The increasing application of non-linear loads in power system causes additional losses in transformers resulting in premature damage. Manufactures and users of transformers realise the importance of this phenomenon and it is vital to adopt a procedure to prevent it thereby enhancing the reliability of power system. To achieve this, the most common method is derating of transformers. This paper intends to review derating of transformers under nonsinusoidal operation, for which all available approaches are classified into four major methods including IEEE recommended, analytical, experimental and finite elements based method. For each method, the fundamental theory, significant factors related to derating, test techniques as well as advantages and disadvantages are discussed. The methods are then evaluated and compared with each other from different points of view. Moreover, the overall trend of a more precise derating method is suggested. This review clarifies the research areas which require attention in the future to advance the subject.

Supplying non-linear loads causes increased losses in transformers which eventually leads to their reduced life spans. Therefore, transformers are derated in order to protect them against premature loss of life. To do this, load losses including ohmic loss and winding eddy current (WEC) loss need to be estimated. This study suggests an improved analytical approach using finite element method (FEM) which includes all material characteristics and geometrical structures in order to calculate WEC loss under non-sinusoidal load current in each winding individually. By adopting this procedure, harmonic loss factor as a dominant parameter in transformers derating is estimated. By emphasising the region in which the maximum WEC loss occurs, an additional factor (F MECL) based on the physical phenomena involved is introduced using FEM. On the basis of the aforementioned concepts, a new relationship is presented for transformer derating. Ultimately, the suggested method and the IEEE standard are applied to derate a distribution transformer and the results are discussed. In addition, the proposed method is validated using a thermal model and its advantages over the IEEE derating method is presented.

The “Thorn Hill Section” is an amazingly complete and well exposed section of rocks that has served at least four generations of geologists as a reference for early Cambrian through early Carboniferous stratigraphy of the Southern Appalachians. Eastward from War Ridge along 8.8 mi (14 km) of U.S.25-E, across Clinch Mountain to Poor Valley Ridge, Grainger County, Tennessee, virtually every unit between the Rome and the Grainger formations in the Southern Appalachians is exposed in the 10,912 ft (3,326 m) thick sectio (Fig. 1). The section is bounded by two major thrust faults-the Copper Creekfault and the Saltville fault; the Rome Formation is the hanging wall forboth faults. Most of the section is embraced by the Avondale, 7½-minute topographic quadrangle with the remainder on the Dutch Valley, 7½-minute Quadrangle. The stratigraphic descriptions given here are synopses from Walker (1985). The stratigraphy here represents a westward thinning edge of a thick wedge dof Paleozoic sedimentary rocks whose history is recorded in three stratigraphic sequences bounded by unconformities of regional extent (Fig. 2). Sequence I embraces Cambrian through Early Ordovician, Sequence II the middle Ordovician through Early Devonian, and Sequence III Late Devonian through Early Mississippian. The stratigraphic descriptions given here are synopses from Walker (1985). The stratigraphy here represents a westward thinning edge of a thick wedge of Paleozoic sedimentary rocks whose history is recorded in three stratigraphic sequences bounded by unconformities of regional extent (Fig. 2). Sequence I embraces Cambrian through Early Ordovician, Sequence II the middle Ordovician through Early

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