GERALD AKSHERIAN

ILLUSTRATED DICTIONARY OF ELECTRICAL POWER ENGINEERING

Generation, Transmission, Distribution

VOLUME II G - P

© Gerald Aksherian, author / publisher, New York 2016

Cover Design and Interior Design by the Author

Cover Photo by © Patrick Jennings

ISBN 978-0-692-68431-3

All rights reserved; no part of this publication maybe be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the author / publisher.

Federal Copyright Registration NumberTXu001968666

This volume contains the second portion of Illustrated Dictionary of Electrical Power Engineering, Generation, Transmission, Distribution, letters G through P.

486

G

MAIN ENTRIES, DERIVATIVE MAINS, List of Graphs, Charts, Tables and Biographies GALVANOMETER GAP GAS GAS INSULATED SUBSTATION

GENERAL RATING SEISMIC REQUIREMENTS SERVICE CONDITIONS SPECIFICATIONS TESTS

GENERATION GENERATOR

GENERAL DIRECT AXIS GROUNDING LOAD LOSSES START VOLTAGE

GENERATOR, ASYNCHRONOUS (INDUCTION) GENERATOR CLASSIFICATION

CLASSIFICATION BY APPLICATION /PERFORMANCE CLASSIFICATION BY ELECTRICAL TYPE CLASSIFICATION BY ENCLOSURES AND COOLING CLASSIFICATION BY SIZE

GENERATOR PROTECTION and DISTURBANCES GENERATOR RATINGS (Capabilities) and PERFORMANCE CHARAC-

TERISTICS GENERATOR SERVICE CONDITIONS GENERATOR, SYNCHRONOUS GENERAL

INSULATION SYSTEM PARAMETERS RATING TURBINE GENERATOR (steam) TURBINE GENERATOR (hydro)

GENERATOR TEST GENERAL INSPECTION / TESTS GENERATOR ASSEMBLY INSULATION TESTS ROTOR TEST, AC GENERATOR ROTOR TESTS, DC GENERATORS STATOR TESTS, AC GENERATORS TESTS, HYDRO-GENERATORS TESTS, SYNCHRONOUS GENERATORS (with cylindrical rotor)

GRADIENT GROUND / GROUNDED / GROUNDING (earth, earthed, earthing) GROUND-FAULT GUY

GRAPHICAL ILLUSTRATIONS

1 Figure FG-1 Hindu Kush Hydro Power Plant AC, Generator, in Turkmenistan. Built in 1909, capacity 1.35 MW

2 Figure FG-2 DC Generator Operating Principle

3 Figure FG-3 Typical engine-generator set

4 Figure FG-4 Reactive power capability curve for syn-chronous generator

5 Figure FG-5 Synchronous generator connection to the power grid

6 Figure FG-6 DC shunt generator equivalent circuit

7 Figure FG-7 Three-phase synchronous generator. equivalent circuit

8 Figure FG-8 Generator neutral grounding methods.

9 Figure FG-9 Grounding of generator with no neu-tral ground

10 Figure FG-10 Synchronous generator connection to the power grid

11 Figure FG-11 Electrolytic electrode

12 Figure FG-12 Plate grounding electrode

13 Graph GG-1 Gas insulated substations

14 Graph GG-2 Generators

TABULATION 1 TG-1 Generators’ Speed Ratings

2 TG-2 Temperature rise for synchronous generators.

3 TG-3 Voltage ratings, for 60 Hz three, and single-phase generators

4 TG-4 Voltage ratings, for 50 Hz three, and single-phase generators

BIOGRAPHIES 1 BG-1 GALILEO Ferraris, 1847 –1897

2 BG-2 GAUSS, Johann Carl Friedrich, 1777-1855

3 ------- GEORGE Green, 1793-1841

4 BG-3 GILBERT William, 1544-1603

5 BG-4 GRAMME, Zénobe Théophile, 1826 -1901

6 BG-5 GRAY, Stephen, 1666-1736

7 BG-6 GROVE, William Robert, 1811-1896

487

G

G The letter symbol for gauss, a unit of magnetic flux den-sity in cgs (centimeter-gram-second) electromagnetic sys-tem of units. It is equivalent to 10-4 tesla in unit of SI (Inter-national System). It was abandoned in 1948. [17/1-9]

Standard letter symbol for quantity of conductance in In-ternational System (SI) of units. The unit is siemens [17/1-14]

giga, a prefix of factor 109 to International System (SI) of decimals. It is one thousand million. [17/1-17]

Potential gradient, (volt per cm)

Gb The letter symbol for gilbert, a unit of magnetomotive force in cgs (centimeter-gram-second) electromagnetic sys-tem of units. It is equivalent of 0.796 ampere. It was aban-doned in 1948. [17/1-9]

Gv Potential gradient at which corona begins to appear.

