E. Gulski

Classification of partial discharges

For a long time, classification of partial discharges was performed by eye, by studying discharge patterns at the ellipse of an oscilloscope screen. The introduction of digital processing techniques allowed automation of the recognition procedure. These procedures are reported and applied to a number of actual HV constructions which suffer from partial discharges. The results of these tests show that a quite satisfactory recognition of discharges takes place. >

Computer-aided recognition of discharge sources

Making use of a computer-aided discharge analyzer, a combination of statistical and discharge parameters was studied to discriminate between different discharge sources. Tests on samples with different discharge sources revealed that several parameters are characteristic for different types of discharges and offer good discrimination between different defects. >

Computer-aided measurement of partial discharges in HV equipment

A previously developed method of partial discharge (PD) recognition is used to evaluate PD in HV devices. Using conventional discharge detection (bandwidth approximately 400 kHz), the PD patterns are studied. By means of unambiguous statistical operators like skewness, kurtosis, number of peaks, etc., quantitative information about the discharge source can be obtained. In the case of an unknown defect, a combination of these operators is compared to the same set of operators for a known configuration. In this way, a statement can be made on the character of a discharge source. The use of this technique in evaluating different discharges in HV cable and in 400 kV SF/sub 6/ insulation confirms the usefulness of the new approach. >

Digital analysis of partial discharges

In this paper relevant aspects of digital processing of partial discharge (PD) as measured by conventional PD detection methods are discussed. Moreover, a systematic study of PD quantities is presented and discussed within the scope of practical PD analyzers, including recognition of defects in certain HV insulation configurations. >

Neural networks as a tool for recognition of partial discharges

The application of three different neural networks (NNs) to the recognition of partial discharge (PD) is studied. Results of PD measurements on simple two-electrode models, as well as on models of artificial defects in industrial objects, are presented. The PDs are measured using conventional discharge detection, and PD patterns are processed by previously developed statistical tools. Mathematical descriptors are used as input patterns for a backpropagation network, Kohonen self-organizing map, and learning vector quantization network. All three NNs recognize fairly well the PD patterns of those insulation defects for which they were trained. On the other hand, the NNs could misclassify those PD patterns for which they were not trained. The classification of PD patterns by NNs can be influenced also by the structure of the particular NN, the value of the convergence criterion, and the number of learning cycles. >

The use of fractal features for recognition of 3-D discharge patterns

This work presents further results on the use of fractal features for recognition of 3-D partial discharge patterns. Two fractal features, the fractal dimension and lacunarity were calculated from 3-D discharge patterns and their power to discriminate among various discharge patterns was analyzed. The results indicate that fractal features possess fairly reasonable discriminating abilities. >

Monitoring and Diagnostic of Transformer Solid Insulation

Liberalization of the energy market has put increasing pressure on both electricity producers and distributors for lower costs. Since maintenance is a major expense account, such companies will be inclined to reduce maintenance budgets. At the same time, increased liability for nondelivered energy increases the costs of sudden failure of a component. Transformers are such a component; they are often an essential link in the distribution network. In order to reconcile both decreasing maintenance spending and reliable service, condition-based maintenance (CBM) is often proposed. The basis of a successful application of CBM lies in obtaining information on transformers so that on the one hand a critical condition will be noted early enough to take measures; on the other hand so that only minimal maintenance is being applied to transformers still in good condition. This paper will review a series of often-mentioned techniques in order to assess what the value of this technique will be for CBM, and whether it can be used for condition monitoring.

Advanced partial discharge diagnostic of MV power cable system using oscillating wave test system

To obtain a sensitive picture of discharging faults in power cables the PD should be ignited, detected, and located at power frequencies that are comparable to operating conditions at 50 or 60 Hz. In this way, realistic magnitudes in [pC] and reproducible patterns of discharges in a power cable can be obtained. PD measurements during service as well as on-site continuous energizing at 50 (60) Hz of MV cables are not always economically realistic for on-site inspections. Different energizing methods have been introduced and employed during recent years. Therefore, based on the assumption that sensitive detection of critical PD sites occurs by a method mostly similar to 50 Hz energizing conditions, a method as introduced for on-site PD diagnosis of MV cables is discussed: oscillating wave test system (OWTS).

Pattern analysis of partial discharges in SF/sub 6/ GIS

The measurement of partial discharge(PD) of several faults in gas-insulated system (GIS) is discussed. Phase-resolved PD patterns have been measured using three different PD detection measuring systems: according to the IEC 270 recommendations, a VHF/UHF measuring system with narrow band filtering, and the UHF measuring system with wide band filtering. PD patterns are compared using computer-based discrimination tools. The influence of the selected center frequency on the PD patterns is discussed for the narrow band VHF/UHF measuring system. The influence of the number and type of GIS components between the discharging defect and the capacitive coupler on the shape of the PD patterns is analyzed. For several GIS components the signal reduction is studied. It was found that the shape of PD patterns is independent on the used PD detection circuit and the propagation path of the PD signals. As a result, discrimination and classification of PD distributions of several studied defects are possible using digital tools.

On-site testing and PD diagnosis of high voltage power cables

In addition to after-laying of new-installed high voltage (HV) power cables the use of on-site non-destructive on-site testing and diagnosis of service aged power cables is becoming an important issue to determine the actual condition of the cable systems and to determine the future performances. In this paper based on field experience an overview is presented on on-site testing and partial discharge diagnosis of HV power cables with regard to on-site testing methods: energizing, diagnostic aspects, possibilities and implications for new and service aged power cables.