Phasor domain fault analysis of bulk power systems uses a linear model, where generators are represented as Thevenin equivalents and loads are neglected. However, due to the highly nonlinear, current-limited, and proprietary behavior of controllers dictating the response of renewable sources to faults in the power grid, this model breaks down. This paper significantly advances the state of research in this field by proposing a framework that can correctly perform short circuit analysis in bulk power grids for any penetration of inverter-based resources, without neglecting loads. Unlike previous methods that approximate the total fault current as sum of the contributions of all source currents, this framework uses the fundamental properties of bus impedance matrix to accurately determine the part of source current that actually reaches the fault. Additionally, in cases where the voltage fluctuations in two successive iterations are large, the proposed framework breaks down this large change in to small changes, which solves the convergence issue reported in literature for faults electrically farther away from the source. The method is tested for accuracy, convergence, and scalability by comparing its results with results from time-domain simulations of faults on the IEEE 39-bus transmission system.

The modernization of distribution systems necessitates a sufficient number of inexpensive but accurate current sensors for effective monitoring, control, and protection. Recent research indicates that noninvasive, inexpensive magnetic field sensors can accurately measure the flux density existing at their location. However, in a distribution system, the flux density measured by a sensor is a function of multiple currents. The novel contribution of this article is to provide a closed-form mathematical solution to calculate individual phase currents from the total flux density, given the pole configuration of the distribution feeder. The model is first validated through COMSOL simulation. Then, it is validated through laboratory experiments using tunnel magnetoresistive (TMR) sensors. The minimal errors resulting from both validations are explained.

With the rapid growth of wind generation in the United States, it is crucial to develop reliable fault models of renewable generation units and farms. This paper develops controls for a variable-speed doubly fed induction (Type-3) wind turbine generator (WTG) such that its fault response complies with the new IEEE-2800 standard requirements. The model is conceived in electromagnetic transient (EMT) platform. The paper also examines the feasibility of the fault response of such WTGs to be captured as a voltage-controlled current source (VCCS) in the sequence domain for phasor domain short circuit analysis. Additionally, since wind farms comprise numerous machines, inverters, pad-mounted transformers, and collector cables, this paper explores a physics-based hypothesis to advocate the use of an aggregated farm equivalent model by avoiding detailed EMT modeling of each component without losing accuracy in modeling the farm's fault response. The hypothesis is validated through EMT simulations of a wind farm, demonstrating how a Type-3 WTG farm can be aggregated for short circuit studies with minimal errors.

This article summarizes the three-year technical activities of the IEEE Task Force (TF) on behind-the-meter (BTM) distributed energy resources (DERs): estimation, uncertainty quantification, and control. The potential grid services from BTM DERs are discussed in detail. The paper also reviews the state-of-the-art for BTM DERs visibility, uncertainty quantification, and, optimization and control. Furthermore, different aspects of the market structures associated with BTM DERs are covered, including emerging market and business models. Finally, needs and recommendations are provided for additional areas such as system protection, computing capabilities, algorithm development, market structure design, cyberinfrastructure and security, and hardware and software developments.

The transition from Synchronous Generators (SGs) to Inverter-Based Resources (IBRs) has resulted in a wide array of problems in power systems. The dynamics of IBRs differ from the dynamics of SGs, which has impacted the impedance (Z) trajectories seen by the distance relays during stable and unstable power swings. This study analyzes the impacts of different types of Phase-Locked Loops (PLLs) of Grid Following (GFOL) photovoltaic (PV) inverters on the magnitude of the rate of change of positive sequence impedance used for detecting Stable Power Swings (SPS). The variations of Z trajectories with respect to the changes in control parameters of Synchronous Reference Frame PLL with additional Low pass filter (LSRF PLL), Multiple Reference Frame (MRF) PLL, and Dual Second-Order Generalized Integrator (DSOGI) PLL are also studied. The impacts of varying penetration of PV and relay locations are also investigated. A modified IEEE-39 bus system with GFOL PV is utilized for the studies. The PVs adhere to IEEE Standard 2800 -2022 and have Low Voltage Ride- Through (LVRT)/ High Voltage Ride-Through (HVRT) and dynamic voltage support capabilities. This study shows that the PLL parameters and bandwidth influence the operation/maloperation of the relays during SPS. Time-domain simulation results from PSCAD are validated with theoretical analysis.

Inverter-based resources (IBRs) such as solar and wind plants are being connected in large numbers to the power grid. Additionally, fossil fuel-based generation is being phased out, resulting in the loss of rotor inertia, a key contributor to the transient stability. Unlike a synchronous generator (SG), an IBR’s response to a disturbance depends on its controls, involving factors such as operating mode, current limits, and grid code requirements. Therefore, the large-signal behavior of IBRs and their impact on transient stability must be studied. This paper presents hypotheses rooted in the physics of the transient stability phenomenon, choosing the most accurate models for IBRs to study the phenomenon, and documents simulation results on the IEEE 9-bus test system. The simulation results corroborate the hypotheses and highlight the impact of different control designs and operating modes on the critical clearing time (CCT), the metric considered for transient stability in this paper.

