Showing papers on "Partial discharge published in 1980"

On the Mechanism of Dielectric Breakdown of Solids

Abstract: The mechanism of dielectric breakdown in solids, according to recent experimental evidence, involves the creation of a gaseous channel through the dielectric. The high conductance of breakdown appears to be associated with this channel, not with conduction through the solid itself. The central problem in the theory of dielectric breakdown in solids is thus to explain the development, in a strong electric field, of a macroscopic gaseous channel through the dielectric before the large change of conductance characteristic of dielectric breakdown. Recent experimental results will be reviewed and a gaseous model of breakdown in solids will be described in terms of four stages: Formative, Tree Initiation, Tree Growth and Return Streamer. The model is still in the stage of phenomenological development.

Diagnostic Technique of Gas Insulated Substation by Partial Discharge Detection

Abstract: To make more reliable operations of Gas Insulated Substation (GIS), the detecting methods of internal irregularities from outside of enclosure before major insulation failures occure are required. Internal irregularity may cause a partial discharge, then the methods to detect the partial discharge chemically, mechanically, electrically and optically, are developed and those methods are applied to GIS model simulating the intemal irregularities and GIS in field operation. Investigation leads to the excellent results that those developed methods are able to be applied for GIS to confirm the reliability.

Dielectric Characteristics of SF6 Gas for Application to HVDC Systems

Abstract: Dielectric problems of SF6 gas insulated DC apparatuses were investigated. The DC breakdown voltages of the SF, gas gap become lower with larger electrodes. The decrease can be estimated fairly well for electrode areas of 101 to 104 cm2 on the basis of the statistical distribution of the initial breakdown field strength for small electrodes. Preceding the gap breakdown large dark currents start to flow at the field of 5 MV/m, which are caused by metal particles on the anode. However, this current can be eliminated by sufficient cleaning of the anode. The DC dielectric strength of spacers supporting high voltage conductors is decreased by metal particles, but is only as low as that for the lightning impulse voltages. Moreover, breakdown voltage of spacers are not affected by DC polarity reversal tests when done under contamination with metal particles or when clean. As a result of these investigations most of the technical difficulties that arise in the gas insulation of HVDC power apparatuses could be eliminated.

Effect of Water of Electrical Properties of Extruded Synthetical Insulations Application on Cables

Abstract: This paper presents the results of a study on water treeing in extruded insulation of cables. We show our in service experience for medium, high and extra high voltage polyethylene insulated cables and the results of investigations undertaken on a very small number of broken down cables, all failures owing to water treeing.

Glow discharge heating apparatus

Abstract: Typically, a bottom of a cup-shaped electrode opposes to that of a similar electrode through a predetermined gap and in a mixture of helium and hydrogen. A step-up transformer connected across an AC source through a resistor applies a voltage in excess of a discharge breakdown voltage for the gap across the electrodes to cause a pilot glow discharge between them before the source voltage reaches a glow hold minimum voltage for the electrodes. A rectified voltage resulting from a transformer connected across the resistor turns a bidirectional triode thyristor on to apply the source voltage across the electrodes through the conducting thyristor. This smoothly transits the pilot glow discharge to a glow discharge between the electrodes. The latter discharge heats a liquid forcedly flowing along inner surfaces of the electrodes. Also an auxiliary electrode can be operatively coupled to the electrodes to cause similarly a pilot glow discharge between it and either one of the electrodes. For a DC source a tubular anode surrounds a middle portion of a tubular cathode through which a liquid flows.

Analysis of q-n and φ-q characteristics of partial discharge in several electrode systems

Abstract: This paper describes some new aspects of the reration between partial discharge characteristics and several void model structures in terms of statistical features of partial discharge pulse magnitudes against applied voltage phase. Newly proposed parameters here are the skewness and kurtosis of a φ-q pattern (applied voltage phase versus cycle mean discharge magnitude) and have been found to represent the partial discharge characteristics of various kinds of void structures more destinctively than conventional partial discharge parameters such as maximum apparent discharge maginitude qmax and mean discharge current Iq do. Typical dependence of the skewness and the kurtosis on applied voltage in three kinds of IGI (Insulation-Gas-Insulation) void structures are discussed.

Location of Partial Discharges in Power Transformers by Computation and Measurement of Capacitively Transmitted Voltage Pulses

Abstract: The voltage distribution in a power transformer after a partial discharge has occurred is calculated. The results are compared with voltages, measured at the terminals of the transformer. A partial discharge prediction curve, based on the calculated capacitive distribution is constructed, by which the location of partial discharges is improved. The location method is based on peak values or capacitive pulses measured at the terminals. Calculation of the complete winding resonances after a partial discharge is found not to be accurate enough for internal corona location purposes.

