Duval [70] developed a triangle, Figure 4.15, based on the relative percentage
of methane, ethylene and acetylene gas. The triangle is divided into six regions
representing high energy arcing, low energy arcing, corona discharge and hot spots.
The triangle has the advantage that a diagnosis is always given – but, of course, this
will always imply a fault! Hence it must only be used in conjunction with individual
levels of gases which imply the possibility of a fault.