Generator Circuit Breakers - IEEE Web Hosting
Generator Circuit BreakersGary MeekinsAreva T&D770-904-2927General ReviewWhy ?GCB Standards andHow they apply to GCB’s1Generator Circuit-BreakersWhy / BenefitsGenerator Circuit Breakers were used in multi-unit stations where a numberof relatively small generators were connected to a common bus. The rapidincrease in generator size and system fault current levels soon exceeded theinterrupting capabilities of this type of switchgear. The unit concept was thenadopted where each generator had a separate steam supply [and] auxiliarysystems [are] directly connected step-up transformer and high sidebreaker(s). . . . advances in circuit breaker design(s) have made the generator circuitbreaker concept a viable alternative even at the 250 kilo-ampere levelrequired for some applications.IEEE – Atlanta ChapterA major advantage of the generator circuit breaker is that fault currentcontributions from the generator can be interrupted in 5 to 7cycles (now it's 3- 5 cycles) for faults in the isolated phase bus or on the high side of thegenerator step up transformer.Other advantages include the elimination of transfer of auxiliary loads(auxiliary transformer remains connected to the system), and improvedreliability when the generator is synchronized with the system.(IEEE Transactions on Power Apparatus and Systems, Vol. PAS-I02, No.9, September 1983)21
GCB StandardsC37.013Generator circuits experience conditions that are not common and are certainly moredemanding than those experienced in normal distribution circuits. These uniquecharacteristics require breakers that have been specifically designed and tested. IEEEhas developed the only standard known world wide specifically addressing therequirements for this applicationThe first editions of the standard, C37.013, focused on large power stations. Laterrevisions included applications on smaller generation plants and today, the standard isbeing revised to include comments from the international community.IEEE – Atlanta Chapter(Are All Circuit Breakers Created Equal? Certainly NOT When it Comes to Generator CircuitWilliam Long and Dr. Kirkland Smith: Eaton Technology and Eaton Cutler-Hammer Business, respectively)3Generator Circuit-BreakersWhy / BenefitsDIAGRAMWITHOUT GCBH.V. NETWORKIEEE – Atlanta ChapterDIAGRAM WITH GCB42
Generator Circuit-BreakersWhy / Benefits A GCB is a protection device for the transformer . . . . . .Protection of the GSU transformer against generator-fed shortcircuit currentsIEEE – Atlanta Chapter 5Protection of the Generatoragainst system-fed shortcircuit currentsGenerator Circuit-BreakersWhy / BenefitsIEEE – Atlanta ChapterPKG2R, 24 kV, 275 kA, installed in 1977 :interrupted a 250 KA fault in 1995.PKG - Installed in the USA63
Generator Circuit-BreakersWhy / Benefits The GCB is an effective protection devicefor the transformer and the generator Starting and maintenance stagesSynchronization and normal conditionsAbnormal conditions including: Overvoltages, un-balanced loadShort circuitIEEE – Atlanta Chapter Step up transformer sideGenerator sideOut of Phase Requirements7Generator Circuit-BreakersWhy / Benefits Specific technical constraints : IEEE – Atlanta Chapter Transient recovery voltageAsymmetrical currentRate of rise recovery voltage in kV/µsCapacitorsOut of phase84
Standards – DefinitionsDefinitions that should be understood that are specific togenerator circuit breakers. Rated maximum voltage of a generator circuit breaker: Generator source short circuit current System source short circuit current Rated continuous current of a generator circuit breaker Rated mechanism fluid operating pressure of aIEEE – Atlanta Chaptergenerator circuit breaker (if applicable!) Rated Interrupting time of a generator circuit breaker9Standards – DefinitionsInfluence of Station Design ConfigurationaIEEE – Atlanta ChapterA short circuit current can be initiated at the following points: a - Location a is called a system source short circuit current.The transformer-fed fault current can be very high because the full energy ofthe power system feeds the fault. The low impedance of the transformer andthe short, very lowloss buses connecting the generator, generator circuitbreaker, and transformer, do little to limit the fault current because of their verylow impedance. To clear these kinds of faults, generator circuit breakers mustbe tested and proven capable of interrupting not only the high symmetrical faultcurrent, but also the higher asymmetrical fault currents resulting from extremeDC components of fault current, up to 75% as required in section 5.8 of IEEEC37.013.105
