Determining the “age” of paper insulation

Investigations of paper cable samples retrieved from service are frequently called for to support surmises of a mechanism of failure or to estimate the remaining life of the cable. There is rarely a great deal of information about the operating conditions that the cable has been subject to, especially for medium voltage cables. The investigator is forced to derive as much information as possible from the very few analyses that can be made on the sample itself. The paper gives an account of one of the methods used to squeeze as great an interpretation as possible out of some simple measurements by applying the ageing characteristics of cable paper determined in laboratory studies and the electrical and thermal characteristics of the cable materials