UHF detection of particles in a co-axial GIS bus duct in the presence of spacers

Presence of particles within the GIS duct causes partial discharges which radiates electromagnetic waves in the UHF range. Hence the presence of particles could be detected indirectly by sensing the EM waves using UHF sensors. In this paper an attempt has been made to calculate the electromagnetic fields at UHF sensor locations in a bus duct. Initially to simplify the analysis, the GIS is taken as a straight circular co-axial waveguide without the presence of any spacers or bends or junctions. The time domain output of UHF couplers receiving these EM waves has been computed and presented in this paper. It matches well with the experimentally measured values for a GIS bus duct of similar dimensions. Later, the effects of spacers on EM fields are considered. The technique has been further extended to locale the particle by using three UHF couplers and by comparing the amplitude and time of arrival of the signal, both in the presence and absence of the spacer.