Water treeing is one of the main forms of degradation of XLPE insulation used in medium-voltage and high-voltage cables when the insulation is exposed to water. Water trees gradually reduce the electrical breakdown strength of cables and are one of the main causes of failures of early designs of extruded medium-voltage cables after only five to fifteen years in service. As partial discharges are not involved in their growth, water trees have proven to be difficult to detect in cables in situ using non-destructive techniques. However, insulation containing water trees has lower insulation resistance and higher dielectric losses and the measurement of the resistance and these losses is being used to assess the condition of the insulation. The insulation resistance and dielectric loss are sensitive to the measurement technique and also to parameters such as temperature, voltage, frequency and the severity of the water treeing. There are presently several techniques available commercially. Electrical utilities presently have a choice of measurement techniques but generally lack the expertise to make informed decisions regarding which technique to use and, more importantly, how to interpret the data from such tests to assess the condition of their cable system. SC D1 identified the need for a guide to inform cable system owners and users about water treeing and to inform them what tests were available to detect treeing in cables. A joint WG was set up in liaison with SC B1 to prepare such a guide. This brochure is the result of the JWG and provides a review of the measurement techniques available to detect and measure the extent of water treeing in XLPE cable insulation and discusses the interpretation of data, including a discussion of the limitations. This independent review will help electrical utilities, or other users of XLPE insulation subjected to wet conditions, to evaluate non-destructive water tree detection techniques and give guidance on how to interpret the data obtained from such tests.
Non destructive water-tree detection in XLPE cable insulation
MONTANARI, GIAN CARLO;
2012
Abstract
Water treeing is one of the main forms of degradation of XLPE insulation used in medium-voltage and high-voltage cables when the insulation is exposed to water. Water trees gradually reduce the electrical breakdown strength of cables and are one of the main causes of failures of early designs of extruded medium-voltage cables after only five to fifteen years in service. As partial discharges are not involved in their growth, water trees have proven to be difficult to detect in cables in situ using non-destructive techniques. However, insulation containing water trees has lower insulation resistance and higher dielectric losses and the measurement of the resistance and these losses is being used to assess the condition of the insulation. The insulation resistance and dielectric loss are sensitive to the measurement technique and also to parameters such as temperature, voltage, frequency and the severity of the water treeing. There are presently several techniques available commercially. Electrical utilities presently have a choice of measurement techniques but generally lack the expertise to make informed decisions regarding which technique to use and, more importantly, how to interpret the data from such tests to assess the condition of their cable system. SC D1 identified the need for a guide to inform cable system owners and users about water treeing and to inform them what tests were available to detect treeing in cables. A joint WG was set up in liaison with SC B1 to prepare such a guide. This brochure is the result of the JWG and provides a review of the measurement techniques available to detect and measure the extent of water treeing in XLPE cable insulation and discusses the interpretation of data, including a discussion of the limitations. This independent review will help electrical utilities, or other users of XLPE insulation subjected to wet conditions, to evaluate non-destructive water tree detection techniques and give guidance on how to interpret the data obtained from such tests.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
