Analysis of lightning-caused distribution transformer failures

Lightning-caused transformer failures in distribution systems

“…These field results contrast with the conclusions of earlier studies conducted in Australia [3], [4], Norway [5], and the USA [6] - [12], according to which the installation of secondary arresters is an important measure for reducing transformer failure rates. However, they are in line with the findings from computer simulations, in which not only the characteristics of the utility distribution networks but also the electric behaviors of the main system equipment and components (transformers, surge arresters, insulators, and crossarms) were reproduced as closely as possible [1], [2]. …”

“…The analysis of the dismantled transformers revealed that in four cases (one in Santiago and three in São Francisco) the point of failure was on the LV winding and in three of these cases the transformer was protected by secondary arresters. The analysis of the hypothesis of the failures on the LV side due to direct strikes to the primary circuit was presented in [1]. These field results contrast with the conclusions of earlier studies conducted in Australia [3], [4], Norway [5], and the USA [6] - [12], according to which the installation of secondary arresters is an important measure for reducing transformer failure rates.…”

“…As nearly 75 % of the failures occur in rural areas, a specific section of a 25 kV rural network, in which a transformer protected with LV arresters was damaged [1], was considered in most of the simulations. This network section is shown in Fig.…”

“…MV surge arresters, whose residual voltage is about 80 kV, were represented through their voltage-current curve provided by the manufacturer. Additional details of the simulations can be found in [1], [2].…”

“…The distribution transformer failure rate of AES Sul, a power company whose concession area is partly located in this region, is about 6 % per year in that area. AES Sul supplies energy to 118 cities and serves more than one million customers with over 54,000 installed distribution transformers [1]. All transformers (15 kV and 25 kV) are protected with medium voltage (MV) arresters, but over the period 2003-2011 (8 years), approximately 47 % of the failures have been attributed to lightning [2].…”