Showing papers on "Partial discharge published in 1978"

A minicomputer-based partial discharge measurement system

Abstract: In order to make a comprehensive study of partial discharge phenomena, an advanced measurement system has been developed, which utilizes a minicomputer having functions such as memory, data processing and judgement. The system is so designed to process positive and negative pulse trains appearing in phase of a.c. voltage and is provided basically with three functions; repetition vs. pulse height characteristics, time and phase domain pulse height distribution characteristics and phase domain pulse repetition characteristics. Several techniques are introduced to improve signal-to-noise ratio in partial discharge measurement. It can accommodate further modification in data processing when it is necessary in future.

Degradation Product Analysis for Polymeric Dielectric Materials Exposed to Partial Discharges

Abstract: Partial discharge phenomena appear to play an important role in insulation failure, and thus the analysis of products resulting from such degradation may lead to an understanding of insulation breakdown mechanisms and more accurate determination of insulation lifetimes. Progress in the area of degradation product analysis is reviewed for solid and liquid insulating materials.

Corona charging element

Abstract: Corona discharge electrodes are coated with compressed dielectric materials. A corona discharge electrode is placed under tension and coated with a molten, viscous dielectric material, such as glass, while under tension. The dielectric material is allowed to cool so that the dielectric material becomes bonded securely to the corona discharge electrode. The tension upon the corona discharge electrode is released thereby causing a compression of the dielectric material adhered thereto. The resulting dielectric coated corona discharge electrode has a substantially improved life and delivers substantially uniform currents.

Critical Examination of the Dissipation Factor Tip-Up as a Measure of Partial Discharge Intensity

Abstract: Bridge measurements of the dissipation factor tip-up at increasing voltage are generally assumed to give a correct measure of discharge intensity. It has been shown earlier that even when the tip-up is entirely caused by discharges it does not represent an unambiguous measure of discharge intensity, because ?tan? depends on both the amplitude and the phase of the discharge pulses. The validity of theoretical expressions describing the dependence of ?tan? and ?C on pulse phase is confirmed by experimental results and by calculations of the effects of higher harmonics. The information from Schering bridge measurements can be improved by using simple functions, given in the paper, of measured values of the capacitance and dissipation factor. These functions permit separate estimations of discharge intensity and phase. Empirical examples of the variation of these functions with voltage are given. Finally, the high sensitivity of ?tan? to harmonic distortion of the bridge voltage is discussed. This indicates that bridge measurements of partial discharge characteristics must be performed with a distortionless bridge voltage.

Impulse Breakdown in PMMA under Miegavolt, Nanosecond Excitation

Abstract: Single impulse dielectric breakdown tests were performed on thick (0.16 to 1.91 cm) polymethylmethacrylate (PMMA) specimens using a uniform field geometry with 7.5 cm diameter Bruce contour electrodes. The applied voltage rose within 20 ns to 2 MV, remained there about 30 ns and decayed in about 65 ns. In some cases, specimens were deliberately altered by surface scribing, pin pricking, drilling small dimples, drilling holes in portions of laminated specimens, and combinations of these. Light emission during the breakdown pulse and damage morphology were studied. Results of these experiments include the following: Each specimen contained many partial channels as well as a main breakdown path. The number varied greatly with overvoltage. Specimens 0.16 cm thick (peak field 12 MV/cm) contained about 2000 partial tree-like channels in various stages of growth, while 1.91 cm thick specimens (peak field 1.1 MV/cm) contained about 20 partial channels. In all unaltered specimens, the channels originated at the anode surface. However, when deep cavities were intentionally introduced into the cathode surface, channels originated at these artificially produced defects as well as on the defect-free anode surface. Intense light emission occurred from both the partial channels and the main discharge channel. The main discharge path is formed only after one of the partial discharge channels has grown completely across the specimen.

Breakdown in Ceramic Capacitors Under Pulsed High-Voltage Stress

Abstract: Failure in ceramic capacitors due to high-impulse voltages was investigated to determine the parameters which limit the breakdown voltage. It was found that the breakdown field strength is a function of the dielectric constant, the dielectric thickness, and the capacitor area. There was little correlation between the breakdown voltage and the rated voltage. Breakdown usually occurred at the edge of the electrodes, and only small changes in capacitance and dissipation factor resulted.