Standards – DefinitionsInfluence of Station Design ConfigurationbIEEE – Atlanta ChapterA short circuit current can be initiated at the following points: b – Location b is called a generator source short circuit current.Generator-fed fault currents, while lower in magnitude, are subject to another type ofvery demanding condition called “Delayed Current Zeroes”. This uniquecharacteristic of the fault current comes from the very high X/R (inductive reactanceto resistance) ratio of the circuit and the operating conditions of the generator, whichcan combine to produce a DC component of the fault current exceeding 100%! Thismeans the asymmetrical fault current peak becomes so high, and its decaybecomes so slow, that the first current zero can be delayed for several cycles.Since circuit breakers rely on a current zero crossing in order to interrupt, generatorcircuit breakers must be able to withstand longer arcing times and greater electrical,thermal, and mechanical stresses when clearing this kind of fault.11Standards – DefinitionsInfluence of Station Design ConfigurationcIEEE – Atlanta ChapterA short circuit current can be initiated at the following points: c – Location c is called a high voltage generator source shortcircuit current, but of a smaller current than location b.126
Standards – DefinitionsInfluence of Station Design ConfigurationDifferent station configurations have different characteristics . . .and therefore, each applicable breaker characteristics should be definedrespectively.Half-Sized TR ConfigurationIEEE – Atlanta ChapterFor a system source fed fault (A2)in the adjacent figure, the shortcircuit current and the TRVparameters seen by the individualcircuit breakers are related toeach step up transformer’s rating.Half-sized transformer unit system13Standards – DefinitionsInfluence of Station Design ConfigurationHalf-sized Generators ConfigurationIEEE – Atlanta ChapterFor a system source fed fault (A3),the short circuit current is higherbecause the fault is also fed by thegenerator, G2. However the TRV rateis lower because of the G2 generatorwinding’s capacitance. If the generatorG2 is out of service, the situation is thesame as for a fault in A2 of the firstfigure, except that the generator is halfthe rating.Half-sized Generator Configuration147
Standards –Ratings & Required CapabilitiesThe ratings and requiredcapabilities of a generator circuit breaker are the listed maximum limitsof operating characteristics based on well defined service conditions andshall include the following electrical performances, as a minimum: IEEE – Atlanta Chapter –O–Rated Maximum voltagePower frequency 50 / 60 HzRated continuous currentRated dielectric withstandRated short circuit duty cycleRated interrupting timeRated closing timeRated short circuit currentTransient recovery voltage (TRV) ratingRated load switching capabilityCapacitance current switching capabilityOut of phase current switching capabilityExcitation current switching capabilityRated control voltageRated mechanism fluid operating pressure (if applicable)15Standards –Ratings & Required CapabilitiesRated Maximum Voltage Ratedmaximum voltage.IEEE – Atlanta ChapterThe rated maximum voltage applied to a generator circuit breaker is thehighest r.m.s. value for which the circuit breaker is designed and is theupper limit for operation.The rated maximum voltage is equal to the generator’s maximumoperating voltage times 1.05.168
