Limitations in the application of on-line and off-line PD measurement systems

The first underground cables to be installed in the UK were paper-insulated cables and their installation dates back as early as the 1920´s. Although the manufacturing technology was primitive compared to that available today, there are still 50–60 year old cables that remain in working condition. In the modern power system, these cables are both an asset and a liability. Failure can lead to interruptions in supply and customer minutes lost, indices used by the regulator to reward distribution network operators. Companies are therefore under pressure to somehow improve the performance of cable assets. However, the economic costs relating to the replacement of all cable assets at the end of their life are prohibitive and strategies to determine the relative health of cable assets are becoming increasingly important.