Current Differential Protection Research Articles

A Multi-Terminal Current Differential Protection Setting Method for Fully Weak-Infeed Distribution Networks Based on Restricted Enumeration Method

A Multi-Terminal Current Differential Protection Setting Method for Fully Weak-Infeed Distribution Networks Based on Restricted Enumeration Method

Differential protection scheme for distribution network with distributed generation based on improved feature mode decomposition and derivative dynamic time warping

With the progress of communication technology, the cost of optical fiber and 5G continues to decrease, and data transmission becomes more convenient and fast, making it possible to realize differential protection of distribution network by various intelligent algorithms using signal waveforms. Aiming at the problem that the traditional relay protection device can not meet the actual demand when the single-phase ground fault occurs in the distribution network with distributed generation, this paper proposes a new differential protection scheme. The characteristic mode decomposition improved by the whale optimization algorithm is used to decompose the zero-sequence current waveform collected at both ends of the line. Based on the basic principle of current differential protection, the derivative dynamic time warping of the component with the largest fault feature can effectively solve the problem that the grounding current of the distribution network cannot meet the working requirements of the differential protection device, and ensure the safe and stable operation of the system. Finally, based on MATLAB software, the performance of this method is comprehensively evaluated by simulating different fault conditions, so as to ensure the feasibility and accuracy of this method in the case of diversified faults when the distributed generation is used as part of the power supply.

Centralized event-based protection based on communication infrastructure of medium voltage direct current network

Direct current (DC) distribution systems play a crucial role in integrating various DC systems, renewable energy sources, and power loads. Single-ended protection methods are inadequate for ensuring high-speed selective protection due to the lack of boundary elements, while current differential protection methods can be affected by line-distributed capacitance currents. Therefore, an event-based protection scheme is proposed that uses communication infrastructure and the first derivative of the transient fault current to provide a selective protection system for Medium Voltage Direct Current (MVDC) networks. The scheme utilizes Intelligent Electronic Devices (IEDs) to transmit events to the Intelligent Protection Center (IPC) via a communication network, which compares them to identify the faulty section. The proposed protection scheme is effective in detecting and isolating faults, even under challenging network conditions, as demonstrated by simulation results on a two-terminal topology MVDC distribution network using the PSCAD/EMTDC platform.

Protection adaptability analysis method for photovoltaic grid-connected generating system

Inverter power sources such as photovoltaic inverters and SVG have unique fault characteristics compared to traditional synchronous motors due to their unique power generation methods, circuit topology, and low-voltage traversal control strategies. The power grid faces various adverse effects due to the ongoing expansion of photovoltaic power station (PV power station) capacity. How to comprehensively analyze the impact of photovoltaic power stations above 1000 MW on power grid relay protection has become a problem. Therefore, a protection adaptability analysis method for photovoltaic grid-connected generating systems is proposed, which is suitable for engineering analysis before the connection of large-capacity PV power stations to ensure the safety of the power system. And it is found that current differential protection exhibits better adaptability than distance protection.

Reference Phasor-Based Data Self-Synchronization Scheme for Line Current Differential Protection in Active Distribution Networks

Reference Phasor-Based Data Self-Synchronization Scheme for Line Current Differential Protection in Active Distribution Networks

Adaptive Quasi-Power Differential Protection Scheme for Active Distribution Networks

With the massive integration of distributed generations (DGs), distribution networks gradually become more active and flexible. Conventional overcurrent protection is difficult to adapt to such active distribution networks (ADNs). Current differential protection (CDP) is a good choice for solving this issue, but the multi-branch structure of ADNs especially the unmeasured T-connected load branch affects the protection’s sensitivity. Therefore, the paper proposes a quasipower differential protection (QDP) scheme based on Tellegen’s theorem. First, the feasibility of applying Tellegen’s theorem to ADNs was analyzed. On this basis, reasonable protection criteria were designed for different scenarios of ADNs. Then, an adaptive protection scheme was established, which can automatically adjust the criteria depending on the presence of Tconnected branches within the protected section. Finally, extensive simulations were carried out in an ADN model using PSCAD/EMTDC software. The simulation results demonstrate that the proposed protection scheme has excellent adaptability to network topologies, fault types, fault resistances, and network structures of ADNs.

Interoperability Challenges in Multivendor IEC 61850 Devices for Parallel Power Transformer Differential Protection

Interoperability of GOOSE messages is essential for the proper operation of protection schemes such as the parallel power transformer (PTRF) differential protection scheme, especially when using multivendor IEC 61850 devices. GOOSE messages allow for fast and reliable communication between intelligent electronic devices (IEDs) and are based on Ethernet communication. To ensure the interoperability of GOOSE messages between multivendor devices, adherence to the IEC 61850 standard specifications is crucial. The standard defines the format and content of GOOSE messages, including the data object model, data types, and communication protocols. Third-party testing and certification programs can also ensure compliance with the standard and help guarantee interoperability between different vendors. Device conformance with these standards does not ensure interoperability when devices from various manufacturers are utilized. Interoperability is necessary between the relevant devices from various vendors to provide system power stability and protection. If multivendor device interoperability is achieved, power utilities will be able to utilize multivendor devices in substations. The study investigates and provides comprehensive methods for achieving IEC 61850 standard-based interoperability problems in parallel with PTRF’s current differential protection schemes between IEDs (SEL-487E and MiCOM-P645) produced by different vendors under fault conditions. In a lab-scale environment with RTDS for real-time simulation in Hardware-in-the-Loop (HIL), the designed technique is simulated and tested.

A Fast and Sensitive Current Differential Protection for MMC-HVDC Lines

A Fast and Sensitive Current Differential Protection for MMC-HVDC Lines

Design and Analysis of Reliable Current Differential Protection Through Improved Power-Line Communication

Design and Analysis of Reliable Current Differential Protection Through Improved Power-Line Communication

A Sympathetic Inrush Identification Method Based on the Time-Frequency Energy

Sympathetic inrush is a phenomenon caused by the energization of the neighboring unloaded transformer. It may cause current differential protection to operate in the wrong way. Due to the lack of a special and continuous identification method, this paper studies the inherent feature of the two transformers during sympathetic inrush. Then a substation-area current signal based on the feature is constructed and its characteristics are analyzed. The time-frequency energy of the current signal is extracted based on the synchrosqueezed wavelet transform (SWT) since the SWT can process the transient signals accurately. The extracted energy is taken as the basis of the identification criterion. The simulation results conducted by PSCAD/EMTDC software prove the accuracy and effectiveness of the proposed method.

A Current Differential Protection Scheme for Distribution Networks with Inverter-Interfaced Distributed Generators Considering Delay Behaviors of Sequence Component Extractors

The high-level proliferation of inverter-interfaced distributed generators (IIDGs) in modern distribution networks (DNs) has changed system topologies and fault current signatures, which compromises the protective relays in DNs. Investigating IIDG fault behaviors-based protection scheme will benefit the grid’s safety and stability. This paper proposes a novel current differential protection (CDP) scheme that considers the delay behaviors of positive- and negative-sequence component extractors for IIDGs in DNs. A frequency-domain analytical model of the fault current for a grid-connected IIDG with the PQ control strategy and a low-voltage ride-through (LVRT) capability is investigated. The dynamic behavior of the IIDGs considering the sequence-component extractor based on the Pade approximation is presented, where the T/4 delay extractor of the IIDGs causes a two-stage behavior in the fault transient process. It is found that a 5 ms error between the measured and actual values after the fault will affect the transient characteristics of the IIDGs. The transient current generated by the IIDGs during grid faults contains a large number of low-order harmonic components within the range of 0–200 Hz, which is significantly different to the current provided by the power grid. Therefore, the proposed CDP scheme uses protective relays at both terminals to obtain the required transient electric quantity using the Prony method. By constructing the frequency-characteristics ratio (FCR) and the exchanging FCR between two terminal relays, the developed protection criteria are implemented. The accuracy of the fault analysis method, whose maximum computational error is below 0.1%, and the feasibility of the proposed protection scheme are demonstrated by using a 10 kV DN in a PSCAD/EMTDC simulation, which can be applied to various fault conditions and traditional DNs without IIDGs.

A Two-Terminal Directional Protection Method for HVDC Transmission Lines of Current Fault Component Based on Improved VMD-Hilbert Transform

The traveling wave protection of high voltage direct current (HVDC) transmission lines is susceptible to the influence of transition resistance. As a backup protection, current differential protection has absolute selectivity, but usually requires an increase in delay to avoid misoperation caused by distributed capacitance on the line, resulting in a longer action time. Based on this, a two-terminal directional protection method for HVDC transmission lines is proposed based on Sparrow Search Algorithm (SSA)-Variational Mode Decomposition (VMD) and Hilbert phase difference. On the basis of analyzing the directional characteristics of the current fault component at both ends of the rectifier and inverter sides under different faults, SSA is first used to optimize the parameters of VMD. The residual components representing the direction of the current fault component at both ends are extracted through VMD, and then the Hilbert phase difference of the residual components at both ends is calculated to identify faults inside and outside the line area. In addition, fault pole selection can be achieved based on the ratio of the sum of multi-band Hilbert energy of single-terminal voltage fault components at the positive and negative poles. Simulation experiments have shown that the proposed protection scheme can quickly and effectively identify fault and has good tolerance to transition resistance and noise interference.

Phase-angle adaptive current differential protection for active distribution network

With the distributed generator to be attached to the distribution network, the current differential protection scheme may have some problems, resulting in maloperation or rejection of protection. This paper investigates the current distribution properties of an active distribution network with branches of undetected load and draws the conclusion that undetected load may cause differential protection maloperation. The differences in fault properties of differential protection in transmission network scenarios and distribution networks containing distributed generator are evaluated, leading to the conclusion that differential protection applied to active distribution networks may have reduced resistance to transition resistance and that poor signal synchronization conditions in distribution networks may lead to larger synchronization errors. A phase-angle adaptive current differential protection is proposed. It adaptively adjusts the phase angle constraint using the magnitude of the power frequency full current component proportion at both sides of the line. It can accommodate the protection needs of various operation modes of distribution networks containing distributed generator, and has the characteristics of strong resistance to transition resistance and strong phase shift braking ability. The correctness of the suggested protection scheme was verified using the PSCAD platform.

Power Differential Protection for Transformer Based on Fault Component Network

Current differential protection has been widely used as the primary protection of transformers. However, inrush currents during transformer energization can cause misoperation of the protection when the second harmonic restraint algorithm fails. This paper proposes a power differential protection scheme based on the fault component network (FCN), which is free from inrush detection and computationally cheap. First, the fault component differential power (FCDP), defined as the differential active power of a transformer in the FCN, is analyzed under different conditions. Second, a transformer protection scheme is presented based on the FCDP and the traditional differential power. A removal algorithm of decaying direct current (DDC) offset is developed to accurately estimate the FCDP. The performance of the scheme is tested under various conditions, including internal faults, external faults and transformer energization. The simulations using PSCAD, and Real Time Digital Simulator (RTDS), experiments in the Electrical Power Dynamic Laboratory (EPDL) and real recording data validate that the proposed method can protect the transformer reliably.

ANALYSIS OF DIFFERENTIAL RELAY PROTECTION ALGORITHMS AND THEIR MODELLING IN MATLAB

The paper is devoted to identifying the prospects for software implementation of differential relay protection. The purpose of this study was to analyse the algorithms of the devices' operation, which allowed to create a mathematical model in the MATLAB software environment with the prospect of integration in the form of a single regional relay protection server into the unified energy system of Ukraine. It has been established that virtual models have both advantages and disadvantages compared to digital-analog devices. Their positive feature is that, due to the block principle of construction, it is possible to easily change not only the parameters but also the configuration of the primary network. The disadvantage is that the configuration of virtual protections differs from the configuration of their prototypes - real relays and terminals. The article evaluates the existing, widely used methodology and considers the actual algorithms of two-stage differential relay protection. It is established that differential protection has two stages: 1 - fast-acting differential current cut-off; 2 - sensitive differential current protection with inhibition from through current and recovery from magnetisation current surges. A simplified diagram of a fragment of the electrical system and differential relay protection of a transformer are developed and presented in MATLAB. The algorithms are considered in detail, and it is established that with their help and with the help of the considered principles of differential protection in the Simulink package, the logic of the model is implemented similarly to the logic of microprocessor-based transformer protection "RS-83DT2" of RZA Systems LLC, SPAD 346 C of ABB. Based on the modelling results, the oscillograms of primary currents of normal mode and emergency modes with external and internal short circuits are obtained. The conclusions establish the prospects of using this model and algorithms for the development of a software solution for the relay protection server and for future integration into the integrated power system.

Mathematical Morphology-Based Fault Data Self-Synchronization Method for Differential Protection in Distribution Networks

Conventional overcurrent protection is hard to apply to modern distribution networks with high penetration of distributed generations and flexible operation modes. Current differential protection (CDP) is considered to be a good solution, but the expensive cost of data synchronization equipment limits its application. Fault data self-synchronization (FDSS) methods realize the approximate data synchronization according to the features of measured currents at both terminals, which makes it possible to achieve the low-cost CDP. However, the existing FDSS methods still have shortcomings such as low accuracy or complicated steps. In this paper, the principles and defects of existing FDSS methods are first analyzed, and then an improved FDSS method based on mathematical morphology (MM) is proposed. This method is realized by MM filter and MM-based peak-valley detection algorithm, which has higher synchronization accuracy and anti-noise ability. More importantly, in this method, the reference time required for synchronization can be obtained in the pre-communication process, which is easily implemented. The simulation based on PSCAD-MATLAB verifies the effectiveness of the proposed method under different fault conditions and its improvement compared with the existing method. Finally, the RTDS-based hardware test platform is used to verify the differential relay prototypes developed based on the proposed method.

Injection Harmonic Current Differential Protection Based on Control-Protection Synergy for Distribution Networks with IBDGs

The high penetration of inverter-based distributed generations (IBDGs) leads to traditional distribution networks’ complex and variable fault characteristics. Traditional passive detection protection methods can hardly meet the stability and reliability requirements. To solve this problem, an injection harmonic current differential protection (IHCDP) scheme based on the idea of control-protection synergy is proposed in this paper. By analyzing the circuit structure, control strategy, low-voltage-ride-through characteristics of IBDGs, and short-circuit currents provided by IBDGs, an injection-control strategy of characteristic harmonic currents (CHCs) based on the d-axis and q-axis is proposed. According to the change of short-circuit currents provided by the IBDG, the amplitude of CHCs is adaptively corrected to strengthen the fault characteristics and ensure that the distribution network harmonic injection protocols are always satisfied. An IHCDP criterion based on the distortion rate of the negative-sequence component of CHCs is proposed by analyzing the fault characteristics of the CHCs after injection. To effectively eliminate the dead-zone problem during symmetrical short-circuit faults, the proposed IHCDP utilizes the distortion rate of A-phase CHCs. The feasibility of the proposed protection scheme is demonstrated by the theoretical analysis and simulation results in this paper.

A novel protection strategy for DC microgrid considering communication failure

DC microgrid has become an important part of supporting “carbon peaking, carbon neutralization” and building a low-carbon energy system. However, the short-circuit current of the DC microgrid rises rapidly and has a great impact, threatening the normal operation of the DC microgrid. As the main protection strategy for removing short-circuit faults, current differential protection can quickly and selectively remove fault lines, but it depends on communication. In addition, a high impedance short circuit may also lead to the failure of the current differential protection strategy. To improve the quick action and sensitivity of DC microgrids protection strategy, a differential protection strategy based on the bus power gradient is proposed, and to further solve the problem of protection failure caused by communication failure or communication data loss, an improved composite strategy for DC microgrids considering communication faults is proposed. In the case of normal communication, the power gradient differential protection detects and removes the short-circuit faults; In the case of communication failure, the power gradient differential protection is blocked and local power gradient protection is started. The problem of protection strategy failure caused by communication failure was solved without adding measuring devices. Meanwhile, the power differential gradient changed more violently than the current or voltage during the failure, which improved the protection sensitivity. Finally, simulation and experiment prove the effectiveness of the proposed strategy.

Waveform dissimilarity factor-based protection for main transformers in wind farms

Current differential protection (CDP) is widely used as main protection for transformers due to its high reliability and selectivity. Owing to non-fundamental frequency current, magnetizing inrush and current transformer (CT) saturation, CDP may undergo slow operating speed when the internal fault occurs. When the external fault occurs, CDP may false operate. Furthermore, given the disadvantage of Hausdorff distance being extremely sensitive to abnormal data, a new metric that reveals the dissimilarity degree of two waveforms is presented, namely waveform dissimilarity factor (WDF). WDF has inherent immunity to abnormal data. Subsequently, WDF-based protection for main transformer is proposed herein. In order to reduce the adverse effects of magnetizing inrush and CT saturation and accurately identify internal faults, the reward and punishment mechanism is designed. The protection principle is elaborated and its operating characteristics are analyzed under various conditions. Finally, by constructing the DFIG-based wind farm, PSCAD is used to verify the advantages of the novel protection algorithm based on WDF. Its performance is widely assessed in various scenarios in detail, including magnetizing inrushes, minor and server internal faults, inter-turn fault, turn-to-ground fault, internal fault with CT saturation and external fault with CT saturation, data loss, abnormal data, and CT error. The results show that the novel protection scheme has the characteristics of fast, secure, and robust.

Adaptive additional current-based line differential protection in the presence of converter- interfaced sources with four quadrant operation capability

As typical representatives of converter-interfaced sources with four quadrant operation capability, battery energy storage station (BESS) and VSC-HVDC station behave differently with synchronous generator. This leads to the high risk of incorrect operation of current differential protection (CDP), seriously threatening the security of transmission network. Motivated by this issue, this paper presents adaptive additional current-based differential protection (AAC-DP). Adaptive additional current is introduced to modify the criterion of current differential protection. Ulteriorly, the unified expression of adaptive additional current for internal and external faults is designed. Adaptive additional current can increase the sensitivity during internal fault, whereas it improves the security during external fault. The sensitivity and dependability of AAC-DP was widely evaluated by changing operation mode, fault condition, and type of power source using PSCAD and RTDS-based experimental platform. Also, the adverse factors, such as saturation and error of current transformer(CT), and noise, were taken into account; thereof, the excellent security of AAC-DP was confirmed. The results confirm that AAC-DP exhibits excellent performance in operating speed, sensitivity, the adaptation to fault behaviors of BESS and VSC-HVDC, and robustness against saturation and error of CT, and noise.