Interruption Capability of Gases and Gas Mixtures in a Puffer-Type Interrupter

SF6 gas has been widely used in arc interruption applications for the past 20 years. Reported here is a systematic, comprehensive effort to search for and evaluate gases and gas mixtures suitable as an arc interruption medium potentially superior to SF6. The search began with several hundred gases, narrowed down to about forty, and finally fifteen gases and gas mixtures were evaluated in a full size puffer-type interrupter under 60-Hz high-power conditions. The results showed SF6 stood out as having the best interruption ability with several mixtures having ~80 percent of SF6' s performance.     

Spectroscopic Approach to the Analysis of High Current Arcs in SF6

Spectroscopic observations were carried out on transient free-burning arcs drawn by separating copper/tungsten electrodes in SF6 gas. The peak value of the arc current was varied up to 60 kA. A new optical method was developed to measure temperature and pressure profiles of the arc taking the magnetic pinch force into account. The arc voltage calculated from the obtained temperature and pressure profiles agreed well with electrical measurements. The results made it clear that the composition of the arc changes significantly at the critical instantaneous current of 10 kA. Above 10 kA the arc is composed of the electrode vapor, while it contains SF6 gas below 10 kA.     

Mechanisms for Temperature Decay in the Freely Recovering Gas Blast Arc

Energy loss mechanisms for the extinguished gas blast arc channel in free recovery are defined and their comparative magnitudes are explored for both N2 and SF6 gases. The arc channel temperature decay rate is found to follow at least two time constants: one corresponding to the transit time of the channel gas and the other to a later period. In addition, the influence of the gas pressure and of the initial conditions of the arc channel and the surrounding hot gas mantle at current zero on the decay rate of the channel temperature are investigated.     

Study of a circuit-breaker arc with self-generated flow. II. Theflow phase

For pt.I see ibid., vol.16, no.6, p.606-14 (1988). The experimental results presented concern the variations of the mean electric field and gas mass flow during this phase. The most important part consists of a modeling of the evolution of the interruption arc during the decrease of the current from 1000 A to 0. In this modeling, based on the conservation equations of mass and energy, the boundary conditions are determined by an approximate separate modeling of the arc whereas turbulence is treated through Prandtl's approximation. This theoretical study has been developed in the case of SF₆ and nitrogen. The computed values of the electric field and temperature show that the arc has a quasi-stationary behaviour as long as the current intensity is greater than a few tens of amperes, for a decay rate of 1.35 A/μs. The energy losses are governed by radiation at high current and by turbulence conduction at low current. The most important results concern the conductance, whose evolution time constant, immediately prior to current zero, is 3.5 μs in SF₆ and 15 μs in nitrogen. The difference is essentially due to variations with temperature of thermal conductivity and specific heat in two gases     

Electric power switches

A review is given of the physics and engineering behavior of arcs in vacuum and axial gas blast under the conditions found in high-voltage circuit breakers. The topics included are: the zero energy switch; current limiting switches; arc control; the gas-blast circuit breakers; the low-current gas-blast arc; arcing with ablation; interruption dynamics; arc modeling; vacuum as a switching element; the vacuum arc; the constricted arc; and the properties of SF₆     

Study of the Arc and of the Interaction between Arc and Operating Mechanism in SF6 Puffer Breakers

The article deals with studies of the arcing performance of SF6 puffer breakers at currents of up to 80 kA and voltages of up to 200 kV, using an interrupter unit fitted with viewing windows. The studies are mainly concerned with the behavior of the arc at current zero and with restrike phenomena under various conditions. In addition to measurements of the electrical variables and the pressure variation, the tests cover the use of high-speed cameras, spectroscopic diagnostic methods, and schlieren methods. The density fields and flow fields derived from the latter are used to optimize the gas flow. On the basis of the breaker data and those of its operating mechanism a method for computing the essential variables, e.g., pressure, gas flow, back pressure, and contact travel, is developed. The variation of these parameters as a function of the interrupter data for various currents and with due allowance for the interaction between the arc and the operating mechanism must be known if the breaker design is to be optimized. The method uses simplified equations for the gas flow and the arc. The relationship between the gas data (e. g., density, enthalpy, speed of sound, electrical conductivity, and dielectric strength) and the temperature is taken into account by using approximation functions. The temperature of the arc core is matched to the test results.     

