July 3, 2011

Electrical Engineering Terms - S

  • S.I.R. - System Impedance Ratio
  • Sag - The amount of vertical displacement of an overhead conductor between support points. Sag is a consideration when designing a pole or tower line and will be a determining consideration in the overall height of the structure. Sag varies with the temperature.
  • SAIDA - A distribution system reliability measure of the system average interruption duration index. It is commonly measured in customer minutes of interruption and is commonly used as an electric service performance metric.
  • SAIFI - A distribution system reliability measure of the system average interruption frequency index. It measures sustained outages and interruptions and is a metric for the entire power system.
  • SAT - Site Acceptance Test. Validation procedures for equipment executed with the customer on site.
  • SCADA - Supervisory Control and Data Acquisition.
  • Scaling Resistor - A resistor added to an output circuit of measurement equipment to provide a scaled voltage output. The output is not a "true" voltage output and may be susceptible to loading errors.
  • Schematic Diagram - A diagram which shows, by means of graphic symbols, the electrical connections and functions of a circuit.
  • SCP - Substation Control Point. HMI computers at substation level allowing the operators to control the substation.
  • SCS - Substation Control System.
  • Sealed Cell (Battery) - Cells that are free from routine maintenance and can be operated without regard to position.
  • Self Discharge (Battery) - The decrease in the state of charge of a battery or cell, over a period of time, due to internal electro-chemical losses.
  • Semi-Con - The semi-conducting material extruded over the insulation on medium voltage insulated cables.
  • Semi-Crystalline - See "Multi-Crystalline".
  • Semi-cutoff (Lighting) - Luminaire light distribution is classified as semi-cutoff when the candlepower per 1000 lamp lumens does not numerically exceed 50 (5.0%) at an angle of 90 degrees above nadir (horizontal), and 200 (20%) at a vertical angle of 80 degrees above nadir. Thi
  • Separator (Battery) - A porous, insulating material placed between plates of opposed polarities, to prevent internal short circuits.
  • SER - Service Entrance Cable.
  • Series Connection - For DC circuits, a way of joining batteries, electrical devices and wires in such a way that positive leads are connected to negative leads. This is generally done to increase voltage.
  • Server - A computer that provides the information, files, web pages, and other services to the client that logs on to it.
  • Service Drop - An overhead service conductor runs from a utility company pole to the point of connection to the building's service entrance conductors.
  • Service Entrance Cable - The conductors that connect the service conductors (drop or lateral) to the service equipment of the building.
  • Service Life (Battery) - The total period of useful life of a battery, normally expressed in the total number of Charge/Discharge cycles.
  • Setting - The limiting value of a 'characteristic' or 'energizing' quantity at which the relay is designed to operate under specified conditions. Such values are usually marked on the relay and may be expressed as direct values, percentages of rated values, or mult
  • SEU - Service entrance cable.
  • SFC - Sequential Function Chart. One of the IEC 61131-3 programming languages.
  • Shock Hazard - A dangerous electrical condition associated with the possible release of energy caused by contact or approach to energized parts.
  • Short Circuit - 1. A load that occurs when at ungrounded conductor comes into contact with another conductor or grounded object. 2. An abnorman connection of relatively low impedance, whether made intentionally or by accident, between two points of different potential.
  • Short Distribution (Lighting) - A luminary is classified as having a short light distribution when its max candlepower point falls between 1.0MH - 2.25MH TRL. The maximum luminaire spacing-to-mounting height ratio is generally 4.5 or less.
  • Shotgun Stick - A specialized hot stick that allows the capture of certain types of clamps and devices in its hook. It is also called a "Grip All" stick.
  • SI - See "International System of Units".
  • Sidewalk (lighting) - Paved or otherwise improved areas for pedestrian use, located within public street rights-of-way also containing roadways for vehicular traffic.
  • Sidewall Pressure - The force exerted on a cable as it is dragged around a bend. The longer the pull and the tighter the bend radius, the higher the sidewall pressure will become. High sidewall pressure damages cable. There is a higher chance of destroying cable by high s
  • Silicon - A chemical element (Si), atomic number 14, semi-metallic in nature, dark gray, that is an excellent semiconducting material and is the most common semiconducting material used in making photovoltaic devices.
