Operation Of Protective Devices Research Articles

Robust distance protection for cross-country faults in power grids with high penetration of inverter- based resources

Cross-country faults can adversely affect the operation of protection devices. Relays whose pickup is based on overcurrent or impedance elements are more likely to fail during cross-country faults. The failure can be expressed as an unnecessary trip of all phases during a single-phase fault or even blocked relay functions. Relays may also fail to operate due to low fault currents, which is the case when power grids make use of many inverter-based resources (IBR) or when two simultaneous faults occur in the same phase and in different locations. This paper proposes a Recursive Discrete Stockwell Transform (RDST) method for addressing the mentioned challenges. The energy content computed by the RDST is used for fault detection and faulty phase selection. A robust distance relay model is proposed to ensure correct relay performance and is combined with a directional and an impedance trajectory module. The proposed method performance is thoroughly evaluated by applying real-time simulations for 6480 different cross-country faults, including three repetitions, four different generators (Synchronous generators, Wind turbine type-III, Wind turbine type-IV), two rating powers, three different fault distances, five different types of faults, and six grid codes. Ninety cases are also tested with real devices in hardware in the loop. Simulation results confirm the method's ability to detect different fault types, even during low fault currents, and to ensure high accuracy in phase selection.

Intelligent Monitoring of Protection Devices in Power system with Enhanced Faster R-CNN

Relay protection devices are necessary to guard the power system safety and stability. With the significant number of substations and relay protection devices, the maintenance workload has become difficult due to limited manpower, posing hidden dangers to the reliable operation of protection devices. In view of this, this article proposes an enhanced Faster R-CNN algorithm to diagnose the relay protection devices based on image monitoring. The proposed algorithm uses RestNet50 as the main tool to recognize features from input images to generate feature maps. Meanwhile, to improve the image detection accuracy, the Non-Maximum Sup-pression (NMS) algorithm in regional suggestion network (RPN) is optimized from solid thresh-old to soft threshold. By combining the images captured by the surveillance camera, intelligent inspections are conducted on the status of the pressing plate, fiber bending, external object retention, and other items in the relay protection device. A great number of samples are used to train networks for different tasks. The results indicate that the enhanced Faster R-CNN has a higher image recognition rate, and the recognition accuracy of each inspection item for the protection device is higher than 95%.

Effect of photovoltaic penetration level and location on power system transient stability during symmetrical and unsymmetrical faults

Due to the constant growth in the power demand and the raised risks from unsustainable energy resources, it is essential to continue investigating the operations of renewable energy sources (RESs), such as photovoltaic (PV) systems. Integrating conventional power system with PV plants creates challenges that affect the overall stability of the power system. In this work, the effects of PV penetration levels, PV location, type of faults, and inertia reduction of the conventional synchronous generators on the transient stability of the power system are examined. This is done on 9-bus system based on the critical clearing time values required for the operation of protective devices. It is found that higher PV penetration levels increase the critical clearing times resulting in an improved stability response. Further, the stability of the system under distributed- or concentrated-PV generation depend highly on the location of the PV. Moreover, extensive analysis on the impact of a variety of faults on systems stability are provided (symmetrical vs. unsymmetrical, permanent vs. temporary). The findings of this study indicate that systems experiencing symmetrical faults had lower critical clearing times and tend to be less stable than systems under unsymmetrical faults. Also, the system stability is notably more impacted by permanent faults as opposed to temporary ones with a case of an increase of 80 ms (29.62%). Finally, the negative effect of conventional system inertia reduction on the systems stability is demonstrated with differences reaching 250 ms (28% reduction).

