A review of faults detectable by gas-in-oil analysis in transformers

IEC Publication 60599 provides a coded list of faults detectable by dissolved gas analysis (DGA): PD = partial discharges; D1 = discharges of low energy; D2 = discharges of high energy; T1 = thermal faults of temperature < 300/spl deg/C; T2 = thermal faults of temperature 300/spl deg/C < T < 700/spl deg/C; T3 = thermal faults of temperature > 700/spl deg/C. The IEC TC10 databases of DGA results corresponding to faults identified by visual inspection of faulty transformers in service have been presented in a previous paper (see IEEE Elec. Insulation Mag., vol. 17, no. 2, p.31-41, 2001). The present paper reviews these DGA results in a more user-friendly graphical form. It also reviews the DGA results of laboratory models attempting to simulate these faults, as published in the scientific literature or technical reports. The specific case of on-load tap changers (OLTC) is reviewed much more extensively, and separately, since DGA interpretation in this case must take into account the large background of residual gases resulting from the normal current-breaking operation of the OLTC. Particular attention is also given to DGA results related to PDs and low-temperature thermal faults.