Showing papers on "Partial discharge published in 1985"

Acoustical Technology Applications in Electrical Insulation and Dielectrics

Abstract: Acoustical waves travel by molecular interaction, and as a consequence, wave attenuation and transit time can be extremely sensitive to changes in the media in which they propagate. With careful acoustic measurements, a wide variety of media properties can be monitored. These range from variations in gas mixtures and pressure, to changes in material density, porosity, and crystal size and orientation. Acoustical technology can also be applied in the listening mode to sense the tiny acoustic emissions from partial discharges in dielectrics, and from stress, strain, and other events. Many of these acoustic techniques are ideal for applying to the science of electrical insulation and dielectrics, and in this paper these different methods are described and evaluated. The subject is introduced with an outline of ultrasonic partial discharge (PD) diagnostics and nondestructive evaluation, with emphasis on acoustic factors which affect accuracy. It is then shown how the use of acoustic waveguides can improve diagnostic PD measurements in hostile and inaccessible locations. In a completely different application, a technique is described in which sound velocity measurements in gas mixtures are used for predicting electrical strength. Other valuable acoustical applications which are outlined are the monitoring of sounds from bouncing particles on metal surfaces and from gas bubbles generated in liquid dielectrics. From this latter phenomenon the temperature of a hot metal surface in a liquid can be estimated. A related subject which is also discussed is the attenuation of sound waves by gas bubbles in a liquid dielectric.

Prediction of Treeing Breakdown from Pulse Height of Partial Discharge on Voltage-Phase Angle

Abstract: This paper describes the change in the partial discharge (PD) characteristics due to the growth of electrical trees in insulating materials under the application of an AC voltage. An electrical tree consists of branch-like dielectric breakdown paths. Investigation of a number of characteristic PD parameters shows that the φ-q distribution profile has a good correlation with tree growth. The φ-q distribution expresses the average pulse height as a function of the AC voltage-phase angle. The distribution indicates a common profile for trees growing in both epoxy resin and polyethylene. Tree growth in these materials can thus be detected by monitoring the profile of the φ-q distribution, and the final breakdown can be predicted from the tree growth.

Corona discharging device

Abstract: A corona discharging device having a corona discharging electrode to which a high voltage is applied to produce corona discharge. The high voltage applied to the corona discharging electrode is provided by superposing an AC voltage to a DC voltage. The DC voltage and the AC voltage are determined such that the corona discharging current has only the polarity which is the same as that of the DC component voltage. The corona discharge is stabilized and hardly produces a non-uniform discharge.

Transversely excited gas laser and method for the operation thereof

Abstract: OF THE DISCLOSURE A transversally excited gas laser whose main dis-charge is initiated by a corona discharge triggered between auxiliary electrodes. The auxiliary electrodes are thereby respectively composed of a conductor which is enveloped by a jacket of dielectric which forms a single part. The jacket is provided with an incision between the two conductors parallel to the longitudinal axis, facing the main discharge path, and also is metallized at its outside. The incision projects UV light of the corona discharge into the region of the main dis-charge path and thus generates free electrons where they are most effective. The outside metallization increases the capacitance of the auxiliary electrode arrangement; and as a result, the corona discharge is intensified. The main dis-charge may possibly also be delayed such that the firing ensues in a more greatly ionized gas. The result is that the laser becomes more independent of changes in the high voltage, the gas pressure and the gas composition and thus may be used in sealed-off CO2 lasers for mobile employment.

Comparison of Three Techniques of Partial Discharge Measurements in Power Transformers

Abstract: The paper presents a comparison of partial discharge (PD) measurements taken on 140 large power transformers using radio-influence voltage (RIV) meters calibrated in pV according to NEMA 107 Standard and also with the aid of wide-band and narrow-band PD detectors calibrated in pC according to IEC Publication 270. Results are presented in the form of pC/?V ratios and compared to data from the literature. In conclusion the RIV measuring technique is considered inappropriate for PD measurements on power transformers, although it can be employed to detect the presence of the discharges.

