PRIMARY PRINCIPLE
A GIS and GIL installation consists of a network of
co-axial transmission lines which act as a wave guide
for electromagnetic signals of PD, with an inherently
low loss. In the absence of barriers and discontinuities,
attenuation at I GHz in a wave-guide of this size
(typically 0.5 m diameter) would be only 3 to 5 d B h .
In practice, multiple reflections at discontinuities
within the GIS and GIL chamber cause a reduction in
signal strength that has been observed to be in the
region of ZdB/m [l].