The surface average temperature and the electrode temperature distribution are key parameters to predict the electrode erosion. Experimental research on the arc erosion has been carried out in a model circuit breaker, in which CO2 is filled in the chamber and Cu-W is used as the contact material. The surface average temperatures of plug contact exposed to electric arc with sinusoidal currents of 5kA were determined by a high-speed pyroscope. In order to establish a relationship between the average temperature of the contact surface and current squared, the data statistics and fitting curves in the current-rising and current-falling stages were given. It has been found that there are two different types of arc erosion processes by comparing the temperature-current squared curves. In other words, the structure of contact surface and the electrode material change significantly after repeated arc erosions

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.2023.1.20Plasma Physics and Technology 10(1):20–23, 2023 © Department of Physics, FEE CTU in Prague, 2023SURFACE AVERAGE TEMPERATURE MEASUREMENT OF CU-WCONTACT MATERIAL BURNING IN CO2: PRELIMINARY STUDYY. Zhou, J. Humphries, J. Spencer∗, J. YanDepartment of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, U. K.∗ joe@liverpool.ac.ukAbstract. The surface average temperature and the electrode temperature distribution are keyparameters to predict the electrode erosion. Experimental research on the arc erosion has been carriedout in a model circuit breaker, in which CO2 is filled in the chamber and Cu-W is used as the contactmaterial. The surface average temperatures of plug contact exposed to electric arc with sinusoidalcurrents of 5 kA were determined by a high-speed pyroscope. In order to establish a relationshipbetween the average temperature of the contact surface and current squared, the data statistics andfitting curves in the current-rising and current-falling stages were given. It has been found that thereare two different types of arc erosion processes by comparing the temperature-current squared curves.In other words, the structure of contact surface and the electrode material change significantly afterrepeated arc erosions.Keywords: circuit breaker, CO2, switching arc, surface temperature.1. IntroductionElectrode temperature measurement has been intro-duced and developed in the field of contactors [1],vacuum interrupters [2–4] and gas circuit breakers[5, 6] from low-voltage to medium and high-voltagelevels. Contact surface temperature, which plays animportant role in the recovery of the post-arc dielectricstrength, was measured for different types of contactmaterials in molded case circuit breakers [1, 5, 6]. Interms of vacuum interrupters, the main purpose ofanode surface temperature measurement is to deter-mine the current interrupting performance, which ismust not exceed a certain limit temperature. In dif-ferent types of contact structure, such as plate, axialor transversal magnetic field contacts, the movementbehavior of arc root and the current density value willbe different, which changes the electrode temperaturedistribution [2–4].At the arcing stage [3, 4] or post-arc stage [1, 2, 5, 6]under different current levels, the methods for mea-suring the contact surface temperature can be dividedinto three categories, which are optical emission spec-troscopy in the near infrared spectral range (NIR),video thermography and pyrometry [3]. The advan-tage of NIR spectroscopy is that it does not need totake into account the change of the emissivity withtemperature and surface condition. But the NIR spec-tra should be measured at the fixed position of thecontact surface with an exposure time of 1 ms or less[3], which makes the measured temperatures averagedvalues with stronger weighting of the higher tempera-tures. Thermography has high temporal and spatialresolution of the temperature determination. Duringthe arcing period, the plasma radiation should beconsidered and subtracted out from the total signalof high-speed camera. The surface temperature canbe obtained from the ratio between two or multipleradiation intensities without knowledge of the emis-sivity. Pyrometry is a common method to measurethe average temperature of contact surface, whosetemperature range is 200–4000 K and acquisition timebetween 10 µs and 1 s. Pyrometer, as commerciallyavailable devices, has simple setup and arrangement.So far, there are few researches on the temperaturemeasurement of arcing contacts in high-voltage gascircuit breakers. In this contribution, experimentalresearch on the arc erosion has been carried out ina model circuit breaker [7]. Considering that car-bon dioxide (CO2) is the main SF6 alternative gasaddressed for high-voltage