An analysis of the August 9th 2019 GB transmission system frequency incident

This paper presents an analysis of the August 9th 2019 GB transmission system frequency event which saw 1.1 million customers disconnected from the electricity system. Using publicly available data and dynamic system simulation, a detailed event timeline is presented that very closely matches the observed system response on the day. This allows for an independent assessment of system operation and response services during the incident, and of various uncertainties around what happened. A number of alternative scenarios are modelled that show how better response provision or better adherence of distributed generation to the latest protection setting guidance could have avoided the disconnection of demand. A thorough discussion of the key lessons that can be learned from the system event is given. This identifies issues for multiple stakeholders to address including the Electricity System Operator, Distribution Network Operators, generator owners and regulators.