Coupling unit for the operative monitoring of the high-voltage wingings and the connected output leads in electric high-voltage machines and apparatus, by means of partial discharge determination and breakdown spark measurement

Abstract: Coupling unit for the operational monitoring of the high-voltage winding (SW) and the connected electric output lines in electric high-voltage machines and apparatus, particularly of three-phase stator windings in turbo-generators including their generator output lines (5.1, 5.2, 5.3) and/or in transformers and converters by means of determining partial discharges and measurement of the breaking spark in the high-frequency range, where the above-mentioned machines and apparatus are connected via generator output leads or other connecting line to each other and are connected to ground potential via network protection capacitors. The respective coupling unit (AE1, AE2, AE3) is coupled to one each of the three legs (5.1, 5.2, 5.3) of the generator output lead (5), and the network protection capacitor (C 1 , C 2 , C 3 ) of each phase are connected to ground potential (B) via a measuring impedance. Furthermore, the shielded measuring lines (4.1, 4.2, 4.3) brought from the measuring voltage terminal of the measuring impedance to the partial discharge measuring device, are conducted through a filter.

Preventing Failures in Outdoor Distribution-Class Metalclad Switchgear

Abstract: Failure of the insulation in distribution-class metalclad switchgear may release large amounts of energy resulting in an explosive hazard to adjacent equipment and personnel. Many such failures have occurred in older outdoor and generating station switchgear within Ontario Hydro. The failures have often been caused by partial discharge (PD) activity and surface tracking which destroy organic bus support insulation. Test methods have evolved to help locate deteriorating insulation in the field, and to qualify new insulation systems. The life of the switchgear can often be extended by incorporating appropriate preventive maintenance. To improve our ability to locate deteriorating switchgear insulation economically, a prototype continuous monitoring system has been developed which is sensitive to partial discharges, thus allowing plenty of warning (usually several years) that the insulation system may be in trouble. The probability of ``false alarms'' from this system has been greatly reduced by monitoring both acoustically and electrically simultaneously. Tests in two metalclad switchgear installations have shown the system to be immune to extraneous noise, while maintaining sensitivity to partial discharges. The installation of the monitoring system in stations prone to insulation problems enhances the reliability and safety of metalclad switchgear, and greatly reduces repair costs.

Ramp Technique for DC Partial Discharge Testing

Abstract: A stepwise ramp technique has been used successfully in direct current (dc) partial discharge (PD) testing on high voltage components and on resin-packaged HV devices such as the Faint Object Camera for the Space Telescope. PD data is acquired separately on part-way ramps to rated voltage and on the intermediate voltage plateaus. For test specimen intended for dc service, this ramp method gives more information about insulation integrity than purely quiescent dc measurements. This is especially true for specimens of high resistivity which causes the discharge frequency to be deceptively low at constant dc voltage. By contrast, during ramping upwards the voltage distribution is capacitive, and the PD behavior resembles that of an ac test. This gives many more pulses in the voids, and without the undesirable heat produced if 60 Hz ac were applied. PD histograms are presented on various materials, with and without intentional defects. Influence of test parameters such as ramping speed are discussed. Experience with a variety of samples and commercial HV capacitors, as well as their life test performance, can lead to approximate acceptance/rejection criteria.

Partial discharge deterioration of epoxy resin for electronic parts

Abstract: Recently many electronic parts are widely used for the power electric field, such as power transistor module, diode and solid state relay. These are encapsulated with solid insulating materials such as epoxy resin or silicon rubber. In these category of parts, majority of electrical failures has been caused by inadequate material selection or workmanship error for encapsulation systems. It is suspected that the cause of the electrical failures is due to partial discharge (PD) in voids of insulating materials or in cracks in the vicinity of conductors. Accordingly, the test on PD has been performed for these products. Although PD quantity (e.g. PD current, Qmax), decreases gradually during voltage application with ordinary electrical PD measurements, while solid insulating materials degrade along with time and finally result in electrical breakdown [1,2].