GALILEO Ferraris (October 30, 1847 – February 7, 1897) An Italian physicist and electrical engi-neer, noted mostly for his studies of al-ternating current and independent dis-covery of the rotating magnetic field, a basic working principle of the induc-tion motor. Ferraris gained a bachelor's degree in engineering and became an assistant of technical physics near the Regal Italian

Industrial Museum. Ferraris inde-pendently researched the rotary magnetic field in 1885. Ferraris experimented with types of asyn-

chronous electric motors. The research resulted in the devel-opment of an alternating-current motor. In 1888, Ferraris

published his research in a paper to the Royal Academy of Sciences in Turin (Nikola Tesla filed his application in US patent office for induction motor on October 12, 1887, a year earlier.) Ferraris worked at the Italian Industrial Institution, a school of electrical engineering (the first school of this kind in Italy; subsequently incorporated in the Politecnico di Torino). In 1896, Ferraris joined the Italian Electrotechnical Association and became the first national president of the organization. [192]

galvanic action Formation of electric current in an elec-trolyte equipped with two electrodes of dissimilar metals. [ga]

GALVANOMETER An analog instrument to detect, measure, and determine the direction of very small currents by means of mechanical effect caused by current-carrying coil in a mag-netic field. Galvanometers are based upon the discovery by Hans C. Oersted that a magnetic needle is deflected by the presence of an electric current in a nearby conductor. The term "galvanometer" itself, is in common use by 1836, de-rives from the surname of Italian electricity researcher Luigi Galvani, who discovered that electric current could make a frog's leg jerk. Modern galvanometers are of this moving-coil type and are called d'Arsonval galvanometers (after Arsène d'Arsonval, a French physicist). [180][ga][[196]

ammeter galvanometer A galvanometer calibrated for measurement of much higher values of electrical current than usual by means of a shunted low resistance to its coil. [ga 120/231]

astatic galvanometer An instrument whose action depends on the torque produced by a suspended astatic magnetic system by the current circulating in the system of fixed coils. The control is by a permanent magnet or by

GALILEO Ferraris (BG-1)

astatic needle rod spark gap

488

magnets so arranged as to affect one part of the suspended magnetic system only. [120/231]

astatic Having no particular directional characteristics. [ahd]

astatic needle Two magnetic needles of equal moment mounted in opposition. [120/36]

ballistic galvanometer Galvanometer to measure the value of an electric charge, momentary current, or mag-netic properties of iron - by reading the amplitude of the first swing or kick (ballistic) of its moving needle element. [180][122/1609-1613; 1615][ga]

calibrated galvanometer A galvanometers with a an added a resistor either in parallel or in series to its coil, turns it into calibrated for an ammeter or a voltmeter re-spectively. [ga]

d’Arsonval galvanometer It is a moving coil galva-nometer first invented by D’Arsonval, French physicist, 1851-1940, and named after him. [122/1606]

difference galvanometer A galvanometer to measure the difference between two currents. [180]

galvanometer constant The number by which the gal-vanometer reading shall be multiplied to get the actual quantities. [ga]

moving-coil galvanometer A galvanometer in which a coil carrying a current moves in the field of a permanent magnet. [180]

multiplying galvanometer A reference to early design of galvanometers in which the effect of magnetic field of the instrument was increased by using multiple turns of wire. [192, ga]

potential galvanometer A galvanometer calibrated for measurement of voltage, potential, by means of a series high resistance to its coil. [ga 120/213]

reflecting galvanometer An earlier version of galva-nometer built to indicate the presence of very small cur-rent but unable to measuring it. [122/1608, ga]

sine galvanometer One of earlier version of galvanom-eter similar to tangent galvanometer, except its coil is movable about a vertical axis, and the instrument is more accurate. [122/1602, 1605]

string galvanometer A galvanometer in which the moving element is a conductive thread which is able to move between the pole pieces of a permanent magnet or of an electromagnet. [180]

tangent galvanometer Earlier version of galvanome-ter. It works on the basis of the tangent law of magnetism, which states that the tangent of the angle a compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields. It was first described by Claude Servais Mathias Pouillet in 1837.

vibration galvanometer A galvanometer in which the natural frequency of the moving element is adjusted to resonate with the frequency of the current to be measured or detected. [180]

GAP An air opening, an empty space between things.

