Impact of allocated and unallocated Distributed generation on improvement of transient stability

One of the most important items in transient stability investigation is critical clearing time in power system. In this paper, the proposed criterion to evaluate transient stability is chosen critical clearing time because this criterion is very suitable to show transient stability characteristics in difference position from power system. Critical clearing time is defined maximum time duration that disturbance can be applied without instability in phase angle of main synchronous generators. This paper focuses on the comparing critical clearing time in two situations. In first situation, DGs are set in all the load bus and critical clearing time is investigated. In second situation, DG has been optimally allocated with Particle Swarm Optimization (PSO) method and critical clearing time is investigated.