Arc-Gas Flow Interactions in a Double-Nozzle Flow System

The physical phenomena in cold and arc heated double-nozzle gas flows have been investigated for SF6 by interference and shadow methods. The cold-flow phenomena are discussed as a basis for a better understanding of the arc-gas flow interactions, their interference pattern is clearly interpreted: the observed fringes, which also can be calculated theoretically, are lines of constant flow velocity. In the case of arc heated flows a sharp distinction is made for the first time between different types of arc-gas flow interactions. At low peak currents the interference pattern still shows a cold gas flow around the arc. At higher current levels a fringe system, which indicates a density reduction, expands into the volume around the nozzles; however, the flow is still directed towards the gap between the nozzles. In contrast to this case the strongest form of interaction is characterized by the appearance of arc heated gas, which flows turbulently back into the high-pressure volume. The radial temperature distribution for a special arc has been calculated theoretically and is discussed in detail.     

Simplified Estimation of Critical Quantities for Short-Line Fault Interruption

From analyses of equations derived in a previous paper for critical interrupting conditions for an arc shunted by both resistance and capacitance in parallel, or for short-line fault interruption with capacitance shunting, further analytical expressions useful for prediction of limiting conditions are derived. Examples, based on observed relations of Cassie-Mayr arc model parameters to current rate of change for a particular SF6 blast circuit breaker, show realistic plots of limiting short-line fault currents versus line length with capacitance shunting. Also shown are required capacitance shunt values as functions of busfault current, fault fraction, line length, and number of series breaks. Included in the equations are circuit voltage and frequency and line surge impedance. Finally, it is shown that similar relations can be derived by using an approach suggested by A. M. Cassie in 1939.     

Electrical conductance decay of arc columns in some common gases

Experimental measurements are reported of the conductance decay following current interruption of wall stabilised arcs in air, nitrogen, argon, oxygen and helium within the current range 6–42 A. The results are compared with the predictions of several analytical models so that the influence of various gas properties and processes may be estimated. Measurements in the molecular gases show clearly how the arc structure affects the recovery. The results in the inert gases differ to some extent from the predictions of the simple models.     

SF_6气体及其衍生物的红外光谱分析

SF6气体大量应用于气体绝缘组合电器(GIS)中。通过化学方法检测SF6气体及其衍生物是检测GIS设备故障的一种重要方法。该文采用红外光谱技术分析了三种情况下的GIS设备内SF6气体组成情况,得出S2F10气体含量可以用来分析GIS故障原因是否为强火花或者电弧放电引起;CF4气体可以用来表征GIS设备内绝缘气体的绝缘状态。另外,研究表明,GIS设备在线运行时,绝缘气体气室密封失效、造成气体泄漏,引入新的气体杂质的问题比较严重。所以在进行GIS设备维护工作时,绝缘气室的密封维护工作十分重要。文章在研究GIS设备绝缘气体SF6红外谱图的基础之上提出了建立基于红外光谱技术的GIS设备故障诊断专家系统的意见。     

Experimental Investigation on Arc Phenomena in SF6 Puffer Circuit Breakers

A detailed observation of an arc in a model puffer-type SF6 gas circuit breaker in the current range between 10 and 50 kA (rms) has been carried out. It was found that the arc column remained stable on the center axis during the high-current region, then became turbulent near current zero. It was found that the time interval during which the turbulent arc was observed decreased with increasing values of the peak current. These phenomena indicated that the thermal effects of high-current arcs remain even at current zero. It also was observed that the arc diameter at the nozzle throat outlet was smaller than that at the throat (29 mm), even at a current as high as 70 kA (instantaneous), and that the boundary of gas flow at a downstream region had a very large diameter when the arcs were present. However, around current zero the boundary diameter became as small as that without arc.     

Application of High Current and Current Zero Simulations of High‐Voltage Circuit Breakers

This paper reports on the use of computational fluid dynamic (CFD) simulations to predict the interruption behaviour of high‐voltage circuit breakers (HV‐CB) using the self‐blast principle. Two different levels of accuracy of the arc model are proven to be sufficiently accurate for simulating the high‐current phase and the period around current zero (CZ). For the high‐current phase, a simplified equivalent model of the arc is implemented to predict the pressure build‐up, and even more important to accurately trace the hot gas from the arcing zone into the exhausts and the heating volume. A detailed analysis of the gas mixing in the heating volume for different arcing times and current amplitudes showed the optimum geometrical design of the heating volume. For the CZ phase, a more detailed arc model is needed including the effects of ohmic heating, radiative energy transfer, and turbulent cooling fully resolved in space and time. The validation with experiments was done and shows good agreement which justifies the use of the implemented model. With it, scaling laws varying only one parameter at a time (pressure and applied current slope) were derived and confirm previously found empirical laws. This is of particular interest, as it is very difficult to derive such scaling laws from experiments where the scatter is always very large and where it is impossible to vary only one parameter at a time. The influence of the most important geometrical parameters of the nozzle on the interruption performance is shown. In addition to previous experimental indications of this, the simulation reveals that turbulent cooling on the arc edge is the main reason for the difference in interruption performance. Moreover, the exact spatio‐temporal build‐up of arc resistance and with it the detailed understanding of the arc interruption process is possible and shown here for the first time. These simulations enable us to predict HV‐CB performance and to minimise the number of development tests and are routinely used in new development projects. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of a circuit-breaker arc with self-generated flow. I. Energytransfer in the high-current phase

