M - to N-phase transformer models in phase co-ordinates

M- to N-phase transformers (M ¿¿ N) are considered in the phase co-ordinate frame of reference. Equivalent circuits are derived for zig-zag, Scott, T-T and star-double-star transformers, and the connection tables are given for use in assembling the nodal-admittance-matrix terms in the usual way for power network analysis. The paper concludes with an example of a polyphase load-flow analysis of a network containing some of these transformers.