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The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SIR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton[TM], a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed. Index Terms--Surfactant, Triton[TM], erosion resistance, mechanical properties, nanofiller, dispersion, dielectrics, silicone, nanocomposites.

Variable-speed pulsewidth-modulated (PWM) drives allow for precise speed control of induction motors, as well as a high power factor and fast response characteristics, compared with nonelectronic speed controllers. However, due to the high switching frequencies and the high dV/dt, there are increased dielectric stresses in the insulation system of the motor, leading to premature failure, in high power and medium- and high-voltage motors. Studying the degradation mechanism of these insulation systems on an actual motor is both extremely costly and impractical. In addition, to replicate the aging process, the same waveform that the motor is subjected to should be applied to the test samples. As a result, a low-power two-level high-voltage PWM inverter has been built to replicate the voltage waveforms for aging processes. This generator allows for testing the insulation systems considering a real PWM waveform in which both the fast pulses and the fundamental low frequency are included. The results show that the effects of PWM waveforms cannot be entirely replicated by a unipolar pulse generator. Index Terms--High voltage, insulation testing, inverter-fed drive motors, power electronics, pulsewidth modulated (PWM).

In this paper, the degradation processes in stator-bar groundwall insulation that is subjected to steep-front voltage pulses, at different temperatures, are studied. The test conditions include pulse voltage amplitudes up to 6 kVp and pulse switching frequencies up to 3 kHz in ambient temperatures of 23 [degrees]C, 120 [degrees]C, and 155 [degrees]C. During the aging process, the surface temperature is monitored with an infrared camera to determine the regions with highest temperatures and the partial discharge (PD) activity. The visual examination of failed bars confirmed that the groundwall insulation in these regions is degraded. Index Terms--Adjustable-speed drives, converters, dielectric heating, groundwall insulation, induction motor, partial discharge (PD), pulse voltage, solid-state switches.

The paper reports on tests done on four commercial room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings aimed at achieving information on the relative performance of the coatings with respect to aging. The initial characterization of the coatings includes the identification of the primary filler type, concentration of filler, the amount of free fluid, and the molecular species of the free fluid. Soxhlet extraction and gas chromatography tests show considerable depletion of fluid after accelerated aging tests in acid-water and the associated changes to the physical properties is assessed by standard mechanical tests on coupon size specimens. The effect of acid-water aging on the hydrophobicity is assessed by measurements of the static contact angle and the onset of leakage current in an incline plane test. Several field aged coatings are assessed for residual LMW fluid which is compared to accelerated aging tests. Index Terms--RTV silicone rubber coating, HVIC, accelerated aging, depletion of fluid, hydrophobicity, de-polymerization, Soxhlet extraction, lifetime, gas chromatography, LMW fluid.

This paper reports on the heat erosion resistance of various silicone rubber compositions under infrared laser heating that simulates the dry band arcing phenomenon on outdoor insulation. The composites are made using a two-part addition cure silicone rubber, with various amounts of alumina, natural silica, or fumed silica, nano- or micron size, and different amounts of Triton[TM] X-100 surfactant. It is shown that the surfactant greatly improves the dispersion of nanosized particles, yielding composites that are more homogeneous, with improved resistance to heat ablation. Significantly improved dispersion in the presence of surfactant is confirmed by SEM analysis for some nanofillers, while very little effect is observed for others. The surfactant is beneficial up to the point where the filler surface is saturated with the additive. Fumed silica is shown to impart greater heat ablation resistance than natural silica and alumina. Furthermore, a distinct protection mechanism appears to be operative for fumed silica and natural silica as opposed to alumina. Index Terms--Surfactant, Triton[TM] X-100, erosion, nanofiller, dispersion, dielectrics, silicone, composites.

In this paper, a MOSFET-based pulsed power supply capable of supplying square pulses of up to 3000 V and widths from nanoseconds to milliseconds is presented and used for an investigation into electroporation-mediated delivery of a plasmid DNA molecule into the pathogenic bacterium Escherichia coli O157:H7. It was concluded that increasing the electric field strength and pulse amplitude resulted in an increase in the number of transformants. However, increasing the number of pulses had the effect of reducing the number of transformants. In all the experiments, the number of calls that were inactivated by the exposure to the pulsed electric field were also measured. Index Terms--Bacterial transformation, DNA transfusion, electroporation, Escherichia coli.

