Post-arc Current Research Articles

Post-arc Current Measurement in Mechanical Circuit Breakers for Hvdc Applications

Post-arc currents contain valuable information on the breaker’s performance. In this paper, the dimensioning procedure for a measurement system for such currents, based on a diode clamped shunt resistor is presented. Based on synthetic low and high power tests, the performance of a mock-up is evaluated. Finally, the post-arc current of a model gas circuit breaker, designed for use in DC applications, is measured.

Influence of the AMF Arc Control on Voltage Distribution of Double-Break VCBs

This paper investigates the influence of the axial magnetic field (AMF) arc control on voltage distribution (VD) of double-break vacuum circuit breakers (VCBs) in order to gain balanced VD, and thus enhance the breaking capacity. The interaction of vacuum arc plasma, postarc current (PAC), and AMF is discussed. We conduct the breaking test of double-break VCBs with externally applied AMF of a different pulsewidth, magnitude, and a different moment. The PAC, postarc charge, and the VD are measured to analyze the relationship between the AMF arc control and the VD. The optimal AMF arc control and the relationship between the AMF magnitude and the unbalanced voltage ratio are gained when the grading capacitors were 400 pF. The experimental test showed that the proper AMF arc control can improve the unbalanced VD. The mechanism is that the proper AMF arc control can make the postarc charge small and stable, so the unbalanced postarc charge, which caused the unbalanced VD is limited.

Investigation on the current-zero characteristic of vacuum circuit breakers

The current-zero characteristic of vacuum circuit breakers (VCBs) has an important influence on the dynamic dielectric recovery and the success of the breaking test. In the paper, the characteristic of the post-arc current, post-arc charge and the post-arc conductance at current-zero is researched to obtain the influence of the arc memory on the current-zero characteristic and the post-arc characteristic. Based on the synthetic test circuit, the test plat of the current-zero characteristic is set up and the test VCB is a transparency vacuum interrupter in order to observe the development and extinguishing process of the vacuum arc by the high speed CMOS camera. The distribution law of post-arc characteristic is gained by measuring and processing the post-arc current. The relationship between the post arc charge and the final position of last cathode spot is investigated. The current-zero characteristic of VCBs supply the base for controlling vacuum arc, improving the breaking capacity, which maybe also useful to VCBs with multi-break.

Research of Arc Chamber Optimization Techniques Based on Flow Field and Arc Joint Simulation

The preliminary design of an arc chamber in the 550 kV SF6 circuit breaker was proposed in accordance with the technical requirements and design experience. The structural optimization was carried out according to the no-load flow field simulation results and verified by no-load pressure measurement. Based on load simulation results such as temperature field variation at the arc area and the tendency of post arc current under different recovery voltage, the second optimal design was completed and its correctness was certificated by a breaking test. Results demonstrate that the interrupting capacity of an arc chamber can be evaluated by the comparison of the gas medium recovery speed and post arc current growth rate.

Research on the Reignition Problem and Interruption Characteristics of Series Connected Vacuum Interrupters

When vacuum interrupters are connected in series, some merits of this structure will be seen and a lot of improvements are expected. This paper describes our investigations on the reignition problem and interruption characteristics of series connected vacuum interrupters. In vacuum interrupters, CuCr (Cr: 25%) is not sufficient at the voltage level <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&gt;}{\rm 120}~{\rm kV}$</tex></formula> because of saturation of material. Thus, we should add some material or use completely new material to replace it. By connecting two interrupters in series, the reignition problem sufficiently reduced. Simultaneously, compared with spiral electrode, axial magnetic field has an advantage on voltage sharing because it has a smaller fluctuation of postarc current. In addition, this was confirmed by the experiments with practical ac vacuum interrupters and nuclear fusion experiment dc interrupters. For dc circuit breakers (CBs), because of special characteristic, insulation recovers instantly, and this can be used for dc current breaker for subway and Tokamak nuclear experimental devices. For the application of ac CBs, as with series connection, no reignition happens, and it can be used in the Japanese market for the section separator in super express train.

