Showing papers on "Partial discharge published in 1976"

Switching surge strength of large air gaps: A physical approach

Abstract: A method is introduced for the determination of the sparkover voltage of practically any configuration subjected to switching impulses of any polarity, applied to one or more electrodes When the discharge process is governed by the phenomena occurring at a positively charged electrode. The method is applied to some configurations, especially chosen to show its important features, and the results obtained are compared with actual test results. It is finally shown which are the directions in which the studies on the discharge phenomenon could improve the precision and the applicability of the method.

Partial discharge characteristics of oil-immersed insulation systems under DC, combined AC-DC and DC reversed polarity voltage

Abstract: Breakdown characteristics of insulating oil, under combined ac-dc voltage and dc reversed polarity voltage, and partial discharge characteristics of oil-immersed insulation, under combined ac-dc voltage and polarity revesal of dc voltage Were made clear by elementary experiments. After that, a numerical dc field mapping method for electric field analysis of two-dimensional configurations which consist of composite insulation and field mapping methods under combined ac-dc voltage and dc reversed polarity voltage were proposed. Futhermore, partial discharge characteristics of transformer insulation under dc, combined ac-dc voltage were experimentally made clear by practical trial models.

On-Line Digital Computer System for Measurementof Partial Discharges in Insulation Structures

Abstract: An outline is given of the nature of partial dischargesoccurring in insulation structures, in particular in oil impregnatedconfigurations. It is suggested that conventional discharge measuringsystems are not always able to assess significant parameters becausemuch of the available information is inevitably discarded during thehigh-voltage tests. A mobile computer-based data-acquisition system hasbeen developed for recording and storing, in digital form, the statisticalinformation present. The equipment described is capable of recordingand analyzing the small disturbances produced by partial dischargesunder practical conditions. The computer programs enable the time ofoccurrence and the magnitude and polarity of the pulses to be recorded;in addition, digital transient-event recorders can be programmed toaccept slow partial discharge shapes or ultrasonic transducer outputsfor storage in the computer system. A wide range of playback programsare described and possible methods of presenting the results are discussedusing examples obtained from a 50-kV high-voltage test arrangement.The problems of hardware development are outlined, including thoseof interfacing and operation in hostile environments. The economics ofsuch a system are mentioned and methods of effecting cost reductionsare suggested.Finally, this paper suggests that if on-line characterization of partialdischarges becomes possible then the results of discharge measurementswill have greater significance than at present, especially in those borderlinecases where interpretation of results is difficult.

Partial-Discharge Phenomena and the Effect of Their Constituents on Polyethylene

Abstract: A method of investigating partial-discharge phenomena andtheir effect on polyethylene is described. A physical study was carriedout with air at atmospheric pressure and gaps between 2 and 14 mm.It is shown, that with this range of gaps and with dielectric walls, astreamer process appears as in the case of a positive point and a metallicplane.The evolution of the polyethylene samples after the aging producedby the constituents of the discharge, i.e., UV radiation and electronsand ions of low energy, was studied by means of IR spectroscopy. Ifthe discharge is of the streamer type it might be possible to attributethe deterioration to the concentration of ions at its tip; however, IRspectroscopy and scanning electron microscopy have shown thatalthough the ions were more reactive they were not sufficiently so toexplain the damage caused by corona discharges.

Partial Discharge Characteristics of Silicone Liquids

Abstract: New safety and environmental considerations in the design and operation of modern public transportation systems exclude the use of materials that can cause fire and ecological hazards. Therefore, the power transformers in trains and subway stations require new safer insulating liquids. The askarels or polychlorinated biphenyl (PCB) liquids have been classified as nonflammable, but recent investigations have indicated that spills of these chlorinated liquids may have adverse ecological effects. The manufacture and use of PCB's in Japan have been prohibited by law. To meet environmental and toxicological requirements, new insulation systems for transformers were developed using silicone insulating liquids. In the evaluation of a high-voltage transformer insulation system, it is important to study partial discharge behavior in the insulating liquid. This paper describes measurements of partial discharge inception voltage and of discharge pulse amplitudes at higher test voltages in silicone liquids. The initial partial discharge inception phenomenon in both silicone liquids and mineral oils is the same and is probably related to the presence of contaminants such as water and particles in the liquids. But the further development and growth of the discharges in the liquids seem to be dependent on the chemical and physical properties of the insulating liquid. During the partial discharge measurements, it was observed that small amounts of solid material were formed on the electrode. Chemical analysis showed the material to be cross-linked polymeric siloxanes. The quantity of gelied material is a function of the partial discharge intensity and the duration of discharges.

