Protection and Control of IBR Dominated Power Systems

Protection and control systems have been designed on the principle of protecting specific protection zones via protection functions appropriate to the needs of the specific protection zone. Over the years, protection functions have been designed by considering the characteristics of legacy power systems, i.e. the characteristics of a synchronous machine dominated power system. Salient characteristics of the legacy power system are: (a) high fault currents, (b) fault current with high levels of negative and zero sequence currents. These characteristics are changing as the system moves into an inverter dominated system with the characteristics of: (a) reduced fault currents and (b) suppression of negative and zero sequence components of the fault currents. These changes affect the performance of protection and control systems and increase possibilities of relay mis-operations. Annual reports by NERC provide many examples of the shifting characteristics and instances of relay mis operations. This paper describes the effects of IBRs on legacy protection and control and provides solutions to the problem. It describes a new relay based on dynamic state estimation which is immune to the characteristics of IBR dominated power systems.