Analysis of slots in horizontal plates of T-beams in shell-form power transformers

•The paper focuses on an analysis of the use of slots to reduce stray losses of the T-beams in transformers.•No general way to reduce stray losses of the T-beams in transformers has previously been presented.•The results of this research are compared with the values given by an analytical formula.•This research is based on analytical and experimental study.•This research analyzed: rounded/unrounded slots, dimensions of one slot, number of slots.

A systematic analysis of the use of slots to reduce stray losses in the horizontal plates of the T-beams in shell-form power transformers is presented. In the paper, the horizontal plate of T-beams is modeled as a rectangular stainless steel plate subjected to a perpendicular uniform magnetic field generated by a Merritt coil. The results are compared with the values given by an analytical formula for calculating the losses in a stainless steel plate without slots. The following important design alternatives are analyzed and discussed: (1) plates with rounded slots; (2) plates with unrounded slots; (3) effect of width and length of one slot; (4) effect of the distance between slots; (5) effect of number of slots. It has been found that substantial loss reduction can be obtained when drilling a few slots. Measurements of flux densities were done for seven shell-form power transformers. Using the measurements we calculated the losses in the plates using formula. Using the results of the design alternatives the efficiency of the use of slots in plates of real T-beams was demonstrated. Finally, a structural analysis was made to study the impact of slots in an experimental slotted T-beam.