Arc erosion behavior depends on varieties of factors, such as the shape and material of contacts, the gas type and the pressure filled in the chamber. In this contribution, experimental research on the gas-blasting and free-burning conditions was carried out in a model circuit breaker to investigate the gas blowing effect on the mass loss of arcing contacts. SF6 was filled in the chamber and copper-tungsten was used as the contact material. Three different peak current amplitudes (5/20/35kA) were selected, and the average mass loss of plug contact was measured after five consecutive arcing tests. The erosion physical process between arc root and contact material is extremely complex. The mass loss was estimated with four different indexes, which include integral of current squared, thermal stress, transferred electric charge and arc energy. It has been found that the arc energy can be used to represent the degree of arc erosion to relate the gas-blasting and free-burning conditions

Humphries, James

Spencer, Joseph

Yan, Joseph

Zhou, Yannan

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

doi:10.14311/ppt.2023.1.32Plasma Physics and Technology 10(1):32–35, 2023 © Department of Physics, FEE CTU in Prague, 2023EXPERIMENTAL STUDY OF ARC EROSION IN GAS-BLASTING ANDFREE-BURNING CONDITIONS IN HIGH-VOLTAGE CIRCUIT BREAKERSY. Zhou, J. Humphries, J. Spencer∗, J. YanDepartment of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, U. K.∗ joe@liverpool.ac.ukAbstract. Arc erosion behavior depends on varieties of factors, such as the shape and materialof contacts, the gas type and the pressure filled in the chamber. In this contribution, experimentalresearch on the gas-blasting and free-burning conditions was carried out in a model circuit breaker toinvestigate the gas blowing effect on the mass loss of arcing contacts. SF6 was filled in the chamber andcopper-tungsten was used as the contact material. Three different peak current amplitudes (5/20/35 kA)were selected, and the average mass loss of plug contact was measured after five consecutive arcingtests. The erosion physical process between arc root and contact material is extremely complex. Themass loss was estimated with four different indexes, which include integral of current squared, thermalstress, transferred electric charge and arc energy. It has been found that the arc energy can be used torepresent the degree of arc erosion to relate the gas-blasting and free-burning conditions.Keywords: arc erosion, gas-blasting, free-burning, mass loss.1. IntroductionIn modern electrical power systems, high voltage cir-cuit breakers (HVCBs) have been designed and usedto carrying, interrupting and making the current innormal/fault operating conditions. After normal/faultcurrent interruptions, it leads to an electrical degra-dation of interrupting unit, which is typically re-ferred to contact erosion and nozzle ablation. Theeroded/ablated mass loss and geometry change resultin larger contact resistance, lower pressure build-upand less interrupting capability. The severity of theelectrical degradation depends on different parame-ters, such as the current amplitude, the arcing time,the shape/material of contact/nozzle and the arc ex-tinguishing system [1].As the components directly exposed to switchingarcs, the electrical lifetime of arcing contacts deter-mines the reliability and service lifetime of HVCBs.During short-circuit current interrupting process, thecurrent has to be transferred from the hot arc plasmato the relative colder contact surface of the arcing con-tact [2]. The degradation of arcing contacts is mainlycaused by arc erosion. The contact material aroundthe arc root attachment will be eroded due to thequantities of energy fluxes from the high temperaturearc plasma. The main mechanisms of arc erosion inHVCBs are material evaporation and droplet/particlesplashing, which are determined by the energy in-jected into the electrode, the temperature of electrodesurface, and other environmental factors [3, 4].It is important to assess the degree of erosion ofarcing contacts and predict the remaining service life-time of HVCBs. The prediction methods are mainlydivided into two categories. In the first category, thepresent working states of HVCBs are recognized andevaluated by measuring different physical parameters,such as the dynamic contact resistance [5], arc spectra[1] and radiated signals [6]. In the second category, theremaining electrical lifetime of HVCBs is determinedbased on the peak current amplitude, transferred elec-tric charge, thermal stress and arc energy [7–9].So far, a few research has been done to study thegas blowing effect on the arc erosion in HVCBs. Inthis paper, experimental research on the gas-blastingand free-burning conditions has been