Field Experience With a Condition-Based Maintenance Program of 20-kV XLPE Distribution System Using IRC-Analysis

Abstract

Asset management strategies are amongst the most important tools to address the economical, reliability, and operational requirements of extensive distribution networks in the environment of increasing deregulation. The key objectives are full utilization (i.e., exploitation of available network reserves), investment for expansion, and maintenance including asset replacement. The paper will focus on the methodology and the results of a condition-based preventive maintenance concept as part of the overall asset management strategy. As an example, the condition of 20-kV XLPE service aged cables of a German distribution grid is evaluated and categorized. The "isothermal relaxation current analysis" (IRC-Analysis), which is a nondestructive and nonpartial discharge diagnostic method, is used to assess the cable conditions. Obtained categories are combined with the impact of one distinct cable on local system reliability in order to optimize replacement strategy. This concept called "reliability centered maintenance" is applied by the author's company Lechwerke AG (LEW AG). As a result, the annual budget to guarantee service quality could be reduced substantially.

Individual failure rates for transformers within a population based on diagnostic measures

“…For example, the failure rate has been used to link maintenance and reliability to develop a reliabilitycentered asset maintenance method [21]. This method has been applied to 20-kV XLPE service aged cables [22], or to wind power plants [23,24]. The failure rate is also an input parameter in riskbased maintenance optimization [25] or to demonstrate the effect of imperfect preventive maintenance [26].…”

Cable Diagnostic Focused Initiative

“…It measures the time constant of trapped charges within the insulation as they relax by measuring the discharge current over time after the application of a prescribed DC voltage [55], [56].…”

Condition assessment of XLPE insulated cables based on polarization/depolarization current method

“…It is quite suitable for the diagnosis of the XLPE cable insulation. According to the measured A-factor, the cable condition can be classified as good, middle, old and critical [24,25]. In experiments, many scholars use the parameter to assess the cable condition, only to find that the diagnosis results are seriously influenced by the accuracy of the measured current [26,27].…”