Number Of Partial Discharge Pulses Research Articles

Phase-resolved partial discharge analysis of different types of electrode systems using machine learning classification

Partial discharge (PD) measurement is a diagnostic technique used for electrical insulating systems. The establishment of a highly accurate PD diagnostic technique has become necessary in recent years. Therefore, in this study, we analyzed a phase-resolved PD signal using machine learning classification for different types of experimental electrode systems. A polyethylene sheet was used as the sample, and PD was generated by applying a high AC voltage to four different types of electrodes. The number of PD pulses was counted from the raw data as preprocessing to calculate the feature value for the machine learning. The PD generation rate was defined for each phase angle section. Four types of machine learning algorithms were adopted for the classification of the electrode system: k-NN (k-nearest neighbor algorithm), logistic regression, decision tree, and random forest. The best accuracy was obtained by using the random forest algorithm (0.97), and it was found that k-NN also demonstrated good performance. The parameter dependencies were also evaluated for each algorithm. Based on the results generated by the random forest, it became clear that there were phase angle sections that were of high importance. The reason for the result was discussed from the perspective of (i) the difference due to the electrical circuit parameters (modified abc-model) and (ii) the stochastic fluctuation of PD signal.

WITHDRAWN: Analysis of partial discharge patterns of natural ester oil and mineral oil used in power transformer

Abstract The liquid insulation used for power transformer over the years is petroleum based mineral oil because of it availability and good electrical, chemical insulation properties. However because of its poor biodegradability, low flash point and concern over environment nowadays mineral oil has been replaced with biodegradable oil. Natural ester oil is made from natural substances like soyabean, which are environment friendly, almost fire proof and have great electrical insulation properties. Partial discharge is considered to be one of the main reasons for degradation of insulations in power transformers. In this paper comparative study of experimental results of partial discharge patterns of mineral and natural ester oil are discussed. The experimental setup was designed as per IEC Standard. Power transformer insulation is modeled as pigtail specimen and tested for partial discharge behavior by applying stress more than inception voltage of mineral and natural ester oil. Phase resolved partial discharge pattern are used to analyze the results. It was found that Natural ester oil has better inception voltage compared to mineral oil and also number of partial discharge pulses and PD magnitudes are less compare to mineral oil.

Surface potential decay and DC surface flashover characteristics of DBD plasma-treated silicone rubber

This paper presents an investigation on DC flashover voltage of silicone rubber (SiR) improved by dielectric barrier discharge (DBD) plasma treatments under ambient atmospheric pressure air. DC surface conductivity, surface potential decay (SPD), DC surface flashover voltage, partial discharge magnitude, Fourier transform infrared (FT-IR) spectrograms, and surface water contact angles are measured to analyze the influence of plasma treatment on the SiR. It is found that the speed of SPD increase consistently with the plasma modification time. The tendency of flashover voltage is increasing at first and then decreasing with the increased time of the plasma treatment. The magnitude and number of partial discharge pulses increase apparently with the increased plasma treatment time. Physicochemical measurements indicate that more amount of polar groups appear on surface after the DBD plasma modification, whereas the surface water contact angles decline continuously with the increased plasma modification time. However, the hydrophobicity is recovered after 30 d exposure in the air. It is demonstrated that the SPD is accelerated significantly due to the increased surface conductivities and density of shallow traps. However, the reduction of flashover voltage after longer time of the plasma treatment is attributed to the increased mobility of charge carriers on the sample surface.

Improvement in anti-static property and thermal conductivity of epoxy resin by doping graphene

This work investigates the effect of graphene filler in epoxy resin with the purpose of developing an improved thermally conductive epoxy encapsulation material for electronic devices. The findings in this work show that the thermal conductivity increases by a factor of about 1.6 times with 0.1 wt% loading of graphene in epoxy resin. The increase in the rate of surface charge verifies an improved anti-static property. On examining the phase resolved partial discharge patterns, it is observed that the inception voltage and the number of partial discharge pulses is lower for the filled epoxy compared to that of the neat epoxy. The increase in the rate of surface charge decay indicates an improved anti-static property. The findings in this paper provide a reference in the development of materials with improved thermal conductivity and anti-static properties for graphene/epoxy materials for use in the packaging of electronic devices.