Behavior of High Voltage Miachine Insulation System in the Presence of Thermal and Electrical Stresses

Abstract: This paper presents the results on a resin-rich machine insulation system subjected to varying stresses such as electrical (2.6 to 13.3 MV/m) and thermal (40 to 155° C) acting together. Accelerated electro-thermal aging experiments subsequently have been performed to understand the insulation degradation The interpretations are based on several measured properties like capacitance, loss tangent, ac resistance, leakage current, and partial discharge quantities. The results indicate that the changes in properties are not significant below a certain temperature for any applied stress, Beyond this temperature large variations are observed even for low electrical stresses. Electrothermal aging studies reveal that the acceleration of the insulation degradation and the ultimate time to failure depends on the relative values of temperature and voltage stresses. At lower temperatures, below critical, material characteristics of the system predominate whereas beyond this temperature, other phenomena come into play causing insulation deterioration. During aging under combined stresses, it appears that the prevailing temperature of the system has a significant role in the insulation degradation and ultimate failure.

Partial discharge characteristics in phase domain for various cylindrical voids

Abstract: As the shape and the size of a void in a insulation system affect considerably the progress of the deterioration of the insulation performance if partial discharges (PD's) occur in the void, it is important to estimate both of the two parameters. Conventional PD characteristics are however ineffective to estimate the shape of a void. Therefore the relationship between the shape of a cylindrical void and the statistical characteristics of PD's occurring in the void is investigated in terms of φ-q distribution profile as well as conventional PD characteristics such as the maximum apparent discharge magnitude (qmax). The φ-q distribution profile describes the average pulse height as a function of the phase angle of an applied AC voltage and was found to be sensitive to the structure of a void in which PD's occurred[1].

Noise removal circuit for use in a partial discharge measuring device of a high voltage apparatus

Abstract: A noise removal circuit for use in partial discharge measuring device of a high voltage apparatus. The circuit includes a first phase shift/reduction device responsive to an input signal for passing it directly while delaying it by a predetermined time and for reducing the delayed signal from the directly passed signal a second phase shift/reduction device for passing an output of the first phase shift/reduction device directly while delaying the output by the predetermined time and for reducing the delayed signal from the directly passes signal, and a phase shift/multiplying device for directly passing an output signal of the second phase shift/reduction device while delaying it by a time twice the predetermined time and multiplying the directly passed signal with the delayed signal.

Automatic insulating characteristic analyzer

Abstract: PURPOSE: To enable a smaller size, a lighter weight and improved warkability of the equipment, by arranging a high voltage function generator, a commercial frequency AC generator, a high-voltage changeover switch, a detection circuit, a computing circuit and a display unit. CONSTITUTION: A high-voltage function generator 33 generates a superlow frequency high voltage with a desired waveform to analyze the insulating characteristic of a sample or a probing voltage as DC voltage and a commercial frequency generator 32 a probing voltage as AC voltage with the commercial frequency as low voltage. On the other hand, a high-voltage changeover switch 35 selects either probing voltage generated with generators 32 and 33 to be applied to a sample 10. Then, detection circuits 39 and 41 detect electric phenomenon when the probing voltage is applied to the sample and the arithmetic circuits 42W45 for individual tests compute insulating characteristics on the basis of the electric phenomenon detected with these detection circuits and the results are displayed 46. This enables the measurement of all of insulation resistance, electrostatic capacitance, tan δ, partial discharge start voltage, partially discharged charge and the like with only one unit. COPYRIGHT: (C)1987,JPO&Japio