This letter describes a high-resolution technique called thermally stimulated depolarization current (TSDC) that can be used for the measurement of space charge accumulation in the medium voltage magnet wires operating on pulsewidth modulated (PWM) inverters. Index Terms--Fast rise time pulses, induction motors, inverterfed drive motors, magnet wires, space charge injection.

The paper presents the experimental results on accelerated aging of enameled wires with and without nanofiller in the coating under partial discharge (PD) activity. The residual life of the wires, and the surface roughness as measured by a scanning electron microscope (SEM), are used to evaluate the effects of the nanofiller. The surface erosion in the specimens without nanofiller is considerably greater, which is 1120-1270 nm, under pulse aging; whereas, in specimens with ~1%, by wt, fumed silica (Si[O.sub.2]) nanofiller it was measures to be 230-250 nm. An evaluation of the residual life of the wires, aged under high frequency ac waveforms, reveal that the wires with Si[O.sub.2] achieved a life that is twice the life of conventional wires. The two-parameter Weibuil distribution of dielectric strength data show that the value of the shape parameter, [beta], increases from 2.6 to 11.4 for the coatings with nanoffilers indicating that the material becomes more homogeneous and exhibits fewer defects. Finally, the paper discusses possible reasons for the reduction in surface erosion and improvements in breakdown strength of enameled wires filled with various types and concentrations of nanofillers. Index Terms--Adjustable speed drives, dielectric strength, fast rise time pulses, inter-turn insulation, nanofilled enameled wires, residual life, standard deviation.

The paper presents the results of the study on the influence of insulator profile on the aging performance of silicone rubber (SIR) insulators in salt-fog. Experiments have been conducted on various two-shed arrangements at 35 V/mm average stress and 0.25 S/m salt-fog conductivity level. The work is also extended to include commercial 15 kV class insulators with different profiles. Shed spacing, shed diameter, alternate shed design and shed shape are the parameters investigated in this study. The low frequency harmonics of the leakage current, early aging period (EAP), and equivalent salt deposit density (ESDD), are used to evaluate the aging performance of different designs. Insulator profile is shown to greatly influence the aging performance of SIR insulators. Shed shape proves to be the most important parameter to be considered in designing non-ceramic insulators profiles. Also, as the shed spacing decreases, the performance of SIR insulators improves. Simulation results using FEMLAB[C] show that the electric field on insulators is below the corona onset at both dry and wet conditions. Dry band arcing is therefore the main electrical cause for aging in distribution class insulators and it is possible to improve the pollution performance of SIR insulators using appropriate profiles as suggested in this work. Index Terms--Leakage current, silicone rubber insulators, aging.

One of the most important factors in an artificial pollution test of transmission and distribution insulators of power systems is the short-circuit current of the source. Most laboratories do not have strong source and test transformers. In this paper a test setup has been introduced to improve the performance of high-voltage laboratories for pollution test. It is based on adding an output capacitor and compensator reactors in a cascade setup. Beside simulations, clean-fog test method was used to determine the flashover voltage (FOV) of insulators that selected from overhead lines. Using the developed setup, there is an error in FOV less than 30% compared with a stiff setup in light pollution for ceramic cap and pin insulators. Higher levels of pollution cause the higher error in FOV in all cases. Although the error increases with pollution level, it is smaller in the case of composite insulators. The error decreases depending on the hydrophobicity of silicon rubber. So the less hydrophobic the insulator surface, the greater the error in FOV. Index Terms--Cascade, flashover, insulator, pollution, short-circuit current.

The paper describes the investigation of the failure mechanisms of medium voltage inter-turn insulation, as a consequence of pulse aging. To study the performance and failure behaviour of enameled wires, models of inter-turn insulation are prepared with enameled wires having polyimide and nano-filled coatings. The aging of such bar samples is attained by sinusoidal (60Hz), fast repetitive unipolar voltage pulses, and high frequency ac waveforms. To establish the residual strength of the bar samples, dc breakdown voltages are determined before and after the aging. In addition, the thermally stimulated depolarization current (TSDC) is used to provide information about the relaxation processes, such as the disorientation of the dipoles and the release of charges from the trapping sites in enameled wires. The various trapping levels, which have discrete energy differences with distinct peaks in the thermograms, are discussed in terms of space charge polarization. Index Terms--Form-wound stator coils, inter-turn insulation, nano-filled enameled wires, partial discharge inception voltage, residual strength, space charge injection, charge trapping levels.

