Evaluation of flitch plate losses in power transformers

Although Eddy current losses in flitch plates of large power transformers m ay form a small part of total transformer losses, they are important becaus e they can appear concentrated in a small area and cause hazardous hot-spot s. An analytical method to calculate flitch plate eddy loss is a very usefu l practical guide to a transformer designer, but for high power transformer s, a more accurate analysis by techniques such as the Finite Element Method (FEM) is desirable. A series of 2-D FEM simulations, using a statistical t echnique - orthogonal array design of experiments, have been carried out to find the effect of various factors on the losses in a mild steel flitch pl ate. The procedure for carrying out the experiments and the results obtaine d thereof are presented. The more involved analysis of slotted flitch plate s, has been done using 3-D FEM. Loss and eddy current patterns in mild stee l and stainless steel flitch plates have been studied. In both cases, the e ffect of the number of slots and slot length on the losses is discussed. Ef fect of slots on eddy current pattern is explained. Results of simulation o f laminated flitch plate are presented. The eddy loss distribution obtained by 3-D PEM electromagnetic analysis is used in 3-D FEM thermal analysis to estimate temperature rise of the flitch plate. Verification of 3-D FEM ana lysis has been done by measurement of temperatures on a slotted mild steel flitch plate of a 33 MVA, single phase, 220/132/11 kV auto-transformer. The estimated temperatures have been found to be in good agreement with that o btained by measurements.