In order for transmission systems to accommodate more power transfer with less network expansion by building new transmission lines, it can be a good measure to operate under optimal generation direction (GD) under existing networks. In this paper, the problem considering static voltage stability to determine the optimal GD is solved by a PSO algorithm, in which the continuation power flow (CPF) process is used to calculate the loading margin (LM) for each particle. Three objective functions are suggested for different purposes, including maximum loading margin (LM), minimum generation cost, and minimum generation cost and maximum LM as well. In the tests, to validate the effectiveness of the proposed method, the results derived with the respective objectives and from the cost participating factor (Cost PF) approach are made comparison. And, under each GD, with an SVC installation on the specified critical bus, how much the LM that can be increased is also investigated.