Four-phase transmission systems and estimation of effectiveness of their application for power transmission from the Three Gorges Plant to East China

New type four-phase AC transmission systems (TS) allow a radical improvement of the technical, reliability, environmental and economic characteristics of bulk power transmission over long and very-long distances. Four-phase AC with 90° phase shift is the basis of these four-phase TS. Practical application of four-phase TS requires the construction of phase-converting transformers to transform three-phase AC into four-phase AC and vice versa which offers no fundamental difficulty. Ther effectiveness of the application of four-phase TS is illustrated by solving the problem of power transmission from the Three Gorges hydroelectric power plant to Eastern China over distances upwards of 1000 km. The four-phase 1150/√3 kV TS have unquestionable advantages on the strength of technical, economic, reliability and environmental characteristics in comparison with ±750 kV DC TS, double-circuit 1150 kV AC TS and single-circuit 1150 kV heightened SIL TS