Relay Operation Research Articles

Improved Transformer Differential Protection by Adaptive Pickup Setting during Momentary Over-Fluxing Condition

The differential relaying scheme is universally adopted as the main protection for power transformer. In certain situations, like temporary over-fluxing, this differential protection may malfunction. This is due to unbalance in primary and secondary current, as the saturated core does not reflect equal ampere-turn on either side. This article presents detection of over-fluxing condition against the internal fault based on the fifth harmonic component of differential current. As per the estimated level of the fifth harmonic concerning the fundamental component of differential current, the pickup setting of percentage bias characteristic will be modified to avoid maloperation. Once the over-flux condition is sensed, the algorithm activates timer-based V/f protection to protect the equipment. The proposed algorithm is validated on PSCAD software and after the collection of data, MATLAB software is used for further validation. The proposed algorithm is validated under various test conditions like normal load, external fault, internal fault, and over-fluxing. It is observed that the algorithm accurately detects internal fault in the transformer or blocks the relay operation under momentary over-fluxing situations. Further, to assassinate the competency of the proposed scheme, a practical test is performed on a single-phase transformer available in laboratory. The data for various test cases are captured with the help of DSO, and the collected data has been migrated to computer where the proposed algorithm is examined. After analyzing all the results, it is cleared that the proposed algorithm can prevent transformer isolation during momentary over-fluxing conditions.

Sensitivity analysis of transient short circuit current response to the penetration level of non-synchronous generation

The increasing penetration of inverter connected non-synchronous generation (NSG) in future power systems may result in a large displacement of synchronous generators. Hence, the dynamic characteristics of the power systems may change in ways that have not been experienced yet. In particular, short circuit (SC) current response in future power systems might be significantly affected due to the increased penetration of such generation. In turn, this can significantly affect both the operation of protective relays and the relay settings. This is due to different characteristics of SC currents injected to the grid from NSG, compared to the conventional synchronous generation. This paper focuses on investigating of transient SC current response in future power systems with high penetration of NSG. Hence, to address this, in this paper we investigate the impact of a wide range of factors that influence the SC current contribution from NSG based on fully-rated converter technology. Our analysis also considers the impact of different fault ride through (FRT) controls, designed according to different grid codes, on the SC current response of NSG. Then, the sensitivity of the transient SC current to the increased penetration of NSG is monitored and analyzed. Firstly, simulation studies are conducted using a single-machine infinite bus test system where the SC response of a NSG is comprehensively studied. Secondly, our findings are also tested and verified using IEEE 9-bus test system at different penetration scenarios of NSG using DIgSILENT PowerFactory.

A Comprehensive Dual Current Control Scheme for Inverter-Based Resources to Enable Correct Operation of Protective Relays

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays.

Adaptive fast protection technique for uncompensated/compensated double‐circuit transmission lines connected to large‐scale wind farms

The penetration of large-scale offshore wind farms in power grids has a negative effect on the operation of the conventional distance relays. In this study, a new protection technique is presented for uncompensated/compensated double-circuit transmission lines utilising one-end current measurements. The proposed protection technique does not require any information regarding the transmission line parameters, wind farms, or the compensation devices. In addition, the errors in phasor estimation due to the generated sub-harmonics and inter-harmonics by the wind generators are avoided as the current samples are directly used. Comprehensive studies are implemented on PSCAD/EMTDC software considering numerous cases of external and internal faults. In addition, the double-circuit transmission line is modelled using the frequency-dependent phase model and the mutual-coupling between both circuits are considered. The recorded results confirm the high efficacy of the proposed protection technique with respect to fault type, fault location, and fault resistance.