Standards –Ratings & Required CapabilitiesRated continuous currentThe rated continuous current of a generator circuit breaker is the designated limit ofcurrent in rms amperes at power frequency, which it shall be required tocontinuously carry without exceeding any stated limitations Continuous Current LimitersFrequencyo50 Hz 60 Hz (derated)oSite temperature: 40 C as max. standardoBusbar temperature 90 / 70 C for IEC 105 / 80 C for ANSI (derated)InstallationoIEEE – Atlanta Chapter Outdoors (derated) IndoorsIPB Cooling/Ventilationo17Standards –Ratings & Required CapabilitiesRated continuous current – Curve 1105/80 CEntraxe maxiIntérieur60HzP nominaleAmbient ( C)Curve 140Curve 2BusBarPhase-PhaseLocationEntraxe maxiIntérieurFrequencyPressureCurve 2Performance (curve 1) at Ambient Temp60HzP nominaleIEEE – Atlanta ChapterEnclosure (K)25Performance (curve 2) at Ambient TempHeat-Rise Curves 20.09580008500900095001000010500Current (A)11000115001200012500Ambient max ( C)90/70 C10.013000189
Standards –Ratings & Required CapabilitiesRated dielectric strength &External insulationTable 4a – Schedule of dielectric strength forac generator circuit breakers and external insulation(Ref. IEC)(Ref. Voltage1-minute, dry1.2 x 50 µs waveLightning(kV, rms)(kV, rms)(kV, rms)(kV, peak)LineColumn 1Column 2Column 3Column 417.2520602128.252875317.58.25 / 15389515.5501104IEEE – Atlanta ChapterInsulation Withstand Voltages (1)52427601256363880150 (2)(2)The lightning impulse is still 150 kV peak as there are no generator rated 36kV with a lightning impulse at 170 kV peak.The rated dielectric withstand of agenerator circuit breaker is it’svoltage withstand capability withspecified magnitudes and waveshapes. In the event of loss ofinsulating medium, the generatorcircuit breaker shall be able towithstand 1.5 times the voltageunder the following conditions:A – In the open position, the phaseopposition voltage across thecontacts, the phase to ground, andthe line to line voltage betweenphases are to be withstood.B – In the closed position, the phaseto ground and line to line voltagebetween phases are to bewithstood.19Standards –Ratings & Required CapabilitiesRated Short-Circuit Duty CyclesThe rated short circuit duty cycle of a generator circuit breaker shall bemade of two unit of operations with a 30 minutes interval betweenoperations(duty cycle: CO – 30 minutes – CO)IEEE – Atlanta ChapterThis means two full short circuit interruptions separated by 30 minutesbetween each short circuit closing. This is designed to protect powerplants and generators in particular, because two close-opens at full shortcircuit might damage the generator and the step up transformers. Thesetypes of short circuit are very unlikely and after a full short circuit, it is veryunlikely that the plant manager will try to close again after 30 minutes.2010
Standards –Ratings & Required CapabilitiesRated Interrupting Time Rated Interrupting TimeIEEE – Atlanta ChapterThe rated interrupting time of the generator circuit breaker is the maximumpermissible interval between the energizing of the trip circuit at rated controlvoltage and rated fluid pressure of the operating mechanism and theinterruption of the main circuit in all poles on an opening operation. Typicalvalues are approximately 60 – 90 ms with the actual time being dependent onthe rated short circuit current.21Standards –Ratings & Required CapabilitiesRated Short-Circuit Current The highest rms value of the symmetrical component of the three-phase short circuitcurrent; Generally, the rated Isc rms value is derived from the system source side. The GSU’slow impedance and the short, low-loss bus connection usually makes this fault thehighest rating; It is measured from the envelope of the current wave at the instant of primary arcingcontact separation, and is the current that the generator circuit breaker shall be requiredto interrupt at the rated maximum voltage and rated duty cycle. The short circuit currentsource is from the power system through at least one transformation; Establishes also, by ratios defined later in the text, the highest current that the generatorcircuit breaker shall be required to close and latch against and to carry; and Typical values of short circuit current, three-phase system are:IEEE – Atlanta Chapter50 kA, 63 kA, 80 kA, 100 kA, 120 kA, 160 kA, 180 kA, 200 kA, 250 kA, 275 kA.2211
