Circuit Breaker Contacts Research Articles

Characterization of the Surface Layer of Ag/W Electrical Contacts

Materials for electrical contacts in circuit breakers must meet a stringent set of property requirements including excellent thermal conductivity, electrical conductivity, corrosion resistance and arc erosion resistance [1]. In most cases, no simple metallic alloy can meet these requirements, and metal-matrix composites must be used instead. The metallic matrix phase in such composites is usually silver, due to its excellent electrical properties, and the most common reinforcements used are Mo, W and WC [2]. The properties of the composite depend critically on microstructural parameters such as phase volume fractions, morphologies and distributions. Here we present data from our studies on Ag/W composite contacts and some of the potential complications in the characterization of such materials are discussed.

Research on High Voltage Circuit Breaker Mechanical Faults Online Monitoring

In power transformation and distribution system, unplanned blackouts caused by high voltage circuit breaker faults accounted for more than 60% of the total accidents [, most of the circuit breaker faults are caused by mechanical faults. Base on circuit breaker electrical characteristics, this paper present a method of circuit breaker mechanical faults on-line monitoring. Switching on-off of circuit breakers contacts can be equivalent to a time-varying capacitance, based on equivalent circuit model, the relationship between reactive component and time can be concluded. Processing circuit breakers contacts electric signals with orthogonal decomposition and least squares curve fitting method to highlight the main characteristics of the mechanical faults. These processed data collected from different running state can create a database, taking this database as diagnostic basis to diagnose whether mechanical faults occur to circuit breaker.

Monitoring of HV Generator Circuit Breaker Contact Ablation Based on Acoustic Emission

High-voltage (HV) generator circuit breaker (GCB) is a key protective element for isolating HV generators in case of faults, or operational reasons. GCB typically has a double contact system. During the breaking operation process of the GCB, at first the nominal contact opens; after a while, the arcing contact opens with a minimum time-elapse between the two operations. An arc ignites when the arcing contact opens. This arc should concern the arcing contact only because the nominal contact is not designed to withstand arcs. However, after each operation the arcing contact is slightly ablated because of the arc. The ablation due to arcing makes the contact shorter and shorter. Therefore, the time interval between the two opening operations also gets shorter. For proper operation of the GCB, a minimum time interval for the commutation of the current from the nominal contact system to the ablation contact system has to be assured. In this paper, a noninvasive direct ablation measurement method based on acoustic emission is presented. This is aimed at monitoring the delay in the time instant of the start of arcing contact touch as it gets shorter due to ablation, from the acoustic emission signals. Test results carried out on real breakers substantiate the proposed approach.

The Design of the Vacuum Circuit Breaker Contact Quality Detection System Based on FPGA

According to the characteristics of vacuum circuit breaker contacts infrared image, put forward a kind of easy hardware implementation of the dynamic threshold Prewitt edge detection and refinement algorithm. Using DSP Builder designed realtime vacuum circuit breaker contacts quality realtime online detection system based on FPGA and used hardware circuit simulation in Matlab and Simulink environment, the simulation results show this design method has many advantages: the edges fine, positioning accuracy high and truly reflect the physical boundary. Realized the vacuum arcing chamber contact wear realtime online detection function, the abrasion of the vacuum arcing chamber contact timely is displayed to monitor staff, and ensured reliable work of the vacuum circuit breaker.

Influence of Eddy Current Effect on the Circuit Breaker Contact Mechanism Heat Loss

With the three-dimensional field analysis software Ansoft Maxwell 3D, the three-dimensional finite element model of the contacts pair is established. They belong to a kind of miniature circuit breaker. The simulation is carried out in the transient magnetic field. Under the condition with or without eddy current effect, we get the position and numerical solution of the contact mechanism heat loss under different short-circuit current.

Investigation of the Arc of a Vacuum Circuit Breaker in a fixed Gap using the Triggering method.

