The energetics of gas flow and contact erosion during short circuit arcing

The processes governing the movement of short circuit arcs in circuit breakers are complex and variable and the detailed understanding of these processes is incomplete. This paper presents a new approach to our understanding of the short circuit arcing process by concentrating on the bulk thermal behavior and energetics of the arcing and gas flow during contact opening. It is shown how considerations of the arc power and the heating and vaporization of the contact material can be used to examine the flow of gas through the arc chamber and the erosion of contact material. Experimental data from a flexible test apparatus and arc imaging system along with measurements of pressure and arc current and voltage are used as the basis of the analysis. It is demonstrated how the air initially present in the arc chamber will be rapidly expelled from the arc chamber to leave an arc burning in the products of contact volatilization. Data on mass and volume flow rates are presented as well as estimates of the gas velocity in the contact region. These data provide information on the nature of the gas flow in the arc chamber as well as contact erosion during the arcing process. Arcing conditions of interest are short circuit faults (10/sup 3/-10/sup 4/ A) in low voltage (220-380 VAC) circuit breakers.     

Arc motion and gas flow in current limiting circuit breakers operating with a low contact switching velocity

Arc motion in low voltage (240 VAC) high current (10/sup 3/-10/sup 4/A.) current limiting-circuit breakers is dominated by arc root mobility. The mobility is influenced by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. The influences of arc chamber material, contact material, and contact opening speed, are investigated to improve arc control for a low contact opening velocity.     

Arc root commutation from moving contacts in low voltage devices

This paper focus on the arc commutation from a moving contact and in particular on the anode motion of a high current arc in low voltage current limiting circuit breakers. Recent investigations have observed that the anode arc root motion is affected by arc chamber geometry. It was previously assumed that cathode root motion was the dominant process. The study uses a flexible test apparatus with a solid state high speed imaging system. The experimental results presented show the influence of arc chamber venting, current level, current polarity and contact velocity on arc motion, Particular emphasis is made on the anode motion. The physical processes occurring in the anode root are discussed and related to the observed motion. The results show that the anode root is retarded at the tip of the moving contact and that this is primarily related to the venting process in the arc chamber     

Anode and cathode arc root movement during contact opening at highcurrent

This paper presents experimental research into the behavior of short circuit break arcs ignited between opening contacts. The investigation is applied to arc chamber geometries commonly used in miniature circuit breakers (MCB). The movement of the anode and cathode roots are individually plotted from optical data, allowing the relative motion to be compared. The effect of a range of MCB configurations on the arc root motion has been investigated. The experiment was configured so that the fixed contact was always the cathode. The results show that the two are roots do not move away from the contact region simultaneously. Often the cathode root moved off the fixed contact and away from the contact region before the anode root commutated from the moving contact. The delay in anode root commutation leads to a delayed cathode root movement. These events are explained in terms of arc root emission processes     

Voltage-current characteristics of breaking arc at constant opening speed in the air

Voltage-Current (VI) characteristics of breaking arc between electrical contacts have been investigated for several contact materials (Au, Ag, Cu, Pt, and Ni). The purpose of this paper is to investigate the VI-characteristics and minimum arc voltages of the breaking arcs that occur between slowly opening (1.0 cm/s) contacts, and compare these results with those of Holm. Experimental circuit is resistive, which has 5-/spl Omega/ circuit resistance. Experiments were carried out in the air at atmospheric pressure for supply voltages 30, 42, and 54V. The time evolutions of arc voltage, arc current and gap length were measured simultaneously. The VI-characteristics and minimum arc voltages were obtained from those measured values. The results showed that minimum arc voltages for each contact material (Au, Ag, Cu, Pt, and Ni) agreed with those of Holm. On the other hand, VI-characteristics of Au, Ag, Cu, and Pt contacts agreed with those of Holm, but VI-characteristics of Ni electrical contacts disagreed with those of Holm. The difference for VI-characteristics between Ni electrical contacts and the others was because of lower electric field of the arc column for the case of nickel electrical contacts.     