air-gap A gap in the ferromagnetic portion of a magnetic circuit such as in a rotating machine. [180/411.40-17]

main air-gap The minimum distance between the relatively moving parts of a magnetic structure such as in a rotating ma-chine. [180/411.40-18]

butt gap A gap between the edges of adjacent turns of helical tapes applied to a cable component. [180/461. 16-02]

differential gap Difference between the upper and lower switching values depending on the direction of the change of the input variable for every position of a multi- position switching element. [180/351.28-36][ga]

gapless Not possessing gaps, series, or parallel as in gap-less arrester. [70/3.34]

maximum permitted gap Highest value of gap, de-fined according to the electrical apparatus group, the vol-ume of the flameproof enclosure, and the length of the flameproof joint. [180/426.06-04]

measuring gap Spark gap to measure peak voltage as a function of the flashover distance between its two elec-trodes, generally spheres. [180/313.01.26][ga]

protective gap A gap placed between live parts and ground to limit the maximum overvoltage that may other-wise occur. [2/881][24]

protective level of the bypass gap The maximum in-stantaneous voltage (including tolerance) appearing across the capacitor immediately before or during opera-tion of the bypass gap. [2/881]

rod gap Means of measurement of peak values of direct high voltage during high voltage tests. For the purpose, a standard rod gap has been developed. [76/17 ga]

standard rod gap A gap between the ends of the two one half-inch square rods cut off squarely and mounted on supports so that a length of rod equal to or greater than one-half the gap spacing overhangs the inner edge of each support. It is in-tended to be used for the approximate measurement of crest voltages of direct high voltage tests. [2/1097][76/17.6, ga]

series gap An intentional gap(s) between spaced elec-trodes. It is in series with the valve element of the arrester substantially isolating the element from line or ground or both, under normal line voltage conditions. [85/2.3] [70/3.72]

shunt gap Intentional gap(s) in an arrester between spaced electrodes that is electrically in parallel with one or more valve elements. [70/3.74]

spark-gap Air dielectric between two electrodes that may be a combination of several basic shapes that is used to protect power equipment and circuits from damage due to voltage stress in excess of their dielectric capabilities. A device utilized widely in surge arresters. [ga] [85/9] De-vice with two or more electrodes between which an elec-tric discharge is initiated under specified conditions. [180/

151.13-33] protective spark gap A protective device which consists of

an open air-gap between one or more energized electrodes in series, and an electrode connected with earth. [180/604.03-49]

rod spark gap Spark gap made of two rods set in line Oppo-site to each other. [180/604.03-49]

horn spark gap gas formation

489

horn spark gap Spark gap made of two or more upright ver-tical rods splaying out at the top to facilitate arc extinction. [180/604.03-49]

sphere gap Means of measurement of peak values of al-ternating high voltage, lightning impulse voltage, switch-ing impulse voltage. For the purpose, a standard sphere gap has been established. [76/17 ga]

standard sphere gap Peak voltage measuring device con-structed and arranged in accordance with prescribed standards, consisting of two metal spheres of the same standard diame-ters, operating gear, insulating supports, frame, leads, etc. The voltage measurement consists in establishing a relation be-tween high voltage, as measured by the sphere gap, and the indication of a voltmeter connected in the control circuit of the equipment. [76/17.2 ga]

GAS The state of matter distinguished from the solid and liq-uid states by relatively low density and viscosity, relatively great expansion and contraction with changes in pressure and temperature, the ability to diffuse readily, and the spon-taneous tendency to become distributed uniformly through-out any container [ahd] A substance in the gaseous state. [ahd]

atomic gases Also referred to as “pure gas” or “noble gas,” made up either of individual atoms like neon, or el-emental molecules made from one type of atoms, or com-pound molecules made from variety of atoms like helium (He), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). [192][ga]

characteristics For gases, they are described through the use of four physical properties or macroscopic charac-teristics: pressure, volume, chemical groups, (number of particles) temperature. [192][ga]

electric discharge (in a gas) The e passage of an elec-tric current through gases and vapors by the production and movements of charge carriers under the influence of an electric field. The phenomenon results in the emission of electromagnetic radiation which plays an essential part in all its applications in lighting. [180]

electron gas Aggregate of free electrons that exhibits some of the properties of a gas. [180]

electronegative gas Gas which capture free electrons and forms negative ions thereby arresting the formation of electric discharges. [180/212.17-01]$A gas with higher elec-tronegativity number, attracts more electrones. Gases, known as electronegaticve gases, possess good insulating feature such as SF6 , and others, hydrocarbon refrigerants CCl2F2, and CCl4. [ga]

elemental gases Multiatom chemical elements at stand-ard temperature and pressure (hydrogen, nitrogen, oxy-gen), combined with halogens, and fluorine grouped with noble gases (helium, neon, argon, krypton, xenon, radon). [192, ga]

explosive gas atmosphere A mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapor or mist, in which, after ignition, com-bustion spreads throughout the unconsumed mixture [180]

external gas pressure cable (gas compression cable) A pressure cable usually pipe-type used in electric high and extra high voltage power systems, in which the

pressurizing fluid is a gas separated from the insulation by a diaphragm. [180] [ga]

