Adaptive transformer thermal overload protection

This paper is based on a report of the same title, prepared by Working Grou p K3 of the Substation Protection Subcommittee of the Power System Relaying Committee of the Power Engineering Society of the IEEE. The paper begins w ith background information on the causes, measurement techniques, and conse quences of overheating in mineral-oil-immersed power transformers. Then tec hniques for adaptive transformer thermal overload protection based on the r eal-time solution of the transient heating equations are presented. An adap tive overcurrent protection implementation, and the related functional requ irements, are discussed. The equations of Clause 7 of the 1995 IEEE Guide f or Loading Mineral-Oil-Immersed Transformers are used in the analysis, with a slight modification to allow for continuously varying ambient temperatur e.