This index assesses the risk of a partial or complete breakdown of the electrical properties of the solid or liquid insulation. Transformers contain regions of high electrical stress. The presence of contaminants such as water or gases in the oil or paper, reduce their dielectric strength. In the case of low dielectric strength, changes in the operation of the transformer, such as a sudden increase in load, increases the risk of a complete breakdown of the insulation and formation of a fault current.
There are a number of indicators to determine the dielectric strength. The water content of the paper (WCP), the water content of the oil (WCO), and the degree of polymerization (DP) are derived from measurements made by the HealthSense using Aurtra's algorithm. Dissolved gas analysis (DGA) provides information on the levels of gases and contaminants in the oil which can indicate the presence and growth of breakdown.
The Dielectric Risk Index graph gives a succinct view of how the risks scored in each sub-index is affecting the major index.
The Dielectric Risk Index is assessed with the combination of the following sub-indexes related to the insulation condition as shown in the graph:
High levels of hydrogen indicate the risk of partial discharges resulting from dielectric breakdown .
 Lelekakis, Nick, et al. “Ageing Rate of Paper Insulation Used in Power Transformers Part 1: Oil/Paper System with Low Oxygen Concentration.” Ieee Transactions On Dielectrics And Electrical Insulation, vol. 19, no. 6, 2012, pp. 1999–2008.
 Lelekakis, Nick, et al. “Ageing Rate of Paper Insulation Used in Power Transformers Part 2: Oil/Paper System with Medium and High Oxygen Concentration.” Ieee Transactions On Dielectrics And Electrical Insulation, vol. 19, no. 6, 2012, pp. 2009–2018.
 IEEE, "Guide for Diagnostic Field Testing of Fluid-Filled Power Transformers, Regulators, and Reactors." IEEE Std C57.152-2013, vol., no., pp.1-121, 21 June 2013.
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 IEEE, "Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers." IEEE Std C57.104-2008 (Revision of IEEE Std C57.104-1991), vol., no., pp.1-36, 2 Feb. 2009.
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