Diagnostics of the Cathode Sheath Expansion After Current Zero in a Vacuum Circuit Breaker

Langmuir probes operating in the electron saturation current mode were used to detect the time of the arrival of the cathode sheath at the probe position. The probe current was measured just before and after current zero (CZ) followed the transient recovery voltage in a gap with copper electrodes. Probe measurements were accompanied with the detection of the postarc currents. Basic plasma parameters such as electron temperature and density were measured in the vicinity of the arcing gap. The data set allowed us to reconstruct the sheath dynamics after CZ.

Interaction of a Vacuum Arc With an SF6 Arc in a Hybrid Circuit Breaker During High-Current Interruption

A hybrid circuit breaker consists of a series-connected vacuum- and SF6 interrupter. The vacuum interrupter has the function to withstand very steep-rising transient recovery voltages, whereas the SF6 interrupter is stressed with the peak of it. Full scale tests are described of a 145-kV prototype, which is subjected to short-line faults based on 63 kA. During these tests, current through the breaker and voltages across both interrupters were monitored with a high-resolution measurement system. It is shown that the principal idea works correctly. From measured results, it is demonstrated that the interaction between the two arcs of completely different physical nature has a positive effect on the interruption: Immediately before current zero, the SF6 arc assists the vacuum arc to interrupt, whereas after current zero, the vacuum arc assists the SF6 arc in the recovery against the recovery voltage. From the analysis of the measurements, it becomes clear that high values of post arc current (up to 30 A) have (at least initially) a positive effect on the breaker performance. Detailed modeling of the interaction of arc-arc and arc-circuit is described, showing a good agreement with the measured results. The model is used to predict the voltage distribution across both interrupters when other (capacitive) voltage grading is applied in the design than present during the tests.

Vacuum circuit breaker current-zero phenomena

Post-arc current phenomena that occur when interrupting high currents with vacuum circuit breakers have been investigated. High resolution measuring equipment has been used to measure both the post-arc current and the arc voltage in the current-zero region. Three examples of frequently observed phenomena are described. The first describes the phenomenon that in the event of a current-chopping, the current is zero for a short period of time just before the natural alternating current zero, but continues to flow afterwards, in the form of a post-arc current. The second and third example deal with the post-arc phenomena after currents that are much higher than the test breaker's rated short-circuit current. These examples show a low-voltage period after current-zero. Apparently, during this post-arc period, the residual plasma between the breaker's contacts conduct well. In addition to the voltage-zero period, the voltage trace in the third example also shows evidence of current-chopping. This means that the plasma conducts poorly just before current-zero, but conducts well immediately afterwards. The post-arc current model of Andrews and Varey is verified with measurements.

Influence of contact distance on the appearance of vacuum arcs with different AMF contacts

Measurements with vacuum interrupters equipped with bipolar axial magnetic field (AMF) contacts have shown that the post-arc current magnitude and its duration fall with shortened arcing time, and decreasing gap distance, respectively. Simulations of post-arc currents point out that this dependency may result either from different arc diameters or different ion densities around current zero. To clarify this, high-speed movies of vacuum arcs up to 60 kA root mean square were taken, using contacts with a bipolar and quadrupolar axial magnetic field structure. The gap distance was varied by delayed contact opening. Moreover, switching experiments with sealed experimental interrupters under 36 kV conditions with a bipolar AMF arrangement in comparison with a quadrupolar arrangement showed that the bipolar contacts yielded higher interruption capability, in correlation with lower post-arc currents. In order to study the reasons for these phenomena, optical investigations of the arc appearance were carried out under variation of the relevant parameters.

Investigations on the series connection of two switching gaps in one tube in vacuum

Presently, there is a wide interest to study the extension of the vacuum switching principle toward higher voltages. This work studies the behavior of two vacuum arc gaps in series within the same vacuum vessel. The arrangement investigated uses a common center shield for both gaps, yielding asymmetrical conditions in the high-current, as well as in the post-arc phase. The voltage distribution during arcing is nearly equal at low and at high currents, while in an intermediate range, a strong asymmetry exists. The arc where the shield has anodic polarity stays diffuse and remains at a lower voltage, while the other, already constricted arc is characterized by a considerably higher, fluctuating voltage. Investigations with only one gap show that the post-arc current is higher when the shield is post-arc cathode because this current is determined by the growth of a space-charge sheath in front of the cathode. Consequently, in a double-break arrangement where the post-arc current is the same for both gaps, the voltage distribution is uneven in the sense that during the post-arc current flow the gap with the cathodic shield takes over a lower portion of the total transient recovery voltage (TRV). Despite the uneven voltage distribution, the breaking capacity of a double-break arrangement more than doubles in comparison with that of a single break. In case of the breakdown of the first gap, the other gap often takes over the complete TRV temporarily without final failure of both gaps.

