Terminations
The weakest links in a cable system are often the terminations (As can be seen above in figure 2) or cable joints, mainly because they require on-site assembly.
Cables do fail due to a number of factors, such as the ingress of moisture and water into the joint, which can lead to catastrophic arcing failure of the joint; corroded sheath that lets water enter the insulation; overloaded; mechanical damage; and natural aging causing insulation properties to change state and leads to cable failures.
Undertaking On-Line Partial Discharge testing of cables in the field does requires extensive experience to know where to place the various numbers of sensors, (it is not possible to use one sensor) and analyse this data from the various sensors as it is being recorded in real time.