Protection system design and configuration for extreme weather and emergency grid operating states

Protection system design and configuration philosophies are usually focused on delivering reliable, sensitive, and selective protection of grid assets. Following a number of major system disturbances in the early to mid-2000s, however, configuration practices evolved to better consider the impact of protection designs on wider grid reliability. In particular, there was a growing recognition of the importance of relay loadability, grid-generator protection coordination, and generator ride-through on the ability of power grids to avoid blackouts in response to major disturbances. This paper will review the recent experience with, and potential future impact of, extreme weather on short circuit fault characteristics, asset failures, and protection performance. The objective of the paper is to identify key protection design and configuration considerations which can be used to reduce the risk of partial or total system collapse. The paper begins by summarising the common forms of extreme weather and how they have impacted grids around the world. Section 2 focuses on the impact of extreme weather on short circuit levels and fault characteristics. These impacts primarily derive from abnormal generation dispatches, generator curtailment and outages, multiple concurrent scheduled and unscheduled line, cable, and transformer outages, and partial and full substation outages. The third section reviews past experience with extreme weather events and protection design philosophy. It gives specific reference to communications system redundancy, circuit breaker failure (CBF) designs considering low circuit breaker gas pressure in extreme cold, and relay microprocessor performance when ambient temperature exceeds device rating. The final section discusses system protection considerations including load-shedding, cascade tripping, power swings, and system defence plans as well as presenting methods for identifying potential protection issues due to extreme weather.