Development and implementation of risk indicator for power transformers based on electrical measurements

Any failure of a power transformer can result in serious consequences for a power system. Bushing failures, mechanically damaged windings or deterioration of solid insulation may cause unexpected power line cut-offs and financial losses to a company. Faulty operation of the on-load tap changer (OLTC) caused by increased contact resistance, contact misalignment or broken drive mechanism also reduces reliability. In order to minimize risk, data obtained from various diagnostic tools needs to be interpreted to evaluate the technical condition of a particular transformer, as well as generalized to provide systematic information for asset manager. In this paper, condition indexing is used to develop a risk indicator based on the results of electrical measurements for transformer windings and core, bushings and OLTC. Also results from a case study based on data of different transformers installed in the transmission system in Latvia are provided.