Fault Clearance Research Articles

Исследование влияния отклонений параметров моделей синхронных генераторов на результаты расчета динамической устойчивости электроэнергетической системы

One of the important tasks solved in planning the electric power system (EPS) operation is the assessment of its transient stability. Use of incorrect parameters for EPS element models, in particular synchronous generators (SG), contributes to the occurrence of errors when determining the operating conditions of power systems, and, therefore, can lead to a decrease in the reliability of EPS operation. This article is devoted to the study of the impact of errors in SG model parameters on the transient stability assessment results. The analysis presented in this article allows us to substantiate the relevance of the SG parameter estimation task using a “passive experiment”, such as synchronized phasor measurements. This research is based on the theory of electrical circuits, mathematical description of electrical machines and transients in EPS, as well as statistical analysis. Computational experiments have been carried out in the software package MATLAB using the simulation modeling environment “Simulink”. During the research, two different multi-machine EPS models have been used, including the well-known “IEEE 9-bus” system. To quantitatively assess the influence of SG parameter uncertainties on transient stability analysis, the values of the maximum permissible fault clearance time are determined, as well as the values of the maximum power output of generating equipment in prefault conditions. The authors have carried out a comprehensive analysis of the influence of deviations in SG model parameters on the maximum fault clearance time, as well as on the maximum power output of generating equipment in the prefault conditions for a given fault duration. During the study, two approaches have been considered; in each case, the EPS transient stability assessment has been performed almost automatically, and quantitative indicators have been computed for the influence of SG model parameter deviations on the outcome of EPS transient stability analysis. Analysis of the computational experiment results has demonstrated a significant influence of the SG model errors on the errors in calculating certain transient stability-related parameters. For the considered scenarios, the spread of errors in calculating the maximum fault clearance time reached 100 % relative to a base-case (errorless) result, and the error in calculating the maximum power output of generating equipment in prefault conditions for a given fault duration may reach 20 % relative to the errorless result.

A data‐driven transient stability‐based approach for out‐of‐step prediction in power systems

AbstractThis paper presents a prediction‐based algorithm designed to address out‐of‐step (OOS) conditions in power systems. The algorithm utilizes generator data obtained from phasor measurement units. The transient stability of a multi‐machine power system is evaluated using the equal‐area criterion (EAC). The proposed algorithm calculates the characteristics of the P‐δ curves within the EAC framework after a large disturbance. The critical P‐δ trace is determined by analysing the cumulative energy in the acceleration area following fault clearance. The stability margin of the rotor angle is then computed based on the actual active power and its relationship with the critical curve. The algorithm predicts the occurrence of OOS by comparing the measured active power with the corresponding value on the critical curve. Furthermore, a complementary strategy is proposed to predict the OOS condition in integrated inverter‐based power systems. The effectiveness of the proposed algorithm is validated through simulations conducted on the 73‐bus IEEE test power system.

Optimized wide area backup for distance relay tele-protection with security adjustment

Tele-protection schemes efficiently clear faults at line ends, but failures in the telecommunication link or relay malfunction can cause delayed fault clearance, network instability and significant power loss. Hence, this paper presents a reliable protection method as a backup for tele-protection schemes which is designed based on nearby distance relays zone pickup. The proposed protective method introduces a novel ability to adjust sensitivity to fault events through a security factor index. This method can adapt to network uncertainties or changes in topology, using one-step calculation of optimal values based on the least square error method and provides the fast adaptation to network changes. In addition, it enables the fault detection even if a relay fails at one of the faulted line terminals. Performance evaluation of the proposed method has been done based on the reliability indices through a wide simulation of fault scenarios on the IEEE 9-bus system. Considering the possible uncertainties, the test results have shown that the proposed method is more efficient with 98.5 % dependability compared to the conventional tele-protection schemes. While this index is evaluated at 90 % and 92.5 % in the PUTT and POTT schemes, respectively.

