Features of Main Power House Transformers for Queenston Plant

Interest in the main step-up transformers for the New Queenston generating station of the Hydro-Electric Power Commission of Ontario centers largely about their great physical size and the heavy short-circuit currents to be dealt with. Physically they are the largest single-phase transformers in operation today. In spite of the fact that they are for 25-cycle service, to our knowledge even their kv-a. rating is exceeded by only one bank of single-phase transformers now in operation, namely, the 70,000-ky-a., 60-cycle bank at the Colfax Station of the Duquesne Light Company. Figures are given for the weights and dimensions of these transformers and their component parts as well as the performance calculated from test results. The mechanical forces in 25-cycle transformers are inherently high because of the relatively large number of turns necessary to develop the voltage, and because of their relatively low impedance to the flow of short-circuit currents. As the forces depend upon the square of the ampere-turns, it is evident that both the above conditions contribute materially toward increasing the forces. To understand the bracing necessary to withstand the electromagnetic forces developed under short-circuit conditions, it is necessary to understand the nature of these forces as well as their magnitude.