Practical consideration of mechanical measurements in cable diagnostics

The measurement of mechanical properties of insulating materials are widely used methods in cable diagnostics. Due to the stresses of operation the mechanical and dielectric properties also changes, therefore the deterioration of dielectric properties can be followed by mechanical measurements, too. Most of mechanical properties can be measured in laboratory, according to the IEC 60811 standard, but e.g. a simple hardness testing on the cable sheath can be performed as on-site test. In this paper, the most common measurement methods of mechanical properties are introduced and the practical issues of the application are discussed by the measurement of mechanical parameters of service and laboratory aged low voltage cable samples and the effectiveness of the measurements are compared. The results show that the thermal aging of low voltage cables can be effectively monitored by a simple hardness testing on the PVC sheath of cable.