Electrical breakdown of mineral oil under non-uniform fields

Abstract: The dependence of the direct electrical breakdown voltage of degassed transformer oil and of gas-saturated oil on gap length for a point-sphere electrode system has been studied for the two polarities of the point The effects of anodization of the sphere electrode on the breakdown voltage against gap characteristics have also been examined The critical gap length at which the breakdown voltage is the same for both polarities of the point has been found to depend on the nature of the insulating film on the sphere electrode and on the type of gas dissolved in oil The discussion of the results is based on the propagation of a corona discharge from the point electrode and the possibility of formation of a back streamer from the sphere electrode

Corona discharge detecting device

Abstract: There is provided a device for detecting corona discharges generated in a high voltage generator which is operated by high frequency pulses, for example in a high voltage transformer which is used in the horizontal deflection circuit of a television receiver.

Mobile bridge test apparatus and method utilizing a sub-power frequency test signal for cable system evaluation

Abstract: This apparatus is for evaluation installed cable systems, including those that are already in use. The apparatus measures dissipation factor, partial discharge (corona) and insulation resistance of the cable system; all of these being necessary to determine the condition of the cables. This invention is unique, in that it can be used with installed cable systems that have their metallic shielding grounded; and the apparatus can be mounted on a truck or trailer for movement to any place where an installed system is to be evaluated.

Independent initiation technique of glow discharge production in high-pressure gas laser cavities

Abstract: A trigger circuit which operates independently of the main discharge circuit can be used to initiate glow discharge useful for gas laser excitation. By utilizing independent trigger means, such as auxiliary dielectric electrodes, the main discharge can be controlled by modulating only a small part of the total energy input to the laser cavity. The main discharge gap of the laser is prestressed to a voltage below the spark breakdown voltage threshold of the electrode assembly under static conditions but above the glow discharge voltage of the electrode assembly. When the trigger means is pulsed to supply free electrons to the discharge gap the glow discharge is initiated between the electrodes independent of the need for modulating the main power to the gap.

Corona discharge device with grid grounded via non-linear bias element

Abstract: A corona discharge device including a corona discharge electrode, an opposing electrode disposed opposite to the corona discharge electrode, a high voltage alternate current source electrically connected between the two electrodes, and a grid provided in a corona discharge current flow path between the two electrodes. The grid is grounded through a nonlinear bias element.

Electron-acceleration type flatgas-discharge panel with internal memory functions and method of driving for same

Abstract: A flat display panel uses a DC gas-discharge and has flat discharge display elements, which elements have three electrodes composed of a cathode, a grid and an anode and a discharge stabilizing resistor. An auxiliary discharge is formed by using the discharge stabilizing resistor, the cathode and the grid in an auxiliary discharge space defined between the grid and the cathode. A main gas discharge is formed in a main discharge space defined between the anode and the grid by mainly using electrons in a plasma, produced in the auxiliary discharge space, which are diffused and accelerated into the main discharge space. The flat discharge panel, in order to provide a memory function in the main discharge is driven by the use of pulse voltage applied between the anode and the grid.

Fluctuation Mechanism of D. C. Partial Discharge in Polyethylene and Impulse Noise in Submarine Cable

Abstract: It has been made clear theoretically and experimentally that the d.c. partial discharge in polyethylene occurs in accordance with the Poisson process. This phenomenon is explained by assuming that the fluctuation of the d.c. partial discharge is due to the fluctuation of the current density, that is, the fluctuation of the carrier concentration in polyethylene. The repetition rate of the d.c. partial discharge is closely related to the current density, and is expressed as f=f0Vnexp (-W/kT) (n=4, W=1.0 eV). It is then possible to estimate the number of impulse noises as a result of the d.c. partial discharge occurring in a cable, and to clarify the effect of the d.c. partial discharge on data transmission.

Partial discharge measurement's over the frequency range 0.1 Hz to 50 Hz

Abstract: The need for partial discharge (corona) measurements at very low frequencies is explained and the results of tests on epoxy resin samples are given for the frequency range 0.1 Hz to 50 Hz. As no suitable commercial generator was available, a new type of low-frequency low-noise generator has been developed and this is described. The discharge detection system is also explained in the paper. This includes a pulse discrimination system for eliminating unwanted pulses from outside the test component. This was particularly useful when measuring discharges in a short length of cross-linked polyethylene cable, in the presence of discharges over its ends.

Gas discharge display unit - enables gas discharge in discharge space to be insensitive to anode voltage

Abstract: The unit has a gas filled, gas tight envelope with a plate shaped control structure (12) dividing the envelope interior in two parts. It comprises at least one plasma electrode pref. parallel to the control structure, placed in one envelope part (discharge space), and a luminous screen electrode (acceleration anode) in the other part (post-acceleration space). The control structure consists of a matrix of row and column wires spaced at crosspoints by insulators with through holes. The plasma electrode is so placed, that a gas discharge can burn in the discharge space, while the acceleration anode is so close to adjacent wires of the control structure (control electrodes), that even a voltage of several kV in the post-acceleration space cannot trip a gas discharge.

