Showing papers on "Partial discharge published in 2012"

Effect of semiconductive nanoparticles on insulating performances of transformer oil

Abstract: In this paper, TiO2 semiconductive nanoparticles with a large relaxation time constant is added into transformer oil to form semiconductive nanofluids (SNFs), with the aim of enhancing insulating characteristics. ac, dc and lightning impulse breakdown voltage and partial discharge (PD) characteristics of oil samples before and after modification were measured according to ASTM standard methods. It was found that SNFs have ac, dc and lightning impulse breakdown voltage up to 1.2 times compared with pure oil. Meanwhile, the partial discharge resistance of SNFs was also dramatically improved. Charge trap and transportation characteristics of both samples have been measured by thermally stimulated current method (TSC) and pulse electroacoustic technique (PEA). It was found that electron shallow trap density and charge decay rate are greatly increased in semiconductive nanoparticles modified transformer oil. It is proposed that electron trapping and de-trapping processes in the shallow traps could be one of the main charge transport processes in dielectric liquids.

A perspective on online partial discharge monitoring for assessment of the condition of rotating machine stator winding insulation

Abstract: Partial discharges (PD) are small electrical sparks that can occur in liquid or solid insulation systems in high-voltage equipment, and can eventually cause failure of the equipment [1]���[3]. Partial discharge testing has been used for more than 80 years as a factory quality control tool to find manufacturing defects that could eventually lead to equipment failure. We believe that Johnson was the first to measure PD on operating high-voltage equipment, in the 1940s [4]. His aim was to find an online method to determine whether stator winding coils or bars were vibrating excessively in the stator magnetic core. These vibrating coils lead to abrasion of the high-voltage electrical insulation and to eventual failure. A symptom of the insulation abrasion process was that PD (or what he referred to as slot discharge) occurred between the surface of the coil and the stator core. By measuring the PD online, he could indirectly detect the movement of coils, which indicated that failure was likely. The measurement had to be made online because, if the generator were not operating, no magnetic forces would be acting on the coils; thus, the air gaps that are a necessary precursor of PD would not be as large. Johnson was successful in identifying those generators that were suffering the most from this problem, which was caused by the introduction of the first thermoset insulation systems and by workmanship variations that were magnified by an inadequate method of securing the coils in the stator slots for the novel insulation system. The success of the Johnson online PD measuring system inspired other machine manufacturers and even a few utilities to develop their own methods [5], [6]. The main reason Johnson needed online PD measurement was that loose windings do not produce as much PD when the motor or generator is not operating. Thus one of the important reasons for performing online PD tests is to monitor the condition of the equipment under normal operating electrical, thermal, and mechanical stresses. However, with the current emphasis on extending times between maintenance outages, and the push to reduce testing costs in general, the main reason now given for online PD measurement is to avoid shutdown of the equipment, which would be necessary for an off-line PD test or other diagnostic test. Although we believe online PD monitoring was first applied to rotating machines, the same reasons are valid for other electrical equipment, such as oil paper cable joints or terminations, distribution class switchgear, gas-insulated switchgear, and power transformers [2], [3].

Development simulation and experiment study on UHF Partial Discharge Sensor in GIS

Abstract: A partial discharge (PD) sensor based on two-arm equiangular spiral antenna is designed and optimized in this research, and key parameters which mainly influence the performance of sensor are optimized. Through simulation and contrastive study, the key parameters' values are confirmed, which improves the sensor's performance to a great extent. To match the impedance of the sensor and the coaxial transmission line, a kind of micro strip impedance transformer which is of an exponentially gradual type is designed, the parameters of which are defined through simulation. Two improvement schemes for the designed transformer are also proposed to make an easy package and installation for the sensor and the transformer. Then, the physical model is made and tested. The results of simulation and test show good agreement, and verify that the sensors designed can meet the GIS internal partial discharge monitoring requirements well in bandwidth, performance and size, etc. The designed impedance transformer (IT) achieves impedance matching within the sensor and transmission line in ultra wideband range, and also enhances the sensitivity of the sensor.

