This paper reports on experiments with ultra-high pressure nitrogen arcs in a self-blast type switch design. The effect of filling pressure on nozzle mass loss and pressure-rise in the heating volume were investigated. An arc current peak of 130 A at 190 Hz and a fixed inter-electrode gap of 50 mm were used throughout the experiment. The arc burns inside a polytetrafluoroethylene nozzle with a gas outflow vent in the middle. Nitrogen filling pressure of 1 bar, 20 bar, and 40 bar was tested, which also covers the supercritical region. Moreover, to study the effect of vent size on blow pressure near current zero, three different vent dimensions were investigated.  By increasing the filling pressure, the energy deposited in the arc increases as a result of increased arcing voltage. It was observed that the pressure-rise in the heating volume is linked to the filling pressure, while the vent size plays a crucial role in the blow pressure near current zero. The nozzle mass loss per unit energy deposited in the arc is found to be independent of the filling pressure

Abid, F.

Niayesh, K.

Støa-Aanensen, N. S.

English

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

doi:10.14311/ppt.2019.1.23Plasma Physics and Technology 6(1):23–26, 2019 © Department of Physics, FEE CTU in Prague, 2019NOZZLE WEAR AND PRESSURE RISE IN HEATING VOLUME OFSELF-BLAST TYPE ULTRA-HIGH PRESSURE NITROGEN ARCF. Abida,∗, K.Niayesha, N. Støa-Aanensenba Department of Electric Power Engineering, Norwegian University of Science and Technology, 7491, Trondheim,Norwayb SINTEF Energy Research, 7465, Trondheim, Norway∗ fahim.abid@ntnu.noAbstract. This paper reports on experiments with ultra-high pressure nitrogen arcs in a self-blasttype switch design. The effect of filling pressure on nozzle mass loss and pressure-rise in the heatingvolume is investigated. An arc current peak of 130A at 190Hz, and a fixed inter-electrode gap of50mm are used. The arc burns inside a polytetrafluoroethylene nozzle with a gas outflow vent in themiddle. Three different nitrogen filling pressures were tested: 1, 20 and 40 bar, which also covers thesupercritical region. To study the effect of vent size on blow pressure near current zero, three differentvent dimensions were investigated. The energy deposited in the arc increases with the filling pressure.It is observed that the pressure-rise in the heating volume is linked to the filling pressure, while thevent size plays a crucial role in the blow pressure near current zero. The nozzle mass loss per unitenergy deposited in the arc is found to be independent of the filling pressure.Keywords: ultrahigh pressure arc, nozzle wear, supercritical fluid, arc discharge.1. IntroductionThe interruption chamber of a medium voltage (MV)gas circuit breaker is generally filled at atmosphericpressure or at a slightly elevated pressure of a fewbar. Due to safety reasons, these MV gas circuitbreakers are almost never filled with extremely highpressure. For gas circuit breakers, the interruptionperformance is believed to be related to filling pressuredue to the increase of gas flow rate near current zero(CZ) [1]. Switchgears placed at the seabed for subseapower transfer applications have the potential to befilled with extremely high filling pressure. By fillingthe interrupting chambers of such switchgears at thesurrounding pressure, the complexity and cost of theencapsulation can be substantially reduced.When the pressure and temperature of a gas exceeda critical point, the gas enters into the supercritical(SC) region. High density, high heat conductivity, highdiffusivity, absence of vapour bubbles and self-healingproperties are some of the unique features of an SCfluid. For gas circuit breakers, the properties of SCfluids are believed to be in favour of improved currentinterruption performance [2]. For nitrogen (N2), thecritical point is 126K and 33.5 bar. Nitrogen is chosenin this work due to its environmentally benign nature,good insulation strength and low critical pressure.There are few publications on gas discharges inultra-high pressure medium in general, among whichalmost none of them cover high energy arc dischargestypical for power switching applications [2, 3]. Re-cently, some efforts have been made to investigate arcdischarges in SC N2 at tens of bars filling pressure.The arc voltage is reported to increase with fillingpressure, without any abrupt change during the tran-sition from gas to SC state [4]. A higher arc voltageresults in an increased energy deposition in the arcchannel. Moreover, the arc