Partial Discharge Current Waveform Research Articles

Nanosecond Partial Discharge Current Waveforms with Polyethylene Naphthalate Films on IEC(b) Electrode

The polyethylene naphthalate (PEN) film has been widely applied as a heat‐resistant thin insulation film and sensor film. For the safe and long application of the film in various products, one significant characteristic is the partial discharge (PD) resistivity. In this study, a well‐known IEC(b) electrode is used to measure PD characteristics such as the maximum partial discharge, qmax and fast PD current waveforms at AC peak voltages of 1–3 kVp and 50–1000 Hz over PEN films with thicknesses of 75, 50, or 25 μm. All experiments are conducted at room temperature of ~20 °C. The positive PD current is defined as the current flowing from a high‐voltage electrode to a ground electrode. The positive and negative qmax increased rapidly with the applied voltage increase but remained almost the same for the applied voltage frequency changes. The PD current duration time was less than 40 ns for the positive current and 30 ns for the negative current at all voltages, frequencies, and film thicknesses. It was deduced that the positive current peak magnitude was approximately twice of the negative one at all applied voltages, frequencies, and film thicknesses. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Analysis of the correlation between GIS partial discharge current waveform and charge quantity with UHF signals

The Ultra-High Frequency (UHF) method, as a crucial technology for online GIS monitoring, struggles with the issue of being unable to accurately reflect the number of partial discharges, which poses a significant challenge for this technique. To examine the relationship between partial discharge waveforms, charge quantity, and UHF signals, a physical field model of partial discharge is developed using finite element simulation software, allowing a comparison of the peak-to-peak values of UHF signals with the parameters of the partial discharge current. Research demonstrates a roughly linear relationship between the peak-to-peak values of UHF signals and the magnitude of the partial discharge current but no definitive connection with the discharge quantity. These significant findings guide the quantitative detection of partial discharges in electrical equipment using the UHF method.

Super High Frequency Wideband Measurement of Partial Discharge Current Waveform in Mineral Oil

Super High Frequency Wideband Measurement of Partial Discharge Current Waveform in Mineral Oil

Comparison of PD Current Waveforms between Aged and New Insulation Oils and Oil Types by Super-Wideband Measurement

Liquid insulators such as mineral oil and silicone oil have excellent cooling and insulation performance, but impurities, dissolved gases and/or moisture in the liquid are known to have a significant influence on insulation performance. So far, the authors have shown that partial discharge (PD) current waveforms in mineral oil differ significantly depending on degassing treatment condition and on positive and negative polarity by super high frequency-wideband measurement. In this paper, using aged mineral oil which was used in a distribution transformer over 48 years, difference in PD current waveforms between new and aged mineral oil and between mineral and silicone oils as difference in insulation oil type were investigated by the super high frequency-wideband measurement system, so-called “SHF_PDPW system” with a 33GHz oscilloscope. In addition, PD-emitted electromagnetic (EM) waves in those oils were measured with an antenna with sensitivity in the UHF band, and differences in the polarity and relationship between PD current and PD-emitted EM waves were investigated from the viewpoint of applicability of the UHF method.

Identification of Partial Discharge Defects Based on Deep Learning Method

Since repetitive partial discharge (PD) leads to insulation breakdown, it is one of the most critical defects that affect operation life of electrical equipment. In this paper, four kinds of PD defects are identified with deep learning (DL) method according to the current waveforms. A modified IEC-60270 experiment platform with ultra-high frequency (UHF) and current probe is built to acquire PD current waveforms and their corresponding detecting pulse current and UHF pulse signal. Fourier transform, principle component analysis, and t-distributed stochastic neighbor embedding methods are applied to visualize the data set, which proves the feasibility of classifying the PD current waveform. Two basic parts of this DL framework are sparse autoencoder layer and softmax layer, the former extracting features of the input signal and the latter operating as the classifier. Hyper-parameters of the network such as sparsity, activation function, number of hidden nodes, and network depth were discussed. The final classifying accuracy of the proposed method is up to 99.7%, that is much better than the traditional identifying method. A comprehensive blind test is designed to prove the general validity and robustness of the proposed model.

Accurate power transformer PD pattern recognition via its model

In this study, a transformer model is proposed to simulate the behaviour of a real transformer, under presence of different types of defects which contribute to partial discharge (PD) generation, as closely as possible. Five different types of defects (scratch on winding insulation, bubble in oil, moisture in insulation paper, very small free metal particle in transformer tank and fixed sharp metal point on transformer tank) are implemented artificially into these transformer models to investigate the resultant PD current signal magnitude and characteristics. Time-domain PD current waveforms are recorded on those transformer models which have one type of those defects. The resultant statistical PD current wave shapes and texture features are extracted from these captured PD current signals. The principal component analysis (PCA) is used to reduce the dimension of feature spaces which are required to develop the inputs for the classifier. The principal components obtained through PCA are applied to the support vector machine classifier, as an input. The classification results indicate that the extracted texture features (using grey-level covariance matrix) preserve the best characteristics for separation of the related patterns of those five defect models, accurately.

