July 3, 2011

Electrical Engineering Terms - O

  • OA - Oil-Air, a cooling classification for transformers now classified as ONAN. Oil type, Natural convection flow through cooling equipment and in windings, & Air external cooling medium.
  • Occasional Traffic - Refers to a grade level Reinforced Polymer Concrete or Fiberglass Reinforced Plastic Box or Cover load rating of 20,800lbs. This rating is derived from double wheel loading of 16,000 lbs with an impact factor of 30% added (16000 x x1.30).
  • Off Peak Power - Power supplied during designated periods of low power system demand.
  • Off-Load Tap Changer - A tap changer that is not designed for operation while the transformer is supplying load.
  • OHL - Overhead Line
  • Ohm - A unit of electrical resistance defined as the resistance of a circuit with a voltage of one volt and a current flow of one ampere.
  • Ohm's Law - E=IR; I=E/R; R=E/I; Where E = Voltage impressed on a circuit, I = current flowing in a circuit and R = circuit resistance. Ohm's Law is used for calculating voltage drop, fault current and other characteristics of an electrical circuit.
  • Oil Breakers - A type of high voltage circuit breaker using mineral oil as both an insulator and an interrupting medium. Typically, these units were produced for use at voltages from 35 kV to as much as 345 kV. Generally, these are older types and no longer produced for
  • OLTC - See "On Load Tap Changer"
  • Omni directional Antenna - This is like a dipole antenna because it radiates its signal 360 degrees horizontally; however, its signal is flatter than a dipole's allowing for higher gain.
  • On Load Tap Changer - A tap changer that can be operated while the transformer is supplying load.
  • One-Axis Tracking (Photovoltaic) - A system capable of rotating about one axis for tracking of the sun.
  • Open Link - A fuse used on overhead electrical distribution systems that is held in place by two springs. This device and its holder have generally been replaced by Fused Cutouts where the fuse element in an arc tube.
  • Open-Circuit Voltage (Battery) - The voltage of a cell or battery when it is not delivering or receiving power.
  • Opening Time - For a CB the time between energizing of the trip coil and the instant of contact parting. With a relay the operating time is defined as the time which elapses between the application of a characteristic quantity and the instant when the relay operates.
  • Operating Current - The current used by a lamp and ballast combination during normal operation.
  • Operating Current (of a relay) - The current at which a relay will pick up.
  • Operating time Characteristic - The curve depicting the relationship between different values of the characteristic quantity applied to a relay and the corresponding values of operating time.
  • Operating Value - The limiting value of the characteristic quantity at which the relay actually operates.
  • OPGW - Optical Ground Wire - a ground wire that includes optical fibers to provide a communications link.
  • Oscillograph - An instrument for measuring alternating electric current or voltage by capturing the wave form. Electric Utilities use a variant called a Prefault Recorder, where the wave forms are stored for a short time on an ongoing basis and saved if the system sees
  • OSHA - Occupational Safety and Health Administration. Government agency which seeks to assure the safety and health of America's workers by setting and enforcing standards; providing training, outreach, and education; establishing partnerships; and encouraging c
  • OSHA 29 CFR 1910, Subpart S-Electrical - Occupational Safety and Health Standards. Section 1910 Subpart S-Electrical Standard number 1910.333 specifically addresses Standards for Work Practices.
  • OSI 7-layer model - The Open System Interconnection 7-layer model is a model developed by ISO for modeling of a communications network.
  • Outage - The state of a component or part of a power system that is not available for service because of some event associated with the component of power system. These are the longer term events (several seconds to hours) caused by external factors such as trees
  • Outage, Forced - 1. An outage that results from conditions directly associated with a power system component requiring that it be taken out of service either automatically or after switching operations can be performed. 2. An outage by improper operation of equipment or
  • Outage, Scheduled - An outage that results from intentionally taking a power system out of service, normally for maintenance or replacement.
  • Output common mode interface voltage - An unwanted alternating voltage which exists between each of the output terminals and a reference point.
  • Output Current of a transducer - The current produced by the transducer which is an analog function of the measurand.
  • Output Load - The total effective resistance of the circuits and apparatus connected externally across the output terminals.
  • Output series mode interface voltage - An unwanted alternating voltage appearing in series between the output terminals and the load.
  • Output Span - The algebraic difference between the lower and upper nominal values of the output signal.
  • Over current Relay - A protection relay whose tripping decision is related to the degree by which the measured current exceeds a set value.
  • Over range - The specified maximum operating point for which the stated accuracy condition applies.
  • Overcharge (battery) - The forcing of current through a cell after all the active material has been converted to the charged state (after 100% charged). The result will be the decomposition of water in the electrolyte into hydrogen and oxygen gas
  • Overload - The specified maximum magnitude of the input quantity that can be applied for a specified period of time without causing damage.
  • Overshoot Time - The overshoot time is the difference between the operating time of the relay at a specified value of the input energizing quantity and the maximum duration of the value of input energizing quantity which, when suddenly reduced to a specific value below th
  • Oxygen Recombination - The process by which oxygen generated at the positive plate during charge reacts with the pure lead material of the negative plate and in the presence of sulfuric acid and reforms water.



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