On the Nature of Dielectric Loss in High-Voltage Insulation

Abstract: Experimental observations have been made on resin samples containing one single cavity and on micaceous high voltage insulation. The results conflict with the generally accepted mechanism of voltage variation of the electrical characteristics of such samples, which mechanism is based on the influence of internal partial discharges. One different dissipative mechanism, namely the interfacial polarization or Maxwell-Wagner effect, is considered to fit these observations on a semi-quantitative basis. It takes into account the increase of the electrical conductivity of the surfaces struck by partial discharges, and the increase of the resistivity of the solid part of the insulation during its ageing under voltage. The relative contribution of these two mechanisms to the variation of the loss with applied voltage is influenced by voltage, temperature, frequency and of course, by the nature of the materials. According to the proposed model, the significance of some test specifications which consider the variation with applied voltage, of electrical properties of HV insulations, should be reconsidered.

D.C. Partial Discharge and Current in Polyethylene

Abstract: Simultaneous measurement of D.C. partial discharge and electric conduction was carried out. The following results were obtained: (1) The number of partial discharges occurring per unit time and also the electric current obey an exponential law exp (-W/kT) with the same activation energy, W. This indicates that the number of discharge sites does not vary with temperature and that partial discharge is governed by the electric current. (2) The number of partial discharges increases more rapidly than the electric current with the increase in the applied voltage. This means an increase of discharge sites with the increase in voltage. (3) The time dependence of the number of partial discharges is related to that of the electric current and the position of discharge sites between the electrodes in the sample. (4) The generation of partial discharges follows the Poisson distribution, showing that discharge sites have no correlation with each other.

Dielectric formed by a thin-layer polymer, a process for producing said layer and electrical capacitors comprising this dielectric

Abstract: A dielectric thin layer consisting of polymerized perfluoro-2-butene: (C F.sub.3 -C F=C F-C F.sub.3).sub.n presenting very good characteristics for production of single or multi-layer capacitors, obtained with a rapid deposition by glow discharge in an a.c. electrical field. The glow discharge is carried out in the gaseous phase of perfluoro-2-butene under highly reduced pressure and an a.c. voltage of 300 volts, the maximum rate of layer formation (0.7 micron per minute) being obtained for a frequency of 13.56Mc/s, at a temperature of 0° C. under a pressure of 0.1 Torr when the useful power of the glow discharge is of 5 to 10 watts.

Development of ±400 KV/±High and Medium-Pressure Oil-Filled Paper Insulated DC Power Cable System

Abstract: This paper describes the steps to be taken to optimize the design of oil-paper insulated power cable for high voltage dc operation. Experimental data is presented on models to establish the steady-state dc dielectric strength and the switching surge polarity reversal dielectric strength of oil-paper insulations. Laboratory data is presented on factory made prototype cables tested under voltage stress conditions applicable to a ±600 kV dc system. Optimized designs of high-pressure oil-filled pipe-type and medium-pressure oil-filled self-contained cables are presented.

Breakdown of Solid Insulating Films by Partial Discharge Using Sinusoidal and Pulse Voltages

Abstract: An experimental technique is described for measurement of the relative resistance of solid insulating films to breakdown by partial discharge using an IEC(b) electrode geometry together with sinusoidal voltages of frequencies from 1 to 60 kHz and pulse voltages at a repetition rate of 15.625 kHz. The technique is employed for determining the accelerated lifetime of polyimide and PVC films. The temperature rise under discharge condition was also measured. The results show that within the 100 minute time limit of these tests, lifetime is accelerated as the applied peak-to-peak voltage is increased, lifetime is accelerated linearly with frequency, and lifetime is independent of the voltage waveform. The results suggest that life with pulse voltage may be estimated from the results of an equivalent simple sinusoidal voltage test. Temperature measurements indicate that the specimen temperature increases with the applied voltage and frequency. The technique provides a rapid means of evaluating the performance of solid insulating films at a relatively low frequency.

Partial discharge testing of generator insulation

Abstract: Progressive degradation of high-voltage generator insulation whether due directly to the erosive effects of internal or slot discharge, or to other debilitating factors such as heat and vibration, may be detected and monitored as a function of time by in-situ partial-discharge tests. This paper describes new diagnostic test techniques for assessing the condition of generator insulation with a minimum of service interruption. An improved means of coupling or data acquisition is described, as well as a versatile single-channel pulse height analyzer with characteristics adequate for a field application of this type. Some typical test data are given. These studies were sponsored by the Canadian Electrical Association and are presented with their permission.

