Large power transformer-based stray-field loss modeling and validation

A series of transformer-based benchmark models, referred to as Problem 21 Family, are well established to model stray-field loss generated in the structural components of large power transformers. The configuration of the benchmark family, the engineering background of every member model, and the typical measured and calculated results for each model is presented. The new developments of Problem 21, such as the extension to model the saturation state, the electromagnetic behavior inside the laminated sheets, and the variation of iron loss with the excitation current, are highlighted.

I. INTRODUCTION

The stray-field loss and local overheating problems are quite challenging to the electromagnetic design and analysis of large power transformers, especially for UHV (ultra HV) and EHV (extra HV) power transformers due to the requirement of very high reliability. The stray-field losses are generated in various passive conducting components, composed of magnetic, non-magnetic, isotropic and anisotropic material. The problem involves non-linearity, eddy current and/or hysteresis phenomena inside a large 3-D solid or laminated geometry with very thin penetration depth. Moreover, there is additional iron loss which is caused in the laminated sheets by the normal leakage flux. The major difficulty coming from the experiment is that it is difficult to separate the stray-field loss from the measured total power loss.