Optimization of UHF Hilbert Antenna for Partial Discharge Detection of Transformers

Abstract: Partial discharge (PD) online monitoring is an effective tool of inspecting insulation defects and identifying potential faults in power transformers Ultra-high-frequency (UHF) approaches have caught increasing attention recently and been considered as a promising technology for online monitoring PD signals The size of a UHF sensor for PD online monitoring of transformer is a critical factor for practical installation inside transformer This communication presents a compact fourth order UHF Hilbert fractal antenna with desired performance and suitable size for easy installation Actual PD experiments were carried out for four typical artificial insulation defect models while the antenna was used for PD measurements The experimental results show that the proposed Hilbert fractal antenna is suitable and effective for UHF online monitoring of PDs in transformers

Partial discharge patterns in high voltage insulation

Abstract: Partial discharge (PD) is an electrical discharge, which does not bridge the electrodes between an insulation system completely under high electric field stress. PD events may affect the performance of insulation system because in long term, it may cause the breakdown of insulation system and failure of high voltage component due to repetition of PD events. In this work, two techniques of analysing PD data have been studied; the phase resolved partial discharge (PRPD) pattern and pulse sequential analysis (PSA) techniques. These two techniques were used to distinguish three main types of PD; they are corona, void and surface discharges. PD data were obtained from the measurement in high voltage laboratory in the University of Southampton, UK. In the end of the analysis, comparison between the PRPD and PSA methods was done to evaluate the advantages and disadvantages between the two techniques.

Electro-acoustic detection, identification and location of partial discharge sources in oil-paper insulation systems

Abstract: The detection of Partial Discharges (PD) is a reliable technique to analyze the status of electrical insulation in power transformers. Phase resolved partial discharge patterns are being complemented with high frequency pulse waveform analysis, in order to identify discharge sources. In addition to this, acoustic techniques are being implemented trying to locate PD sites in large power transformers. In this work, an inductive loop sensor will be used to identify two different PD sources by means of the energy distribution of the detected waveforms. Additionally, these PD sources will be located by means of acoustic measurements with an electrical reference, through the analysis of the acoustic activity detected for each sensor individually.

Location of partial discharge sources in power transformers based on advanced auscultatory technique

Abstract: In the paper a new partial discharge (PD) location technique based on acoustic emission and conventional partial discharge detection method is presented. Synergetic combination of two methods allows obtaining a high accuracy of the insulation fault location and reducing the time of measurement procedure. Several cases of practical application of the new technique for PD location in the power transformers tested in an HV laboratory and in a substation are discussed.

Partial discharge within a spherical cavity in a dielectric material as a function of cavity size and material temperature

Abstract: For high-voltage components, the measurement of partial discharge (PD) is a useful tool for performance assessment of electrical insulation. In this study, experimental measurements of PD activity for different spherical cavity sizes and material temperatures have been performed. A simulation model representing PD behaviour within spherical cavities in homogeneous dielectric materials has also been developed. The model has been used to study the influence of cavity size and material temperature on PD activity. Comparison of measurement and simulation results has been undertaken. The model uses a finite element analysis (FEA) method along with MATLAB code. It has been found that certain parameters in the model are both cavity size and temperature dependent. Thus, critical parameters influencing PD behaviour for different cavity sizes within the material and material temperatures can be identified; these are the charge decay time constant, cavity surface conductivity, electron generation rate (EGR), PD inception and extinction fields and the cavity temperature decay time constant.

On partial discharge measurement in dielectric liquids

Abstract: Partial discharge detection in dielectric liquids requires particular PD measurement techniques and instruments. Simultaneous partial discharge (PD) measurements that are employed on insulating liquids, using dual narrow/wide band detectors, are described. Narrow band PD detectors, which are of the integrating type are suitable for the measurement of the total charge transfer in pC of the overall discharge event. Wide band measurement techniques permit the acquisition of the discrete PD pulses in dielectric liquids, that comprise the overall PD pulse burst signal. These PD pulse bursts are comprised of discrete high frequency pulses of usually ascending magnitude charge transfers. The time position of these pulses within the pulse burst is determined by the times at which the Paschen's minima occur across the expanding cavity due to the small size of the microcavities. In order for them to undergo discharge requires enormously high internal pressures (ca 10 MPa) to ensure a sufficient number of charge carriers. The life duration of these cavities is of the order of several's, with the cavity collapsing, when its size reaches dynamic instability.