Fault Detection Using Artificial Neural Network and Wavelet Transforms for Power Transformer

Abstract: The requirement for a stable supply of electrical energy to meet the needs of the modern world has expanded dramatically, necessitating near-faultless power system functioning. The main goal is to reduce the frequency and duration of undesired power transformer outages by imposing a high point demand that includes criteria for dependability (no false tripping) and operating speed (quick fault detection and clearance time). For many years, the second harmonic restraint concept has been widely applied in industrial applications. It employs the discrete Fourier transform (DFT) and frequently confronts issues like lengthy restrain times and the inability to distinguish internal defects from magnetizing inrush circumstances. As a result, artificial neural networks (ANNs), a strong tool for artificial intelligence (AI) that can imitate and automate information, have been suggested for defect identification and tracking in normal and inrush conditions. For the investigation of power transformer transient conditions under diverse settings, the wavelet transform (WT) is utilized, which has the capacity to extract information from transient signals in both the time and frequency domains at the same time. In the MATLAB/SIMULINK environment, all of the above-mentioned conditions of a power transformer to be investigated in a power system are modelled.

Security-constrained unit commitment model considering frequency and voltage stabilities with multiresource participation

The rapidly increasing proportion of renewable energy sources has led to a reduction in the relative share of synchronous units, which has resulted in a decline in the inertia of the power system and a decrease in its voltage support capacity. This has led to several issues related to the frequency and voltage stabilities of the power system. To ensure these frequency and voltage stabilities, it is necessary to maintain a number of synchronous units online in the day-ahead generation schedule. First, the dynamic frequency change process after a power system fault is discussed, and a linear expression is derived for the frequency stability constraints involving energy storage systems and wind turbines. Second, the short-circuit capacity of the bus is characterized to describe the strength of voltage support, and the minimum short-circuit capacity requirement of the bus is solved based on the transient voltage recovery problem after clearance of the short-circuit faults. The total short-circuit capacity provided by the unit to the bus is then calculated through the network reactance matrix to establish the voltage stability constraint. Subsequently, the security-constrained unit commitment model considering frequency and voltage stabilities (FVS-SCUC) is established. Finally, the effectiveness of the proposed model is demonstrated through a numerical simulation of the IEEE-39 system comprising storage and wind turbines. The model ensures the frequency and voltage securities of the system, and the renewable energy output is improved upon considering energy storage. Thus, the overall system cost was reduced by nearly 30% by considering the frequency regulation effects of the energy storage system and wind turbine as well as the voltage regulation effects of the energy storage system.

Improved assembly DC circuit breaker based on resonant current injection.

DC circuit breakers (DCCBs) with high breaking capacity and low cost are necessary for quick fault clearance in DC networks. The assembly DC circuit breakers (ADCCBs) have a main breaking section (MBS) and a sub-breaking sections (SBS) for each line, which greatly reduce the cost. But in conventional operation, it bears high voltage for a long time when there is a main switch grounding process in any line fault action. To address this problem, a multiport assembly circuit breaker based on current injection (CI-MPACB) is proposed, which is able to generate a resonant current with increasing amplitude by controlling the duty cycle of Integrated Gate-Commutated Thyristors (IGCTs). Then the resonant current is injected into the SBS to generate current zero crossing and arc extinction. A complex frequency domain circuit analysis is performed on the MBS to describe the action logic as well as the commutation characteristics. In addition, the parameters of each component of the MBS are subject to multiple constraints and reasonable design to ensure the fault current could be cut off quickly and reliably. The cost of existing design is greatly reduced due to the design idea of resonant current injection device parameter selection. Finally, a PSCAD/EMTDC simulation confirms the opening viability of CI-MPACB and the accuracy of the parameter design. The test results show that the designed CI-MPACB can cut off DC fault lines.

