High Current Interruption Research Articles

Calculation of Transient Puffer Pressure Rise Takes Mechanical Compression, Nozzle Ablation, and Arc Energy Into Consideration

Thermal puffer-type gas circuit breaker (GCB) has a high dielectric and current interruption capability. In order to design a good thermal puffer GCB, it is important to know the blast pressure for arc cooling. Although pressure calculation programs have been developed and used for design work, the basic characteristics, such as contribution of nozzle ablation gas to puffer pressure rise, amount of back flow gas to puffer chamber, and pressure distribution along gas passages during current interruption, are not well known. In this paper, pressure rise, mass flow, and temperature calculations were carried out using a new calculation model, which takes mechanical compression by puffer piston, nozzle ablation in the nozzle throat and arc energy into consideration. By analysis of the calculation results, we found the pressure rise mechanism is as follows. While fixed contact located in the divergent part of nozzle, all of the ablation gas generated from the nozzle wall cannot be exhausted from the nozzle and it leads to high-pressure generation in the nozzle throat. This pressure causes transfer of hot ablation gas back to the puffer chamber via gas passage. The puffer pressure increases thermally due to temperature rise by this mechanism. At a longer arcing time, as high puffer pressure was already established in the puffer chamber, the nozzle ablation gas cannot flow back to the puffer chamber. Besides as mass flow through nozzle is limited by low gas density, the puffer pressure rise is obtained by the mechanical compression of puffer piston.

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

Measurement of the Copper Vapor Density in a Magnetically Stabilized High-current Vacuum Arc by the Laser Absorption Method

The high-current interruption ability of the vacuum interrupter depends on the state of the residual plasma remaining between electrodes after an current zero. In this study, the copper vapor density around the current zero with a half-period of 1 ms and a peak current of 3 kA arc was measured using the laser absorption method. The copper vapor density found to be 8×1017 m-3 at current zero and was found to be independent of current zero gradients and arc current peak. After current zero, the copper vapor density decayed with a time constant of approximately 400 μs. The decay time observation by LIF signal agreed well with that of the absorption method. This decay time of the copper vapor density can be explained based on the calculation of the cooling characteristics of the cathode spot crater which supplies copper vapor.

Multilayer contact material based on copper and chromium material and its interruption ability

Contact material based on copper and chromium (CuCr) is widely used for vacuum interrupters (VIs) and has found worldwide acceptance in medium-voltage applications, especially for high-current interruption. Contact material with a weight content of chromium between 25 and 60 wt.% is almost exclusively used. A new contact material was established based on a multilayer system to improve the interruption ability and mechanical properties and reduce the contact resistance. After a combined sintering and melting process in a high-vacuum furnace, a material of high density and low gas content is produced. The finished blank consists of the following layers: CuCr-sheathing, copper bulk material, and a stainless-steel support resulting from the lost mold. It turned out that the higher thermal and electrical conductivity as well as mechanical properties of the multilayer contact material improved the interruption ability of the VI. Investigations of switching behaviors were carried out in standard VIs. Additionally, the standard chromium content of 25 wt.% in CuCr and the influence of higher chromium content was investigated with respect to interruption ability. Afterwards, the microstructure on the contact surface was analyzed with scanning electron microscopy and energy dispersive X-ray.

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.

Technical Trend of Environment-friendly High Voltage Vacuum Circuit Breaker (VCB).

Vacuum Circuit Breakers (VCBs) have widely been used for low and medium voltage level, because of their high current interruption performance, maintenance free operations and environment-friendly characteristics. The VCB is now going to be applied to higher voltage systems for transmission and substation use. In this paper, the recent technical trend and future perspectives of high voltage VCBs are described, as well as their technical background.

Recovery of breakdown strength of a vacuum interrupter after extinction of high currents

Relevant phenomena during the period of the recovery of the dielectric strength of vacuum interrupter (VI) are reviewed. Metal vapor, residual charge and the effects of molten contact surfaces reduce the breakdown strength after the interruption of high currents. Metal droplets seem to play only a secondary role during the recovery phase. Instability of liquid protrusions is suspected to initiate breakdown if the electric field strength exceeds 10 kV/mm at the molten contact surfaces (undisturbed field). Key parameters are surface temperature and vapor density. Breakdown during recovery of the dielectric strength depends not only on the value of the voltage applied but also on the duration of the high voltage stress. A spontaneous triggering event in the presence of metal vapor appears to initiate breakdown at conditions below the Paschen breakdown limit. This type of breakdown events limits the interruption performance of VI's.

