Current Differential Relay Research Articles

Cyber-Immune Line Current Differential Relays

Cyber-Immune Line Current Differential Relays

A New Approach to Current Transformer Saturation Compensation for Transmission Line Differential Protection

A non-linear autoregressive network with external inputs (NARX) model to reconstruct the current transformer (CT) secondary waveform distortion in the presence of protected transmission lines is presented. The qualitative analysis carried out on the autonomous model reveals the accurate performance of the current differential relay, because of the ability of the NARX to make accurate predictions and signal reconstruction even when faced with noisy or incomplete datasets. The suggested method uses samples of the line-protected remote current signal to produce a desired waveform. The unsaturated section is artificially expanded because it can estimate up to one sample after saturation with a respectable level of accuracy. The proposed method is evaluated by MATLAB and PSCAD software. The effectiveness of the suggested method for different fault types under varied situations has been proved. The simulation outcome confirms the method’s high accuracy concerning the unusual system conditions in the presence of CT saturation.

Enhancing grid protection: The crucial role of resistive-type superconducting fault current limiters in transmission line current differential relays

Superconducting fault current limiters (SFCLs) offer an efficient means of limiting fault currents and supporting system reliability. However, they weaken the fault characteristics and reduce the sensitivity of traditional relay protection. The seamless integration of SFCLs with protective relays remains a complex and under-explored area, impeding their widespread industrial adoption. In parallel, current differential protective (CDP) relays are almost the primary protection for all high-voltage electrical equipment and are the cornerstone of global power system security. This paper fills a critical knowledge gap by researching the intricate interaction between resistive superconducting fault current limiters (R-SFCLs) and current differential protective relays. Our investigation commences with a comprehensive mathematical analysis, while researching the influence of R-SFCLs on CDP operation. Subsequently, we conduct a series of comparative experiments using the Matlab Simulink software platform. These tests evaluate the sensitivity, dependability, and security of CDPs in scenarios with and without R-SFCLs. The simulation results not only confirm the accuracy of our analytical framework but also shed light on the multifaceted relationship between R-SFCLs and CDPs. This research contributes to a deeper understanding of how R-SFCLs can be effectively integrated into power systems, offering a roadmap for enhancing grid protection.

Cyber intrusion detection for line current differential relays in DC distribution system

Line current differential relays (LCDRs) are used as a promising solution for DC system protection. Such relays rely on communication channels (for remote end data) for decision and therefore, are susceptible to cyber intrusions. The false data injection (FDI) based cyber attack is one of the prominent threats, which may cause unintentional tripping of LCDRs. This paper presents a cyber intrusion detection algorithm based on the change in slope of the superimposed component of current in both ends of the line segment. The proposed algorithm distinguishes cyber attacks from the internal faults. The case studies are carried out on an IEEE 37 bus distribution system modified into a DC distribution test system in a real-time OPAL-RT environment. The performance of the proposed method is tested for different conditions including high resistance fault, FDI attack, load change, switching effect and signal with noise.

Enhanced sensitive phase alpha plane scheme against high resistance ground faults

Abstract Phase-based Alpha (α) Plane Relaying (APR) scheme has numerous advantages over the Current Differential Relay (CDR) for transmission line protection. Since the large Restraining Region (RR) in the APR makes high security against CT saturation, channel delay, line charging current and synchronization error. However, the APR loses its sensitivity for high resistance ground faults, especially single line to ground faults under outfeed conditions. Also, losing its dependability under close-in low resistance three-phase faults. Thereby, the sequence-based APR provides enhanced sensitivity with the cost of computational burden and complexity. Hence, in this paper, the concept of the average value (I Avg) of both end instantaneous currents is used as an auxiliary logic. In which, the polarity of I Avg is incorporated as an add-on logic to the conventional APR to confirm high resistance internal faults. Thereby, the requirement of sequence components can be avoided (negative and zero). To validate the proposed auxiliary logic, it is tested for the WSCC (Western System Coordinating Council) 9-bus, 110 kV, 50 Hz. System. The simulated results under various fault cases found authenticated results. In addition, the comparative assessment and validation with real-world data reveal the enhanced sensitivity of the proposed logic under high-resistance ground faults.

