The power transformer is an important element of the power system on a national as well as international level. The different structures and features of the transformer park create the necessity for individual risk assessment to increase the reliability of the power system. This paper presents the early stages of the development of a power transformer technical condition index using the risk matrix method for the power transformer park of Latvia. Power transformer park of Latvia has a large reserve base but it is noticeably aged. The age, regularity of replacement, diagnostic periodicity and other specific features of the power transformer park have to be taken into account during the development of a risk matrix with a suitable mathematical model.