+Ve and -Ve sequence network

+Ve Sequence Network

 In simple words +Ve sequence voltage means normal three phase voltage with correct phase sequence, -Ve sequence voltage means three phase voltage with reverse phase sequence and for zero sequence voltage all three voltages are equal and in phase. Thus +Ve sequence impedance is the impedance offered by power system when +Ve sequence voltage is applied to the system. Obviously this network will have voltage sources at respective locations. Such system we have discussed earlier.

-Ve Sequence Network

All synchronous generators produces voltages of correct phase sequence only. Also it is common logic to consider that line impedance or transformer impedance does not depends upon phase sequence of the voltage applied to it. Thus generally –Ve sequence network is equivalent to +Ve sequence network except voltage source removed from +Ve sequence network.