Adaptive reactive power control strategy for grid-forming inverter under symmetrical fault

Abstract Due to the inability of the grid-type control method to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the proportional decrease of synchronous machines, the power grid exhibits insufficient resistance to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. In response to these challenges, grid-forming inverters have emerged. Under symmetrical faults, the low-voltage ride-through of grid-forming inverters is often accompanied by a frozen reactive power environment, resulting in a direct output of increased voltage and reactive current. However, an elevated reactive power command can cause a sharp increase in the potential amplitude within grid-forming inverters. After the grid fault is cleared, the excessively high internal potential can cause a short-term and rapid increase in terminal voltage, potentially leading to overvoltage, which is detrimental to the operation of grid-connected devices. To address this issue, this paper first employs a grid-forming inverter controlled by a virtual synchronous machine control method. Using the grid positive-sequence voltage as a reference value, it identifies whether a voltage drop fault has occurred. Based on this, an adaptive reactive power control strategy is proposed, which can promptly achieve the same effect as the frozen reactive power environment during faults, while also promptly restoring the reactive power environment after fault clearance, thereby avoiding overvoltage issues. The feasibility of the proposed method is verified through the establishment of a simulation system.

Adaptive low voltage crossing strategy for symmetrical faults of networked inverters

Abstract Due to the inability of grid-following control methods to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the decreased proportion of synchronous machines, the grid exhibits insufficient resilience to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. Grid-forming inverters have emerged to address this issue. During symmetrical faults, the low-voltage ride-through of grid-forming inverters often involves freezing the reactive power loop, resulting in a direct output of higher voltage and reactive current. However, an increase in reactive power command leads to a sharp rise in the internal potential magnitude of grid-forming inverters. Upon clearance of the grid fault, the excessively high internal potential may cause a rapid, short-term increase in terminal voltage, potentially resulting in overvoltage, which is detrimental to the operation of grid-connected equipment. In response to this issue, this paper proposes an adaptive low-voltage ride-through control strategy for grid-forming inverters under symmetrical faults controlled by a virtual synchronous machine control method. Initially, a virtual synchronous machine control model is established. Limiting current is achieved through the construction of a fixed virtual impedance loop. The issues associated with fixed virtual impedance current limiting are analyzed, leading to the proposal of an adaptive virtual impedance control strategy. Finally, the feasibility of the proposed method is verified through simulation experiments.

Signal Envelope-Based Adaptive Power Swing Blocking

This research paper proposes detection of faults during power swings by using a peak envelope-based method to prevent incorrect distance relay operation. Distance relays should not operate during power swings except to remove a correctly detected fault event. In this study, distinction between faults and power swings is achieved by correctly observing fault occurrence based on dynamic thresholds generated by peak envelopes. The method utilizes a DC offset current in determining the fault inception and fifth harmonic voltage to assess the fault clearance. If the current surpasses the calculated threshold due to fault existence, the relay is allowed to operate. Re-blocking the relay after fault clearance is achieved in the case of a higher value of the voltage than the threshold value. Current and voltage data obtained from two different test systems simulated in PSCAD for various scenarios have been used in the proposed algorithm developed in MATLAB. In order to show the effectiveness of the proposed method, the results on the second test system have also been compared to the results of selected methods in the literature. It has been perceived that the developed method has a high accuracy and provides an appropriate time range for relay and breaker operation.

Fault Detection and VSC-HVDC Network Dynamics Analysis for the Faults in Its Host AC Networks

High-voltage direct current (HVDC) transmission is preferred over high-voltage alternating current (HVAC) for long power lines for asynchronous power grid interconnection and high-level renewable energy integration. The control and protection functions associated with HVDC systems help with fast and secure clearance of faults. The control and protection challenges in the embedded HVDC network are of great concern for the stable and secure operation of an HVDC network. The DC fault current may reach an extremely high level in a rather short period because of the low impedance in a DC system, which is dangerous for converters, and disturbances in the AC network directly influence the performance of the HVDC system. Sometimes, faults on the AC side may lead to disconnection or failure of the DC link, causing reliability problems as well as huge economic losses. AC and DC protection solutions are being developed for HVDC systems to enhance their sustainability and reliability. As such, AC and DC faults should be detected and cleared at a faster rate. Therefore, in this article, the feasibility of the synchro-squeezed transform (SST) is analyzed for detection purposes. For more accurate and faster detection, the signal is first decomposed using the empirical mode decomposition (EMD) technique, and then the SST is applied. A discrete Teager energy (DTE) spectrum is obtained with the processed signal, which works as the detection index. The algorithm shows low sampling frequency requirements, with higher efficiency and reliability for the purpose. PSCAD/EMTDC version 4.6 software and MATLAB 2022a software is used for the modeling and simulation.