radius decreases as thefilling pressure increases [5].To investigate the effect of gas flow for very highpressure arc discharges, a self-blast arrangement isadopted in this paper. A self-blast switch design isstudied in a fixed electrode arrangement where the arcburns inside a polytetrafluoroethylene (PTFE) nozzlewith a gas outflow vent in the middle. During the highcurrent phase, the PTFE nozzle will ablate. Some ofthe ablated mass escapes through the vent and therest causes a pressure rise in the heating volume. Thecompressed gas in the heating volume creates a back-flow of relatively cold gas near CZ to cool the arc forcurrent interruption. To study the effect of vent sizeon blow pressure near CZ, three different vent dimen-sions are investigated. Experiments are conducted atthree different N2 filling pressures: 1 bar (atmosphericpressure), 20 bar and 40 bar (supercritical region). Inthis paper, the effect of filling pressure on mass lossof the PTFE nozzle and consecutive pressure rise inthe heating volume is reported.2. Experimental setupThe electrical setup is shown in Figure 1(a). Thetest circuit consists of the charging and dischargingsections of a 7.2µF high voltage (HV) capacitor bank,C. The capacitor bank is charged through a diode-resistance unit (RC–DC) from a HV source. Once thecapacitor bank is charged to a predefined voltage, it isdisconnected from the grid by switch SC. Afterwards,23F. Abid, K. Niayesh, N. Støa-Aanensen Plasma Physics and TechnologyHV sourceVoltage measurement CRC DCSERELArcing chamberSDSCFlangePenetratorHV miniature cableMetal structureInsulator supportHV probePressure tank(a) Current measurementCTRVRTRV(b) Ring electrodePin electrode Figure 1. Experiment setup, (a) electrical circuit, (b) interior connection of the pressure tank.4 mm50 mm25 mmIHeating volume [3.17 cm3]Ring electrodePin electrodePTFE tubeVentPressure sensor(d) Φ Φ= 2 mm4 mm4 mm4 mm(a) (b) (c) Φ= 3 mm Φ= 3 mm Figure 2. Cross sectional view of the vent of threedesigns. (a) design a, (b) design b, (c) design c.Electrode arrangement, nozzle, heating volume, (d)Longitudinal view.the switch SD is closed which results in a currentflow through the inductor, L and further through acopper ignition wire (40 µm diameter) inside the arcingchamber. The inductance of L, and the chargingvoltage of C are kept constant to generate a currentamplitude of 130 A in the first half cycle at a frequencyof 190 Hz for all the experiments conducted. As the arcresistance varies with the filling pressure, the dampingof the LC oscillation also changes. Hence, only thefirst half cycle is considered for all cases. A parallelresistive-capacitive branch (RTRV–CTRV) is placedacross the arc to generate a controlled initial rate ofrise of recovery voltage (IRRRV) of 43V/ µs after CZ,see Figure 1(a).A pressure tank of 15.7 litres rated for 500 bar, isused as arcing chamber. The interior connection of thepressure tank is shown schematically in Figure 1(b).A HV miniature cable is inserted into the pressuretank using a cable penetrator. The arc burns betweenthe pin and the ring electrode. The arc is initiatedby melting of a copper ignition wire. To investigatethe effect of gas flow on the arc based on self-blastprinciple, the arc is ignited inside a 4mm diameterPTFE nozzle with vents in the middle. The electrodearrangement, nozzle and the heating volume are shownschematically in Figure 2(d). A heating volume of3.17 cm3 is attached on the ring electrode where theablated gas is stored during the high current phaseand generates a back-flow of the stored gas near CZ. Inthis paper, three different vent sizes are investigated:2 opposite holes of Φ = 2mm (design a), 2 oppositeholes of Φ = 3mm (design b), and 4 opposite holes Φ= 3mm (design c), see Figure 2(a-c). Three differentfilling pressures are investigated in this paper: 1 bar,20 bar and 40 bar, which also covers the supercriticalregion. For each filling pressure all three designs aretested with a new nozzle.A HV probe measures the arc voltage across theelectrodes while a current shunt is used to measure thearc current. A piezoelectric pressure sensor is mountedon the heating volume to measure the pressure rise,as can be seen in Figure 2(d). The pressure sensoris recess-mounted, and a vinyl electric tape is usedto protect it from the thermal blast. All the dataare sent to the control room via optical fibre linksand stored in a digital oscilloscope with a samplingrate of ten samples per microsecond. For mass lossmeasurement, weight measurement with an accuracyof 0.1mg is carried