Partial discharges in power-cable joints: their propagation along a crossbonded circuit and methods for their detection

Abstract: A method of measuring the discharge activity on cable systems has been developed to assist in assessing and monitoring cable joints. Partial discharge activity in the cable joints is detected by measuring the currents produced in the links between bonding cables which are brought to the surface to achieve sheath transpositions. The high-frequency components of this current may be detected using current transformers around the links and a radio-frequency amplifier. The output of the latter may then be used to give an alarm indication of any significant rise in these components caused by discharges in the joints. To relate the measurements at a link position to the discharge activity in the cable joint an analytical model of the cable system has been developed to describe the propagation of pulses through a crossbonded-cable system. The results of this analysis have been compared with measurements made on two operational cable circuits, and its impact on the design of a monitoring system discussed. Instrumentation is being developed for installation on CEGB 275 and 400 kV cable circuits. Sensors and the detector would be fitted at each stop-joint bay with an alarm activated in a substation when the level exceeds a preset value.

A New AC Current Testing Method for Non-Destructive Insulation Tests

Abstract: A new nondestructive diagnosis method is developed mainly for stator coil insulation of high voltage rotating machines as a result of analysis and experience on the behavior of a current of a sample under ac voltage application. A newly-defined parameter Y, measured in this method, equals tan, plus y, where y closely relates to void volume ratio in a sample. A new apparatus to measure Y automatically is also developed which shows experimentally several advantages in a practical test. Y-V patterns and y-V patterns by this method are verified to correlate well to insulation condition and residual breakdown voltage of a sample.

Partial discharge location in gas-insulated switchgear*

Abstract: Floating components and free-conducting particles in gas-insulated switchgear (GIS) cannot be easily located in long bus runs or substations. Such sources of partial discharge produce electromagnetic pulses which propagate (and reflect) with little attenuation or dispersion within GIS. Cross- or auto-correlation analysis of pulse trains arriving at terminals of a substation or gas-insulated cable should permit accurate source location. Under EPRI sponsorship, a digital correlator and ancillary (pulse coupling) apparatus necessary to locate individual sources of partial discharge is being developed.

Metal encapsulated HV switch partial discharge measurement - is by LV stimulation of internal voltage converters

Abstract: A method of measuring partial discharges in metal encapsulated high voltage switching equipment involves using the metallic capsule as a measurement screen. It enables full screening of the entire measurement circuit, considerable reduction of the cost of measurement, and yet ensures a high measurement sensitivity. An inductive voltage transducer inside the equipment capsule, either as a part of the original circuit or specially built in, produces the last high voltage. For this purpose its low voltage winding is supplied with an excitation voltage via a low voltage high frequency filter. Several voltage convertes in parallel may be stimulated from a common source. Part of the capsule is fitted with capacitors for discharge measurement and is insulated from the remainder of the capsule.

Partial-discharge pulse height distributions and frequencies for positive and negative dc corona in sf6 and sf6-n2 mixtures*

Abstract: The voltage and pressure dependence of partial-discharge pulse height distributions and pulse repetition rates have been investigated for compressed SF 6 and SF 6 -N 2 mixtures using a fast multichannel analyzer. Positive and negative dc corona were generated using a point-plane stainless steel electrode geometry with a gap spacing of 1.24 cm and a tip radius of 0.07 mm. For SF 6 the positive corona pulses are typically an order of magnitude larger in amplitude than negative corona pulses although their repetition rate is lower. The tendency for SF 6 positive corona pulses to develop as bursts with a burst length that increases with increasing voltage and decreasing pressure is clearly exhibited by the pulse height spectra. The negative corona in SF 6 tends to begin as large pulses which eventually give way to a near glow condition as voltage is increased, although a steady glow, such as occurs in pure N 2 , was never observed. The observed pulse height spectra appear to be sensitive to gas composition as is evident from measurements made with gases containing varying relative concentrations of SF 6 and N 2 . Attempts are underway to correlate observed changes in pulse height spectra with corona-induced chemical changes in the gas using a gas chromatograph-mass spectrometer system.

