Showing papers on "Partial discharge published in 1982"

Fundamental Limitations in the Measurement of Corona and Partial Discharge

Abstract: The theoretical sensitivity of conventional partial discharge detectors is compared with that obtained from ultra wideband (UWB) (up to l GHz) detection systems. The comparison indicates that for relatively lossfree distributed systems, such as SF6 insulated bus, the UWB system is up to two orders of magnitude more sensitive. UWB detection also embodies additional advantages such as facilitating the location of discharge sites and the rejection of external electrical noise. For discharge detection in plastic-insulated cables, true UWB detection is not practical because of frequency-dependent attenuation effects, although certain gains in sensitivity can be achieved with a detector bandwidth of up to 10 MHz.

Propagation of partial discharge pulses in shielded power cable

Abstract: The design of concentric-neutral plastic-insulated power cables has been optimized for the transmission and distribution of large quantities of 60-Ηz power at high voltages. Understanding the mechanism of high frequency propagation in these cables is important in order to evaluate the sensitivity of partial discharge measurements [1,2]. Partial discharges in the solid insulation generate frequencies ranging to several hundred MHz [3]. With wide band detection, location of discharge sites in cable through pulse propagation timing techniques is also possible [4,5,6].

Electromagnetic Techniques for Fault and Partial Discharge Location in Gas-Insulated Cables and Substations

Abstract: The fully enclosed nature of gas- insulated substations substantially increases the difficulty of testing, maintaining, and troubleshooting the switchgear. Under EPRI sponsorship, Ontario Hydro has developed systems for fault location in gas cables and partial discharge location for cables and substations.

Silent discharge type pulse laser device

Abstract: A silent discharge type pulse laser device having a pair of opposing electrodes, at least one of which is an electrode covered by a dielectric, which is mounted opposite to a metallic electrode with a silent discharge space in between, a laser resonator consisting of a total reflection mirror and a partial reflection mirror mounted opposite to each other with the silent discharge section in between, a source of high frequency voltage for supplying to the pair of electrodes a high frequency voltage having a predetermined period for silent discharge, and a controller for controlling the high frequency voltage from the source with respect to a first interval and a second interval that form a period longer than the period for silent discharge. The high frequency voltage is supplied to the silent discharge section at a first peak voltage value during the first interval and at a second peak voltage value during the second interval, wherein the second peak voltage value is sufficient to cause a discharge but insufficient to excite laser oscillation.

Method and device for detecting and locating fault and/or partial discharges in a gas-insulated electrical equipment

Abstract: A device and a method for detecting and locating faults and/or partial discharges in a gas-insulated electrical equipment, such as gas-insulated bus or cable, a gas-insulated substation or a gas-insulated switchgear. The detecting device comprises a plurality of field coupled current sensors located at given intervals inside the housing of the equipment for detecting any variation of the current flowing through the conducting element extending inside this housing. Each sensor consists of a toroidal helix pick up coil, preferably a differentiating Rogowski coil, located in an annular cavity machined in the wall of the equipment housing and extending all around the conducting element. Each cavity is connected along its entire length to the inner surface of the housing wall by a slit having opposed side walls sufficiently spaced apart to be insulated from each other. Each sensor gives a signal which is proportional to the detected variation of the current. A control circuit is connected to each of the sensors for comparing their signals and measuring the time interval between all the signals given by the sensors of a given variation current, and thereby determining where is located the fault or partial discharge having caused this given variation of current. The main advantages of this device are that it is not electrically connected to the circuit carrying the main current and it is not influenced by the voltage drop associated with the flow of current on the inside surface of the annular cavities. Moreover, the sensitivity of the device is a function of the number of turns in the pick up coil, and therefore can be very high.

A New Method for Detection and Location of Distributed Partial Discharges (Cable Faults) in High Voltage Cables Under External Interference

Abstract: Todays partial discharge (PD) detection and location methods in high voltage cables are limited by the influence of external interferences as well as by the type and properties of the cable and by the nature of PD impulses. The problems of the existing methods could be overcome by the development of a new electronic PD detection and location method of high sensitivity and accuracy. It allows the recording and evaluation of partial discharges in HV cables even under the influence of external interference. The accuracy of location is 99.8% yielding a sensitivity down to 1 pC.

