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Electrical Insulation, IEEE Transactions on

Issue 1 • Date Feb. 1992

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Displaying Results 1 - 21 of 21
  • Volta Colloquium on partial discharge measurements [Special Issue Intro.]

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  • Investigation of prebreakdown currents in vacuum interrupters

    Page(s): 174 - 180
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    The authors attempted to measure the current growth prior to delayed discharges with high temporal resolution and high sensitivity. The quantity of charge within a microdischarge was found to vary. Depending on the charge, it was possible for the shield potential to be affected, or for a disruptive discharge to be initiated between the contacts. The probability of delayed discharges was very low at low currents but increased at higher currents. With the majority of the recorded delayed discharges, the observation can be explained on the basis of a trigger discharge occurring between a charged particle and the side of the contact. In several cases cathode spots carrying currents on the order of 10 A with no observed reduction in voltage over a period of ⩽300 μs were observed. Some delayed discharges were preceded by increasing predischarge currents. The breakdown discharge took place after a critical emission current had been reached. The desorption of gas molecules on the anode surface is regarded as the cause View full abstract»

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  • A Galerkin formulation of the boundary element method for two-dimensional and axi-symmetric problems in electrostatics

    Page(s): 135 - 143
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    The authors propose to process the Fredholm integral equation relating potential to an unknown source density function by the Galerkin weighted residual technique. In essence, this allows them to optimally satisfy the Dirichlet condition over the entire conductor surface. Solving the resulting equations requires evaluation of a second surface integration over weakly singular kernels, and the increased accuracy comes at some computational expense. The singularity issue is addressed analytically for 2-D problems and semi-analytically for axi-symmetric problems. The authors describe how the integrals are evaluated for both the standard and Galerkin boundary element functions using zero, first, and second order interpolation functions. They demonstrate that the Galerkin solution is superior to the standard collocation procedure for some canonical problems, including one in which analytical charge density becomes singular View full abstract»

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  • Practical implementation of ultrawideband partial discharge detectors

    Page(s): 70 - 81
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    It is shown that significant improvements in partial discharge (PD) measurement can be achieved through the use of ultrawideband (UWB) coupling techniques. These enhancements are principally in the areas of increased sensitivity, external noise rejection, and better understanding of the physics of the PD process. Examples of the improvements achievable by the use of UWB techniques are discussed for the cases of rotating machines and GIS. A new PD coupler which has a frequency response extending into the GHz range is demonstrated to enable reliable discrimination of PD signals from noise on operating turbine generators. Preliminary results from a fundamental study on PD in epoxy resins, show that there are two types of PD phenomena, `fast' and `slow' View full abstract»

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  • Measurement of partial discharge in solid dielectrics with a microprocessor-based system

    Page(s): 106 - 113
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    The authors discuss briefly the basic aspects of partial discharge (PD) measuring techniques with special emphasis on the problem of detecting the amplitude of discharge pulses having transient decaying sinewave shapes. After a short account of the recent multichannel pulse-height analysis techniques of collected data and of the use of a computerized system for calculating multiple discharge parameters, a new digital system for PD measurement and computer data processing is presented View full abstract»

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  • Miniature partial discharge calibrator synchronized by capacitive coupling

    Page(s): 181 - 183
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    A new partial discharge calibrator is described. The device, suitable to operate in a floating position, generates synchronized pulses at the mains frequency. Synchronization is achieved by capacitive coupling to the mains with a cable wound around the power leads. This solution yields a device of 60 mm×45 mm×20 mm, allowing partial discharge detector calibration with reduced error View full abstract»

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  • Computer-aided recognition of discharge sources

    Page(s): 82 - 92
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    Making use of a computer-aided discharge analyzer, a combination of statistical and discharge parameters was studied to discriminate between different discharge sources. Tests on samples with different discharge sources revealed that several parameters are characteristic for different types of discharges and offer good discrimination between different defects View full abstract»

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  • Recent advances in partial discharge measurement capabilities at NIST

    Page(s): 114 - 129
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    Three techniques for measuring the properties of partial discharges (PDs) are described. The first is concerned with an advanced, real-time PD measurement system that allows a complete characterization of the stochastic properties of PD. With this system it is possible to measure a set of conditional PD pulse-amplitude and pulse-time separation distributions from which memory effects characteristic of the discharge phenomena can be quantified and interpreted. Results for pulsating negative corona discharges in gases are shown. The second technique allows PD location in cables using time-domain reflectometry with appropriate statistical analysis. With the third technique, simultaneous measurements are made of the optical and electrical characteristics of PD in liquid dielectrics using fast photography combined with broadband. low-noise pulse current measurements View full abstract»

