Acoustic detection can be effective [80–82] but, due to the high attenuation of
acoustic signals at flanges etc., each section must be tested in turn.
In relation to electrical detection, within the factory environment, a standard
IEC60270 type approach can be used as described earlier in this chapter. Alternatively,
rather than using large coupling capacitors, electric field sensors can be
incorporated at a standard flange cover/inspection hatch within the GIS. Essentially,
the gas gap capacitance between the busbar in the GIS and the chamber wall acts
as the coupling/high voltage capacitor. The low voltage impedance coupled to the
sensor is essentially as described previously.
These methods have all been described previously, although it is interesting to
see how they are applied in GIS. However, a novel method of electrical detection has
been developed for field measurements on GIS and it is this which is of particular
interest in this section.
The principle of this UHF technique (further details can be found in Chapter 2) is
that the current pulse which forms the partial discharge has a very fast risetime and
byproducts.