Optimal Selection of Time-Current Characteristic of Overcurrent Protection for Induction Motors in Drives of Mining Machines with Prolonged Starting Time

The aim of this study is to analyze the effects of mine power network impedance on the starting time of induction motors, as well as on the operation of overcurrent protection relay. Proper selection of the time-current characteristic of overcurrent protection is crucial for the operation of the drive. A specific feature of mining power grids is their high impedance, which results from long cable lines with relatively small cross-sections. This causes relatively large voltage drops and significantly reduces the starting torque of the motor. Reduced starting torque increases the starting time and intensifies the motor overheating. This study analyzes a series of standardized time-current characteristics used in Invertim company protection devices. A simulation study of startup current and starting time was conducted for an exemplary medium-power motor with a large inertia fan at different values of power supply voltage below the rated value. Parameters of the motor equivalent circuit were calculated on the basis of manufacturer data. A new shape of the time-current characteristic has been proposed that would allow for prolonged starting at significant voltage drop in the mine network, ensuring protection from failed starting. This solution can be implemented in digital protection relays in addition to the standard characteristics.

Protective Coordination of the OCR with the Voltage Component in a Closed-Loop Power Distribution System with the FCL

Recently, the requirement of the electrical energy from the renewable source has been growing in the South Korea since government’s energy plan to generate the electrical power of 20% as renewable source. In addition, these renewable power plants have been constructed on not only the existing power plant’s side but also customer’s side. These changes in power distribution system cause the fault current to increase higher and to reverse the direction of the fault current. Variable countermeasures to reduce the fault current have been studied and the introduction of the superconducting fault current limiter (SFCL) in the power distribution system, one of them, has been actively reported. However, the installation of the SFCL can affect the power system protection because of the fault current’s decrease or increase, which depends on the construction of the power distribution system. Especially, the application of the SFCL in a closed-loop power distribution system can cause the delayed trip operation or the fast trip operation of the over-current relay (OCR), one of the representative protective devices widely used in a power distribution system. This change can influence on the existed protective coordination. In this paper, the OCR with voltage component, one of the methods to suppress its trip operation’s change in a power distribution system with a closed loop construction due to the application of the SFCL, was suggested and the protection coordination between the OCRs in a power distribution system with a closed loop was analyzed. It was confirmed that a simple using voltage component in the OCR could cause the trip variation of the reverse direction OCR in loop power system and it can be improved by matching the relaying voltage components.

Adaptive Mho Characteristic-Based Distance Protection for Lines Emanating From Photovoltaic Power Plants Under Unbalanced Faults

The exclusive fault characteristics of photovoltaic (PV) power plants and the existence of fault resistance cause a high probability of failure in operation and unwanted operation of distance relay with conventional mho or quadrilateral characteristic. Different from the fixed operation zones of conventional mho and quadrilateral characteristics, the adaptive mho characteristic presented herein can adaptively adjust its operation zone to solve the aforementioned issues. The basic principle of adaptive mho characteristic-based distance protection is described and the uniform expression of adaptive setting impedance is derived. Subsequently, taking the fault characteristics of PV power plant into consideration, the method of solving the phase angle of fault current is presented, which is the key to calculating adaptive setting impedance. The performances of the proposed protection scheme are evaluated by extensive digital simulations. The proposed protection scheme exhibits satisfactory robustness against the fault resistance and excellent adaptability to different grid codes. It can not only discriminate the internal and external faults occurring in the lines emanating from the PV power plant but also correctly identify the fault direction.

System Integrity Protection Scheme for Enhancing Backup Protection of Transmission Lines

Contingencies such as faults, loss of generation or load may produce undesirable relay operations which can lead to cascade tripping causing system catastrophic failure. Thus, security of power system protection is a major concern for utilities. In this article, an approach based on system integrity protection scheme is proposed for enhancing the security of protection functions. Synchronous data measurements from strategic portions in the system are utilized for separating fault from stressed conditions. Determining the vulnerable relays (VR) which may maloperate during a stressed condition and incorporation of remedial strategy are proposed. It includes two algorithms; the first of which computes the relay margin to form a look-up table containing VR at different fault scenario and operating condition, in offline studies. Then, in accordance with the real-time system conditions, the relay characteristics are set for VRs based on the local information to avoid maloperation. The second is activated during critical heavy loading condition that may lead to voltage collapse and determines the load to be shed based upon sensitivity calculations of relay operation margin. The proposed method is tested for an IEEE-39 bus New England system as well as validated on real-time digital simulator (RTDS) platform for various operating scenarios and found to be robust. Thus, improvement in security of protection operation is achieved without compromising the dependability factor.

