Power Arcs Research Articles

The Power of Chaos

The Power of Chaos

Electrical Characterization and Modeling of High Frequency Arcs for Higher Voltage Aerospace Systems

Arcing in future high-voltage aerospace systems could occur more frequently and cause irreversible damage to electrical components, system structure and increase the risk of fire. While arcs seen in low-voltage aerospace systems tend to be long-duration and low-energy events, higher power but short-duration arcs may occur in high-voltage aerospace systems if they are readily detectable by system protection. This paper investigates the characteristics of high current arc faults generated at the AC frequencies expected in future rotating machines used for higher voltage aerospace systems. As such, arcs with a peak current up to 4.6 kA are generated at frequencies in the range of 0.5-2 kHz using an underdamped RLC circuit, under pressures of 0.2-1 bar absolute. High frequency arcs exhibit a similar characteristic to lower frequency arcs. A reduction in pressure results in lower arc voltage and arc power. Arcing tests at atmospheric pressure may therefore represent a worst-case scenario and the development of a low-pressure test environment may not be necessary. A black box model is developed to provide good agreement with experimental arc voltage waveforms for different parameters investigated in this study. This is a generalized modeling approach to estimate high-frequency high-voltage arcing characteristics without recourse to experiment.

Novel Approach for the Monitoring of Single Phase-to-Ground Fault Associated with Power Arc

This paper presents a general theoretical overview of a novel approach for the monitoring of the single phase-to-ground fault associated with power arc. Although several existing fault protection methods have been employed in order to resolve the power arcing faults associated with the single phase-to-ground faults, still ongoing research is trying to develop efficient methods that could help to suppress completely these dangerous power arcs from the systems. The operation of the protective relays and fuse systems is quite often questionable during recurrent failures in detecting the electric arcs as expected, especially during these arcs earlier events of formation. The most relevant reason causing these traditional faults protective switchgears seldom failures, limitations and drawbacks include essentially the varying amounts of resistance associated with these previously mentioned power arcs. Subsequently, the electric arcs related impedance and that of the power system tend to limit the arcing fault currents and voltages quantities at very low rates. Hence preventing the existing fault protective devices and switchgears to detect these arcs hazards, as long as the arcing fault related currents and voltages quantities are kept for a relatively long period of time below the nominal setting values of both the relays and the fuses systems. Subsequently, the entire power distribution system experiences the devastating effects of theses dangerous parasitic electric arcs hazards. However, in order to overcome the limitations, the disadvantages and the drawbacks of the above mentioned conventional fault protective devices, this paper divorces completely with the traditional practices in order to propose a radio measurement method.

Radiation of long and high power arcs

The operators working on electrical installations of low, medium and high voltages can be accidentally exposed to short-circuit arcs ranging from a few kA to several tens of kA. To protect them from radiation, according to the exposure limits, we need to characterize the radiation emitted by the powerful arc. Therefore, we have developed a general experimental and numerical study in order to estimate the spectral irradiance received at a given distance from the arc. The experimental part was based on a very long arc (up to 2 m) with high ac current (between 4 and 40 kA rms, duration 100 ms) using 3 kinds of metallic contacts (copper, steel and aluminium). We measured the irradiance received 10m from the axis of the arc, and integrated on 4 spectral intervals corresponding to the UV, visible, IRA + B and IRC. The theoretical part consisted of calculating the radiance of isothermal plasmas in mixtures of air and metal vapour, integrated over the same spectral intervals as defined in the experiments. The comparison between the theoretical and experimental results has allowed the defining of three isothermal radiation sources whose combination leads to a spectral irradiation equivalent to the experimental one. Then the calculation allowed the deduction of the spectral description of the irradiance over all the wavelength range, between 200 nm and 20 μm. The final results indicate that the influence of metal is important in the visible and UVA ranges whereas the IR radiation is due to the air plasma and surrounding hot gas and fumes.