Contact material and arc current effect on post-current zero contact surface temperature

Optical radiation measurements of contact surfaces were made after current-zero of a high-current (>10kA/sub p/) arc, to determine how much the contact surface temperature at and after current zero was affected by a change in contact material and arc current. Contact surface temperature was measured for different types of "typical" contact materials (AgW and AgC) commonly used in molded case circuit breakers (MCCBs). The average temperature at the contact surface was measured by using photodiodes in conjunction with a narrow band filters and long-range microscope. A 250-A rated MCCB was modified, with renewable chamber walls and contacts, and used as a test bed to insure that these results can be directly applied to MCCBs in the 125 to 250-A range. Uniform and repeatable arcing conditions were maintained by using an electronically timed capacitor bank source, timed contact part, and a well-maintained arc chamber. Along with other important engineering properties of the contacts (arc erosion, temperature rise), this data can be useful for selecting contacts for circuit breaker applications.     

双晶片压电驱动器的研究

为实现较大的驱动力和速度,提出一种新型压电驱动器,研究了驱动器输出性能随压电泵工作腔数、频率的变化规律。制作驱动器,分别进行十腔串联压电泵/五腔压电泵并联、3~5个压电振子工作、50~400 Hz频率下的输出试验。结果表明,压电泵并联时驱动器的最佳输出功率较大;工作的振子数目不同,存在不同的最佳频率使驱动器的输出速度最大,相同的频率使输出推力最大;最佳频率时,驱动器的输出与工作的振子数目呈正比。在150V、380Hz时驱动器输出功率最大,此时输出速度和推力是10.72mm/s、57.7N。     

The influence of arc chamber wall material on arc gap dielectricrecovery voltage

The dielectric breakdown strength of an arcing contact gap after current zero was compared when using alumina, polyamide 6/6 (PA 6/6), and polyoxymethylene (POM) arc chamber wall materials. Plasma characteristics were obtained for each material by applying a reverse recovery voltage across the open contacts at a predetermined delay time after current zero. Ablation from each type of chamber wall material produced different plasma compositions each with different recovery voltage, arc voltage, and pressure characteristics. Tests were performed for an arcing current of 12 kA_p, for one half-cycle using symmetric AgW contacts. A thermal breakdown model along with an exponential curve fit to the measured results were used to obtain the initial holdoff voltage and plasma time constant for each material. PA 6/6 and POM had similar time constants with PA 6/6 having slightly better performance. Two types of breakdown mechanisms were identified-thermal and dielectric     

基于辐射电磁波监测技术的断路器开断性能研究

断路器在开断电流时,当触头两端的电压高于触头间灭弧介质的击穿电压时,动静触头将发生击穿,产生开关电弧,并激发空间高频的电磁波向外辐射。向空间辐射的高频电磁波信号与灭弧气体特性、机械特性及绝缘结构等多种因素相关,反映着断路器的开断能力。本文仿真计算了断路器辐射电磁波的过程,建立试验研究平台,测量对比了全新触头和退役触头开断过程中辐射电磁波的波形,开展了基于辐射电磁波监测技术的高压断路器开断性能研究。研究结果表明:随着触头表面烧蚀程度的增加,断路器开断性能下降,更容易发生电弧重燃,燃弧时间相对于全新触头会有明显的增加,同时对外辐射电磁波的持续也增多,辐射电磁波的持续时间可以作为判定断路器开断性能的判据。本文的研究内容为辐射电磁波监测技术在断路器开断性能的评估提供了技术参考与依据。     

Investigation of arcing effects during contact blow open process

A theoretical model has been developed to simulate the blow open process considering contact constriction force, contact spring force, and plasma pressure. Meanwhile, monochromatic high speed imaging technique has been used to characterize arc behavior, contact vapor distribution and determine contact blow open gaps. Modeling results are in good agreement with test results. The results show that plasma pressure has a significant effect at the initial arcing stage of a blow open process, but it decreases rapidly due to the increase of arc gap and the gas pressure equilibrium around moving contacts. The plasma pressure and the contact spring force (or applied magnetic force) basically determine the arcing time during the blow open process. However, contacts can be held open by plasma pressure till current zero if piston type arc chamber is employed. Higher contact spring force results in shorter arcing time, higher arcing current and more likely leads to contact weld. Due to the fact of arc pressure decreasing rapidly during the blow open process, the blow open contact gap is less than 2.5 mm for all the contactors tested at the blow open current level. The results indicate that larger allowed arc gap does not necessarily reduce contact weld possibility, since other factors such as arc motion and heat conduction through contacts also have strong influence on contact weld     