carried out atthe arcing test platform, in which three different peakcurrent amplitudes have been selected (the range isfrom 5 kA to 35 kA). The erosion physical processbetween arc root and contact material is extremelycomplex. The mass loss of the plug contact can beestimated with four different indexes, which includeintegral of current squared, thermal stress, transferredelectric charge and arc energy.2. Experimental investigation2.1. SetupThe testing circuit breaker unit is a modification ofa 245 kV/40 kA SF6 live tank self-blast HVCB. InFigure 1, the main circuit of the experimental systemis composed of a charging circuit, a capacitor bank,a dump circuit, a test current trigger circuit and atest circuit breaker. The capacitor bank is used asthe power source of the arcing current, which has acapacitance of 35 mF, a maximum charging voltageof 6.3 kV and a maximum stored energy of 695 kJ.There are four ignitrons to turn the current on oroff in the main circuit, which are the dump ignitron,DC ignitron, forward and reverse AC ignitrons. Anignitron is a gas-filled tube used to control the currentin a circuit. The arc voltage and current are measuredusing a high voltage probe (Tektronix P6015 A) and32vol. 10 no. 1/2023 Arc erosion study in high-voltage circuit breakersFigure 1. Schematic diagram of the main circuit.Figure 2. Schematic diagram of the HVCB (Top: Gas-blasting; Bottom: Free-burning).a Rogowski coil respectively, and the data is recordedby a digital oscilloscope (Tektronix DPO 2024).The schematic diagram of the HVCB unit with andwithout a nozzle is shown in Figure 2, which gives therelative positions of arcing contacts in the interruptionchamber. The tulip contact with the nozzle can movevertically along the axis of the chamber, in which thenozzle has been used to generate an axial flow onthe switching arcs. When the HVCB unit is in theopen position, the fully opened gap length betweenthe tulip contact and plug contact is around 120 mm.2.2. Experimental resultsFive consecutive arcing tests were carried out to ob-serve the repeatability in the results in the presenceof arc instability at each current level. The massof arcing contacts was measured by weighing beforeand after one group test, and the mass loss can becalculated with accuracy of 1 mg. As shown in Fig-ure 3, the mass loss of plug contact in gas-blastingcondition is larger than that in free-burning condition,especially under the condition of 35 kA current peakvalue, the average mass loss is 640 mg, twice that un-der free-burning condition. The measured arc voltage,current, power and electrical conductance waveforms(Figure 4), corresponding to gas-blasting and free-burning conditions, are presented and analyzed atthree different peak current amplitudes (5/20/35 kA).3. DiscussionIn order to define some certain criteria indicating themass loss of arcing contacts at different current levels,four typical macroscopic parameters were selected fortentative studies, which include integral of currentsquared M1, thermal stress M2, transferred electriccharge M3 and arc energy M4.Figure 3. Measured mass loss of plug contact at differ-ent current levels under gas-blasting and free-burningconditions.M1 =∫ t0i(t)2dt (1)M2 =∫ t0(|i(t)|α + q |i(t)|α+1)dt (2)M3 =∫ t0|i(t)| dt (3)M4 =∫ t0u(t) · i(t)dt (4)Where u(t), i(t) and t are arc voltage, current andarcing time, respectively, and α and q are empiri-cal constants. Parameter α varies from 1.2 to 2.0while 1.7 is most frequently used, and parameter q forSF6 HVCB has also been determined experimentally,which is 0.01 in this paper [8, 9].As shown in Figure 5, the average mass loss ofplug contact is plotted as a function of integral ofcurrent squared during arcing time, thermal stress,transferred electric charge and arc energy. Erosionprocess of electrode has a random stochastic nature.Considering that after multiple erosion, the materialand microstructure of Cu-W contacts will change,so a new contact for arc erosion was tested at eachcurrent level, and the average mass loss was used tocharacterize the erosion degree under different arcingconditions. The slope of the fitted curves can beused to characterize the increase rate of mass losswith parameters under gas-blasting and free-burningconditions. It is found that the slopes of the black andred fitting curves varying with arc energy are close toeach other, which is different from the fitting curvescorresponding to the other three parameters.Arc erosion is typically expressed as mass loss percharge. The charge transferred is calculated by mea-suring arc current and arc duration. It is determined33Y. Zhou, J. Humphries, J. Spencer, J. Yan Plasma Physics and TechnologyFigure 4. Arc voltage, current, power and electrical conductance waveforms under gas-blasting and