Combined Very Low Frequency and Monitored Withstand Test — How to apply the new way of cable condition assessment

Condition-based maintenance is an important and necessary strategy for coping with today´s asset management requirements for an electric utility system operator. However, this requires an exact knowledge of cable conditions. Testing and diagnostic methods which provide meaningful results and are simple and economical to apply in the field are a prerequisite. The Monitored Withstand Test (MWT) meets these requirements. The MWT consists of a combination of already established methods like a simple Very Low Frequency (VLF) withstand test and a VLF tan-delta diagnosis. The result of such a combination provides the system operators additional information on the cables condition for optimal planning of repairs or replacements to minimize downtimes. Meanwhile the Monitored Withstand Testing is an important part of recently introduced IEEE standards (IEEE400-2012, IEEE400.2-2013). Also this reflects the increasing importance of combined testing and diagnostics. The following article describes the different test methods and highlights the benefits of the combination with the help of a practical use case.