Scaling Laws for Gas-Blast Circuit-Breaker Arcs during the High Current Phase

A steady state nozzle arc model based on the boundary layer integral method is established and scaling laws are derived. For affinely related nozzles, the solution is uniquely determined by a nozzle coefficient N, which is related to the stagnation conditions, the arc current, and the dimensions of the nozzle. Tests have been performed on nozzle arcs in air using two geometricaly similar nozzles at three stagnation pressures. A good agreement between theory and experiment is obtained which indicates that circuit-breaker arcs can be scaled. To avoid nozzle clogging, the nominal current density at the throat (I/At) should not exceed the highest permissible nominal current density at the throat. For all affinely related nozzles, this upper limit of current density at the throat is proportional to ?p0?t, where p0 is the stagnation pressure and Zt the distance of the throat from the nozzle entrance. The overal arc voltage exhibits the precurrent-zero static behavior as indicated by Browne's composite arc model.     

The DC Arc in a Supersonic Nozzle Flow

The boundary layer integral method at its second level of approximation has been used to study the DC arc in a supersonic nozzle flow. It is shown that with the inclusion of the arc momentum balance, the critical point of the flow is, generally, not the sonic point of the external flow. The speed, at which a disturbance propagates relative to the external flow, is in general supersonic and is dependent on the arc conditions. The arc model is capable of predicting the axial electric field, the arc size and the axial pressure distribution as a function of current. For affinely related nozzles, the solution is determined by a parameter N, which is related to zt, the stagnation condition and the nominal current density at the throat (I/At). Numerical results are given for a particular nozzle shape although the method of analysis is general. Practical implications as regards nozzle design for a gas blast circuit breaker are briefly discussed.     

Nature of convection-stabilized DC arcs in dual-flow nozzlegeometry. I. The cold flow field and DC arc characteristics

An experimental investigation of the steady-state low current air arcs in a dual-flow nozzle system is presented. The cold flow field with no arc was determined for various nozzle geometries, i.e. two- and three-dimensional and orifice nozzles, and nozzle pressure ratios. Supersonic flow separation and oblique and detached shock waves were observed in the flow field. Using a finite-element computer program, the Mach number contours were determined in the flow field for various nozzle-gap spacings and pressure ratios. In addition, the DC arc voltage and current measurements were made for an electrode gap spacing of ≈5.5 cm and current levels of I≈25, 50, and 100 A for the three nozzle geometries. The arc voltage and arc power increased rapidly as the flow speed increased from zero to sonic velocity at the nozzle throat. The shock waves in the converging-diverging nozzles resulted in a decrease in the overall resistance by about 15%     

Untersuchungen über die thermische Belastbarkeit und die Form von Düsen zur Führung von Hochstromplasmen

The electrical and thermal limitings of nozzle are calculated from electrical dates of argon arcs for guiding and constricting high current plasmas. The electrical field strength in nozzles resulted from the arc characteristics. Hence it follows the maximum nozzle length as a function of nozzle diameter and amperage. From the arc power converted in the nozzle the power density resulted at the nozzle wall. By use of known material functions of nozzle material the needed wall thicknes of nozzle and quantities and velocities of cooling water are calculable. The experimental verification of the results gives the following relation between the minimum nozzle diameter and amperage for argon arcs using the best nozzle cooling d [cm] = 10^?3 I [A]. With superposed gas flow values are riched up to d [cm] = 0,5 · 10^?3 I [A]. The attainable current density is 6 · 10³ A cm^?2 without superposed gas flow and 6 · 10⁴ A cm^?2 with superposed gas flow. New nozzle typs for plasma technological uses ensue from the results of investigations.     

任意长度喷管型面设计方法在气动激光器喷管设计中的应用

 将一种新的任意长度喷管型面设计（ALN）方法应用于气动激光器喷管型面设计,在相同的喷管出口设计马赫数、喷管喉部高度及喷管扩张段长度条件下,设计了4条ALN方法喷管型面,并和一条最短长度（MLN）喷管型面作对比,采用2维气动激光器增益场仿真方法对5个喷管的小信号增益场进行仿真。计算结果表明:ALN方法可以有效地实现增益场分布的控制,选择合理的设计参数得到的喷管长度比MLN喷管更短,小信号增益更大。     

The Local Electrical Properties of Gas Blast Arcs near Current Zero

Results are reported of experiments performed on a model air-blast circuit breaker to determine the distribution of voltage along the axis of the arc gap during the current zero period, following half sinusoidal current pulses of frequency 85 Hz. The air-blast was sustained by a reservoir pressure of 6.89 × 105 N/m2. Measurements were made following peak currents of 3 and 8 kA, with copper and carbon upstream cathodes, different separations of upstream cathode from nozzle inlet and different conditions downstream of the nozzle throat. The results have enabled the conductance decays at various axial positions to be determined and these have been related to the improved circuit breaking performance observed by other authors when the nozzle and arc gap geometries are optimized. Although a detailed theoretical analysis awaits the measurement of other fundamental plasma properties, an approximate evaluation of the role played by various basic processes has been made.     

