Commissioning tests are the final check on the cable, in order to pinpoint eventual problems caused during the installation process. In such conditions very low frequency power supply are the most fitting solution. In fact, comparing with the HV field, resonant test sets can be even more expensive than the cable system.
VLF generators are easy to carry on and can be energized with normal LV power supply. Due to the mainly capacitive load a voltage generator working at 0.1 Hz can easily energize long cables with a relatively low power.

The equipment under test is disconnected from the load and the noise is low enough to enable a time domain reflectometry analysis. Together with the Partial Discharge test it is possible to perform some macroscopic diagnostic techniques such as: polarization index and tangent delta of the cable under test.
The combination of the diagnostic results of the 3 testing techniques covers very well the possible insulation ageing problems those can occur in the lifetime of the asset.