Showing papers on "Power-system protection published in 2010"
TL;DR: A brief introduction to the PMU and wide-area measurement system (WAMS) technology is provided and the uses of these measurements for improved monitoring, protection, and control of power networks are discussed.
Abstract: Synchronized phasor measurements have become a mature technology with several international manufacturers offering commercial phasor measurement units (PMUs) which meet the prevailing industry standard for synchrophasors. With the occurrence of major blackouts in many power systems around the world, the value of data provided by PMUs has been recognized, and installation of PMUs on power transmission networks of most major power systems has become an important current activity. This paper provides a brief introduction to the PMU and wide-area measurement system (WAMS) technology and discusses the uses of these measurements for improved monitoring, protection, and control of power networks.
1,000 citations
TL;DR: In this article, a protection scheme using digital relays with a communication network is proposed for the protection of the microgrid system and the increased reliability of adding an additional line to form a loop structure is explored.
Abstract: Microgrids have been proposed as a way of integrating large numbers of distributed renewable energy sources with distribution systems. One problem with microgrid implementation is designing a proper protection scheme. It has been shown that traditional protection schemes will not work successfully. In this paper a protection scheme using digital relays with a communication network is proposed for the protection of the microgrid system. The increased reliability of adding an additional line to form a loop structure is explored. Also a novel method for modeling high impedance faults is demonstrated to show how the protection scheme can protect against them. This protection scheme is simulated on a realistic distribution system containing a high penetration of inverter connected Distributed Generation (DG) sources operating as a microgrid. In all possible cases of operation the primary and secondary relays performed their intended functions including the detection of high impedance faults. This system is simulated using Matlab Simulink's SimPowerSystems toolbox to establish the claims made in this paper.
456 citations
04 Nov 2010
TL;DR: This work proposes two algorithms to place encrypted devices in the system such as to maximize their utility in terms of increased system security, and illustrates the effectiveness of these algorithms on two IEEE benchmark power networks under two attack and protection cost models.
Abstract: State estimators in power systems are currently used to, for example, detect faulty equipment and to route power flows. It is believed that state estimators will also play an increasingly important role in future smart power grids, as a tool to optimally and more dynamically route power flows. Therefore security of the estimator becomes an important issue. The estimators are currently located in control centers, and large numbers of measurements are sent over unencrypted communication channels to the centers. We here study stealthy false-data attacks against these estimators. We define a security measure tailored to quantify how hard attacks are to perform, and describe an efficient algorithm to compute it. Since there are so many measurement devices in these systems, it is not reasonable to assume that all devices can be made encrypted overnight in the future. Therefore we propose two algorithms to place encrypted devices in the system such as to maximize their utility in terms of increased system security. We illustrate the effectiveness of our algorithms on two IEEE benchmark power networks under two attack and protection cost models.
419 citations
TL;DR: In this paper, the protection issues of lowvoltage microgrids are presented and extensions to the novel LV-microgrid-protection concept has been developed based on simulations with PSCAD simulation software.
Abstract: Realization of future low-voltage (LV) microgrids requires that all technical issues, such as power and energy balance, power quality and protection, are solved. One of the most crucial one is the protection of LV microgrid during normal and island operation. In this paper, protection issues of LV microgrids are presented and extensions to the novel LV-microgrid-protection concept has been developed based on simulations with PSCAD simulation software. Essential in the future-protection concept for LV microgrids will be the utilization of high speed, standard, e.g., IEC-61850-based communication to achieve fast, selective, and reliable operation protection.
351 citations
TL;DR: In this paper, the authors analyzed dc faults, their transients, and the resulting protection issues in a multiterminal dc wind farm with a voltage-source inverter (VSI) connection at the onshore grid.
Abstract: The multiterminal dc wind farm is a promising topology with a voltage-source inverter (VSI) connection at the onshore grid. Voltage-source converters (VSCs) are robust to ac-side fault conditions. However, they are vulnerable to dc faults on the dc side of the converter. This paper analyzes dc faults, their transients, and the resulting protection issues. Overcurrent faults are analyzed in detail and provide an insight into protection system design. The radial wind farm topology with star or string connection is considered. The outcomes may be applicable for VSCs in the multi-VSC dc wind farm collection grid and VSC-based high-voltage direct current (HVDC) offshore transmission systems.
301 citations
TL;DR: In this paper, a series dynamic resistor (SDR) was proposed to avoid the doubly-fed induction generator (DFIG) control being disabled by conventional crowbar protection during fault conditions.