Analyses of Axial Energy Distribution in Decaying Arc of SF6 Gas Circuit Breaker

Adopting a transient arc analyzing program, the authors analyzed the axial distribution of arc characteristics near the current-zero point, proving that while almost all portions of total arc resistance were shouldered in downstream arc, zero conductivity was achieved in the nozzle throat arc. It was also proved that in the presence of transient recovery voltage (TRV) with initial fluctuations, such as initial TRV (ITRV), an interruption was accomplished by combined effects of the downstream and the nozzle throat arc.     

Production of long,laminar plasma jets at atmospheric pressure with multiple cathodes

Plasma jets from conventional non‐transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non‐transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device.     

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.     

A Current-Zero Arc Model Based on Forced Convection

A simplified arc model based on the integral method is used to study the arc behavior in a supersonic nozzle. Emphasis is placed on the energy balance of the overall arc, which extends to the arc thennal boundary. Similarity rules for aerodynamic and electrical quantities are established, and a quantitative definition of current zero period is given. Computations have been done for two nozzle geometries. The nozzle geometry plays the role of shaping the arc, thereby affecting the axial electric field distribution. Performance curves in terms of the critical rate of rise of recovery voltage (rrrv)c and di/dt at current zero are established. It has been found that (rrrv)c can be seriously affected by the distortion of the current waveform near current zero due to arc-circuit interaction. When experimentally measured current waveform is used as an input, a good quantitative agreement is obtained for the Liverpool orifice arc [1] between theory and experimental results. A satisfactory agreement has also been achieved for the axial electric field distribution without adding a turbulence term into the energy equation. The limitations of the present arc model is also discussed in detail.     

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     

Zur numerischen Beschreibung rotationssymmetrischer wandstabilisierter Lichtbogenkonfigurationen

A method is outlined which gives a numerical describtion for some configurations of axially symmetrical constricted electric arcs. For this purpose the equations of single fluid model of plasma physics are decoupled in such a way that only the heat flux potential, the axial velocity, the radial velocity, the average axial pressure gradient, and the average axial electric field have to be calculated simultaneously considering a given set of boundary conditions. In this paper the method is applied to the Koppelmann arc. In addition the paper reports upon some experiences in applying this method to the computation of further arc configurations.     

超音速喷嘴叶栅造型设计及数值分析

分析了超音速喷嘴内部的流动机理并研究了超音速喷嘴的设计方法,对某液体火箭发动机用氢涡轮超音速喷嘴叶栅进行了改型设计。设计采用尖边喉部和光滑过渡喉部两种方法,其中光滑过渡喉部喷嘴型线设计采用具有局部修改能力的三次非均匀B样条曲线。对超音速喷嘴叶栅复杂内流的全三维数值模拟结果表明:改型叶栅流动性能明显改善,效率提高,光滑过渡喉部喷嘴性能优于尖边喉部喷嘴。     

Processes and properties of electric arc stabilized by water vortex

Experimental investigation of an electric arc stabilized by a water vortex was carried out in a DC arc plasma torch for the power range 90-200 kW. Volt-ampere characteristics of the arc as well as the power balance were determined separately for the part of the arc column stabilized by water and for the remaining part between the nozzle exit and the external anode. The temperature of arc plasma close to the nozzle exit was determined by emission spectroscopy. Negatively biased electric probes in the ion collecting regime were used for determination of the plasma flow velocity. The measured temperatures up to 27000 K, and velocities up to 7 km/s are higher than the values commonly reported for plasma torches with DC arcs stabilized by a gas flow. Mass and energy balances within the arc chamber were determined from the experimental results. The radial transport of the energy by radiation was identified as a decisive process controlling the arc and plasma properties. The balance of radial energy transport was studied. The ratio of energy spent for evaporation of the water to the energy absorbed in the evaporated mass is very low in the water stabilized arc. This is the principal cause of high plasma temperatures and velocities found by the measurements     

The Dynamic Behavior of Nozzle Arcs

The dynamic behavior of ac arcs in a supersonic nozzle has been investigated. The close coupling between the arc and its external flow determines the arc characteristics as well as the flow transients within the nozzle in a gas-blast circuit breaker. For affinely related nozzles, the dynamic behavior of the system is found to be fully determined by two nondimensional parameters: the nozzle coefficient N [17] and the nondimensional frequency ? which is the product of the angular frequency of the current and the time scale of the system. Of these two parameters, ? controls the qualitative behavior of the arc and its external flow. When ? is of the order of 10-2 or less, a quasi-steady period of arcing exists. Arc modeling can then be conveniently divided into a quasi-steady-state (hence dc) phase and a current-zero period.     