Abstract When the contacts of a Vacuum circuit breaker (VCB) with current flowing through it, is separated, an arc is generated. The Arc is usually supported by ionized gas or ionized metal vapour derived form the metal contact. This arc is an essential component of the interrupting process and capability of the Vacuum circuit breaker. The object of this paper is to trigger, record, observe and analyze the dynamic image of the Vacuum arc when it ignites in a short gap and at a low voltage. A CMOS high speed digital camera will be used to record the images of the arc. The characteristics of the arc in its diffused and constricted state, the degree of changes between the two states, and the direct relationship between the voltage and current will also be observed. The life time of the Vacuum arc will be 10ms

SF6 high voltage circuit breaker contact systems under lightning impulse and very fast transient voltage stress

In the past few years gas insulated high voltage circuit breakers have improved considerably, in particular with respect to required drive energy for operation, compactness and reliability. A further reduction in size implies increasing operational field stress inside the breaker and, thus, a reduction in built-in safety margins. If the design comes closer to its physical limits, in particular the dielectric coordination of the contact systems becomes more and more challenging. The aim of the present work is to identify factors that may influence the dielectric coordination of contact systems with reduced coordination margin. The breakdown probability distribution of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> insulated multi-contact systems was investigated with the focus on two aspects. First of all, the breakdown probabilities under lightning impulse (LI) stress were measured. These indicated that it is not feasible to extrapolate the breakdown probability curves of single contacts to a combined full contact system. Secondly, the findings on the same contact system stressed with very fast transient voltages (VFT) showed a considerable reduction in breakdown voltage and suggested a significant increase in the main contact breakdown probability, compared to the LI tests. The results and interpretation within this work identified the polarity and voltage shape dependent breakdown initiation of different contacts as causes for circuit breaker contact system failure.

초고압 SF6 가스 차단기 투입 시 아크접촉자 내전압 특성 연구

The non-controlled closing of High-voltage SF6 gas circuit breaker can cause transient current and overvoltage in the field. The controlled closing technology is an effective way to reduce transient current and voltage, prevent equipment failures, and improve power quality. For the development of controlled closing, it is obviously necessary to determine the withstand voltage between arc contacts of High-voltage SF6 gas circuit breaker in making operation. This paper focuses on decrease of pressure and density of SF6 gas that can affect withstand voltage between arc contacts in making operation. The dielectric strength between arc contacts could be improved by minimizing the decrement of pressure and density of SF6 gas obtained by simulation and test and moreover the rate of decrease of dielectric strength (RDDS) of arc contacts could be foreseen.

Study of Carbon Nanotubes in Cu-Cr Metal Matrix Composites

A novel metal matrix composite (MMC), Cu-Cr-MWCNT (copper-chromium-multiwalled carbon nanotube), was manufactured using a powder metallurgy technique. Cu-Cr alloy is widely adopted for contacts in vacuum circuit breakers. MWCNT was incorporated in an effort to enhance electrical conductivity and decrease the usage of Cr as strategic metal. Optimized milling conditions and sintering profiles were utilized to minimize any significant damage to the MWCNTs but yet provide homogeneous distribution of all constituents. Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to determine the crystal structure orientation, microstructure, and morphology, respectively, of the composite. Raman peak shift and intensity ratios assessed the stresses induced and the degree of disorder of MWCNTs in the composite. TEM indicated carbide and oxide formations in the composite. SEM images revealed the presence of MWCNTs within the metal matrix. The corrosion resistances of the composite with and without MWCNTs was determined by cyclic potentiodynamic polarization (ASTM F 2129-08) in phosphate buffer saline solution at 37 °C.

Numerical Study on Arc Plasma Behavior During Arc Commutation Process in Direct Current Circuit Breaker

This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker (DCCB) contact system. A three-dimensional magneto-hydrodynamic (MHD) model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.