PD and BD Probability Distribution and Equi-Probabilistic V-t Characteristics of Oil-Filled Transformer Insulation

Abstract: Probability distributions of partial discharge (PD) and dielectric breakdown voltage were investigated for the typical components of oil-filled transformer insulation.

Partial Discharge Testing under Direct Voltage Conditions

Abstract: DC partial discharge (PD) (corona) testing is performed using a multichannel analyzer for pulse storing, and data is collected during increase of voltage and at quiescent voltage levels. Thus high voltage ceramic disk capacitors were evaluated by obtaining PD data interspersed during an accelarated life test. Increased PD activity was found early in samples that later failed catastrophically. By this technique, trends of insulation behavior are revealed sensitively and nondestructively in high voltage dc components.

Vacuum monitor device and method for vacuum interrupter

Abstract: An abnormally high vacuum pressure of a vacuum interrupter is detected from outside of the interrupter in response to electromagnetic wave signals generated by an electric discharge derived in response to a voltage difference and depending upon Paschen's law. Since the above-mentioned electric discharge is quite different from so-called partial discharge, even when the fixed and movable contacts are closed (i.e., under hot-line condition), it is possible to detect poor vacuum pressure on the basis of the electric discharge existing between the fixed and movable contact rods including two contacts and the main shield, as well as when the two contacts are open. The vacuum monitor according to the present invention comprises a rod or loop antenna fixedly or movably disposed near a conductive material of or connected to the vacuum interrupter and a detection section including, in particular, a 2 to 20 KHz band-pass filter.

Avalanches in insulating gases

Abstract: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication

Light emission from polyethylene subjected to highly divergent fields

Abstract: It is well known that polymers such as polyethylene can deteriorate under high electrical stress. This deterioration is usually in the form of electrical trees when the polymer is dry or water or electro-chemical trees in a wet environment. The tree initiation, before the tree becomes visible, is not fully understood. There is evidence that light is emitted during the electrical tree initiation process at both cryogenic and room temperatures [1,2]. Light has also claimed to have been detected during the growth of water trees [3]. This light has been attributed to electroluminescence or partial discharges ocurring in small voids near the needle tip. Previous studies have not attempted to detect partial discharges while measuring the light. This paper describes initial results of tests to measure simultaneously the light and partial discharge characteristics from a needle/plane electrode system in polyethylene.

Vacuum monitor for vacuum interrupter and use of the vacuum monitor

Abstract: A vacuum monitor for a vacuum interrupter which can detect a poor vacuum pressure from the outside of the interrupter on the basis of the electromagnetic wave signals generated by the electric discharge existing in accordance with a prebreakdown voltage depending upon Pashen's law when vacuum pressure increases within the vacuum interrupter. Since the above-mentioned electric discharge is quite different from so-called partial discharge, even when the fixed and movable contacts are kept closed (i.e. under hot-like condition), it is possible to detect poor vacuum pressure on the basis of the electric discharge existing between the fixed (8) and movable (9) contact rods including two contacts (10, 13) and the main shield (16), as well as when the two contact are kept opened. The vacuum monitor according to the present invention comprises a rod or loop antenna (21) fixedly or movably disposed near a conductive material of or connected to the vacuum interrupter and a detection section (20) including, in particular, a 2 to 20 kHz band-pass filter (24).

An interferometric measurement of gas temperatures in corona discharges

Abstract: An optical interferometer has been used to measure the increase in gas temperature in a point-to-plane corona discharge in air as a function of radial and axial position. For a corona current of 150 mu A, a 10 mm gap and a point radius of 0.35 mm, a maximum change in temperature of approximately 6K was observed. The authors' results suggest that under these conditions, where the corona voltage is approaching the spark breakdown voltage, the predominant ionisation process is two-step ionisation.