The radiation field of a hypersonic nozzle flow

This paper discusses features of the spectra observed looking axially towards the throat of a hypersonic nozzle in a chock tunnel assembly. At the throat, the gas is optically opaque, whilst at the nozzle exit the gas is optically thin. In principle, the radiation field may be controlled by varying the nozzle shape and it may therefore be used for optical modelling of other radiation fields, of differing physical dimensions. Requirements for implementing this programme are discussed.     

Plasma expansion and current flow in a vacuum arc with a smallanode

A low-density plasma flow in a vacuum arc with a small anode, which intercepts only part of the cathodic plasma jet, was studied theoretically using a two-dimensional approximation. The plasma expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the plasma was determined by a self-consistent solution of the gasdynamic and electrical current equations. Magnetic forces from the azimuthal self-magnetic field were taken into account. The influence of the ratio of the anode radius to initial plasma jet radius on the plasma density, velocity, current distribution, and anode sheath potential drop is analyzed. It is shown that the mass and current flow in a 500 A arc are compressed near the axis. This leads to an increase in the plasma density by a factor of two and in the axial current density by a factor of 1.5     

Plasma generation for the plasma cutting process

This study is an attempt to estimate the overall properties, viz. the thermal power and force, of an intense plasma jet produced by a plasma cutting torch, and to relate the properties of the plasma to the diameter of the nozzle of the plasma torch and the flow rate of plasma-forming gas. For cutting metallic plates using a thermal plasma, a narrow plasma jet is produced by means of a transferred electric are between an electrode in a plasma torch and the material to be cut. The power density and pressure exerted by the plasma jet on the material at the region of cut needs to be high so that a straight cut, without dress at the bottom of the plate, can be obtained. A simple theory to describe the behavior of the arc in a plasma cutting torch has been developed to predict the are radius, pressure, and arc voltage at the nozzle exit as a function of are current for a range of nozzle sizes and air flow rates. The results obtained are in good agreement with the measured values for an air plasma cutting torch nominally rated for 100-A operation. The relationships between the mass flow rate of plasma gas, plasma power, and arc force have been discussed in the light of design of plasma torches for plasma cutting     

层流等离子体制备球形氧化铝粉末的实验研究

为研究非转移弧层流等离子体制备面向新材料领域的μm级球形氧化铝粉末的能力,使用自制的非转移弧分段式阳极层流等离子体球化设备,以载气送粉的方式,对η相的不规则μm级三氧化二铝粉末进行等离子体球化处理,并采用均匀设计法,研究等离子体发生器和送粉器不同的工作参数对氧化铝粉末球化率的影响规律。结果表明,实验所采用的直流非转移弧层流等离子体发生器能有效制备球化率接近100%的高球化率球形氧化铝粉末。实验发现,高球化率、高分散性和粒径大小均匀的球形氧化铝粉末可在不同工艺参数组合下制备,并证明了采用非转移弧分段式阳极层流等离子体发生器可实现较低功率下制备较高球化率球形氧化铝的可行性。实验还通过XRD与PDF卡片索引技术对球化前后的氧化铝粉末进行了物相定性分析,发现η相的氧化铝粉末经射流作用转化成了Corundum型的氧化铝粉末。     

小功率等离子体射流的流特性

采用焓探针对小功率(5kW)热喷涂等离子体射流的焓、温度和速度进行了测量和计算。研究了气体成分、流量、电弧电压和电流对等离子流体的焓、温度和速度分布的影响。结果表明,对于单一氩气等离子体,当使用新喷嘴时,增大氩气流量能够使喷嘴内部电弧弧根向出口方向移动,从而增加等离子体射流的焓、温度和速度。对于Ar-N2等离子体,增加气体中氮气的含量,会提高等离子电弧电压,在同样的输入功率下,改变等离子电流和电压对等离子体的焓、温度和速度影响较小。对于Ar-N2等离子体,增加氢气含量会明显地提高等离子射流的速度和热传递。