APTP Articles

Cable Condition Assessment

HV Diagnostix is offering a testing service for customers to practically evaluate the benefit of LIRATM technology to diagnose the condition of their cables.

The technology, developed and marketed by Wirescan in Norway, uses Frequency domain reflectometry to obtain a detailed and repeatable signature from the cable. The cable signature is a measure of the impedance of the cable along the length of the cable.

Changes in impedance are produced by terminations and joints but also by a number of damage mechanisms that may be in progress within the cable structures. The degradation can be occurring in the insulation or in other conductive or structural parts of the cable system.

Damage can be caused by mechanical stresses, water ingress, over-heating, premature ageing, corrosion etc.

The technology is not seen as a replacement for existing diagnostic methods but as complementary. For example, a high TD reading may trigger a LIRA test to try and locate the position of the degradation that is causing the high TD. Many types of damage do not produce PD but can produce easily detectable impedance changes. Comparison of the signatures between phases can also yield valuable information.

Figure 1 - Impedance change at 16m coinciding with crossing of other HV cable

Below are two examples of tests that were performed on cables in New Zealand recently. In the first case an unexpected impedance change was measured on all phases at around 16m. Upon further investigation this was determined to be a crossing point of another HV cable. 

The test is a low-voltage test and can be used on cables tens of kms long. It can be performed easily by a relatively unskilled operator and the results can be emailed for analysis. To this end HV Diagnostix has a small, rugged loan unit that is available for customers to use to perform the diagnostics on a cable under our remote supervision. There is no charge for the hire of the unit for this evaluation.

Currently we are also including this analysis when we perform our full PD and TD diagnostic assessments of cables.

Contact Gary Catlin on +64 (0)22 681 7589 for a discussion on how we can assist you with your cable testing.

Figure 2 - The customer has been advised of the unexpected reflections at 30-40m on white and blue phase

Gary Catlin - HV Diagnostix NZ