Direct current (dc) protection hardware must measure, process, and respond to faults within tens of microseconds. Modern microcontroller processing speeds allow for devices to implement a functional dc protection scheme within this ten-microsecond span. The following paper illustrates the challenges and solutions involved in implementing a novel protection algorithm onto hardware. The paper then describes the algorithm's performance in a realtime, hardware-in-the-loop (HIL) environment using a 1 MHz sampling rate. By analysis of test results, the paper identifies the unique issues created due to the filter used in the relay. It assesses the impact of these issues on the accuracy of fault location and the functioning of the protection scheme. Based on the assessment future work is proposed.

Traditional visualization of power system is performed through supervisory control and data acquisition (SCADA) systems and state estimator algorithm. Though decades of development and implementation efforts coupled with modern computing resources have resulted in a robust and dependable visualization tool, the measurements fed to the SCADA system are scalar values and are not synchronized at a precise timestamp. Typically, a new set of measurements is available every 2-4 s, which is sufficient for steady-state analysis. With recent advances in sensing, it is possible to get measurements of better quality at a faster rate. Recent generation of phasor measurement units measure and transmit synchronized phasor values of voltages and currents at 60 fps. The purpose of this chapter is not to show how to assimilate these measurements with the current SCADA system, but to explore the possibility of creating another visualization layer independent of SCADA that can provide more insight in to real-time dynamic events taking place in power systems. A concept of supervisory protection is also explored to increase security of protection schemes by detecting relay misoperations. Results are presented from published research papers to facilitate critical evaluation of the feasibility of these concepts.

This paper studies the impact of dynamic voltage support and active power recovery rate in a grid-connected large-scale Photovoltaic (PV) generator on Power Swing Blocking (PSB) protection used to detect Stable Power Swings (SPS). The reactive power priority (Q-priority) mode is considered during Low Voltage Ride-Through (LVRT)/High Voltage Ride-Through (HVRT). The dynamic voltage support is implemented using K-factor. The K-factor is varied to observe its impact on the power swing impedance trajectories and magnitude of the rate of change of positive-sequence impedance (|dZ/dt|). The impact of active power recovery rate during fault recovery on power swing trajectories and |dZ/dt| are also presented. The modified IEEE-39 bus system with a Synchronous Generator (SG) replaced by a Grid-Following (GFOL) PV generator is utilized for the studies. The PV has LVRT/HVRT capabilities and complies with IEEE Standard 2800-2022. The different test cases studied are simulated using PSCAD software.

Fault response of an inverter based resource (IBR) is dictated by its control scheme, making it markedly different from the response of a synchronous source. This has led to misoperation of distance relays when fed by IBRs. Published literature is mostly focused on changing the control design of inverters, but this approach is not practical, as these controls are proprietary and beyond the reach of utilities. To resolve this issue, this paper proposes a method for a source-agnostic distance relay that works in time-domain. Using only single ended measurements, the relay detects, classifies and locates any fault on the line it monitors. The method does not require any polarization technique. It is shown to work for unbalanced lines of any length, for transmission or distribution system with any number (even 100%) of IBRs, is immune to load encroachment, decaying dc offset and prefault currents. With very limited communication, it is also shown to be immune to fault resistance.

This paper focuses on the validation and hardware implementation of a novel, source-agnostic, time-domain distance relay, addressing the limitations of traditional distance relays in systems with high penetration of inverter-based resources (IBRs). It demonstrates the superiority of the proposed relay over the only time-domain commercial solution available in industry today using hardware-in-the-loop (HIL) setup. Additionally, the paper details the hardware implementation and testing of the relay algorithm on a Texas Instruments TMS320F28379D microcontroller (MCU), highlighting its practicality and efficiency.

Over the past few years, transmission grid in the USA has seen numerous unintentional tripping events of large-scale inverter based resources (IBRs). These trippings were primarily caused by non-standard settings and certain fault ride through controls implemented in the inverters, resulting in ‘subcycle overvoltage’ at the inverter terminals while recovering from a fault event. This paper first recreates the sub-cycle overvoltage scenario using a validated scaled farm model based on a real-world renewable farm. Using the simulation results and physics-based hypotheses, it identifies the root cause of the problem. Then, from mathematical analysis of the post-fault waveforms it proposes a control-based solution to comprehensively resolve this overvoltage issue in solar farms and in Type-4 wind farms. The solution logic is successfully implemented on a real-time platform. The solution, which is triggered by the dominant oscillation frequency in the post-fault voltage waveforms, and regulates the reactive power to successfully counter the rise of subcycle overvoltage, requires no hardware modifications, and can be implemented as a firmware upgrade in existing inverter controllers that are susceptible to the overvoltage-induced trippings.

Hybrid renewable farms with a mix of solar and wind resources, along with a battery energy storage system (BESS) are growing. Such farms include numerous inverters, pad-mounted transformers, collector feeders, and dc-side components depending on the type of generation. Additionally, inverters in such farms typically employ different control strategies, such as ‘grid following’ (GFL) and ‘grid forming’ (GFM), based on the resource type or system requirements, where an inverter exhibits similar steady-state response but different fault behavior. This paper lays out a physics-based hypothesis to advocate the use of an aggregated model, while avoiding detailed modeling of all components of a hybrid farm. The hypothesis is substantiated by simulations of a hybrid farm using Electro-magnetic Transient (EMT) simulation, documenting how hybrid farms should be aggregated for short circuit studies with minimal errors.

