Power transformers are considered important and expensive items in electrical power networks. In this regard, the early discovery of potential faults in transformers considering datasets collected from diverse sensors can guarantee the continuous operation of electrical systems. Indeed, the discontinuity of these transformers is expensive and can lead to excessive economic losses for the power utilities. Dissolved gas analysis (DGA), as well as partial discharge (PD) tests considering different intelligent sensors for the measurement process, are used as diagnostic techniques for detecting the oil insulation level. This paper includes two parts; the first part is about the integration among the diagnosis results of recognized dissolved gas analysis techniques, in this part, the proposed techniques are classified into four techniques. The integration between the different DGA techniques not only improves the oil fault condition monitoring but also overcomes the individual weakness, and this positive feature is proved by using 532 samples from the Egyptian Electricity Transmission Company (EETC). The second part overview the experimental setup for (66/11.86 kV–40 MVA) power transformer which exists in the Egyptian Electricity Transmission Company (EETC), the first section in this part analyzes the dissolved gases concentricity for many samples, and the second section illustrates the measurement of PD particularly in this case study. The results demonstrate that precise interpretation of oil transformers can be provided to system operators, thanks to the combination of the most appropriate techniques.

Theoretical investigation of the onset voltage of negative corona on stranded conductors is described in this paper. The method of calculation is based on the criterion developed for the formation of repetitive negative corona Trichel pulses. This calls at first for an accurate calculation of the electric field in the vicinity of stranded conductors. The investigated gap is a three-dimensional field problem. To solve this problem, a new modification of the charge simulation technique is presented, where the simulation charges are helical of infinite length. Laboratory measurements of the onset voltage on stranded conductors are carried out to check the accuracy of the present calculations. The effects of varying the field nonuniformity on the onset voltage values are investigated. The calculated onset voltage values for stranded conductors agree satisfactorily with those measured experimentally.

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This paper presents theoretical investigation of conducting particle-initiated breakdown in gas-insulated coaxial configuration under high direct voltage. The presence of contaminating conducting particles could seriously deteriorate the dielectric strength of high voltage gas-insulated substations (GIS) and gas-insulated transmission lines (GITL). This deterioration depends on the shape of the particle, the type and the pressure of the gas insulation, and the electric field. The calculated breakdown voltage initiated by particle is obtained by streamer breakdown criterion. The breakdown voltage calculation calls first for an accurate calculation of the electric field on and around the particle surface. The investigated gap is a three-dimensional field problem due to the asymmetrical space arrangement of the particle inside the gap. The particles studied are of many different shapes and sizes such as spheres, filamentary (wire) particles and fine spheres simulating the surface roughness. To solve this problem, charge simulation technique is used. The calculated field values are utilized in evaluating the breakdown voltage. The effects of varying the field nonuniformity, particle shape and size, gas type and pressure on the breakdown voltage are investigated. The calculated breakdown voltage values agree satisfactorily with those measured experimentally and with those obtained theoretically before.

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Theoretical investigation of the onset voltage of negative corona on stranded conductors is described in this paper. The method of calculation is based on the criterion developed for the formation of repetitive negative corona Trichel pulses. This calls at first for accurate calculation of the electric field in the vicinity of stranded conductors. The investigated gap is a three dimensional field problem. To solve this problem, a new modification of the charge simulation technique (CST) is presented, where the simulation charges are helical of infinite length. Laboratory measurements of the onset voltage on stranded conductors are carried out to check the accuracy of the present calculations. The effects of varying the field nonuniformity on the onset voltage values are investigated. The calculated onset voltage values for stranded conductors agree satisfactorily with those measured experimentally.