ОГЛЯД ПРИНЦИПІВ СЕЛЕКТИВНОСТІ ЗАХИСТІВ В РОЗПОДІЛЬЧИХ МЕРЕЖАХ СПОЖИВАЧІВ НАПРУГОЮ 0,4 кВ

The analysis of existing principles of selectivity indicates the complexity and incompleteness of ensuring the coordination of the operation of protection devices in distribution networks of 0.4 kV consumers. Current selectivity is ensured only in the area of action of short-circuit currents. To ensure it, electromagnetic or electronic decouplers with a constant deceleration setting are required. This type of disconnectors is used to perform time selectivity and limit the thermal impact of short-circuit currents on the electrical installation and device. The use of devices with "pseudo-time" selectivity ensures the selectivity of the operation of automatic switches in the area of short-circuit currents. Selectivity "SELLIM" is provided with a speed of 0.01 s, but it is possible only in automatic circuit breakers "Schneider Electric". Logical selectivity requires a communication channel between switching devices and the presence of circuit breakers with appropriate communication ports. It is easiest to ensure selectivity by using switches from the same manufacturer using selectivity tables. But such a solution is not always found in practice. The method of energy selectivity allows, taking into account the ratio between ratings, to implement either partial selectivity or full selectivity up to the limit of the breaking capacity of automatic switches. To ensure energy selectivity between two or more current-limiting devices, it must be taken into account that depending on the location of the short circuit, a different number of circuit breakers will be involved in limiting the emergency current, and therefore, the value of the limited current will also be different. By using circuit breakers with a high level of current limitation and a tripping speed that is inversely related to the short-circuit current, full selectivity can be provided at several levels of the network. This makes it possible to simplify the analysis of selectivity, minimize electrodynamic and thermal effects and reduce the level of voltage drop due to the action of a short circuit. Improvement of electrical installation protection systems makes it possible to design power supply systems without excessive reserves of electrical equipment overload, which reduces their cost, dimensions and weight. On the other hand, in the event of malfunctions in the operation of electrical equipment, this limits emergency currents and prevents failure of the undamaged part of the electrical installation, which significantly reduces downtime. Key words: selectivity, relay protection devices, circuit breakers, electrical devices, 0.4 kV network.

Performance Assessment of Frequency Selective Grounding for Grid-Connected Photovoltaic Systems

Photovoltaic (PV) panels and their grid-connection circuitries have to be grounded to comply with various standards and industrial codes. Objectives of grounding a PV system include limiting ground currents and potentials, supporting the operation of protective devices therein, and preventing the accumulation of static charges on PV panels. These objectives can be translated into design constraints for an impedance to connect a PV system to the ground. This paper presents the design and performance assessment of a frequency selective grounding (FSGR) for grid-connected PV systems. The proposed FSGR is composed of a parallel <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$C$</tex-math></inline-formula> circuit, which provides a resistive path for dc currents and a low capacitive impedance path for harmonic currents. The FSGR is designed and experimentally tested for a 2 kW, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$3\phi$</tex-math></inline-formula> , laboratory grid-connected PV system under fault and non-fault conditions. The performance of the proposed grounding is also compared with the solid grounding under similar conditions to further assess its capabilities. Experimental results show that the FSGR can reduce ground currents, limit ground potentials, and reduce the dc leakage currents. These observed features are complimented with minor effects on the operation of protective devices in a grid connected PV system.

Reconfiguration of Active Distribution Networks Equipped with Soft Open Points Considering Protection Constraints

The purpose of active distribution networks (ADNs) is to provide effective control approaches for enhancing the operation of distribution networks (DNs) and greater accommodation of distributed generation (DG) sources. With the integration of DG sources into DNs, several operational problems have drawn attention such as overvoltage and power flow alteration issues. These problems can be dealt with by utilizing distribution network reconfiguration (DNR) and soft open points (SOPs). An SOP is a power electronic device capable of accurately controlling active and reactive power flows. Another significant aspect often overlooked is the coordination of protection devices needed to keep the network safe from damage. When implementing DNR and SOPs in real DNs, protection constraints must be considered. This paper presents an ADN reconfiguration approach that includes DG sources, SOPs, and protection devices. This approach selects the ideal configuration, DG output, and SOP placement and control by employing particle swarm optimization (PSO) to minimize power loss while ensuring the correct operation of protection devices under normal and fault conditions. The proposed approach explicitly formulates constraints on network operation, protection coordination, DG size, and SOP size. Finally, the proposed approach is evaluated using the standard IEEE 33-bus and IEEE 69-bus networks to demonstrate the validity.

