Power Generation Basics and Glossary of Terms
Calculate the power usage of electrical generators using common electrical formulas for sizing and unit conversion. Learn how to convert KW to KVA, single-phase to 3-phase load, and more.
Alternating Current (AC) — a current which reverses in regularly recurring intervals of time, has alternative positive and negative values and occurs 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.
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. 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 capable of making, carrying for a specific time and automatically breaking currents under specified abnormal circuit conditions, such as a 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 that is operated by an electric coil and 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 equipment.
Efficiency Factor (EFF) — the ratio of output power to input power in an electric motor.
Electric Utilities — all enterprises engaged in the production and/or distribution of electricity for use by the public.
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 (Standby) Power — an independent reserve source of electric power, upon failure or outage of the normal power source, provides stand-by electric power.
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.
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 or 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 unit of measure is the same as resistance (ohms).
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 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.
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 the manufacturers and users of electrical products.
Neutral — the point common to all phases of a polyphase circuit, a conductor to that point, or the return conductor in a single phase circuit. The neutral in most systems is grounded at or near the 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.
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:
Amperes = Volts ÷ Ohms
Ohms = Volts ÷ Amperes
Volts = Amperes × Ohms
Overload Protection — the effect of a device operated 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.
Power Factor (PF) — the ratio of the true power to the 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.
Reactance—the component of impedance that does not dissipate energy. Inductive reactance stores magnetic energy and hinders the flow of alternating current.
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 — an 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, one of which is neutral.
Standby 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.
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 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.
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 two points on a conducting wire carrying a constant current of one ampere when the power dissipated between the points is one watt.
Voltage — electromotive force, or 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.