Performance analysis of cooperative nonorthogonal multiple access with improved time switching simultaneous wireless information and power transfer protocol

AbstractIn this study, improved time switching (ITS) simultaneous wireless information and power transfer (SWIPT‐ITS) protocol along with cooperative nonorthogonal multiple access (CNOMA) downlink (DL) transmission are integrated (termed as CNOMA‐SWIPT‐ITS) for DL transmission. CNOMA‐SWIPT‐ITS scheme transfers information to the users and performs energy harvesting (EH) for relay operation from cell center user (CCU) to cell edge user (CEU). Furthermore, the scheme transfers different symbols using the time duration of EH at the CCU and performs cooperative relaying (CCU to CEU) to enhance the channel capacity of the users. The performance of CNOMA‐SWIPT‐ITS scheme is measured in terms of ergodic sum capacity and outage probabilities. Finally, simulation and analytical results demonstrate the superiority of the proposed scheme over conventional CNOMA based SWIPT schemes and typical orthogonal multiple access based ITS SWIPT scheme.

Implementation of Support-Vector-Machine-Based Relay Coordination Scheme for Distribution System With Renewables

During islanded mode, the fault current seen by the relay is less as compared to the system in a grid-connected mode. Due to this, the conventional overcurrent relay faces protection challenges, such as relay miscoordination, delayed operation, or failure (blinding) in relay operations. This article proposes a relaying scheme, which uses a support vector machine (SVM)-based classification approach to solve the protection issues. The algorithm integrates the merits of both the radial basis function (RBF) and the multiclass Cubic SVM classifier. The RBF classifier can identify the relay jurisdiction and helps prevent false tripping. The multiclass cubic classifier has been designed to find the SVM class with appropriate relay tripping time. Without using any extensive communication facility, the proposed scheme coordinates the relays and maintains the coordination time interval (CTI) within the desired limits. Irrespective of the mode of operation and configuration of the system, the tripping time and CTI value of the SVM relay is better as compared with the conventional overcurrent relay. The decision function of both classifiers is simplified and programmed in a 200-MHz 32-bit microcontroller. The prototype of the proposed relay is tested on a 400-V four-bus laboratory-type distribution system by creating faults at different locations. The results obtained indicate the ability of the proposed method to perform the real-time operation in a microcontroller-based hardware platform.

Effective microgrid restructuring in the presence of high DG proliferation

Distributed generators bring in promising benefits as well as question the efficacious relaying operation of the conventional radial distribution systems on the penetration. Among different types of interface machines, synchronous generators upon increased penetration create major disruptions to the existing operation of relays and circuit breakers due to their high fault current capability. Hence, this work employs reconfiguration as a strategy to mitigate the protection issues imposed by a highly proliferated DG network. As restructuring also has the capability to create relay miscoordinations, a vigilant identification of optimal structure is carried out. 22.9% loss reduction, 24.3% reduction in the sustained interruption hours faced by an average consumer and 35.8% decrease in the maximum electricity price paid by the consumer at a load point are achieved for the practical 52-bus microgrid while attempting to reconfigure in view of addressing the protection challenges. 21.84% drop is observed in total size of fault current limiters as well. 33 and 69 bus benchmark systems transformed to a microgrid are also employed to validate the proposed reconfiguration strategy. New tie-line combinations are searched for each test system in a view to look for a superior structure giving out best results in the context of study.

Towards energy transition: conjoint assessment of large-scale PV system performance and interconnection impacts in isolated microgrid

Environmental, energy security and electricity demand concerns stimulate solar-grid integration. However, intermittent, non-dispatchable PV characteristics may challenge passive grid operation. This paper contains the comprehensive planning and assessment of a 2 MWp CdTe-based PV system deployment proposed for hybrid operation in an isolated 11 kV 10-bus microgrid in Brunei. The presented approach combinedly assesses PV system performance and scenario-based interconnection impacts based on a detailed PV system model considering deployment conditions. Various interconnection points with multiple sets of feeder-specific measured load profiles are examined. Results show the PV system designed for maximum annual generation achieves performance ratio of 90.6%. While time-series power flow assessment reveals grid operation enhancement, there are concerns at times of generation-demand mismatch requiring proper genset sequencing and reactive power management. Meanwhile, faster relay operating time and reverse fault current are demonstrated in existing protection scheme. Dynamic grid stabilities are preserved in various generation intermittency and loss events, including the most challenging condition of further inertia and spinning reserve reduction reaching a frequency of 96.02%. Finally, optimal interconnection point fulfilling multi-objectives on losses, voltage profile and line reserve capacity is identified. The findings indicate a good prospect of the synergy for advancing energy transition. The analysis could facilitate RE planning and policymaking.