This study deals with the first phase of operation, corresponding to the energy transfer between arc and gas and to the pressure rise. The experimental study is devoted to measurements of current, arc voltage, and pressure variations in N₂ and SF₆. For currents of the order of 10 kA the mean measured electric field was about 32 V/cm in SF₆ and 36 V/cm in N₂. Through a bibliographical study and a modeling approach of the interruption arc, an analysis of the role of the different mechanisms of energy transfer between the arc and SF₆ was conducted. With a 10 kA pulse, about 80% of the transfer is found to be due to convection and the rest to radiation from the arc. This transfer results in an overpressure of nearly 1 bar in SF₆ and 2 bar in N₂. It appears that the operation of this type of circuit breaker is limited to high currents: for currents below 7 kA the overpressure is lower than 0.5 bar, which does not provide efficient blowing at current zero     

Dielectric Recovery of an Axially Blown SF6-Arc after Current Zero: Part I?experimental Investigations

The results are presented of a model experiment to investigate the dielectric recovery of an axially blown sulphur hexafluoride (SF6) arc after current zero. With the aid of Schlieren pictures and interferometry, the temperature decay after current zero is observed up to the point of complete recovery of the gap. The dielectric recovery is directly measured by applying voltage pulses across the gap which causes breakdown at different times after current zero. Residual charges, which play a role in the early recovery phases, are detected using a specialiy developed technique. Variations of the shape of the voltage pulses and the geometry cause characteristic changes of the recovery, which support the interpretation of the experimental data.     

一种高稳定半导体激光器驱动电源的设计与分析

设计了一种高稳定半导体激光器驱动恒流电源,分析和讨论了集成运放负反馈型恒流源的负载、温度特性以及稳定精度。给出了LD注入电流稳定度的测量结果,LD注入电流稳定度可达10^-6,用稳定的激光器观察了充有约1．3kPa缓冲气体的自然铷的D2吸收谱线。此外,该电源还具有抗击浪涌击穿、断电保护和过流保护等多种功能。     

双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

Some Aspects of Current Interruption Physics in High Voltage Circuit Breakers

Recent results of experimental and theoretical investigations on current interruption processes are presented with a focus on SF₆ high voltage circuit breakers. Various aspects of thermal interruption at the zero crossing of the current are shown, including the scatter and the distribution of arc voltage shortly before CZ and the role of turbulence. The thermal interruption capability of air and CO₂ are compared to that of SF₆. Investigations on the dielectric recovery are shown for SF₆ and CO₂. The breakdown voltage during the dielectric recovery can be described by simple streamer and leader inception models. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Messung und Deutung des Leitwertabklingens zylindrischer Bögen

The decay of the electrical conductance of the column of a cascaded arc (100 A) after current interruption is measured for the gases N₂, SF₆, CO₂ and Ar. Numerical computations of temperature and conductance decay are in good agreement with experiment for Ar but for N₂ and SF₆ there are drastic deviations. An interpretation of the decay processes is given by the aid of a simple model for the energy transfer including nonequilibrium processes with regard to recombination in the wall near arc regions. Introducing the model by a formal manner in the computer program leads to good agreement with experiment.     

Contact temperature and erosion in high-current diffuse vacuum arcson axial magnetic field contacts

We have investigated the surface heating effects of drawn vacuum arcs for several industrial designs of axial magnetic field (AMF) contacts, using near infrared (IR) photography of the Cu-Cr arcing surfaces with an image-intensified charge-coupled device (CCD) camera and an IR pyrometer. This enables detailed contact temperature mapping immediately after a half-cycle of arc current. The very homogeneous temperature distribution observed at current zero stands in contrast to the visually nonhomogeneous high-current diffuse arc, which was studied in separately reported experiments using high-speed digital photography and arc voltage measurements. The peak temperature at current zero increased relatively linearly with the peak current I_P, and reached well beyond the melting range. We combine the temperature maps with a heating model to determine the thermal sheath thickness after arcing and its dependence on I_P. The results suggest that near the interruption limit of AMF contacts, the interaction of the stable high-current arc with the anode and cathode is dominated by processes induced by flowing liquid metal, which redistributes the heat input from the axially concentrated arc over most of the contact surface. Furthermore, the flow of liquid metal off the cathode and anode faces contributes to the overall contact erosion