Enhancement of electrical insulation performance in power equipment based on dielectric material properties

Abstract: Research and development results of enhancement techniques of electrical insulation performance for higher electric field application in power transmission/substation equipment, such as transformers, switchgears and cables, are described, especially based on the view point of dielectric materials. Firstly, the electric field analysis, field optimization and field measurement techniques are introduced to discuss higher electric field stress applications in power equipment. Secondly, material types, including gases, liquids, solids, vacuum and their composite systems are discussed to make power equipment with higher insulation performance, lower losses, lower environmental impact and higher reliability. In the process of development, a highly sophisticated new approach to clarify the physical mechanisms of partial discharges was developed and applied. By the introduction and applications of the above mentioned new electrical insulation techniques based on dielectric materials, concepts of future power equipment with higher electric field stress are proposed. This paper is based on the Whitehead Memorial Lecture given at the IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP) 2011 in Cancun, Mexico.

Insulation performance of three types of micro-defects in inner epoxy insulators

Abstract: Gas insulated switchgear (GIS) has been widely applied in power equipment since the late 1960s due to its reliability and compactness. Because epoxy insulators in GIS are important insulation components that affect the dielectric withstand level and the equipment lifetime, high voltage tests and sensitive partial discharge (PD) tests have been carried out on them in the factory. If a latent defect occurs inside an actual epoxy insulator, its size is predicted to be small, such as a micro-defect, because it will have passed rigorous tests and multiple inspections at the factory. Although many studies have clarified the fundamental phenomena of deterioration caused by PD occurring due to defects in inner epoxy, little is known about the actual size of such defects and their effect on insulation properties. Therefore, to assess the risks associated with aging GIS equipment, it is essential to understand the actual size of latent defects in inner epoxy insulators of GIS and the impact the defects have on the insulation performance. The puncture properties and PD characteristics of artificial micro-defects of cracks, voids, and delaminations produced using an accurate estimation technique and precise production control were investigated and are described. The results suggest that an estimation method using electric field analysis is useful for designing the defect shape and that the breakdown voltage depends on the three-dimensional shape of the defect. Techniques for accurate estimation of small defects in epoxy resin and stable production of micro-defects have thus been achieved.

Estimation of partial discharge inception voltage of magnet wires under inverter surge voltage by volume-time theory

Abstract: This paper discusses a novel estimation method for partial discharge inception voltage (PDIV) of magnet wire under inverter surge voltage application. We focused on the generation probability of initial electrons, which induce PD under high electric field and short rise time of surge voltage, by means of Volume-Time theory. We applied the Volume-Time theory to PD inception phenomena in a wedge-shaped air gap of twisted pair samples composed of enameled wires, and estimated PDIV in consideration of initial electron generation probability with temporal and spatial change in electric field distribution. We could estimate PDIV under different waveforms of applied surge voltage for different specifications of enameled wires. PDIV estimated by the extended Volume-Time theory agreed well with the measured PDIV. The estimated PDIV decreased with the increase in the rise time of applied voltage waveform, which corresponded to the V-t characteristics in the time range of inverter surge voltage.

Simulation of the reignition of a discharge behind a dielectric layer in air at atmospheric pressure