Cross-Correlation Method for Power Arcing Source Monitoring System

Power arcs do not only cause important economic loss, but also lead to serious deterioration of the entire power system equipment. With the aging of the distribution networks, the development of power arcs detection and location techniques has been paid more attention. Once an arcing fault has been detected at a monitoring station its location is obtained from the electromagnetic radiation signals. The most common location techniques are based on Time Difference of Arrival (TDOA), Directional Finding (FD) and Propagation Attenuation (PA). In this paper, cross-correlation method in connection with TDOA is used to locate power arcing faults. In the experiment, strategically placed antennas and the arrival time’s delay of dominant component of the wide-band electromagnetic signals radiated from the sources are used. The power electric arc was produced by a tree leaning on a current conducting cable. The experiment proves that cross-correlation method combined with TDOA can be used to locate power arcs accurately.

52.1: Invited Paper: New Developments in Projection Light Sources—Shorter Arcs and Miniaturisation

AbstractNew developments of UHP lamps with higher power and shorter arcs (even below 1mm) fulfill the optical demands of future projectors and novel displays. In addition a new technology is presented which leads to a reduction of the lamp ignition voltage from 20kV to 5kV. This enables a further step in system size reduction.

Electrical breakdown of small gaps in vacuum

The comparison of the characteristics of an electric arc breakdown in vacuum between two silver or silver-nickel alloy convex electrodes, enabled us to show experimentally that the process initiating discharge in vacuum is the electronic emission at the micrometer scale. Increased content of nickel in the alloy improves the insulation and achieves high resistance to erosion for low power arcs. Heating in vacuum demonstrates the multiple layer structure of studied alloys. Secondary electron microscopy and energy dispersing spectroscopy of the electrode surfaces after breakdown, as well as the measurements of fall and delay times, enabled us to evidence the origin of the electric arc.

Numerical fault arc simulation based on power arc tests

AbstractMore than 200 power arc tests were carried out with original arrangements of overhead line insulators and arcing fittings for 20 kV, 110 kV and 220 kV. With an adequately modelled network, short‐circuit currents in the range of 2 kA to 12.5 kA can be realized. Analysis of the measurements shows that a typical arc voltage time function can be attributed to each insulator type and arrangement. Using the measured variables, which were digitally recorded and stored on optical media, an existing numerical arc model has been enhanced, which can be applied in an electromagnetic transients program to reproduce the dynamic and random behaviour of power arcs for any insulator arrangement, current and system voltage.

DC arc excitation — is it obsolete?

The significance of direct current arc plasmas as radiation sources for optical emission spectroscopy is discussed. Their development is discussed in view of the other radiation sources such as flames, discharges under reduced pressure and high-frequency plasmas. It is shown, that the wall-stabilized arc as one of the current-carrying DC-plasma arcs is also today still of use, for instance, for the analysis of powder samples. Transferred arc plasmas also include a series of plasmajets of which the three-electrode DC arc plasma (DCP) is commercially available. The significance and use of these arc discharges are compared with those of other radiation sources such as the inductively coupled plasma (ICP) and the glow discharge lamp, by means of the number of publications made in the course of time. For the analysis of solid samples, DC arcs can be universally used; they have high power of detection and are simple and therefore cannot, up to now, be replaced. Because of the low investment and operation costs, the DCP is a viable alternative to the ICP for the analysis of solutions. Furthermore, the power of detection of the DCP is comparably high and is in some cases, because of the high tolerable salt concentrations, even higher than in the case of the ICP. Matrix effects, however, are high in the case of DCP, due to varying concentrations of easily ionized elements. The capabilities of high power arcs with respect to lower matrix effects and a possible increase of the dynamic range by use of different lines of the elements to be determined are discussed. It is also claimed that the availability of different commercial DC arc systems is prerogative for their further development.

Experiences of wall interaction in JET

The first year of operation of JET has recently terminated, and the first thorough interior examination has taken place. The work has been carried out jointly by JET staff and a Culham Laboratory team working under a Task Agreement. Erosion features attributable to run-away fast electrons, to unipolar arcs, and to rare power arcs have been identified. Sputtering and evaporation processes are seen and redeposition and cross-contamination of elements within the torus are clearly observed. Severe local effects of thermal excursions are seen on protection plates. Detritus recovered from the vacuum vessel includes metallic droplets and films, and fibrous material, probably from clothing. Surface analysis on long term samples, on limiter components and on probes exposed for short periods at selected phases through the pulse have shown that during tokamak operation more material overall is transferred from the main vacuum chamber wall than from the limiters themselves.