Fault current control of MMC in HVDC-connected offshore wind farm: A coordinated perspective with current differential protection

The modular multilevel converter (MMC) based high-voltage dc (HVDC)-connected offshore wind farm (OWF) is power electronic converter dominated power system, where the conventional current differential protection may not operate effectively. Based on the basic operation principle of the current differential relay, this paper points out that the phase difference (ϕdiff) of fault currents from MMC and OWF should be limited within a specific range, i.e. (-ϕdiffmax, ϕdiffmax), to guarantee the reliable tripping of the current differential relay. Yet, the highly control-dependent fault currents from the MMC and OWF could yield an arbitrary ϕdiff that might beyond (-ϕdiffmax, ϕdiffmax), which leads to the possible malfunction of the current differential relay. To tackle this challenge, the coordinated control method of MMC is proposed to align the phase angle of its fault current with that of the OWF, such that ϕdiff ∈ (-ϕdiffmax, ϕdiffmax) can be always guaranteed, so as the reliable operation of the current differential relay. Finally, the proposed coordinated control is verified by the electromagnetic transient (EMT) simulations in PSCAD and the real-time digital simulator (RTDS).

Anomaly-Based Detection of Cyberattacks on Line Current Differential Relays

Currently, the architecture of Line Current Differential Relays (LCDRs) is designed to respond to internal faults on the protected line using local and remotely-communicated current measurements. However, this architecture cannot distinguish between real faults and cyber-induced attacks whose goal is to cause false tripping of the line protected by the LCDR. In this paper, we propose an Anomaly-Based Scheme (ABS) for detecting false-tripping attacks against LCDRs, in the form of relay attacks, replay attacks, general false-data-injection attacks, and time-synchronization attacks. The ABS employs the Isolation Forest algorithm, which is trained on features determined from local current measurements to confirm real faults and differentiate them from false-tripping attacks. No trip command will be issued unless the sensed fault is confirmed as a non-attack by the ABS. The performance of the proposed ABS is tested and validated using the IEEE 9-bus benchmark in PSCAD/EMTDC environment. Simulation results show that the proposed ABS: (i) can accurately detect different categories of cyberattacks, (ii) does not negatively impact the accuracy of the fault-detection function, and (iii) is robust to the change in the power system’s operating point.

A Coordinated Multi-Element Current Differential Protection Scheme for Active Distribution Systems

This paper introduces a current differential protection scheme, appropriate for application in medium voltage active distribution systems, where it is desired to keep the greatest possible number of loads and DG units energized during a fault. Conventional two-terminal percentage current differential relays are used to form successive, time-current-coordinated, differential protection zones. Multiple time-delayed differential elements in each protection zone guarantee coordination with the zone's lateral protection devices, as well as between successive differential protection zones. Sensitive time-delayed differential elements protect against relatively high-resistance faults, while instantaneous differential elements minimize protection speed whenever possible. Additional emergency differential elements deal with post-fault topology changes and breaker failure conditions enhancing the overall scheme's performance. The proposed scheme is applied to a model of real medium voltage distribution system with distributed generation, considering a ring topology operation. A detailed simulation-based study proves the applicability and enhanced performance of the proposed scheme.

Improvement of power transformer differential protection through detection and exploitation of the negative sequence currents

Introduction. Power transformers are the most important and the most expensive equipment used in transport and distribution of electrical energy. Their failure results in huge economic losses. Despite the great advances in the design of power equipment in recent years, the feeble link in the chain remains the insulation weakness of coil turns of the power transformer. The novelty of the proposed research consists in the development of a new procedure for diagnosing and localizing the occurrence of turn to turn short-circuits in the windings of three-phase power transformer. The main problems of the current differential relay are short circuits of one or more turns of a transformer winding. Hence a new approach using' the amplitude comparison between the negative sequence currents' is developed and a digital discriminator internal / external fault is applied to discriminate turn to turn faults among the other ones. The proposed procedure is based on the exploitation of the negative sequence currents. The purpose of using this new procedure is to identify small faults inside power transformer coils and to distinguish inner faults from the outer faults by using an ameliorate circuit. The method used in this paper is a novel algorithm which based on the comparison between the negative sequence current amplitudes and to calculate the corresponding phase angle shifts. The performance of the proposed procedure has been confirmed by MATLAB/Simulink environment. The results of simulation reveal the efficiency of the suggested procedure, and indicate that this procedure can provide fast and sensitive approach for detecting low level turn-to-turn faults.