In this paper, the effect of pulsed electric fields (PEFs) on naturally contaminated orange juice was investigated. A 2-log reduction in a colony count for the naturally grown microorganisms was achieved after application of 120 pulses/mL at a PEF level of 46 kV/cm. Also, the effect of the PEF on microorganisms inoculated in orange juice was studied. Compared to the naturally grown microorganisms, about l-log more reduction was observed with inoculated microorganisms that were subjected to the same PEF conditions. The results suggest that other factors like the increased temperature and antimicrobial additives might be required to enhance the killing efficiency. A 20 [degrees]C increase in temperature prior to the application of the PEF resulted in about 1-log more reduction in microorganisms. Index Terms--Electroporation, nonthermal pasteurization, pulsed electric fields (PEFs).

The standard methods available to test tracking and erosion resistance of filled silicone rubber do not allow to delineate the fundamentals of the thermal degradation, although the heat from the dry band arcing is the main degradation factor. In this work a thermal imaging camera is used to investigate the performance of filled silicone rubber in an inclined plane test, and a scheme is established to relate the temperature and the electrical discharge energy. Further, an infrared laser technique, based on constant energy approach, is developed to study the material performance under laser heating. The technique consists of applying a certain amount of infrared laser energy during a set time period, in order to produce erosion in the silicone rubber samples. Through correlation studies the applicability of the proposed laser technique to rank silicone rubber samples with various fillers has been validated. The laser tests show identical ranking of samples when compared to samples ranked using inclined plane tests, yet offering significant advantages of being faster, simpler, and reproducible. Index Terms--Outdoor insulation, composites, erosion resistance, silicone rubber, dry band arcing, diagnostics, high voltage, fillers.

In this paper, the effectiveness of stress grading coatings (SGCs) on form wound stator coil groundwall insulation under fast rise time pulses is analyzed. The combined performance of the stress grading coating and the semiconductive slot coating is studied under fast rise time transient voltages. During the rapid rise of voltage, the high stress moves from the stress grading coating to the semiconductive coating at the end of the slot. According to the results, it is evident that the design of both the stress grading and semiconductive slot coatings must be done together for effective stress relief. The use of materials with varistor behavior in the stress grading coating, combined with a high conductivity semiconductive slot coating, is analyzed as a solution to the high stress that develops at the slot end of form wound stator coil groundwall insulation of inverter fed drive (IFD) motors. Index Terms--Fast rise time pulses, field dependent conductivity, form wound stator coils, inverter fed drive motors, semiconductive slot coating, stress grading coating, varistor material.

Many industrial applications like high-field food sterilization require short-duration fast-rise-time high-voltage pulses. Measurement of such narrow steep-front high-voltage pulses are always difficult, considering the potential levels and the time scales involved. In addition, by nature, liquid foods are highly conductive, hence, any small change in circuit inductance has substantial influence on the measured pulse. Further, the oscillations introduced by the circuit parameters influence the voltage magnitude and the effective treatment time. Hence, these points must be taken into account while computing the total treatment time and the energy actually spent, as these parameters influence the kinetics of food processing. In this paper, the effects of load impedance, the circuit inductance, and the location of the probe position that influence the shape of the measured pulse with liquid foods as load are discussed. It has also been shown that knowing the low-voltage conductivity of the food to be treated, and with a realistic estimation of circuit inductance, it is possible to predict the shape of the pulse under different test conditions using PSPICE circuit models. Index Terms--Food sterilization, high voltage, microbial killing, pulsed electric field.

Pores occur naturally in cell membranes. Application of an electric field generates a force which tends to open the pore, a mechanism known as electroporation. The force generated depends on the electric field in the pore and the difference in dielectric constant between the fluid in the pore and the membrane. In this paper, we use transient finite-element analysis to investigate the field as a function of time in a system which consists of an electrolyte, an ellipsoidal bacterial cell membrane, and cytoplasm within the cell membrane. For this shape of cell, the field in the cell membrane is caused largely by the relaxation of the field in the cytoplasm. In addition, we compute the force on the pore wall, both in an analytic approximation and numerically as a function of time during a variety of applied voltage waveforms, using transient finite-element analysis. The numerical data are in good agreement with the analytic approximation and provide a basis for judging the efficacy of waveforms for sterilization based on a 'figure of merit' which is suggested in the paper. Index Terms--Cell membrane, electroporation, pulsed power, sterilization, transient finite-element analysis.

