This paper addresses the challenges posed by high Grid-Following (GFL) Photovoltaic (PV) penetration on the dynamic performance of memory-polarized mho relays, crucial for close-in fault protection in power systems. Traditional memory-polarized mho relays, designed for synchronous generator-dominated systems, utilize a scalar weight to dynamically expand their mho characteristics based on memory voltage, enhancing resistive reach. However, the unique transient behavior of Inverter-Based Resources (IBRs) like GFL PV during faults can disrupt this mechanism, compromising relay reliability. To overcome this limitation, this research introduces a novel algorithm that employs a complex weight parameter in the memory polarization process, replacing the conventional scalar approach. This complex weight allows for more precise and adaptable control of the mho characteristic’s dynamic expansion, enabling the relay to better respond to the complex voltage and current transients introduced by GFL PV. The study investigates the dynamic expansion of the mho element’s maximum diameter (dmax) and memory vector angle (θm) under various fault scenarios (three-phase, single-line-to-ground, and line-to-line) to evaluate the algorithm’s effectiveness. The proposed complex weight algorithm is validated across diverse fault types, varying complex weight factors, and different fault resistances, considering GFL PV generators with reactive power priority and IEEE Standard 2800–2022 compliant Low/High Voltage Ride-Through capabilities. The results demonstrate significantly enhanced reliability and stability of memory-polarized mho relays in systems with high GFL PV penetration, showcasing the superior performance of the complex weight approach.

Ferroresonance, a non-linear and unpredictable disturbance, is rare compared to traditional power system faults occurring in power systems. This rarity, coupled with its complexity, makes it a challenging phenomenon to be detected and identified. This work presents a detection and classification scheme for ferroresonance and its modes. It is carried out by continuously processing the three-phase voltage and current signals using the discrete wavelet transform (DWT). The developed models are simulated in electromagnetic transient software and processed using the DWT to extract fault signatures and predictors. A decision tree classifier is trained to detect and classify a disturbance as ferroresonance using an adaptive time based on the disturbance class. The computational burden of the detection and classification process is significantly reduced by using the superimposed component of the voltage and current to detect transient inceptions before classification. Furthermore, the classification of different modes and classification from other non-linear faults, such as arcing faults, is discussed. The adaptive timing and detection scheme demonstrates that the proposed methodology is efficient and can classify the disturbance into different modes.

Unlike synchronous generators, the fault response of grid-forming (GFM) inverter-interfaced distributed generators (IIDGs) is notably governed by the selection of control and current limiting strategies rather than inherent physical traits. While recent research has focused on the sequence domain fault model of GFM IIDGs, a research gap exists in elucidating the influence of control and current limiting schemes on this model's characteristics. This article aims to fill this void by examining how different control and current limiting schemes influence the positive and negative sequence impedances in the phasor-domain fault model of GFM IIDGs. This investigation encompasses droop-based, virtual synchronous machine-based, and virtual oscillator-based reference generation controls alongside rotating and stationary reference-frame-based voltage controls. Furthermore, saturation-based, latching-based, circular and virtual impedance-based current limiting schemes are analyzed. To achieve this goal, a thorough numerical simulation study is conducted. Findings indicate that outer reference generation controls exhibit minimal impact. Conversely, the choice of voltage control and various current limiting schemes emerge as the predominant factors shaping the sequence models of GFM IIDGs. These analyses and results are instrumental in devising reliable protection strategies within inverter-based grids, as a comprehensive understanding of electrical elements in the sequence domain is imperative for effective protective measures.

This paper investigates the influence of dynamic voltage support on Positive Sequence Memory-Polarized (PSMP) mho relays in the presence of Grid Following Photovoltaic (PV) generators. The widespread integration of Inverter-Based Resources (IBRs) has significantly altered power system dynamics. Traditionally, memory polarization in mho elements has ensured reliable operation during close-in faults. A dynamic expansion of mho characteristics results from the use of memory voltage for polarizing the mho elements, enhancing the resistive reach in systems dominated by Synchronous Generators (SGs). However, the fault current characteristics of IBRs differ from SGs, potentially compromising the dynamic mho expansion behavior. This work explores how dynamic voltage support employed by large-scale PV generators affects the expansion of PSMP mho characteristics. The PV generators used in this study have reactive power priority and Low Voltage Ride-Through /High Voltage Ride-Through capabilities and are compliant with the IEEE Standard 2800-2022.

The restructuring of the power system by replacing Synchronous Generators (SGs) with Inverter-Based Resources (IBRs) has resulted in a drastic change in power system dynamics. Positive Sequence Memory Polarized (PSMP) mho elements have been used to ensure the reliable operation of mho relays during close-in bolted faults. The use of memory voltage for polarization of the mho element causes dynamic expansion of the mho characteristics. In an SG-only system, the memory polarization-induced dynamic expansion of these mho characteristics helps to increase the resistive reach. However, as the integration of IBRs increases, the dynamic mho expansion will be affected due to the different fault characteristics of IBRs. Most IBRs currently integrated into the power system are Grid-Following (GFOL) type, which uses Phase-Locked Loops (PLL) for synchronization. The variations in control parameters and bandwidths of the PLLs used in the GFOL IBRs may also affect the dynamic mho expansion. The studies presented in this paper demonstrate the impact of different types of PLLs and their control parameters on the dynamic expansion of PSMP mho relays. For this analysis, a modified IEEE-39 bus system with a GFOL Photovoltaic (PV) generator is used. The PV s have Voltage Support (VS), Low Voltage Ride-Through (LVRT)/ High Voltage Ride-Through (HVRT) features and comply with IEEE 2800–2022 standard.