Developments in fast load shedding

This paper describes a smart load shedding scheme that monitors plant loads, plant generation and generation/utility supply reserve to select the minimum number and lowest priority loads for shedding. The paper first gives an overview of industrial power system dynamics undergoing loss of supply contingencies and existing load shed practices, such as undervoltage, underfrequency, frequency rate of change or contingency based load shedding. It will examine the impact of speed of load shedding on stability. The paper goes on to describe a load shed system that continuously calculates the generation reserve available and shed-able load available in real time by acquiring analog power measurements from generators and utility supplies through IEC61850 GOOSE (Generic Object Oriented Substation Event) messaging. This fast load shed scheme uses the reliability and redundancy of modern Ethernet networks and has simplicity compared to traditional systems. Application solutions are presented and analyzed that handle the required data acquisition using communications and protection devices typically present at an industrial facility, along with means to disseminate load shedding commands with sub-cycle speed to thousands of shed-able loads. Actual performance results from such a load shed system are presented.