Abstract: This paper proposes a new converter protection method, primarily based on a series dynamic resistor (SDR) that avoids the doubly-fed induction generator (DFIG) control being disabled by crowbar protection during fault conditions. A combined converter protection scheme based on the proposed SDR and conventional crowbar is analyzed and discussed. The main protection advantages are due to the series topology when compared with crowbar and dc-chopper protection. Various fault overcurrent conditions (both symmetrical and asymmetrical) are analyzed and used to design the protection in detail, including the switching strategy and coordination with crowbar, and resistance value calculations. PSCAD/EMTDC simulation results show that the proposed method is advantageous for fault overcurrent protection, especially for asymmetrical faults, in which the traditional crowbar protection may malfunction.
279 citations
TL;DR: In this article, the authors proposed a unit protection relays to protect large power transmission grids based on phasor measurement units, the principle of the protection scheme depends on comparing positive sequence voltage magnitudes at each bus during fault conditions inside a system protection center to detect the nearest bus to the fault.
Abstract: Current differential protection relays are widely applied to the protection of electrical plant due to their simplicity, sensitivity and stability for internal and external faults. The proposed idea has the feature of unit protection relays to protect large power transmission grids based on phasor measurement units. The principle of the protection scheme depends on comparing positive sequence voltage magnitudes at each bus during fault conditions inside a system protection center to detect the nearest bus to the fault. Then the absolute differences of positive sequence current angles are compared for all lines connecting to this bus to detect the faulted line. The new technique depends on synchronized phasor measuring technology with high speed communication system and time transfer GPS system. The simulation of the interconnecting system is applied on 500 kV Egyptian network using Matlab Simulink. The new technique can successfully distinguish between internal and external faults for interconnected lines. The new protection scheme works as unit protection system for long transmission lines. The time of fault detection is estimated by 5 msec for all fault conditions and the relay is evaluated as a back up relay based on the communication speed for data transferring.
231 citations
TL;DR: In this paper, the authors proposed a powerful high-speed traveling-wave-based technique for the protection of power transmission lines, which uses principal component analysis to identify the dominant pattern of the signals preprocessed by wavelet transform.
Abstract: This paper proposes a powerful high-speed traveling-wave-based technique for the protection of power transmission lines. The proposed technique uses principal component analysis to identify the dominant pattern of the signals preprocessed by wavelet transform. The proposed protection algorithm presents a discriminating method based on the polarity, magnitude, and time interval between the detected traveling waves at the relay location. A supplemental algorithm consisting of a high-set overcurrent relay as well as an impedance-based relay is also proposed. This is done to overcome the well-known shortcomings of traveling-wave-based protection techniques for the detection of very close-in faults and single-phase-to-ground faults occurring at small voltage magnitudes. The proposed technique is evaluated for the protection of a two-terminal transmission line. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach is reliable for rapid and correct identification of various fault cases. It identifies most of the internal faults very rapidly in less than 2 ms. In addition, the proposed technique presents high noise immunity.
215 citations
TL;DR: This paper presents an enhanced implementation methodology for the associated discrete circuit model of a power-electronic converter in a field-programmable gate array-based real-time power systems simulator, which eliminates the need for corrective measures to reduce error and provides scalability.
Abstract: This paper presents an enhanced implementation methodology for the associated discrete circuit model of a power-electronic converter in a field-programmable gate array-based real-time power systems simulator. The simulator is intended for the testing and performance evaluation of digital control/protection platforms based on the hardware-in-the-loop concept. The salient features of the proposed implementation are: 1) It eliminates the need for corrective measures to reduce error due to the lack of synchronization between the simulation time-grid and output signals of the control/protection platform; 2) it provides scalability, that is, it maintains calculation time, within each simulation time step, nearly fixed irrespective of the system size; and 3) it enables the use of a small simulation timestep, for example, a couple of hundreds of nanoseconds for the overall system, in contrast to the microseconds range time-steps used in the existing simulators. Thus, it is also able to provide a wide frequency bandwidth for the simulation results. This paper also reports the implementation results and their verifications corresponding to real-time simulation of two converter units based on less than 60-ns calculation time within each simulation time step. The scalability property is also verified based on real-time simulation of six converter units.
173 citations
TL;DR: A summary of the IEEE Power System Relaying Committee report on the System Integrity Protection Schemes (SIPS) survey is presented in this paper, which describes industry experiences with this category of protection schemes applied to protect the integrity of the power system.
