And +ve. seq. would be equal to -ve. seq......zero seq. would be zero, refer my paper, " Microprocessor based fault type detection and load balance control of power transformer, using symmetrical components ......."..
Please check the "Westinghouse Power Engineers' Handbook" or the undergraduate text by Stevenson & Grainger (the chapter on Unsymmetrical Faults). Both references are equally good, and should be able to guide you through the calculations.