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2 Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2 2004

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Experiences from on-site dielectric spectroscopy measurements on power transformers

Blennow J., Ekanayake C., Bartnicki A., Gubański S.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2004

Vol. 40, nr 15

62-69

Dielectric spectroscopy field measurements were conducted both in frequency domain (FDS) and in time domain (PDC) on ten power transformers, most of them rated 130 kV/40 MVA. In addition, oil samples were taken for moisture content analyses and for conductivity measurements. The transformers selected for the measurements were of different types, originating from different manufacturers and having different age, up to 50 years old. Some of them have been known as being in bad condition. In general, the majority of the transformers were low loaded prior to the measurements. On two of the units the measurements were performed both before and after oil regeneration. Results of the oil analyses are compared with estimates obtained from the well-known XY-model and the simplified X-model. The results of the modelling show that both FDS and PDC provide information about the state of insulation. Oil temperatures as well as thermal equilibrium are critical factors for obtaining reliable results. The spectroscopy measurements provide better estimates of moisture content at low sample temperatures than the traditional Karl Fisher analyses.

Dielectric spectroscopy measurements on oil impregnated paper / pressboard samples

Ekanayake C., Graczkowski A., Walczak K., Gubanski S. M.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2004

Vol. 40, nr 15

113-120

Dielectric response analyses of oil-paper/pressboard insulation in power equipment have been introduced for condition monitoring. This paper presents results of a laboratory study where dielectric spectroscopy measurements in frequency domain were performed on oil impregnated pressboard samples containing different amount of moisture (0.6% - 4%). Such data are necessary for correct interpretation of the diagnostic measurements. The measurements were earned out in the frequency range of 0.1 mHz - 1 MHz at temperatures between 20 °C and 80 °C. The measured dielectric response data were used for obtaining information on the change of activation energy and dc conductivity of pressboard with moisture content. The responses obtained were used to derive master curves. Furthermore, the influences of the non-linear behaviour and oil layers on the total dielectric response were discussed.