Frequency Excursions
Leading Indicator: Frequency Excursions

View high frequency excursions

Frequency Excursions are an important measurement of operating reliability. Based on historical data and analysis, it appears that the real-time balancing control capability of the Eastern Interconnection may be declining. If true, this could begin to challenge system operators’ ability to maintain reliable operations.

The large differential between the number of abnormal frequency events in each interconnection,
requires the y-axis scale to be logarithmic. During 2008 there was a reduction of about 30-percent in the number of low frequency events during the on peak period in the Eastern interconnection, and an increase of about 35-percent in the Western Interconnection. The Eastern six-year increasing trend in the number of low frequency events reversed during 2008, and the western five year decreasing trend reversed to increase during 2008.

About this Leading Indicator

The ability to maintain load-generation balance at all times is a key indicator to measure real power balancing control performance. Prolonged system recovery performance could indicate at-risk operations, decline in frequency response or degradation of regulation and reserve sharing capability.

The Frequency Trigger Limits (FTLs) are defined as thresholds. An FTL-Low alarm is generated when interconnection frequency is lower than FTL-Low for 5-minutes or more. The FTL-Low is 59.950 Hz for Eastern Interconnection and 59.856 Hz for Western Interconnection.

An FTL-High alarm is generated when interconnection frequency is higher than FTL-High for 5-minutes or more. The FTL-High is set at 60.050 Hz and 60.144 Hz for Eastern and Western Interconnection respectively.