Low voltage switching apparatuses efficiency depends on the speed of movement of the switching arc from the contacts to the quenching chamber. The paper is focused on investigation of this movement of an arc. Measurement of radiation spectra of the electric arc burning inside miniature circuit breaker and moving to quenching chamber are presented. Measured radiation spectra contain suitable atomic spectra lines for calculation purposes. The problems connected with the measurements are discussed. The main part of the paper deals with a calculation of temperature of the investigated plasma of the arc. Atomic lines database of National Institute of Standards and Technology was used as a spectral data source for the calculations

Pecek, D.

Simek, D.

English

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

doi:10.14311/ppt.2017.3.265Plasma Physics and Technology 4(3):265–268, 2017 © Department of Physics, FEE CTU in Prague, 2017EXPERIMENTAL TEMPERATURE MEASUREMENTS IN MINIATURECIRCUIT BREAKERD. Simek∗, D. PecekFaculty of Electrical Engineering and Communication, Brno University of Technology, Technicka 3058/10,616 00 Brno, Czech Republic∗ xsimek18@stud.feec.vutbr.czAbstract. Low voltage switching apparatuses efficiency depends on the speed of movement of theswitching arc from the contacts to the quenching chamber. The paper is focused on investigation ofthis movement of an arc. Measurement of radiation spectra of the electric arc burning inside miniaturecircuit breaker and moving to quenching chamber are presented. Measured radiation spectra containsuitable atomic spectra lines for calculation purposes. The problems connected with the measurementsare discussed. The main part of the paper deals with a calculation of temperature of the investigatedplasma of the arc. Atomic lines database of National Institute of Standards and Technology was usedas a spectral data source for the calculations.Keywords: switching arc, miniature circuit breaker, atomic emission spectroscopy, temperaturemeasurement.1. IntroductionLow voltage circuit breakers are electrical apparatuseswidely used for breaking of short-circuit currents andoverloads. Those devices are divided into three maingroups: miniature circuit breakers (MCB), moldedcase circuit breakers (MCCB) and air circuit breakers(ACB). Miniature circuit breakers are the smallestbreakers of those groups. These devices are the mostcommon devices in the standard switchboards.One of the crucial parameters of circuit breaker isa breaking capacity, which depends on arcing timeof MCB. Long arcing time may cause damages dueto a very high temperature of an arc. On the otherhand, short arcing time may create overvoltage acrossthe insulation. Arcing time is affected by movementspeed of contacts, arc movement from contact area tothe quenching chamber and quenching chamber effi-ciency. Arc movement between the moving contactsof MCB were experimentally observed recently usinglaser arc imaging technology [1]. Another approachof an analysis of this phenomenon are computer simu-lations. Some interesting simulations of the contactopening process were presented in [2]. Simulation ofarc movement to the quenching chamber includingtemperature calculation inside MCB under specificconditions was performed [3]. Temperature maximumwas found at about 20 000K in this simulation.The temperature of an arc is significant parameterof quenching. The main goal of our measurement wasto find out the development of the arc temperatureduring switching off process because of its effects tothe speed of quenching. Optical emission spectroscopywas used as a mean of obtaining the arc temperatureinside the MCB. MCBs are usually made of plastic,silver plated copper and ferromagnetic materials whichare all affected by the arc. Parts whose are in directcontact with an arc are generally made of copper.Therefore, plasma inside miniature circuit breakeroften contains copper vapour, which is clearly visiblein its radiation spectrum. It allows calculation of thetemperature and other important physical propertiesusing atomic lines of copper.Figure 1. Block diagram of emission spectra measure-ment.Block diagram of measuring circuit is shown inFigure 1. Spectrometer was used as measuring instru-ment. CCD chip is commonly used as a detector.2. Experimental setupMeasurements were performed in the High current lab-oratory of the Centre for Research and Utilization ofRenewable Energy. 16MVA three phase asynchronousgenerator was used as a power supply. Excitation ofgenerator were 13%. Series of special resistors andcoils were used for the current and power factor ad-justment. Current flew to the test bench 1 throughthe 16MVA high current transformer with conversionrate 4800V/250V. Investigated device was miniaturecircuit breaker with B characteristic, nominal currentof 10A and tripping capacity of 10 kA. Optical fiberwas used for necessary separation of measuring devicesfrom the power circuit and transmission of light froma specific position to the input slit of the spectrom-eter. The Avantes Avaspec ULS-3648TEC was usedas spectrometer. Data were stored and processed inlaptop using AvaSoft 8.0 software.265D. Simek, D. Pecek Plasma Physics and TechnologyFigure 2. Diagnostic holes positions (investigatedpoints).The arc was burning inside the circuit breaker, thussmall holes were drilled for diagnostic purposes alongthe arc runner, see Figure 2.3. Measurement procedure1. Test circuit were calibrated to these parameters:Uef = 42V, Ief = 2.8 kA, cosϕ = 0.5, f = 50Hz.2. Calibration of spectral sensitivity of the spectrom-eter