Investigations of partial discharge measuring techniques using epoxy resin samples with several voids

Abstract: For partial discharge(PD) tests in high-voltage equipment it is possible to use different measuring techniques and PD quantities, described in IEC-Publ 270 These methods are applied to epoxy resin samples with one or two natural cavities

The Effect of Polarity Reversals on the Dielectric Strength of Oil-Impregnated Paper Insulation for H.V.d.c. Cables

Abstract: A laboratory investigation involving tests on models and on full-sized cables has been carried out into the behaviour of oil-impregnated paper insulation under the simultaneous action of a pre-stressing direct voltage and a voltage surge of either the same or opposite polarity. It has been found that the dielectric strength does not depend on the level or polarity of the pre-stressing direct voltage or on the duration of the surge, except when a series of reversed polarity surges is applied at intervals of a few seconds, progressively increasing the level until breakdown occurs. In this typical case reductions from 130 MV/m at zero d.c. to 45 MV/m at 100 MV/m d.c. have been observed and explained in terms of bubble formation and growth in the paper tape "butt-spaces" adjacent to the metallic conductors. This effect is entirely eliminated by increasing the oil pressure to suppress bubble formation.

Electric spark machine provided with indicator to indicate electric discharge machining condition

Abstract: PURPOSE:To improve an operation by detecting respectively a normal electric discharge, a sustained arc discharge time, and no-discharge time wherefrom only the normal discharge time is detected to indicate as a pulse efficiency. CONSTITUTION:A device incorporating the first and the second comparison amplifiers 8, 9 which detect in comparing with a voltage applied by a level set units 4, 5 that may optionally set an electric discharge pulse in a normal discharge time and a sustained arc discharge pulse from the discharge voltage pulse that applies across the electrodes wherein the electrode 2 and the workpiece 3 are formed, the third comparison amplifier 7 to detect in comparing the voltage applied from a level set unit 6 with an across-electrode voltage pulse immediately applying said discharge voltage pulse, a logical circuit 12 which permits to produce only a discharge time pulse in a normal discharge time by taking a logical product of said respective amplifier, and a switch circuit 14 which controls switching an averaged electric discharge power source pulse by the output of said circuit and an indicator 17.

Thermal Brealdown and Thermal Runaway Phenomena in EHV Cables

Abstract: The paper describes a new method of estimating thermal breakdown in EHV oil-impregnated paper-insulated cables with some experimental data. In the analysis it is shown with the computed results that the heat generation in the insulation can be exactly approximated by the average temperature of the insulation. In addition this method can calculate the critical voltage at which EHV cables go into thermal breakdown. The values here calculated compare agreeably with the breakdown voltages of 500 kV OF cables.

Partial Discharge Location in Transformers and Reactors by Waveshape Recognition

Abstract: A technique for the location of partial discharges in transformers and reactors is described. The unique nature of the terminal voltage waveform resulting from a discharge occurring at a particular position along the winding is exploited to give the required location information. This waverorm is compared with waveform sets obtained by calibration, using cross-correlation techniques. The results of preliminary experiments are presented and areas of further development are outlined.

Elecrtospark type gas treating system

Abstract: PURPOSE: To provide an electrospark type gas treating system which is capable of causing discharge at a wide range of space, whose pressure loss owing to the flow of the gas to be treated is small, and which is capable of treating a large flow of gas. CONSTITUTION: When several KV-several tens-of-KV DC voltage is impressed on the clearance between a discharge wire 3 and a metallic cylindrical earth electrode 9, light glow discharge called corona discharge is caused only at the range of intensified electric field in the vicinity of said discharge wire 3, and the gas introduced through an inlet 1 is subject to the electronic impact of discharge to activate or dissociate. In such a gas treating system, a dielectric 8 is fitted between said both electrodes 1 and 9 to prevent discharge from generating spark which effect short circuit when discharge range is expanded by impressing high pressed voltages. Thereby, discharge range can be expanded considerably and very stabilized discharge can be obtained even with a relatively low impressed voltage. COPYRIGHT: (C)1979,JPO&Japio

The partial discharge and breakdown characteristics of insulating tapes immersed in liquid nitrogen

Abstract: Electrical power apparatus operating at cryogenic temperatures offers advantages over conventional equipment and research is continuing to produce superconducting generators and cables in addition to cryoresistive cables. Although there have been a limited number of studies of the behaviour of electrical insulation for such equipment,1,2 the operating stresses have not been evaluated and little is known of the ageing mechanisms. This paper describes the initial results of a project to determine suitable operating stresses and to study the deterioration of polymeric tapes immersed in a cryogenic fluid while subjected to high electric stresses. Partial discharge and breakdown characteristics of fibrous insulating sheets with and without artificial cavities are reported.

Partial discharge tester

Abstract: PURPOSE:To measure accurately partial discharge occuring in a sample by separating partial discharge occuring in the sample from that occuring in other places than the sample in high voltage partial discharge circuit at the insulation test of electric apparatuses.

