Current pulses during water treeing detection system

A detection system has been developed to seek signals associated with water treeing. In this paper, Part 1 of two parts, the test system is found able to detect fast pulses generated by charges as small as 1.2 fC and slow pulses with current amplitudes as small as 66 nA, with 27 MHz bandwidth. Such pulses are studied in the following paper. The detection system functions in real time and non-invasively, using the common configuration of a dielectric between electrodes. Very low noise, wide bandwidth transimpedance (current in, voltage out) preamplifiers detect very small and fast current pulses in two ground electrodes which monitor the same sample respectively at an `active' (treeing) region, and a `reference' (no treeing) region. The currents in the sample are observed by their image currents in the electrodes. Noise that appears identically in both channels (e.g. corona) can be ignored by a fast logic circuit that selects data to be recorded. Noise components that are different in the two channels and their effects also are studied; they are small enough to be defeated primarily by a fast discriminator. An averaging mode is sometimes used to characterize signals and further reduce noise when one signal type is recurrent; noise artifacts in those averages are identified. A means is developed to observe the phase of the 60 Hz HV when short events are recorded. The detection system is studied carefully in this paper for confidence in the ultimate conclusions. The use of the system to study events during water treeing is described in the following paper     

A new adaptive technique for on-line partial discharge monitoring

The insulation system of HV apparatus deteriorates due to partial discharges (PD). PD tests are carried out successfully in shielded laboratories to verify the insulation quality and to rectify defects left during the manufacturing process. A variety of techniques exists for this purpose. It is also desired to monitor the insulation when equipment is in operation. Unfortunately, the performance of PD test equipment is adversely affected by interference signals. The sinusoidal signals of low and high frequency, due to their correlation, make the measurement difficult and sometimes even impossible. This paper describes the design of an adaptive digital filtering technique and its successful application to the on-line/on-site detection of PD current pulses generated in HV insulation in the presence of sinusoidal noise signals. The technique is based on Wiener optimal filtering theory and its characteristics are investigated. The adaptive filter of this system has a time-varying response and is self-tuning to each low and high frequency noise component. The filter remains active until the signal-to-noise ratio is significantly increased and it can be used for weak PD pulse integration. Theoretical background of the technique and the results of laboratory and field tests are presented     

A new methodology for the identification of PD in electrical apparatus: properties and applications

Applications of a new methodology, aimed at the identification of defects occurring in insulation systems of HV apparatus and based on partial discharge (PD) measurements, are presented in this paper. This methodology relies upon the digital acquisition of a large amount of PD pulses and separates the acquired pulses into homogeneous subclasses. Signal processing tools recognize the presence of noise among the different classes. Identification of basic PD source typologies (i.e., internal, corona and surface discharges) is then achieved, resorting to fuzzy algorithms. The proposed procedure is applied to measurements performed on different HV apparatus, such as cables, transformers and rotating machines. The purpose of this paper is to show that the identification process is robust, regarding the measuring circuit, and flexible, so that it can constitute an advanced tool for condition based maintenance, guiding maintenance experts in making decisions on the condition of the insulation system under test.     

Current pulses during water treeing procedures and results

The procedures and results are described for an experiment to seek electrical current signals during water treeing, and to characterize any that exist. The apparatus was described in the companion paper Part 1 (see ibid., vol.3, no.4, pp.515-22, 1996), where the sensitivity characteristics, and noise effects were assessed carefully because such signals had not been detected before. In this Part 2, the use of the several modes of the apparatus is described for various conditions of signal, noise, and phase resolution. Methods of identifying and eliminating noise artifacts are described. A method is described for resolving the HV phase existing when a fast event occurs. Four types of pulsed currents are studied; two are noise (1-channel and 2-channel noise) and two are signal (fast and slow pulses). Each has unique characteristics as to the channel(s) in which it occurs, amplitude, shape, and phase of the 60 Hz HV when it occurs. It is observed that two types of pulsed signals originate only in the region where water treeing is occurring; any conclusion that they are produced by the water treeing process is inferred from that observation. The `fast pulse' signal lasts only a few days, is <25 ns wide, contains 1 to 4 fC charge, and occurs only at the water treeing region and only when the 60 Hz HV waveform is zero and falling. The `slow pulse' signal appears after a few days, is 35 to 60 μs wide, has 70 to 125 nA peak, and occurs only at the water treeing region and only when the 60 Hz HV waveform is at the negative minimum     