Condensed metal vapor on alumina ceramic in vacuum interrupters

Investigations have been carried out on the dielectric performance of the ceramic (high-purity alumina, Al/sub 2/O/sub 3/) surface in vacuum interrupters after switching. In order to examine the influence of the shielding on the protection of the ceramic surface against metal vapor condensation different types of vacuum interrupters (VIs) have been tested: VIs with and without shielding. Additionally, two contact materials CuCr: 75:25 wt% and WCAg: 56:4:40 wt% have been investigated to compare the adhesion of different metal vapors to alumina ceramic surfaces. After having performed a HV conditioning of the VIs, dc arcs with arbitrary arcing times were triggered between the contacts simulating the generation of metal vapor during high current interruption and load break switching. Between the arcing tests the insulation levels of all VIs have been tested by means of HV ac source. Afterwards the VIs were opened and the microstructure of the metallic condensate on the inner ceramic surface was analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The integral chemical composition of the metallic film was investigated by inductive coupled plasma (ICP).

Effects of Cr content on the interruption ability of CuCr contact materials

The effects of Cr content in CuCr contact materials, especially on high current interruption, have mostly been examined in experimental chambers rather than in actual vacuum interrupters (VIs). Possible interactions of the contacts with their surroundings, both electromechanical and gaseous, may require commercial VIs for a more realistic test determination of the effects of Cr content on the overall performance. In this work, the Cr content in CuCr contacts is varied from 5 wt% to 75 wt% and tested in our 38-kV axial magnetic field (AMF) type VIs. The material properties of electrical conductivity, hardness and total VI resistance are measured as a function of the Cr content. AC and impulse voltage withstand capabilities are tested before and after short-circuit current interruption tests. Contact erosion behavior is examined with VIs subjected to only a half cycle arcing duty. Results show that for this particular AMF VI design, a 30 wt% Cr content gives the best current interruption performance.

Vacuum interrupters with axial magnetic field contacts based on bipolar and quadrupolar design

Axial magnetic field (AMF) contacts are applied within vacuum interrupters especially for high short-circuit currents. In this paper, two AMF contact designs based on a bipolar and a quadrupolar magnetic field arrangement and their characteristics are presented. In the first section, both principles are discussed. This is followed by three-dimensional field simulations performed by means of a finite-element-analysis program. The magnitude of the axial magnetic flux density, the phase shift between current and magnetic flux density, and the residual AMF after current zero are investigated during arcing with a constant contact gap. Furthermore, the influence of motion during the contact opening on the previously-mentioned parameters is investigated. An important parameter during the design phase of AMF electrodes is the electromagnetic attractive force, which is provided by the AMF contacts during current flow. This force can reduce the required contact force provided by the drive of the vacuum circuit breaker. Finally, it is reported about the short-circuit performance of both contact systems. Contact plates after high-current interruption are presented revealing the arcing behavior during the high-current phase.

Short-circuit phenomenon through hot gas ejected from molded case circuit breakers during high current interruption process and prevention of its occurrence

An experimental investigation on short-circuit phenomenon through ejected hot gas between source-side terminals in molded case circuit breakers (MCCBs) was performed. The rate of occurrence of the short-circuit phenomenon was found to increase with the peak value of the breaking current and with the order of the breaking test. The conductance of the ejected hot gas was also found to rise with the peak value of the breaking current and with the order of the breaking test. These results indicate that the hot gas of high conductance is the cause of the short-circuit phenomenon. Some effective means were taken in the MCCB to reduce the conductance of the hot gas. Decreasing the conductance of the hot gas successfully prevented the occurrence of short-circuit phenomenon. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 22–29, 2000

Physical and theoretical aspects of a new vacuum arc control technology-self arc diffusion by electrode: SADE

Our new vacuum arc control technology SADE doubles the high current interruption capability of our conventional axial magnetic field technology. First, we describe the vacuum arc motion behavior recorded by a high speed charge-coupled device video camera. This arc behavior is closely related to axial magnetic field intensity. In particular, it depends on the profile of the externally generated axial magnetic field. The anode spot is likely to move to the highest magnetic field intensity. Second, we describe analytical results for concentration of vacuum arc at the anode side contact surface. This analysis implies the possibility of an ideal magnetic field profile and intensity for vacuum arc control. Finally, we describe experimental results for vacuum arc control compared with the physical and theoretical results mentioned above, and we show a practical electrode configuration for vacuum interrupters and its application in a high current interruption experiment.