Standards –Ratings & Required CapabilitiesRated Asymmetrical CurrentSystem and Generator Source 3-Phase Faults The rated short-circuit current isdefined by 2 values: the r.m.s value of the symmetrical(a.c.) component; the percentage of d.c. component.The a.c. and d.c. components aredetermined as indicated in the figureIacIdcIEEE – Atlanta Chapter% d.c. 100 x (IDC / IAC ) [IAC Isymp]The requirements for asymmetrical system-source interrupting capability of a generatorcircuit breaker at rated maximum voltage and for the rated duty cycle is composed of therms symmetrical current and the percentage dc current component.The value of the dc component is percent of the peak value of the symmetrical short circuitcurrent are given in the standard in the figure below for primary arcing contact partingtimes in milliseconds.23Standards –Ratings & Required CapabilitiesRated Asymmetrical Current – Cont’dSystem Source 3-Phase FaultsThe asymmetrical interrupting capability:DC component in percentage of the peakvalue of the symmetrical three-phasesystem source short-circuit current.The degree of asymmetry a at the time tcp isdetermined by the following equation:a Idc / Iac degree of asymmetryWhere the dc component are: IEEE – Atlanta ChapterI dc I ac e tcpτ Where t 133 ms.2412
Standards –Ratings & Required CapabilitiesRated Asymmetrical Current – Cont’dGenerator Source Faults Forthree phase faultsThe required asymmetrical generator source interrupting capability of a generator circuitbreaker at rated maximum voltage and for the rated duty cycle is made of the rmsgenerator source symmetrical current and a dc component.IEEE – Atlanta ChapterThe ac component of the short circuit current, when the source is from a generatorwithout transformation may decay faster than the dc component. The decay of the accomponent is governed by the generator’s sub-transient and transient time constants(Td”, Td’, Tq”, Tq’) and the decay of the dc component by the short circuit time constant,Ta Xd” / ωRa where Xd” is the direct axis sub-transient reactance and Ra representsthe armature resistance.Generally, the generator fed source faults will be lower in magnitude but zero currentcrossings will be greater than those of the system source faults due to the higher X/Rratios. The maximum required degree of asymmetry of the current for the condition ofmaximum required degree for asymmetry is 130% of the peak value of symmetricalcurrent for the generator fault as opposed to 75% on the system fed fault.25Standards –Ratings & Required CapabilitiesRated Asymmetrical Current – Cont’dGenerator Source FaultsThe highest value of asymmetry occurs when, prior toAn example of short circuit current for agenerator source fed fault.the fault, the generator is operating in the underexcited mode with a leading power factor.Under such a condition, the DC component may behigher than the symmetrical component of the shortcircuit current and may lead to delayed current zero’s.In the case where the generator is carrying load witha lagging power factor prior to the fault, theasymmetry will be lower, and delayed current zerosIEEE – Atlanta Chaptershould not be expected.2613
GCB – DiscussionsTECHNICALDelayed current ZerosInterruption - With an Asymmetrical CurrentIEEE – Atlanta ChapterTa X ' ' d / ω ( Ra )27GCB – DiscussionsTECHNICALDelayed current ZerosContact PartInterruption - With an Asymmetrical CurrentTa X ' ' d / ω ( Ra Rarc )Arc Resistance, from thecontact separation, forces thecurrent to the Zero crossing.IEEE – Atlanta ChapterIdc2814
Standards –Ratings & Required CapabilitiesRequired Closing, Latching and Carrying capabilitieson a short time The short circuit current into which the generator circuit breaker must close isdetermined by the highest value of either the system source short circuit current orthe generator. Closing and latching any power frequency making current (50 Hz or 60 Hz) whosemaximum crest (peak making current) does not exceed 2.74 times the ratedsymmetrical short circuit current the maximum crest (peak making current) of thegenerator source short circuit current, whichever is higher. The ratio of the maximum asymmetrical short circuit peak current at ½ cycle to therated short circuit current of the generator circuit breaker is determined by thefollowing formula:IEEE – Atlanta ChapterIpeak 2 (e t / 133 1) 2.74Isym The carrying time on short circuit current is limited to 0.25 second for a generatorcircuit