Analysis of Dielectric Barrier Discharges under Unipolar and Bipolar Pulsed Excitation

In this work we experimentally examine the characteristics of a dielectric barrier discharge reactor driven by two distinct pulsed high voltage (HV) generators. Firstly, the operation under a HV generator delivering positive high voltage pulses with short (tenths of ns) rise and fall times in a low (up to 100 Hz) repetition frequency is illustrated. Then the DBD obtain with the use of a bipolar generator with a larger frequency range (several tenths of kHz) having rise and fall times in the microsecond scale is depicted. In the unipolar excitation regime two discharges per HV pulse occur: a first one during the rising part (or the plateau) of the applied high voltage and a second one during the falling part of the HV signal. On the contrary, the bipolar regime here studied presents a single discharge per HV pulse. Electrical as well as optical measurements give insight in the discharge characteristics in both excitation cases. Several electrical characteristics have been more particularly analyzed such as the quantity of transferred charge, the peak and the average plasma power and the power factor. These preliminary results show that the unipolar case could prove efficient to produce a reactive plasma but higher frequencies (i.e. several tenths of kHz) are needed than the ones used in the present work ones (only up to 100 Hz).     

GSM与模糊诊断的绝缘子在线监测

提出并实现了基于GSM网络的线路绝缘子远程分布在线监测与集中式模糊逻辑诊断系统。在前台监测单元获取绝缘子串的泄漏电流有效值、泄漏电流峰值、泄漏电流脉冲频度、电晕电流和温、湿度等数据 ,利用数字信号处理器预处理 ,借助GSM网络传输 ,并通过后台模糊逻辑诊断系统管理线路绝缘子的运行状态。     

Investigation of gas bubble formation at spark erosion in small working gaps

Gas bubble formation, especially in small working gaps, has an important influence on the spark erosion process. This paper demonstrates that the gas bubbles originate from electrical discharge in the dielectric. Investigations are carried out for two typical dielectrics: hydrocarbon (n-dodecane) and de-ionized water. From the experimental results obtained with single pulses conclusions are drawn about what happens at discharge sequences like in a micro-erosion process.     

Electroluminescence due to impulse voltage in cable-grade XLPE

Underground power cables in service are inadvertently subjected to impulses generated by lightning and switching surges that are superimposed on the ac voltage at which they operate. HV transients caused by lightning and switching operations not only radiate large electromagnetic fields but also impose additional stresses on the insulation and could initiate deterioration which can continue under normal operating conditions. Electrical breakdown of HV cables is a local phenomenon and electrical aging at local sites in the polymeric insulation occurs by molecular dissociation of the polymer and formation of new chemical bonds. This process usually involves the electronically excited states of the molecules that give rise to radiative phenomena, such as electroluminescence (EL). Analysis of EL can help to clarify the degradation mechanisms that occur at points of electrical stress enhancement and lead to cable breakdown. The EL technique is several orders of magnitude more sensitive than the commonly employed partial discharge detection and can provide a better understanding of the various time dependent mechanisms such as space charge injection, trapping and decay that can lead to insulation failure. The characteristics of EL in crosslinked PE subjected to impulse voltage, are described in this paper. Impulses having the same polarities as the half cycles of the ac voltage on which they are superimposed give rise to the largest number of EL pulses. Also, more EL pulses are emitted when impulses are applied at the peaks of the positive and negative half cycles than at the zero crossing of the ac voltage. This suggests that the amount of charge injected and trapped into the polymer plays a crucial role for EL emission     

Effect of short HV pulses on bacteria and fungi

The survival of three kinds of microorganisms under strong-pulse electric field conditions was investigated with a possible application of the electric pulse method for sterilization of consumable liquids. The results of the investigations of survival ratio of Gram-negative (Escherichia coli, Yersinia enterocolitica) and Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacteria and yeastlike fungi (Candida albicans) are presented. The HV pulses with peak voltage U=0 to 100 kV and rise time t_n= 0.5 to 1.2 μs were applied. The microorganisms were suspended in an NaCl solution with γ=6 to 13 mS/cm conductivity and pH=7.2. The experimental setup and the dependency of the microorganism survival ratio on the rise time, peak voltage and on the number of pulses applied, are presented. It has been found that the lethal effect on microorganisms caused by HV pulses depends on the pulse parameters as well as on the kind of microorganism being treated     

Low energy single stage high voltage impulse generator

High voltage (HV) impulse generators are employed widely for testing of HV apparatus, as such tests are codified in a range of standards. As a result, insulation properties under impulse waveforms are of interest in the design of HV apparatus. This creates a need for very low energy laboratory impulse generators which can be used to test laboratory scale samples, often in conjunction with sensitive electronic instrumentation to measure sample dielectric properties. Since the sample is often the only isolation between the impulse generator and the electronics, failure of the sample will result in exposure of the electronics to the energy stored in the generator. This paper provides design details for a very low energy (/spl sim/1 nF storage), single-stage impulse generator which provides "clean" double exponential waveforms.     

