Comparative Study of Grain Oriented and Non–Oriented Electrical Steels in Magnetic Shunts of Power Transformers

This paper presents a comparative study of the use of grain oriented electrical steels (GOESs) and non-oriented electrical steels (NOESs) in magnetic shunts of power transformers. The electrical steels are analyzed and compared in magnetic shunts of a real 190 MVA three-phase, three-legged power transformer. 3-D finite element (FE) simulations are carried out to evaluate the stray loss and thermal impact of the GOES and NOES shunts in the power transformer. The shunts are modeled utilizing their magnetization properties and the structural elements of transformer are modeled utilizing surface impedance boundary conditions. To validate the simulation results the load losses are measured and estimated without and with magnetic shunts and they are compared with FE simulation results. A difference of 9 % is calculated between measurements and simulations of stray losses in transformer with shunts. Finally, a cost analysis is carried out to compare the material and manufacturing costs of GOES and NOES shunts. The NOES shunts produced 9 % more stray losses, 80 % more eddy current losses, and they increased 2 % the weight of transformer compared with GOES shunts. A maximum material cost reduction of 26 % is obtained using NOES shunts. The transformer did not present temperature problems with the use of NOES shunts. The results presented in this paper show that NOES shunts are as effective as conventional GOES shunts in reducing the stray losses, temperature, and costs in power transformers without putting in risk their operation.