Experimental Evaluation of Protecting High-Voltage Electrical Transformers Using Water Mist with and without Additives

Suppression of high-voltage (HV) electrical fires is difficult because it requires fire-extinguishing agents with good isolation properties as well as high fire-suppression efficiency. In the work presented herein, water mist with and without various water mist additives (WMAs) was utilized to suppress HV transformer oil fires. The WMAs included ionic alkali-metal salt and fluorocarbon surfactant, and nonionic hydrocarbon and fluorocarbon surfactants. At the same concentration, the surfactants were more efficient at extinguishing fires compared with the alkali-metal salt. The fluorocarbon surfactant was more efficient at extinguishing fires than the hydrocarbon surfactant, achieving flame extinction in 18 % of the time required when using natural water (NW). Besides, the effects of WMAs on the insulating properties of the water mist were studied. The gap breakdown test showed that the NW mist could increase the breakdown voltage of air by up to 5 % at 70-cm gap distance. Comparatively, the nonionic WMAs did not affect the insulating property of the NW mist, with the mist containing 1.0 % ionic KHCO3 solution enabling a reduction of up to 16 % in the breakdown at 70-cm gap distance while increasing the leakage current of the simulated insulator by up to 250 % at its nominal voltage. Finally, field tests were performed where NW mists were discharged onto a charged 220-kV high-voltage transformer. This study proves that NW mist and mists with nonionic WMAs are suitable for protecting HV electrical equipment, having important implications for extending the applications of water mist.