Effects of multiple interruptions on post-arc current, reignition, and lifetime of distribution breaker

The purpose of this investigation is to study the interruption performance of the Molded Case Circuit Breaker (MCCB) currently used for the protection of low-voltage circuits. It is anticipated that interruptions, especially numerous high-current interruptions, will degrade interruption performance. In order to investigate the performance change after many interruptions, it is important to understand the interruption characteristics. Multiple-interruption experiments at large currents were conducted and the phenomena which govern the success or failure of interruption were identified. It was shown that after multiple interruptions a post-arc current begins to flow and that the duration of the arc is ten to a few hundred microseconds. In order to explore the relationship between the post-arc current and the degradation of the interruption characteristics, the conditions governing the post-arc current were investigated experimentally. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(4): 42–49, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10358

Analysis of Thermal Recovery for SF6 Gas-Blast Arc within Laval Nozzle

In this paper we describe a method of estimating the thermal recovery characteristics in a Laval nozzle. The post arc current was calculated according to the decreasing rates of current and the upstream pressures. A two-dimensional differential arc model was used to analyze the arcing phenomena. The radiation energy transport and the turbulence effects were calculated using the semi-experimental arc radiation model and the Prandtl mixing length model, respectively. The electric field and the magnetic field were calculated with the same grid structure used for the simulation of the flow field. The arc model has been coded into “PHOENICS” which is a commercial computational fluid dynamics (CFD) program. In order to investigate the thermal recovery characteristics after current zero, the simulation of steady-state arc of 1000 A DC, the simulation of transient arc generated by the current which decreases with the rate of di/dt=27.0 and 13.5 A/µs before current zero, and the simulation of hot-gas flow were carried out in an upstream pressure range of 0.68–6.82 MPa. The obtained results were verified by comparison with the test results presented by the research group of GE Co. (General Electric Company).

Current-zero measurements of vacuum circuit breakers interrupting short-line faults

Current zero measurements are performed during short-line fault interruption tests of vacuum circuit breakers. This switching cycle is characterized by a very steep transient recovery voltage. High-resolution measurements of near current-zero arc current and voltage were carried out. Various reignition modes (occurring between 0 and 75 ms after current zero) were observed due to insufficient arcing time or current in excess of the short-circuit breaking current. The relationship between post-arc current/charge, reignition mode, and transient recovery voltage is discussed in this paper. In addition to the classical post-arc current, already described in the literature, another late post-arc current was observed reaching values up to several tens of amperes after severe thermal arcing stress. All interrupters interrupted at the first or second current zero under the rated conditions of short-line fault current and transient recovery voltage.

Current zero behavior of vacuum interrupters with bipolar and quadrupolar AMF contacts

Axial magnetic field (AMF) contacts are applied in vacuum circuit breakers to interrupt high short-circuit currents. A magnetic field parallel to the current flow in the arc column improves the breaking capacity by affecting the arc mode. Depending on the design of the contacts, this magnetic field can take different directions over the contact surface. In this paper, measurements of bipolar and quadrupolar AMF contact systems are presented. For bipolar arrangements, the polarity of the field changes once and for quadrupolar arrangements twice. Due to different eddy current paths, the residual magnetic field at current zero is significantly higher for the quadrupolar arrangement. The breaking capability of two contact systems was investigated and completed by measuring the post arc current.

Post-arc Current and Re-ignition after Many Interruptions by MCCB and the Endurance

The purpose of this investigation is experimental research of many interruption performance for Molded Case Circuit Breaker (MCCB) currently used for the protection of a low voltage circuit. It is anticipated by interruption especially by high current many interruptions that the interruption performance will decrease. In order to investigate the performance change by many interruptions, it is important to grasp an interruption characteristic.The interruption experiment was conducted in large current for many times, and phenomena which are one of factors of the successes or failure of interruption, were observed. By carrying out the numbers of interruption it is shown that post-arc current begins to flow and duration of the arc is ten to a few hundred micro seconds. In order to explore relation between post-arc current and a decrease of an interruption characteristics, experiment conditions of post-arc current was investigated.

