# PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

## TL;DR

This paper evaluates the accuracy and reliability of PMU-based ROCOF measurements for power system applications, especially under transient conditions, and assesses their feasibility in real-time grid control scenarios.

## Contribution

It provides a comprehensive analysis of PMU-based ROCOF estimation methods, compares different algorithms and models, and validates their practical application in real-time power system control.

## Key findings

- PMUs are accurate ROCOF meters with low harmonic distortion.
- Transient events challenge the synchrophasor model's assumptions.
- PMU-based UFLS can effectively support grid restoration in real-time simulations.

## Abstract

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.