Determination of Power Transformer Ratings for the Pennsylvania-New Jersey-Maryland Interconnection

This paper documents procedures to be used by member companies of the Pennsylvania-New Jersey-Maryland Interconnection to establish normal and emergency thermal ratings for power transformers affecting the Interconnection. The method can also be used to select the nameplate ratings of new transformers. Insulation systems containing the older standard kraft papers (55°C rise), and also the newer improved insulation (65°C rise), used after approximately 1958) are both considered. A complete review of the principles, parameters, and limits necessary to determine thermal performance and ratings was undertaken. The rating method was expressed in the form of a computer program, which all companies of the Interconnection have agreed upon, to ensure consistent ratings for any given application of power interchange transformers.