Differential Protection Relay Research Articles

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.

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.

Cybersecurity Enhancement of Transformer Differential Protection

Abstract: The increasing use of information and communication technologies (ICT) in the operational environments of power grids has been essential for operators to improve the monitoring, maintenance, and control of power generation, transmission, and distribution; however, this has come at the expense of increasing the grid's exposure to cyber threats. This paper looks at cyberattack scenarios that target protective relays in substations, which can be the most important part of protecting power systems from abnormal conditions. The overall performance of the power grid could suffer significantly if the relays' operations are disrupted, possibly resulting in widespread blackouts. Utilizing the potential of machine learning to detect anomalous behavior in transformer differential protective relays, we investigate methods for improving substation cybersecurity. In order to find cyberattacks, the proposed method looks at operational technology (OT) data from the substation current transformers (CTs). Power frameworks recreation utilizing OPAL-RTHYPERSIM is utilized to create preparing informational collections, to simulate the cyberattacks and to evaluate the network safety enhancement capability of the proposed AI calculations. Terms in the index include differential protective relays, transformers, operational technology, cyber physical systems, and machine learning.

Current state of the problems of functioning of relay protection and automation complexes used in an active adaptive network

THE PURPOSE. To analyze the influence of series compensation devices on the operating modes of power transmission lines. To identify problems of functioning of relay protection and automation complexes when they are used on power transmission lines with a series compensation device.METHODS. The analysis of literature data and data of international information exchange is carried out.RESULTS. The study describes the relevance of the topic, considers the main elements of an electric power system with an active adaptive network; reveals the current state of affairs on the use of elements of an active adaptive network in the Unified Energy System of Russia, as well as prospects for further implementation of these elements in the Unified Energy System of the Russian Federation. The study shows the scope of application of series compensation devices with the inductive resistance for their placement on power transmission lines, and the optimal distance between series compensation devices, as well as the optimal parameters of the capacitive resistance relative to the resistance of the network. The study discloses problems of functioning of various types of relay protection and automation on power transmission lines with a series compensation device.CONCLUSION. The use of a reactance series compensation device on the line causes problems of functioning for all types of relay protection and automation devices, namely: current, remote, differential and reclosing automation. At the moment, for the listed types and kinds of protection, there are scientific developments to solve these problems with their inherent advantages and disadvantages. The study indicates the most acute disadvantages of the differential relay protection.

Setting Free Fault Location for Three-Terminal Hybrid Transmission Lines Connected With Conventional and Renewable Resources

Three-terminal hybrid transmission lines (TTHTLs) are attractive from both environmental and commercial view. Hybrid transmission lines are growing due to urbanization, connecting an industrial load and renewable integration. A TTHTL comprises sections of both overhead lines and underground/subsea cables or overhead lines with different X/R ratios. Faulted section identification (FSI) is key for defining the adaptive/selective auto-reclosing scheme and estimation of the fault location for TTHTLs. In this paper, FSI and fault location algorithms are proposed without using the parameters of any line section. Novelty of the methodology lies in a two-stage approach to the problem. In the first stage, series impedance parameters of all the sections are calculated using closed loop formulae. These parameters are then utilized in identifying the faulted section. In the second stage, the above calculated line section parameters and faulted section are used to estimate complete line parameters including shunt capacitance and subsequently the fault location. The advantage of the proposed method is that it does not require an initial guess of the line section parameters, is non-iterative in the first stage, and provides correct fault section identification for TTHTLs. These features make it suitable for designing the selective auto-reclosing protection scheme for the TTHTLs within traditional protection relaying hardware. More importantly, the series impedance parameters calculated in the first stage constitute good initialization values for the non-linear problem of estimating the complete line parameters. This results in better convergence of the algorithm and accurate parameter estimation. The developed solution is verified using the PSCAD/EMTDC simulations for TTHTLs connected with conventional and different inverter-based renewable resources. The performance of the proposed solution is compared with commercially available solutions, and it is found to be accurate. This solution is amenable for implementation in line differential protection relays without additional infrastructural changes.

Transformer Internal and Inrush Current Fault Detection Using Machine Learning

Preventive maintenance in the transformer is performed through a differential relay protection system, and it protects the transformer from internal and external faults. However, the Current Transformer (CT) in the differential protection system mal-operates during inrush currents. CT saturates due to magnetizing inrush currents and causes false tripping of the differential relays. Moreover, identification of tripping in protection relay either due to inrush current or internal faults needs to be diagnosed. For the above problem, continuous monitoring of transformer breather and CT terminals with thermal camera helps detect the tripping in relay due to inrush or internal fault. The transformer’s internal fault leads to high breathing process in the transformer breather, never for inrush currents. During inrush currents, CT temperature is increased. Continuous monitoring of breather and CT of the transformer through thermal imaging and radiometric pixels detect the causes of CT saturation and differentiates maloperation. Hybrid wavelet threshold image analytics (HWT-IA) based radiometric pixels analysis of the transformer breather and CT after de-noising provides an accurate result of about 95% for identification of the false tripping of differential protection system of transformer.