Apparatus for measuring partial discharge generating position of cable

Abstract: PURPOSE:To measure the partial discharge generating position of a cable without generating a measuring error, by determining direct wave arrival time difference by a measuring cable and an auxiliary cable connected to said cable at the other terminal through a coupling condenser and having the same standard and length as said cable. CONSTITUTION:The other terminal of a main cable 1 equipped with a joint 8, across which impedance changes, is connected to an auxiliary cable 9 having the same standard and length as the main cable 1 through a coupling condenser 10. When high voltage is applied to the core wire 1a and the insulator 1b of the cable 1 from one terminal thereof, partial discharge is generated at the dielectric breakdown point A between said one terminal and the joint 8 and the high voltage pulse reflected from the point A directly reaches to said one terminal at first and detected through a condenser 4, a detection impedance 5 and an amplifier 6 and memory 14 is triggered. In addition, the direct wave corresponding to the reflective wave from the other terminal of the cable 1 through the cable 9 is detected through an amplifier 13 and stored in the memory 14 and the measurement of a partial discharge position without a measuring error is performed on the basis of the detection time interval of both direct waves without exerting influence upon the reflective wave from the joint 8.

A new method for the location of partial discharge sites using modulated X-rays

Abstract: It has been known for at least 20 years that X-rays passing through a partial discharge may modify both discharge magnitude and repetition rate. The effect is subtle, however, and may be completely masked by discharge signals from other sites. A new method has been proposed and experimentally verified wherein discharge sites are found by scanning an insulation system with a modulated X-ray beam, and subsequently recovering a signal at the modulation frequency from the output of a conventional PD detector, using correlation and/or spectral analysis techniques. As a test object is scanned by the X-ray beam, knowledge of PD sites is obtained when a signal at the modulating frequency is recovered. The technique is applicable to a wide range of practical insulation systems and offers high spatial resolution and noise immunity.

Improvement in the Instrumentation for Partial Discharge Location in Cables

Abstract: An instrument for detecting and locating partial discharges on power cables has been developed. This paper describes some recent improvements that have been incorporated. It also presents new experimental data which show that low level discharges on cables the length of full reels can be located. Documentation is also included which shows that it is possible to locate each of more than one simultaneously operating sources of noise on a cable.

Measuring method for partial electric discharge of high voltage equipment

Abstract: PURPOSE: To decide the generation of partial electric discharge, the existence of a fault and its kind precisely by making a high frequency signal generated due to the partial discharge correspond to the phase of an applied voltage and dividing the signal in each section corresponding to a fixed phase angle to detect the signal. CONSTITUTION: The high frequency signal superposed to a partially-charged voltage is detected by a high frequency transformer 11. An analog switch (AS) 13 executes switching every 90° change of the phase of the partially charged voltage and sends the high frequency signal amplified by an amplifier 12 to integrators 14, 14'. The high frequency signal is integrated by the integrators 14, 14' synchronously with the phases of the applied voltages and a post AS 13' is switched by a control signal outputted from an A/D converter 15 to input an analog-like detecting signal corresponding to the high frequency signal. Then the detecting signal from the integrators 14, 14' is converted into a digital signal by the converter 15. Then, the digital signal, a synchronizing pulse and an encoded pulse are E/O converted 16 and the converted optical signal is sent to the supervisory side through an optical fiber 17. COPYRIGHT: (C)1987,JPO&Japio

Resistance separation structure in measurement of partial discharge of power cable

Abstract: PURPOSE:To facilitate the setting of a separation resistance value and impedance matching, by exposing the terminal part of a power cable to be measured, and providing a resistance paint layer connecting the space between external semiconductive layers and a resistor connecting the space between external blocking layers. CONSTITUTION:The space between the external semiconductive layers 2, 2 of the separation part 4 of the predetermined terminal part of a power cable to be measured is covered with an insulating layer 3 to provide a resistance paint layer 12 mutually connecting the semiconductive layers 2, 2 while a fixed resistor 13 is connected between the external blocking layers 1, 1 of the separation part 4. Herein, the resistance paint layer 12 relaxes the electric field of the separation part 4 and the influence of partial discharge generated in a terminal connection part 6 in inhibited by its high resistance. In addition, the fixed resistor 13 takes matching with detector impedance 11. By this mechanism, a partial discharge current generated in the side of the cable 7 flows to a partial discharge measuring instrument 15 and a discharge current generated in the side of the terminal connection part 6 is not almost flowed. Therefore, the setting of a separation resistance value and impedance matching can be facilitated.

