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It is because negative sequence impedance of rotating machinety is generally different from that of positive sequence impedance. Change, if necessary, the impedances that represent rotating machinery in the positive sequence network.It is because these devices have only positive sequence-generated voltages. of 3-phase generators and motors in the positive sequence network. The negative sequence network can be readily obtained from positive sequence network with the following modifications : It is also represented by one line diagram and is composed of impedances offered to the negative sequence currents. Negative sequence network: The negative sequence network for a given power system shows all the paths for the flow of negative sequence currents in the system. Motor loads are included in the network as generated e.m.f.For transmission lines, the shunt capacitances and resistances are generally neglected.All resistances and magnetising currents for each transformer are neglected as a matter of.Current limiting impedances between the generator’s neutral and ground pass no positive sequence current and hence are not included in the positive sequence network.Each generator in the system is represented by the generated voltage in series with appropriate reactance and resistance.

While draw­ing the positive sequence network of a given power system, the following points may be kept in view: It is represented by one-line diagram and is composed of impedances offered to the positive sequence currents. Positive sequence network: The positive sequence network for a given power system shows all the paths for the flow of positive sequence currents in the system.