Electric utility grids rely on voltage and frequency stability. A variety of events can cause voltage and frequency instability. A critical characteristic of a grid is its ability to ride through the event which triggered the instability and return to stable operation.
Two recent grid events illustrate the potentially very different effects of events which destabilize grids, the total blackout on the Iberian Peninsula in April 2025 and the PJM “blip” in July 2026.
The Iberian Peninsula event was initially triggered by an unusual frequency oscillation originating from a still unidentified source, followed by a second oscillation approximately 20 minutes later. Operators attempted to stabilize the grid by increasing voltage. Generation trips in southern Spain then removed approximately 2.2 GW of generation, or approximately 7% of active generation. The following combination of overvoltage and oscillations led to cascading inverter trips and frequency collapse.
At the time of the incident, the grid was powered 71% by inverter-based resources (IBR), 11% by nuclear, 5% by natural gas and 13% by other resources. Therefore, the inertial available to stabilize the grid was quite limited. The cascading generation disconnections occurred in less than one minute, resulting in a total blackout which required approximately 10 hours to restore. The blackout resulted in several deaths and major societal inconvenience and cost.
The grid event in Virginia was initially triggered by a fault in a transmission line serving several data centers. The resulting voltage and frequency disturbance caused protective systems at the data centers to disconnect from the grid and switch to onsite backup power systems, rapidly removing approximately 3 GW of load from the grid, approximately 3% of the load on the grid at that time.
The voltage and frequency disturbance was detected throughout the PJM system. However, no generation sources disconnected from the grid and the grid operators were able to rapidly stabilize the system. System stability was aided by the predominance of conventional generation capacity which provided significant inertia. Very little IBR capacity was active on the system at the time of the disturbance.
The comparison of these two incidents and their resulting effects present challenges for Failure Mode and Effects Analysis. The initial trigger in both cases was frequency and voltage instability. The failure mode in the Iberian Peninsula blackout was cascading disconnection of IBRs which are reliant on the grid for frequency and voltage stability. The lack of sufficient inertia on the Iberian Peninsula grid left it sensitive to instability.
Dominion Energy and the PJM grid were able to ride through the disturbance in large part because of the inertia provided by conventional generation sources on the grid and the very low contribution of IBRs. The fact that the magnitude of the load disconnection on the PJM grid was less than half the magnitude of the initial generation disconnection on the Iberian Peninsula grid was also likely a factor.
It will be important to determine the percentage of IBRs on a grid which make it prone to failure in the event of voltage and frequency instability. It would be best not to make that determination in the field.
Originally published here.
Good assessment in easy to understand terms. Texas has had such outages, but not widely reported. I am sure we will have more as the rush is still on to build more wind and solar, especially solar going forward. We do have good gas coverage for the most part.
I am sure the new plans for the 765 kV transmission project would help this build up but at what cost to the ratepayer.
Big oil and gas are behind the scam for better ESG scores, still a thing, as is their build out of wind and solar. But there are many other fingers in the pie, just not the ratepayers! Until now~