Analysis and Improvement of the Plant Health Index Used by Eskom to Assess the Condition of the Power Transformers in its Distribution Fleet.

There 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…