Long-period ageing tests on solid-type cables

For the assessment of quality of ¿ solid¿ or ¿ massimpregnated ¿ paper-insulated extra-high-voltage cables, no combination of simple tests has been found to approach in informative value an accelerated ageing test conducted at a medium over-voltage with severe cycles of conductor loading. The paper describes the technique employed by the authors in carrying out such tests and the methods used to correlate the results obtained with performance in actual service. The life-test histories of a number of experimental cables have been selected to illustrate a general discussion of the phenomena observed, and a relation between the over-voltage of the test and the life Of the cable has been established. The paper reports a programme of work that has extended over at least 8 years, and it has proved possible to demonstrate by means of a family of curves the general trend of improvement over this period. The results obtained indicate that 60-kV solid-type cables are practicable and that the possibility of 132-kV solid-type cables meeting commercial requirements cannot be overlooked. Arising from the more uniform quality of impregnation that is achieved to-day, it is probable that a majority of the breakdowns now experienced on test are determined by inconsistencies in the make-up of the solid components of the cable. It is proposed to discuss in greater detail the influence of other factors in a further paper.