Review of Methods for Addressing Challenging Issues in the Operation of Protection Devices in Microgrids with Voltages of up to 1 kV That Integrates Distributed Energy Resources

With the large-scale integration of distributed energy resources (DER) into passive distribution networks with voltages of up to 1 kV, these networks are being converted into microgrids. When the topology and operating conditions change, several challenging issues arise related to the functioning of the protection devices (PD) that are in operation. Most DERs, including renewable generators, are integrated into microgrids by means of inverters. In the event of short circuits (SC) in microgrids, these DERs provide a fault current contribution of no more than 1.2–2.0 Irated at the fault location. This makes it difficult to identify the fault location and to carry out the selective disconnection of the faulty element by means of conventional PDs. This article provides an overview of engineering solutions for improving conventional protection schemes that have been historically used in passive distribution networks, as well as for creating modern protection schemes based on innovative principles and new methods. The use of adaptive protections built on decentralized and centralized principles in most cases ensures the reliable protection of microgrids. Modern intelligent electronic devices (IEDs), where protection functions are implemented, rank higher with respect to their technical perfection in terms of reliability, sensitivity, selectivity, and speed performance. The use of multi-agent systems in the implementation of modern protection schemes requires the availability of broadband communication channels, which hinders their use because of the high cost. The combined use of fault current limiters (FCL) and energy storage systems (ESS) allows for the reliable operation of microgrid protections. The use of modern PDs ensures the reliable operation of DERs and power supply to consumers in microgrids, both in the case of grid-connected and islanded operation modes. Since there is no unified concept of designing protection schemes for microgrids with DERs, the choice of specific approaches to the design of protection schemes should be based on the results of a comparative technical and economic analysis of different options.

Impact of the Separation of the Continental Europe Power System on January 8, 2021 on the Work of the Bosnia and Herzegovina Power System

Abstract After the separation of the Continental Europe power system on 8th January 2021 in two synchronous zones, the electric power system of BiH (EPS BiH) shows a significant increase in frequency and voltages and oscillations of active and reactive power. The paper discusses the operation of protective devices in the BiH power system when the system was operating at high frequencies and voltages and had oscillations of active and reactive power. As a consequence of this behaviour in the EPS BiH there was activation of distance protections (DP) in substation (SS) 220/110 kV Prijedor 2 and overhead transmission lines (OHL) 220 kV Prijedor 2 - Međurić and OHL 220 kV Prijedor 2 – Sisak were disconnected. This was followed by activation of generator protections (reverse power protection and under-excitation protection) and outages of generator units in Hydro Power Plant (HPP) Salakovac, Thermal Power Plant (TPP) Kakanj, HPP Mostar, HPP Bočac, HPP Peć Mlini and HPP Jajce 2.

Distribution systems protection considering aspects of coordination and time-dependent response for reliability evaluation

A detailed representation of the time-dependent characteristics of a protection system requires a more complex modelling of two elements that are typically outside of the reliability evaluation scope: short circuit current and response given by protection devices. The first requires that aspects such as fault type, affected phases, location and fault resistance are modelled, while the second depends on a proper representation of protection time-current curves. The proposed methodology creates a simulation model where the up and down cycle of components is merged with the operation of protection devices and the fault characteristics using sequential Monte Carlo Simulation. A comparison between the classical approach and a more representative protection modelling highlights the benefits of a time-dependent representation of the performance of protection systems.

Protection Coordination of Radial Distribution Networks Connected with Distributed Generation Considering Auto-reclosing Schemes by Resistive Superconducting Fault Current Limiters

AbstractRadial distribution networks are normally protected against fault currents by fuses and reclosers. This protection is coordinated in a way that reclosers clear temporary faults before the melting of fuses and fuses melt to clear permanent faults. Distribution networks, which are recently connected with distributed generations (DGs), incur a variety of issues that are certainly worthy of closer considerations. One of these issues is the operation of protection devices. Recloser-fuse coordination may be lost when DGs are integrated with distribution networks due to the effect of current flowing from DGs during fault period and the breaking of the radiality nature of these networks. The impact of DGs on recloser-fuse coordination depends on penetration level, location, and type of DG. Recloser-fuse coordination of radial distribution networks connected with DGs can be kept by connecting resistive superconducting fault current limiter (R-SFCL) in series with the DG to limit the fault current contribution of DG during the fault period. However, when considering the auto-reclosing scheme of the recloser, recloser-fuse coordination may be lost even if R-SFCL is connected. This paper shows the effectiveness of R-SFCL to restore recloser-fuse coordination without considering auto-reclosing scheme. It also proposes solution methods based on three different configurations of R-SFCL to maintain recloser-fuse coordination when auto-reclosing scheme is considered. Simulation results illustrate the effectiveness of the proposed configurations of R-SFCL to keep recloser-fuse coordination. All simulations are performed using MATLAB/Simulink package.