Fault Ride-Through Method for Interline Power Flow Controller Based on DC Current Limiter

The interline power flow controller (IPFC) based on a modular multilevel converter with a half-bridge configuration can control the active and reactive power flows of multiple alternating current (AC) lines. However, it forms a multiterminal system on the direct current (DC) side, which leads to DC faults. To reduce the protection and clearance requirements on the DC side of IPFCs, this paper proposes a hybrid current limiter topology suitable for generating a DC-side fault ride-through scheme. The current limiter employs a low-loss branch in steady-state conditions; when the fault occurs, a commutation capacitor and controllable power electronic devices are used to transfer the fault current to the current-limiting branch. To clarify the operating principles of the current limiter, the working states of each stage and electrical stress of each device are analyzed. Different components with varying limiter parameters are also discussed, and optimal parameters to achieve the best limitation effect are discussed. PSCAD simulations show that the proposed limiter can limit the overcurrent effectively, and DC-side fault clearance can be achieved easily with this fault ride-through strategy.

Innovative Fault Current Evaluation Method for Active DC Grids

DC smart grids are a promising solution for the efficient integration of renewable energy sources and loads. Still, their widespread adoption is hindered by significant challenges related to fault response, identification, and clearance. The traditional DC fault analysis method is a useful tool for straightforwardly understanding the behaviour of fault current contributions from DC converters in LVDC networks during a fault. However, when a system with multiple converters and non-negligible fault impedance need to be considered, its accuracy is severely limited due to the assumptions included in the problem solution, thus leading to the following: (a) the dependency of the results’ reliability on fault impedance values and/or other converter fault current contributions; (b) the inaccuracy of the diode current estimation; and (c) the inaccuracy of the conductor joule integral. Thus, these results’ data may be unreliable for designing protection systems for one converter or for an entire network. In order to overcome these issues, this paper proposes an innovative, simple numerical approach to DC fault current evaluation, which can be adopted when the number of converters become significant, or the network is complex. This method arises from the primary interest in solving the circuit to extract the indicators (current peak value and time, joule integral, etc.) necessary for designing circuit protections. This approach proved to grant two main advantages over traditional methods: (a) it provides accurate results, with no need to introduce any specific assumption; (b) it can be structured to manage an arbitrary number of converters; and (c) it reduces the computational processing times and resources necessary to simulate an entire DC network in comparison to other circuit solution software.

Dynamic Power Control In Utility-Connected Microgrids: A Back To Back Converter Approach For Efficient Integration Of Solar And Wind Energy

This research directs the imperative need for robust power management and control in utility-connected microgrids featuring solar and wind energy sources. The suggested method employs back to back converters for precise control on the transfer of both active and reactive power between the microgrid and the utility. The new control strategy operates in two states, effectively sharing power among the utility and the microgrid. An innovative arrangement among DGs ensures seamless load sharing in both grid-connected (GCM) and islanded modes (IM). The back-to-back converters provide complete frequency isolation, protecting the microgrid from voltage or frequency fluctuations from the utility side. The study introduces synchronized relay-breaker operation during faults, along with disabling back to back converters, ensuring smooth resynchronization after fault clearance. System stability is confirmed under different load changes. The proposed control setup proves resilient to changes in grid-side voltage and frequency, ensuring a stable and reliable power-sharing mechanism under various operating conditions. Simulations conducted in MATLAB/SIMULINK validate the efficacy of the proposed control strategy, highlighting its ability to enhance the stability and reliability of utility-connected microgrids incorporating solar and wind energy sources. This study contributes to advancing sustainable energy solutions, advocating for resilient and eco-friendly power systems.Top of Form.