Abstract: This paper is a summary of the IEEE Power System Relaying Committee report on the System Integrity Protection Schemes (SIPS) survey. The SIPS role is to counteract system instability, maintaining overall system connectivity, and/or to avoid serious equipment damage during major system events. The survey describes industry experiences with this category of protection schemes applied to protect the integrity of the power system. It is designed to provide guidance for SIPS users and implementers based on surveyed operating practices and lessons learned. The survey includes a global participation through the comprehensive effort of IEEE and CIGRE.
141 citations
25 Jul 2010
TL;DR: In this paper, a protection scheme using digital relays with a communication network is proposed for the protection of the microgrid system and the increased reliability of adding an additional line to form a loop structure is explored.
Abstract: Microgrids have been proposed as a way of integrating large numbers of distributed renewable energy sources with distribution systems. One problem with microgrid implementation is designing a proper protection scheme. It has been shown that traditional protection schemes will not work successfully. In this paper a protection scheme using digital relays with a communication network is proposed for the protection of the microgrid system. The increased reliability of adding an additional line to form a loop structure is explored. Also a novel method for modeling high impedance faults is demonstrated to show how the protection scheme can protect against them. This protection scheme is simulated on a realistic distribution system containing a high penetration of inverter connected Distributed Generation (DG) sources operating as a microgrid. In all possible cases of operation the primary and secondary relays performed their intended functions including the detection of high impedance faults. This system is simulated using Matlab Simulink's SimPowerSystems toolbox to establish the claims made in this paper.
TL;DR: In this article, a fast detection scheme for symmetrical fault during power swing for distance relay, which is based on extracting the high-frequency component energy of forward and backward traveling waves induced by faults, is presented.
Abstract: The power swing caused by various disturbances will affect distance relay behavior and may result in relay misoperation. This paper provides a fast detection scheme for symmetrical fault during power swing for distance relay, which is based on extracting the high-frequency component energy of forward and backward traveling waves induced by faults. The multiresolution analysis based on wavelet transform has the ability to decompose the analyzed signals into different frequency bands. The selection of mother wavelet and the number of levels of wavelet transform are carefully studied. The fault can be identified by feature extracting from the d1 component of Daubechies-8 (Db8) wavelet transform. The proposed approach is verified by using the IEEE reference model implemented by using the Alternate Transients Program and the test results have been presented in this paper. This proposed method can be used for distance relay operation blocking or monitoring.
TL;DR: In this article, a real-time system protection scheme to prevent voltage instability and maintain a desired amount of post-transient voltage stability margin following the occurrence of a contingency by means of reactive power control is presented.
Abstract: The objective of power system controls is to keep the electrical flow as well as voltage magnitudes within acceptable limits in spite of the load and network topology changes. The control of voltage level is accomplished by controlling the production, absorption as well as flow of reactive power at various locations in the system. This paper presents an approach to determine a real-time system protection scheme to prevent voltage instability and maintain a desired amount of post-transient voltage stability margin (an index of system security) following the occurrence of a contingency by means of reactive power control. This approach is based on the model predictive control (MPC) theory. According to an economic criterion and control effectiveness, a control switching strategy consisting of a sequence of amounts of the shunt capacitors to switch is identified for voltage restoration. The effect of the capacitive control on voltage recovery is measured via trajectory sensitivity. The sensitivity of voltage stability margin with respect to the capacitive control is used to construct a security constraint for post-fault operation in the MPC formulation. The efficacy of the proposed approach is illustrated through applications to the WECC system for enhancing the voltage performance and to the 39-bus New England system for preventing voltage collapse.
TL;DR: In this paper, the performance of the IEEE Power System Relaying Committee report on wide-area stressed power system conditions is described and methods of implementing protection relay functions to prevent further propagation of system-wide disturbances are presented.
Abstract: This paper is a summary of the IEEE Power System Relaying Committee report. It describes the performance of protective relays during wide-area stressed power system conditions. First, the behavior of protection functions during dynamic operating conditions is described. Then, the lessons learned from studying recent wide area disturbances, as well as the operational history of protection performance during stressed system conditions, are analyzed. Finally, methods of implementing protective relay functions to prevent further propagation of system-wide disturbances are presented.
TL;DR: In this article, a new analytic model was developed to take into account of the possible malfunctions of relays and/or circuit breakers, and further to improve the accuracy of fault diagnosis results.
