High-voltage Impulse Research Articles

A new rotating spark gap design

Standard spark gaps have lower time limits of gap recovery when testing with high repetition rate impulses and in high-current high-voltage multiple impulse testing. More important, they are not suitable for the generation of opposite-polarity successive impulses using conventional capacitive-type generation techniques. In this article, an improved design incorporating two rotating spark gaps is described. The new spark gap was used to test ZnO surge arresters with two successive impulses of currents up to 5 kA and voltages up to 50 kV. Time intervals as low as 10 ms were achieved between the two impulses. Both similar and opposite polarity tests were carried out successfully.

Influence of food processing on the immunochemical stability of celery allergens

Celery roots were processed by microwave heating, cooking, drying, γ-irradiation, ultra high pressure treatment and high voltage impulse treatment. The immunochemical stabilities of the three known allergenic structures of celery were tested with sera from patients who were sensitised to celery. In addition, rabbit antisera were used to detect the allergens profilin and Api g 1 on celery immunoblots. The specificity and reactivity of IgE from the patients' sera were investigated by immunoblotting, by an enzyme allergosorbent test (EAST) and by dose-related IgE inhibition experiments. The results of all three methods agreed closely and indicated high antigenic and allergenic activity in native celery which was reduced by thermal processing. The heat-stability of the known celery allergens decreased in the following order: carbohydrate epitopes> profilin>Api g 1. In contrast, the allergenicity was only mildly reduced by non-thermal processing. The results obtained with human IgE were confirmed by an in vitro mediator-release assay that is based on rat basophil leukemia cells (RBL cells) which were passively sensitised with celery-specific murine IgE. With sera from mice that had been immunised with native celery, the native sample and non-thermal celery preparations elicited the strongest mediator release, whereas a weak response was obtained with samples from heat-processed celery. These results agreed closely with the data obtained in allergic patients whose IgE antibodies were directed against the major protein allergen Api g 1. Our results may be helpful in risk assessment and in selecting food preparations which can be consumed without symptoms by a subgroup of celery-allergic patients with a known sensitisation pattern. ©1997 SCI

Experimental study of reaction mechanism of NO x removal by impulse high voltage discharges

(1) H2O plays the most important role in contribution to the removal of NOx under discharge condition. (2) The oxidation of NO to NO2 is attributed to the O atoms and O3 molecules produced from O2 by discharges, and NO2 is subsequently removed from the system by the OH radicals. (3) The O(1D) radicals contribute to the extra amount of OH radicals in addition to the original OH sources, which are the preponderate consumers of NO x . (4) O atoms have a harmful effect on NO removal. (5) The presence of H2O alone appears to be more important than the presence of O2 alone. (6) Combination of O2 and H2O contributes more to the NO x removal in the system than each of them does.

Observation of Prebreakdown Phenomena and Measurement of Dielectric Constant under Microwave Transformer Oils Frequencies in the Mixture of PCB and PXE

The electrical properties such as discharge development under a high voltage impulse having -40 kV crest value and dielectric constant under microwave frequency have been investigated for commercial transformer oil polychlorinated biphenly (PCB) and its mixtures with phenyl-xylene ethane (PXE). The prebreakdown phenomena has been observed by the fast photographing shadowgraph technique. The oneshot photographs have been taken for multiples of 5 nanoseconds delay time. Blumlein Cable Generator is designed and used to create a signal with very short rise time. A point cathode-plane anode system is used to observe the prebreakdown under -40 kV of impulse excitation. The gap distance is taken as 2 mm. and pulse duration as 188 nanoseconds. The dielectric constant of the mixture is experimentally measured between 8.5 GHz and 10 GHz frequencies.

Device for generating sound impulses for medical applications

A device, which is especially made for the generation of shockwaves to detect inner-body objects, is equipped with piezo-ceramic transducer elements which act as an electro-acoustical transducer which can be driven by a high-voltage source with high-voltage impulses to generate shock waves or sound impulses through directed deformations and length changes of the transducer elements is dependent on the given polarization of the transducer elements and the polarity of the high-voltage impulses. The sound energy emitted by the device may then be especially high if the transducer elements are excited and biased with a bias potential before the appearance of a high-voltage impulse and the polarity of the bias potential is opposite to that of the high-voltage impulse.

Impact of Sand/Dust Pollution on the Engineering Design Criteria of High Voltage Air Insulated Networks

Outdoor air insulated, high voltage transmission and distribution networks are frequently exposed to atmospheric pollution in the form of sand and dust storms which can affect the breakdown and prebreakdown characteristics and insulation performance of air gaps. This paper summarizes the findingks of an extensive study carried out to determine the effect of sand/dust contamination on the high voltage impulse breakdown characteristics of different types of air gaps. Analysis of the results of this study highlight the influence of airborne and surface adhering sand/dust contamination on the engineering design criteria to specify clearances of overhead lines and station equipment, design and performance of protective rod gaps and the accuracy of high voltage measurements using sphere gaps.