breaker.29Standards –Ratings & Required CapabilitiesRated Transient Recovery Voltage[TRV]The resistance and stray capacitance of the generator circuit is typically very low.These characteristics combine to produce very high natural frequencies of thecircuit and in turn result in extreme transient recovery voltages (TRV) with highrates of rise (RRRV).IEEE – Atlanta ChapterDuring the interruption, just after the interrupter has been subjected to the plasmaarc, the dielectric strength must be re-established across the contact’s open gap inorder to withstand this fast-rising TRV. In the first phase to clear, the peak value ofthis TRV is nearly double the line-to-line voltage of the circuit, and the circuitproduces that peak voltage within microseconds following the current zero. If theinterrupter is able to withstand that voltage, then the interruption is successful. Ifnot, the gap will break down again, and the fault current will continue to flow untilthe next current zero, when there will be another opportunity to interrupt.Here it is important to note that the critical parameter is how fast the TRV risesacross the recovering gap after the current zero. This is measured by the RRRV,which is proportional to the peak value of the transient voltage in kV, divided by thetime it takes the voltage to reach that peak value in microseconds, so that theRRRV is measured in units of “kV / microsecond”.3015
Standards –Ratings & Required CapabilitiesRated Transient Recovery Voltage (cont’d)[TRV]The TRV parameters are defined as function of the rated voltage (Ur),the first pole to clear factor (kpp) and the amplitude factor (kaf) as follows:2where kpp and kaf are equal to 1.5U c k pp k af U rt3 is determined fromUcand the rate of rise3Uct3IEEE – Atlanta ChapterCURRENTTRANSIENT RECOVERYVOLTAGERECOVERYVOLTAGEDetermined by theNormal FrequencyRecovery Voltage31Standards –Ratings & Required CapabilitiesIEEE – Atlanta ChapterRated Transient Recovery Voltage – Cont’d[TRV]3216
GCB – DiscussionsTECHNICALRe-visting Transient Recovery Voltage[TRV]Reduction of TRV slope by increasing Capacitance60[ kV ]50403020IEEE – Atlanta Chapter10004(f ile t r v 2 .pl4 ; x - v ar t ) v :P 0 08v :P 1v :P 41216[ u s]20v :P 1 0No CapacitanceMore CapacitanceAdditional CapacitanceMost Capacitance33GCB – DiscussionsTECHNICALApplying Capacitors to GCB’sCapacitor Locations and functionXLGXLSC.B.IEEE – Atlanta ChapterVXCXC12Effective forEffective forgenerator-fed faultssystem-fed faults3517
Standards – SpecifyingC37.013 19977.4 Guide to specification7.4.1 GeneralIEEE – Atlanta ChapterWhen requesting proposals for a generator circuitbreakers, the engineer should furnish to the manufacture(s)a specification containing the information outlined in 7.4.2–7.4.6.7.4.2 System characteristics7.4.3 Application7.4.4 Generator circui
generator step up transformer. Other advantages include the elimination of transfer of auxiliary loads (auxiliary transformer remains connected to the system), and improved reliability when the generator is synchronized with the system. (IEEE Transactions on Power Apparatus and Systems, Vol. PAS-I02, No.9, Se
molded-case circuit breakers (MCCB), insulated-case circuit breakers (ICCB) and low voltage power circuit breakers LVPCB). Insulated-case circuit breakers are designed to meet the standards for molded-case circuit breakers. Low voltage power circuit breakers comply with the following standards: ANSI Std. C37.16—Preferred Ratings
IEEE 3 Park Avenue New York, NY 10016-5997 USA 28 December 2012 IEEE Power and Energy Society IEEE Std 81 -2012 (Revision of IEEE Std 81-1983) Authorized licensed use limited to: Australian National University. Downloaded on July 27,2018 at 14:57:43 UTC from IEEE Xplore. Restrictions apply.File Size: 2MBPage Count: 86Explore furtherIEEE 81-2012 - IEEE Guide for Measuring Earth Resistivity .standards.ieee.org81-2012 - IEEE Guide for Measuring Earth Resistivity .ieeexplore.ieee.orgAn Overview Of The IEEE Standard 81 Fall-Of-Potential .www.agiusa.com(PDF) IEEE Std 80-2000 IEEE Guide for Safety in AC .www.academia.eduTesting and Evaluation of Grounding . - IEEE Web Hostingwww.ewh.ieee.orgRecommended to you b
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