Three-electrode low pressure discharge apparatus and method for uniform ionization of gaseous media

Abstract: Uniform, transverse electrical discharges are produced in gaseous media without the necessity of switching the main discharge voltage with an external device which carries the entire discharge current. A three-electrode low pressure discharge tube is charged across its anode (1) and cathode (2) to below breakdown voltage using a dc voltage source (3). An array of resistors (4) or capacitors can be made to discharge to the wire screen anode by means of a low energy high voltage pulse circuit (5) producing sufficient preionization in the region between the anode and cathode to initiate and control the main discharge. The invention has been demonstrated to be useful as a CO2 laser oscillator and pulse-smoother. It can be reliably operated in the sealed-off mode.

Method for detecting partial discharge of power cable

Abstract: PURPOSE:To make it difficult to pick up noises such as broadcasting waves and facilitate the detection of micro electric signals by inserting a partial discharge signal separating circuit in series between a cable to be tested and a high voltage source. CONSTITUTION:High voltage is applied from a power source 2 to the conductors 5 of a power cable 1 through a high voltage power source wire 6, and the earth side 7 of the power source 2 and the shielding layer 8 of the cable 1 are held grounded. A partial discharge signal separating circuit 9 is inserted in series between the conductors 5 and the power source wire 6 near the terminal of the cable 1. An amplifier 17 is connected via a voltage dividing capacitor 16 to the terminals 14, 15, and a converter 1 which converts the output signal thereof to a light signal and transmits the same to an optical fiber 18 and an analyzing device 20 are connected thereto. Thereby, the detection of the signal is carried out on the cable head nearest to the cable to be tested and since the signal is transmitted from here up to the analyzing device by using the optical fiber, the possibility of inclusion of external noises into the detection signal is extremely small and safety is high.

The application of the pulse discrimination system to the measurement of partial discharges in insulation under noisy conditions

Abstract: Various methods of eliminating noise from partial discharge measurements are reviewed and it is pointed out that such techniques may not always be applicable due to environmental conditions and cost. It is explained that, by using the pulse discrimination system originally developed by one of the authors, one may reduce or eliminate filtering and screening and undertake partial discharge measurements in the presence of external interference. The original system was rather slow and the paper describes a new faster version which enables partial discharges to be recorded in the presence of interference pulse rates of around 105 per second. The measurement system has a limited bandwidth and any common-mode radio interference entering the system within this bandwidth can be eliminated by the pulse discrimination system. The test results demonstrate that a single small pulse can be detected when it is buried in interference. The paper also shows that partial discharge characteristics taken under quiet conditions are similar to those recorded with considerable radio and pulse interference. When undertaking measurements under noisy conditions, some of the required pulses are lost as they are superimposed on interference. Methods of gathering data over a number of cycles of the supply voltage are therefore considered.

Partial discharge detector for gas insulated electric appliance

Abstract: PURPOSE:To facilitate the detection of partial discharge generated within the closed bus or the like by providing a one-point grounding wire for metal capsules separated while an electromagnetic probe, a corona pulse amplifier, and a signal converter are connected to respective grounding wires. CONSTITUTION:An electric connector between metal capsules are disconnected in a plurality of sections 5 so that no short-circuit occurs between a sheath current of the metal capsules 3 and 4 induced by the bus current to form a loop. A one-point grounding wire 6 is provided for the sections 5 each thus separated and an electromagnetic coupling current detector 7 (an electromagnetic probe), a corona pulse amplifier 8 and signal converter 9 to the grounding wires to monitor partial discharge for each metal capsules separated from each other. It is found that a corona pulse current flow through the grounding wires 6 overlapping a charged current as any partial discharge is caused in the insulated support in the section 5. The closed container separation section 5 allows the checking of the current from flowing to other grounding lines.

Acoustic emission signatures of arcs and sparks

Abstract: Partial discharge(microsparks) and flashover faults (arcs) associated with electrical power apparatus emit acoustic pressure waves which are useful for detection and location purposes. Although these emissions are modified by different forms of electrical insulation and by the structures involved, it is helpful to know their approximate spectrum signatures and levels so that acoustic sensing systems can be optimized. Based on both observations and some theory, it is demonstrated that generally, high energy (kj) flashover faults radiate maximum acoustic levels in the low frequency region from ∼ 120Hz to ∼10 kHz, whereas, low energy (μJ) partial discharges (P.D.) have maximum acoustic emission at higher frequencies in the ∼10 to ∼400 kHz range. As the acoustic emission levels are approximately inversely related to frequency, then useful measurements can be made over a wide range of frequencies, and it is hoped that the results reported here will help in the selection of acoustic sensors for incipient fault detection. In addition, it is demonstrated that the acoustic emission signatures of positive streamer P. D. from sharp-edged electrodes and metallic slivers in transformer oil; of insulation cavity P.D.; and of bouncing metallic particles in metal enclosures; have unique features which are useful for identification.