Gas insulated electric device and method of inspecting partial discharge thereof

Abstract: PURPOSE: To enable highly sensitive detection of a gas insulated electric device with less noise by providing an electrode of two potentials and a differential amplifier for amplifying the output difference from the electrode. CONSTITUTION: There are provided first electrode 5 facing with energized conductor 1 via an insulating support 2, second electrode 6 mounted via an insulator 7 at a flange 4a in the vicinity of the electrode 5, which electrodes 5, 6 are connected to a detector 8 having a differential amplifier as detecting inputs. Since a metallic capsule 4 similarly detects the noise to the conductor 1, it can detect it highly sensitively. Since the capsule 4 can form second electrode 6 out of the capsule 4, it can not necessarily change the conventional gas insulated electric device. Thus, it can inspect the noiseless state externally from the capsule 4 in high sensitively at the partial discharge occurred at the insulation spacer or the like. COPYRIGHT: (C)1979,JPO&Japio

Partial discharge energy measurements on electrical machine insulation when energised at frequencies between 0.1 Hz and power frequency

Abstract: The paper describes the measuring equipment and also gives the results of partial discharge (corona) measurements taken on a number of electrical machine insulation samples when energised at frequencies between 0.1 Hz and 50 Hz. The discharge magnitude and discharge energy values were obtained using a pulse discrimination system. The results were plotted on a multi-channel pulse height analyser which enabled integrated discharge values to be determined.

New Electrodes for Partial Discharge Endurance Tests

Abstract: This communication describes two kinds of electrode systems, newly developed for partial discharge endurance life tests. These methods give much smaller standard deviations than other cavity discharge methods. They are characterized by their open cavity structure in which the gas can remain the same during an experiment.

Partial discharge performance of lapped plastic insulation for superconducting power transmission cables and the dielectric strength of supercritical helium gas

Abstract: Brookhaven National Laboratory (BNL) has been working on a project to develop a superconducting power transmission cable since 1972. A flexible ac cable with Nb 3 Sn superconductor force-cooled by supercritical helium, was the design selected.1 Any dielectric used in a superconducting cable must have a very low dissipation factor so that the heat load to the refrigeration system is minimized. Differential contraction during cooling makes it impossible to use extruded dielectric, so a lapped, multilayer plastic tape construction was selected, with supercritical helium gas filling the butt spaces between tapes. Evaluation of many different tapes2 has shown biaxially oriented laminated polypropylene tape to be a promising dielectric.

Study of the evolution of electrical treeing by observation of luminous phenomena and discharge detection

Abstract: Fewer articles dealing with discharge detection and light emission which accompanies the discharges than those concerning electrical treeing are published. Kosaki et al.1 are interested in the detection of light emitted at the point of high voltage electrode when charges, injected into the material by field effects, recombine with holes of the lattice. It is therefore a study which aims at clarifying the physical processes involved in the initiation phase, since no treeing configuration is present in the solid when the emission occurs. Calderwood et al.2 have studied low level (4/1000 pc) discharge detection during initiation phase.

Polymer composition for signa transmission parts

Abstract: PURPOSE:To prevent the accumulation of electric charge, generation of partial discharge, and generation of impulse noise in the transmission parts made of plastic, by incorporating a surface active agent in a polymer composition in an amount higher than the equilibrium concentration.

Degradation of composite insulating materials due to partial discharge

Abstract: Experimental researches have been proceeded from the viewpoint of diagonostics on insulation systems to determine the relationship between the voltage endurance life and internal partial discharge. The test-pieces were epoxy resin impregnated mica composites to be used for insulation of electric rotating machine and epoxy resin/filler composite to be used for insulation of casting equipments. Investigation was made for measuring the discharge quantities in the course of time and for residual breakdown voltage. The results of the tests revealed that the discharge quantity is an index that indicates how much and how seriously the insulation are damaged at given point of time, but it can hardly show how fast the damage would develop thereafter. The endurance life of insulation varies in accodance with the discharge quantities which depends on development of breakdown path, thickness of insulation and the applied voltage.

The insulation properties of cryogenic liquid impregnated tapes

Abstract: The partial discharge properties of the cable model insulated with the cryogenic liquid impregnated tape were studied. As we confirmed that the breakdown strength of the paper-like single sheet sample in liquid was dependent on the permittivity ratio of liquid to fiber, the partial discharge inception stress in the butt gap of the cable was analysed using the permittivity ratio of the liquid to the insulation tape. The results showed that the discharge in butt gap was triggered by the surface discharge along the boundary between tape and liquid in the butt gap, and that it was hard to propagate hydrostatic pressure into the butt gaps of the cable lapped with the film such as PE film.