Showing papers on "Partial discharge published in 1995"

A generalized approach to partial discharge modeling

Abstract: An important tool for improving the reliability of HV insulation systems are partial discharge (PD) measurements. The interpretation of such measurements aims at extracting from the measured data information about insulation defects which then are used for estimating the risk of insulation failure of the equipment. Because the physical understanding of PD has made substantial progress in the last decade, it can now be exploited to support interpretation. In this paper a concept is presented which merges the available physical knowledge about various PD types into a generalized model which can be applied to arbitrary insulation defects. This approach will be restricted to PD of the streamer type in gases and at gas-insulator interfaces which cover a large fraction of the cases encountered in technical insulation systems. The generalized model allows us to derive approximate relations between defect characteristics, insulation design parameters and test conditions on one side, and measurable PD characteristics on the other. The inversion of these relations yields rules for extracting defect information from the PD data. The application of the generalized model is illustrated by two simple examples, namely, spherical voids in an insulator and electrode protrusions in SF/sub 6/. >

Partial discharge diagnostics for gas insulated substations

Abstract: A defect such as a free metallic particle or stress-raising edge on an electrode could lead to breakdown in a gas insulated substation (GIS), but may be detected by the partial discharges it generates. Of the various detection means available, most success has been achieved with either acoustic transducers to detect sound waves from the discharge, or electrical couplers to pick up the ultra-high-frequency (UHF) signals generated inside the GIS chambers. All new GIS in the UK are fitted with internal couplers for UHF monitoring, and two examples of continuous monitoring schemes on 400 kV GIS at nuclear power stations are described. Further developments, which are already well advanced, include specifying and measuring the coupler characteristics, making use of expert systems to interpret the UHF discharge data, and extending the monitoring system to include the performance of circuit breakers and other equipment. >

Automated recognition of partial discharges

Abstract: An overview of automated recognition of partial discharges (PD) is given. The selection of PD patterns, extraction of relevant information for PD recognition and the structure of a data base for PD recognition are discussed. Mathematical methods useful for the design of the data base are examined. Classification methods are interpreted from a geometrical point of view. Some problems encountered in the automation of PD recognition are addressed. >

Digital analysis of partial discharges

Abstract: In this paper relevant aspects of digital processing of partial discharge (PD) as measured by conventional PD detection methods are discussed. Moreover, a systematic study of PD quantities is presented and discussed within the scope of practical PD analyzers, including recognition of defects in certain HV insulation configurations. >

Corona source for producing corona discharge and fluid waste treatment with corona discharge

Abstract: A corona source suitable for use in vehicle ignition systems uses a conductive coil that receives an RF input at one end and has a corona discharge site at the other end, with a reference electrode capacitively coupled to the coil. The pitch and the length of the coil are selected to produce a corona discharge in response to an RF input signal at a predetermined frequency and voltage, through quarter wavelength resonation. Either the new resonant coil or other corona discharge devices can be used to remediate fluid-borne wastes by initiating and sustaining RF corona discharges within the fluid. The pulses used to initiate the corona discharge preferably have alternating positive and negative components, with high initial voltages on the positive components to initiate the discharge, followed by lower positive voltage levels to sustain the discharge. Unipolar pulses, preferably with progressively decreasing voltage levels, can also be used.

Partial discharge. XXI. Acoustic emission based PD source location in transformers

Abstract: Acoustic emission-based partial discharge source location has been applied successfully to power transformers in both factory and field environments, and this method is becoming an established test procedure with a high success rate. With the aid of local utilities and utility laboratories that use acoustic emission apparatus daily, we expect further advances in this technology and an improved basis for determining suitable application conditions.

Interpretation of partial discharges at dc voltages

Abstract: The aim of this paper is to give an overview on partial discharges at dc voltage. A model is presented which describes the stochastic discharge process. The model is experimentally verified for internal discharges and for corona in air. In addition, the classification of discharge patterns is discussed. The 3-dimensional histogram describing the number of discharges depending on the discharge magnitude and on the time to the successive discharge is suggested to be used as a base for discharge recognition at dc voltage. Experimental proof is presented to show the strength of this approach. >

Partial discharge plant-monitoring technology: present and future developments

Abstract: The paper discusses the role of partial discharge measurement in the conditioning monitoring of power plant. Following a discussion of recent developments in partial discharge detection and measurement technologies, the problems and challenges for the future in the different technologies are analysed and discussed. For those unfamiliar with partial discharge detection as a condition monitoring tool, a brief discussion on its relationship to insulation degradation is presented as an Appendix.