Double pulse approach of electropulsation: a fluorescence analysis of the nucleus perturbation at the single cell level

Plasmid Gene transfer and expression can be obtained by the application of electric pulses to a mixture of cells and plasmids (electrogenetherapy, EGT). Electropulsation is rather well characterized at the plasma membrane level. But, the transfer to and across the nuclear envelope remains a problem. Biological approaches showed that EGT was more effective during mitosis. Recently the group of Schoenbach showed that nanosecond ultra high field pulses may affect cytoplasmic organelles including the nucleus. The need for high field was linked on one hand on the time scale and on the other on the size of the target. Therefore we made an approach of the alteration of the nucleus induced by a microsecond high electric pulse (μs HV, up to 9 kV/cm, 5 μs). This perturbation was operated alone or a few seconds after EGT pulses (10x, 0.7 kV/cm, 5 ms) needed to introduce the plasmid in the cytoplasm. Structural alterations of the nucleus organization were investigated. This was obtained by a digitized fluorescence approach at the single cell level, using Hoechst dye as a probe with a high affinity to nucleic acids. The first train of pulses (EGT) induced a huge and rapid (<2min) swelling of cells and of their nucleus associated with a decrease of the mean fluorescence of the nucleus. Mean fluorescence level and volume changes were maintained along the next 10 minutes. The application of a μs HV pulse affects the cell volume and transiently the nucleus volume without any effects on the mean fluorescence level in the nucleus.     

弹簧操动机构中DT触点存在的问题及解决方案

针对目前电力系统高压开关弹操机构中弹簧储能触点（即DT触点）在开关电动合闸操作中易烧损的情况进行了分析研究,详细地阐述了弹操机构DT触点易烧损的原因：违背了分合闸回路电流必须由DL触点断弧的基本原则,造成DT触点断弧或首先断弧。提出了解决此问题的基本思路：通过DT触点开、闭合闸脉冲达到控制合闸的目的。以35kV微机保护的控制回路为例给出了二种情况下的解决方案。此方案已在实际中得到了运用,运行情况良好。     

场强型高压带电显示装置

概述了场强型高压带电显示装置研制的背景、原理、结构及其性能特点,经例行试验和装机试运行表明,该产品克服了早期感应式高压带电显示器的抗干扰能力弱和支柱绝缘子式高压带电显示装置的直接接触高压带电体的不安全、易击穿的缺点。适用于户内高压电气设备防止电气误操作。     

Mathematical?Physical Model of Corona from Surges on High-Voltage Lines

A mathematical-physical model of corona current pulses from voltage surges on HV lines is presented. Distributed representation of corona along infinitely long transmission lines is suggested. The surge corona current pulse flows through the transmission line as a series of successive generations of electron avalanches, which develop in the ionization zone around the HV conductor. The initiatory electrons for triggering the current pulse under a positive applied surge are those available in the atmosphere surrounding the HV conductor. The two corona current components, the image component due to the presence of charge carriers (electrons and ions), and the convection component due to the motion of charge carriers in the interelectrode spacing were calculated. The calculated corona current pulse and the charge flow voltage curve agreed reasonably with those measured experimentally for a coaxial transmission line.     

A high‐voltage stimulation chip for wearable stroke rehabilitation systems

In this work, an 8‐channel high‐voltage (HV) stimulation chip for the rehabilitation of stroke patients through surface stimulation is presented. The chip receives control data through its serial peripheral interface and can be controlled by an external microcontroller. It can accordingly generate biphasic stimulation currents with different amplitudes, duration time, frequencies, and polarities for each channel independently. The chip was designed and fabricated using X‐FAB 0.35 µm HV mixed‐signal process. Circuits were carefully designed to ensure their operations under HVs. Our measurement results showed that a supply voltage of as high as 75 V can be achieved, and the current driver can generate biphasic stimuli with current amplitudes up to 4 mA. Copyright © 2015 John Wiley & Sons, Ltd.     