and medium-voltage appli-cations, CO2 was chosen and filled in the chamber.Copper-tungsten (Cu-W) was used as the contact ma-terial, which is 40/60 weight percent by infiltration sin-tering method [8]. The surface average temperaturesof plug contact exposed to electric arc with sinusoidalcurrents of 5 kA were determined by a high-speedpyroscope. By comparing the temperature–currentsquared curves, it has been found that there are twodifferent types of arc erosion processes.2. Experimental investigation2.1. SetupAs shown in Figure 1, a schematic overview of the opti-cal arrangement includes two important experimentalequipment, a high-speed pyrometer (Kleiber 740-LO)and a high-speed camera (Phantom V710). Investi-gations in the center of the plug contact were doneby using a high-speed pyrometer, which is equippedwith a special filter at 2.00-2.20 µm for an extendedmeasured range. Temporal resolution was in the mi-crosecond timescale with the response time of 6 µs.20vol. 10 no. 1/2023 Surface temperature measurement of Cu-W contactFigure 1. Optical scheme of arc erosion test, including anode surface temperature measurement by a high-speedpyrometer and observation of arc root, arc column or droplets/particles by a high-speed camera.Figure 2. Schematic diagram of plasma calibrationto obtain reasonable electrode temperature by parallelmeasurement method.Considering that the arc light has an effect on thesignal of the pyrometer during arcing period, it isnecessary to carry out the calibration work by keep-ing the optical fibre parallel to the tip of the plugcontact (receiving the arc light only) and to obtainthe reasonable surface temperature by subtracting theapproximation of plasma contribution (Figure 2). Theoptical signal entering the high-speed camera is rich,including information of the arc column, arc root anddroplets/particles. Through a reasonable combinationof filter, aperture and exposure time, images of thearc root, arc column and splashing droplets at themoment of arc extinction can be obtained, which is ofgreat help to the analysis of the arc erosion process.Before the arcing contacts are separated, a lowand slowly decaying DC current passes the arcingcontacts and maintains an arc for tens of milliseconds.At a certain point in time after contact separation,a positive half cycle AC current then is generated,and the arc is extinguished automatically at the firstFigure 3. Arc voltage and current waveforms of fourconsecutive arc erosion tests (peak current of 5 kA).current zero crossing point. Since the trigger unit ofthe main circuit and the operating mechanism of thecircuit breaker have a certain degree of dispersion, andconsidering the instability of the arc, it is necessary tocarefully compare the voltage and current waveformsin the continuous arcing tests. The arc voltage andcurrent of four consecutive arc erosion tests are shownin Figure 3.2.2. Experimental resultsDuring short-circuit current interrupting operationsin gas circuit breakers, a considerable part of energyreleased by the switching arc is transferred to the arc-ing contacts and nozzles. Arc voltage and current aretaken as the most basic electrical parameters, fromwhich the arc power can be calculated. In order torelate the average temperature of each test to the arcpower, it is plotted as a time-varying curve as shownin Figure 4. Since the surface average temperature(between −6 ms and −2 ms) exceeds the measurement21Y. Zhou, J. Humphries, J. Spencer, J. Yan Plasma Physics and TechnologyFigure 4. (a) Anode surface average temperature and (b) power waveforms during arcing period.Figure 5. Relationships between surface average temperature and current squared (a) Data statistics in the current-rising stage; (b) Fitting curves in the current-rising stage; (c) Data statistics in the current-falling stage; (d) Fittingcurves in the current-falling stage.range of the pyrometer, the output signal of the high-speed pyrometer is saturated. Therefore, only thetemperature change curves in the current-rising andcurrent-falling stages are given. During the currentrising stage (−9 ms to −4.5 ms), the arc voltage in-creases steadily with the arc length, and the arc poweralso increases quasi-linearly. As the average tempera-ture of the contact surface increases with the numberof erosion, the thermal response of the contact mate-rial to the energy injected into the electrode by the22vol. 10 no. 1/2023 Surface temperature measurement of Cu-W contactFigure 6. Images at the moment of arc extinction(a) the first few arc erosion tests (without splashingdroplets); (b) the last arc erosion test (with splashingdroplets).arc also changes significantly (that is, the amount oftemperature change per unit time). During the cur-rent