Long term testing of water tree retardant crosslinked polyethylene cable

There is a need for cables with water tree retardant (WTR) properties to increase confidence in long service life, particularly as cables can suffer mechanical damage during installation or service with treeing as a consequential result. Such a concern has been expressed by the Regional Electricity Companies (RECs) who are considering a change from paper to polymeric cables for medium voltage (MV) distribution. Long term testing is considered advisable to prove the permanence of the WTR and demonstrate the improved reliability needed to provide long service performance, particularly with regard to the growth of vented trees. The testing philosophy for such an assessment is being investigated by a number of workers worldwide and current European studies are leading towards test regimes with a 2 year duration. The authors describe the work carried out and give the results obtained in the extended test programme on the modified polymer option for WTR. Morphological aspects of water tree growth are discussed