International comparison of HV impulse measuring systems

The authors studied the agreement between laboratory measurements of full and front-chopped lightning impulses at four national laboratories. First, some general information on how standards are maintained and disseminated is presented together with a brief review of the requirements for HV impulse measurements. Then, the comparative measurements made in the four national laboratories are presented and the relative differences are reported. Comparative measurements can be made for full standard lightning impulses to within 1% for crest voltages and to within 5% for front times. These uncertainties may be adequate to allow the calibration of industrial measuring systems to within 3% for crest values and 10% for front times, as is required by the relevant standards, provided the systematic errors of the reference system are sufficiently small     

改进电声脉冲法的交流空间电荷测量新方法

提出一种交流电压下的电声脉冲法空间电荷测试新方法。采用电脉冲作为触发源,利用数字示波器的长存储功能同时获取空间电荷信号和高压交流电压信号,从而避免了传统交流空间电荷测试方法的硬件同步。通过调整脉冲发生器的频率可获取不同相位下的高压交流下的空间电荷响应,并通过平均若干个交流周期的空间电荷信号获得足够信噪比的相位相关的空间电荷信号。通过对低密度聚乙烯工频50 Hz下的空间电荷测量结果表明,在交流电场下,下电极附近区域会形成异号电荷;与传统的交流空间电荷测量系统相比,由于测量时间得到很大程度缩短空间电荷信息能够最大限度保存,并且新系统较老系统有更高的相位分辨率,空间电荷衰减图形更能逼真的反映电荷动态变化。     

Pulsed streamer discharge characteristics of ozone production indry air

Experimental investigation of HV short pulsed streamer discharges in dry air-fed ozonizers under various operating conditions are reported. Ozone concentration, energy input and ozone production yield (efficiency) were measured at various voltages (14 to 37 kV), pulse repetition rates (25 to 400 pulses per second, pps), flow rates (1.5 to 3.0 1/min) and different gap spacings (10 to 20 mm) at a pressure of 1.01×10⁵ Pa in dry air. A spiral copper wire (1 mm in diameter) made to a cylindrical configuration (18 to 38 mm in diameter) in a concentric coaxial electrode system of various dimensions was employed. A magnetic pulse compressor provided the HV and current pulses. Higher voltage and higher repetition rates yielded higher concentrations of ozone at a fixed air flow rate. The present investigation was extended to assess the performance of this pulsed ozone generator using dry air under desired conditions of high concentration and high yield of ozone for industrial applications     

基于紫外光脉冲检测技术的绝缘子电晕特性研究1

首先介绍了利用光电倍增管检测绝缘子电晕产生的紫外光来研究绝缘子电晕特征的研究方法。检测实验表明，电晕紫外光脉冲与电流脉冲有着很好的对应关系，可以采用紫外光作为电晕放电检测特征量。利用该方法检测绝缘子电晕时发现，对于干燥的绝缘子，绝缘子电晕光脉冲中仅含有正电晕脉冲，而当绝缘子表面存在水珠时，光脉冲中明显检测到了负电晕脉冲的存在。该文同时开发了一个自动判断负电晕的时间间隔程序，它能反映负电晕脉冲在电晕中的分布情况。大量的试验证明，如果水珠电晕存在时，绝缘子将会产生大量的负电晕，这也说明水珠将会加剧负电晕，引发负脉冲幅值更快的增长。     

Electrical stress enhancement of contaminants in XLPE insulation used for power cables

The use of XLPE as the insulation for power cables has grown steadily since it first introduction more than 30 years ago. Today XLPE is rapidly becoming the preferred insulation system for even the highest transmission voltages. This preference is due to the high reliability, low dielectric losses, and low environmental impact that can be achieved with XLPE. The positive effects of high quality insulation materials on improved cable performance have been well known since the start of cable making. The purpose of this paper is to investigate the technical background for the cleanliness levels and to quantify the level of performance required from clean materials. The advantages of clean insulation materials are seen at all voltages. However, this work focuses on the technical basis for the benefits for HV and EHV cables, which typically are designed with a water impervious layer to ensure that the cable remains dry throughout its entire lifetime. The presence of metallic contaminants in MV cable is known to enhance the growth of trees by raising the electric stress level locally. The singular impact of cleanliness on the performance of MV cables is somewhat more complicated as it is influenced both by the cleanliness of the insulation and the ability of the insulation material to resist the growth of water trees.