The impact of load-shedding reaction time on power system stability

Industrial electrical power systems are strongly depending on their electrical power supply. In the Oil & Gas industry a loss of power can generate huge financial losses. For that reason it is usual to have an own power generation connected to the industrial grid. Sudden loss of generated power e.g. trip of a generator, but also loss of a big load is a threat for the system stability. For such contingencies a fast automatic load-shedding system re-establishes the balance of generated power and loads. This paper discusses the impact of the reaction time of the load-shedding after a loss of generated power. Also the opposite scenario, shedding of generators after a trip of a big load, is outlined. Compared to a public power grid the system inertia in industrial power systems is relatively small hence an imbalance of production and consumption leads to a big frequency deviation very fast. The paper shows the necessity of a fast load-shedding and considers the available spinning reserve of the connected generators. Based on simulation results and practical experiences guidelines are provided how to determine the expected frequency deviation and how spinning reserve can be considered for an efficient load-shedding.