Wyniki wyszukiwania - BazTech

Ograniczanie wyników

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

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Sortuj według:

Ogranicz wyniki do:

Experimental study of current damages in bearings.

Edvall M., Fyhrman M., Lindsten G., Blennow J., Thiringer T.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

2007

Vol. 46, nr 19

141-146

Failures of bearings in electric motors related to electrical damages started to increase after the introduction of the fast switching pulse width modulated IGBT inverter on the market in the mid 1990s. The aim of this work was to investigate how the damages occur. Shaft voltage, mechanical load, speed, lubricant and discharge energy were some of the parameters considered. The threshold voltage level was found to be mostly dependent on the oil film thickness which in return depends on speed and load. Shaft voltage proved to be the dominant factor in creating damages on the bearing surface. The film is capable of holding a higher voltage before breakdown under high frequency voltages as compared to slowly increasing voltages. Speed and load did not seem to affect the discharge energy but affect the pattern of the damages. Damages were also observed on the bearing lubricated with low impedance grease to the same extent as with conventional grease.

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.