The relationship of partial discharge amplitude distributions with dielectric damage at different levels of voltage and frequency

Abstract: The methods of analysing the various individual partial discharge patterns using discriminating pulse amplitude techniques, in particular a multi-channel analyser (MCA) with several hundred pre-selected amplitude gates/channels, is in many instances a powerful method for assessing the relative quality of electrical insulating materials and systems to discharge attack.

Simultaneous measurement of partial discharge and radio-interference voltage

Abstract: A new instrument has been developed which allows simultaneous measurement of partial discharge (PD) and radio-interference voltage (RIV) in insulation of high-voltage power apparatus. A distinctive feature of this instrument is that it fulfills the low input impedance (150-Ω) requirement of the RIV measuring standard (NEMA 107) at 1 MHz and, at the same time, presents a high input impedance in the frequency bandwidth used for PD measurement; this high input impedance is required for acceptable measurement sensitivity of PD on power transformers. The instrument has shown stable measuring characteristics during the 16 months that it has been in service at the IREQ HV Laboratory where it is used to test power transformers, reactors, disconnecting switches, capacitors, current and voltage transformers, and other apparatus. The HV Laboratory personnel confirm that the device is practical and easy to handle during tests and saves a considerable amount of time.

Wide band measurements of partial discharge in epoxy

Abstract: Continuous observation of partial discharge may enable warning of incipient failure of gas-insulated switchgear (GIS). This paper reports measurements of partial discharges from electric treeing in epoxy, as well as from artificial defects in a GIS test piece. The measurements were performed with an ultrawide detection bandwidth (up to 1 GHz). Some partial discharge pulses have durations of at most a few nanoseconds; a multichannel analyzer capable of responding to such fast pulses was developed for these experiments.

Apparatus for and methods of monitoring partial discharge in high voltage electrical equipment

Abstract: In apparatus for continuously monitoring partial discharge in high voltage electrical equipment thereby to give advance warning of impending breakdown of solid-insulated components (e.g. capacitors 11 to 16), means are provided to distinguish electrical signals indicative of partial discharge from those resulting from noise or external transients. Current pulses in the various partial discharge paths are detected by detectors (21 to 26), and by means of solid-state circuitry (40, 41) their relative polarities are compared and an appropriate signal is made according to the comparison.

Partial discharge measuring device

Abstract: PURPOSE:To make a device small-sized on the whole and to perform partial discharge measurement without stopping the operation of a transformer by generating a calibration pulse from one of two through-type current transformers and connecting a low-pass filter, a high-frequency amplification part, and a display part to the other current transformer. CONSTITUTION:A calibration pulse generation part 23 generates calibration pulses 24, which are applied to a neutral-point line 17 through a current transformer 21. The pulses 24 are detected by a current transformer 22, and a low-pass filter 25 cuts 50 and 60Hz low-frequency components; and a high-frequency amplifica- tion part 26 amplifies about 100Hz partial-discharge pulses, and a display part 27 displays the output of the amplification part. Since the pulses during calibration have known magnitude, the gain of the amplifier 26 is adjusted to adjust the output of the display part 27. Consequently, partial discharge is measured easily without special preparation like stopping a transformer in operation or disconnecting stringing.

Voiceless discharge system gas laser device

Abstract: PURPOSE:To enable to clearly perform division between a discharge part and a non-discharge part by a simple electrode structure by coating an electrode with a dielectric whose region for electrode discharge has a larger specific dielectric constant and region for no discharge has a smaller specific dielectric constant. CONSTITUTION:In a constitution wherein a high voltage is impressed between a ground side electrode and a high voltage side electrode, thus producing the discharge 15 between both the electrodes, at least one of both electrode tubes 8 is coated with two kinds of dielectric whose region for discharge has a large specific dielectric constant and region for no discharge has a smaller specific dielectric constant. Thereby, the discharge part 16 and the non-discharge part 17 are formed on the electrode tube 8, and an inlet 12 and an outlet 13 for cooling water are provided in the neighborhood of both ends of each of these both electrodes. Such a constitution enables clearly perform division between the discharge part 16 and the non-discharge part 17 by the simple electrode structure.