A new protection method for the power transformers using Teager energy operator and a fluctuation identifier index

• Using a high-frequency based method, a very fast protection algorithm is provided. • Teager energy operator is a very fast and simple method for the extraction of high-frequency components of the signal. • A very simple index is proposed here which makes the internal fault identification really fast. • A very simple and fast method is provided for the fault type classification. • The algorithm is successfully tested by the experimental signals. Transformers are one of the most important tools of a power system. Differential protection relays with the second harmonic restraint criterion are traditionally used for the transformer protection. This conventional criterion may fail to perform properly in some cases which results in the incorrect relay operation. A novel high-frequency-based algorithm is proposed in this paper to discriminate between the magnetizing inrush currents and the internal faults. Teager energy operator (TEO) is used here to extract high-frequency information from the differential current signals. Differential currents resulted from an internal fault have more high-frequency transients than those resulted from a magnetizing inrush and this is the basic principle used in the proposed algorithm. A very simple and effective operator is proposed in this paper to quantify the overall high-frequency transients of a signal. The proposed algorithm uses a quarter of a cycle of the differential currents along with the very simple mathematical operators to do its task. Therefore, this is a very fast and simple algorithm. The algorithm is tested by the simulated and experimental test signals. Results show the robustness and reliability of the proposed algorithm.

Analysis of the Impact of a Modular SSSC on the Operation of Transmission Line Protection Relays using a Hardware-In-the-Loop Configuration

This paper evaluates the impact of a modular Static Synchronous Series Compensator (m-SSSC) on the operation of communication-assisted line distance and differential protection relays. The m-SSSC system incorporates an over-current protection feature to trigger the bypass mode of operation during grid faults. A case study is analyzed for a 220 kV transmission line and an m-SSSC with a reactive power rating of 80 MVAr per phase using a Hardware-In-the-Loop configuration. The obtained results show the impact of the m-SSSC system on the distance protection operation during some cases of high resistive faults. The differential protection operation was not affected by the mSSSC.

Duty Cycle-Based Differential Protection Scheme for Power Transformers

In general, a power transformer is equipped with differential protection relay with the second harmonic restraint criterion to improve reliability. However, this criterion may fail in some cases, resulting in incorrect operation of protection relay. Therefore, to further upgrade the performance of differential protection, this paper proposes a duty cycle-based scheme as complement. Firstly, the waveform of the differential current in one cycle and its two derived waveforms, constructed by translating and taking absolute, are transformed into corresponding square waves, respectively. Then, duty cycles of these square waves are calculated, and three criteria are presented to quantify the differences between the duty cycles of disturbances and faults. Finally, the criteria and the second harmonic restraint are combined through three logic gates to form the proposed scheme for protection. A large number of simulation experiments have verified the effectiveness of the proposed scheme, which outperforms the frequently used protection schemes.

Negative-sequence current integral method for detection of turn-to-turn faults between two parallel conductors in power transformers

This paper presents a new algorithm for detecting turn-to-turn faults in power transformers. Turn-to-turn faults between two parallel conductors have been taken into account, since they are the most difficult to detect due to the smallest short-circuit current level, especially when they are located close to the middle of the coil. Generally, standard differential protection relays fail in such a case, when low number of turns are shorted. Therefore, a new method was proposed here that is based on the combination of the negative-sequence current integral criterion and the unique differential quantities. The sensitivity and security of the presented method are analyzed and discussed. The performance of the proposed algorithm and three other commonly used methods have been tested with the signals generated using the MATLAB/Simulink program. The results confirm that the proposed algorithm is very sensitive to turn-to-turn faults and gives sufficient stabilization under external faults with CT saturation.

An intelligent differential protection of power transformer based on artificial neural network

This paper describes the application of artificial neural network (ANN) techniques for protecting small power transformer 2 kVA (Terco type). ANN network trained according to the primary and secondary currents data under NN tool, this network performs as a function of differential protection relay. Symmetrical and unsymmetrical faults are analyzed using Matlab environment. ANN network senses the difference in the internal current of both transformer sides and sending a trip to the circuit breaker (CB) at moment of fault occurrence. All the voltages and the currents waveforms affected with the fault and the response time increased according to this technique. Finally, the trip signal and the quick disconnect time were improved according to ANN technique.

SIMULATION OF TRANSFORMER DIFFERENTIAL PROTECTION IN THE MATLAB ENVIRONMENT

Currently, relay protection is based on microprocessor units, which have expanded functionality in comparison with traditional electromechanical means. For the correct operation of these devices, it is necessary to enter the actuation settings, which are calculated manually taking into account the characteristics of a particular power system. Modeling of relay protections in the MatLab environment allows reducing the role of the human factor and minimizing possible errors. (Research purpose) The research purpose is to develop a model of differential relay protection of the transformer in the MatLab Simulink environment. (Materials and methods) The article presents a model of a power system with a power two-winding transformer and differential relay protection with the functions of a current cut-off, differential protection with bias and blocking of the magnetization current surge. (Results and discussion) In the external short-circuit mode, the current protection does not acts, which indicates that the differential protection against external short circuits is detuned. In the short-circuit mode, current cut-off and protection with bias are triggered from the sides of the lower and higher voltages, which also indicates the adequacy of the model. Testing in the magnetization current surge showed that with the 0.15 detuning setpoint recommended by manufacturers of relay protection devices, the protection is blocked for more than 15 seconds, which is unacceptable in practice. The adequate operation of the relay protection is noted at a setpoint of 0.7. The dependence of the harmonic composition of the magnetization current surge on the switching moment on the transformer relative to the transition of the supply voltage through zero was revealed. (Conclusions) The developed model implements the functions of differential protection of the transformer, adequately reproduces all the processes of digital signal processing in microprocessor relay protection units, allows you to check the correctness of functioning in different modes and at different actuation settings.

Simulasi Pencegahan Blackout Akibat Gangguan Hubung Singkat Di Luar Zona Proteksi Diferensial Pada Jaringan Distribusi Closed Loop Penyulang Kompetensi dan Potensial

One way to improve the reliability of the power distribution system is to design a good protection system, which is selective, sensitive, reliable, fast, and easy. Through the simulation in this study, the protection system that has been installed will be compared, namely a closed-loop system with differential relay protection with a protection system with additional logic at the relay output, focusing on busbar disturbances belonging to customers substations. The result is that the protection system that has been installed has a drawback, namely when there is a disturbance in the busbar of the customer's substation, the two feeder circuit breakers in the loop system will trip with the required clearance time of 765 milliseconds, while after adding logic to the relay output, when it occurs there is only one feeder circuit breaker that trips while another tripped circuit breaker is at the substation with the required clearance time of 524 milliseconds, so there is only one customer who experiences a blackout.

A Detailed Testing Procedure of Numerical Differential Protection Relay for EHV Auto Transformer

In power systems, the programmable numerical differential relays are widely used for the protection of generators, bus bars, transformers, shunt reactors, and transmission lines. Retrofitting of relays is the need of the hour because lack of proper testing techniques and misunderstanding of vital procedures may result in under performance of the overall protection system. Lack of relay’s proper testing provokes an unpredictability in its behavior, that may prompt tripping of a healthy power system. Therefore, the main contribution of the paper is to prepare a step-by-step comprehensive procedural guideline for practical implementation of relay testing procedures and a detailed insight analysis of relay’s settings for the protection of an Extra High Voltage (EHV) auto transformer. The experimental results are scrutinized to document a detailed theoretical and technical analysis. Moreover, the paper also covers shortcomings of existing literature by documenting specialized literature that covers all aspects of protection relays, i.e., from basics of electromechanical domain to the technicalities of the numerical differential relay covering its detailed testing from different reputed manufacturers. A secondary injection relay test set is used for detailed testing of differential relay under test, and the S1 Agile software is used for protection relay settings, configuration modification, and detailed analysis.

Discrimination of Transformer Inrush Currents and Internal Fault Currents Using Extended Kalman Filter Algorithm (EKF)

The discrimination of inrush currents and internal fault currents in transformers is an important feature of a transformer protection scheme. The harmonic current restrained feature is used in conventional differential relay protection of transformers. A literature survey shows that the discrimination between the inrush currents and internal fault currents is still an area that is open to research. In this paper, the classification of internal fault currents and magnetic inrush currents in the transformer is performed by using an extended Kalman filter (EKF) algorithm. When a transformer is energized under normal conditions, the EKF estimates the primary side winding current and, hence, the absolute residual signal (ARS) value is zero. The ARS value will not be equal to zero for internal fault and inrush phenomena conditions; hence, the EKF algorithm will be used for discriminating the internal faults and inrush faults by keeping the threshold level to the ARS value. The simulation results are compared with the theoretical analysis under various conditions. It is also observed that the detection time of internal faults decreases with the severity of the fault. The results of various test cases using the EKF algorithm are presented. This scheme provides fast protection of the transformer for severe faults.

