Minimum headway is one of key factors in railway system operation. Most railway passengers normally expect that a next train will arrive at their platform as soon as possible. Due to economical and safety aspects, headway between two consecutive trains must be kept over its critical value. In this paper, multi- train simulation associated with dynamic load flow program instructed in MATLAB is employed. A 50-km AC railway power system is used for test. This test was conducted by decreasing train headway until voltage collapse occurs. As a result, the minimum train headway that causes the voltage collapse for this test system is 50 s. This confirms that the proposed algorithm can be effectively used to identify the point of voltage collapses in AC railway power systems.