1.1 Problem definition

In interconnected power systems, the forced outage of one of the main generating units would lead to unstable voltage profile at a number of B. B.s, that definitely does not meet the power quality regulations. This unsatisfactory operating condition may result in the disconnection of a number of loads according to certain priority list, or to reschedule the operation of existing units. Another solution could be the reconfiguration of the network. These solutions are really costly and would be penalized. The introduction of prescheduled controlled (e. g. fuel cell) or non-controlled (PV or wind) DG will offer a better solution.

1.2 Scenario of voltage collapse

Figure (1) shows the schematic diagram of an interconnected power system; consisting of several generating units and voltage levels. This system has been proposed by as test system for studying the problems associated with interconnected networks installing distributed generation[6]. The installed capacity of this system is 12 GW. The voltage collapse is initiated by the following events:

1- A ramp change of loads connected to the nodes N204 and N206 to 80% by rate 20%/min.

2- Unit M4 outage is recorded at t=3min.

3- Double line outage of V451 and V452 (which connect nodes N4 & N5) at t=5 min.

4- Line outage V2_3 (which connect nodes N102 & N103) at t=6 min.

This scenario is a common practice in interconnected power systems combining generation units and distribution networks supplying a variety of load types. Moreover, the ramp change of loads at two non-adjacent nodes reflects a real slice of dynamic loads. On the other hand, it gives the proper way to simulate the added DG at these nodes in order to test the voltage collapse problem.