out before and after five tests ofall the new nozzles.3. Results and discussionsA typical measurement of the arc voltage, arc current,and pressure rise in the heating volume for design aat 40 bar filling pressure is shown in Figure 3. Theignition wire melts at approximately 0.2ms markedby a voltage peak. The pressure in the heating volumestarts building from approximately 0.5ms. The pres-sure rises to a maximum of 13.5 bar at approximately0.8ms. Afterwards, the back-flow of stored gas fromheating volume starts and flows out completely atapproximately 2.9ms. The CZ occurs approximately24vol. 6 no. 1/2019 Ultra-high pressure nitrogen arc Figure 3. Arc voltage, current and pressure rise inheating volume for design a at a filling pressure of40 bar.at 2.61ms where the current is interrupted by the self-blast test switch. The over-pressure in the heatingvolume at CZ in this case is approximately 1.64 bar.The back-flow of stored gas in heating volume nearCZ cools the arc, which can be seen by the extinctionpeak of the arc voltage.3.1. Pressure rise in heating volumeThe measured over-pressures in the heating volumefor three designs at three different filling pressures areplotted in Figure 4. The measured pressure-rise in theheating volume is different for different vent dimen-sions. As the hole size in the vent is increased, moreablated PTFE vapour leaves the arcing zone throughthe vent instead of contributing to the pressure buildup in heating volume. As a result, design a showshigher pressure rise in comparison with design b andc for any specific filling pressure.The vent dimension also plays a crucial role in theoutflow of the stored gas. The heated N2 and PTFEvapour flows out more slowly in design a comparedto other designs. In contrast to design a, the storedgas leaves completely in design b at approximately1.75ms. As a result the over-pressure at CZ is low fordesign b. For design c however, a negative pressurerise in the heating volume is observed at 20 bar and40 bar filling pressure, indicating a gas intake throughthe hole.The filling pressure also has a significant effect onthe pressure-rise in the heating volume. For all designs,the highest pressure rise is observed for 40 bar fillingpressure, followed by 20 bar and 1 bar. The rate ofchange of over-pressure in the heating volume aroundCZ determines the gas flow rate, hence, the effectivecooling of the arc. The measured over-pressures atCZ for all the cases tested are presented in Table 1.3.2. Mass loss of PTFE nozzleFive tests were conducted for each filling pressure andfor each design. Among them, the only design thatresulted in successful current interruption in the first Figure 4. Pressure rise in the heating volume as afunction of filling pressure for different designs.Filling pressure [bar] 1 20 40Design a 0.81 1.31 1.64Design b 0.27 0.53 0.28Design c 0.15 0.96 1.07Table 1. Over-pressure in the heating volume at CZ[bar].two CZ was design a. The current interruption indesign b and c happened after first, second or severalhalf cycles. Consequently, only design a is consideredfor mass loss analysis.As the filling pressure increases, the energy deposi-tion in the arc increases too as a result of the increasedarcing voltage. From the measured arc voltage andarc current, the energy deposited in each test is cal-culated until the current is interrupted. At 1 bar, atotal nozzle mass loss of 9.2mg was measured afterfive tests, while the total energy deposition of fivetests was approximately 313 J. For 20 bar and 40 bar,the mass losses measured after 5 tests were 31.1mg(851 J) and 42.3mg (1186 J), respectively. Afterwards,the mass loss per unit energy deposited in the arc atdifferent filling pressure is calculated, which is shownin Table 2. It can be seen that although the overallmass loss in PTFE nozzle increases with the fillingpressure, the mass loss per unit energy deposition isnot strongly dependent on the gas pressure.3.3. Current interruption performanceThe number of successful interruptions after first halfcycle among the five tests conducted for each case areplotted in Figure 5. For design a at 1 bar pressure,the current was interrupted 4 times among the 5 testsconducted. The number of successful interruptionincreased to 5 out of 5 for both 20 bar and 40 barfilling pressure using design a. For design b, however,the interruption performance deteriorated for all fillingpressures. Interruption performance is observed to25F. Abid, K. Niayesh, N. Støa-Aanensen Plasma Physics and TechnologyFilling pressure [bar] 1 20 40Total energy