gas-absorbing liquid An insulating liquid which ab-sorbs gas when its gassing characteristic under electrical stress is tested under standardized conditions. [180]

gas-accumulator relay A relay so constructed that it accumulates all or a fixed proportion of gas released by the protected equipment and operates by measuring the volume of gas so accumulated. [24/36]

gas-barrier insulator A space insulator specifically designed to prevent passage of gas from one side to the other. [24/36]

gas-blast circuit-breaker A circuit-breaker in which the arc develops in a blast of gas. Where the gas is moved by a difference in pressure established by mechanical means during the opening operation of the circuit-breaker, it is termed a single pressure gas-blast circuit-breaker. Where the gas is moved by a difference in pressure estab-lished before the opening operation of the circuit-breaker, it is termed a double pressure gas-blast circuit-breaker. [180]

gas conduction (discharge) Electric conduction in a ionized gas [180]

self-maintained gas conduction Gas conduction for which the necessary charge carriers are produced without the aid of an external ionizing agent . [180]

non-self-maintained gas conduction Gas conduction for which the necessary charge carriers are produced with the aid of an external ionizing agent [180]

gas content (of an insulating liquid) The volume of gas dissolved in the unit volume of an insulating liquid, gen-erally expressed as a percentage [180]

gas current An unintended ion current resulting from collisions between electrons and residual gas molecules in a vacuum tube. [180]

gas density, nominal The manufacturer’s recom-mended operating gas density (usually expressed as pres-sure at 20°C). [24/36]

gas density minimum The minimum (below normal) operating gas density at which the gas insulated substation and its components are certified to meet their assigned electrical ratings.[241/3.7]

gas discharge The passage of electric current through a gas or vapor [180]

gas-evolving liquid An insulating liquid which evolves gas when its gassing characteristic under electrical stress is tested under standardized conditions. [180]

gas evolving switch A switch in which the gas is evolved and moved by the thermal action of the arc. [180]

gas-filled transformer A sealed transformer, except that the windings are immersed in a dry gas that is other than air or nitrogen. [19/3.150]

gas formation The process by which gas is evolved by an insulating liquid when subjected to high thermal and/or

gas generator properties

490

disruptive discharge conditions [180]

gas generator Installation used in industrial electro-heat systems to obtain endothermic or exothermic protective atmospheres from fuel gases, ammonia and liquid organic compounds [180]

gas insulated line (gas insulated circuit, GIC, depre-cated) An electric line whose conductors are contained in a enclosure and insulated with a compressed gas. Used in high and extra high voltage electric power systems.[180] [ga]

gas insulated metal-enclosed substation A substa-tion which is made up with only gas insulated metal en-closed switchgear.[180]

gas-insulated metal-enclosed switchgear Metal-en-closed switchgear in which the insulation is obtained, at least partly, by an insulating gas other than air at atmos-pheric pressure. Such switchgears usually are made for high and extra--voltage power systems. [180][ga]

gas-insulated substation (GIS) A compact, multi-component assembly, enclosed in a grounded metallic housing in which the primary insulating medium is a com-pressed gas and that normally consists of buses, switch-gear, and associated equipment. [24/36] To explore further see main entry GAS- INSULATED SUBSTATION

gas-insulated surge arrester A metal-enclosed surge arrester specifically designed for use in a gas-insulated substations. [241/3.10]

gas leakage Loss of insulating gas by accidental and gradual escape from the pressurized system. [24/36][ga]

gas-oil sealed system For power and distribution trans-formers, it is a system in which the interior of the tank is sealed from the atmosphere, over the temperature range specified, by means of an auxiliary tank to form a gas-oil seal-operating on the manometer principle. [19/3.151] An oil preservation system in which the interior of the tank is sealed from the atmosphere, over the temperature range specified, by means of an ancillary tank or tanks to form a gas-oil seal operating on the manometer principle. [224/2.9.2]

gas pressure relay A relay designed to operate by the gas pressure in the protected equipment. [24/36]

gas-proof (or vapor-proof) machine A machine where the entry of a specified gas or vapor under prescribed con-ditions cannot interfere with operation of the machine. [180]

gas ratio The ratio of the ion current in a tube to the elec-tron current that produces it. See also electrode cur-rent.[2/476]

gas release The relief of dissolved gases from an insu-lating liquid due to changes in solubility conditions. [180]

gas seal Sealing arrangement in a bearing assembly in-tended to minimize the leakage of gas to or from the ro-tating machine through a bearing [180][2/476]

gas-tight area The part of the contact area that is not affected by gases under specified conditions. [180]

gas-tube surge arrester A gap, or gaps, in an enclosed discharge medium, other than air, at atmospheric pressure,

designed to protect apparatus or personnel, of both, from high transient voltage. [12-4/10]