Considerations on the insulation degradation characteristics by functional tests

Abstract: This paper describes the results of various insulation degradation characteristics measured in functional tests using form-wound motorettes and discusses on the effective insulation diagnostics. The measured insulation degradation characteristics are insulation resistance, dissipation factor, discharge intensity, discharge phase, partial discharge characteristics, y, etc. and breakdown voltage. Different types of functional test were carried out to evaluate the thermal life and voltage endurace life of the insulation system. The paper concludes that the insulation degradation characteristics make a drastic change with the type of degradation stress and a new location method to detect the local degradation will be needed to develop.

Voltage Breakdown Testing of Relays in the 1000-V Range

Abstract: The ac voltage breakdown between adjacent conductors separated by an insulator on relays has been examined using two types of breakdown test sets and a sensitive corona (partial discharge) detector. A large difference in the breakdown voltages was observed on relays from the same population using two breakdown test sets. The characteristics of the test sets were examined to identify the cause of the breakdown difference. The breakdown voltage is independent of the voltage ramp speed from 55 to 8300 V/s. It is also independent of the series resistance up to 300 k\Omega. The different detector systems do not contribute to the breakdown difference. The output capacitance of the breakdown test sets appears to be quite important to the voltage breakdown of the samples. Modification of the output of the test sets leads to similar breakdown values. The prebreakdown discharges observed using the corona detector suggests that breakdown is a gas breakdown type. Effects on the insulator surfaces caused by the testing are considered in light of the prebreakdown discharge measurements and are expected to be minimal. These results should be applicable to the moderately high voltage testing of other products, although the numerical values will probably differ.

Insulation inspecting method and device

Abstract: PURPOSE:To establish partial discharge in an insulating tissue so that deterioration judging data are accurately obtained by impressing a DC high voltage linearly upon the tissue in a manner to rise and fall. CONSTITUTION:The voltage rectified at 1 at a low level is converted at 2 into a low voltage having a high frequency of several kHz and then is boosted at 3 to a high voltage so that it is impressed as a positive and negative DC high voltage upon a test piece 8 through a polarity changer 14 and a high voltage rectifying circuit 4. The voltage waveforms thus impressed are divided by a divider 7 and compared with and referred to the output voltage waveforms of a standard voltage generator 5 which is programmed in advance in a comparing and referring device 6. The control is made such that the low voltage rectified output level is increased and decreased in case of any shortage. And, the generator 5 commands the linear boost, hold at constant voltage and linear fall and inverts the polarity of the voltage. As a result, the test piece is supplied with the DC high voltage which repeats the linear variations to positive and negative polarities.

Partial discharge inception and breakdown studies on model sheet-wound, compressed sf6 gas-impregnated polymer film-insulated windings

Abstract: An investigation was made of advanced concepts for gas-insulated power transformers and experimental studies have been made on model turn-to-turn insulation structures comprised of sheet aluminum conductors insulated with two sheets of polymer film impregnated with compressed SF/sub 6/ gas Precautions were taken to eliminate particles using electrostatic techniques during winding of the models Partial discharge inception and breakdown measurements were made at 60 Hz applied voltages and room temperature; the effect of polymer film thickness was also investigated

Apparatus and method for generating a glow discharge

Abstract: This invention provides a laser or high voltage switch which has two spaced apart main discharge electrodes which define between them a main discharge gap, a discharge inducing member that is of an insulating material and which provides a planar or curved trigger discharge surface adjacent the electrodes and partially or completely bridging the main discharge gap, and an auxiliary conductor on the other side of the discharge inducing member to the main discharge electrodes and capacitively coupled to one of them by a distributed stray capacitance, such that when an excitation pulse is applied across the main discharge electrodes an initial capacitively initiated low order trigger discharge occurs onto the trigger discharge surface, and preferably across the surface from one main discharge electrode to the other. This trigger discharge photo-ionises a gas in the main discharge gap to cause a glow discharge between the main electrodes. The auxiliary conductor may be sheet like and may be either part of a pulsing circuit or it may be directly electrically coupled to one of the main discharge electrodes. The conductor may be shielded by a shielding member to vary the capacitive coupling between the conductor and the main discharge electrode. One or both of the main discharge electrodes may have a curved portion and a sharpened portion to induce a corona discharge.