Pulse-sequence analysis: a new method for investigating the physics of PD-induced ageing

Abstract: A new method is presented of partial discharge data analysis for the investigation of space charge and degradation phenomena in high-voltage insulation systems. The basic principles of the pulse-sequence-analysis (PSA) are illustrated and the characteristic differences with regard to standard procedures that have been established during the past few years are outlined. A description is given of an electronic partial discharge acquisition system, which is designed on a plug-in interface board for a standard PC to perform long-term measurements of all the discharge parameters required for the succeeding analysis. Electrical treeing in polyethylene is used to demonstrate the usefulness of the method. It is shown that information on the physics of treeing phenomena especially with regard to the influence of local space charges and their build-up and decrease over time as well as the development of the local degradation can be obtained by considering correlations between consecutive discharge pulses. Some experimental results from different stages of the electrical tree growth are analysed and their meaning with regard to the local microscopic phenomena inside the tree or in the vicinity of the tree tips discussed. This paper is based on an oral presentation at a conference on Partial discharge, September 1993, Canterbury, titled 'Pulse-sequence analysis, a way to get a better insight into the physics of discharges'.

Neural network system using the multi-layer perceptron technique for the recognition of PD pulse shapes due to cavities and electrical trees

Abstract: A neural network system, utilizing the multi-layer perceptron approach has been applied to distinguish between power cable insulation partial discharge pulse shapes that are characteristic of cavities and electrical trees. The neural network was found to be capable of recognizing the differences in PD pulses produced by single cavity and electrical tree discharge sources. It also could differentiate between the discharge pulse forms emanating from electrical trees of different lengths; likewise, it was able to recognize changes in the shape of the discharge pulses with time due to aging effects. However, as these recognition capabilities relate only to comparisons of single discharge sources on a one-to-one basis, the application of neural networks to PD pulse shape recognition on actual power cables, where a number of different discharge sources may be discharging simultaneously, is quite premature at this time without more detailed exploratory work on complex discharge patterns. >

Broadband couplers for UHF detection of partial discharge in gas-insulated substations

Abstract: The paper describes investigations of the UHF performance of a disc coupler designed for continuous monitoring of partial discharge in gas-insulated substations and indicates how the UHF sensitivity can be improved. Resonant frequencies of the disc are calculated, and the coupler is shown to be most sensitive at these frequencies. The bandwidth of the coupler can be extended by coupling the UHF signal from the edge of the disc, allowing detection of a greater number of the possible resonant modes of the disc, including the dominant, lowest frequency mode. Sensitivity to the UHF signals generated by partial discharge can be further improved by various means. The disc can be earthed at certain points while still retaining the coupling function. A novel nonresonant experimental coupler design is also presented, based on the design techniques used for broadband log-spiral antennas. The frequency response of the spiral coupler is much flatter than that of a comparable disc coupler.

Partial discharge pulse distribution pattern analysis

Abstract: Statistical data analysis has been recently requisite for partial discharge (PD) study. This has been enabled by the recent development of microprocessors or the downsizing of computers. It is important to pay more attention to profiles of a packet of PD pulses on the voltage phase angle. Statistical parameters such as skewness and kurtosis have been intensively investigated for PD analysis. More recently, the neural network algorithm has been utilised especially to discriminate PD signals from noise signals for insulation diagnosis.

Discharge pattern recognition in high voltage equipment

Abstract: The paper considers the diagnosis of HV constructions which suffer from partial discharge (PD). Using previously developed statistical techniques the properties of discharge patterns are quantified in a fingerprint. Through the analysis of different defects and their fingerprints in HV constructions, the practical implication of these techniques is discussed. Furthermore, different possibilities of developing a data bank for the recognition and diagnosis in HV components are shown.

Partial discharge signal generation transmission and acquisition

Abstract: The phase resolved partial discharge detection technique (or 'PD pattern recording technique') is applicable to field measurements, particularly if combined with disturbance rejection techniques and non-conventional pick-up circuits. Electromagnetic disturbances can be eliminated by filtering in the time domain (impulse noise gating) and/or in the frequency domain (down-mixing). The PD patterns not only reveal the PD physics and thus help to identify the defect type, but also serve to evaluate the efficiency of the disturbance rejection procedure.

Partial discharge detection: theoretical and practical aspects

Abstract: The phenomenon of electricification by electrostatic induction is introduced. This fundamental approach allows the concepts of Poissonian and Laplacian induced charge to be clearly developed. These concepts form the necessary basis for partial discharge detection analysis. Thereafter a quantitative theory is developed. This field-theoretical approach furnishes the correct input parameters for the subsequent study of the detection-circuit response, in which the electrodes of the field analysis serve as the input terminals in the circuit analysis. Subsequently the response of a basic partial-discharge detection circuit is examined with reference to the induced-charge signal. It is concluded that the maximum value of this signal will be most accurately determined if a detection circuit with a longtime constant is employed.