Research on Opening and Closing Process for Outdoor Vacuum Circuit Breaker Contacts

As is known that the vacuum circuit breaker contact materials of breaking capacity and welding performance are affected by the mechanical properties and fracture characteristics of contact material, but they haven't been paid attention now. The mechanical failure for circuit breaker contact wear is studied and the process characteristics are described for contact opening and closing. When the thermal stress analysis for the moving contact is finished, the displacement and stress cloud map can be gotten by the thermal deformation of moving contact. When the crash analysis for the static and moving contact is finished, the deformation of contact can be gotten. In this analysis, a reference will be provided for the same type of circuit breaker contacts designed in the future and some relevant measures can be taken to prolong the mechanical life of breakers.

차단기 트립코일 이상감지 장치

The circuit breaker of power distribution board is essential part for the protection of electrical disaster from load short, trouble of power system. For the normal operation of circuit breaker, trip coil of the circuit breaker can cut the mechanical contact of circuit breaker from the detection of power system troubles.BR This paper presents a design and experimental results of trip coil fault detection system for the real time monitoring of the circuit breaker. The designed system is consisted by the trip coil fault detector which is connected to the each circuit breaker and remote monitoring unit. The trip coil fault detector can detect the impedance and operating voltage of the trip coil, and the detected values are compared with the normal state. And the remote monitoring unit can be connected to the 32 channels of trip coil fault detectors by serial communication. From the designed system, the fault and normal states of the trip coil can be remotely monitored in real time.BR The designed system is verified by the practical circuit breaker of power distribution board. And the results shows the effectiveness of the designed system.

Effect of temperature on mechanical characteristics of copper–chromium composite

The structure, hardness, strength and plasticity of a microlayer Cu–Cr composite for interrupter contacts in vacuum circuit breakers, which is obtained by electron beam physical vapour deposition, were studied over a temperature range of 290–1070 K. Correlation between the hardness and strength of the composite was established.

Synthesis of a nanocrystalline composite W–25 wt.%Ag powder by high energy milling

W–Ag pseudo-alloys are used in electric contacts of circuit breakers. They are produced by sintering of W–Ag powder mixtures followed by hot pressing or rolling to increase density. High energy milling (HEM) can enhance sintering of systems that present low sinterability because it improves dispersion, promotes refinement of the phases and produces composite particles. This work investigates the effect of HEM upon a W–25 wt.%Ag powder mixture. Phase dispersion, evolution of the shape and size of the particles during milling and the influence of strain on the crystal structure are investigated. The milled powders consist of composite particles that were formed in the first 25 h of milling. Longer milling times improve the distribution of phases inside the composite particles. The formation of the composite particles involves sequential steps of deformation, fragmentation, cold welding, work hardening and piercing of particles of the hard phase in the soft phase. The crystal lattice of W and Cu is damaged, but is not amorphized.

Investigation on Erosion of Cu/W Contacts in High-Voltage Circuit Breakers

The prediction and understanding of the erosion process of the Cu/W arcing contacts in high-voltage circuit breakers is important for the improvement of the breaker lifetime. The change of the contact geometry due to erosion is a main factor, which influences the lifetime. It is known that the ablation of contact material depends at least on parameters like the arcing current-amplitude, arcing time, total charge, and contact material properties. Based on experimental results, a method for an improved prediction of the erosion was derived. The experiments have been carried out in a SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> self-blast circuit breaker test device with commercial high-voltage circuit breaker contacts at a current amplitude up to 45kA RMS and arcing time up to 17ms. From the power balance at the electrodes, the material erosion due to evaporation is calculated. The resulting erosion rates are in good agreement to the experimental results and explain that the specific erosion scales with current, polarity, and the arcing time. This indicates that erosion in this range of arcing stress occurs mainly due to evaporation of contact material and less to emission of droplets

Dynamics of arc phenomena at closure of electrical contacts in vacuum circuit breakers

