Analysis and Improvement of the Plant Health Index Used by Eskom to Assess the Condition of the Power Transformers in its Distribution Fleet.
AbstractsThere are 4359 transformers installed on Eskom's (Africa's largest utility) distribution network. The transformers range from 1MVA to 160MVA units within a voltage range of 2.2kV to 132kV. An ideal transformer health assessment is based on four parameters being the paper life, dissolved gas analysis, condition of the auxiliary components and electrical diagnostic tests. At present there is limited availability to assess the last two parameters, and DP data is also inconsistent. As a result each Distribution Operating Unit employs the use of the Plant Health Index (PHI) as an indicator of the condition of the transformers on their network. The Plant Health Index uses oil sampling data such as dissolved gas analysis, moisture in oil, electric strength and degree of polymerisation to rank the transformers into four categories, namely: low risk, low to medium risk, medium risk and high risk. The index makes use of the data most readily available to the operating units and the accuracy of the ranking system is dependent on the quality of the transformer information captured. This paper is an analysis of the current PHI, and provides insight into its drawbacks and plots a path forward for the utility with the goal of identifying unhealthy plant early enough to address the problem and prevent in service failures.
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