The net zero mass loss phenomenon on opening switching contactswith AC loading

Studies are conducted on silver metal oxide contacts on a purposed built apparatus to investigate the extent of contact erosion under opening (break) operations. The contacts are opened between 0.1 and 0.8 ms^-1 at particular point-on-wave, t_POW, of the ac waveform. Current loading of up to 30 A rms, I_rms is investigated. Contact material deposition, as well as mass loss, is observed and is found to balance at particular current values and point-on-wave opening leading to a net zero mass loss on the contacts. Results are presented on mass change for each contact against the two parameters of current and point-on-wave. An arc duration characteristic, ζ, is plotted against current, I_rms which has a net zero mass loss. The characteristic is shown to be the same for both silver tin oxide and silver cadmium oxide but is influenced by the opening velocity. The metallic and gaseous ion transfer mechanisms of the arc discharge are presented as the main processes behind this phenomenon     

Short arc duration laws and distributions at low current (<1 A)and voltage (14-42 VDC)

In the automobile industry, safety and comfort equipment require more and more switches which are operated over a wide range of electrical, mechanical and ambient conditions. In the low electrical power range, i.e., near minimum current and voltage, shorts and fluctuating arcing may occur. Using a testing apparatus capable of rapid measurements with high temporal resolution (0.2 ns) we have measured and analyzed arc durations on break in a pure resistive circuit near minimum arc current and voltage Ob exp(I//i_b)]. The lifetime and current intensity of the burst (t_b, i_b) are deduced for various contact materials. In addition, the histogram of arc duration fluctuations is well fitted by multiGaussian distributions centered around a multiple of the burst time. This confirms the burst mechanism and introduces the concept that arc duration values are discrete. On the other hand, the plot of arc occurrence in the first regime clarifies the significance of the minimum arc current (100%) and yields the current limit for arc appearance (0%). Finally, high voltages (14-28-42 V) and inductances (1 μH-10 mH) can produce long arc durations with the result that we may enter into the cathodic arc     

A novel InP/InGaAs TEBT for ultralow current operations

A novel InP/InGaAs tunneling emitter bipolar transistor (TEBT) is fabricated and demonstrated. The studied device exhibits a very small collector-emitter offset voltage of 40 mV and an extremely wide operation regime. The operation region is larger than 11 decades in magnitude of collector current (10/sup -12/ to 10/sup -1/A). A current gain of 3 is obtained even if the device is operated at an ultralow collector current of 3.9 /spl times/ 10/sup -12/A (1.56 /spl times/ 10/sup -7/A/cm/sup 2/). Furthermore, the common-emitter breakdown voltage of the studied device is higher than 2 V. Consequently, the studied device shows a promise for low supply voltage, and low-power consumption circuit applications.     

Frequency spectra of the arc current due to opening electriccontracts in air

Frequency spectra of the electromagnetic noise due to arc current caused by Ag contacts upon opening in air at atmospheric pressure are described. To take into consideration the fast transients and high-frequency discharge phenomena at the contacts, a distributed constant model consisting of relay contacts and a coaxial distributed constant line is introduced. An experiment carried out under conditions of low circuit current (3.84 A) and low source voltage (48 V) is reported. The results indicate that the frequency spectra of the arc currents depends on the length and terminal conditions of the line connected to the contacts     

A novel concept for fault current tolerable contactors

It is critical in the development of new contactors and starters to enable the product to avoid or minimize contact welding during short circuit events. The IEC 60947-4-1 or UL 508E Type II coordination requires that a contact weld can be easily broken without significant deformation after short circuit events, and the new standard of IEC 60947-6-2 mandates no contact welds after short circuit events. In this paper, a novel concept has been developed and investigated to allow significant fault current tolerance improvement for next generation contactor and starter product lines. An innovative design of the movable contact bridge utilizes the magnetic force generated by the fault current to "latch" the contacts open until current zero and reclose after current zero. This delay of contact reclosing allows the molten contact surface to solidify and minimizes or even eliminates contact welding altogether. This design does not require a size increase of the product to achieve this performance and adds minimal cost. Test evaluation has been carried out to verify this concept. The test results show that the contacts close about 1.5 to 2ms after current zero and achieve no contact welding after short circuit events with proper current limiting by the upstream circuit protector.     

