Calculation of Resonant Frequencies in GIS for UHF Partial Discharge Detection

One of the different measurement techniques for partial discharges (p. d.) in gas insulated substations (GIS) works in the frequency range above 300 MHz called Ultra-High-Frequency (UHF) range. This paper gives a review of the GIS-relevant part of the theory of electromagnetic wave propagation and modes in this UHF-range. For the application of the UHF-narrowband method in practice typical UHF-p. d.-spectra are explained. In addition to this review new computations of the reflection of waves at spacers are presented. The corresponding attenuation for different wave modes is discussed. Practical conclusions are drawn from these new results.