High-efficiency shock-wave generator for extracorporeal lithotripsy.

In extracorporeal lithotripsy, the electro-acoustic efficiency of electrohydraulic generators is limited by the inductance of the electrical discharge circuit. A new shock-wave generator is described that uses a coaxial discharge line enabling electro-acoustic efficiency to be greatly increased. The line is built using a para-electric ceramic with a relative dielectric constant of 1700, manufactured for use in high-voltage impulse mode. A coaxial spark gap, with minimal inductance, has been developed to obtain the triggered breakdown of the discharge line. Shock waves are created with a coaxial electrode plugged directly into the spark gap and immersed in an electrolyte of degassed saline. Electrode gap and electrolyte resistivity are adjusted to match the resistivity of the electrolyte volume between the underwater electrodes to the characteristic impedance of the line. The discharge line generates in the medium a rectangular current pulse with an amplitude of about 6000 A and a rise time of 50 ns. Compared with conventional generators, measurements of the expansive peak pressure pulse show an increase of 105% at 10 kV, 86.5% at 12 kV and 34.5% at 14 kV charging voltage. Electro-acoustic efficiency is found to be 11% instead of 5.5% for a conventional discharge circuit.

A high-voltage low-cost wide-band fiber optic transmission system with improved linearity

The paper presents the design, development and performance evaluation of an analog fiber optic link. It also describes the way the link was implemented as part of an approved high-voltage impulse measuring system, replacing the coaxial cable between the capacitive divider and the recording site. This link proved to have a large bandwidth of 105 MHz combined with a linearity of 0.6% and a very low cost. Results from tests were compared with those taken with the same measuring system using the coaxial cable for transmitting the impulses. The comparison shows that the measuring system with the optical link is better than the approved one with regard to important parameters, such as the response time and the steepness of the voltage collapse.

Highly sensitive measurement of surface charge distribution using the Pockels effect and an image lock-in amplifier

A visualization and a quantification technique for a latent electric charge image on a dielectric material has been developed by using the Pockels effect and a computer imaging technique. An optical phase modulation technique and a computer image lock-in amplifier technique were used to improve the signal-to-noise ratio. The measurement system has several improved performances; sensitivity of surface change of 1 nC cm-2, spatial resolution of 200 mu m and discrimination of charge polarity. The basic principle of advanced electro-optic surface charge measurement is described and the typical surface charge distribution of positive discharge streamer produced by a high impulse voltage (5 kVpeak) is demonstrated. Also, comparison is made between the modulation method and the non-modulation method.

Scanning Acoustical Microscopy

Abstract One of Olympus' not well known product in the American market is the UH3 Scanning Acoustic Microscope (SAM). This state of the art, highly versatile microscope has many applications from non-destructive imaging to biomedical analysis, to pharmaceutical applications to name a few areas of current industrial interest. The principle behind SAM is quite simple, and uses the basic physical laws of reflection. High frequency sound waves are mechanically produced by a piezoelectric crystal. A high voltage impulse spike starts the crystal vibrating at its preset resonant frequency emitting acoustical plane waves through a medium with a relatively high sound velocity such as sapphire. The waves are made to converge by a half-spherical lens at the bottom of the sapphire rod. The diameter of the lens is less than one millimeter and depends on the operating frequency. The lower the frequency, the larger is the diameter of the lens.

Radiated interference from a high voltage impulse generator

High voltage switching operations radiate large electromagnetic fields. These cause interference to sensitive electronic equipment. For example, the environment of most concern are those of high voltage substations and high voltage research laboratories. This paper evaluates electric and magnetic field measurements obtained during the breakdown of an SF/sub 6/ gas gap when a 4/400 /spl mu/s pulse was applied from a high-voltage impulse generator. Building upon previous work concerning initial results in terms of the E-dot and H-dot measurements, this paper also includes the evaluation of the E and H field magnitudes to determine the extent of equipment interference within the vicinity of switching/pulse operations. In addition, these laboratory results were extrapolated to allow comparisons to be made with results from previous studies investigating switching operations within a substation environment. The implications regarding EMC immunity standards and the level of interference is discussed.

インパルス高電圧測定系とその比較校正試験に対する誤差評定

インパルス高電圧測定系とその比較校正試験に対する誤差評定

Exponential fitting algorithms for digitally recorded HV impulse parameter evaluation

Standard analysis of high voltage impulses comprises determination of parameters describing the recorded impulses. These include peak value, front time, and time to half-value. This paper describes several fitting algorithms intended to facilitate extraction of these parameters from recorded data. These algorithms were used to fit bi-exponential models to smooth lightning and switching impulses, to lightning impulses having oscillatory fronts or peaks where the evaluation of the waveform parameters is based on the construction of a smooth curve, and to tail-chopped lightning impulses. The overall effectiveness of these algorithms and their influence on parameter estimates are presented and discussed. >

Optimal electric conditions in electrical impulse chemotherapy.