This paper proposes a new real and reactive power coordination controller for a unified power flow controller (UPFC). The basic control for the UPFC is such that the series converter of the UPFC controls the transmission line real/reactive power flow and the shunt converter of the UPFC controls the UPFC bus voltage/shunt reactive power and the DC link capacitor voltage. In steady state, the real power demand of the series converter is supplied by the shunt converter of the UPFC. To avoid instability/loss of DC link capacitor voltage during transient conditions, a new real power coordination controller has been designed. The need for reactive power coordination controller for UPFC arises from the fact that excessive bus voltage (the bus to which the shunt converter is connected) excursions occur during reactive power transfers. A new reactive power coordination controller has been designed to limit excessive voltage excursions during reactive power transfers. PSCAD-EMTDC simulation results have been presented to show the improvement in the performance of the UPFC control with the proposed real power and reactive power coordination controller. Index Terms--FACTS, unified power flow controller (UPFC), coordination controller.

Silicone rubber samples having various concentrations and mean particle sizes of either alumina tri-hydrate or silica fillers, prepared by room temperature and heat cured under pressure (hot pressed), are tested for erosion resistance in the ASTM D2303 inclined plane tracking and erosion test. Their corresponding thermal conductivities are determined using a transient temperature technique in which an infrared laser is employed as the heat source and a thermal imaging camera as a temperature detection device. Scanning electron microscope observations show greater filler bonding to the silicone matrix in the hot pressed samples than in the room temperature vulcanized samples leading higher thermal conductivity and increased resistance to erosion, for both ATH and silica filled samples. The correlation study shows a strong relationship between the erosion resistance and the thermal conductivity of the tested samples, highlighting the importance of an outdoor insulating material to have high thermal conductivity in order to withstand dry band arcing. The results can be used to provide guidance on filler selection for silicone rubber compounding for outdoor insulation applications. Index Terms--Thermal conductivity of silicone rubber, erosion resistance of filled silicone rubber, inclined plane tracking and erosion test of filled silicone rubber.

Silicone rubber samples, filled with 30% alumina trihydrate, subjected to the ASTM inclined plane test, show good correlation between the measured harmonic power components of dry band arcing and the surface temperature recorded with a thermovision camera. The simultaneous study of the low frequency Fast Fourier Transform and variations in temperature shows that when the temperature rises above 100[degrees]C there is a well defined increase in the low frequency harmonic components of the measured power; however, this trend is not verified by the fundamental component. The eroded mass of the samples is measured independently by a laser approach and a model to rank the tested samples using the Inclined Plane Test is developed. The model is validated by applying it to both the recorded harmonic power components and temperature, resulting in the correct ranking of damage on the samples tested in the Inclined Plane test. Index Terms--Inclined plane test, dry band arcing, surface temperature, erosion resistance, thermal degradation, filled silicone rubber, erosion resistance.

The paper presents the results of a study on the effect of shed design on the aging performance of silicone rubber (SIR) insulators in salt-fog. The experiments on a single shed design at 35 V/mm average stress and 0.25 S/m salt-fog conductivity level are reported. Shed diameter, location and inclination angle are the parameters investigated in the study. The low frequency harmonics of the leakage current, early aging period, equivalent salt deposit density (ESDD), and physical damage are used to evaluate the aging performance of various designs. Insulators having sheds with 100 mm diameter show a better performance than those having 80, 60 and 40 mm diameter sheds. The inclination angle of the sheds is shown to have a significant effect in reducing the leakage current to a very low value but simulation results using FEMLAB[R] show that a steep inclination angle results in field enhancement beneath the shed that may lead to corona damage of the shed. A cup shaped design for the shed is shown to have a low leakage current level and a !ow field enhancement beneath the shed. Index Terms--Silicone rubber, ageing, electric field calculation, polymeric insulators, non-ceramic insulators, outdoor insulation, leakage current, harmonics, erosion.