gas turbine set Thermal generating set in which the prime mover consists of a gas turbine. [180] See also tur-bine generator

ignition temperature of an explosive gas atmos-phere The lowest temperature of a heated surface at which, under specified conditions, the ignition of a flam-mable substance in the form of a gas or vapor mixture with air will occur. IEC publication 79-4 standardizes a method for the determination of this temperature. [180]

incandescent lamp, gas-filled Incandescent lamp in which the luminous element operates in a bulb filled with an inert gas.[180]

inert gas Any gas that can be used in the laboratory to protect sensitive substances from reacting with the oxygen of the air. Pure nitrogen can be used in principle, but a `noble gas’ such as argon is usually preferred.[204]

insulating gas A gas with negligibly low electric con-ductivity, used to separate conducting parts at different electrical potentials. [180]

conductivity The ability to allow electric current pass through. For pure molecular gas at moderate electric stress and at moderate temperature in the absence of any ionizing effect – conductivity to be practically zero. [59/8-2]

dielectric breakdown The point of increased voltage well above the level an insulation was designed and capable of withstand for, at which point the insulation will no longer be able of sustaining its dielectric qualities. As a result, the insu-lation will `breakdown’ and collapse. At this point, the three different types of dielectrics react differently. The solid dielec-tric, ends up with physical rupture, and short circuiting. Gas and liquid dielectrics however, will be restoring their dielectric qualities by self-healing process. Disruptive discharge, flash-over, sparkover, passage of an arc follows dielectric break-down. In uniform electric field, breakdown takes place at a critical voltage – the product of the pressure and spacing. To explore further relevant terms, see main entry DIELECTRIC [180/604.03-38][59/8-3][ga]

dielectric constant Dielectric constant k fore insulating gases, is a function of the molecular electrical polarizing abil-ity, and the gas density, it is independent of magnetic and elec-tric fields. Dielectric constant for air, is one, whereas dielectric constant for SF6 gas is 1.002. [59/8-2, ga]

dielectric strength Characterizes the strength of insulating property of gas. It is the maximum electric field strength gas can withstand before it breaks down. Dielectric strength de-pends on the properties of insulating medium, and distance be-tween electric poles applying the voltage. The unit is kV/mm. [17/2.56, ga] By American Standards Association, (ASA) it is defined as the maximum potential gradient that the material can withstand without rupture. It is often referred to as break-down voltage divided by the thickness between elec-trodes.[59/5-9][ga]

relative dielectric strength High electric strength for gases at high pressure. Atmospheric pressure as the lower limit of high pressure, and depending on type of gas used, the upper limit of pressure is set. Relative dielectric strength for gases, is the dielectric strength between the lower and upper limit pressure applied to achieve the desired strength. [72a/2814] [59/8.4]

properties (of gas) Highly compressible dielectric medium, usually of low conductivity, and with a dielectric constant only a little greater than unity. except at high pressure. In high

SF6 gas non-continuous enclosure

491

electric fields, gas may become conducting as a result of im-pact ionization of the gas molecules by electrons accelerated \by the field and by secondary process, which produce partial breakdown (corona) or complete breakdown. [59/8-1][ga]

SF6 gas Sulfur hexafluoride. A combination of sulfur and flu-orine. Has peculiar property for extinguishing the electric arc. The dielectric strength of SF6 in on average 2.5 times that of air, and, by increasing pressure, the dielectric strength also in-creases around 3.5 bar of relative pressure, SF6 has the same strength as fresh oil. [ga 192]

internal gas pressure cable Pressure cable in which the pressurizing fluid is a gas in contact with the insula-tion: it may be self-contained or pipe-type cable. [180]

plasma gas Any gas, vapor or fluid to be brought to the state of plasma. [180]

plasma An electrically neutral, highly ionized gas composed of ions, electrons, and neutral particles. It is a phase of matter distinct from solids, liquids, and normal gases. [ahd]

protective gas A gas used to maintain pressurization or to dilute flammable gas or vapor to a concentration well below the lower explosive limit. The protective gas may be air, nitrogen or any other non-flammable gas, or a mix-ture of such gases.[180]

residual gas Small quantity of gas molecules present in an evacuated space. [180]

GAS-INSULATED SUBSTATION (GIS. See Graph GG-1) Substa-tions where the medium for isolating the phases and the ground is not air but gas filled in an enclosure. The gas uti-lized in these substations is SF6 (sulfur hexafluoride) or mixed with CF4 (carbon tetrafluoride). Both are inert gases, colorless and odorless, non-flammable. These substations are known as GIS. • A compact multicomponent assembly enclosed in a grounded metallic housing in which the pri-mary insulating medium is a compressed gas and that con-sists of buses, switchgear, and associated equipment. [24] • Under this main entry explored are terms on technical re-quirements for the design, fabrication, testing, and installa-tion for gas insulated substations. The terms are grouped ac-cordingly as given below:

GENERAL RATINGS SEISMIC REQUIREMENTS SERVICE CONDITIONS SPECIFICATIONS TESTS

See Graph GG-1 Gas Insulated Substation

GENERAL Definitions of terms in general use associated with engineering, construction and operation of gas-insu-lated substations. [ga]

capacitor voltage coupler A device for ultra-high fre-quency partial discharge measurement, and diagnostic monitoring. [242A/6.10] See also main entry COUPLED / COU-PLER / COUPLING

capacitive coupling Coupling between electric circuit elements, by which a voltage between the terminals of one of them gives rise to an electric charge in another element. [180] See also main entry COUPLED / COUPLER / COUPLING

catastrophic failure A failure of any portion of the GIS due to internal or external faults that results in sufficient

damage to that portion of the GIS that is cannot be re-turned to service without major repairs. [242A/3.1] See also SEISMIC REQUIREMENTS/failure mode

circuit A path which ensures continuity of flow of elec-trons if it is closed.

auxiliary circuit All control, indicating and measuring circuit, also referred to as secondary circuit. [241/3.2][ga]

main circuit All conducting parts of the gas insulated substation assembly included in or connected to the cir-cuits that is switching devices are designed to close or open. [242/3.23]

compartment A separate division, section, a cell, room, or chamber One of a subdivision, or a cell of a larger enclosure such. Any gas section of the gas-insulated substation assembly that can be isolated from the system by internal or external means. [24/18][ga]

GIS compartment Any gas section of the gas-insulated sub-station assembly that provides gas isolation. [241/3.3]

transition compartment A compartment specifically de-signed for joining gas-insulated substation equipment of dif-ferent design or manufacture. The compartment provides the necessary transition for the current-carrying conductor and the enclosure. [241/3.15]

continuous monitoring The process of sampling the state of some phenomenon at a time interval shorter than the time constant of the phenomenon. [241/3.5]

design earthquake The greatest earthquake postulated during the life of the gas-insulated substation that the user wishes to see it survive in operating condition.[242/3.12]

design philosophy Studies the aspects of failure modes; general considerations; maximum working stress; seismic and other loads for GIS defined below: [242/4.7.5][ga]

failure modes Takes into consideration the analysis of prob-able mode of failures such as overstressed displacement fail-ure; under-stressed displacement failures; leakage; dielectrics; fatigues; exposure and aging.

general consideration Takes into consideration center of gravity for heavy section of GIS assembly; reserve strength and reserve operation limits; component ratings; relative mo-tion; and equipment failure modes.

maximum working stress Takes into consideration for steel structures and aluminum structures; for non-metallic ma-terials.

seismic and other loads Takes into consideration dead load; temperature rise due to current and ambient factors; in-service gas pressure; short circuit currents; wind pressure; mechanical operation impacts, and possibly others. [242/4.7.5][ga]

design pressure (working pressure) The maximum steady- state gas pressure to which a gas-insulated substa-tion enclosure is subjected under normal operating condi-tions. [242/3.13]

enclosure A surrounding case or housing used to protect the contained GIS equipment such as buses and other parts under pressurized gas. [ga]

continuous enclosure A bus enclosure in which the consec-utive sections of the enclosure are electrically bonded together to provide a continuous current path through the entire enclo-sure length.

non-continuous enclosure A bus enclosure in which the consecutive sections of the enclosure are electrically insulated from each other, although each section is connected to ground.

492

Graphic GG-1 GAS INSULATED SUBSTATIONS

(Terms in areas explored in this dictionary)

GAS INSULATED

SUBSTATION

(GIS)

GENERAL TERMS

RATINGSof Equipment:

Current Voltagetemperature.

SEISMIC REQUIREMENTSCriteria EarthquakeSeismics Failures

Performance Adequacy.

SERVICE CONDITIONSNormal Specific

Other Service Conditions.

SPECIFICATIONSSpecific environmental

conditions for GIS Specifications by the

Purchaser and the Supplier Proposal by

the Supplier Equipment and services by the Purchaser and the

Supplier

TESTSField Tests

Qualification Tests for Electrical and

Mechanical Operation Routine Tests

Type Tests Production Tests.

enclosure currents SF6

493

(The construction prevents longitudinal currents from flowing beyond each enclosure section. This design is no longer in common usage.) [241/3.13]

enclosure currents The currents that result from the voltage induced in the metallic enclosure by effects of currents flowing in the enclosed conductors. [242/3.14]

metallic enclosure A grounded, leak-tight enclosure that contains the compressed insulating gas and associated electri-cal equipment. [241/3.12]

single-phase enclosure A metallic enclosure containing the buses and/or devices associated with one phase of a multiple-phase system. [242/3/35]

three-phase enclosure A metallic enclosure containing the buses ands or/devices of all phases of a three-phase system.