was carried out.3. Optical fiber was adjusted to the investigatedpoint 1.4. Test circuit was switched on and the overloadwas interrpted by the tested sample.5. Radiation spectrum was saved into the laptop.6. Procedure from 3 to 4 was repeated several times.7. Optical fiber was shifted to next point and spectrawere saved.8. Radiation spectra lines were identified.9. Relative radiation intensities of suitable lines werecalculated.10. Boltzmann plot was created for each point andthe temperature was calculated.11. Temperatures for each point were plotted intothe graph ordered from the nearest to the fearthestdistance from the contact pair of the breaker.12. High speed videos of investigated points weretaken in second part of measurements.4. Results and discussionThe high-speed video were taken by a Photron SA-X2high-speed camera. One picture of the high-speedvideo is shown in the Figure 3.Figure 3. Picture cut out of high-speed video.In this case, voltage and current were measured bydata acquisition system of the laboratory during thetest. Waveforms of voltage and current during theone of tests are presented in the Figure 4.High-speed video in combination with waveformsallow evaluation of important parameters of the test.Evaluated parameters are presented in the Table 1.Parameter Units ValueVoltage switching peak (V) 100Maximum current (A) 880Switching off time (ms) 2.5Reaction time (ms) close to zeroLever movement delay (ms) 0.8Lever movement duration (ms) 4.2Table 1. Important parameters of the test.Example of radiation spectrum can be seen in theFigure 5. Radiation spectrum of copper is suitablefor calculation purposes, because it contains appropri-ate lines. The spectral lines are intensive and haveappropriate distance between each other. Copper wasprobably evaporated from the arc-runner or contacts.λ measured λ database Element510.2 nm 510.6 nm copper514.9 nm 515.3 nm copper520.5 nm 520.9 nm silver521.4 nm 521.8 nm copper546.2 nm 546.5 nm silver577.9 nm 578.2 nm copperTable 2. Assignment of elements.Measured spectral lines were assigned to elements266vol. 4 no. 3/2017 Experimental Temperature Measurements in Miniature Circuit BreakerFigure 4. Waveforms of voltage and current during the test.Figure 5. Example of the spectrum measured at the point 5.using NIST database [4], see table 2 .Figure 6. Temperatures measured at investigated points.Temperatures measured at investigated points arepresented in the Figure 6.The arc temperature was calculated about 15 600Kas maximum temperature near the contact systemof the breaker. The temperature sharply decreaseswith decreasing distance from the contact system to8 600K at the point 3. At the point 4, there is anincrease of temperature to 10 600K. At the point 5temperature decreases to 9 000K because of splitterplates cooling.It is important to mention that the temperaturecalculation may be affected by a few complications.The first one is a spectral lines shape deviation. Itdepends on spectrometer resolution and measurementconditions. The second problem corresponds withdatabase using. The transition strength and the tran-sition probability, or Einstein coefficient were takenfrom the NIST database. The NIST database statesthat the values used for calculations has accuracy ofC+ class. That means accuracy more than 82%.Another problem is related to the database usingagain. NIST database cannot cover all experiment con-ditions of the spectral line measurement. That meansthat the database contains lines measured under dif-ferent pressures, humidity, ambient temperatures etc.267D. Simek, D. Pecek Plasma Physics and Technology5. ConclusionsThe aim of the measurement was to find out the tem-perature of the arc inside miniature circuit breakerduring the switching off proccess. Temperatures mea-sured at investigated points are presented in Figure 6.Atomic emission spectroscopy was used for spec-tra measurement. High-speed videos helped to findout important times for diagnostic of the breakerbehaviour under this conditions. Temperature wascalculated from the relative intensity of spectral linesof copper. Calculated values correspond to realisticassumptions, although the calculation contains sim-plifying assumptions.AcknowledgementsAuthors gratefully acknowledge financial supports fromthe Ministry of Education, Youth and Sports of the CzechRepublic (NPU I programme, project No. LO1210 andfaculty project No. FEKT-S-17-4374) and from the CzechScience Foundation under project No. GA 15-14829S.References[1] J. Qu, S. Yuan, Q. Wang, and X. Li. Application oflaser arc imaging technology to observe arc behaviourand contact motion. Plasma Physics and Technology,2(2):183–186, 2015. URL:http://ppt.fel.cvut.cz/articles/2015/qu.pdf.[2] Y. Wu, M. Rong, Z. Sun, X. Wang, F. Yang, and X. Li.Numerical analysis of arc plasma behaviour duringcontact opening process in low-voltage switching device.Journal of Physics D: Applied Physics, 40(3):795–802,2007. doi:10.1088/0022-3727/40/3/016.[3] M. Rong, F. Yang, Y. Wu, A. B. Murphy, W. Wang,and J. Guo. Simulation of arc characteristics inminiature circuit breaker. IEEE Transactions onPlasma Science, 38(9):2306–2311, 2010.doi:10.1109/TPS.2010.2050703.[4] National Institute of Standards and Technology.Atomic spectra database lines form. URL:https://physics.nist.gov/PhysRefData/ASD/lines_form.html.268

Experimental Temperature Measurements in Miniature Circuit Breaker

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Experimental Temperature Measurements in Miniature Circuit Breaker

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