  • Simplex Communications System - A communications system in which data can only travel in one direction.
  • Single Element Transducer - A transducer having one measuring element.
  • Single Phase - Single Phase electric power refers to the distribution of electric power using a system in which the voltage is taken from one Phase of a three Phase source. Single Phase distribution is used when loads are mostly lighting and heating, with few large ele
  • Single-Phase - This implies a power supply or a load that uses only two wires for power. Some "grounded" single phase devices also have a third wire used only for a safety ground, but not connected to the electrical supply or load in any other way except for safety grou
  • Single-Shot Reclosing - An auto-reclose sequence that provides only one reclosing operation, lock-out of the CB occurring if it subsequently trips.
  • Sintered Plate (Battery) - The plate of an alkaline cell, the support of which is made of sintered metal powder, and into which the active material is introduced.
  • Skin Effect - In an ac system, the tendency of the outer portion of a conductor to carry more of the current as the frequency of the ac increases.
  • Sky Wire - See "Static Wire"
  • Sleeve - See "Compression Splice".
  • Soap - Slang for "Cable Pulling Lubricant".
  • SOE - Sequence of Events
  • Solar Cell - See "Photovoltaic Cell".
  • Solar Energy - Energy from the sun. The heat that builds up on surfaces exposed to the sun is an example.
  • SOTF - Switch on to Fault (protection).
  • Spacing-to-Mounting Height Ratio - Ratio specification used to insure that fixtures are adequately spaded, thus preventing "hotspots"
  • Span - 1) Refers to the distance between two poles of a transmission or distribution line. 2) The algebraic difference between the upper and lower values of a range.
  • Spark Test - A high-voltage test performed on certain types of conductor during manufacture to ensure the insulation is free from defects.
  • Specific Conjuctive Test - A conjunctive test using specific values of each of the parameters.
  • Specific-Gravity (Battery) - The weight of the electrolyte compared to the weight of an equal volume of pure water. It is used to measure the strength or percentage of sulfuric acid in the electrolyte.
  • Spill Light - Unwanted light directed onto a neighboring property. Also referred to Light Trespass.
  • Split Phase - A split phase electric distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. It is the AC equivalent of the former Edison dir
  • Spread Spectrum - A wireless communications technology that scatters data transmissions across the available frequency band in pseudorandom pattern. Spreading the data across the frequency spectrum greatly increases the bandwidth which in turn can reduce noise and provide
  • Spring Winding Time - For spring-closed CB's, the time for the spring to be fully charged after a closing operation.
  • ST - Structured Text, one of the IEC 61131-3 programming languages.
  • Stability - The ability of a device to maintain its performance characteristics over a specified period of time.
  • Stability Limits of a Protection System - The r.m.s. value of the symmetrical component of the through fault current up to which the protection system remains stable.
  • Stability of a Protection System - The quantity whereby a protection system remains inoperative under all conditions other than those for which it is specifically designed to operate.
  • Stability of Transducer - The ability of a transducer to keep its performance characteristics unchanged during a specified time, all conditions remaining constant.
  • Stage 3 Emergency - In the state of California, if power reserves ever fall below 1.5 percent, Cal-ISO, the independent system operator in California, will declare a Stage 3 emergency and the state's investor-owned utilities, may be ordered to immediately reduce the demand f
  • Standard calibration - The nominal point at which a measurement device is adjusted.
  • Starter - A device used in conjunction with a ballast for the purpose of starting an electric discharge lamp.
  • Starting Current - Current required by the ballast during initial arc tube ignition. Current changes as lamp reaches normal operating light level.
  • Starting Relay - A unit relay which responds to abnormal conditions and initiates the operation of other elements of the protection system.
  • Starved Cell (Battery) - A cell containing little or no free fluid electrolyte solution. This enables gasses to reach electrode surfaces readily, and permits relative high rates of recombination.
