Fault diagnostics in oil filled electrical equipment: Review of duval triangle and possibility of alternatives

Fault diagnostics, identification and location in oil filled electrical equipment has been a challenging task which has been under critical focus of scientists in decades. One of the most successful methods of fault diagnostics and identification in such electrical equipment is the Duval triangle, which uses 3 fault gases; methane, ethylene and acetylene. The percentages of these gases are calculated and used to represent the sides of the triangle in a triangular coordinate system. Similar faults map onto a specific region of the triangle. Parallel lines representing the gas percentages are drawn from the sides to intersect at a particular point which identifies the fault. But is there a possibility of using different combination of gases? There are seven gases mainly used for fault diagnostics and identification: hydrogen, methane, acetylene, ethylene, ethane, carbon monoxide and carbon dioxide, thus taking three gases at a time, there are thirty five different triangles. According IEC 60599 standards faults in oil filled electrical equipment are grouped into five categories; partial discharge(PD), electrical discharge of low energy(D₁), electrical discharge of high energy(D₂), thermal fault in paper and/or oil with temperature below 700°C (T₁ & T₂) and thermal fault in oil and/or paper with temperature 700°C above (T₃). This research aim is to find out the possibility of an alternative triangle(s) to Duval by mapping one hundred and seventeen fault cases visually inspected and documented in IEC TC 10 databases. The faults are located in a triangle and analysed whether they coalesce on a particular region. Further for each fault class, standard deviation is calculated. If this deviation is less than that calculated for Duval triangle, then that fault is identifiable by that triangle. Also investigated for a particular fault class is whether equipment type has any effect on the fault location within the fault mapped region. From the results, there are some faults which can be better identified using alternative triangles, and that equipment type has no effect on fault localisation. The accuracy of triangular fault identification technique is also compared to that of IEEE key gas and IEC gas ratio techniques.