The effects of unbalances caused by untrasposed EHV transmission lines and unbalanced loads in power system analysis have been thoroughly analyzed and determined;In the steady-state analysis, it is concluded that three-phase representation of the system is necessary and the unbalance analysis needs to be performed at least once under specific system conditions to ensure a safe and normal operation of the system. The newly developed method is proved to be an efficient approach to be used in this type of analysis;In the electromagnetic transient analysis, it is concluded that untransposed transmission lines have no significant impact on the transient overvoltages caused by single line-to-ground fault clearing and, therefore, may be represented fully transposed. It is noted, on the other hand, that unbalanced loads can affect the transients and must be included in the analysis. It has been shown, however, that balanced initial conditions may be used to represent the network and the loads in the system.