Study on effects of DSE-Based instrumentation channel error correction on protective relays

This paper presents the effects of dynamic state estimation (DSE)-based instrumentation channel error correction on protective relays. It discusses the possible mis-operations of relays caused by current transformer (CT) saturation for three typical protection schemes: distance protection, current differential protection and setting-less protection. For each protection scheme, it compares the relay responses with the estimated measurement samples and with the legacy measurement samples, respectively. Extensive cases have demonstrated that when large errors introduced by CT saturation, the legacy measurement samples can lead to slower operations for distance relay in case of internal faults, and unnecessary trip decisions during external faults for current differential relay and setting-less relay. In contrast, with the estimated measurement samples, the relays can correctly identify internal faults and avoid mis-operation in case of external faults.

Current differential relay characteristic for bipolar HVDC transmission line fault detection

This study proposes a new differential relay characteristic to detect internal faults on bipolar HVDC (high voltage direct current) transmission lines and discriminate accurately and in a timely manner both internal and external faults. In comparison with the conventional differential protection characteristic, the proposed relay characteristic avoids the need for an intentional time delay typically required to avoid nuisance fault detection. The sampling currents of the positive and negative poles are obtained from both line ends, and the noise is eliminated from the current signals using a stationary wavelet transform. Initially, a startup unit is utilised to activate the proposed protection scheme. The proposed current differential scheme adopts a biasing technique, which is based on the inherent transient behaviour of the bipolar HVDC system during both external and internal faults. The HVDC transmission line is implemented on the PSCAD/EMTDC platform utilising the frequency-dependent phase model, and it is tested considering numerous internal and external faults. Finally, the proposed current differential relay characteristic is tested considering different fault resistances up to 1000 Ω as well as different fault locations, including internal HVDC line faults and external faults at both rectifier and inverter sides. The obtained results confirm the robustness of the proposed protection scheme for bipolar HVDC transmission lines fault detection.

A Learning-Based Framework for Detecting Cyber-Attacks Against Line Current Differential Relays

Technical developments in communication technology and measurement synchronization have facilitated the design of advanced protection schemes, such as Line Current Differential Relays (LCDRs). However, the superior performance of LCDRs is achieved at the expense of exposing them to cyber-threats, since cyber-induced intrusions against protective relays-which take advantage of the direct control of relays over circuit-breakers-can cause protection system mis-operations. To address this problem, this paper presents a Learning-based Framework (LBF) for detecting False Data Injection Attacks (FDIAs) and Time Synchronization Attacks (TSAs) against LCDRs, and for differentiating them from faults. In the proposed LBF, a Multi-Layer Perceptron (MLP) model is trained based on differential and super-imposed features, which are selected using the Recursive Feature Elimination method. After implementing the proposed LBF in LCDRs, when an LCDR picks up, it initially extracts the features and sends them to the trained MLP model. The LCDR trips the line if the proposed LBF confirms a fault. The performance of the proposed LBF is corroborated using the IEEE 39-bus test system. Evaluation results show that the proposed LBF (i) works independently of a system's operating point and configuration, (ii) is not considerably affected by instrumentation errors, and (iii) can accurately detect FDIAs and TSAs.

STUDI SISTEM PROTEKSI LINE CURRENT DIFFERENTIAL RELAY PADA SALURAN TRANSMISI 150 KV

Increasing electricity demand in South Bali requires a reliable electrical system. Reliableelectrical systems can be achieved in various ways, one of which is the replacement of highvoltage overhead line to high voltage underground cable. The replacement high voltageoverhead line to high voltage underground cable requires adjustment of the protection system.The previous main protection system used in high voltage overhead line is distance relay, whilethe protection system for the new transmission network is line current differential relay. Thepurpose of this study is to analyze GIS Pesanggaran to GI Nusa Dua transmission line’sprotection system. The covered in this analysis is to power flow analysis simulation, 3 phaseshort circuit simulation, relays setting calculation and testing the relays setting.The power flowsimulation showed that the current at peak load from GIS Pesanggaran to GI Nusa Dua is 337A. The 3 phase short circuit simulation showed that the largest short circuit, if a fault occurs onthe GI Nusa Dua of 9.54 kA. The relays setting calcullation showed that of 0,2 A with 20 %slope for Is1 and 2 A with 150% slope for Is2. The results showed that the relays setting hasworked properly.