gas barrier insulator An insulating support specifi-cally designed to prevent passage of gas from one gas compartment to another. [241/3.6]

gas-insulated metal-enclosed substation A substa-tion made up with only of gas insulated metal enclosed switchgear. [180/605.02-14]

gas-insulated surge arrester A metal-enclosed surge arrester specifically designed for use in a gas-insulated substations.[241/3.10]

gas leakage Loss of insulating gas from the pressurized compartment [241/3.11][ga]

GIS assembly A collection of GIS components which are interconnected and ready for insertion as a subassem-bly in a GIS, such as a breaker bay shipping assembly. The term is also used to describe a complete GIS. [241/3.1]

malfunction The loss of capability to initiate or sustain a required function often a protective action, or the initia-tion of undesired spurious action69. [242/3.24]

maximum ground acceleration The maximum value of acceleration input to the equipment during a given earthquake for a particular site. [242/3.25]

mechanical amplification The relationship between response acceleration and ground acceleration. [242/3.3]

mechanical damping A dynamic property that indi-cates the ability of a structure to dissipate energy. (The phenomenon of damping is represented by the damping ratio, a percentage of critical damping. After being forced to deflect and allowed to vibrate, structure with zero damping vibrate indefinitely. Structure with critical damping return to their static or neutral position in the shortest time without oscillation.) [242/3.11]

mechanical mode shape A plot that shows displace-ments of various points in the vibrating structure at a particular instant in time. There is a characteristics mode shape associated with each natural frequency of a vibrating structure. [242/3.27]

mechanical natural frequency The frequency at which a body vibrates due to its own physical characteris-tics (mass, shape, boundary conditions, and elastic forces

69 Certain degree of equipment degradation may be acceptable in one system

and not in another. In such cases, an evaluation of the equipment applica-tion should include a determination that the degree of relay contact bounce,

brought into play) when the body is distorted and then re-leased, while restrained or supported at specific points. [242/3.29]

mechanical resonance A dynamic condition that oc-curs when any forcing frequency of mechanical vibration coincide with one of the natural frequencies of the struc-ture. [242/33.3][ga]

minimum gas density The minimum (below normal) operating gas density at which the gas insulated substation and its components are certified to meet their assigned electrical ratings.[241/3.7]

moisture content The amount of water in parts per mil-lion by volume (ppmv) that is in the gaseous state and mixed with the insulating gas. [242/3.28]

nominal gas density The manufacturer recommended operating gas density (usually expressed as a pressure at 20ºC). [242/3.17]

normal gas density See nominal gas density

periodic monitoring The process of sampling the state of some phenomenon at a sample interval greater 1 s. [242/3.31]

pressure relief device A means for relieving internal pressure in a GIS equipment and preventing explosive shattering of the housing. It is provided with a shield and be vented to provide safe environment for field personnel and GIS equipment. [242/5.2.10 ga]

pressurized bus enclosure A basic component of gas-insulated substation which is a grounded metal enclosure, containing energized high-voltage conductors, and other substation components. [241/5.2]

purchaser See user

response spectrum (mechanical) A plot of the maxi-mum response of single-degree-of-freedom bodies at a damping value expressed as a percentage of critical damp-ing of different natural frequencies when these bodies are rigidly mounted on the surface of interest (i.e. on the ground-response spectrum or on the floor for a floor-re-sponse spectrum) when that surface is subjected to a given earthquake’s motion by intervening structures. [242/3.34]

retransmit contacts Auxiliary contacts on an annunci-ator that provide an output to a remote device to indicate that the annunciator has been actuated. [242/3.3]

SF6 Sulfur hexafluoride, heavy, nontoxic gas, highly elec-tronegative, with very high dielectric strength of about 89 kV/cm-bar. It consists of 1 sulfur atom surrounded by 6 fluorine atom. Inorganic, colorless, odorless, and non-flammable greenhouse gas. Transported as a liquefied compressed gas. It has a density considerably higher than the density of air. Its most application is as gaseous die-lectric medium in high voltage electrical industry such as gas insulated switchgears and substations (GIS), high-voltage circuit breakers, and other electrical equipment,

changes in device calibration, or degradation of pressure-retaining bound-aries are within acceptable limits

soil structure interaction criteria for seismic stress

494

often replacing oil filled circuit breakers because it has a much higher dielectric strength than air or dry nitrogen. [192, ga]

soil structure interaction (SSI) A general concept for effect caused by the influence of the soil dynamic behav-ior on the response of a structure.[242/3.36]

spacer An insulator used to support the inner conductor in the enclosure. [241/3.14][ga]