Abstract: When a fault occurs on a section or a component in a given power system, if one or more protective relays (PRs) and/or circuit breakers (CBs) associated do not work properly, or in other words, a malfunction or malfunctions happen with these PRs and/or CBs, the outage area could be extended. As a result, the complexity of the fault diagnosis could be greatly increased. The existing analytic models for power system fault diagnosis do not systematically address the possible malfunctions of PRs and/or CBs, and hence may lead to incorrect diagnosis results if such malfunctions do occur. Given this background, based on the existing analytic models, an effort is made to develop a new analytic model to well take into account of the possible malfunctions of PRs and/or CBs, and further to improve the accuracy of fault diagnosis results. The developed model does not only estimate the faulted section(s), but also identify the malfunctioned PRs and/or CBs as well as the missing and/or false alarms. A software system is developed for practical applications, and realistic fault scenarios from an actual power system are served for demonstrating the correctness of the presented model and the efficiency of the developed software system.
20 May 2010
TL;DR: In this paper, the authors examine several ways synchrophasors are being used: • Voltage stability detection and correction • Load/generator shedding • Islanding control • Intermittent generation source control and grid interconnection.
Abstract: Synchrophasor data consist of analog and digital values with an associated precise time stamp. With precise time, these quantities are collected from various locations, time-aligned, and then processed as a coherent data set. Synchrophasors have generally been used for visualization and post-event analysis. However, new technologies allow synchrophasors to be processed in real time. Synchrophasor systems are now being used for real-time wide-area protection and control. This paper examines several ways synchrophasors are being used: • Voltage stability detection and correction • Load/generator shedding • Islanding control • Intermittent generation source control and grid interconnection Each application includes a discussion of how synchrophasors provided a unique solution and benefit over traditional solutions. Application performance, speed, data requirements, and equipment are also reviewed. We also discuss a future time-synchronized control solution.
TL;DR: In this article, a multiagent-based adaptive wide-area current differential protection system is proposed, where a power grid is divided into primary and backup protection zones dynamically online with the help of a developed expert system, and relay agents of these zones cooperate to perform a differential relaying function.
Abstract: This paper proposes a multiagent-based adaptive wide-area current differential protection system. A power grid is divided into primary and backup protection zones dynamically online with the help of a developed expert system, and the relay agents of these zones cooperate to perform a differential relaying function. Predictive self-healing strategies have been proposed to prevent misoperation of the relay agent, and the communication system has been simulated. The performance of the proposed adaptive wide-area current differential protection system based on computer simulation is presented in this paper.
TL;DR: In this paper, a fault direction estimation technique for a series-compensated line using phase change in positive-sequence current and magnitude change in the positive sequence voltage at fault is proposed.
Abstract: Series capacitor imposes problems to line protection and other online decisions. The directional relaying issues during voltage and current inversions in a series-compensated line are addressed in this paper. A conventional directional relaying algorithm uses fault voltage and current phasors to derive the decisions and, thus, finds its limitation at voltage or current inversion. This paper proposes a fault direction estimation technique for a series-compensated line using phase change in positive-sequence current and magnitude change in the positive-sequence voltage at fault. The technique is evaluated by using data simulated with EMTDC/PSCAD for a series-compensated line, and the dynamic performance of the algorithm is also studied.
TL;DR: This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems and the calibration methodologies which have been developed to overcome measurement and loop latencies.
Abstract: This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems. The environment allows an entire laboratory power-network topology (generators, loads, controls, protection devices, and switches) to be placed in the loop of a large power-network simulation. The system is realized by using a real-time power-network simulator, which interacts with the hardware via the indirect control of a large synchronous generator and by measuring currents flowing from its terminals. These measured currents are injected into the simulation via current sources to close the loop. This paper describes the system architecture and, most importantly, the calibration methodologies which have been developed to overcome measurement and loop latencies. In particular, a new ?phase advance? calibration removes the requirement to add unwanted components into the simulated network to compensate for loop delay. The results of early commissioning experiments are demonstrated. The present system performance limits under transient conditions (approximately 0.25 Hz/s and 30 V/s to contain peak phase- and voltage-tracking errors within 5° and 1%) are defined mainly by the controllability of the synchronous generator.
TL;DR: Its effectiveness as a protective device for the wind-turbine system is verified with the several case studies by time-domain simulation based on the power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) software.
