The technology, developed and marketed by Wirescan in Norway, uses Frequency domain reflectometry to obtain a detailed and repeatable signature from the cable. The cable signature is a measure of the impedance of the cable along the length of the cable.
Changes in impedance are produced by terminations and joints but also by a number of damage mechanisms that may be in progress within the cable structures. The degradation can be occurring in the insulation or in other conductive or structural parts of the cable system.
Damage can be caused by mechanical stresses, water ingress, over-heating, premature ageing, corrosion etc.
The technology is not seen as a replacement for existing diagnostic methods but as complementary. For example, a high TD reading may trigger a LIRA test to try and locate the position of the degradation that is causing the high TD. Many types of damage do not produce PD but can produce easily detectable impedance changes. Comparison of the signatures between phases can also yield valuable information.