Partial discharge characteristics of solid insulation containing spherical cavities of small diameter

Abstract: This paper reports on a continuing investigation of the partial discharge characteristics of micron-size cavities embedded in a solid dielectric. Partial discharges in large cavities in solid insulation are known to cause progressive deterioration of the insulation and ultimate breakdown.1 A large number of voids in the diameter range one to tens of micrometers are known to be produced in the process of manufacture of extruded cross-linked polyethylene cables.2 It is conceivable that discharges could occur in some of these micro-voids and cause gradual degradation of the plastic similar to discharges in large cavities in solid insulation. In order to study the partial discharge (p.d.) behavior of solid insulators containing micron-size cavities under high-voltage stress, spherical cavities (microspheres) up to tens of micrometers in diameter were introduced into the solid in known proportions. The effect of the size and concentration of the microspheres in the solid were investigated and compared to the p.d. behavior of samples which contain no artificially-introduced microspheres.

Some aspects of the electrical behaviour of a cryogenic coaxial wrapped insulation

Abstract: The paper summarizes some results obtained recently and relative to different aspects of the electrical bevaviour of a coaxial tape wrapped insulation in helium under high electric stresses and up to breakdown. The effect of various parameters-taping and impregnation- is analysed.

One Consideration on Short-Gap, Atmospheric Discharge

Abstract: The discharge characteristics at 760 Torr of air of needle-sphere electrodes with narrow gaps of 1mm or less are discussed in order to gain an understanding of the structure and mechanism of discharges such as those used in DC discharge-type plasma display panels (PDP). At the initiation of the discharge, the streamer corona is more predominant in 0.1 mm-gap discharge than in 1.0 mm-gap discharge. Pulsed discharge is observed to shift to DC discharge by increasing the average discharge current. The threshold current is observed to be larger in 0.1 mm-gap discharge than in 1.0 mm-gap discharge. With the use of a needle cathode, DC discharge is held at a smaller current than with other configurations and polarities. It can be estimated that the thickness of the cathode dark space and of the negative glow is smaller than 10 µm.

Corona in insulating liquids and in combinations of paper and liquid

Abstract: Voltage breakdown is perhaps the most important factor in the performance of electrical equipment in service At high voltages corona* may lead to voltage breakdown especially over a period of time In liquid impregnated insulation systems, corona often varies tremendously with time in both magnitude and repetition rate, which complicates both its measurement and the understanding of its influence

Partial Discharge in Liquid Nitrogen

Abstract: Results are presented of experiments on partial discharge in liquid nitrogen, including insulation breakdown characteristics of liquid nitrogen, partial discharge characteristics of composite insulation systems, lifetime of polymer films, impulse breakdown of polymer films in liquid nitrogen, etc. The partial discharge characteristics of liquid nitrogen are examined with increasing liquid-nitrogen pressure. It is concluded that a composite insulation structure of polymer film and liquid nitrogen can be used as effective electrical insulators at cryogenic temperatures.

Analysis of the species created by corona discharges and of their interactions with surfaces

Abstract: Electrical discharges in various gases may produce chemical species which can cause damage to solide surfaces of different materials. In air, for example, ozone, metastable states of molecular oxygen, atomic oxygen and nitrogen oxides are produced. Furthermore, in the case of corona discharges,those species are pushed in preferred directions by electrical wind. As a matter of fact, in the case of corona discharges, there is an electrical wind 1 resulting from the momentum given to the gas molecules by impact or drag of the ions as they move out of the high field region. The particles of the gas are swept away by this electrical wind towards low field regions and flow around encountered surfaces. The experiments presented in this paper were made with a point to plane system.

Laboratory and field partial discharge studies by a utility

Abstract: This paper describes partial discharge tests and evaluations made by Philadelphia Electric Company on solid dielectric extruded cables which were giving unsatisfactory service. Both theoretical calculations and actual measurements are presented and are related to the analyses of the causes of poor cable performance.

Partial discharge test as a non-destructive diagnostic tool for electrical apparatus

Abstract: Partial Discharge test is a non-destructive over-potential test which demonstrates the condition of the insulation prior to breakdown. Such a test is assuming greater significance particularly in high voltage apparatus where an economical design of insulation is desirable. Partial discharge tests are being introduced as routine tests for high voltage apparatus. Various methods are in use for partial discharge tests. Of these methods, measurement by discharge detector gives quantitative information. In this paper results of discharge measurements on two typical high voltage coils, one completed motor and a transformer are given. Results of discharge tests on a few typical insulating materials are also given.