Kalyan Koppisetty

Nano/Micro Dielectric Surface Flashover in Partial Vacuum

In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered Al2O3 (nano/micro-composite dielectric) samples in partial pressure of nitrogen. The flashover studies are conducted separately using DC and 20 kHz AC signals. The voltage, current, and light emission waveforms are obtained. The optical data is collected by a video camera and a photomultiplier tube (PMT). The nano/micro composite dielectric samples used in the experiments are produced in-house by mixing 1:10 weight ratio of AI2O3 powder with epoxy resin of known properties. Throughout this study, copper electrodes are used and are placed over the dielectric samples to initiate surface flashover events. The results of surface flashover voltages as a function of pressure are presented. Additionally, optical emission characteristics along with the voltage and current waveform data are also presented.

Breakdown characteristics of helium and nitrogen at kHz frequency range in partial vacuum for point-to-point electrode configuration

Power devices operating in partial vacuum, such as aerospace systems or space environment are susceptible to partial discharges, corona, or volume discharges due to the partial vacuum conditions. These power systems also operate under frequencies and waveforms quite different from those studied and developed for earthbound power distribution systems. In this paper, we present our studies on the breakdown characteristics of helium and nitrogen gases under positive square-pulsed voltage at frequencies varying from 50 kHz to 200 kHz in partial vacuum, for a point-to-point electrode configuration. It is observed that high frequency breakdown voltage is lower than the dc breakdown voltage under the same experimental conditions and electrode geometry. Also, breakdown voltage versus pressure curves exhibited a Pashcen like behavior. Breakdown voltages of helium and nitrogen as a function of signal frequency are also presented.

Nano-dielectric materials in electrical insulation application

High performance electrical insulation materials and structures must be free from unwanted and unpredictable dielectric breakdown through the insulator as well as surface flashover along the interface between the insulator and the ambient or vacuum. The last decade has witnessed significant developments in the area of nano-particulate and nano-dielectric materials, and significant effects of nano-scale fillers on electrical, thermal, and mechanical properties of polymeric materials have been observed. Surface flashover is one of the major issues in electrical insulation in power systems operating either in space (vacuum or partial vacuum) or atmospheric (earth-bound) environments. Thus, development of new and advanced materials to be used in power systems requires extensive studies on electrical insulation characteristics of these materials before they can be used in commercial systems. Most of the research in characterization of nano-dielectric materials has been for systems operating in atmospheric environment; there are limited or no data for systems using these materials in space environments. In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered Al/sub 2/O/sub 3/ in partial vacuum. The flashover studies were conducted separately using DC and AC signals. Surface flashover voltage and current waveforms of the samples and light emission waveforms and video images during the breakdown were recorded. Optical data collected by a video camera along with the PMT light emission data are analyzed and the results of the optical emission characteristics of surface flashover are presented along with the electrical data. The samples used in the experiments were produced by using either epoxy resin of known properties or by mixing known quantities of Al/sub 2/O/sub 3/ with epoxy. The electrode material placed over the dielectric samples was copper.

Gaseous breakdown at high frequencies under partial vacuum

High voltage devices and systems operating in space environment are usually subjected to partial discharges or corona discharges due to the partial vacuum environment, and these activities within a power system are usually considered as major design problems. Currently, space power systems operating, at voltages higher than the traditional 28 V systems are being considered. Furthermore, the availability of high power electronic devices operating at higher switching frequencies makes the corona and partial discharge problems more important than before. Our initial studies conducted in the laboratory suggest that the corona inception voltage levels at high frequency are indeed lower than the dc breakdown voltages for various pressures. Thus, this work will present the breakdown data obtained for ac-voltages at 10 kHz to 30 kHz in partial vacuum environment. Furthermore, results will be compared with the data available in the literature, and further research work in high frequency breakdown in partial pressure environment will be discussed.

Partial vacuum breakdown characteristics of helium at 20 kHz for inhomogeneous field gap

In general, power devices and systems operating in vacuum or space environment are more susceptible to partial discharges, corona, or volume discharges due to the partial vacuum conditions. Additionally, high frequency operation of a power system is a contributing factor in lowering the breakdown voltage of insulation. In this paper we present our studies on the breakdown characteristics of helium operating in DC and 20 kHz AC field in partial vacuum, for a point-to-point and point-to-plane electrode configurations. Breakdown voltage as a function of pressure in the range of 27 to 400 Pa (0.2 to 3 torr) for both the DC and 20 kHz AC cases is presented. Voltage and current waveforms along with the optical emission waveform of the breakdown events are also presented. A variable DC power supply for DC and an in-house built variable DC-offset-AC power supply for the high frequency breakdown experiments are used. A high voltage probe and a Pearson current sensor are used for the voltage and current detection, and a photo-multiplier-tube with a digital pico-ammeter and a video camera are used for the optical signal detection of this set-up. The breakdown voltage as a function of pressure for both the AC and DC experiments, along with voltage breakdown waveforms for both electrodes are presented.