free-burningconditions. (a) 5 kA, (b) 20 kA, (c) 35 kA.Figure 5. Mass loss of fixed arcing contacts (plug contact) as a function of (a) Integral of current squared duringarcing time; (b)Thermal stress; (c)Transferred electric charge; (d) Arc energy.34vol. 10 no. 1/2023 Arc erosion study in high-voltage circuit breakersFigure 6. (a) Schematic diagram of arc erosion process(Left: Free-burning; Right: Gas-blasting); (b) Energyexchange between electrode and arc in gas flow field.by weighing the mass of the electrode carefully be-fore and after arcing tests. The normalization ofmass loss to charge transferred works relatively wellonly when the differences of arc voltage are relativelysmall. From a physical point of view, mass loss per en-ergy is a better and more fundamental normalization.The background arc erosion physics is extremely com-plex, but the relationship between arc energy and arcerosion process can be analyzed from a macroscopicpoint of view. A schematic diagram of arc erosion pro-cess under free-burning and gas-blasting conditionsis shown in Figure 6. In free-burning condition, thecontact material is heated up and melted during thetransfer of arc energy into the electrodes. The massloss of the contacts is caused by the evaporation andsplashing erosion modes. When the strong gas flowacts on the molten material on the contact surface,it will cause greater mass loss. Therefore, the gasflow field has an important influence on the mass loss,especially in the 35 kA arcing condition.4. ConclusionIn this paper, arc erosion experimental study of gas-blasting and free-burning conditions has been doneat three different peak current levels (5/20/35 kA).The average mass loss of plug contact under gas-blasting condition was 9/93/640 mg, corresponding to5/20/35 kA arcing tests, which was greater than thatunder free-burning conditions (2/76/324 mg). Arc en-ergy can be used to build a link of arc erosion betweenthese two conditions. Further experimental and simu-lation research will be carried out to investigate thegas blowing effect on the arc erosion in HVCBs.AcknowledgementsOne of the authors would like to thank the financial sup-port from Chinese Scholarship Council (CSC).References[1] Z. Wang. Study on the Mechanisms and PredictionMethods of Arcing Contact Erosion of High-Voltage SF6 Circuit Breaker. The University of Liverpool (UnitedKingdom), 2018. doi:10.17638/03026544.[2] J. Tepper, M. Seeger, T. Votteler, et al. Investigationon erosion of Cu/W contacts in high-voltage circuitbreakers. IEEE transactions on components andpackaging technologies, 29(3):658–665, 2006.doi:10.1109/TCAPT.2006.880476.[3] Y. Cui, C. Niu, Y. Wu, et al. Experimental study onthe transformation of the W70Cu30 anode erosion modein DC gaseous arcs—better insights into mechanisms ofelectrode erosion behavior using in situ diagnosis.Journal of Physics D: Applied Physics, 52(47):474001,2019. doi:10.1088/1361-6463/ab395f.[4] Y. Cui, Y. Wu, C. Niu, et al. Evolution of anodicerosion components and heat transfer efficiency for Wand W80Ag20 in atmospheric-pressure arcs. Journal ofPhysics D: Applied Physics, 53(47):475203, 2020.doi:10.1088/1361-6463/ababcf.[5] M. Landry, O. Turcotte, and F. Brikci. A completestrategy for conducting dynamic contact resistancemeasurements on hv circuit breakers. IEEETransactions on Power Delivery, 23(2):710–716, 2008.doi:10.1109/TPWRD.2008.917694.[6] A. C. de Oliveira, E. G. da Costa, A. J. R. Serres,et al. Application of bioinspired antennas in themonitoring of high voltage circuit breakers. IEEETransactions on Power Delivery, 37(5):4418–4426, 2022.doi:10.1109/TPWRD.2022.3170309.[7] M. Mohammadhosein, K. Niayesh, A. A.Shayegani-Akmal, and H. Mohseni. Online assessmentof contact erosion in high voltage gas circuit breakersbased on different physical quantities. IEEETransactions on Power Delivery, 34(2):580–587, 2018.doi:10.1109/TPWRD.2018.2883208.[8] A. Muharemovic, M. Kapetanovic, A. Ahmethodzic,and A. Fetahagic. Arcing contacts and nozzle conditiondiagnostics by means of measure of thermal stresses. InCIGRE Colloquium, Asset Management of SwitchingEquipment and New Trends in Switching Technologies,pages 118–123, 2003.[9] M.-H. Kim, K.-H. Kim, A. Smajkic, et al. Influence ofcontact erosion on the state of SF6 gas in interrupterchambers of HV SF6 circuit breakers. In 2014 IEEEInternational Power Modulator and High VoltageConference (IPMHVC), pages 466–469. IEEE, 2014.doi:10.1109/IPMHVC.2014.7287312.35

Experimental Study of Arc Erosion in Gas-blasting and Free-burning Conditions in High-voltage Circuit Breakers

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Experimental Study of Arc Erosion in Gas-blasting and Free-burning Conditions in High-voltage Circuit Breakers

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