Abstract: This paper presents simulations of an air plasma discharge at atmospheric pressure in a point-to-plane configuration with a dielectric layer in the path of the discharge. First, the dielectric layer is placed on the cathode plane and we study the influence of the permittivity and thickness of the dielectric on the positive streamer discharge dynamics and the dielectric surface charging. We show that the velocity of the surface discharge on the dielectric surface depends on the capacitance of the dielectric layer and decreases as this capacitance increases. Conversely, the amount of positive surface charge deposited by the positive surface discharge on the dielectric surface is not directly related to the value of the capacitance of the dielectric layer. However, the amount of surface charge deposited increases as the capacitance of the dielectric layer increases. Second, the dielectric layer is placed in the air gap as an obstacle for the propagation of the first streamer discharge ignited at the point electrode. In this case, after the impact on the dielectric, the first discharge spreads along the upper dielectric surface and we show that, depending on the location of the dielectric layer, its permittivity, its thickness and its opacity to radiation, a second discharge may reignite or not below the dielectric layer. During the discharge dynamics, positive charges are deposited on the upper surface of the dielectric and negative charges are deposited on its bottom surface. For all conditions studied in this work, we show that surface charge deposition on both faces of the dielectric layer has a small influence on the discharge reignition below the dielectric layer. Finally, with two closely spaced dielectric layers in the path of the discharge, a series of spreading/reignition for each dielectric layer is observed.

Evolution of pd patterns in polyethylene insulation cavities under AC voltage

Abstract: In the framework of developing defect-based life models, in which breakdown is explicitly associated with partial discharge (PD)-induced damage growth from a defect, ageing tests and PD measurements were carried out in the laboratory on polyethylene (PE) layered specimens containing artificial cavities. PD activity was monitored continuously during aging. A quasi-deterministic series of stages can be observed in the behavior of the main PD parameters (i.e. discharge repetition rate and amplitude). The evolution of the parameters reflects the physicalchemical changes taking place at the dielectric/cavity interface during the aging process. PD activity shows similar time behavior under constant cavity gas volume and constant cavity gas pressure conditions, suggesting that the variation of PD parameters may not be attributed to the variation of the gas pressure. It is speculated that the change of PD activity is related to the composition of the cavity gas, as well as to the properties of dielectric/cavity interface.

Electrical Model and Experimental Analysis of the Atmospheric-Pressure Homogeneous Dielectric Barrier Discharge in He

Abstract: A dynamic electrical model for a plane-parallel configuration homogeneous dielectric barrier discharge (DBD) is investigated using the MATLAB Simulink. The electrical model is based on an equivalent electric circuit, in which the DBD is represented by a voltage-controlled current source associated to a resistance and a capacitance value. In addition, a plane-parallel DBD cell filled with He gas is used for the experiments, and a sinusoidal voltage of up to 5-kV peak value at frequencies of 10 kHz is applied to the discharge electrodes for the generation of homogeneous discharges. The electrical characteristics of homogeneous DBD under different operating conditions are studied using the electrical model simulations and experiments, and a comparison between them is conducted. It is shown that the simulated voltage and current waveforms and Lissajous figures are consistent with the experimental ones, which validates the functionality of the model. The dynamic behavior of the discharge parameters (such as gas gap voltage, discharge current, discharge consumed power, and transported charges), which are not measurable in the real process, is studied with the electrical simulation model, and the voltage-current curves are also obtained from simulation and used to analyze the evolution trajectory of the homogeneous DBD.

Power cable partial discharge signal denoising method based on wavelet analysis

Abstract: The invention provides a partial discharge signal denoising method based on wavelet analysis, which belongs the technical field of signal processing, and is mainly applied to power cable partial discharge signal denoising. The method for performing intelligent denoising processing on power cable partial discharge signals specifically includes: selecting optimal wavelet basis by using minimum description length (MDL) standard of the information theory, selecting a denoising method, performing wavelet decomposition according to a certain decomposition level, processing wavelet coefficients according to different threshold functions, performing wavelet reconstruction according to the processed wavelet coefficients, and achieving the denoising. The partial discharge signal denoising method solves the problem of manual screening of conventional partial discharge signal denoising, thereby achieving the purpose of the intelligent denoising of the partial discharge signals.

Partial Discharge Signatures of Defects in Insulation Systems Consisting of Oil and Oil-impregnated Paper

Abstract: Partial discharge measurement is a common method for monitoring and diagnostics of power transformers, and can detect insulation malfunctions before they lead to failure. Different parameters extra ...