New aspects of UHF PD diagnostics on gas-insulated systems

Gas insulated switchgears (GIS) have been increasingly introduced as main substation equipment since the late 1960s thanks to their high reliability, safety, and compactness. The UHF method to diagnose partial discharge (PD) is broadly employed in the field as an advanced insulation diagnostic technology. There are three primary factors related to the PD signal detection characteristics using this UHF method; namely the frequency spectrum of the PD signal itself inside GIS, the propagation characteristics of the PD signal inside the GIS tank, and the detection characteristics of the sensor measuring the PD signal. Accordingly, to further improvement of the diagnostic technique based on the UHF method, the PD phenomenon itself and its propagation characteristics should be clarified and the measurement system refined. From these perspectives, the present study reviewed the recent and latest findings concerning the PD phenomenon and its propagation characteristics inside GIS as well as the PD measurement system verification methods and diagnostic technologies, and summarized typical examples. Firstly, with regard to the PD phenomenon, measurement up to the high frequency band exceeding 10 GHz (even 30 GHz) clarified that the rise time of the PD current waveform is several tens of picoseconds, shorter than previously known. In the case of PD in micro-defects inside the epoxy insulator, however, the rise time is relatively long, in the order of nanoseconds, and a crack is the most critical defect. Subsequently, with regard to UHF PD diagnostics/monitoring technology, a novel technique using PD current waveform characteristics has been developed, and a more advanced PD diagnostic algorithm has been established by clarifying the influence of the shape and GIS internal structures on the electromagnetic wave propagation characteristics. Less uncertain and simplified calibration and verification technologies are also proposed both for a single UHF sensor and the entire UHF measurement system. These new technologies and further advanced studies in future are expected to make the UHF method more convenient and sophisticated.

Effect of Terminating Resistance on High Frequency Behaviour of Rogowski Coil for Transient Measurements

Partial Discharge (PD) current measurements have been widely used to assess the insulation condition of power components. Rogowski coil is a low cost current sensor specifically meant for high frequency transient diagnostics such as PDs in high voltage (HV) power apparatus. This paper presents the design of Rogowski coil for transient measurements. For the designed prototype of Rogowski coil, correct selection of terminating resistance is of high importance to calibrate its response for accurate measurement of the PD current waveforms. Effect of terminating resistance for the coil model is analysed based on theoretical, practical and simulated investigations. Simulated model of the coil is used to determine the behaviour of induced current through non-physical inductive and capacitive elements of Rogowski coil. The Electromagnetic Transient Program-Alternative Transient Program (EMTP-ATP) is used to implement and to analyze the model of Rogowski coil. The comparison of practical and simulated results validates the designed model of the coil. The paper explores EMTP-ATP as an efficient tool to analyze and modify the transient behaviour of Rogowski coil for high frequency pulse measurements.DOI: http://dx.doi.org/10.5755/j01.eee.19.7.2070

Streamer and leader discharge propagation characteristics leading to breakdown in electronegative gases

This paper describes the propagation characteristics and mechanisms of partial discharge (PD) leading to breakdown (BD) in electronegative gases such as SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas mixtures for AC voltage application. An established PD measuring system of highly time-resolved PD current and light intensity waveforms, streak and light emission images enabled us to discuss the physical mechanisms of PD generation and propagation in terms of space charge behavior. Experimental results revealed that the time-resolved PD generation was divided into different groups composed of the first large PD and the subsequent small PDs; the former was identified as the leader discharge, and the latter corresponded to the streamer discharges. The successive generation of the streamer and leader discharges was interpreted by the change of critical volume size. The time-resolved PD generation characteristics leading to BD were also measured and discussed. The leader discharge would be obliged to take a detour along the periphery of the positive space charge area in the vicinity of the needle electrode, and finally result in BD in electronegative gases

Insulation properties of a CO2/N2 50% SF6 gas mixture in a nonuniform field

AbstractThis paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO2/N2/SF6 gas mixture in a nonuniform field. These voltage characteristics were investigated with ac high voltage by changing the mixture rate of each gas of CO2, N2, and SF6 gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO2 gas into a N2/SF6 mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF6 in N2/SF6 gas mixture is 50%, with the addition of 1% CO2 the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N2/50% SF6 gas mixture and pure SF6 gas, respectively. Moreover, those voltage characteristics of a CO2/N2/SF6 gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to discuss the corona stabilization effect, which seems to be one reason for the drastic increase in the breakdown voltage. These results and breakdown mechanism of the CO2/N2/SF6 gas mixture are discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter, and PD current waveforms. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 34–43, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10019

Development of detection and diagnostic techniques for partial discharges in GIS

This paper describes detection and diagnostic techniques for partial discharges in gas insulated substations (GIS). Partial-discharge current waveforms of SF/sub 6/ gas and external noise characteristics of actual substations were investigated, and a measuring system having sensors in GIS and employing frequency range of VHF band was developed. By this system, detecting very small partial discharges of several 10 pC level has become possible. Also, a neural network system, focusing attention as a method for recognizing patterns, was applied for determining causes for partial discharge in GIS, and its applicability has been proved. >