The paper presents the results of using the fundamental and the low frequency harmonic components of leakage current to study aging of silicone rubber in salt-fog. Experiments have been conducted on RTV and HTV coated rods at different fields (0.25-0.6 kV/cm) and conductivities (1000 to 2500 [micro]S/cm). The onset of dry-band arcing on samples could be determined by measuring the low frequency harmonic components. A correlation has been found between the fundamental and low harmonic components of leakage current and different forms of aging. Where erosion could be associated with an increase in the level of both the fundamental and low frequency harmonic components of leakage current. For example, surface damage for HTV rods occurred when the fundamental component of leakage current was greater than 2 mA. On the other hand, when the samples approached failure, the fundamental component of leakage current reached relatively high values ( > 6 mA for HTV rods and > 2 mA for RTV rods) and the low frequency harmonic components of the leakage current tended to decrease. The results suggest that both the fundamental and low frequency harmonics of leakage current can be used as a tool to determine both the beginning of aging and end of life of silicone rubber in salt-fog. Index Terms--Silicone rubber, aging, harmonics, leakage current, failure mechanisms, salt-fog, erosion, polymeric insulators, composite insulators, outdoor insulation.

The paper presents an investigation on the use of partial discharge (PD) as a means to study the development of leakage current (LC) on silicone rubber insulators in a salt-fog chamber. Simultaneous measurements of LC and PD on dead-end type silicone rubber insulators exposed to different combinations of electrical stress and salt-fog salinity are performed. The results show that for an electrical stress of 33 V/mm applied to the insulator, the average LC experiences gradual changes and reaches a critical level (around 1 mA) where dry-band arcing is observed after 20 minutes at 2300 [micro]S/cm, and after 25 minutes at 1800 [micro]S/cm. The corresponding PD levels reach hundreds of pC after 15 minutes at 2300 [micro]S/cm, and after 20 minutes at 1800 [micro]S/cm. For a salinity corresponding to 1800 [micro]S/cm and stress of 26 V/mm, the LC changes much more gradually and reaches the critical level only after approximately 60 minutes. The corresponding PD reaches hundreds of pC after 30 minutes and more than 1500 pC after 60 minutes. Pattern recognition techniques have been applied to investigate the transition from corona to dry-band arcing. The features extracted from the maximum and mean apparent charge trends are found to be useful to cluster and classify the two phenomena. Simultaneous visual observations of the discharges on the insulator surface support the results. The investigation, therefore, shows that PD is a sensitive method for detecting the transition from corona from water droplets to dry-band arcing and an alternative method for studying the early aging stage of silicone rubber insulators.

Modeling of the electrical parameters of an electrostatic precipitator (ESP) with dust loading under pulse energization is difficult, and little progress has been made in the past. A method for modeling a wire-cylinder ESP under pulse energization based on the characteristics of Trichel pulses, and a means of dealing with the particle charging under such conditions are presented. The quantitative studies of the interactions between ion space charge and particle charging and their influence on the electric potential and field distributions have been numerically obtained under nanosecond pulse energization. The results show that the time-averaged current increased with applied peak voltage, pulsewidth, and pulse frequency and decreased with increased dust loading as expected. The space-charge density distribution was significantly influenced by the dust loading under pulse energization conditions. The proposed model is valid as long as the width of the applied voltage is less than 1 [micro]s. Index Terms--Back corona, charge density, dust loading, electric field, electrostatic, high resistivity, particle charging, precipitator, pulse energization, space charge.

Removal of zinc-rich ash and mercury from a gas stream using prototype electrostatic precipitators (ESPs) has been investigated. Dust particles collected from the thermal plasma ash volume reduction system of the Matsuyama, Japan, municipal incineration plant were used to study the performance of an ESP to collect zinc-rich ash. The ash was analyzed by neutron activation analysis using the nuclear reactor at McMaster University, Hamilton, ON, Canada. Collection efficiency as high as 99.9% was obtained in the removal of Zn from the flue gas with dc energization of the ESP. The mercury concentration was measured using a cold vapor atomic absorption spectrometer after sampling (OSHA-140 method) from the flue-gas stream. As a function of concentration, the mercury collection efficiency was higher at a higher concentration of mercury. Higher collection efficiency was obtained under negative dc energization compared to other modes of energization of the ESP; however, power consumption under the pulse application was much smaller compared to dc energization. Index Terms--Coal-fired power plant, electrostatic precipitator, fly ash, flue gas, mercury, particle charging, particulate contamination, pulse power, trace elements, zinc.