Deterioration mechanisms of paper cables

A sizeable proportion of the 11 kV and 33 kV distribution network in the UK consists of cable installed over 30 years ago. For 11 kV cables the integrated total circuit kilometres is equal to just over 90% of the installed cables reported to Offer in 1993; for the 33 kV cables the total is 66% of the 1993 figure. There will have been many changes introduced into the cable networks over the years which will have taken a proportion of these older cables out of service but it is a reasonable assumption that a large fraction of presently operating circuits consist of cables which have been operated for over 30 years. The author discusses the condition of the older cables and considers the deterioration mechanisms for metallic sheaths, paper cables and liquid impregnated cables