Transition from constricted to diffuse vacuum arc modes during high AC current interruption

Modes of high AC current vacuum arcs between butt contacts at a fixed gap of 10 mm during the decrease of current to zero, in the current range from 8-25 kA peak, were characterized. Three groups of arc modes were featured: (1) constricted without or with a small number of autonomous cathode spots, (2) constricted with a considerable number of cathode spots beyond the concentrated cathode root, and (3) diffuse modes. It was shown that the most typical high-current vacuum arc mode during a decreasing current is the local constricted discharge situated on the contact edge, which coexists with a dissipate discharge created by groups of autonomous cathode spots. The threshold current for the transition from the constricted to diffuse arc was measured.

High-current interruption in vacuum circuit breakers

High-current interruption in vacuum circuit breakers

High-current interruption in vacuum circuit breakers

The aim of this project was to find a correlation between contact gap length and switching behavior of a vacuum circuit breaker. A large number of interruption experiments were executed in a vacuum chamber with butt type contacts made of Cu, CuCr 50/50 and AgWC. The currents to be interrupted varied from 2.5 to 32 kA. The rate of change of current and recovery voltage were kept at a fixed value at current zero. Many re-ignitions of the dielectric type, scattered over a wide range of re-ignition voltages, were observed and only a few of the thermal type. The total amount of energy dissipated in the vacuum chamber appears to be determinative for the type of re-ignition. On Cu severe anode spot melting was found, whereas CuCr and AgWC suffered little anode melting. The wide range of re-ignition voltage values found shows that a straight correlation with the contact gap length can not be defined. At 5 to 10 /spl mu/s after current zero a 'second' post arc current did appear.

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.

Conductance Diagnostics in Hot Gas Ejected from a Molded Case Circuit Breaker during High Current Arc Interruption

Conductance Diagnostics in Hot Gas Ejected from a Molded Case Circuit Breaker during High Current Arc Interruption

Numerical modeling of vacuum arc interruption based on the simplified plasma equations

The paper presents the numerical implementation of the state-variable model of the high current arc interruption. The differential equations governing the sheath development in vacuum plasma after the main frequency current zero (CZ) are coupled with the electrical circuit equations representing the power system and solved simultaneously using Advanced Continuous Simulation Language software (ACSL). The mathematical formulation of the are interruption is in the form of a black-box, i.e. the two "external" variables are voltage, u(t) and current, i(t). Other black-box variables are "internal", i.e. they are only needed to specify the physical conditions of the arc plasma. These internal variables are: plasma density, N/sub io/, its space distribution between contacts at CZ and its time decay due to diffusion, ion velocity, v/sub i/, time delay between the beginning of the Transient Recovery Voltage (TRV) and CZ, t/sub o/, and the equivalent arc diameter at current zero, D.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Possibility of high current interruption of vacuum interrupter with low surge contact material: improved Ag-WC

High-current interruption experiments were carried out on low-surge contact material Ag-WC set in axial magnetic field electrodes. The most influential factors on high-current interruption are the contact material, the axial magnetic field, and the initial opening speed. Though the interruption ability of conventional contact material was limited up to 20 kA, the ability of the improved material rose up to 40 kA in the test using the laboratory model vacuum circuit breaker.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Capacitor switching capability of vacuum interrupter with CuW contact material

The authors carried out shunt capacitor switching tests on 24 kV model vacuum interrupters with contact materials CuW and CuCr. The restriking probability of the contact material CuW is lower than that of CuCr. The contact material CuW is also an excellent candidate for shunt capacitor switching except for its high current interruption ability. The restriking probability of a 24 kV, 25 kA vacuum interrupter with contact material CuW is calculated as 10/sup -5/, which is practically zero.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>