Piezoelectric reflecting transducer for partial discharge acoustic signals

Abstract: The paper presents a new design for a piezoelectric transducer for acoustic signals emitted during partial discharges in power transformers. Testing results of its metrological parameters are presented. Examples of partial discharge oscillograms recorded using the new transducer in the measuring path are shown.

Optical investigations of the spatial and temporal development of partial discharges in polyethylene

Abstract: As a part of the investigation of partial discharges and their deterious interactions with solid insulation material, two partial discharge types, slowly and rapidly developing discharges, have been investigated. This paper summarizes the nature of the two discharge types, with emphasis on the rapidly developing discharges which have been investigated most recently.

Partial discharges in polymer insulation

Abstract: Evolving power conditioning system requirements in many technological areas will place severe demands upon long-lived, repetitive, pulse-power components. A major pacing system component in this high reliability, repetitive pulse-power technology is the energy storage capacitor [1]. Recently, increasing availabilities of quality plastic films, especially polypropylene, and the discovery of the excellent properties of perfluorocarbon liquids for impregnation fluids, make spirally-wound, plastic film/liquid impregnated capacitors a leading candidate for high energy density, repetitively operated, pulse discharge energy storage devices. The dominant lifetime-limiting mechanism in this type of high energy density capacitor is a direct result of partial discharge activity at the buried foil edges, where the electric field is maximum. Objectives of ongoing research programs include the characterization and understanding of the mechanisms of this and related partial discharge phenomena.

Inner abnormality monitor for oil-filled electric apparatus

Abstract: PURPOSE:To make it possible to detect the existence of an inner abnormality in an early stage through monitoring the existence of an inner discharge with high accuracy by detecting both a discharge pulse and an ultrasonic pulse generated accompanying the inner discharge in an oil-filled electric apparatus. CONSTITUTION:A discharge pulse detecting element 15 is disposed between a grounding conductor 14 of a tank 10 of an oil-filled electric apparatus and the ground, while an ultrasonic pulse detecting element 20 is mounted on the tank 10. When an inner discharge occurs in a winding 11 of the oil-filled electric apparatus, the discharge pulse is detected by the element 15 and fed to a comparator-discriminator circuit 30 as a pulse signal with a given width. On the other hand, the ultrasonic pulse generated in the winding 11 by a partial discharge propagates through the insulating oil in the tank 10 and is detected by the element 20 when reaching the wall of the tank 10 and fed to the circuit 30 as a pulse signal with a given width. The circuit 30 obtains the detection time difference between the pulse signal of the discharge pulse D and the pulse signal of the ultrasonic pulse S. When the time difference is smaller than a prescribed time tmax, the circuit 30 judges an inner abnormality to be generated and transmits an output signal to an output circuit 40.

Electrode area and stressed volume: Two apparent effects of large-volume oil insulation

Abstract: Analysis of the dielectric degradation observed in large-volume oil insulation revealed that the phenomenon can be interpreted in terms of an apparent effect of either the electrode area or the stressed volume. A semi-empirical method was developed for quantitative evaluation of the dielectric degradation of large-oil-volume insulation. The method applies the weak-link theory to an oil gap, assuming an apparent effect with a unit element of known breakdown probability distribution determined from experimental data.

Acoustic emission spectrum signatures from capacitors under AC and transient conditions

Abstract: In order to improve diagnostic∗ testing, the acoustic emission spectrum signatures from model and full-size power capacitors were examined under ac and transient conditions. Acoustic emissions were monitored from the foil and insulation structure, poor electrical contacts and from partial discharge or corona activity. It was found that noise apparently associated with the aluminum foil occurs at a frequency near 27 kHz, and that it is generally best to monitor the acoustic emissions from both contact arcing and partial discharges or corona at a frequency of ∼80 kHz.

