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This paper describes the way that white noise (including quantised input section sampling) imparts errors onto frequency and rate-of-change-of-frequency (ROCOF) measurements. The main paper focus concerns the use of filtered heterodyned (i.e., Fourier) analyses for single-phase and three-phase systems, and the filtered Clarke transform for three-phase systems. The rules and equations governing the effect of white noise on frequency and ROCOF are formulated for these techniques, explaining the subtle effects of aliasing, splitting signals and noise into their positive and negative frequency components, and the correlation or decorrelation of noise. It is shown that—as expected—for three-phase ac measurements, averaging three single-phase Fourier measurements produces the same performance against noise as using a method based on Clarke’s transform, if identical filtering is used. Furthermore, by understanding the theory behind the frequency and ROCOF measurement processes, it is shown that to achieve the lowest RMS errors, in the presence of front-end white noise (alone, ignoring other dynamic signal and power quality aspects), a filter which provides ~40 dB/decade attenuation (i.e., a two-boxcar cascade) is recommended for a frequency measurement, but a filter which rolls off at ~60 dB/decade (i.e., a three-boxcar cascade) is recommended for a ROCOF measurement. [ABSTRACT FROM AUTHOR]

The new amendment to the phasor measurement unit (PMU) standard C37.118.1a makes several significant changes compared with the standard C37.118.1 (2011). This paper highlights some of the most important changes, with a particular emphasis applied to how those changes relate to the way that an M-class PMU filter needs to be designed. In particular, there is a delicate tradeoff between passband flatness (the bandwidth test) and stopband rejection in the out-of-band (OOB) test. For a PMU algorithm using frequency-tracking and adaptive filters, it is shown that passband flatness can be relaxed to about 2.5 dB, but that the stopband needs to begin up to 14.8% closer to 0 Hz than for a fixed-filter PMU. This is partly due to the exact procedures of the C37.118.1a OOB testing and partly due to the adaptive nature of a frequency-tracking PMU filter section. Both the above lead to modified filter masks being required for frequency-tracking devices compared with the mask required for fixed-filter devices. The M-class PMU with a reporting rate of 25 Hz is the most difficult to design, for reasons given in this paper. The validity of the masks is shown using filter Bode plots and simulated C37.118.1a test results of a fixed-filter and frequency-tracking device, which have been designed to meet the masks defined in this paper. [ABSTRACT FROM PUBLISHER]