Abstract: This paper describes the study to analyse the effect of the superconducting fault current limiter (SFCL) on an electric power grid with the wind-turbine generation, which is a representative renewable energy source. Its connection to a power system might more easily increase the short-circuit current during a fault toward its maximum utilization level, which is closer to the rating of circuit breaker, when compared to the case without the wind-turbine system. This can aggravate the reliability of the overall power system. The SFCL can provide the quick system protection during a severe fault. The performance of dynamic damping improvement by the SFCL is evaluated in the existence of the wind-turbine generation system. Therefore, its effectiveness as a protective device for the wind-turbine system is verified with the several case studies by time-domain simulation based on the power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) software.
TL;DR: In this article, the authors used particle swarm optimisation (PSO) for an effective training of ANN and the application of wavelet transforms for predicting the type of fault in electric power system.
Abstract: Fault classification in electric power system is vital for secure operation of power systems. It has to be accurate to facilitate quick repair of the system, improve system availability and reduce operating costs due to mal-operation of relay. Artificial neural networks (ANNs) can be an effective technique to help to predict the fault, when it is provided with characteristics of fault currents and the corresponding past decisions as outputs. This paper describes the use of particle swarm optimisation (PSO) for an effective training of ANN and the application of wavelet transforms for predicting the type of fault. Through wavelet analysis, faults are decomposed into a series of wavelet components, each of which is a time-domain signal that covers a specific octave frequency band. The parameters selected for fault classification are the detailed coefficients of all the phase current signals, measured at the sending end of a transmission line. The information is then fed into ANN for classifying the faults. The proposed PSO-based multi-layer perceptron neural network gives 99.91% fault classification accuracy. Moreover, it is capable of producing fast and more accurate results compared with the back-propagation ANN. Extensive simulation studies were carried out and a set of results taken from the simulation studies are presented in this paper. The proposed technique when combined with a wide-area monitoring system would be an effective tool for detecting and identifying the faults in any part of the system.
20 May 2010
TL;DR: In this paper, the authors present a tutorial in this challenging area where protection principles and applications mix with communications and signal processing, addressing the common design constraints and utility-driven application needs.
Abstract: Line current differential protection creates challenges for relay design and application. From a design perspective, the distributed nature of the line current differential system imposes limits on the amount of data that can be exchanged between the system terminals and calls for data alignment schemes to enable the differential protection principle. From the application perspective, line current differential schemes are concerned with CT saturation, particularly in dual-breaker applications; in-zone reactors and line-charging current; in-line and tapped transformers; sensitivity to high-resistive faults; single-pole tripping; security on channel impairments; application to lines with more than three terminals; and so on. This paper reviews technical solutions to the line current differential design and application, addressing the common design constraints and utility-driven application needs. The paper is a tutorial in this challenging area where protection principles and applications mix with communications and signal processing.
05 Apr 2010
TL;DR: In this paper, a complex system overview of a power grid network is presented, where three mitigation strategies, homogeneous load reduction, targeted range-based load reduction and use of distributed renewable sources in combination with islanding, have been suggested.
Abstract: This paper presents a complex systems overview of a power grid network. In recent years, concerns about the robustness of the power grid have grown because of several cascading outages in different parts of the world. In this paper, cascading effect has been simulated on three different networks, the IEEE 300 bus test system, the IEEE 118 bus test system, and the WSCC 179 bus equivalent model. Power Degradation has been discussed as a measure to estimate the damage to the network, in terms of load loss and node loss. A network generator has been developed to generate graphs with characteristics similar to the IEEE standard networks and the generated graphs are then compared with the standard networks to show the effect of topology in determining the robustness of a power grid. Three mitigation strategies, Homogeneous Load Reduction, Targeted Range-Based Load Reduction, and Use of Distributed Renewable Sources in combination with Islanding, have been suggested. The Homogeneous Load Reduction is the simplest to implement but the Targeted Range-Based Load Reduction is the most effective strategy.
TL;DR: The positive feedback-based anti-islanding schemes invented by the authors are highly effective in preventing islanding without causing any degradation in power quality as discussed by the authors, and their performance is investigated for inverter-based distributed generators.
Abstract: The positive-feedback-based anti-islanding schemes invented by the authors are highly effective in preventing islanding without causing any degradation in power quality. This paper presents the basic principles of these schemes and their design guidelines. Moreover, their performance is investigated for inverter-based distributed generators (DGs). The parametric study reveals the factors significantly influencing the performance of these schemes. The simulation results demonstrate the effectiveness of these schemes.