Practical Aspects of Apparent Charge Partial Discharge Measurements

Abstract: While other industries have adopted charge measurement methods to monitor partial dis'charge severity, the power transformer industry has used RIV methods as the standard test. Very little practical comparative information has been published which relates these two methods. RIV meters can be used as charge indicators by making appropriate charge calibrations on the transformer under test. These procedures have been used to make parallel charge and RIV measurements on selected large power transformers. The results of these measurements show that there is no simple relationship between these two units of measurement. The actual relationship is a function of several transformer design parameters including physical size, type, and ratings. The results suggest that, for a given design type, RIV techniques may become less sensitive to partial discharge severity as transformer size increases. The results also show that RIV instruments can be used with charge calibration procedures to provide a more uniform measure of transformer quality.

Partial Discharges in a Cylindrical Void with a Metal Rod Electrode

Abstract: The distributions of the rate of partial discharge magnitudes, here called the discharge intensities, were studied in artificial voids having configurations proposed earlier for the endurance testing of materials using a multichannel analyzer, while the following parameters were varied: applied voltage, polarity, test duration, void sealing, void gap, ambient gas, rod geometry and treatment of the specimens. The intensity of partial discharges was to some extent affected by all of these factors, but the gas in the void was particularly significant. The differential rate density of discharge intensity is largely controlled by the availability of negative ions for dissocation or the presence of overstressed high field regions. Many of the parameters varied in the present study affected these features. Sporadic discharges were noted where the quantity of charge was greater than the theoretical maximum values by a factor of up to two. This was noted with all geometries. The occurrence of discharges to the wall of the void was the source of the above disparity.

Device for diagnosing insulation

Abstract: PURPOSE:To diagnose the insulation highly accurately at a low temperature at which partial discharge is not generated, by computing a void ratio based on the initial value of the earth capacitance of a sample which is insulated by a solid state insulator and the measured values of the capacitance obtained later on. CONSTITUTION:The initial value COL of the earch capacitance of the sample 5 wherein electrodes 1A and 1B are insulated by the solid state insulator 2 is measured by a capacitance meter 4 and stored in an initial memory 6. The earth capacitance COX of the sample 5 is measured by the same method based on the following diagnoses and processed by a differential circuit 8 and a divider 9 together with the capacitance COL stored in the memory 6. A value K which is proportional to the void ratio t2/t based on the equation I is computed and shown by a K display 10. Therefore the partial display is not generated at the void part, the void ratio is computed and displayed at a low voltage, and the highly accurate insulation diagnosis can be performed. In the equation, epsilon is the permittivity of the insulating material.

Method for detecting dielectric breakdown of electric apparatus

Abstract: PURPOSE:To prevent the dielectric breakdown accident during execution of a withstand voltage test by detecting the dielectric breakdown voltage from the partial discharge pulses generated intermittently in the insulator of an electric apparatus. CONSTITUTION:The voltage from a high voltage power source 1 is imposed on a stator coil 2 which is a test specimen Cx, and the voltage is boosted until the insulation of the coil 2 breaks down by a stepwise boosting method of holding the voltage for 1 minute at a 5-kV step. The partial discharge pulses generated in the insulator of the coil 2 at tis time are measured with a partial discharge measuring device 3 and a synchroscope 4. The voltage in which the large partial discharge pulses generating intermittently at intervals of several Hertz - several tens Hertz begin to grow sharply is detected, whereby the dielectric breakdown is detected.

Partial discharge current measuring method for power cable

Abstract: PURPOSE:To enable shield for electrostatic and electromagnetic noise without using a shield room, and to achieve small-sized measuring circuits, by constituting a low-pass filter with a cable connected to a power cable to be measured. CONSTITUTION:An LPF consisting of a magnetic substance 3 such as ferrite, a coil conductor 41a wound around it, a shield semiconductor 7, an insulator 8, a sheath shield 41b, a sheath 41b' is of cable shape to form an LPF cable 41. Partial discharge of a cable 1 can be measured by coupling this cable 41 to the cable 1 to be measured through cable heads 91, 91 of gas insulation connected to a sensor 33 of a discharge separation circuit via a couping capacitor cable 42. With this constitution, the measuring circuit is made small in size, and electrostatic induction and electromagnetic noise can be shielded without using a shield room, allowing to measure partial discharge simply and surely.