Using dynamic load models to compute electromechanical transients in distributed generation-enabled industrial microgrids

Abstract

Large-scale construction of distributed generation (DG) facilities by industrial enterprises helps cut the costs of production and improve competitiveness. Asynchronous motors (AM) and synchronous motors (SM) represent the bulk of load in industrial microgrids. Electromechanical transients in such grids are shared between generator sets (GS) of DG facilities and the load; the parameters of such processes are in significant correlation with the GS and load parameters. This paper discusses the key peculiarities of calculating the transients in cases of severe emergency-related disturbances that are associated with deep and long-lasting voltage sags. Calculations show that the initial critical active power deficit, which substantially alters the quality of the transient, depends mainly on the load composition and on the total power of running motors. It further proves the need to make adjustments for the algorithms and settings of power system protections deployed in the external and internal grids, and for the settings of the GS / load protections and automations. The paper proceeds to present the causes and consequences of voltage collapse, and concludes with recommendations on the development and implementation of contingencies. It discusses how load transients affect the normal operation of generator sets at DG facilities, why the latter could switch to asynchronous operation, and what that could entail. The paper lists permissible simplifications of dynamic load models usable in transient calculations; it also demonstrates the key principles of AM equivalence.