Effect of physico-chemical degradation of epoxy resin on partial discharge behavior

Abstract: Epoxy resin coated electrode specimens were subjected to partial discharges (PD) in air at twice the discharge inception voltage for durations ranging to 5000 h. The PD behavior was characterized by a transition from initially large pulse type discharges (- 200 to 300 pC) to either small pulse (- 1 pC), pseudoglow, glow discharge, or a combination thereof. Although these different forms of discharges were capable of occurring simultaneously, each type tended to prevail over certain periods of the exposure time. The physical and chemical nature of the degradation products formed on the surfaces of the epoxy resin also varied accordingly, indicating that each discrete form of discharge exerts its particular effect on the overall degradation process. Droplet formation on the central portion of the epoxy surfaces typified the large pulse discharge regime, whilst crystals formed within the transition region over which small discharge pulses (- 1 pC) were usually superimposed upon a continuous glow (pseudoglow and true glow regime). The droplets were identified as being partially comprised of a mixture of acids, mainly formic, glycolic, glyoxalic and nitric acids, whilst the crystals consisted of hydrated oxalic acid. Since similar results were obtained with discharges in both air and nitrogen, the effects of gas phase reactions on the PD activity would appear to be only of secondary importance compared to the reactions taking place on the surface of the epoxy resin. Since the test cell design did not allow any pressure variation within the discharge gap, the observed discharge transition cannot be attributed to pressure changes such as may take place within occluded cavities. Nevertheless, the transition observed here is similar to what is found with actual stator bar type insulation, suggesting that pronounced chemical and physical modifications on the surface of the physical cavity inclusions in the bar insulation may account for the characteristic PD behavior observed as a function of time.

The dynamics of a high‐pressure ac gas discharge between dielectric coated electrodes near breakdown threshold

Abstract: An analytical theory of a high‐pressure gas discharge between two metal electrodes covered with an insulator is presented. The theory is applicable when the voltage applied to the gap between electrodes only slightly exceeds the breakdown voltage. Analytic expressions for the electric field, electron and ion current densities, as a function of time and space, and an analysis of the stability of the discharge are given. A detailed discussion of the role of metastables in the discharge dynamics is included. The discharge in a plasma display cell is used as an example to demonstrate the utility of the theory.

Effect of overvoltage on the risetime and amplitude of PD pulses

Abstract: A two-dimensional mathematical model has been employed to characterize the pulse or spark breakdown behavior of a short gap in air. It has been established that the form or shape of a breakdown current pulse is very much determined by the overvoltage developed across the gap. Large overvoltages lead to intense space charge effects, which appreciably modify the breakdown current pulse form, leading to more rapid rise times, greater peak current amplitudes and reduced pulse widths. In so far as the overvoltage across a given cavity affects the rise time and amplitude of the pulse resulting from a spark type discharge, the response of a conventional partial discharge pulse detector is necessarily a function of the overvoltage developed across the cavity. >

Cable partial discharge location pointer

Abstract: A method and apparatus for detecting the location of an incipient fault in an insulated power system which includes the application of an excitation voltage to a power line to produce a partial discharge signal pulse at a fault (34) along the power line. The surface of the power line is scanned with two axially spaced sensors (30, 32) disposed adjacent the surface of the power line, the sensors detecting the partial discharge signal pulse to produce discrete detected pulses. These detected pulses are combined to produce a combined signal having an amplitude level which reaches an extreme value when the fault is located equidistantly between the sensors. The sensors are moved along the power line until the fault is located substantially equidistantly between the sensors as indicated by the extreme amplitude level of the combined signal.

Gas discharge display panel having communicable main and auxiliary discharge spaces and manufacturing method therefor

Abstract: A gas discharge display panel which provides sufficient contrast and good accuracy and is high in yield. When a voltage is applied to auxiliary discharge electrodes, auxiliary discharge occurs in an auxiliary discharge space and excited charged particles communicate with a main discharge space through a priming path made in a discharge space separation bulkhead. In this state, when an alternating voltage is applied between bus electrodes on a front substrate, main discharge occurs in the main discharge space, causing Xe atoms in the sealed gas to generate ultraviolet rays, causing a phosphor to emit light. However, since the auxiliary discharge is shielded by a bulkhead and a barrier rib, the phosphor does not emit light when only auxiliary discharge occurs.

