Parallel Wincings in Multiwinding Transformers [includes discussion]

The growth in size and complexity of power systems has resulted in a trend toward multiwinding power transformers. A frequent consideration in the application of these multiwinding transformers is the possibility of paralleling secondary windings. This paper is a study of the impedance relations and winding arrangements necessary to secure proper paralleling. Use is made of both equivalent circuits and the fundamental transformer equations. The mesh network, although unwieldy for many circuit problems is ideal for visualizing the suitability of specific winding arrangements for paralleling. If the impedance links between the supply terminal and all the secondary terminals are equal, the secondaries will divide load equally when paralleled. While equivalent circuits can be used to establish the impedance relations for transformers with relatively few windings, the n-winding transformer can be handled more effectively by returning to the transformer equations. Although the treatment of the problem is presented in terms of a single supply winding with a multiplicity of paralleled secondaries, it applies equally well to a group of paralleled supply windings feeding a single loaded secondary.