Transient stability studies of a 'vertical-to-horizontal' transformation of power systems on a real time digital simulator

A large-scale implementation of distributed generation (DG) in the power system can cause a gradual transition from the current 'vertically-operated power system', which is supported mainly by several huge centralized generators, into a future 'horizontally-operated power system', having also a large number of small to medium-size distributed (renewable) generators. In this paper the transient stability of a power system that undergoes such a ' vertical-to-horizontal' transformation is studied on a real time digital simulator (RTDS). A 9-bus power system with 3 centralized generators is used as a test system. Scenarios to simulate the 'vertical-to-horizontal' transformation of the test system are developed by shutting down centralized generators in the test system and by replacing them with DG units implemented in the load buses. The DG units are implemented as converter-connected units, synchronous machines, or a combination of those. To study the transient stability in each scenario, 3-phase temporary faults are applied in order to determine the critical clearing time (CCT)