Dynamic phenomena accompanying electrical contact closure in vacuum circuit breakers are considered as consecutive stages, including breakdown, touch, compression, restitution, bridging, and arcing at bouncing. The hybrid mathematical model is elaborated to describe dynamics of the arc and forces acting in the contact gap. The model uses experimental oscillograms of current, voltage and contact displacement and nonlinear equations for arc, anode and cathode temperature fields, and contact motion. Experiments are carried out using a standard vacuum circuit breaker with laser sensors for the measurement of contact gap. The special difference path method is applied to take into account oscillations of a fixed contact. The axisymmetric Stefan problem with two free boundaries corresponding to melting and evaporation interfaces is solved to find dynamics of contact evaporation. It is shown theoretically and confirmed experimentally that in the range of high currents, the force of metallic vapor pressure at arcing in vacuum is comparable with magnetic repulsion force and should be taken into consideration. Two mechanisms of vapor pressure formation and evolution are discussed, which occur due to explosion of micro-asperities at contact touch or due to arcing after bridge rupture at contact bouncing.

A study of capacitive current switching capability by flashover characteristics between contacts of circuit breakers

AbstractThis paper describes the capacitive current interruption capability of circuit breakers from the viewpoint of flashover characteristics between the contacts of breakers. The authors obtained flashover characteristics between the contacts having a short gap between them by comparing the data for new contacts and the data for contacts eroded after having been exposed to three interruptions at T60 according to amended regulations JEC 2300 (1998) and IEC 62271‐100 (2001). Comparison of the flashover characteristics and the electric field calculations obtained by measurements using new and eroded contacts have shown that the deterioration of dielectric strength amounts to 10 to 20%. The authors also conducted flashover tests for the contacts and nozzle after a significant number of interruptions. The total number of interruptions can be considered as the maximum possible number of interruptions according to CIGRE research. The deterioration of dielectric characteristics is 10 to 30%. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 28–37, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10281

Effect of Metallic Vapour Pressure on the Vibration of Electrical Contacts in Vacuum

Vibration or bouncing of electrical contacts at closure is a reason of failure occurring in relays, contactors, circuit breakers and other electrical equipment due to arc erosion and welding. Experimentally observed bouncing of electrical contacts in vacuum circuit breakers cannot be satisfactorily explained by elastic restitution force or electrodynamic repulsion. This paper attempts to estimate the influence of metallic vapour pressure generated by arc in the contact gap on contact motion. The mathematical model describing these phenomena includes a non-linear differential motion equation for a movable contact piece, heat equations for anode and cathode (Axisymmetric Stefan's problem with two free boundaries for melting and evaporation), a differential equation for the arc column, and non-linear algebraic equations for near-electrode regions. The special method of majorant functions is applied for the solution of this problem. It is found theoretically and confirmed experimentally that the vapour force at contact bouncing is sometimes comparable and may be greater than the contact spring force even in vacuum. Some aspects of resonance phenomena, when the frequency of mechanical oscillations is close to the frequency of alternative current are also discussed.

A Study on Capacitive Current Switching Capability by Flashover Characteristics between Contacts of Circuit Breakers.

This paper describes the capacitive current interruption capability of circuit breakers from the view point of flashover characteristics between contacts of breakers. Authors obtained flashover characteristics between contacts of breakers with short distance by comparing with new condition and eroded condition after 3 shots of T60 according to new JEC 2300 (1998) and new IEC 62271-100. By comparison of flashover characteristics and electric field calculation obtained by the measurement of new and eroded contacts, deterioration of the dielectric capability is of 10 to 20 %. Authors also conducted flashover tests for the contacts and nozzle after significant number of interruption. The total amount of interruption can be considered as the maximum possible interruption according to CIGRE research. The deterioration of dielectric capability is of 10 to 30 %.

3-D finite element analysis of repulsion forces on contact systems in low voltage circuit breakers

Low voltage circuit breakers which interrupt fault currents rapidly are widely used in power distribution systems. It is necessary, for the optimum design of circuit breakers, to analyze electromagnetic forces on the contact systems equipped with arc rupturing parts. In this paper, the forces generated by currents and flux densities are obtained by using the 3-D finite element method taking into account current constriction and variations in arc diameter. It is shown that the 3-D analysis is capable of evaluating new designs of LV circuit breaker contact systems.