Abstract:  By simulating the cold spray test with different number of nozzles falling off, the influence of explosion, high- temperature and other special factors on the foam spray fire extinguishing system of UHVDC converter transformer was investigated, and the failure analysis of the foam spray fire extinguishing system was also carried out. The results showed that the working pressure, effective spray amount and coverage area of the spray nozzles were significantly affected by the proportion of falling nozzles. When the proportion of falling nozzles was more than 20% , the working pressure and effective spray amounts of nozzles were lower than the standard requirements. Meanwhile, the spraying range dropped and the spraying area shrank, thus the full coverage cannot be formed. There was even a risk of an extended fire caused by a jet of water after the nozzles falling off. In this case, the scheme of enhancing the liquid supply flow of the system was easy to form a blind area for fire extinguishing, which cannot meet the fire extinguishing requirements. 

Key words:  , UHVDC converter transformer, fire extinguishing system, foam spray, failure analysis