Glossary of Electric Utility Industry Terms
OA – A transformer-cooling designation referring to Oil-to- Air heat transfer in which the transformers tank, with or without radiators, is the main way the transformer cools itself. (See FA and FOA) The OA, FA, FOA designations have been changed. See ONAN for the new designations. (EUSO, EDS, CAEDS, IESO)
OASIS – See Open Access Same-Time Information System
Ohm – A quantity that impedes the flow of current. An Ohm is defined as follows. When 1 volt is present in a circuit and 1 Ampere flows, the circuit has 1 Ohm. Ohm is named after George Ohm (1789 – 1854) who showed that the amount of current flowing through a conductor was directly proportional to the applied voltage. It is represented by the Greek letter Omega ( Ω ).
ONAN – The current transformer-cooling designation as detailed in IEEE Standard C57.12.00-2000. (See OA, FA and FOA for the old designation.)The first letter refers to the type of insulating liquid. The letter O refers to insulating liquids with a flash point of 300° C or less. The letter K refers to insulating liquids with a flash point greater than 300° C. The letter L refers to insulating liquids with no measurable flash points.
The second letter refers to how the cooling liquid is circulated internally in the transformer. N is for Natural convection. F is for Forced cooling using pumps, with the cooling liquid using convection to flow through the windings. D is for forced cooling using pumps, with the cooling liquid being Directed from pumps into the windings.
The third letter refers to the external cooling method. A is for Air cooling and W is for Water cooling.
The fourth letter refers to the method of circulation for external cooling. N is for Natural convection. F is for Forced circulation which would be fans for air external cooling, or pumps for water external cooling.
OA/FA/FOA, under the old designation, would be ONAN/ONAF/OFAF under the new designation. (EUSO, EDS, CAEDS, IESO)
Open – A physical separation in a conductor. It is a shortened term for “open circuit.”
Open Access Same-Time Information System– An internet-based system that provides transmission access to customers in North America by providing availability, capacity and prices. It is the primary method used for reserving transmission services. It provides equal access to all potential users of the transmission systems. (EUSO, System operator classes)
Open Bay – A term used to describe a substation design in which the circuit breakers are not enclosed in any type of building.
Open Circuit – A physical separation in a conductor.
Open Delta – A transformer connection that allows 3-phase service from 2 primary phases and a neutral, and which uses two single-phase transformers. (EUSO, CAEDS, EDS, IESO)
Open Leg – A physical separation in a phase conductor in a 3-phase system, or in the non-neutral conductor in a single-phase system. (CAEDS, EDS, IESO)
Open Neutral - A physical separation in a neutral conductor. (A neutral conductor is a current-carrying wire or cable that has zero voltage between it and ground.) An open neutral in a secondary service can cause high voltages in part of a customer’s facility, and at the same time low voltages are appearing in other parts of the facility. (CAEDS, EDS, IESO)
Open Wire Secondary – Three conductors with 120/240 volts that run pole to pole below the primary conductors (primary conductors are on top of the pole in an overhead distribution system). It is called “open wire” because the three wires are clearly visible as opposed to a design in which the three conductors are bundled together.
Operator – A person responsible for the minute by minute functioning of a specific part of an electric utility system. (See the various types listed immediately below) (EUSO)
Operator, Substation – A person responsible for the minute by minute functioning of an enclosed area (most often enclosed by chain-link fence) of an electric utility system in which voltages are changed. These enclosed areas are called substations. Substation operators work at the substations, as opposed to remotely working from a computer screen. (EUSO)
Operator, System – A person responsible for the minute by minute functioning of a transmission and/or distribution system, including the substations. System operators monitor and control the system(s) remotely using a computer system.
Operator, Control Room – A person at a generating plant responsible for the minute by minute functioning of one or more generators, along with the generators’ prime mover. In some plants, these operators are called generator operators. Using computer systems, control room operators monitor and control the equipment from a room in the generating plant.
Operator, Generator - A person at a power-production plant (generating plant) responsible for controlling minute by minute production of the power. In some plants, these operators are called control-room operators. Using computer systems, generator operators monitor and control the equipment from a room in the generating plant.
Operator, Plant - A person at a generating plant (power production plant) responsible for the minute by minute functioning of the systems other than the generator and prime mover. These systems include the coal other fuel handling systems, boiler-water handling systems and condenser-water systems.
Overhead Ground Wire - Steel cable(s) installed above the phase conductors in a distribution or transmission line. The steel cable is grounded. The purpose of the steel cable is to protect the phases from lightning strikes. Lightning will usually strike the steel cable and be diverted into the earth. Overhead ground wires are also called static wire, shield wire, sky wire (in Canada) and ridge wire (in parts of Alabama). (EUSO)
Overload – An amount of current flow that exceeds that for which the circuit, component or system was designed. (EUSO, IESO, System operator classes)