As one step toward the future smart grid, condition monitoring is important to facilitate the reliability of grid asset operation and to save on maintenance cost [1]. Most failures of the power grid are caused by electrical insulation failure, and a key indicator of such electrical failure is the occurrence of partial discharge (PD). Therefore, one focus of condition monitoring is to detect PD, especially in the early stages, to prevent a serious power failure or outage.

An overview of state-of-the-art partial discharge analysis techniques for condition monitoring

Partial discharge classifications: Review of recent progress

Partial discharge (PD) classification in power cable accessories and high voltage equipment in general is essential in evaluating the severity of the damage in the insulation. In this article, the PD classification was realised as a two-fold process. Firstly, measurements taken from a high-frequency current transformer (HFCT) sensor were represented as features by means of a transformation to the classifier and secondly, the probabilistic neural network (PNN) classifier itself was capable of effectively recognising features coming from different types of discharges. The feature that was used as a fingerprint for PD characterisation was extracted from the moments of the probability density function (PDF) of the wavelet coefficients at various scales, obtained through the wavelet packets transformation. The PNN classifier was used to classify the PDs and assess the suitability of this feature vector in PD classification. Four types of artificial PDs were created in a high voltage laboratory, namely corona discharge in air, floating discharge in oil, internal discharge in oil and surface discharge in air, at different applied voltages, and were used to train the PNN algorithm. The results obtained here (97.49, 91.9, 100 and 99.8% for the corona, the floating, the internal and the surface discharges, respectively) are very encouraging for the use of PNN in PD classification with this particular feature vector. This article suggests a feature extraction and classification algorithm for PD classification, which when combined together reduced the dimensionality of the feature space to a manageable dimension, and achieved very high levels of classification.

Feature extraction of partial discharge signals using the wavelet packet transform and classification with a probabilistic neural network

Partial discharge (PD) source classification aims to identify the types of defects causing discharges in high voltage (HV) equipment. This paper presents a comprehensive study of applying pattern recognition techniques to automatic PD source classification. Three challenging issues are investigated in this paper. The first issue is the feature extraction for obtaining representative attributes from the original PD measurement data. Several approaches including stochastic neighbour embedding (SNE), principal component analysis (PCA), kernel principal component analysis (KPCA), discrete wavelet transform (DWT), and conventional statistic operators are adopted for feature extraction. The second issue is the pattern recognition algorithms for identifying various types of PD sources. A novel fuzzy support vector machine (FSVM) and a variety of artificial neural networks (ANNs) are applied in the paper. The third issue is the identification of multiple PD sources, which may occur in HV equipment simultaneously. Two approaches are proposed to address this issue. To evaluate the performance of various algorithms in this paper, extensive laboratory experiments on a number of artificial PD models are conducted. The classification results reveal that FSVM significantly outperforms a number of ANN algorithms. The practical PD sources classification for HV equipment is a considerable complicated problem. Therefore, this paper also discusses some issues of meaningful application of the above proposed pattern recognition techniques for practical PD sources classification of HV equipment.

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Pattern recognition techniques and their applications for automatic classification of artificial partial discharge sources

The genesis of the research work presented in this paper constitutes the issue of the effective and efficient recognition of single-source one-time partial discharge forms that can occur in insulation systems of power transformers. The paper presents research results referring to the use of single-direction artificial neural networks for recognizing basic partial discharge forms that can occur in paper-oil insulation impaired by aging processes. The research work results presented show the recognition effectiveness of basic partial discharge forms depending on the descriptor of the analysis of the acoustic emission signal analysis. The detailed cognitive aim was selection of input parameters and an artificial neural network which would be the best, considering recognition effectiveness and processing time, and which could be used as a classifier in an expert diagnostic system making identification of partial discharges measured by using the acoustic method possible.

Application possibilities of artificial neural networks for recognizing partial discharges measured by the acoustic emission method

Partial discharge (PD) detection, measurement and classification constitute an important tool for quality assessment of insulation systems utilized in HV power apparatus and cables. The patterns obtained with PD detectors contain characteristic features of the source/class of the respective partial discharge process involved. The recognition of the source from the data represents the classification stage. Usually, this stage consists of a two-step procedure, i.e., extraction of feature vector from the data followed by classification/recognition of the corresponding source. The various techniques available for achieving the foregoing task are examined and analyzed; while limited success has been achieved in the identification of simple PD sources, recognition and classification of complex PD patterns associated with practical insulating systems continue to pose appreciable difficulty.

N.C. Sahoo

Papers

Trends in partial discharge pattern classification: a survey