Burnthrough Of GIS Enclosure Due To Power FaulT ARCS

Enclosure burnthrough in gas insulated substations due to power arcs has to be prevented for personnel safety and operational reasons. Many studies on burnthrough have been published giving different experimental results. Thus, the estimation of burnthrough times on the basis of this published data seems difficult. This paper summarizes the present status of experimental and theoretical studies on burnthrough and shows, that the data appears more homogeneous if the experimental conditions are considered. Formulae based on theoretical analysis seem less practicable than those empirically found. One of these empirical formulae gives reliable and conservative estimates of burnthrough times in actual equipment and is recommended for general use. In the discussion of actual field experience it is emphasized that auto-reclosing in GIS increases the risk of burnthrough and thus the practice should be very carefully reviewed. Areas requiring further investigations are indicated.

Optimization of a heat engine based on a dissipative system

A new class of heat engine is analyzed in which the working fluid operates in a dissipative process, never in equilibrium. The conditions are found for stability and for the generation of work. Then the optimal path is found for operating the general dissipative engine by means of optimal control theory. The optimal cycle consists of arcs of constant power and of approximately instantaneous adiabats. If the heat flow is a function of temperature only, then the constant power arcs become isotherms. An upper bound is found to the power output. Two examples are worked out in detail: a light-driven dissipative engine whose absorption is a step function of temperature, and a light-driven dissipative engine whose working fluid undergoes a chemical reaction (isomerization), absorbing light in the isomeric form favored at high temperatures.

Fault Location in SF6 Insulated Conductors Using Direct Fluxgate Magnetometry

Gas insulated substations (GIS) are becoming more popular for substation design largely due to reduced space requirements as well as environmental benefits. Isolated phase designs generally consist of a single cylindrical conductor enclosed in a coaxial aluminum tank (or sheath). Pressurized SF6 is usually used for electrical insulation. For increased reliability, instrumentation methods have been developed to detect the location of power arcs which occur within the enclosed containers. Under EPRI funding, we have developed a new technique in which the location of a fault is detected by directly measuring the axial component of the 60 Hz magnetic field which appears outside the sheath during the flashover. The instrument is a specialized form of "fluxgate" magnetometer modified to allow long life using inexpensive batteries. The magnetometer output is coupled directly to a switching circuit which operates a "magnetic disc" indicator. When a fault is registered, the disc indicator exhibits a bright color which can be easily read from a distance of 10-15m. The instrument is proposed for use at areas within the substation which are more prone to flashovers, especially near dielectric spacers which support the inner conductor every few meters. Flashover measurements indicate that the sensor reliably detects a fault current of 4 kA or larger under typical substation conditions. This sensor is attractive for retrofitting existing gas-insulated systems in that installation does not require shutting down the system.

Porcelain and Composite Longrod Insulatoes - A Solution for Future Line Requirements

Insulators of the longrod-design have been in use in Central Europe for more than 40 years; in several countries they have replaced the previous cap and pintype insulators (in the USA often referred to as suspension-type insulators). More recently, the advantages of longrod insulators have found new places of installation also in other countries, specifically in high-voltage transmission lines being confronted with heavy solid-layer pollution problems. Theoretical considerations anticipate also considera advantages with an HVDC-insulation. Of special interest is also the longrod design as composite longrod insulator. In spite of their worldwide application and the excellent service experiences gained - especially in the case of conventional longrod insulators - the technical characteristics of these insulators are not yet adequately known in many places. Thus, this paper presents a survey on the electrical and mechanical properties as well as the insulation performance under pollution, performance under power arcs, and the interference-voltage behavior. Furthermore, the particulars and differences during installation and operation of these insulators in comparison to strings of cap and pin-type insulators are pointed out. The technologically sensible dimensioning limitations are described. The observations prove that longrod insulators represent an advantageous solution and are best suited for future line requirements.

A Test for the Effect of High Energy Arcs on the Flash-over Strength of Insulators in Compressed SF6

A test method for evaluation of solid insulating material for insulators in Compressed Gas Insulated Transmission (CGIT) systems has been developed. The test measures the ability of an insulating surface to withstand voltage after being subjected to a high energy power arc across its surface. The test has been used to evaluate several different solid insulators in SF6 at 0.4 MPa. The test circuit is designed to effect an efficient transfer of energy from a capacitor bank to an arc on the insulator surface. Voltage reversals in the capacitor bank are minimized. Flash-over of the insulator is initiated using an impulse generator. After exposing the insulator to the arc, the power frequency flash-over voltage is used as a relative measure of the ability of the material to withstand power arcs. The test circuit, sample geometry and representative measurements are described. Epoxy systems with the best performance in these tests showed little or no decrease in power-frequency flash-over voltage after arcing, while large reducitons were observed in other epoxies after only a few power arc-overs. This arc damage test was developed as part of an ERDA Contract to develop a prototype 1200 kV CGIT system.