Partial discharge mechanisms in voids related to dielectric degradation

Abstract: The usefulness of time-resolved measurements is shown for the study of degradation processes of insulating materials associated with partial discharges. Using an optimised test set-up the different stages in the degradation process can be recognised. The possibilities for using the time-resolved method in practice are discussed. A promising combination of classic and time-resolved measurements is presented and clarified by the first results obtained with the discharge analysing system TEAS.

A new adaptive technique for on-line partial discharge monitoring

Abstract: 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. >

Partial discharge measuring method

Abstract: PROBLEM TO BE SOLVED: To provide a discharge electric charge amount corresponding to a specified occurrence frequency by processing a discharge pulse signal in digital manner SOLUTION: At a discharge detecting circuit 11, a specimen C is applied with a specified AC voltage, for detecting a discharge pulse occurring at the specimen C While the analogue discharge pulse is digital-converted at an A/D conversion circuit 12, a discharge pulse signal of a unit time, for example 1 second is fetched at a CPU 14, each of m-numbers of pulses occurring within the time is provided with an address, while each address is allowed to have an information about the magnitude of pulse, which is through digital process such as this, stored in a storage circuit 13 After that, according to such condition as occurrence frequency and extraction time set by a constant setting circuit 15, a CPU 14 takes a stored m-numbers of data out of the storage circuit 13, extracts n-th in data size for acquiring its magnitude to provide a discharge electric charge amount

Static electrification and partial discharges induced by oil flow in power transformers

Abstract: This paper presents the study of the major parameters on static electrification, using full-scale shell type transformers (570 MVA, 405 kV and 100 MVA, 500 kV). The consequences of static electrification on the dielectric strength and the conditions of partial discharge occurrence also are studied with oil flow rate up to 5 times the nominal value. It shows that the leakage currents are strongly influenced by temperature, applied voltage and oil flow rate Q. The latter is the most influential parameter. The winding leakage current I varies as Q/sup n/, where 1/spl les/n/spl les/3. The maximum value of I is observed at room temperature (20/spl deg/C) when the transformer is energized. >

Separation of partial discharges from pulse-shaped noise signals with the help of neural networks

Abstract: The paper introduces a method to separate partial discharges (PDs) from pulse-shaped noise signals using a neural network. After a short introduction to the problems of PD measurements on-site, the structure of neural networks and their ability for pattern recognition is presented. The adaptive resonance theory (ART) architectures, which are suitable for PD measurement, and especially the fast simulating algorithm ART 2-A, are explained. To ensure the suitability of the chosen network for PD measurement, the electrical noises and PD signals measured on a distribution transformer as well as on a high voltage transformer are classified. Furthermore, it is shown that the same algorithm with changed parameters can make a contribution to PD localisation in a transformer. This takes place with the help of calibration pulses, which are injected in different points of a transformer coil. It is shown that the ART 2-A network is able to classify these pulses in accordance with their origin for the distribution transformer. The paper ends with an examination of the signals measured on a power transformer under high voltage on-site.

UHF detection of leader discharges in SF/sub 6/

Abstract: The ultra-high frequency (UHF) technique of partial discharge detection has been used to study the partial discharges produced by electrode protrusions and surface contamination in a gas insulated substation (GIS). The paper describes the stages of discharge development from inception to breakdown. The work has shown that the UHF technique may be used to identify distinct phases of discharge activity corresponding to discharge inception and a prebreakdown condition. The prebreakdown activity is detected as an increase in the UHF signal magnitude which has been attributed to the formation of leader-type discharges. These discharges form an essential part of the breakdown process, and their detection can be used to identify when the system is close to breakdown. The paper describes a filtering technique that may be employed to optimize the sensitivity of UHF leader detection. >

Corona discharge ignition system

Abstract: A corona source suitable for use in vehicle ignition systems uses a conductive coil that receives an RF input at one end and has a corona discharge site at the other end, with a reference electrode capacitively coupled to the coil. The pitch and the length of the coil are selected to produce a corona discharge in response to an RF input signal at a predetermined frequency and voltage, through quarter wavelength resonation. Either the new resonant coil or other corona discharge devices can be used to remediate fluid-borne wastes by initiating and sustaining RF corona discharges within the fluid. The pulses used to initiate the corona discharge preferably have alternating positive and negative components, with high initial voltages on the positive components to initiate the discharge, followed by lower positive voltage levels to sustain the discharge. Unipolar pulses, preferably with progressively decreasing voltage levels, can also be used.