VLF systems are advantageous in that they can be manufactured to be small and lightweight; making them useful – especially for field testing where transport and space can be issues.
Because the inherent capacitance of a power cable needs to be charged when energised, system frequency voltage sources are much larger, heavier and more expensive than their lower-frequency alternatives.
The VLF test can be used in a number of ways: High voltage withstand tests are used in conjunction with partial discharge measurements on solid dielectric cable and accessories within manufacturing plants to ensure the quality of completed cable system components from MV to EHV.
Withstand tests can be conducted using a variety of voltage sources from DC to 300 Hz and are simple to operate and the equipment may be inexpensive.
Some observations for the VLF withstand test are (Based on CDFI results):[3] Medium voltage distribution cables and their accessories form a critical part of power delivery systems.
Using the IEEE 400.2, three different criteria are applied for diagnosing a cable insulation system using the Tan δ value.
Even at higher voltages the criteria for detection (e.g. in Cigre WG B1.28) and severity calculation are not defined and not dependent on the measured properties of the PD.
Proponents of this approach will argue that these differences detract from the commercial benefits offered by the competing voltage sources.
Probability Insulation failure is a stochastic process and it is erroneous to identify single events and attribute this to a particular source.
Failure of an insulation system after a good diagnostic indication (or vice versa) is to be expected for any test using any voltage source.