Wireless device for the detection of explosions and activation of a shock wave absorber

Existing problems of security is strongly connected to terrorist and accident explosions and fires. Physical protection of critical infrastructure requires the creation of reliable system providing quick and accurate identification of the hazards and subsequent transmission of the alarm signal to the protection device. The paper describes the basic requirements and structure of the wireless device for the detection of explosions. Proposed wireless device consists of transmitter and receiver modules. A transmitter module contains the sensors and a microprocessor equipped with a blast identification software. A receiver module produces an activation signal for the operation of protection devices. The paper presents the test results of the proposed wireless device, carried out in the underground experimental base of the G. Tsulukidze Mining Institute.

Stacked Auto-Encoder-Based Transients Recognition in VSC-HVDC

For overhead long-distance high voltage direct current (HVDC) transmission lines, transients are produced due to complicated field conditions and lightning activities. To ensure reliable operation of protection devices, accurate recognition of faults and disturbances is quite critical. The most popular recognition methods include threshold-based ones which require the proper setting of the threshold value, and classifier-based ones that need suitable feature extractions. These methods depend heavily on the experience of engineers or experts and are ineffective in dealing with the variation of system parameters. In this paper, a transient recognition method based on stack auto-encoder (SAE) is proposed to characterize different transients and to avoid human interferences. A symmetrical ±500kv HVDC system is modeled to illustrate the performance of the proposed method. The effect of some factors, such as noises and conductors, are discussed and compared. The simulation results demonstrate that the proposed SAE-based recognition has excellent potential in transient recognition of practical HVDC systems.

Detection of current transformer saturation phenomenon for secured operation of smart power network

Any secured operation of smart grid highly depends on the signal transmitted through Intelligent Electronic Device (IED) to/from the external source. For this, the healthy operation of system components is essential. Error in measurement due to transient response of instrument transformers such as current and voltage transformer may degrade the healthy operation of protection devices. To mitigate this issue and to improve the function of protective devices, an integrated filtering approach is applied for the determination of the current transformer (CT) saturation interval. The method helps in detecting the exact saturation period so that signal reconstruction or time delay logic can be applied to avoid the error-in-estimation process. The proposed integrated filtering approach is tested for different critical cases through a developed model in EMTDC/PSCAD platform. Results for noisy signal obtained through real-time digital simulation (RTDS) is also presented. The method is also compared with the existing method and found more reliable to be implemented.

Development of fault section identification technique for low voltage DC distribution systems by using capacitive discharge current

The increasing importance of energy efficiency has led to several studies related to the construction of a reliable low voltage DC (LVDC) distribution system. Specifically, studies on a protection scheme that considers the fault characteristics of an LVDC distribution system are essential to improve system reliability. When compared to a conventional distribution system, the most distinct feature of an LVDC distribution system is the existence of a capacitive discharge current from converters under a fault condition that results in the prompt operation of protection devices. Therefore, this study involves proposing a precise and rapid technique to identify the fault section in an LVDC distribution system. The technique involves two stages, namely: an analysis stage to analyze the capacitive discharge current and a decision stage to identify the fault section based on the fault type. A detailed discussion of each step is presented and its feasibility is verified based on the results of simulations with an ElectroMagnetic Transients Program and MATLAB®.

A Study on Transient Characteristics in Low Voltage DC Distribution System resulted from the Operation of Protective Device in AC Side

In recent, DC-based power system is being paid attention as the solution for improving the energy efficiency as distributed generations based on renewable energy and digital devices increase. The interest is gradually extended to Low Voltage DC (LVDC) distribution system. To establish the standards for LVDC distribution system, the studies on various aspects based on the comparative analysis between AC system and DC system have conducted. Protection schemes for LVDC distribution system are also included, but most researches have focused on transient characteristics under DC faults so far. This paper, therefore, analyzes the transient characteristics in LVDC distribution system resulted from the operation of protective device by AC fault. Furthermore, it is proposed the considerations to construct the reliable protection schemes. For this purpose, theoretical analysis with the equivalent circuits of LVDC distribution system is performed, and then the analysis results are verified through simulations with ElectroMagnetic Transients Program.

