Analysis on the effect of sub-harmonic frequencies on P class phasor measurements
The introduction of power electronic devices, series capacitors, wind and PV installations into the power grid has become common in recent times. A consequence to the use of these technologies are anomalies in the sub-harmonic frequency spectrum. As PMUs can be strategically placed at different parts of the power grid which are spread over a wide geographical area, measurements obtained from them have proven to be useful for both real-time and offline analysis. The IEEE C37.118.1a-2011 standard and its recent 2018 update, the IEC/IEEE 60255-118-1-2018, are widely accepted as benchmark sources for the performance of a PMU and provide reference models for both P and M class variants. While the standard specifies performance requirements under steady and dynamic conditions, behavior under practical scenarios can be vastly different due to several factors, one of which being the presence of sub-harmonic frequencies. This paper presents a study on the effects that such sub-harmonic frequencies may have on P class phasor measurements captured during various power system conditions. A power system model is designed and subjected to several system conditions involving the presence of sub-harmonic frequencies. The three-phase voltage and current signals obtained from the model are used to generate P class phasor measurements as per the IEEE reference model and are further employed for analytical purposes specific to each scenario. A critical analysis is presented between data obtained via this method as well as dedicated fault recording and analysis equipment. The study highlights the expected challenges associated with the usage of these measurements for analysis applications and the considerations that need to be made.