Effect of voltage and capacitance in nanosecond pulse discharge enhanced laser-induced breakdown spectroscopy

Abstract: The laser ablation fast pulse discharge plasma spectroscopy (LA-FPDPS) technique has demonstrated its validity to enhance the optical emission of laser-induced plasma. It has the potential to improve the performance of traditional LIBS measurement. Very recently, LA-FPDPS with a nanosecond pulse discharge circuit has been developed, which has a better capability to enhance the optical emission intensity of laser plasma compared with that using a microsecond pulse discharge circuit. In this paper, the effect of the discharge capacitance and discharge voltage on the optical emission of soil plasma generated by LA-FPDPS with a nanosecond pulse discharge circuit is evaluated in detail. In addition, the stability of the time delay between the laser firing and discharge, and between the discharge and optical emission, has been carefully investigated.

Application of contact analysis on evaluation of breakdown strength and PD inception field strength of solid-solid interfaces

Abstract: Interfaces between solid insulating materials are generally weak regions in electrical insulation systems, particularly if the electrical stress is applied in parallel direction. This paper presents a theoretical mechanical model for estimating average size of air-filled voids at the interface as a function of surface roughness and contact pressure. It is argued that the interfacial breakdown strength (BDS) is governed by the discharge inception stress (Ev) of the void with the most likely estimated dimension. The estimated values of the breakdown strength and partial discharge inception electric field strength (PDIE) were compared with the results from measurements using XLPE specimens with interfaces energized in longitudinal direction. The measured ratio of increase of breakdown strength was found to be in good agreement with the estimated breakdown values of the most likely interface's void. Additionally, it was found out that the air pressure inside voids was not affected by applied contact pressure. The estimated PDIE values was found to be in agreement with the measured values, in the case of rough surfaces, but not for smooth surfaces. The results indicate that the mechanical contact approach using the motif description of surface roughness may improve the understanding of the factors influencing the PDIE of electrically stressed interfaces.

Investigation of partial discharge activity by a conducting particle in transformer oil under harmonic AC voltages adopting UHF technique

Abstract: A methodical experimental study was carried out to understand the partial discharges initiated due to particle movement in transformer oil under high frequency ac voltage and under harmonic ac voltages (with different THDs), by adopting UHF technique. It is also observed that irrespective of order of harmonics, increase in THD of the supply voltage shows reduction in levitation voltage. The rise time of the partial discharge current pulse formed due to particle movement is few ns. It is observed that the frequency content of the signal radiated due to partial discharges generated due to particle movement in the electrode gap lies in the UHF signal range, with its dominant frequency near 1 GHz. The supply voltage frequency and the time required for 100 UHF signals to form shows inverse relationship. When the applied voltage is increased above levitation voltage, the UHF signal magnitude formed due to particle movement increases, irrespective of supply voltage frequency. Ternary diagram clearly indicates that irrespective of frequency of the supply voltage, the UHF signal location in the ternary diagram is the same.

A Transformer Partial Discharge Measurement System Based on Fluorescent Fiber

Abstract: Based on the physical phenomena of optical effects produced by the partial discharge (PD) and on the characteristics of fluorescent fiber sensing of weak fluorescent signals, a PD measurement system using a fluorescent fiber sensor was designed The main parameters of the sensing system were calculated, an experimental testing platform for PD simulation in the lab was established, and PD signals were then detected through ultra-high frequency (UHF) and optical methods under a needle-plate discharge model PD optical pulses in transformer oil contained signal-peak and multi-peak pulse waveforms Compared with UHF detection results, the number of PD pulses and the elapsed PD pulse phase time revealed a good corresponding relationship However, PD signal amplitudes presented the opposite, thus indicating that PD UHF signals reflected pulse amplitude value, whereas PD optical signals reflected pulse energy magnitude The n-u-φ three-dimensional distributions indicated that most of the PD signals concentrated in the nearby industrial frequency voltage peak value Overall, the proposed fluorescent fiber sensing system design can be used successfully in transformer PD signal detection

A Gliding Discharge in Open Air Sustained by High-Voltage Resonant AC Power Supply

