurs when the incoming system returns
to normal.
Transformer — A
static electric device consisting of a single winding, or two or
more coupled windings, used to transfer power by electromagnetic
induction between circuits at the same frequency, usually with
changed values of voltage and current.
Underwriters Laboratories (UL) — An
independent, non-profit U.S. organization that tests products for
safety.
Volt — A
unit of measure of electric potential and electromotive force,
equal to the difference of electric potential between 2 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 difference in electric potential, expressed in volts.
Watt — A
unit of measure of electrical power, equal to the power used when
one volt causes one ampere to flow in a circuit.
Wye Connection — See
Star Connection.
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