Fast Assessment Method for Transient Voltage Stability of Photovoltaic Receiving‐End Grid

The incorporation of renewable energy on a broad scale into power grids increases the complexity to the issue of transient voltage stability in power systems. This research presents a rapid evaluation technique for assessing the stability of voltage fluctuations in power grids that receive electricity from photovoltaic sources. At first, a receiving‐end system model was developed, which includes photovoltaics, and an alternative circuit of the virtual induction motor (IM) is obtained by utilizing the Thevenin equivalent. Second, the torque balance equation and the Kirchhoff voltage equation are interconnected to determine the unstable slip of the IM following a malfunction. Finally, by merging the unstable slip with the conventional transient stability discriminant index, the effects of different photovoltaic outputs, IM ratios, and system contact impedances on transient voltage stability are investigated. The proposed method avoids the computational burden of solving the differential‐algebraic equations describing the complex transient processes of the IM. It also obviates the necessity of iteratively modifying the receiving load or fault clearance time in the simulation platform to achieve the constrained stability condition of the system’s transient voltage. The transient stabilization of voltage results is efficiently obtained by directly solving algebraic equations.

An Improved DC Power Electronic Transformer Based on Voltage Balancing Converter for Bipolar Distribution System

This paper proposes a bipolar dc power electronic transformer (DCPET) with monopole fault operation capability for medium voltage / low voltage DC (MV / LVDC) distributions. Compared with the conventional bipolar LVDC topology, the proposed DCPET considers the reduced number of switching devices and the normal operation under monopole faults, which improves power supply reliability. The dc fault ride-through (FRT) strategy is further proposed in this paper to increase the power supply reliability under LVDC short-circuit faults. To reduce the short-circuit current and maintain the LVDC voltage, the switching device reversely series with the capacitor is blocked after the fault. Thus, the fault current is restricted, and power supply recovery time after fault clearance is reduced. Moreover, the LLC resonant converter adopting phase shift control outputs stable fault criterion current to assist the fault location and removal for the protection system. Finally, a downscaled prototype is built to verify the proposed topology and FRT strategy by experiments.

Fault Recovery Analysis of Grid-Forming Inverters With Priority-Based Current Limiters

Grid-forming (GFM) inverters are required to operate robustly against grid faults. However, due to the limited over-current capability of inverters, current-limiting controls are usually applied to protect these semiconductor devices, which may prevent GFM inverters from a successful fault recovery. To understand this phenomenon, this study analyzes the fault recovery process of a GFM inverter with a priority-based current limiter. According to whether the GFM inverter can ensure transient stability and exit the current-limiting mode after fault clearance, three post-fault scenarios are identified, including <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">normal operation, current limitation, and oscillations</i> . Further, the impacts of the short-circuit ratio and control parameters on the post-fault behavior of GFM inverters are demonstrated. To illustrate the implications of these theoretical results, typical numerical examples are presented. Finally, the theoretical findings are validated through experimental tests.

LoRaWAN-based IoT protocol for three levels central protection scheme in MT-HVDC networks with ANFIS-PSO restoration algorithm

A new three-level adaptive central protection scheme has been introduced for multi-terminal high voltage direct current (MT-HVDC) transmission grids. The primary protection is based on a differential relay, while two backup protection levels are proposed: a local dv/dt under-voltage relay and a centralized overcurrent relay at the AC grid side. The coordination of these three protection levels is managed based on a convenient coordination time. The communication between the central protection unit and the Fault Isolation Devices (FIDs) is established using the LoRaWAN-based Internet of Things (IoT) protocol. In case of fault clearance triggered by the third protection level, the faulty line is detected and isolated using the adaptive neuro-fuzzy inference system (ANFIS) algorithm. The restoration process of the healthy lines focuses on minimizing load shedding and line power loss. The protection scheme proposed in this article has been implemented and tested under various fault conditions using the MATLAB/Simulink® environment. The results demonstrate the effectiveness and efficiency of the proposed protection scheme in detecting and isolating faulty lines in MT-HVDC transmission grids, along with a rapid restoration technique.

