Cable diagnostic testing is predictive in nature, determining the relative amount of degradation of a cable and establishes the likelihood that the cable will continue to perform properly in service. For asset managers, assessing aging and the overall condition of service-aged cable systems is instrumental for planning purposes, for example, to determine what needs to be replaced or upgraded on the network.
The principal cable diagnostic tests include partial discharge (PD), tan delta (and variations of tan delta), return voltage method (RVM), and isothermal relaxation current (IRC) tests. While tan delta tests and their variations can be categorized as tests sensitive to global or local problems (even though as “averaging” tests, local problems may be difficult to see), a PD measurement is sensitive to local problems. It should be noted that PD is not detectable in the field as a result of water trees but may be detectable if electrical trees are formed. “Water trees can cause electrical trees to form as a result of a lightning impulse, switching surges, or excessive test voltage levels and durations.” (IEEE 400.2 – 2013)
Megger employs some of the world’s greatest experts in cable test and diagnostics; with such a variety of possible applied sources and diagnostic methods, Megger can help guide you in determining what is appropriate for your cable assessment needs.