Method of and device for diagnosing insulation

Abstract: PURPOSE:To enhance the measuring accuracy of a device for diagnosing an insulator by averaging the generation of partial discharge pulses and measure the insulating degree digitized by counting the generated pulses by raising and lowering the high DC voltage to the insulator to generate a partial discharge. CONSTITUTION:A high frequency voltage raised through a high frequency stepup transformer 3 is converted through a high voltage rectifier 4 and polarity switch 5, etc. into a high DC voltage, which is then applied to an article 10 to be tested. This high DC voltage is divided through voltage dividing resistor 9, and the divided voltage is compared with the output voltage waveform from predetermined function generator 12 at a differential amplifier 13. When there is any difference between the output voltage waveform and the divided voltage, the output level of a low voltage rectifier circuit is regualted by a phase control circuit 14. Thus, the applied DC voltage is controlled in proportion to the output voltage from the function generator 12. When the high DC voltage is applied to an article 10 to be tested, a partial discharge occurs at the article 12. The pulse voltage signal thus obtained is compared with the standard voltage to form a rectangular waveform pulse having predetermined amplitude and duration. A recorder 28 simultaneously records the applied voltage and the rectangular waveform pulse thus generated, and a pulse counter 29 counts and indicates the accumulated rectangular pulses.

Gas type laser beam generator

Abstract: PURPOSE:For reducing the whole structure of this system, to generate partial discharge between the third electrode provided in the vicinity of a cathode and said cathode so that no high voltage may be impressed between the cathodes of a plurality of discharge tubes. CONSTITUTION:Third electrodes 20A and 20B are provided in the vicinity of the cathodes of first and second discharge tubes 2A and 2B, and connected to the + side terminal of a DC power source 12 through the medium of a high-resistor 21 by means of an electric wire 22. Immediately after the start of the discharge of said discharge tube 2A which has made the first discharge after starting, said discharge tube 2B does not start main discharge, but partial discharge is generated between a cathode 4B and an electrode 20B. Therefore, the voltage between cathodes 4A and 4B does not become excessive since the voltage of said cathode 4B is lower than that generated by a DC power source 13. Consequently, the insulation distance l between insulating tubes 5A and 5B can be decreased. If said third electrodes 20A and 20B are installed on the flow lower gas flow course side of said cathodes 4A and 4B, good results can be obtained since charge particles easily reach anode side.

Electrical discharge apparatus and a gas laser pumped by an electrical discharge through the gas

Abstract: In electrical discharge apparatus, such as a gas laser, in which a glow discharge is to be produced in a gas between two electrodes, at least one pre-ionizing member is placed near the discharge space and extending between the electrodes so that current flows in the member which is made of intermediate resistivity material such as crystalline semiconductor material. As a result, the discharge space is pre-ionized which assists initiation of the main discharge. The pre-ionization may be due to the formation of numerous small arcs between the electrodes and the member and the resulting production of ultra-violet light.

Partial discharge measurement with pulse height analyzer

Abstract: Partial discharge measurements and data processing are very significant factors in the study of partial discharge phenomena and the development of diagnostic techniques for insulation used in electrical machines. Partial discharges have many time-varying parameters which can be measured and analysed. In order to introduce laboratory automation in the study on partial discharge phenomena, a new system using commercial multi-channel analyzer and minicomputer has been developed. Several experimental results show it could become a more useful system for diagnostics provided more essential data processing programs are developed.

Partial discharge detector

Abstract: PURPOSE:To separate a pulse current attributed to a partial discharge from an electric noise and make possible measurement at positive and negative polarities by combining diodes which run positive-polarity current and negative-polarity current. CONSTITUTION:If a partial discharge occurred in the equivalent electrostatic capacity of a test sample, an electric current is, is' runs, causing a negative-polarity current i2 to run through a diode 8 and a positive-polarity current i1 through a diode 9. Then these currents flow into an output impedance Zp. In this case, the positive- and negative-polarity currents i3, i4 due to the current is' run through D15, 12 and 13, 14 respectively. In addition, the currents iN, iN' run according to polarity on account of an electric noise generated by an impedance Zp on the power supply side, but to not run through D8, 9. Consequently, in case a reduced oscillation waveform of the current is runs, the terminal voltage of Zp is equal to the waveform of the current is. The currents is', iN, iN' do not run through Zd, so that a pulse current attributed to a partial discharge is detected at Zd of a detector 16 and a noise voltage generated at Zp is not detected.