The increasing integration of inverter-based resources (IBRs) into the transmission network impacts traditional phasor-based distance relays designed for synchronous generators (SGs), leading to frequent misoperations. Source-agnostic protection schemes address this issue by operating independently of the source type and controls. This paper proposes a comprehensive time-domain distance protection scheme featuring both main and backup functions, using source-agnostic distance and directional relays. The proposed protection scheme reliably detects and isolates faults within the protected zone and securely restrains from operating for faults outside the protected zone. The effectiveness of the proposed scheme is validated using PSCAD simulations, demonstrating its high selectivity, dependability, and security.

Over the last decade, the power grid has seen a significant increase in renewable energy sources such as wind farms and solar photovoltaic (PV) plants. These farms consist of dozens of inverters, pad-mounted transformers, and collector feeders that, if modeled in detail, introduce a significant compu-tational burden. This paper presents a physics-based argument for simplification of such modeling, and illustrates through electromagnetic transient program (EMTP) simulations that a simple aggregated model of a farm can be created for short circuit studies without losing accuracy in the results. It also shows how an equivalent inverter can be created based on the ratings and number of individual PV or type 4 wind turbine generator units. lowering the modeling and computational burden of simulating solar and type 4 wind farms in EMT simulations

Protection relays are confronted with numerous issues due to the transition in generation from synchronous generators (SGs) to Inverter-Based Resources (IBRs). IBRs usually do not have inherent inertia. Grid integration of IBRs can impact the impedance trajectories of power swings seen by the distance relays. This may cause maloperations of the relays during stable power swings (SPS) and unstable power swings (UPS) with present blinder settings. The impact of penetration of Photovoltaic (PV) generations on the operations of Power Swing Blocking (PSB) and Out-of-Step Tripping (OST) functions in a SG dominated system is analyzed in this work. A modified IEEE-39 bus system with Grid Following (GFOL) PV generators with PQ control scheme is used in this work. One of the SGs of IEEE-39 bus system is replaced with PV generation (13.5% penetration). The PVs have Low Voltage Ride Through (LVRT) and voltage support capabilities and adhere to the IEEE 2800-2022 standard. SPS and UPS for the IEEE-39 bus system are studied through different cases (with and without PV) simulated in the PSCAD software. The results presented in this work demonstrate that the penetration of PQ control-based PV generators may increase the speed of impedance trajectories which may, in turn, cause maloperations of the PSB and OST functions. There is a need to review the existing blinder settings used for detecting SPS and UPS in the presence of PV generators.

With increasing penetration of inverter based resources (IBR) in distribution systems, the distinction between fault and load current is lost due to the current limiting feature of inverters. This may render the fault undetectable to traditional overcurrent relays. Voltage assisted overcurrent relays and machine learning-based relays have been shown to be promising in this regard. This paper compares the performance of the two relays in a distribution system with 100% IBR penetration using the voltage and current measurements obtained at inverter terminals.

The bus impedance matrix (Z-bus) carries information about the Thevenin equivalent impedance (TEI) looking from different nodes of a linear network. Although a power system is nonlinear because of constant PQ loads and controlled power injections from sources, a conventional power system fed by synchronous generators is linear during fault, and can be represented by Z-bus, which is useful in power system analyses such as short circuit analysis. However, with the increasing penetration of inverter-based resources (IBRs) in the system, the assumption of linearity of the faulted network does not hold. Consequently, the applications of the analyses based on TEI are affected-for instance, certain protection schemes that are set using short circuit analysis are affected. This paper analyzes how the Z-bus of the power system network is affected with the increasing penetration of IBRs. The intention is to foster research on finding alternatives to the established practices that use Z-bus for analytics. IEEE nine bus transmission network simulated in PSCAD is used as a test case for this study.

The design of a reliable protection scheme for microgrids often requires communication between protective devices and microgrid controllers. The authors have developed such a communication assisted scalable protection scheme with a self healing feature to protect a microgrid with 100% Inverter Based Resources (IBRs). The communication assisted scheme must be validated in real time with cyber physical co-simulation for successful demonstration. In this regard, the paper presents a co-simulation platform between a simulated power system model using RTDS and physical protective devices. The primary protection of the scheme is programmed in SEL 421-7 relay and backup protection is programmed in MATLAB on a generic computer acting as a microgrid controller. The IEC 61850 models are used to communicate between SEL-421-7 relay and RTDS, whereas TCP/IP communication connects the microgrid controller to RTDS. The paper's focus is to demonstrate the co-simulation platform with communication links established using both protocols and validate the proposed scheme in real-time on the IEEE 123 node distribution feeder. The paper explains the configuration of the IEC 61850 and TCP/IP communications as the interface requires proper hardware and software setup. The real time performance indicates the Hardware In the Loop (HIL) framework as a competent testing environment for the developed protection scheme for microgrids.