Recognition of Traveling Surges in HVDC with Wavelet Entropy

Traveling surges are commonly adopted in protection devices of high-voltage direct current (HVDC) transmission systems. Lightning strikes also can produce large-amplitude traveling surges which lead to the malfunction of relays. To ensure the reliable operation of protection devices, recognition of traveling surges must be considered. Wavelet entropy, which can reveal time-frequency distribution features, is a potential tool for traveling surge recognition. In this paper, the effectiveness of wavelet entropy in characterizing traveling surges is demonstrated by comparing its representations of different kinds of surges and discussing its stability with the effects of propagation distance and fault resistance. A wavelet entropy-based recognition method is proposed and tested by simulated traveling surges. The results show wavelet entropy can discriminate fault traveling surges with a good recognition rate.

A Fault Clearing Method in Converter-Dominated Microgrids With Conventional Protection Means

The integration of converter-interfaced distributed generation in microgrids has raised several technical issues, including the successful operation of protective devices during faults. The protection issue is associated with the lack of large current injection during a fault, due to limits imposed by the semiconductor switches. This paper proposes a fault-detection and clearing control strategy method for symmetrical and asymmetrical line faults in a looped microgrid. The protection devices are simple overcurrent devices with the same settings, due to the looped microgrid topology. The proposed method is applied without using any kind of physical communication. The fault is detected by measuring indirectly the microgrid impedance. After the fault identification, the distributed energy resources (DERs) adjust their control in order to inject a current proportional to the measured microgrid impedance, according to a droop curve. This means that the DER closer to the fault injects a relatively larger current, achieving by this way a selective coordination of the protection means. The effectiveness of the proposed control strategy is evaluated through detailed simulation and experimental tests.

A mixed integer programming model for optimal fault section estimation in power systems

Abstract This paper proposes a methodology to deal with the fault section estimation problem in electrical power systems. The main motivation for this study lies in the fact that operators of control centers usually are subject to information overload during great contingencies. The fault diagnosis is formulated as an optimization problem and solved through two stages: classification of events at equipment level and the fault section estimation. The first stage consists of a heuristic based on Bayes’ theorem that provide the input to the second stage where a mixed integer programming model is solved by commercial package in order to determine the faulted section. Several fault scenarios from a real Southern Brazilian subsystem were considered to validate the methodology. The results show that the proposed method can correctly identify the faulted section even in case of multiple faults or in case of improper operation of protective devices.

비대칭 고장전류 저감 기능을 갖는 초전도 한류기의 최적 저항 결정 방안

Fault currents characteristics contain decaying DC offset. First cycle peak value of fault currents is higher than steady-state fault current value. These characteristics can affect the operation of protective device. To reduce the asymmetric fault current, the method using a series connection of two hybrid-type Superconducting Fault Current Limiter(SFCL) components, an auxiliary SFCL and a main SFCL, has been proposed. The auxiliary SFCL limits the first half cycle fault current, while main SFCL limits the steady state fault currents. This paper proposed a decision method of the optimal insertion resistance of auxiliary and main SFCL components. To verify the effectiveness of proposed scheme, the various simulations are performed by using Electromagnetic Transient Program(EMTP).

A multi-agent approach for enhancing transient stability of smart grids

Transient stability, an important issue to avoid the loss of synchronous operation in power systems, can be achieved through proper coordination and operation of protective devices within the critical clearing time (CCT). In view of this, the development of an intelligent decision support system is useful for providing better protection relay coordination. This paper presents an intelligent distributed agent-based scheme to enhance the transient stability of smart grids in light of CCT where a multi-agent framework (MAF) is developed and the agents are represented in such a way that they are equipped with protection relays (PRs). In addition to this, an algorithm is developed which assists the agents to make autonomous decision for controlling circuit breakers (CBs) independently. The proposed agents are responsible for the coordination of protection devices which is done through the precise detection and isolation of faults within the CCT. The agents also perform the duty of reclosing CBs after the clearance of faults. The performance of the proposed approach is demonstrated on a standard IEEE 39-bus test system by considering short-circuit faults at different locations under various load conditions. To further validate the suitability of the proposed scheme a benchmark 16-machine 68-bus power system is also considered. Simulation results show that MAF exhibits full flexibility to adapt the changes in system configurations and increase the stability margin for both test systems.