Share Your Thoughts: Send comments to pemeic@ieee.org

Share Your Thoughts: Send comments to pemeic@ieee.org Duncan WilsonReaders are encouraged to share their views on issues affecting the electric power and energy profession. Send your letters to the editor-in-chief at pem-eic@ieee.org. Letters may be edited for publication.August 2019 Power System Disturbance in the United KingdomTwo articles in the May/June 2023 “Power Outage” issue mention the 2019 power system disturbance in the United Kingdom. However, neither of the articles provided much detail on this disturbance, which occurred on 9 August 2019 and caused approximately 1 million customers to lose power. The sequence of events that happened on that summer evening can be summarized as follows:

A lightning strike occurred on a 400-kV transmission circuit at 4:52 p.m.

Protection systems cleared the resultant fault, and the line returned to normal operation.

Coincident with the lightning strike, there was a loss of approximately 150 MW of small embedded generation connected to the distribution network due to the operation of vector shift protection.

Immediately following the lightning strike, (a) the Hornsea offshore wind farm reduced its output to the grid by 737 MW, and (b) the Little Barford combined cycle power plant power station’s 244-MW steam turbine tripped.

The cumulative loss of 1,131 MW of generation caused a rapid fall in frequency that caused a further 350 MW of embedded generation to disconnect due to the operation of the rate of change of frequency protection.

The system operator had automatic backup power available to cater for the loss of the largest infeed of 1,000 MW as required by the applicable security standards.

The generation lost from (a) vector shift protection operation, (b) the two transmission-connected generators tripping, and (c) the subsequent operation of the rate of change of frequency protection totaled 1,481 MW, which was significantly more than the available backup power.

The system frequency fell very rapidly to 49.1 Hz (nominal frequency 50 Hz).

All the backup power that the system operator had available to manage system frequency was utilized to arrest the frequency fall, and the frequency began to recover.

Just as the frequency began to recover, there was a further trip of a 210-MW gas turbine at Little Barford.

All of the available backup power had already been deployed, and the cumulative generation loss resulted in the frequency then falling to a new low of 48.8 Hz, and secondary backup systems operated to disconnect approximately 5% of the system demand. This load shedding enabled the frequency to recover.

A total of approximately 1 GW of the system’s demand was disconnected during the disturbance. National Grid’s full report on the disturbance can be viewed in the National Grid ESO LFDD 09/08/2019 Incident Report at https://www.nationalgrideso.com/document/152346/download. —Duncan Wilson Digital Object Identifier 10.1109/MPE.2023.3288581Date of current version: 21 August 20231540-7977/23©2023IEEEShell LubricantsCoverSKM Power ToursMastheadDigsilentGrid communicationsS&C ElectronicHendrixPS CADPES supporting our members worldwideGrid data transportA Modern Communications Platform to Enable the Modern GridPrecise Time, All the TimeHierarchical Distribution Grid IntelligenceData Privacy for the GridNext-Generation Power Substation Communication NetworksSynchro- WaveformsShare Your Thoughts: Send comments to pemeic@ieee.orgIn memoriamMeet the candidatesIEEE PES PESOPES meetingsAdvertisers indexIn my viewIEEE PES PublicationsAspen