Surface Flashover Characteristics of Nano Particle Cast EPOXY Resin

Surface flashover across solid insulators in vacuum has found applications in the area of space power systems. One scenario where surface flashover in vacuum can be a problem in space power systems is a spacecraft operating in geosynchronous orbit (GEO) or low earth orbit (LEO) interacts with the local space environment resulting in the differential charging of the spacecraft to electrical potentials of many hundreds to few thousand volts. When this charging reaches a critical value, surface flashover on the solid dielectric insulator may occur, resulting in loss of high voltage isolation and damage to the space power systems on board. Similarly, surface flashover can also occur across insulators in the utility power system in atmospheric pressures as well. In general, random emission of a small number of electrons at the cathode results in positive charging of the dielectric surface at the triple junction, thus initiating surface flashover across the dielectric. In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered Al2O3. The samples used in the experiments were produced by using either epoxy resin of known properties or by mixing known quantities of Al2O3 with epoxy. The electrode material placed over the dielectric samples was copper. The flashover studies were conducted using DC and AC signals separately, and surface flashover voltage characteristics and the breakdown voltage wave forms of samples were determined.

Partial vacuum breakdown of helium at 20 khz for point to-plane geometry

The next generation of space vehicles is likely to utilize higher voltages than the traditional 28 Vdc for onboard power distribution. Such is already the case for the International Space Station (ISS), which utilizes 120 Vdc. The availability of switching power supplies operating at high switching frequencies makes it important to consider the effects of these higher operating frequencies in the context of corona and gas breakdown in space applications. In general, power devices and systems operating in the space environment are more susceptible to partial discharges, corona, or volume discharge due to the partial vacuum environment. Such phenomena within power system components are considered unacceptable in systems where long lifetime and reliability is necessary. The literature suggests that the dielectric strength of certain gases falls off drastically at frequencies over 100 kHz, which is not theoretically predictable W. Pfeiffer (1991). Although there have been studies on the influence of frequency on gas breakdown over specific frequency ranges, this behavior over the range below 1 MHz is not completely understood. In addition, existing data cannot be extrapolated for miniature systems with smaller electrode gaps operating at very low pressures. Our recent studies confirm that high frequency operation in space could be a major concern when designing space power systems Kalyan Kopisetty et al. (2003), and that the breakdown voltage levels at high frequencies (< 1 MHz) can indeed be lower than the DC breakdown voltage levels, at certain pressures. In this paper we present our studies on the breakdown of helium operating at 20 kHz in partial vacuum, for a point-to-plane electrode configuration. An AC voltage source with adjustable DC off-set was used in the experiments. Preliminary results including voltage and current waveforms, along with the light emission data from the discharges are presented. The data suggests that the breakdown is a relatively short event occurring within approximately 5 to 10 microseconds, with a relatively large transient current peak. We observe that once the discharge is initiated, it becomes self-sustaining as long as the applied voltage across the electrodes is not removed. Thus, the light emission from the electrode gap is observed for several cycles, although the voltage and current waveforms indicate this process to be in the microsecond range. It was also observed that the breakdown voltage characteristic exhibits a pattern similar to the typical Paschen curve for DC breakdown in gases

Surface Flashover Characteristics of Nano-Composite Dielectric Materials Under DC and Pulsed Signals in Partial Vacuum

Surface flashover is a major issue in electrical insulation in power systems, both in space or atmospheric environments. In general, random emission of a small number of electrons at the cathode results in positive charging of the dielectric surface at the triple junction, thus initiating surface flashover across the dielectric. Developments in nano-particulate and nano-dielectric materials and effects of nano-scale fillers on electrical, thermal and mechanical properties of polymeric materials have been observed. In this paper, we present experimental results of surface flashover characteristics of epoxy resin and epoxy resin cast with powdered Al2O3 in partial vacuum. The flashover experiments are conducted with DC, AC and repetitive pulsed signals separately. Surface flashover voltage and current waveforms and light emission data with PMT were recorded. The samples used in the experiments were produced by using either epoxy resin of known properties, or by mixing known quantities of Al2O3 with epoxy. The electrode material placed over the dielectric samples was copper

Helium Breakdown Characteristics under 100 kHz Range Pulsed Voltages in Partial Vacuum for Point-to-point Electrode Geometry

In this paper we present our work on breakdown studies conducted in helium at partial vacuum conditions for a point-to-point electrode setup. A high frequency pulsed voltage signal is applied across the electrodes and the voltage-current characteristics are observed. The applied signal consists of a train of square pulses in the frequency range of 50 to 200 kHz with 50% duty cycle and rise/fall times in the range of 20-30 ns. These studies were conducted to understand and compare the role of the pulse repetition rate in electrical breakdown initiation in low pressure conditions. Preliminary data of voltage and current waveforms, along with the light emission data are presented. The optical data collected by a PMT (photo multiplier tube) as a function of the time is presented in comparison to the varying voltage

Optical emission characteristics of helium breakdown at partial vacuum for point to point geometry

In general, power devices and systems operating in vacuum or space environment are more susceptible to partial discharges, corona, or volume discharge due to the partial vacuum conditions. Partial discharge and breakdown measurements have been performed on electrical equipment operating in such environments for over decades. In spite of all the studies, fundamental understanding of partial discharge or corona initiation has not been understood completely. Various means of detection have been used over the years, including the detection of electromagnetic emissions using antennas or by observing the current through the ground cables to obtain a better understanding. The measurements are usually analyzed together with other techniques like visual inspection, transient voltage/current measurements and acoustic/optical characteristics. In this paper we present our work on optical emission characteristics of breakdown events at partial vacuum for point-to-point electrode configuration, operating at 20 kHz frequency in helium. A DC-offset-AC voltage source was used for the high frequency experiments. Preliminary data of voltage and current waveforms along with the light emission data are presented. Optical data collected by a video camera is analyzed and the R/G/B emission characteristics as a function of time are presented.