The relationship was examined between the tumoricidal effect and the electrical variables of in vivo electrical impulse chemotherapy. Donryu rats subcutaneously inoculated with AH‐109AY hepatocellular carcinomas were given a single high‐voltage electrical impulse of varying voltage and duration, 30 min after an intramuscular injection of 4 mg/kg bleomycin. As the voltage (V) was increased from 0 to 5 kV, the tumoricidal effect (E) increased in proportion to the square of the voltage. As the pulse duration (D) was increased from 2.5 to 5.8 ms, the tumoricidal effect increased in direct proportion to it. Combining these results yielded the formula, E=γV2D, which indicates that tumoricidal efficacy was proportional to the applied electrical energy. When the electrical energy was kept constant while varying the voltage and duration of pulse, the anticancer effect was the same, confirming this relationship for lower energy levels.

Accuracy of waveform parameters in digital measurement of single-shot waveforms

In high-voltage measurement, the digital measuring system is used widely because of its attractive features, for example, automatic data acquisition. However, the accuracy in the measurement of both the amplitude and time parameters by the digital measuring system is not known in detail, especially in the measurement of single-shot waveforms. In this paper, the accuracy of the peak value and the virtual front time of the standard lightning impulse without any signal processing of raw data is shown. From these results, the required characteristics for the digital measuring system to satisfy the IEC Draft on digital recorders for measurement in high-voltage impulse test techniques are shown. In addition, the accuracy of the peak voltage and the rise time of the Gaussian pulse is shown.

Closing/opening switch for inductive energy storage applications

A magnetically delayed vacuum switch operating sequentially in a closing mode and then in an opening mode enables the design of a compact electron-beam generator based on an inductive energy store and having only a single switch. Furthermore, the system can be entirely vacuum insulated, with no power feedthrough requiring low inductance or operating at high-impulse voltage levels. Feasibility of the unique power-switching configuration has been explored theoretically, experimentally, and computationally. In a proof-of-principle experiment, a voltage impulse twice the magnitude of the DC charge voltage was observed at a power level of 20 MW. A computational model of the experiment produced results consistent with the experiment, and furthermore, predicted the possibility of achieving much higher power levels in an optimally configured system. >

Modeling of the dynamic performance of transient recorders used for high voltage impulse tests

Digital recorders are becoming more commonly used in the recording of steep-front HV impulses. Although many digitizers exhibit a nonlinear deterioration in dynamic performance with increasing input signal steepness, there is no accepted method for predicting the magnitude of the resulting errors. The authors describe the development and implementation of a computer modeling technique for establishing the magnitude of these errors. The model is based on time-domain test data combined with a basic understanding of the digitizer's operating principles. The model is general in nature and can be used for the prediction of errors generated by any recorder that has systematic errors. The model was used to predict the maximum error which can occur when a particular EBS (electron-bombarded semiconductor) recorder is used to monitor HV impulse tests on power apparatus. Its use allowed for the determination of error limits for records of steep-front impulse tests which will be standardized in the near future. >

Calculating the parameters of full lightning impulses using model-based curve fitting

A brief review is presented of the techniques used for the evaluation of the parameters of high voltage impulses and the problems encountered. The determination of the best smooth curve through oscillations on a high voltage impulse is the major problem limiting the automatic processing of digital records of impulses. Nonlinear regression, based on simple models, is applied to the analysis of simulated and experimental data of full lightning impulses. Results of model fitting to four different groups of impulses are presented and compared with some other methods. Plans for the extension of this work are outlined. >

Comparative measurements of HV impulses to evaluate different sets of response parameters

Results are reported of comparative measurements made in 14 HV (high-voltage) laboratories in ten different countries. The theory of the proposed methods of characterizing the dynamic behavior is given, and the parameters to be used are discussed. Comparative measurements made using 95 systems based on 53 dividers are analyzed. This analysis shows that many of the system now in use, even though they fulfil the basic response requirements of the standards, do not meet the accuracy requirements. Because no transfer measurements were made between laboratories, there is no way to detect similar errors in both the system under test and the reference system. Hence, the situation may be worse than reported. This has led to the recommendation that comparative measurements should be the main route for quantifying industrial impulse measuring systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparative Measurements of HV Impulses to Evaluate Different Sets of Response Parameters

Results are reported of comparative measurements made in 14 HV (high-voltage) laboratories in ten different countries. The theory of the proposed methods of characterizing the dynamic behavior is given, and the parameters to be used are discussed. Comparative measurements made using 95 systems based on 53 dividers are analyzed. This analysis shows that many of the system now in use, even though they fulfil the basic response requirements of the standards, do not meet the accuracy requirements. Because no transfer measurements were made between laboratories, there is no way to detect similar errors in both the system under test and the reference system. Hence, the situation may be worse than reported. This has led to the recommendation that comparative measurements should be the main route for quantifying industrial impulse measuring systems. >