An Intrusion Detection Method for Line Current Differential Relays in Medium-Voltage DC Microgrids

Line current differential relays (LCDRs) detect faults accurately and promptly, by comparing all currents flowing into the line. This type of relay has been identified in the literature as a reliable protection for lines in DC microgrids (MGs). LCDRs, however, lack the required resiliency against cyber intrusions, such as false data injection attacks (FDIAs) and time synchronization attacks (TSAs), due to their high dependence on communication infrastructure and/or the Global Positioning System (GPS). This paper first introduces coordinated attacks—i.e., several almost-simultaneous FDIAs or TSAs that are carried out independently to achieve a specific objective—as potential threats for MGs. Then, through a case study, it shows how coordinated FDIAs and TSAs can initiate a sequence of events that result in instability of an entire MG. Afterwards, an approach is presented to detect FDIAs and TSAs, and to distinguish them from real faults. The proposed method is comprised of passive oscillator circuits (POCs) installed in series with each converter. During faults, the resultant RLC circuit causes the POCs to resonate and generate a damped sinusoidal component with a specific frequency, i.e., $f_{d}$ . However, $f_{d}$ is not generated during FDIAs and TSAs, since unlike faults, which are physical events that trigger the natural frequencies of a system, cyber-attacks happen in the cyber layer without provoking natural frequencies of the physical layer. Thus, an LCDR pickup without detecting $f_{d}$ denotes an FDIA or a TSA. Since $f_{d}$ is locally measured and analyzed by each LCDR, the proposed detection approach cannot be targeted by cyber-attacks. The proposed method is evaluated on a simulated ±2.5 kV DC MG. Numerical analysis confirms that the proposed method (i) is system-independent; (ii) detects FDIAs and TSAs in less than 1 ms; (iii) is sensitive to high-resistance faults; (iv) can determine fault types, and (v) reduces faults’ peak currents.

An Intrusion Detection Method for Line Current Differential Relays

The U.S. Department of Homeland Security (DHS) has recently identified digital relays as targets vulnerable to cyber-attacks. The DHS has also noted that attacks to multiple relays can bring about cascading outages of transmission lines, leading to blackouts. As a result, making protective relays cyber-resilient is a prominent security issue in power networks. Line current differential relays (LCDRs) are among the potentially vulnerable digital relays that are increasingly deployed for protecting critical transmission lines. LCDRs, however, lack the required resiliency against cyber attacks, due to their high dependence on communication systems. This paper unveils that such susceptibilities can result in unwarranted trip signals through false data injection attacks (FDIAs), and so cause instability if several attacks are coordinated. It also presents a solution for detecting FDIAs and distinguishing them from real internal faults. To detect attacks, the proposed method compares the estimated and locally measured voltages at an LCDR’s terminal for both the positive sequence (PS) and negative sequence (NS). To estimate the local voltage for each sequence, the proposed technique uses an unknown input observer (UIO), the state-space model of the faulty line, and remote and local measurements, all associated with that sequence. The difference between the measured and estimated local voltages for each sequence remains close to zero during real internal faults because, in this condition, the state-space model based on which the UIO operates correctly represents the line. Nevertheless, the state-space model mismatch during FDIAs leads to a large difference between measured and estimated values in both sequences. The effectiveness of the proposed method is corroborated using simulation results for the IEEE 39-bus network.