Multiagent System-Based Adaptive Numerical Relay Design and Development: Part I - Firmware

Protection relays that incorporate advanced microprocessors are vital to electrical grids, providing fast and reliable responses to faulty conditions using efficient communication protocols. Instant detection and response to various faults are essential to minimise the risk of damage. Numerical relays can identify faulty conditions and trigger circuit breakers to open, thus preventing further damage to the system. Due to the lack of autonomous decision-making capabilities, existing numerical relays require manual reconfiguration in situations such as a change in network configuration and protection settings. These relays also do not have the ability to coordinate fault clearance when multiple sources supply power to the grid. A comprehensive overview of the research aimed at developing a multiagent system (MAS)-based adaptive protection relay will be provided by dividing it into separate articles such as firmware and hardware. This first part delves into the firmware aspects of this innovative relay, highlighting its adaptive capabilities and key considerations in its development. The second part will provide detailed design descriptions for the hardware features of the relay. An STM32MPU multicore advanced microprocessor is utilised to design and develop the adaptive numerical relay firmware. It incorporates several protection relay ANSI codes, communication protocols, and MAS-based adaptive protection schemes as part of the firmware.

Temporary overvoltage assessment and suppression in heterogeneous renewable energy power systems

Temporary overvoltage (TOV) may arise in renewable energy power systems after the fault clearance due to the plant-level delay. It is challenging to evaluate the TOV of a Multi-Infeed Power Electronic System (MIPES) considering the complex interactions among renewable power plants (RPPs). Moreover, the complexity of the evaluation is further increased when the MIPES is heterogeneous, where RPPs have different structures and control parameters. To tackle these challenges, this paper proposes a method to analytically assess TOV in a heterogeneous MIPES based on grid strength analysis. It is derived that different types of RPPs can be equivalent to similar models, i.e., current source parallel reactance. On this basis, it is obtained that the TOV and safety margin of the system can be assessed based on the heterogeneous generalized short-circuit ratio (gSCR-TOVhet) and the critical gSCR (CgSCR). Thereafter, a solution to suppress the TOV based on the configuration of synchronous condensers is proposed, which provides an effective way to improve the voltage safety of the heterogeneous MIPES. EMT simulations based on various test systems are performed to validate the effectiveness of our method.

On the Problems of Current Limitations in Networks Based on Power Semiconductor Devices

The presence of high short-circuit currents (200–300 kA) in autonomous and generator power systems of low and medium voltage classes, causing a decrease in the switching resource of switching facilities, necessitates the search for ways of limiting the current. The paper proposes a solution to this problem: a semiconductor current-limiting device based on a DC chopper, a DC-to-DC converter. This devices’ features are its low dimensions and losses during typical operation. Semiconductor elements can be arranged quite compactly due to the lack of radiators for cooling, since the cooling process—taking into account the short duration of the current limitation process—is not efficient. The choice of semiconductor devices takes into account the short duration of the current load, as a result of which the temperature of the semiconductor structure does not exceed its permissible value. This paper presents a method for calculating the parameters of semiconductor devices, taking into account the current load as well as adjusting the magnitude of current limitation to a value that can be disconnected by switching devices. The short-term mode of operation of the power semiconductor device with current regulated by the frequency and duty cycle of its operation makes it possible to facilitate the required current limitation in the circuit for the subsequent fault clearance with a typical electrical device. The problem of overcurrent of one of the elements of the limiter is noted, which requires special attention to ensure that the semiconductor device is not overheated. This paper also presents the principle of current limitation, summarizes the results of experimental studies, and analyzes the presented capabilities of a semiconductor current limiter.