Time-induced partial discharge breakdown in laminate structures

Abstract: Insulating materials play a key role in the design and reliable performance of high voltage power equipment. It is well known that most of the failure in electrical apparatus occurs due to electrical breakdown of the insulating medium. Therefore, understanding the mechanism of the failure of the electrical insulation, especially under long-term exposure to high electric fields, and developing techniques to improve reliability of these materials is important for the design of efficient high voltage systems.

Apparatus for testing insulation of power cable

Abstract: PURPOSE: To simultaneously measure a leak current and partial discharge, by providing a DC leakage detection impedance Z 1 wherein DC high voltage is applied to one terminal thereof and a cable to be measured is connected to the other terminal thereof and connecting HPF and a partial discharge detection impedance Z 2 to Z 1 in parallel. CONSTITUTION: A DC high voltage generator 60 is connected to a case 21 and a high voltage is applied between the conductor of a cable 10 to be measured and the sheath 10a thereof through a DC leakage detection impedance (Z 1 ) 22. When the cable 10 generates insulating deterioration, leak current flows and terminal voltage is generated in Z 1 22 and the magnitude of the leak current is displayed on a display device 43 through an optical fiber 50B. When discharge is generated by the insulating deterioration of the cable 10, a pulse is generated and the first wave thereof flows in the path of the head part of the cable 10, HPF 27, a partial descharge detection impedance (Z'2) 23, a case 21 and a cable sheath 70a. The second wave reflected from the remote end of the cable 19 and reflected therefrom to reach the heat part thereof and a third wave, generated when the first wave is reflected from the head part to reach the remove end where reflected to be returned to the head part, are flowed in the same path. The firstWthird wave signals generated at both terminals of Z 2 23 are displayed on a pulse number display device 48 through an optical fiber 50A and the measure ment of partial discharge is performed from display content. COPYRIGHT: (C)1986,JPO&Japio

Development of cross-linked polyethylene insulated cable for cryogenic operation. Final report

Abstract: The development of crosslinked polyethylene (XLPE) insulation structure for cryogenic high voltage cable is described. Models of the cryogenic cables rated 69 kV, 138 kV and 230 kV were made utilizing copper conductors and the insulation structure consisting of extruded XLPE insulation and semiconducting XLPE conductor and insulation shields. The cables were subjected to alternating voltage endurance tests, partial discharge tests and breakdown tests, at 77/sup 0/K. Thermal contraction of the cables cooled from ambient temperature to 77/sup 0/K was also investigated. The XLPE structure was found to have good electrical and mechanical properties at cryogenic temperatures. A method of manufacturing of XLPE insulated cryogenic cables on a modified extrusion line was proposed. A review of the costs of different transmission systems, including one with a laminar cryogenic cable, revealed that the extruded XLPE insulated cryocable may be the most economical for high power transmission.

Partial discharge measuring apparatus

Abstract: PURPOSE:To enable the removal of extraneous noise in stationary waves with the cycle almost doubling the width of an internal partial discharge pulse by employing a filter circuit, a narrow band pass filter and the like made up of a delay circuit and the like. CONSTITUTION:A partial discharge pulse of a gas insulated electric appliance is detected as distinguished from a pulse due to corona discharge in the air with a detection circuit 11 having a detection circuit 14 of an RC parallel circuit with the time constant of wavetail as specified. The detection output thereof passes through a filter circuit 12 composed of circuits 21 and 26 for delaying the pulse width of a partial discharge pulse, circuits 22 and 23 for delaying that by two or three times, addition circuits 24 and 25, a multiplication circuit 27 and the like to remove continuous extraneous noise with the cycle almost doubling the pulse width. It is further processed with an output circuit 13 having a narrow band pass filter 31 with the frequency 10% lower than the center frequency. This enables the removal of extraneous noise in stationary waves with the cycle almost doubling the width of the internal partial discharge pulse thereby ensuring a better measurement of the internal partial discharge pulse.