deposited [J] 313 851 1186Mass loss [mg] 9.2 31.1 42.3Mass loss/energy [mg/kJ] 29.4 36.5 35.7Table 2. Nozzle mass loss as a function of fillingpressure. Figure 5. Number of successful interruption amongthe five tests conducted at different filling pressures forthree designs.deteriorate as the filling pressure increases for designc.For a successful current interruption, effective cool-ing of the arc is necessary. The arc resistance build-upjust before CZ is a key parameter for a successful cur-rent interruption [6]. As the gas filling pressure isincreased, the arc radius decreases, while the tem-perature of the arc column increases. Without thesufficient flow at a higher filling pressure (i.e., 20 bar,40 bar), the arc resistance fails to build up before CZresulting in a poor interruption performance. The rateof change of overpressure near CZ is high in designa for all the filling pressures tested in comparison toother designs, see Figure 4. The gas flow due to highrate of change of over-pressure near CZ results in animproved cooling of the arc and hence, better inter-ruption performance for design a. The filling pressurealso affects the flow field near CZ [7]. Without suffi-cient cooling of the arc, the high filling pressure candeteriorate the interruption performance, in this casedesign b, and c. This paper underpins the importanceof gas flow near CZ for ultra-high pressure N2 arc forcurrent interruption application.4. ConclusionsThe mass loss of PTFE nozzle, pressure rise in theheating volume and interruption performance for arcburning at different filling pressure of nitrogen arereported in this paper. To study the effect of vent sizeon blow pressure near current zero, three different ventdimensions are studied. Based on the experimentalresults following conclusions have been drawn.1. The pressure rise in the heating volume increaseswith the filling pressure. The outlet vent dimensionplays a decisive role in both the pressure rise in theheating volume and the back-flow near CZ. Withproper designing the interruption performance canbe improved for ultra-high pressure nitrogen arcs.2. Total nozzle mass loss is found to increase withthe filling pressure. A high filling pressure alsoconstitutes for a high energy deposition in the arcas a result of high arcing voltage. Nevertheless, themass loss per unit energy deposition in the arc isfound to be less dependent on filling pressures.AcknowledgementsThis work is supported by the Research Council of Norway,project number 280539.References[1] W. Hermann and K. Ragaller. Theoretical descriptionof the current interruption in HV gas blast breakers.IEEE Transactions on Power Apparatus and systems,96(5):1546–1555, 1977.doi:10.1109/T-PAS.1977.32483.[2] J. Zhang, E. van Heesch, F. Beckers, A. Pemen,R. Smeets, T. Namihira, and A. Markosyan. Breakdownstrength and dielectric recovery in a high pressuresupercritical nitrogen switch. IEEE Transactions onDielectrics and Electrical Insulation, 22(4):1823–1832,2015. doi:10.1109/TDEI.2015.005013.[3] T. Kiyan, A. Uemura, B. C. Roy, T. Namihira,M. Hara, M. Sasaki, M. Goto, and H. Akiyama.Negative DC prebreakdown phenomena andbreakdown-voltage characteristics of pressurized carbondioxide up to supercritical conditions. IEEEtransactions on plasma science, 35(3):656–662, 2007.doi:10.1109/TPS.2007.896774.[4] F. Abid, K. Niayesh, E. Jonsson, N. S. Støa-Aanensen,and M. Runde. Arc voltage characteristics inultrahigh-pressure nitrogen including supercriticalregion. IEEE Transactions on Plasma Science,46(1):187–193, 2018. doi:10.1109/TPS.2017.2778800.[5] F. Abid, K. Niayesh, and N. S. StÃÿa-Aanensen.Ultrahigh-pressure nitrogen arcs burning insidecylindrical tubes. IEEE Transactions on PlasmaScience, 47(1):754–761, Jan 2019.doi:10.1109/TPS.2018.2880841.[6] M. Seeger, B. Galletti, R. Bini, V. Dousset,A. Iordanidis, D. Over, N. Mahdizadeh, M. Schwinne,P. Stoller, and T. Votteler. Some aspects of currentinterruption physics in high voltage circuit breakers.Contributions to Plasma Physics, 54(2):225–234, 2014.doi:10.1002/ctpp.201310067.[7] Z. Guo, X. Li, Y. Zhang, X. Guo, and J. Xiong.Investigation on the influence of gas pressure on CO2arc characteristics in high-voltage gas circuit breakers.Plasma Physics and Technology, 4(1):95–98, 2017.26

Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc

https://ojs.cvut.cz/ojs/index.php/PPT/article/download/5581/5163

Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc

Abstract

Similar works

Full text

Available Versions

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