July 3, 2011

Electrical Engineering Terms - R

  • Raceway - An enclosed channel designed expressly for holding conductors and cables, including conduit and tubing, wire ways, and bus ways.
  • RAM - Random Access Memory. When an application is run it is called from the permanent storage area such as hard drive, floppy disk, or CD-ROM, and moved into the RAM where, it sends requests to the CPU. Using faster memory can speed up information process time
  • Range - Nominal operating limits, specified by the lowest calibration point to the highest calibration point.
  • Rated Capacity (Battery) - The number of Amp-Hours a battery can deliver under specific conditions (rate of discharge, end voltage, temperature).
  • Rated Lamp Life - With regard to lighting, the point in time when 50% of a statistically significant number of lamps has failed.
  • Rated Output - The output at standard calibration.
  • Rating - The nominal value of an energizing quantity that appears in the designation of a relay. The nominal value usually corresponding to the CT and VT secondary ratings.
  • Ratio Correction - A feature of digital relays that enables compensation to be carried out for a CT or VT ratio that is not ideal.
  • RCD - Residual Current Device. A protection device which is actuated by the residual current.
  • Reactance - The opposition of inductance and capacitance to alternating current equal to the product of the sine of the angular phase difference between the current and voltage.
  • Reactive Power - A component of apparent power (volt-amps) which does not produce any real power (watts). It is measured in VARs volt-amps reactive.
  • Reading - The expected output at a given input value.
  • Real Power - The average value of the instantaneous product of volts and amps over a fixed period of time in an AC circuit.
  • Recloser - A switching device that rapidly recloses a power switch after it has been opened by an overload. In reclosing the power feed to the line, the device tests the circuit to determine if the problem is still there. If not, power is not unnecessarily interrupt
  • Recombination (Battery) - State in which the hydrogen and oxygen gasses normally formed within the battery cell during charging are recombined to form water.
  • Reel - A cylinder device used to hold wire and cable until installed. There are standard reel sizes that are used in the electrical industry that are either wood (non-returnable) or steel (returnable).
  • Reference range - A specific range of values of an influence quantity within which the transducer complies with the requirements concerning intrinsic errors.
  • Reference value - A specified single value of an influence quantity at which the transducer complies with the requirements concerning intrinsic errors.
  • Refererence Conditions - Conditions of use for a transducer prescribed for performance testing, or to ensure valid comparison of results of measurement.
  • Reflector - A device used to re-direct the luminous flux from a light source by the process of reflection.
  • Refractor - A device used to re-direct the luminous flux from a light source by the process of refraction.
  • Regulating Transformer - A transformer used to vary the voltage, or phase angle, of an output circuit. It controls the output within specified limits and compensates for fluctuations of load and input voltage.
  • Regulation - See "Voltage Regulation".
  • Regulator - A device that is used to control the voltage of a circuit by raising and lowering it. Howard Industries is a manufacturer of Regulators.
  • Reinforced Polymer Motor - Also referred to as "RPM". See "Polymer Concrete".
  • Relay - Numerical - A protection relay which utilizes a digital signal processor to execute the protection algorithms in software.
  • Relays - Distance - Relays used on transmission lines that use a variety of sensors and measurements to determine when an unusual condition exists at some distance, out on the transmission circuit.
  • Relays - Over-current - Protective relays used on power systems that detect excessive currents and send signals to protective devices, such as power circuit breakers.
  • Relays - Voltage - Protective relays used on power systems that detect when line voltage has gone outside of an acceptable range, either up or down, and send a signal to a protective device or system.
  • Remote Control Point - The remote control point is a SCADA interface. Several RCP's may be managed with connections are done at a gateway or at substation computers.
  • Resealable Cap (Battery) - A safety vent valve which is capable of closing after each pressure release from within a cell.
  • Resetting value - The limiting value of the characteristic quantity at which the relay returns to its initial position.
  • Residential (Lighting) - A residential development, or a mixture of residential and small commercial establishments, characterized by few pedestrians during nighttime hours. This definition includes area with single-family homes, townhouses, and/or small apartment buildings.
  • Residual Current - The algebraic sum, in a multi-phase system, of all the line currents.
  • Residual Voltage - The algebraic sum, in a multi-phase system, of all the line-to-earth voltages.
  • Resistance - The opposition to current flow, expressed in ohms.
  • Response Time - The time for a measurement device's output signal to reach 99% of its final value after a step change in the applied input.
  • Restricted Approach Boundary - An approach limit at a distance form an exposed live part within which there is an increased risk of shock, due to electrical arc over combined with inadvertent movement, for personnel working in close proximity to the live part.
  • Reversible Output Current - An output current which reverses polarity in response to a change of sign or direction of the measurand.
  • RHH - A rubber or XLPE insulated conductor designed to be used at operating temperatures up to 90 degrees Celsius in dry locations.
  • RHH-2 - A rubber or XLPE insulated, moisture resistant conductor designed to be used at operating temperatures up to 90 degrees Celsius in dry and wet locations.
  • Ridge Pin - A device that allows the mounting of a pin type insulator to a pole. The ridge pin is bolted to the top of the pole and the insulator is screwed onto the threads at its top.
  • Ripple - The magnitude of AC fluctuation in a DC signal, after filtering. Ripple is usually expressed as a percentage of rated output.
  • Ripple Content of the Output - With steady-state input conditions, the peak-to-peak value of the fluctuating component of the output.
  • Riser Pole - A pole used to transition from overhead and underground cables.
  • RJ-11 - Registered Jack 11. Standard telephone connector which has a tab that snaps into the socket and must be pressed to be removed from telephone or socket. Usually houses two wires but is capable of housing up to four.
  • RJ-45 - Registered Jack 45. Connectors used to connect computers to LANs or phones with many lines. It is able to house up 8 wires that is twice as many wires as the RJ-11.
  • RMS - See "Root-Mean-Square".
  • RMU - Ring Main Unit.
  • ROCOF - Rate of Change of Frequency.
  • Root-Mean-Square - The effective value of alternating current or voltage. The RMS value equates an AC current or voltage to a DC current or voltage that provides the same power transfer.
  • Router - Device utilized to route data from one local-area network to another or to a phone line's long-distance line.
  • RPM - Reinforced Polymer Mortar. See "Polymer Concrete".
  • RTO - Regional Transmission Organization.
  • RTS - Request to Send. An RTS is a message sent by a networked device to its access point, seeking permission to send a data packet.
  • RTU - Remote Terminal Unit. An IED used specifically for interfacing between a computer and other devices. Sometimes may include control, monitoring, or storage functions.
  • RW (Lighting) - Roadway Width



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