Post-arc current reconstruction based on actual circuit breaker measurements

During short line fault (SLF) tests on three poles of a 72.5 kV, 31.5 kA, 60 Hz SF6 puffer circuit breaker, some remarkably large post-arc currents were measured. For all the measurements performed on the three poles of the specific breaker, no physical post-arc currents could be detected in the measurement data, except for two cases. Both ‘post-arc currents’ occurred as a last successful interruption of a circuit breaker pole. After these specific interruptions, the circuit breaker poles were degraded so much that only reignitions occurred. In order to verify the observed ‘post-arc currents’, computations are made based on the more accurate voltage measurements.

Influence of interrupted current amplitude on the post-arc current and gap recovery after current zero-experiment and simulation

For commercial vacuum circuit interrupter valves with radial field contact, the post-arc current (PAC) waveform was measured after short circuit current interruption applying a transient recovery voltage (TRV) of about 15 kV/s (RRRV). Keeping the current decline di/dt at current zero constant, the power frequency (PF) current amplitude I/spl circ//sub PF/ was varied from 0.5 up to two times of the rated short circuit current. Significant influence of I/spl circ//sub PF/ on the gaps memory is shown in particular effecting the post-arc current duration which varies in a range between 2 and 8 /spl mu/s. Based on the existing physical models an interpretation of the results is given. It is shown that the memory effect influences the gap recovery time. The experimental results were further used to determine the parameters of the sheath growth model described by Andrews and Varey (1971). The initial ion density is fitted according to the current ramp di/dt before current zero (CZ) and according to the measured Q/sub PF/=/spl int/i/sub PF//spl times/dt during the arcing phase. The results of two different test procedures were applied in order to separate the effect of current ramp di/dt and Q/sub PF/=/spl int/i/sub PF//spl times/dt. The influence of both parameters and of the rate of rise of the recovery voltage du/dt (RRRV) on the sheath edge velocity could be demonstrated by simulation.

Upon the influence of the post-arc current on the low voltage switching process in vacuum

The paper presents one stage of the scientific research, performed for the investigation of the post-arc (p.a.) current within low voltage switching process in vacuum, when interrupting short-circuit currents of high values. A large power equipment, supplied by the mains and providing an accurate reproduction of the processes, concerning the short circuit phenomenon (U=1.5 kV; I=100 kA) was used. An experimental model, which can reproduce the switching conditions of the power circuit-breaker in vacuum, was available as well. The influence of an axial magnetic field on the p.a. current and the switching process was also explored.

Dielectric recovery of copper chromium vacuum interrupter contacts after short-circuit interruption

The recovery of a vacuum interrupter gap after short-circuit interruption was measured by application of an overshooting transient recovery voltage (TRV) several tens of microseconds after current zero. Copper chromium contact materials were employed varying in composition (25 and 50% chromium content), gas content, and production method. The gap failure was either pure dielectric or it was dominated by a significant postarc current. Therefore, postarc current phenomena were experimentally investigated focused on the relationship among the postarc current, the power frequency current amplitude, and the gap length. It was found that two postarc current maxima exist: the first strongly dependent on the power frequency current, and the second on the field strength. A correlation among postarc current facilitated failures, the ultimately dielectric recovery, and the erosion rate of the material was found. Strong indication is given that all of these effects are dominated by the metal vapor pressure rise given by the constricted rotating arc. A significant influence of the material properties can be drawn from these experiments, allowing a good estimation of the capability for short-circuit current interruption, thus providing a useful tool for material development.

Measurements and modeling in the current zero region of vacuum circuit breakers for high current interruption

Post-arc current and voltage measurements with high time resolution were carried out with industrial vacuum circuit breakers for investigating their current zero conditions and current interruption. Based on experimental results, plasma parameters were estimated by means of a modified "continuous transition model." Dielectric effects in the post-arc current zero region were detected and modeled. At lower current amplitudes (I/spl circ/<16 kA), typical post-arc currents were obtained. At higher current amplitudes, the probability of higher post-arc current charges increases without the occurrence of breakdowns. It has been shown that charge generation takes place in the post-arc current region.