Comment and discussion on digital processing of PD pulses

Some of the more salient aspects of the digital processing technology of PD signals are examined. Most of the efforts in this field are concentrated on the application of digital analyzers for pulse height analysis, pattern recognition and identification of the physical phenomena. It is demonstrated that errors in the signal processing unit can lead to dominant mistakes in the interpretation of the test results     

The use of fractal features for recognition of 3-D dischargepatterns

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     

Inference of PD in electrical insulation by charge-heightprobability distribution. Diagnosis of insulation systemdegradation

This paper deals with application of stochastic procedures for the analysis of PDHD (partial discharge height distributions) detected during life of insulation systems. Experiments of accelerated aging under electrical stress were carried out on both an artificial flat cavity and a 23 kV epoxy-resin insulator, where PD are already active at the beginning of aging. A correlation between aging time and PDHD features is observed during long-term voltage application, until breakdown, on both objects. In particular, the PDHD analysis is approached by means of the Weibull function. It is shown that the time evolution of shape and scale parameters can provide diagnostic indications on aging amount, incoming failure and thus on the reliability of insulation systems     

PD pattern analysis during induced test of large power transformers

The partial discharge (PD) measurements on power transformers are studied with a view toward discrimination and classification of different discharge sources. For this purpose digital analysis is applied to power transformers and reactors going through acceptance testing. Furthermore, based on these measurements, PD databases have been developed to support the discharge evaluation during induced voltage tests of transformers. Using this technique, a clear distinction is possible between transformers showing different discharge behavior     

Experiences with digital analysis of discharges in high voltagecomponents

The ability of digital PD analyzers to process and store specific information concerning discharge activity can be used for various purposes: discharge recognition and condition monitoring. To exploit these possibilities, a specific fingerprint technique has been successfully used in recent years for off-line and on-line PD measurements of HV components. In this paper diverse practical examples are discussed of applying advanced digital post-processing for the measurement of partial discharges     

PD knowledge rules for insulation condition assessment of distribution power cables

This paper discusses practical experiences in the Netherlands with insulation condition assessment of distribution power cable networks by partial discharge diagnosis and database support. In particular, practical steps are discussed in collecting, analysing and processing the diagnostic data for decision support of utility asset management.     

Standardization of on-line VHF PD measurements on turbo generators

Based on field experiences on a number of different turbo-generators in the Netherlands, several fundamental and applied aspects of on-line very high frequency (VHF) partial discharge (PD) diagnostics are discussed. In particular the systematic results presented in this paper contribute to: 1. the characteristics of different on-line detection using suitable VHF sensors, 2. the methods to suppress disturbances and to distinguish between different types of discharges and 3. the interpretation of measured results to obtain knowledge about the insulation condition     

Influence of aging on classification of PD in HV components

In this presentation the influence of degradation of discharging dielectric on phase-resolved patterns of partial discharges (PD) is studied. Using conventional PD detection and statistical analysis, internal discharges in a flat cavity, and in epoxy insulation of two HV components were analyzed during long term tests. The results indicate that aging progress was accompanied by few consecutive changes in the phase-resolved patterns. This observation might become important for two applications: the developing of databases of different discharging defects, and the analysis of discharge degradation of dielectrics     

Fundamental aspects of PD patterns of on-line measurements onturbogenerators

This paper discusses partial discharge (PD) measurements performed on turbogenerators using the VHF PD detection technique. With this technique it is possible to perform PD measurements on turbogenerators without interruption of their operation. In addition to PD in any particular phase, the recorded patterns can show crosstalk from other phases and disturbances. The membership of each signal source (phase's own PD pattern, crosstalk, disturbances) to the recorded pattern depends on the selected center frequency. By examination of some typical examples, the relationship between the center frequency and recorded patterns is discussed. Furthermore, PD measurements performed over time on the same generator are studied to discuss possible changes in the spectral responses of particular phases of a turbogenerator. By visual comparison of PD patterns as well as computer-based discrimination tools it was found that several center frequencies are suitable to tune the VHF PD detection technique. However, these center frequencies can change in the course of time for a particular phase of a turbogenerator. As a result, in order to avoid a misjudgment on the insulation condition of turbogenerators, the analysis of on-line recorded PD should not be restricted to just one single center frequency     

Pattern analysis of partial discharges in SF6 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