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VLF Testing

Offline Partial Discharge (PD) and Tan Delta testing of HV and MV cables, the Cable PD Mapping service measures and reports on the health of high voltage cables.

The Cable PD Mapping Service™ is a fast, effective and accurate method of assessing the health of cables and locating the issues, without the need for expensive and inconvenient excavations.

Offline VLF Cable PD Mapping

For new installations, or when the customer can obtain an outage, our state of the art Very Low Frequency (VLF) Cable PD Mapping test equipment can be used to determine cable condition. EA Technology’s customised software allows us to accurately determine PD magnitude and location along the length of the cable. This allows the cable owner to manage their assets with increased confidence through recommendations such as regular monitoring and localised repairs to sections where discharge is found.

Our system is safe, non-destructive and has a 25-year track record of success from the UK and worldwide.

Tan Delta Measurements

With the cable taken out of service for PD testing, the VLF test set can also be used for tan delta measurements on the cables as a supplementary test. While partial discharge measurement is suitable for detecting electrical trees, tan delta measurement detects the overall health of the insulation under test. Although it is a bulk measurement it can provide valuable information on the overall health of the insulator and detect ageing of the insulation e.g. through the presence of water treeing or impurities.


  • Locates PD activity before it leads to failure
  • Ideal for pre-commissioning or post-repair
  • Reduces the need for expensive excavations by identifying the location of the problem
  • Reduces the risk of unplanned, expensive outages


  • Identifies and locates PD activity by time-of-flight measurement
  • Works with paper or polymer insulated high voltage cables
  • Produces a detailed map of cable condition and any PD problems
Brad Monaghan
Head of Technical Services

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