A unified approach for processing unbalanced conditions in transient stability calculations

A unified approach has been proposed in the paper for processing unbalanced operating conditions in transient stability calculations. The suggested method combined advantages of both abc phase coordinates and 012 sequence coordinates. The former is used to describe faults since it is suitable to modeling simultaneous faults and the latter is used for time simulation for its sparse nature. Novel fault description and coordinate conversion formulation is presented. The equivalent positive sequence bus admittance matrix is derived for interface with generators in stability simulation. With the new method, the sequence network constitution can be avoided; multiple and simultaneous faults and element parameter unbalance can be simulated easily; and the sparse technology can still be applied for study efficiency. Computer test results show clearly the effectiveness and efficiency of the new method.