A reliable differential protection algorithm for delta hexagonal phase-shifting transformers

Phase-shifting transformers (PST) are exhibited to continuous variations in phase angle. This continuously-varied phase shift can cause miss operation for the current-based differential protection relay by generating false trip signal. This paper discusses the experimental validation of a proposed current differential protection technique. The currents of the exciting winding are calculated based on the relationship between the magnetic and electric characteristics of the transformer. Then, these currents are provided for calculating the restraint and operating currents of the protective relay. The first stage is to design and fabricate the delta hexagonal (Delta/Hex) phase-shifting transformer and, then, constructing a complete laboratory system. PST terminal currents and tapping value are sensed and, then, they are provided to the relay for calculating the excitation current. To check the relay security, different types of external faults are considered. Similarly, extra internal faults, both with and without impedance, are represented to test the relay dependability and sensitivity. Also, the protective relay is checked to discriminate between fault currents that occur during the transformer energization and healthy inrush currents.

Analysis on the behavior of line differential protective relaying with solar PV penetration

Power System Protection is very important in electrical power system as it minimizes power supply interruption to customers, and also prevents damages to electrical equipment. Lately, renewable energy (RE) penetration in power system helps to support and fulfil the increasing demand of electricity to customers. However, the contribution of power from RE such as solar photovoltaic (PV) will increase the fault level and lead to reverse power flow; thus, it will affect power system protection reliability. This paper focuses on evaluating the reliability of differential protection relay during steady state, internal and external faults conditions when the power system is without and with solar PV penetration. Steady state and three-phase symmetrical line fault will be simulated in IEEE 39 bus test system using Power System Simulation for Engineering (PSS<sup>®</sup>E) software.

Transformer Fuses—Mind the Gap

Fuses are commonly used to provide medium voltage (MV) protection to distribution transformers. Unfortunately, there are certain deficiencies introduced when primary-side fuses are used. In paper mill power systems, given the unique organization of the paper mill loads around individual feeders to facilitate load shedding, it may be advantageous to provide transformer differential relay protection from the primary of the transformer to the load side of the main secondary breaker instead of primary fuse protection. This protection can then trip either a primary-side grounding switch (with fuses) or a primary-side feeder circuit breaker using a fiber or a WiMAX (Worldwide Interoperability for Microwave Access) connection. Protection against overload is provided by a secondary main circuit breaker and by design.

Intelligent Differential Protection Scheme for Controlled Islanding of Microgrids Based on Decision Tree Technique

This paper presents an intelligent non-model-based differential relay for protecting microgrid systems in the case of islanding scenarios. For this purpose, by using discrete Fourier transform, different types of electrical signals including voltage and current phasors are processed during fault events by which the most observable signals are estimated to identify system abnormal conditions. In order to identify proper protection signals, an intelligent decision tree (IDT) technique is implemented from which the most effective signals for designing differential protection relay are provided. The proposed IDT-based differential scheme is trained comprehensively in off-line environment using different fault scenarios, both operational and topological. Then, it is implemented in online working mode where, by applying candidate protection signals as input to the proposed intelligent relay, the proper differential protection is derived. The proposed protection relay is an online and non-model-based scheme which can be implemented within a wide range of topologies including mesh and radial topologies in terms of the system operating conditions. The proposed strategy is implemented on a modified IEC case with different fault scenarios. Through considering two grid-connected and islanded system operating modes, the performance of the proposed intelligent differential relay is evaluated. Simulation test results indicate the considerable ability of the proposed technique for proper estimation of decision signals in different fault scenarios within real-time environment.

Optimization of Relay Settings in Jember Substation Power Transformers Based Particle Swarm Optimization

In their operating system, power transformers can experience two disturbances, namely internal disturbances, and external disturbances. Therefore a reliable protection system is needed to deal with these disturbances. The differential relay is the primary protection for the transformer to detect an internal fault in the protection zone. However, if there is an external disturbance or outside the protection zone of the differential relay, the relay will not work. The differential relay protection zone boundary is limited by 2 CT current transformers, where the working principle compares the difference in the value of the differential current entering the relay. Therefore, it is necessary to set the suitable differential relay so that the protection system can work selectively and have reliability. To determine the differential relay setting, the methods used are conventional calculations and the Particle Swarm Optimization (PSO) algorithm. There are two types of differential relays used in the Jember Substation, namely the Toshiba and Micom P642 brands for transformer safety 1, 2, 3, and 4. Based on transformer specification data and CT ratio. In the conventional calculation results, the relay setting produces 0.01A for transformers 1, 2, 3. Still, for transformer 4, it is 0.02A, and for transformers 1, 3 is 0.86A, but transformers 2 and 4 respectively have a value of 0.96A and 1.15A. Then the PSO relay setting algorithm results with the previously described parameters. Transformer 1, 2, 3, and 4 produce 0.8656A. For the value in transformers 1, 2, 3, and 4 itself have a value of 0.01A based on the value of The output is compared with the original setting value of Jember Substation, which is 0.3pu or if it is calculated to equal to 0.866A, the particle swarm optimization algorithm has better accuracy.