station ground A ground grid or any equivalent system of grounding electrodes buried beneath or adjacent to the gas-insulated substation that determines the rise of ground voltage level relative to remote earth and controls the dis-tribution of voltage gradients within the gas-insulated sub-station area during a fault. [242/3.38]

stress The internal resistance a material exerts to being deformed. It is measured in terms of the applied load • The average amount of force exerted per unit area. [192][ga]

acting stress (working stress) The maximum applied or ex-pected mechanical stress in a material during operation of the apparatus of which it is a part and including the stress caused by seismic and other loading, acting independently or simulta-neously as determined by the user.[242/3.1]

allowable stress The maximum stress permitted by applica-ble standards or codes. [242/3.2].

time history (mechanical) The record of acceleration, velocity, or displacement as a function of time which the floor of a building or the ground experience due to an earthquake. [242/3.43]

transient A sub-cycle disturbance in the ac waveform that is evidenced by a sharp, brief discontinuity of the waveform. May be of either polarity and may be additive to, or subtractive from, the nominal waveform such as notch; overvoltage; swell. [342/2.2.84]

very fast transient (VFT) A class of transients generated internally within a gas-insulated substation (GIS) character-ized by short duration and very high frequency. VFT is gener-ated by the rapid collapse of voltage during breakdown of the insulating gas, either across the contacts of a switching device or line-to ground during a fault. These transients can have rise times in the order of nanoseconds implying a frequency con-tent extending to about 100 MHz. However, dominant oscilla-tion frequencies, which are related to physical lengths of GIS bus, are usually in the 20–40 MHz range. [103/32] ][To explore further, see also source code 3/10.5]

user The purchaser, the party owning the projected or ex-isting GIS facility, i.e. the client for the contractor or the manufacturer.[ga] See also derivative main entry further down SPECIFICATION /user

water vapor content The amount of water, or mois-ture, in parts per million by volume (ppmv) that is in the gaseous state and mixed with the insulating gas. [241/3.17]

working pressure See design pressure

zero period acceleration The peak time history accel-eration that can be determined by the merging of response spectra, for all damping values in the high-frequency range (usually above 30 Hz), in which no change in accel-eration occurs with frequency. [242/3.47]

RATING Defines basic performance limitations of GIS equipment such as temperature, voltage, gas pressure, continuous and fault currents, etc. [ga]

equipment ratings Encompasses performance limita-tions on voltage, current, and temperature ratings for GIS station.[241/5.1]

close and latch current rating The rms value and peak value of rated momentary current, which is 1,6 and 2,7 time rated short-time current-carrying value. [241/5.1.6]

continuous current rating The maximum rms current in amperes at rated frequency and at a specific ambient temperature, which a GIS equipment will carry continu-ously without exceeding the allowable total temperature: 2000, 2500, 3150, 4000, 5000, 6300 A. [241/5.1.3][ga]

short-time current carrying rating The current car-ried by GIS equipment for a specified short-time interval selected from the values given by the manufacturer, which for GIS equipment are in kA: 20, 25, 31.5, 40, 50, 63, 80, 100 kA. [24][241/5.1.7]

short-time load current rating A current level per-missible above the rated for a short duration for equipment operating below its rate. The magnitude and the duration of the short-time load current is either calculated or de-rived from tables issued by the manufacturers. [287/4.5] [291/4.4.3.3][ga]

temperature ratings Prescribes temperature limita-tions that all components of GIS station shall meet as fol-lows: [241/5.1.1]

• maximum allowable total temperature of main con-ductor joints: 105ºC

• external surface: 70ºC

voltage ratings Incorporates rated maximum voltage, rated BIL, rated low frequency withstand voltage, rated switching impulse withstand voltage: [241/5.1.2]

◊ rated maximum voltage, kV 72,7; 121; 145; 169; 242; 550; 800.

◊ rated BIL crest, kV: 350;550; 650;750;900;1050; 1550; 2100

◊ rated low frequency phase voltage withstand, kV. 160; 215; 310; 365;425;500;740;960 kV

◊ switching impulse withstand kV 825, 1175, 1550 kV for max. voltage ratings of 362, 550, 800 kV respectively. [241/5.1.2]

For descriptions and definitions of ratings on other com-ponents of GIS stations such as pressurized bus enclosure, gas systems, cable terminations, grounding, etc. see IEEE standards C37.1122 and corresponding IEC standards.

SEISMIC REQUIREMENTS Procedures and guidelines for the seismic design, analysis, and acceptance of gas-insulated substations to ensure functional adequacy under seismic disturbances. [242/4.7]

criteria for seismic stress They are seismic data pro-vided to the manufacturer by the user; site evaluation for designated equipment; and differential motion in the ground. [242/4/7/2, ga]

501