M-4: Interconnection Frequency Response
About This Metric
This metric is used to track and monitor Interconnection Frequency Response. Frequency Response is a measure of an Interconnection’s ability to stabilize frequency immediately following the sudden loss of generation or load. It is defined as sum of the change in demand, plus the change in generation, divided by the change in frequency, expressed in megawatts per 0.1 Hertz (MW/0.1 Hz). It is a critical component to the reliable operation of the bulk power system, particularly during disturbances and restoration. The metric measures the average Frequency Response for all events where frequency drops more than the Interconnection’s defined threshold. While the calculations may show trends from year to year, no attempt has been made in this analysis to determine or state what indicates an “acceptable” level of Frequency Response for any of the interconnections. Rather, they show the relative performance from year-to-year and can be a basis for further root-cause analysis. Further, the Frequency Response should not be compared between interconnections as their bulk power system characteristics differ significantly in terms of number of facilities, miles of line, operating principles and simple physical, geographic and climatic conditions. Some annualized Frequency Responses are higher due to the large number of disturbances in the dataset where frequency changes were greater than the generator deadbands.
For the stabilizing period, the Interconnection frequency response, 72 the Eastern Interconnection, the Québec Interconnection, and the Western Interconnection showed no statistically significant changes from 2019 through 2023. The Texas Interconnection showed a statistically significant improvement for the stabilizing period from 2019 through 2023.
Metric Definition Document
M-4 Interconnection Frequency Response
M-4.1: Inertia and Rate-of-Change-of-Frequency
About This Metric
This metric is used to track and monitor Interconnection Frequency Response between the starting frequency (A-point) and the lowest nadir frequency (C-point). The Interconnection A-C Frequency Response metric data will measure the ability of the Interconnection to arrest a frequency decline before it reaches the first stage of UFLS. Trends and analysis of this data will assist in assessing the impact of changing resource mix and the decline in inertia for the interconnections, as well as identify if additional actions may be needed to assure adequate frequency response in North America.
With the changes in generation resource mix, there is evidence of a decline in inertia in the different interconnections. In the BAL-003-2 Standard, the Interconnection Frequency Response Obligation (IFRO) is calculated on the basis that frequency will be arrested above the first stage of UFLS for the Interconnection Resource Loss Protection Criteria (RLPC).
For the arresting period, the inertia and rate-of-change-of-frequency (ROCOF), the Western Interconnection and Eastern Interconnections showed no statistically significant changes from 2019 through 2023. The Texas Interconnection showed a statistically significant improvement. The Québec Interconnection showed a statistically significant decreasing trend.
Metric Definition
M-4.1 Inertia and Rate-of-Change-of-Frequency
