An automation scheme for emergency operation of an industrial park

Abstract

Many modern industrial plants are designed to operate as a microgrid equipped with local generation. Under normal conditions, the plant is connected to and often mainly supplied by the utility's network. However, during a disturbance on the utility side, it may island from the grid and continue supplying its load using available on-site generation. When local generation is not sufficient to supply the entire load (which is often the case), part of the non-critical loads must be shed so as to ensure that the remaining critical loads receive the required quality of service. The decision to island and the amount by which the load must be curtailed are determined based on the values of the frequency/voltage and their rates of change. In this paper, we first propose a hybrid undervoltage/under-frequency islanding scheme for an industrial park consisting of multiple substations each supplying one or more industrial plants. It is assumed that once the park is islanded from the grid, the substations are instantly formed into multiple islands where all non-critical loads are automatically disconnected. This is done to ensure that individual islands are not affected by potential instability of neighboring networks. However, once the individual islands are stabilized, it is possible to share their available generation capacities to maximize the total load served. This would mean connecting one or more islands together to form bigger ones. We formulate this as a network reconfiguration problem that tries to maximize the amount of load served by reconfiguring the network topology and using backup energy resources. The problem is solved and analyzed for a simplified version of an industrial park, both at steady state and during transients.