  • STATCOM - A particular type of Static Var Compensator, in which Power Electronic Devices such as GTO's are used to generate the reactive power required, rather than capacitors and inductors.
  • State of Charge (Battery) - The available amp-hours in a battery at any point of time. State of Charge is determined by the amount of sulfuric acid remaining in the electrolyte at the time of testing or by the stabilized open circuit voltage.
  • Static IP address - See IP address.
  • Static Relay - An electrical relay in which the designed response is developed by electronic, magnetic, optical or other components without mechanical motion. Excludes relays using digital technology.
  • Static Var Compensator - A device that supplies or consumes reactive power comprised solely of static equipment. It is shunt-connected on transmission lines to provide reactive power compensation.
  • Static Wire - A wire placed above the phase wires of a distribution of transmission circuit to protect against lightning. It is normally galvanized or aluminized steel.
  • STC - Short Time Current rating of a CT.
  • Stick - See Hotstick.
  • Stinger - Slang for the wire connecting a fused cutout or switch to a transformer bushing.
  • Storage Conditions - The conditions defined by means of ranges of the influence quantities, such as temperature, or any special conditions, within which the transducer may be stored (non-operating) without damage.
  • Strand - One of the wires that made up a stranded conductor.
  • Stranded Conductor - A conductor made by twisting together a group of wire strands.
  • Stranded Cost - Assets owned by an investor owned electric utility, normally costs associated with generation-related assets and state-mandated contracts with nonutility generators that may now be uneconomic and unrecoverable in the restructured electric utility industry
  • Stringing - The act of installing overhead electrical wire or conductor.
  • Stringing Block - A sheave used to support and allow movement of a cable that is being installed. These are normally used overhead but there are also specialized designs used at the entrance to a conduit system. Stringing blocks are manufactured by Bethea.
  • Stringing Dolly - See "Stringing Block".
  • Sub-Transmission System - A high voltage system that takes power from the highest voltage transmission system, reduces it to a lower voltage for more convenient transmission to nearby load centers, delivering power to distribution substations or the largest industrial plants. Typi
  • Substation Configuration Language - Normalized configuration language for substation modeling as expected by IEC 61850-6.
  • Sulfation (Battery) - The formation of lead sulfate of such physical properties that it is extremely difficult, if not impossible, to reconvert it to active material.
  • Sulfur-Hexafluoride (SF6) - A very dense, inert, non-conducting gas used inside high voltage equipment to insulate conducting components from surfaces at ground potential. It also is used as an interrupting medium in high voltage circuit breakers.
  • Super Draw Lead - Also known as a split conductor. Historically bushings offered a draw lead rating of 400 amps, but by using Trench's split conductor in COTA bushings the draw leads now have ratings of 3,000 amps.
  • Surge Arrester - See Arrester.
  • Surge Withstand - A measure of an electrical device's ability to withstand high-voltage or high-frequency transients of short duration without damage.
  • Surge Withstand Capability (swc) Test - The SWC test wave is an oscillatory wave, frequency range of 1-1.5 MHz, voltage range of 2.5-3 kV crest value of first peak, envelope decaying to 50% of the crest value of the first peak in not less than 6 micro seconds from the start of the wave. The sou
  • Sweeling (Battery) - The swelling or bulging of a battery case that results from cell vents not allowing enough internal pressure to be relieved.
  • Switch, Network - A Switch connects Client systems and servers together to create a network. It selects the path that the data packet will take to its destination by opening and closing an electrical circuit.
  • Switchgear - A general term covering switching and interrupting devices and their combination with associated control, metering, protective and regulating devices. Also, the assemblies of these devices with associated interconnection, accessories, enclosures and supp
  • Switching Impulses - See "Lightning and Switching Impulses".
  • Switching Surges - A high voltage spike that occurs when current flowing in a highly inductive circuit, or a long transmission line, is suddenly interrupted.
  • System Disturbance Time - The time between fault inception and CB contacts making on successful re-closure.
  • System Impedance Ratio - The ratio of the power system source impedance to the impedance of the protected zone.



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