In active distribution networks (ADNs), power electronic devices like inverters introduce noise interference into fault monitoring signals, compromising identification accuracy. This challenge is particularly pronounced in high-impedance grounding faults, where weak fault signatures degrade conventional detection performance. This study proposes an improved residual CNN architecture, ResNet-Kolmogorov-Arnold-network (R-KAN), for accurate single line-ground fault (SLGF) identification. The method leverages the rich fault features contained in transient zero-sequence current (ZSC) and zero-sequence voltage (ZSV) waveforms following SLGFs in DG-integrated systems. The model employs superimposed ZSC-ZSV images as inputs and replaces standard ReLU activation with KAN functions, reducing linear components and computational burden. A comprehensive dataset generated through PSCAD simulations trains the R-KAN alongside conventional neural networks. Comparative evaluations demonstrate R-KAN's superior classification performance across multiple metrics. Rigorous testing, including high-resistance fault scenarios, noise interference conditions, and missing data cases confirms the model's enhanced generalization capability. Field validation using actual recorded waveforms further verifies the model's practical effectiveness in real-world SLGF identification. The proposed approach addresses critical challenges in modern ADNs by combining advanced network architecture with optimized feature extraction from transient zero-sequence components.

To stabilize the fluctuation of wind power, a composite energy storage system with gravity energy storage and supercapacitor is proposed. Firstly, aiming at the mechanical motion nature of gravity energy storage, a refined mathematical model including mechanical, kinematic and power models is established, and the control strategy of both storage devices is designed. Furthermore, considering the step discrete characteristics of the gravity energy storage power, a double-layer power distribution logic based on the precise selection of the number of energy storage blocks is designed. The gravity energy storage deals with the low-frequency large-amplitude power fluctuation, and the supercapacitor deals with the residual high-frequency power fluctuation and the transient shocks of the gravity energy storage, solving the matching problem between step regulation and continuous power fluctuation. Finally, the simulation models of wind-storage system are built in MATLAB / Simulink, and the short-term fixed grid-connected power mode and long-term load power tracking mode are analysed. The results show that compared with the single gravity energy storage system, the proposed composite system reduces the grid-connected power deviation by 97.6%, effectively eliminates the step fluctuations and transient shocks, and achieves smooth grid-connected and peak load shifting of wind power.

The large doubly-fed pumped storage unit (DFPSU) features AC excitation and variable speed constant frequency power generation. It can be used not only for planned peak shaving and frequency modulation, but also for wide power range follow-up adjustments in response to wind and solar power fluctuations. Studying mathematical modeling methods for internal faults holds significant practical importance. It aids in understanding fault characteristics and determining the optimal main protection configuration. This study establishes a general mathematical model of DFPSU based on branch voltage and flux linkage equations, with its accuracy verified through dynamic simulation experiments. Based on this, the proposed model is applied to batch simulations using an actual large-scale unit as the analysis object, enabling quantitative analysis of the optimal stator short-circuit fault protection configuration. The recommended main protection configurations are: 'zero-sequence transverse differential current protection + split-phase transverse differential current protection + complete longitudinal differential current protection' or 'zero-sequence transverse differential current protection + split-phase transverse differential current protection + double incomplete longitudinal differential current protection'. This configuration provides the most comprehensive protection coverage.

The adjustable speed hydro-generating unit has a complex three-phase alternating current excitation structure. The existing rotor winding short circuit (RWSC) fault diagnosis methods are generally difficult to use to locate the fault location and identify the severity of the fault. Therefore, an offline diagnosis method for the internal RWSC of an adjustable speed hydro-generating unit is proposed in this paper. Firstly, after the unit is shut down, the low-voltage pulse signal is repeatedly injected into the rotor winding by the pulse generator. By comparing and analyzing the voltage response characteristics under different types of short circuit faults, an identification method of rotor winding short circuit fault type and fault phase based on detecting the reverse polarity sub-spike is proposed. Furthermore, the short circuit fault point can be accurately located by combining ensemble empirical mode decomposition (EEMD) with the Teager energy operator (TEO). Finally, the fault factor is constructed based on the area between the characteristic waveform and the zero line, and the quantitative evaluation of the severity of the short circuit fault is realized based on this. The effectiveness of the proposed fault diagnosis and location method is verified by the simulation results.

As an important facility for peak shaving and frequency modulation, the operation safety of pumped storage unit is of great significance for power systems to accommodate new energy power generation. Focusing on stator grounding fault, which have the highest occurrence probability, this paper proposes a fault location method and a multi-solution countermeasure suitable for the winding configuration and parameter characteristics of pumped storage units. Based on the analysis of the fault equivalent circuit, a fault location approach based on the intersection of phasor trajectory is proposed. Combined with a winding potential calculation method based on slot potential analysis, the causes of multiple solutions in fault location results are analyzed and summarized. By introducing injection information or triple harmonic voltage information as auxiliary information, the multi-solution screening is achieved, enabling the determination of a unique fault location. Finally, the effectiveness of the proposed location method is verified by simulation and experimental analysis.

Single-phase stator winding ground fault is one of the most frequent faults in the marine nuclear power platform. The internal space of the platform is compact and contains the nuclear reactor loads, so it is sensitive to the arcing process and needs reliable arc suppression. Therefore, the active voltage-drop arc suppression and fault property identification methods are presented in this paper. For the fault point location method constructed by the fundamental potentials, multiple solutions may be calculated under certain fault conditions. Thus, a low frequency injection-based checking criterion is proposed to determine the unique location result. On this basis, the arc suppression compensation currents containing the fundamental and third harmonic components can be calculated and injected into the generator neutral point. Since the neutral point voltage is controlled to be equal to the amplitude of the fault potential and the phase is opposite, the fault point voltage is suppressed to zero, and effective arc suppression is realized. The fault property identification is realized by using the value difference of the grounding transition resistance. Thus, transient and permanent fault conditions are distinguished. Simulation and dynamic experiment results verify the effectiveness of the proposed method.

With the expansion of cable-based distribution networks and the growing integration of power electronic devices, conventional arc suppression methods face increasing difficulty in addressing the complex characteristics of single-phase-to-ground faults. Additionally, control inaccuracies caused by line impedance significantly limit the effectiveness of existing active suppression technologies. To address these challenges, this paper proposes a coordinated ground fault suppression strategy for distribution networks that accounts for line impedance, by coordinating a substation-side arc-suppression coil (ASC) with feeder-side power router (PR) devices. First, the operational principles and coordination mechanism of the substation-side ASC and feeder-side PR are analyzed, and a capacity allocation scheme is developed to ensure efficient equipment utilization during the arc suppression process. Next, the influence of line impedance on arc suppression is examined under various PR installation positions and feeder ground fault scenarios. To overcome the limitations of conventional methods, a dual-impedance feedforward compensated active voltage arc suppression (DFC-AVAS) strategy is proposed. This method improves fault point voltage suppression by accounting for line impedances between the feeder-side PR and the substation bus, as well as between the substation bus and the fault point, within the zero-sequence voltage feedforward loop. Finally, the effectiveness of the proposed method is validated through simulation.

The development of distributed energy resources has positioned multi-terminal power supply systems as dominant model in distribution networks, typically featuring a structure that is “designed for closed-loop configurations but operated in open-loop mode”. However, short-term outages during maintenance and the increasing demand for uninterrupted power supply pose significant challenges. To address this, distribution networks must enable load-transfer through loop-closing operations for continuous power supply. This paper proposes a loop-closing device based on a dynamic reconfiguration converter (DRC-LCD) to facilitate flexible loop-closing despite voltage mismatches across buses. By enabling flexible transitions between parallel current control (PCC) and series voltage control (SVC) modes, the DRC-LCD enhances converter functionality and utilization. The operating principles of the DRC-LCD are analyzed under various conditions, and its control and switching strategies are designed. Simulations in a 10kV distribution network validate the topology and flexible loop-closing control of the DRC-LCD.

Aiming at the hybrid system composed of parallel cables and bilateral overhead lines in a high-load-density power grid, this paper accurately analyzes the adaptability of distance protection applied to the system and proposes the compensation methods for measured impedance under different fault types. Firstly, the equivalent three-sequence network models are established when faults occur in different regions of the hybrid system. Subsequently, the expressions of the measured impedance for faults in different regions and the accurate zero-sequence current compensation coefficients (ZSCCCs) of ground faults are derived. On this basis, it is concluded that there is a risk of failure to operate for the distance protection zone 1 (DPZ1) when faults occur in the hybrid system, and there is a phenomenon of nonlinear extension and contraction in the protection range (PR) of the DPZ1 when ground faults occur. Furthermore, the measured impedance compensation methods under different fault types are proposed. Finally, the simulation results prove the correctness of the distance protection adaptability analysis of the hybrid system in the high-load-density grid and the effectiveness of the measured impedance compensation methods.

For generator stator ground faults, the active arc suppression method typically needs the large-capacity inverter, leading to huge size and high cost. Moreover, the existing compensated parameter calculation method based on coil potentials cannot suppress arc at the non-coil connection points. To address these limitations, a hybrid flexible arc suppression method is proposed in this paper. By combining with the arc suppression coil grounding method, only the third harmonic and partial fundamental currents need to be compensated by the active arc suppression device, which significantly reduces the inverter capacity requirement. Instead of the coil potential analysis unit, slot potential analysis unit is used to characterize the winding potential distribution. Analytical equations are formulated to precisely calculate the fundamental and the third-harmonic fault potentials across the entire windings. The calculation results are used to determine the compensated parameters, enabling reliable arc suppression at any fault position within the entire windings. Effectiveness of the proposed method is validated by simulation and experiment.

During the operation of Adjustable speed hydro-generating unit (ASHU), due to high speed and large centrifugal force, the rotor winding is easily squeezed and causes short-circuit fault. The development of a reliable protection scheme is imperative. As a new and potential method, the universality of different-frequency differential protection is still limited under wide speed operation conditions. Therefore, a rotor winding short-circuit protection method based on fixed characteristic frequency band is proposed in this paper. Firstly, the internal relationship between the harmonic characteristics of rotor current and slip rate in the case of winding short-circuit fault of ASHU is analyzed. On this basis, the construction method of different-frequency differential current protection criterion based on fixed characteristic frequency band is proposed. Furthermore, combined with the waveform of the dynamic simulation experiment, the Generalized S Transform (GST) is used to carry out time-frequency analysis. The feasibility of the construction approach of the protection criterion is verified. Finally, the experimental results show that the proposed protection method is suitable for the wide speed operation condition of ASHU. It can achieve fast action under rotor winding short-circuit fault (RWSF), and has high selectivity under stator winding short-circuit fault (SWSF), which can effectively avoid protection misoperation.

Doubly-fed variable-speed pumped storage units (VSPSUs) offer significant flexibility for renewable energy integration; however, their extended speed range increases the risk of encountering inherent hydraulic instability zones, such as the hump and S-shaped regions, during transients. Existing LVRT studies primarily target DFIGbased wind turbines and often overlook the massive inertia, hydro-mechanical-electrical coupling, and specific hydraulic constraints of VSPSUs. This paper first derives LVRT requirements tailored to VSPSUs by considering their operating boundaries and inertia characteristics. A quantitative analysis reveals that negativesequence stator flux is the primary driver of rotor overvoltage/current during asymmetrical faults. To address these challenges, a novel LVRT strategy is proposed that integrates negative-sequence demagnetization with a hydraulic-stability-oriented control logic based on quasi-PIR control. The method prioritizes reactive current injection, and when the hydraulic stability margin decreases, the control objective is adaptively shifted toward hydraulic protection by regulating the q-axis rotor current, ensuring that the operating trajectory avoids entering the hump and S-shaped unstable regions. Finally, PSCAD/EMTDC simulations and experimental results demonstrate that the proposed method effectively limits rotor electrical stress while significantly enhancing grid support. Crucially, the results confirm that the VSPSU maintains stable operation without violating hydraulic safety boundaries, even under severe voltage sag conditions.

ABSTRACT For variable‐speed pumped‐storage units with full power converters (FPC‐VSPSUs), converter‐based decoupling control fundamentally reshapes the machine‐terminal measured impedance trajectory during a loss‐of‐excitation (LOE) fault in the excitation system (ES). Consequently, conventional machine‐terminal measured‐impedance‐based protection schemes may suffer from large blind zones and a high risk of failure to trip. To address this issue, this paper presents a comprehensive analysis of the post‐LOE impedance characteristics under two field‐orientated control (FOC) strategies: stator‐flux orientation (SFO) and rotor‐flux orientation (RFO). Under stator‐side unity‐power‐factor operation, it is revealed that, for both FOC strategies, the machine‐terminal measured impedance trajectory moves along or near the real axis during the early LOE stage. Based on this characteristic, an adaptive rectangular LOE protection scheme is proposed, in which the setting boundaries are dynamically adjusted by integrating multidimensional operating‐state information, including rotational speed, operating condition, and FOC strategy. PSCAD simulations and RTDS hardware‐in‐the‐loop (HIL) experiments with an industrial protection relay demonstrate rapid and reliable fault identification over a wide operating range, including low‐active‐power generation conditions, while avoiding maloperation during grid disturbances.

A proportional-integral repetitive controller (PIRC) can be employed in hybrid distribution transformers (HDTs) to control voltages and currents across multiple frequencies for the steady-state performance improvement. However, the transient performance of a PIRC under grid faults or step change conditions deteriorates due to the coupling effect between its proportional and repetitive components. Based on the derived transfer function of the PIRC in relation to the HDT, this article reveals that the mismatched dynamic response speeds between the PI and RC loops are the primary cause of the control coupling effect. This mismatch leads to the accumulation of step tracking errors into the next fundamental frequency cycle in the RC loop. To address this issue, a novel event-triggered PIRC (ET-PIRC) scheme is proposed to eliminate the control coupling effect and enhance the HDT's transient performance. The main contribution of this article is the adoption of an event-triggered control based on the principle of dynamically adjusting the control efforts of the PI and RC loops in response to the step tracking errors, thereby mitigating the inherent coupling between them. During step changes, this approach accelerates the transient response of the PI loop while driving the step tracking error in the RC loop to zero, effectively decoupling the two control loops. The robustness and stability of the ET-PIRC are also examined. Comparative simulation and experimental results validate the feasibility of the proposed control method and its superior transient response performance.

The access of flexible direct-current (DC) transmission converters reshapes the fault characteristics of transmission lines, leading to degraded performance of distance protection methods that rely on fault characteristics typical of traditional synchronous power supplies. To address this issue, this paper proposes a control-protection coordinated distance protection method for transmission lines connected to flexible DC converter stations. During transmission line faults, an enhanced fault ride-through (FRT) control strategy is developed so that the converter station exhibits a positive-sequence controlled voltage-source behaviour, thereby improving the applicability of phase-comparison distance protection. Meanwhile, the reference voltage magnitude is reduced to strictly limit the fault current within the device overcurrent constraints, ensuring converter security. On the protection side, a steady-state validation criterion is employed to identify the completion of the converter transient control adjustment, and the distance element is released accordingly to achieve reliable and fast fault discrimination. PSCAD/EMTDC simulations on a representative flexible-DC-integrated system and dynamic experiment results verify that the proposed coordinated scheme can accurately identify fault direction and location while preserving selectivity under various fault types and locations.

Featured Application The research presented provides a theoretical and practical framework for enhancing the operational stability and protection reliability of full-size converter variable-speed pumped storage units (VSPSUs). By elucidating the complex coupling between electromagnetic transients and control strategies, this work offers a specialized loss-of-excitation (LOE) protection scheme that can be directly integrated into the digital relay systems of modern pumped storage plants.Abstract This paper presents an in-depth investigation into the loss-of-excitation (LOE) protection for variable-speed pumped storage units with full-size converters (FSC-VSPSUs). It elucidates the dynamic interaction between electromagnetic transients and converter control loops under various machine-side converter (MSC) control strategies. The study reveals that units employing voltage-oriented control face a fundamental risk of phase-locked loop (PLL) instability following an LOE event. Given the inadequacy of traditional impedance-based protection for FSC-VSPSUs, a novel LOE protection scheme is proposed. This scheme integrates a dynamically tuned main impedance criterion with an acceleration criterion based on the rate of change of the impedance's real part, incorporating a speed compensation coefficient to accommodate variable-speed operations. Experimental validation on an RTDS platform demonstrates that the proposed strategy accurately identifies LOE faults across various turbine and pumping modes, offering superior response speeds compared to traditional methods and other techniques reported in the existing literature.

In rural or remote areas, single-phase power distribution systems have been commonly adopted for electrical power supplying, due to historical and economic considerations. Residential distributed energy resources (DERs) and single-phase loads typically connect to the medium-voltage grid directly via separate single-phase transformers and converters. These separate connections result in power imbalances, equipment redundancy, increased costs, and issues with power quality and converter coordination for both low-voltage users and the medium-voltage grid. This article proposes a novel V/V-connected hybrid distribution transformer (VV-HDT) designed to integrate loads and DERs efficiently, while actively controlling voltage and current to enhance power quality and isolate faults. It uses a modified V/V transformer for voltage conversion and primary power transmission, with partial power managed by smaller capacity converters. The V/V transformers offer mutual power circuits, providing a hardware basis for resolving power imbalances and facilitating the expansion of needed transformer capacity. This article elucidates the VV-HDT's voltage and current control mechanism, the equivalent model of the modified V/V transformer, port power flow analyses, and the coordination control strategy under normal and grid fault conditions. Simulations and prototype experiments confirm the VV-HDT's effectiveness and control strategy.

The Rotating Asynchronous Machine (RAM) system of a nuclear power plant provides a stable and reliable power supply for the control rod drive mechanism (CRDM) through two parallel generators. At present, the main protection of the generators in the RAM system is only configured with longitudinal differential protection, which cannot reflect the interturn short circuit fault and interbranch short circuit fault of the stator winding. Based on the characteristics of parallel connection of RAM generators in nuclear power plants, this article proposes a dual-generator split phase transverse differential protection and a dual-generator incomplete longitudinal differential protection. Through the internal fault set of the generator and the internal fault potential splitting model of the generator, the quantitative analysis of different main protection configuration schemes is carried out. It is concluded that the existing longitudinal differential protection and the incomplete longitudinal differential protection of two parallel generators can correctly reflect the vast majority of internal short-circuit faults. Finally, the dynamic experiment is carried out to prove the feasibility of the protection method in the actual unit operation.

Generators on offshore oil platforms are often subjected to vibrations caused by wave impacts, which lead to frequent stator ground faults and arc generation. The generator system typically adopts a multi-generator common-bus configuration. If the conventional active arc suppression method based on neutral-point voltage regulation is used, high equipment cost and maintenance complexity are introduced. An active arc suppression method based on terminal voltage regulation is proposed in this paper. The arc suppression device is installed at the terminal side bus. When the stator ground fault occurs in any generator, the fault point voltage is regulated to zero by controlling the terminal voltage of the generator. Reliable arc suppression can thus be achieved, while significantly reducing the total installed capacity and the number of configured devices required for arc suppression. A selective fault location criterion based on the phase of the variation of terminal zero-sequence current before and after arc suppression is also proposed. The faulty generator can be identified after arc suppression. The effectiveness of the proposed method is verified through simulation and experimental results.