Development of a Cyber-Resilient Line Current Differential Relay

The application of line current differential relays (LCDRs) to protect transmission lines has recently proliferated. However, the reliance of LCDRs on digital communication channels has raised growing cyber-security concerns. This paper investigates the impacts of false data injection attacks (FDIAs) on the performance of LCDRs. It also develops coordinated attacks that involve multiple components, including LCDRs, and can cause false line tripping. Additionally, this paper proposes a technique for detecting FDIAs against LCDRs and differentiating them from actual faults in two-terminal lines. In this method, when an LCDR detects a fault, instead of immediately tripping the line, it calculates and measures the superimposed voltage at its local terminal, using the proposed positive-sequence (PS) and negative-sequence (NS) submodules. To calculate this voltage, the LCDR models the protected line in detail and replaces the rest of the system with a Thevenin equivalent that produces accurate responses at the line terminals. Afterwards, remote current measurement is utilized by the PS and NS submodules to compute each sequence's superimposed voltage. A difference between the calculated and the measured superimposed voltages in any sequence reveals that the remote current measurements are not authentic. Thus, the LCDR's trip command is blocked. The effectiveness of the proposed method is corroborated using simulation results for the IEEE 39-bus test system. The performance of the proposed method is also tested using an OPAL real-time simulator.

A Virtual Multi-Terminal Current Differential Protection Scheme for Distribution Networks With Inverter-Interfaced Distributed Generators

The deployments of inverter-interfaced distributed generators (IIDGs) in medium voltage distribution networks may cause undesirable trips or tripping failures of conventional two-terminal current differential protective relays. It is economically and technically unfeasible to reconfigure large numbers of time-synchronized sampling clocks and communication channels for each terminal inside the protected zone. In this paper, a more accurate IIDG mathematical equivalent model is established that considers the control strategies of IIDG, and the profile characteristics of the positive-sequence voltage at each point of common coupling are investigated. Then, a real-time estimation algorithm is introduced for the fault current contribution of grid-connected IIDGs. On this basis, this paper proposes a novel virtual multi-terminal current differential protection scheme. This scheme only necessitates exchanging the electrical quantities between the protective relays at both terminals via an existing two-terminal pilot channel, thus reducing the cost and requirements for communications. The feasibility of the proposed protection is demonstrated in both the PSCAD/EMTDC simulation platform and the RTDS hardware experimental laboratory. A comparison of the proposed protection alongside the conventional protection is also presented. Test results indicate that the proposed protection is widely applicable to various fault conditions, thereby improving the sensitivity and selectivity of conventional protection schemes.

An adaptive limited wide area differential protection for power grid with micro-sources

The operation mode of power grids with intermittent distributed generations (DGs) changes frequently due to the bidirectional power flow. In comparison with the conventional grids, the protection relays in power grids with micro-sources are more difficult to set. To tackle this problem, this paper proposes an extended bus differential protection (EBDP) strategy based on the limited wide area (LWA). In this method, the micro-grids are divided into several protection areas at the core of the bus. The whole protection areas are protected by the wide area current differential relays, which are also configured to protect each component in this protection area. Moreover, the protection areas can be changed adaptively according to the power flow direction. Finally, a micro-grid model with multiple DGs is developed using the PSCAD/EMTDC platform. The simulation results indicate that the proposed adaptive limited wide area differential protection (LWADP) has better performance than the traditional relaying protection in detecting the faulty area in micro-grids and isolating the fault, and can be widely utilized in larger micro-grids.

발전기의 고장 판별을 위한 웨이브릿 변환의 적용

Generators are the most complex and expensive single element in a power system. The generator protection relays should to minimize damage during fault states and must be designed for maximum reliability. A conventional CDR(Current Differential Relaying) technique based on DFT(Discrete Fourier Transform) filter have the disadvantages that the time information can lead to loss in the process of converting the signal from the time domain to the frequency domain. A WT(Wavelet transform) and WT analysis is known that it is possible with the local analysis of the fault and transient signal. In this paper, to overcome the defects in the DFT process, an application of WT for fault detection of generator is presented. This paper describes an selection of mother Wavelet to detect faults of generator. Using collected data from the fault simulation with ATPdraw, we analyzed the several mother Wavelet through the course of MLD(multi-level decomposition) using MATLAB software. Finally, it can be seen that the proposed technique using detail coefficient of Daubechies level 2 which can be fault discriminant of generator.

Saturation Detection-Based Blocking Scheme for Transformer Differential Protection

This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second- and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay.