Frequency tracking fundamentals, challenges, and solutions

How stable is the frequency of the power system on a given day? How does a microprocessor-based relay track power system frequency? Why is frequency tracking important? This paper reviews the fundamentals of frequency tracking and explains, in practical terms, how and why this is done in digital relays. The performance of protective elements at off-nominal frequencies is of key interest. As with all technical areas, designs have evolved over time. This paper also documents the evolution of different designs, exploring each design's merits and why it was implemented. Real-world power system events are used to highlight scenarios that challenge designs. Lessons learned from event analysis are shared. Practical solutions and application advice are provided for each case study.