Abstract: Gliding discharges can generate nonthermal plasma at atmospheric pressure. Therefore, they are widely used in plasma-assisted ignition and combustion. In this paper, the gliding discharge sustained by a resonant ac power supply was obtained with a pin-to-pin electrode geometry, and the characteristics of such discharge were investigated through its voltage-current and discharge images. Inceptive, nonstable, and stable stages involved in this gliding discharge were studied. Experimental results showed that the discharge was first ignited by a spark with a current peak of tens of amperes and soon turned into a stable stage, where the discharge respectively behaved in repetitive spark mode with a current peak of several amperes in a small gap and glowlike mode with a current peak of several microamperes in a relatively large gap spacing. Under a certain situation, a nonstable discharge was observed, which changed from a spark discharge to a glowlike discharge after some time. In addition, both the discharge stability and the breakdown voltage were influenced by the air flow. The discharge became unstable when the air flow exceeded 3 L/min.

A review of condition monitoring of underground power cables

Abstract: Power distribution system relies heavily on a vast network of medium voltage (MV) underground cables for power delivery Condition monitoring technologies can, therefore, play a vital role in attempting to target the cables that pose the most urgent reliability concerns Maintaining or increasing a power system's reliability at minimal cost is an important issue for most network owners Condition monitoring gives the information needed for safe and reliable operation, replacement strategy and hence increases the system reliability Demands for reliable power causes a growing tendency to apply different strategies in the form of condition based maintenance Partial discharge (PD) monitoring is one of the successful diagnostic tools for accessing the insulation condition of MV cables Data acquired by online PD measurements can help in identifying the upcoming faults in such cable networks and possibly forecast the remaining life of the insulation This paper reviews the condition monitoring and diagnostictechniques used forunderground power cables

Study of partial discharge radiated electromagnetic wave propagation characteristics in an actual 154 kV model GIS

Abstract: A method to detect partial discharge (PD) is considered effective for gas insulated switchgear (GIS) insulation diagnostics. In this paper, for a 154 kV model GIS, the influence of the enclosure diameter on PD propagation characteristics was initially investigated using model GIS by varying the enclosure size. Secondly, an experiment was conducted for metallic particles placed in different locations as a source of PD (particle adhering to the center conductor or free metallic particle). Thirdly, an actual PD experiment was conducted in an Lshaped form to study the influence of GIS shape on PD-radiated electromagnetic (EM) waves. In addition, in order to study the experimental results in detail, a simulation using the FD-TD method was conducted for comparison with these experimental results. Following the experiment, the larger the enclosure diameter, the greater the measured amplitude of PD having occurred around the center conductor. In addition, it emerged that, where the particle was close to the center conductor, EM waves propagating due to PD were less likely to be damped compared with the case where particles were placed on the bottom of the enclosure. Furthermore, following the investigation of the propagation characteristics in the L-shaped form, it emerged that, while a high frequency component of frequency exceeding that of the TEM wave component was reflected at the L-shaped part, the TEM wave component passed through almost unaffected by the latter. The propagation of the TEM mode component could be also found via FD-TD analysis.

Feature-oriented de-noising of partial discharge signals employing mathematical morphology filters

Abstract: Noise reduction is one of the important tasks of cable insulation assessment based on partial discharge. This paper has developed a novel attitude in noise reduction, i.e. feature-oriented de-noising. Implementing this idea, a new de-noising filter based on Mathematical Morphology Filters (MMF) is presented where the process of removing white noise mixed with partial discharge signal is executed by employing several simple morphological filters. Comparing with the de-noising process based on Wavelet-transform, in terms of extracted features after de-noising, the proposed method preserves the features of PD pulses better. The performance evaluations and comparisons are examined by simulated and field measured signals.