Perspectives on Soviet Intervention in Africa

The Soviet Union has projected its military power in Africa, first to Angola, then to the Horn of Africa. These developments, in conjunction with the collapse of the Shah's regime in Iran, rapid increases in oil prices, instability in the Persian Gulf and South Asia, and the Soviet military build-up in the context of SALT negotiations, have increased the virulence of debate about the way the United States should respond to the Soviet Union and should define its political, economic, and security interests in Africa, the Middle East, and the Persian Gulf. Much of this debate has been presented in terms of globalist versus regionalist perspectives on U.S. policy toward countries and regions in which the Soviet Union has intervened and projected its military power. Globalists and regionalists ask many of the same questions: What are the principal U.S. interests in a given region? What is the nature and magnitude of the Soviet threat? What policies should the United States pursue to advance its interests and deal with the Soviet Union? But the order or priority of the questions and the weight given to answers frequently differ. Globalists ask first about the behaviors, motivations, and threats of the Soviet Union or other large powers. Regionalists usually start by trying to define U.S. interests in a particular region and to understand the situation in its own terms. Globalists accuse regionalists of having parochial concerns and of being unwilling to see broad U.S. interests; regionalists argue that globalists are frequently ignorant of, and refuse to deal with, the specific conditions in a country and are therefore given to sloganizing about regional power vacuums or arcs of instability.

Fast Circuit Breaker for the Discharge of a Storage Inductor

VERY high power lasers, certain plasma machines, apparatus for the study of high power arcs, and similar equipment, often need a means of storing some tens of MegaJoules, to be discharged in about one millisecond. Capacitor banks of this rating are so large and expensive, that several proposals have been made for the use of rotating machines to store the energy (by G. Gauchon, P. H. Rebut and A. Torossian at the Fifth Symposium on Fusion Technology, Oxford, 1968, and C. Rioux at the Fourth Symposium at Frascati, 1966, and in refs. 1 and 2). The homopolar generator at the Australian National University in Canberra can supply 1.5 × 106 A at 800 V, that is 1.2 MJ ms−1, and it can do this for about 0.1 s. But, for most applications it is an advantage to increase the peak power and reduce the duration of the discharge available from a rotating machine. This report deals with tests on a model of equipment planned to take 20 MJ in 0.3 s from the Canberra generator, and deliver 15 MJ to a load in one millisecond. The model should be able to take 400,000 J from the generator, but the present tests have been limited by the testing arrangements to 100,000 J. The equipment includes several unusual components, however, and their successful operation at this energy is notable.

Properties of an Argon Laser in the Schlieren Study of Gas Flow within an Electric Arc or Plasma

AbstractA diagnostic technique is suggested which will permit studies of gas (law within power arcs or plasmas by the use of a Schlieren system. Experimental evidence is given showing that High Speed (107 P.P.S.) Kine Schlieren photography can be undertaken with a gas laser of moderate power output. Both multiphase and uniphase modes of operation are considered, and a simple form of exposure assessment is given which relates spectral sensitivity (Sλ) of a photographic material with the laser beam in use. A possible method of obtaining pulsed amplification by the opplicotion of a solenoid is discussed.

Characteristics of Power Arcs in Air Gaps

Characteristics of Power Arcs in Air Gaps

Arc Initiation on Heated Metals by a Hydrogen Discharge

AN undesirable phenomenon of importance to experimental investigations of toroidal pinched gas discharges is the formation of unipolar and power arcs at metallic parts of the system exposed to the plasma1. Previous work2,3 has indicated the important part played by insulating inclusions in metals in the process of arc initiation under these conditions. We are investigating the arcing characteristics of refractory metals, exposed to a toroidal discharge in pure hydrogen, as a function of temperature. The results so far obtained support the hypothesis that arcs are initiated through the agency of second phases.