Procedure for Determining the Growth of Water Trees in Cable Samples during 500 Hz Accelerated Ageing

The degradation of cross-linked polyethylene (XLPE) insulated power cables because of water tree growth continues to be a challenge in power cables. Water trees (electrochemical trees) are a known verity that can reduce the breakdown strength of XLPE insulated cables. It is a tree-shaped bush-like structure that can develop in polymeric insulation under the influence of moisture and electric field. The ability to retard the growth of water trees can be evaluated using the accelerated ageing tests procedures such as the SANS 1339. This paper presents a procedure that comprises of three diagnostic techniques for evaluating the presence of water trees in XLPE power cables. It is shown that tan delta measurements, isothermal relaxation current (IRC) and return voltage measurement (RVM) are valuable diagnostic tools capable of determining the growth of water trees.