Experimental evaluation of using the surge PD test as a predictive maintenance tool for monitoring turn insulation quality in random wound AC motor stator windings

Abstract: Turn insulation degradation is one of the major root causes of stator insulation failure leading to motor breakdown. The surge test is the only test available for testing the integrity of turn insulation; however, it is a high voltage pass/fail test that provides an indication only if an arc is instigated between the turns of weakened turn insulation, and therefore does not provide information regarding remaining lifetime. The surge PD test measures the partial discharge (PD) activity under surge excitation, and is used to date for assuring that voltage source PWM inverter-fed motors (IEC 60034-18-41 type I) are PDfree. In this paper, the potential of using the surge PD test as a predictive maintenance tool for turn insulation quality assessment is evaluated. Under the expectation that increasing PD activity in the voids formed by insulation degradation may be detectable before turn insulation failure, the test is performed periodically under accelerated thermal degradation on 6 windings. It is shown that change in the PD inception voltage under the surge PD test can be clearly observed before any other insulation test indicator. The results suggest that the surge PD test can be used for monitoring the condition of turn insulation for providing an early indication of stator insulation problems without the risk of puncturing turn insulation.

Simultaneous measurement of partial discharge using TEV, IEC60270 and UHF techniques

Abstract: This paper explores a means of quantifying the relationship between transient earth voltage (TEV), ultra-high-frequency (UHF) and IEC60270 partial discharge (PD) measurements on a pulse-by-pulse basis for well-defined, laboratory-based discharge sources. Since each technique responds differently to the same PD event, there is no theoretical relationship between the measured quantities; TEV and UHF techniques respond to the rate of change of charge movement, while IEC60270 responds to its integral. Empirical measurement is therefore necessary. Discharge pulses for each system were captured simultaneously using a 3 GHz, 20 GS/s digital sampling oscilloscope. PD amplitudes recorded by the respective systems were analysed and their relationships evaluated. Although these relationships are complex and bear characteristics particular to the PD geometry, the order-of-magnitude variation in amplitude between the sources allows approximate linear interpolation of the relationships when pulses are plotted on a logarithmic scale. The TEV/IEC correlation approximated to 1 µV/pC. The TEV/UHF correlation approximated to 0.05 mV/mV (TEV/UHF). Using TEV data measured at various points at an on-line medium voltage substation, approximate corresponding pC levels have been estimated based on the above relationships. The implications for PD severity judgment are discussed.

Transient Earth Voltage Measurement in PD Detection of Artificial Defect Models in $\hbox{SF}_{6}$

Abstract: This paper mainly discussed the utilization of transient Earth voltage measurement (TEVM) in partial discharge (PD) detection of gas insulation switchgear. Four typical artificial defect models in SF6 such as spikes fixed on high voltage (HV) conductor, suspended metals, voids in dielectric, and metal particles on the surface of dielectric had been used as test objects in ac PD experiments with the aid of the synchronized PD signals sampled from a transient Earth voltage sensor, photomultiplier, Rogowski monitor, and PDCheck system. The measuring results of TEVM results, which included the phase distribution of PD, the relative amplitude, and the pulse number of different voltage thresholds, showed good consistency with three other methods and had better sensitivity of detection in spark or corona PD patterns. For further study, the frequency distributions of the three PD patterns were analyzed and discussed for understanding the different measurement sensitivities showed in different typical defects in SF6 . In addition, TEVM was applied to detect PD under oscillating impulse voltage. As an example, the needle-plane electrode with short gap was adopted under 613.2-kHz oscillating impulse, which showed the effectiveness in this kind of detection.

Comprehensive 3‐capacitors model for partial discharge in power cables

Abstract: Purpose – The paper proposes and presents a comprehensive and integrated circuit model for investigating the behaviour of partial discharges occurring in voids inside the solid insulations of medium and high voltage cables.Design/methodology/approach – The model is based on the well‐known three capacitors model, which is remarkably improved to handle physical parameters such as cavity size, position, shape and pressure, environmental parameters such as cable temperature, in addition to operational parameters such as the contributions of the avalanche of free electrons inside the cavity through considering stochastic time delays.Findings – A complete, flexible and reliable model for partial discharges in voids inside the solid insulation of medium and high voltage cables is presented whose output agrees with experimental reported results.Research limitations/implications – The proposed model deals only with single voids, and the semiconductor layers in the insulation of cables are not considered.Practical ...