Effect of voltage harmonics on pulse repetition rate of partial discharges

The objects of the research are partial discharge processes simulated under the influence of non-sinusoidal voltage. In the context of studying the effect of voltage harmonics on partial discharges, the total harmonic distortion can only be used for rough estimation. The reason for this is that the total harmonic distortion does not take into account the phase angles of the individual voltage harmonic components. Under non-sinusoidal voltage with the total harmonic distortion of 10 % and above, the intensity of the partial discharges in the insulation increases. However, at lower values of the total harmonic distortion, the harmonics can also affect the characteristics of the partial discharges. To solve this problem, it is necessary to carry out a study, increasing the number of voltage harmonics taken into account. To do this, it is possible to use the known three-capacitive equivalent circuit for a dielectric with gas cavity, making appropriate changes to the voltage source. The model was studied using voltage harmonic of the fundamental frequency together with voltage harmonics from the 2nd to the 30th order included. It was found that for the fixed amplitude the phase angle of the voltage harmonics has a decisive influence on the number of partial discharge pulses. In the presence of voltage harmonics, this number can be the same as under the influence of a pure sinusoidal voltage. It can also be 14.3 % less and 14.3 % or 28.6 % greater. In all cases, the value of total harmonic distortion remains the same. The possibility of using high-voltage reference inductive voltage transformers for voltage distortion measurements was studied experimentally. It was found that this is expedient for the region of the maximum value of the magnetic permeability of their magnetic cores, which corresponds to a range of 80–120 % of the transformer rated voltage. Mobile laboratories for checking high-voltage transformers on-site with the addition of appropriate equipment can simultaneously be used to measure a number of power quality indices.

Partial discharge pulse localization in excessive noisy data window

The first step in cable insulation assessment based on partial discharge (PD) analysis is PD detection. In this paper, for the first time, a practical, reliable and robust method for extraction of partial discharge pulses, before any attempts for noise reduction, is proposed which is applicable even when they are intensively polluted with additive noise. The proposed method detects PD pulses and delivers narrowed data windows around the positions of PD pulses in a data window which can lessen computational burden and complexity of any further processing by focusing on that part of data that contain PD pulses. The proposed method is also capable of distinguishing fully noise data windows from data windows containing PD pulses contaminated with noise. The proposed method has no limitation in the number of PD pulses in a data window and their position; and its performance has been examined on simulated, laboratory and field measured PD signals.

Identification of Metallic Particle Defect in GIS Based on Partial Discharge Mechanism

A metallic particle defect seriously degrades an insulation performance of gas insulated switchgear (GIS). Therefore, the estimation of risk of the metallic particle is important to maintain the reliability of GIS. In this paper, based on a partial discharge (PD) mechanism, we suggest a novel method to estimate the metallic particle defect using PD properties, which are the minimum instantaneous voltage of positive PD extinction, the instantaneous voltage of negative PD inception, and the negative PD pulse number from PD generation characteristics of applied voltage phase.

A Transformer Partial Discharge Measurement System Based on Fluorescent Fiber

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.

Simultaneous measurement of partial discharges using IEC60270 and radio-frequency techniques

Partial discharge (PD) measurement is an established condition monitoring technique used to facilitate the detection of incipient faults in high voltage electrical insulation systems such as gas-insulated switchgear and power transformers. By simultaneously recording partial discharge using both the IEC60270 'apparent charge' measurement technique and the more recent Radio Frequency method, which measures the energy radiated from the discharge, it is thought that more information can be gained about the nature of the PD source. Combined measurement has been carried out on various common PD source topologies recreated under laboratory conditions using PD test cells in a range of insulating media including SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , oil and epoxy resin. Test cell geometries include floating electrodes, free particles and protrusions. By plotting apparent charge against the energy of the RF signal for a large number of PD pulses, the relationship between the two techniques can be quantified for a given test configuration. It has been found that the correlation between the two techniques produces characteristic patterns specific to each defect type. It is envisioned that combined RF/IEC measurements will contribute to a more widespread acceptance of the RF technique in terms of its ability to quantify PD severity by relating the RF energy to the more widely accepted IEC60270 pC level.