Towards energy transition: conjoint assessment of large-scale PV system performance and interconnection impacts in isolated microgrid

Environmental, energy security and electricity demand concerns stimulate solar-grid integration. However, intermittent, non-dispatchable PV characteristics may challenge passive grid operation. This paper contains the comprehensive planning and assessment of a 2 MWp CdTe-based PV system deployment proposed for hybrid operation in an isolated 11 kV 10-bus microgrid in Brunei. The presented approach combinedly assesses PV system performance and scenario-based interconnection impacts based on a detailed PV system model considering deployment conditions. Various interconnection points with multiple sets of feeder-specific measured load profiles are examined. Results show the PV system designed for maximum annual generation achieves performance ratio of 90.6%. While time-series power flow assessment reveals grid operation enhancement, there are concerns at times of generation-demand mismatch requiring proper genset sequencing and reactive power management. Meanwhile, faster relay operating time and reverse fault current are demonstrated in existing protection scheme. Dynamic grid stabilities are preserved in various generation intermittency and loss events, including the most challenging condition of further inertia and spinning reserve reduction reaching a frequency of 96.02%. Finally, optimal interconnection point fulfilling multi-objectives on losses, voltage profile and line reserve capacity is identified. The findings indicate a good prospect of the synergy for advancing energy transition. The analysis could facilitate RE planning and policymaking.

An Accurate Non-Pilot Scheme for Accelerated Trip of Distance Relay Zone-2 Faults

The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions.

A graph theoretic approach to accelerate natural cutset prediction during an out-of-step condition

When an out-of-step (OOS) condition occurs in a power system, it splits into multiple islands. This uncontrolled separation happens due to distance relay operation on the lines where electrical centers appear. Real-time phasors obtained from Phasor Measurement Units (PMUs) can be used to track the evolution of electrical centers and identify the natural boundary of separation (cutset). Interestingly, electrical centers do not appear simultaneously on the cutset lines; instead, they evolve at different rates. Hence, the cutset is identified only when the signature of the last electrical center appears. We aim to accelerate the cutset prediction so that the complete cutset is identified when the first electrical center is predicted. For this, we propose a computationally efficient algorithm based on the application of graph theory and clustering technique. Thus, the proposed scheme addresses the significant delay in cutset prediction and thereby increases the time available for controlled islanding. Test results on standard IEEE systems and the All India test system validate the scheme.

Non-contact controlled voltage stabilizer for power supply of household consumers

The article discusses the principle of operation of an optoelectronic voltage relay for switching windings of a boost voltage transformer of a voltage stabilizer. Based on the simulation of the proposed optoelectronic contactless voltage stabilizer using the MATLAB R2014a program, it was determined that the change in the shape of the output voltage curve is close to a sinusoid and coincides with the results obtained by the experimental path. When modeling a voltage stabilizer, the structure of the circuit does not change, but the parameters of the resistor elements corresponding to the open or closed state of the semiconductor device at the time of switching the vents change. The characteristic of voltage changes “input-output” and the analysis of existing voltage stabilizers on the principle of “quality voltage” in rural areas

Classification of Electrical Power System Conditions with Convolutional Neural Networks

Undesirable operation of a distant relay at the occurrence of stressed conditions is a reason for blackouts. There are a few computational intelligent methods available in the literature for avoiding relay maloperations. However, because of variations in the system parameters and expansions of the network, the performance of these techniques can be degraded. To solve this issue, data mining approaches have been introduced. The existing data mining approaches need improvement in terms of accuracy and error rate while discriminating fault and stressed conditions. In this paper, a Convolutional Neural Network (CNN) based classifier is proposed for identifying various faults and differentiating fault and power swing situations. The data are collected from the IEEE-9 bus system by Phasor Measurement Units (PMU) and the proposed CNN classifier model classifies system conditions like normal, fault, and power swing. The outcome shows that the classifier has high accuracy and low error rate compared to other classification models such as Naïve Bayes, Decision Tree, and K-Nearest Neighbor. Furthermore, the proposed CNN model is validated with the use of TensorFlow framework to demonstrate its superior performance.

