In the US power systems, the grid operator is mandated to keep the frequency within a tight range, and can be financially responsible if the monitoring by the North American Electric Reliability Corporation detects a non-compliance.
For example, typical industrial electrical motors consume less power at lower frequencies, adding a small, but noticeable amount of inertia to the system,[9] this effect is diminishing due to switching to modern and efficient variable-speed controls that have much less inertia-like response.
The ULFS disconnects of the load lower the power demand thus slowing down the decrease in frequency, representing an equivalent to increasing the amount of inertia.
[11] High penetration of the variable renewable energy (VRE) created new challenges:[12] The alternatives to the traditional inertia are therefore applied, and by the 2020s Texas (ERCOT) took the lead in the United States due its higher wind power penetration (almost double that of the Western Interconnection, WI) and its relatively small size that made the contingencies there larger in percentage terms (a single failure can take power equivalent to 6.4% of the average load in comparison to 2.6% for WI and 1.3% for the Eastern Interconnection).
[13] The following brute-force means are used to keep the grid reliability in the environment of reduced inertia: Disconnection of the load can be done very quickly (half a second, including the frequency measurement).