falling stage (−4.5 ms to 0 ms), the arc voltagebegins to fluctuate significantly due to the instabilityof the arc column (usually related to the arc shape,arc root movement, etc.). The average temperatureof the contacts begins to drop rapidly, and it can befound that the temperature curve corresponding tothe last test (case d) drops the fastest.3. DiscussionIn order to better describe the change process ofelectrode surface average temperature, the surfacetemperate and current squared are linked together,and the relationship diagrams for the current-risingand current-falling stages are drawn respectively, asshown in Figure 5. It can be found that the sur-face average temperature of the last test (case d) issignificantly different from the previous three cases(a/b/c), that is, there are two different erosion modesin the arcing process under the peak current conditionof 5 kA (evaporation-dominated mode with/withoutsplashing). With the increase in the arcing tests, theevaporation-dominant erosion mode will change fromnon-splashing to splashing type. Through the obser-vation of the arc root area of the plug contact at themoment of arc extinguishing by the high-speed cam-era, bright splashing droplets appeared in the last test(as shown in Figure 6), but this phenomenon was notobserved in the previous few times. This also verifiedthe above point of view.With repeated arc erosion, the copper content of thecontact surface will be reduced. During the currentrising stage, the temperature of the contact materialwill increase rapidly due to the weakening of the cool-ing effect of the copper phase (that is, the copperremoves heat through evaporation, thereby reducingthe temperature of the tungsten skeleton). During thecurrent falling stage, due to the phenomenon of splash-ing droplets, which will take away a part of the energyof the electrode, the contact surface temperature willdrop rapidly.4. ConclusionIn this contribution, experimental research on thearc erosion has been carried out in a model circuitbreaker and the surface average temperature of Cu-Wcontact material has been determined by pyroscope.The energy flux injected from the electric arc heatedup and melted the electrode material. By comparingthe temperature-current squared curves at currentrising/falling stage, it is found that the evaporation-dominant erosion mode has non-splashing and splash-ing types, which has been verified through the obser-vation of the bright droplets/particles at the momentof arc extinguishing. More accurate two-dimensionalelectrode temperature determination by thermographywill be carried out in the future.AcknowledgementsOne of the authors would like to thank the financial sup-port from Chinese Scholarship Council (CSC).References[1] J. J. Shea and X. Zhou. Contact material and arccurrent effect on post-current zero contact surfacetemperature. IEEE Transactions on Components andPackaging Technologies, 29(2):286–293, 2006.doi:10.1109/TCAPT.2006.875881.[2] A. V. Schneider, S. A. Popov, A. V. Batrakov, et al.Anode temperature and plasma sheath dynamics ofhigh current vacuum arc after current zero. IEEETransactions on Plasma Science, 41(8):2022–2028, 2013.doi:10.1109/TPS.2013.2266920.[3] R. Methling, S. Franke, S. Gortschakow, et al. Anodesurface temperature determination in high-currentvacuum arcs by different methods. IEEE Transactionson Plasma Science, 45(8):2099–2107, 2017.doi:10.1109/TPS.2017.2712562.[4] T. Pieniak, M. Kurrat, and D. Gentsch. Surfacetemperature analysis of transversal magnetic fieldcontacts using a thermography camera. IEEETransactions on Plasma Science, 45(8):2157–2163, 2017.doi:10.1109/TPS.2017.2707667.[5] Y. Cui, Y. Wu, H. Sun, et al. A novel method fordetermining the electrode temperature effect on post-arcbreakdown characteristics. In 2022 6th InternationalConference on Electric Power Equipment-SwitchingTechnology (ICEPE-ST), pages 157–160. IEEE, 2022.doi:10.1109/ICEPE-ST51904.2022.9757077.[6] 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.[7] Z. Wang. Study on the Mechanisms and PredictionMethods of Arcing Contact Erosion of High-Voltage SF6Circuit Breaker. The University of Liverpool (UnitedKingdom), 2018. doi:10.17638/03026544.[8] C. Hou, X. Song, F. Tang, et al. W–cu compositeswith submicron-and nanostructures: progress andchallenges. NPG Asia Materials, 11(1):74, 2019.doi:10.1038/s41427-019-0179-x.23

Surface Average Temperature Measurement of Cu-W Contact Material Burning in CO2: Preliminary Study

https://ojs.cvut.cz/ojs/index.php/PPT/article/download/9105/6912

Surface Average Temperature Measurement of Cu-W Contact Material Burning in CO2: Preliminary Study

Abstract

Similar works

Full text

Available Versions

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