The leakage current as a diagnostic tool for outdoor insulation

In order to reduce pollution effects, utilities perform costly maintenance jobs that become very excessive and sometimes ineffective because they are not applied on time. To make a more efficient use of human and material resources, it is necessary the use of diagnostic tools. In Mexico, since 1994, the national utility CFE uses monitoring systems for detecting the leakage current in power lines for the diagnosis of outdoor insulation. The leakage current magnitude which causes an insulator flashover due to contamination depends on its shape, material and design. However, insulator flashover occurs around the same leakage current magnitude. Based on laboratory experiments and on field experiences, the Electrical Research Institute (IIE) has classified the leakage current magnitude in five ranges. In the same way, IIE establishes five flashover risk levels that represent some maintenance action that, the user must perform. It is clear that, insulators with different shapes will have different risk levels for the same range of leakage current. Therefore, for the most common insulators used in Mexico, a relationship between the leakage current ranges and flashover risk levels was established. When the leakage current is continuously monitored, it is possible to generate an alarm about the probability of a dangerous flashover risk level; it is also possible to recommend the necessary maintenance actions. This paper summarizes the field and laboratory experiences obtained with the measurement of the leakage currents. Flashover risk levels with maintenance actions associated are also proposed. This classification could be used in the diagnostic of outdoor insulators in power lines.