Mitigation of DGs Impact on Variable-Topology Meshed Network Protection System by Optimal Fault Current Limiters Considering Overcurrent Relay Coordination

- In this paper, the optimal deployment of fault current limiters (FCLs) in a variable-topology distribution network with distributed generators (DGs) is analyzed. FCLs are used to mitigate the negative impacts of DGs on overcurrent protection system of the distribution network including escalated electromagnetic stresses, costly replacement of some protective devices, and protection miscoordination. A proposed multi-objective optimization scheme is applied to maximize the mitigation effect of FCLs and minimize their total cost. The scheme determines the optimal locations of the FCLs and the associated optimal impedance values. Meanwhile, a particular focus is kept on preserving the coordinated operation of the protective directional overcurrent relays (DOCRs) of the distribution network under any operating conditions. DOCRs coordination preservation is merged into the FCLs allocation problem by a compulsory set of main-backup DOCRs pairs operation constraints for both near-end and far-end faults at every possible network topology. Furthermore, to lessen the cost of FCLs, a new hybrid approach is developed. Firstly, optimal re-adjusting of a selected small percentage of the DOCRs is done for just one time at nearly zero cost. Then, the FCLs allocation problem is solved. Different engineering strategies for maintaining DOCRs coordination are compared for a 33 kV meshed case-study system.

High Impedance Fault Detection and Location in Combined Overhead Line and Underground Cable Distribution Networks Equipped with Data Loggers

Power distribution networks are vulnerable to different faults, which compromise the grid performance and need to be managed effectively. Automatic and accurate fault detection and location are key components of effective fault management. This paper proposes a new framework for fault detection and location for smart distribution networks that are equipped with data loggers. The framework supports networks with mixed overhead lines and underground cables. The proposed framework consists of area detection, faulty section identification, and high impedance fault location. Firstly, the faulty zone and section are detected based on the operation of over-current relays and digital fault recorders. Then, by comparing the recorded traveling times at both ends of lines, which are related to the protection zone, the faulty line is identified. In the last step, the location of the fault is estimated based on discrete wavelet transform. The proposed method is tested on a 20 kV 13 node network, which is composed of overhead lines and underground cables. The method is tested in both balanced and unbalanced configurations. The obtained results confirm the advantages of the proposed method compared with the current state-of-the art.

Development of Theft and Accidental Notification Systems for Two Wheelers

Each year, people within the world are progressively utilizing vehicles particularly motorbikes as their common means of transportation. Beside the increment of motorbike clients, motorbike robbery is additionally existing wild over a long time. In this consideration, a framework had been created for burglary anticipation of motorbike in a less demanding and quicker way. The client of this framework will be informed through an alarm, once the motorbike has been moved in a long remove or in case any wires they disengage to stolen. The bike theft is identified easily through Raspberry Pi Technology with the help of relay operations based on hardware and interlinked with software in mobile application. Whenever the bike is tried to steal or getting away unaware of user, the relay circuit gets activated in the bike and gives buzzer sound with bright lighting indicating as alert to the user in his/her mobile application. Another System idea was likely to get notified relative user for accident of a bike in any condition and to represent fuel levels in the two wheelers in terms of liters. Both the given system are dependable on mobile application like blynk and with Google Assistant enables the user to give the alert to the user is forging with accident. Gyroscope fixed in bike with sensors signaling Raspberry Pi which in turn user gets notification at any time. On other case if user is free from any injury he/she can reset the operation provided in the system. Finally users sometimes find difficulty ahead of analog representation of fuel in two wheeler to know the travel arrangements. So in this system ultrasonic technology implementing in the bike placed at the fuel tank lid senses the fuel level in bike and sends the resulting data to the user through same mobile application with the help of Raspberry Pi.