Measurement of partial discharge

Abstract: PURPOSE:To enable the measurement of a discharge amount without being so much affected by a discharge generating position, by using a plurality of resonance frequencies while synthesizing these outputs. CONSTITUTION:AC voltage HV is applied to a supply cable Ca through a blocking impedance Zb to generate partial discharge. At this time, a discharge pulse is detected by a coupling condenser CK and inputted to tuning amplifiers 3a, 3b having inherent resonance frequencies through a lead wire 1 comprising a coaxial cable and interference preventing impedances 2a, 2b. Said discharge pulse is respectively amplified by resonance frequencies of the amplifiers 3a, 3b and the outputs thereof are synthesized by a mixer circuit 4 and the discharge amount of the cable Ca to be tested is indicated by an indicator 5.

The application of high repetition rate voltage pulses to electrical and thermal aging

Abstract: A critical factor in the research and development of a new insulation system is the accurate assessment of its reliability and expected lifetime during service. The methods to determine reliability generally attempt to accelerate the degradation processes that normally occur in electrical insulation over an extended operating time period. To date, most accelerated aging studies have featured test voltage frequencies and/or temperatures that far exceed typical operating levels. However, these efforts have not been completely successful due to the lack of knowledge concerning the relationships between the temperature, frequency of applied voltage, and the physical mechanisms responsible for dielectric deterioration and breakdown.

Insulation diagnosing apparatus for solid insulator in electric appliance

Abstract: PURPOSE:To elevate the reliability with an accurate early discovery of deterioration in the insulation and prevention of troubles by receiving a sound wave generated based on a partial discharge from a defective part to perform a statistic processing. CONSTITUTION:A void 2 existing in a solid insulator 1 of an electric appliance to be inspected generates a void discharge under the operation voltage and a sound wave 21 generated reaches an acoustic receiving element 3 mounted on the surface of the insulator 1. This signal is counted only for a fixed time with a counter 5 via an amplifier 4 and sent to an arithmetic processor 6. Thereafter, the counter 5 is cleared to count a signal from the element 3 only for a fixed time again. The unit 6 receives data from the counter 5 only for a specified time with time to perform a statistical processing and the results are outputted and indicated on a display 7.

Detection for partial discharge position of high-voltage electric apparatus

Abstract: PURPOSE:To orientate the position of occurrence of partial discharge by arranging >=3 ball-shaped detecting electrodes in optional positions in the insulator of a high-voltage electric apparatus CONSTITUTION:Ball-shaped metallic detecting electrodes 9-1-9-4 are arranged on the inside wall of a tank 8 near the high voltage terminal 5 of a secondary winding 4 on the high voltage side If partial discharge occurs in an optional position when a high voltage is generated on the winding 4, electric charge is induced in individual electrodes 9-1-9-4 When the induced electric charge measured by electrodes 9-1-9-4 then is denoted by qi(i=1-4), a formula is true between space electric charge QS due to the partial discharge and coordinates (x, y, z) of the position of occurrence The position (x, y, z) is orientated in accordance with this formula ((xi, yi, zi) are the coordinates of respective center positions of electrodes 9-1-9-4 and (a) is the radius of electrodes), and thus, the occurrence of partial discharge of the high-voltage electric apparatus is prevented

An introduction to electrical breakdown in dielectrics

Abstract: : This report was written to serve as a text for an introductory graduate course in high voltage engineering at the Air Force Institute of Technology. However, anyone with and undergraduate electrical engineering or physics degree should be able to understand it, if they so desire. The material presented falls into three sections. The first part discusses the basics of kinetic theory of gases, atomic structure, ionization, mobility, diffusion, and electron emission. The second portion covers gas breakdown and the characteristics of the glow, corona, and arc discharges. the final portion provides a very brief introduction to the literature are provided.