Power transformers are subject to several stresses and changes in their operational life, so that they will eventually deteriorate to the point that it fails or must be replaced. Power transformer maintenance allows this aging process to be quantified and tracked to avoid failures. Utilities and service companies schedule power transformer maintenance programs to assess their condition, increase its service life, and provide safe and trouble-free operation.

Power transformer maintenance includes periodic electrical testing of different parameters of the transformer, being common the periodic checking of some key magnitudes such as turns ratio, excitation current, polarization index, insulation resistance, tandelta, winding resistance, short circuit impedance, etc.