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  • Digital location of partial discharges in HV cables

    Page(s): 28 - 36
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    This paper deals with a new digital system for locating partial discharges (PDs) in high voltage (HV) cables under noisy conditions. After an introduction to different PD location methods and their limits, the possibility of PD location through the pulse separation method is introduced. Digital filtering performed with predictor filters is described. Extensive investigations are carried out to determine the effectiveness of these filters, as well as their limitations, in their use for PD and noise separation. The results concerning the application of filtering on PD and noise signals measured on an HV cable under noisy conditions are presented View full abstract»

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  • SF6 and the atmosphere

    Page(s): 184 - 187
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    The gas SF6 is predominantly used for electrical insulation and switching. Its possible environmental effects when released into the atmosphere are assessed. It is shown that the relative contribution of SF6 to the greenhouse effect is <0.01% and that its contribution to stratospheric ozone destruction is <10-7 View full abstract»

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  • Partial discharge diagnosis using statistical optimization on a PC-based system

    Page(s): 93 - 98
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    Personal computer (PC)-aided partial discharge (PD) evaluation needs high-speed electronic devices for on-line measurement and digital conversion of PD signals. The authors include quantities to be measured to evaluate PD signals, which are characterized by a statistical scatter of magnitude and duration and are additionally influenced by noise and a complex time behavior. Using the correct algorithms and parameters, the PC gains some intelligence to discriminate unknown defects. Artificial sample defects, representing sources of PD, have been implanted into a GIS system. By performing a statistical analysis of charge, energy and phase angle on the measured signals, it is possible to solve the diagnosis problem by a noise resistant software solution. The final diagnosis is carried out by pattern recognition, using a specially calculated identification data set, which is compared to reference patterns measured earlier. The strategy takes into account the fundamental differences in the physics of discernible defects View full abstract»

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  • Surface charge distribution during the charging and discharging of electrets produced in electret ionization chambers

    Page(s): 144 - 151
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    Spatial charge distributions during the charging and discharging processes of thin film polymer electrets produced by ionizing radiation in air are presented. The charge distributions were measured for various externally applied potentials and air gap thicknesses of electret ionization chambers (EICs). The results show important limitations in charging electrets with this technique in EIUs of relatively large air gaps, but show excellent results with EICs of small air gaps. Practical problems of achieving maximum charge densities corresponding to the externally applied potential are discussed. The change in charge distributions during the charging and discharging stages with various external potentials and air gaps is also presented and analyzed, and possible causes for the patterns are given. Measurements of charge distributions during discharge describe the neutralization process involved in EICs and suggest limitations to the practical size of chambers View full abstract»

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  • A contribution on the traceability of partial discharge measurements

    Page(s): 130 - 134
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    Commercially used partial discharge (PD) detectors are intended to capture current pulses generated by PD activity in the insulation of a HV test object and then to integrate it, producing a display proportional to the apparent charge. The integration procedure is approximated by a low pass (or bandpass) filter and therefore different partial detectors display different charges on the same measurement setup. The error of the approximated integration is simulated and analyzed, and a new calibrator is proposed which has an adjustable duration current pulse. Using the calibrator, the correct working range of the PD detector can be tested and thus qualified. The new calibrator, as a reference unit, can be considered a base of traceability of PD measurement View full abstract»

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  • The importance of statistical characteristics of partial discharge data

    Page(s): 60 - 69
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    A digital partial discharge (PD) measuring concept which is designed to acquire not only conventional PD charge magnitudes but also statistical characteristics of PD signals which contain most significant information on insulation defects is described. The latter fact is explained by a physical discharge model for discharges within voids in a dielectric. The potential of combining the new measurement concept with a physical interpretation is demonstrated by measurements on artificial defects in laboratory experiments as well as on real HV insulation systems View full abstract»

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  • On the spark to pseudoglow and glow transition mechanism and discharge detectability

    Page(s): 3 - 14
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    The transition mechanism for spark to pseudoglow and glow discharge is examined and the attending question of discharge detectability in an electrical apparatus is considered. The effect of gap spacing or cavity diameter and overvoltage is discussed in terms of experimental observations and theoretical calculations using a two-dimensional mathematical model View full abstract»

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  • Conventional PD measurement techniques used for complex HV apparatus

