Cable Condition Monitoring Using Indenter Measurements

There has been a considerable amount of work worldwide over the last 10 to 15 years on the development of methods for monitoring ageing degradation in polymeric cable materials (see for example EPRI workshop, 1993). Of the many methods assessed, only a few have so far shown practical promise for use in real plant. One of the most promising non-destructive methods is that based on indenter measurements (Carfagno et al., 1989). In this type of test, a small probe (usually with a truncated cone tip) is pushed into the surface of the material under controlled conditions and the load/displacement curve is measured. The slope of the curve is known as the indenter modulus (IM) and shows a good correlation with ageing degradation in a wide range of materials used in both cables and seals. The method can be applied to both thermal and radiation ageing of polymeric materials.