Closed-Loop Control of a Complementary Clamp Piezoworm Actuator

The concept of the complementary clamp piezoworm actuator with a diode-shunted delay circuit was experimentally verified through prototype testing. One clamp uses high voltage to grip and low voltage to release while the other clamp operates in reverse fashion. The resulting piezoworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric stack using the second channel. The piezoworm achieved a speed of 440 mum/s and had a force capacity of 12.5 N when driven in open loop with trapezoidal waveforms. A delay circuit improved the force capacity from 12.5 to 14.7 N using a resistance of 1000 Omega. A closed-loop tracking controller was developed for the prototype. It is shown that the prototype closed-loop system has a repeatability less than plusmn20 nm for a 100 mum step input and can track a 100 mum, 0.05 Hz sine wave with a 1% peak error and less than a 200 nm average error.     

Break arc study for the new electrical level of 42 V in automotive applications

In order to fulfil the increasing need for electric power in automobiles, to satisfy the new environmental requirements and to decrease the weight of cars, the electrical supply, must be changed from the current 14 V to 42 V. In the present work using 42 V, we have studied arc parameters such as break arc duration and extinction gap for different materials, contact opening speeds and circuit loads (correlated with the time constant of the circuit, L/R). We have established that these main arc parameters are greatly enhanced compared to the 14 V arc studied in our previous work. In the case of an inductive or a resistive load, it has been found that there are two domains: a low current domain where the material has no significant effect, and a high current domain where some materials (primarily AgSnO/sub 2/) induce high arc durations and large extinction gap. In addition, increasing the opening speed reduces arc duration in all cases. The increased opening speed can however, increase the extinction gap for inductive loads and decrease it for resistive circuits. We have found that reducing arc duration is always beneficial with regards to erosion but in some cases, however it may increase the extinction gap.     

便携式压电微型泵驱动电源的研制

根据用于烈性药物输注的便携式压电微型泵的使用要求,研制了压电陶瓷驱动器的驱动电源。驱动电源以3 V锂离子钮扣电池供电,通过DC/DC电路和逆变电路为压电陶瓷驱动器提供高的输出电压(200 V,峰-峰值),具有频率可调,体积小,质量轻,功耗低,安全可靠,便于控制的特点。实验表明,驱动电源能满足压电微型泵的使用要求,也适用于以逆压电效应为基本原理的微小压电器件的动态应用。     

An Experimental Study on Minimum Arc Current for Arcs Longer Than a Few Microseconds in Relay Contacts and Possible Reinterpretation of the Meaning Thereof

A minimum arc current value for each contact material is one of the very important factors in consideration and comparison of arc discharge characteristics for proper selection of contact materials. In this paper, Ag and Ag alloy contacts were operated to break various dc load currents in the range of up to 1.5 A with 10–30 V, and occurrence rates of break arcs (having durations equal to or longer than a few microseconds) were investigated at each condition. As a result, it is confirmed that at the conventional minimum arc current level, break arcs on the order of several tens of microseconds occur at occurrence rate close to 100% when sufficient energy is supplied to contacts upon opening. Thus, careful attention should be paid to when using the term “minimum arc current” in order to avoid misinterpretation.      

Nonalloyed ohmic contacts for p/sup +/-type in GaAs base layer in HBTs

Two new metallisation systems, Pd/Pt and Cr/Au, for nonalloyed ohmic contacts on p/sup +/-InGaAs have been compared with the Ti/Pt contact. The observed strong dependence of the contact resistivity on the metal is related to its work function. The lowest resistivities are achieved with Pd/Pt, e.g. 1.2*10/sup -6/ Omega cm/sub 2/ for p=1.7*/sup 19/ cm/sup -3/.<>