    Page(s): 15 - 27
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    The aim of conventional potential discharge (PD) measuring techniques is the quantification of an apparent charge q, which is, in general, provided by band-pass filter techniques. However, as the capability of a filter to integrate signals and its `pulse resolution time' are strongly interlinked with the band-pass characteristics of the filters, the design of conventional PD measuring circuits appears quite arbitrary. The authors discuss, therefore, some deficiencies of the Standards, which are inadequate for designing standardized PD instruments. The interaction between band-pass filter parameters and pulse resolution as defined in IEC Standard 270 is investigated. A complete PD testing and measuring circuit for GIS components is simulated and shows the difficulties in applying conventional PD measuring circuits to such complex systems View full abstract»

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  • Partial discharge distributions in liquid dielectrics

    Page(s): 99 - 105
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    Different dielectric fluids used in HV electrical components were subjected to AC stresses, and the partial discharge (PD) spectra produced under nonuniform and uniform field conditions were recorded with the help of an electrical detector and a multichannel analyzer (MCA) as a function of applied stress. The analysis of the collected data confirms that PD activity in a liquid is a random phenomenon as well as a breakdown process. The presence of PD may be related with the presence in the liquid of bubbles near the electrode interface and with a low density region (vapor phase), which is the first step in the breakdown development. This confirms that PD occurs only in a gas and not in a solid or liquid. In this paper, which is part of an ongoing research project, it is shown that MCA can be a helpful tool in PD measurements and analysis, allowing the demonstration of how the partial discharge inception voltage (PDIV) significantly changes according to the adopted inception criteria View full abstract»

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  • Improvements to the Electrically Stimulated Acoustic Wave method for analyzing bulk space charge

    Page(s): 152 - 161
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    The Electrically Stimulated Acoustic Wave method for observing resident space charge in dielectric insulators involves applying a fast and relatively small voltage pulse across a material containing space charge. The perturbation launches a stress wave which propagates at the velocity of sound and is received by a piezoelectric transducer mounted in the acoustic path. This nondestructive technique does not liberate space charge so that it may be performed in situ during any space charge generating experiment. The improvements to this system allow it to detect space charge distributions that are more broadly distributed than in previous work View full abstract»

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  • Conduction and thermally stimulated discharge currents in aramid paper

    Page(s): 162 - 173
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    Conduction currents and thermally stimulated discharge (TSD) currents were studied in aramid paper at various field strengths and temperatures. At low field strengths the conductivity is ohmic, and at higher field strengths (up to 30 MV/m), ionic conduction is a possible mechanism. The activation energy of low field conduction is determined and at high electric fields the hopping distance for ions is in the range of 4.4 to 8.0 nm. TSD currents are also measured at various poling fields, formation and storage times, and rates of heating. The TSD current shows a peak at 135°C for a rate of heating of 1 K/min and shifts to a higher value when the rate of heating is increased. The peak current and the charge released to the external circuit is proportional to the poling field. The observed peak is attributed to the depolarization of permanent dipoles with a room temperature relaxation time of 5.3×105 s View full abstract»

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  • Location of partial discharges in shielded cables in the presence of high noise

    Page(s): 37 - 43
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    Updated information on a partial discharge location system intended to pinpoint the location of defects and/or faults on a shielded buried underground cable is presented. The system is based on the principle of reflectometry. Its salient characteristics include the following two features: (a) an ability to pinpoint the location of a partial discharge source not only along the cable length, but also along the surface of the trench where it is buried; and (b) the ability to operate in a high noise environment. Recent field and laboratory data obtained on noise and techniques for its mitigation are discussed in some detail. These techniques include analog/digital notch filters for the elimination of AM broadcast noise and an adaptive digital filtering scheme which incorporates the transfer function of the cable for added accuracy View full abstract»

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  • Estimating the location of partial discharges in cables

    Page(s): 44 - 59
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    There are several techniques that can be used to estimate the location of partial discharges in cables, however, certain technical obstacles need to be overcome before acceptance of this type of testing becomes widespread. A review of the theory of signal propagation in power cables is presented along with its relation to partial discharge site location. Fundamental limitations affect the detectability and location accuracy of partial discharges in power cables. The sources of these errors are discussed along with methods that minimize their effects. The advantages and disadvantages of alternative methods for locating partial discharge sites are presented along with a calibration method that improves the accuracy of these methods View full abstract»

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Aims & Scope

This Transactions ceased production in 1993. The current retitled publication is  IEEE Transactions on Dielectrics and Electrical Insulation.

Full Aims & Scope