Surface charge accumulation and partial discharge activity for small gaps of electrode/epoxy interface in sf6 gas

The electrical insulation reliability of solid spacers in gas insulated switchgears (GISs) is an important issue to achieve a safe operation of such equipment. Among different phenomena, charge accumulation represents the most important matter that can degrade the overall performance of these insulation systems. For this respect, this paper discusses the contribution of partial discharge (PD) activity by ac voltage application to charge accumulation in the small gap at the electrode/epoxy interface as one of the weakest points in GIS solid spacers. The partial discharge inception voltages for non-accumulated charge case (PDIV0) and after exposing to PD activity (PDIVn) are measured among different gap lengths, simulating delamination at the electrode/epoxy interface. The PD activity is generated using applied voltage with 1.2×PDIV0 for all gap lengths examined in this study (50~500 ?m). In these measurements, PDIV increased with increasing the number of PD pulses as a result of accumulated charges. The accumulated surface charge density is estimated using the boundary equations and is compared for the different gap lengths. The accumulated charge density was larger for the smaller gap lengths. Comparing PD parameters with accumulated charge density enabled us to identify that the number of negative and positive PD pulses is the main parameter that corresponds to charge accumulation process.

UHF technique for identification of partial discharge in a composite insulation under AC and DC voltages

DC power transmission is gaining considerable importance and converter transformers form an important component in it. An insulation of these transformers is stressed by both ac and dc voltages. Particle contamination is one of the major problems in insulation structures as it generates partial discharges (PD). If a particle is moving between the ground electrode and barrier, the magnitude of partial discharges formed is less compared to that of its movement between two metal electrodes. On the other hand, when the particle is lying over the barrier insulation material, it does not lead to any partial discharge activities as observed under ac/dc voltages. Broadband measurement of UHF signals produced by partial discharges due to particle movement in transformer oil under dc voltages, at high applied electric fields, indicates that the frequency content of the signal lies in the entire UHF range of 300 MHz - 3 GHz. Narrow band measurements of UHF signal due to PD formed by particle movement, at 1 GHz, indicates that, in the presence of barrier, an increase in applied voltage results in increase in number of partial discharge pulses. This phenomenon occurs in converse in oil gap without any barrier. In the presence of barrier, the sequential movement of particle occurs and the magnitude of discharges increases with increase in applied voltage, irrespective of polarity of the dc voltage. The number of discharges that occur under ac voltage is high compared to the dc voltages.

Tree Propagation from an Artificially-Simulated Tree Channel and Characteristics of Partial Discharge

In order to clarify the mechanisms of partial discharge (PD) and tree degradation, PD characteristics of an artificially-simulated tree channel in low-density polyethylene (LDPE) were investigated. During the application of AC voltage, new tree channels were formed at the tip of the artificial channel. PD characteristics of an artificial channel with 2 mm in length and 30 µm in diameter remarkably changed after the inception of very small trees. After the tree inception, the number of PD pulses increased and light emission due to PD extended to a whole channel and new tree channel. A few minutes after the tree inception, the number of negative PD pulses decreased and its magnitude became large. These results suggest the change in PD mechanism by tree inception and tree propagation. From these results, the mechanisms of PD in a tree channel and tree propagation were discussed. These results are applicable to insulation diagnosis.

Partial Discharge Characteristics in an Artificial Air-filled Void under Superimposed Sinusoidal Voltages at LN2 Temperature

Partial discharge (PD) characteristics within an artificial air-filled void contained in a solid insulator were experimentally investigated under superimposed sinusoidal voltages of 60 and 600Hz at liquid nitrogen temperature (77K) to find the effects of the waveforms of distorted sinusoidal voltages on PD characteristics at 77K. The results show that PD inception voltage at 77K is independent of the applied voltage waveform. The results also show that, when the 600Hz component of the superimposed voltage is increased with its constant peak value, PD intensity seems to be independent of the voltage waveform, whereas PD pulse number increases. Since PD charge magnitude and pulse number at 77K were remarkably different from those at 298K, their mechanisms are discussed based on the observation results of residual charge distributions remaining on a void surface subjected to PDs under 60Hz ac voltages at both temperatures.