Electric Glossary

Next >

*Sources:
Edison Electric Institute
US Energy Information Administration
Vectren Energy Delivery of Indiana, Inc. (Vectren South) Tariff for Electric Service

Measurements

Ampere – A unit of measurement of electric current or rate of flow of electricity in a circuit.

Volt – A unit of measurement of electric potential and electromotive force, defined as “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”.

Watt – A unit of measurement of electric power, represented by a current of one ampere under the pressure of one volt in a circuit of unity power factor.  (see also Volt-Ampere).

Kilowatt (kW) – One thousand watts.

Megawatt (MW) – One million watts.

Gigawatt (GW) – One billion watts.

Volt-Ampere (VA) -- A unit used to measure apparent electric power, as opposed true power, which is generally measured with watts.  In a circuit with only resistive load, a volt-ampere and a watt are equivalent.

Kilovolt-Ampere (kVA) – One thousand volt-amperes.  The capacity of electric utility distribution circuits and transformers are typically denominated in kVA.

Watt-hour (Wh) – A unit of measurement of electrical energy equal to one watt of power supplied to, or taken from, an electric circuit steadily for one hour.

Kilowatt-hour (kWh) – One thousand watt-hours. 

Megawatt-hour (MWh) – One million watt-hours.

Technical Terms Related to Generation and Delivery of Power

Apparent Power - The combination of reactive power and true power, the product of a circuit's voltage and current, measured in kVA.  Apparent power is important because the current associated with reactive power heats wires, even though it does not work. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work.  (see also Kilovolt-Ampere)

Alternate Feed – A second or redundant electric feed possibly from a separate distribution substation transformer and feeder circuit with automatic or manual switch over and recovery between the basic and alternate feeds.

Distribution System – The portion of an electric system that is dedicated to delivering electric energy to an end user.

Service Voltages

• Primary Voltage – The voltage of the circuit supplying power to a transformer is called the primary voltage, as opposed to the output voltage or load-supply voltage, which is called secondary voltage.  In power supply practice the primary is almost always the high-voltage side and the secondary the low-voltage side of a transformer, except at generating stations. 
• Secondary Voltage – The output voltage or load-supply voltage of a transformer or substation.  In power supply practice secondary voltage is generally the low-voltage side of a transformer, except at generating stations.

Single Phase – A circuit energized by a single, alternating electromotive force.

Three Phase – A combination of three circuits energized by alternating electromotive forces that differ in phase by 120 degrees.

Transformer – An electrical device for changing the voltage of alternating current.

Transmission – The movement or transfer of electric energy over an interconnected group of lines and associated equipment between points of supply and points at which it is transformed for delivery to consumers, or is delivered to other electric systems. Transmission is considered to end when the energy is transformed for distribution to the consumer.

Transmission System – An interconnected group of electric transmission lines and associated equipment for moving or transferring electric energy in bulk between points of supply and points at which it is transformed for delivery over the distribution system lines to consumers.

Next >