TL;DR: Test results show that the proposed power supply is capable of providing stable outputs with no saturation and low heat generation for the entire range of line conducting currents and can sustain severe conditions such as abnormal impulse currents.
Abstract: This paper presents a novel power supply of online condition monitoring systems for power transmission lines. The proposed power supply obtains energy from the magnetic field induced by transmission-line currents using a specially designed Rogowski coil. The design details of the power supply circuit including the unit for overvoltage and impulse line current protection are given in this paper. The impact to the power supply's reliability caused by abnormal high transmission-line currents is also addressed. Experimental tests, including the short-circuit and impulse-current tests, have been conducted on the power supply to verify its performance under different operating conditions. Test results show that the power supply is capable of providing stable outputs with no saturation and low heat generation for the entire range of line conducting currents and can sustain severe conditions such as abnormal impulse currents.
13 Jul 2010
TL;DR: In this article, the authors proposed a centrality index based on the maximum power flow through the edges of a power system, where the links which carry more portion of power from the source (generator) to sink (load) are given a higher weight in this analysis.
Abstract: Complex network theory has been studied extensively in solving large scale practical problems and the recent developments have given a new direction to power system research. This theory allows modeling a power system as a network and the latest developments incorporate more and more electrical properties as opposed to the topological analysis in the past. In the past, such networks have been analyzed based on shortest path travel and betweenness index. In a power system, the power might not necessarily flow only through the shortest path so this paper proposes a centrality index based on the maximum power flow through the edges. The links which carry more portion of power from the source (generator) to sink (load) are given a higher weight in this analysis. Few simple cases have been explained and then the algorithm has been demonstrated on the IEEE 39 bus system.
26 Jul 2010
TL;DR: Protection issues and challenges arising from the integration of DG into the grid are discussed and traditional and state of the art protection strategies are presented.
Abstract: An effective introduction of distributed generation (DG) into existing distribution networks (DNs) calls for a review of traditional power system protection concepts and strategies. New issues such as activeness of DNs and bidirectional power flow require new protection solutions. This paper discusses protection issues and challenges arising from the integration of DG into the grid. It presents and critically reviews traditional and state of the art protection strategies. Moreover, some alternate protection strategies are proposed and their merits and demerits are discussed.
14 Jun 2010
TL;DR: In this paper, a typical distribution network with distributed generation (DG) is modeled and simulation results for impact of DG on protection system coordination are presented and discussed and some solutions are proposed to cope with these problems.
Abstract: The increasing amount of distributed generation (DG) in distribution networks (DNs) is giving rise to power quality and protection coordination problems. Issues like voltage regulation, flicker, harmonics and loss of coordination between circuit breaker and fuse need to be addressed for integration of DG into DN. This paper discusses these issues with a special emphasis on protection coordination problems. A typical DN with DG is modeled and simulation results for impact of DG on protection system coordination are presented and discussed here. Some solutions are proposed to cope with these problems.
25 Jul 2010
TL;DR: In this article, the impacts of PV power plants are associated with voltage profiles, electrical losses, power factor, capacity planning, power quality, system operations and protection, and mitigation solutions are provided.
Abstract: The impacts of PV power plants are associated with voltage profiles, electrical losses, power factor, capacity planning, power quality, system operations and protection. Currently utility-scale solar PV plants have nominal capacities that are compatible with distribution substation MVA ratings e.g., between 1 MVA and 10 MVA, plans are to develop transmission interconnected PV plants in the 50 – 100 MW power range. These distribution network impacts are discussed and mitigation solutions are provided. A case study of a feeder fully loaded with PV power plants will be discussed.
TL;DR: The worst condition for the correct action of this criterion is presumed and proven, leading to the invention of novel distance protection which can operate rapidly during power swings, and complete self-adaptive distance protection is put forward.
Abstract: To deal with the maloperation of distance protection in the case of power swings, the criterion of “concentric circle” was widely used. This criterion is implemented based on the time difference that the apparent impedance locus passes through boundaries of these two impedance circles. In many cases (e.g., a very fast power swing), it will fail to block. Actually, with regard to different moving loci, the time difference staying within the gap between two circles and the corresponding time staying within the internal operating circle have an inherent relationship. In this paper, the aforementioned relationship is deliberately assumed and demonstrated. The worst condition for the correct action of this criterion is presumed and proven, leading to the invention of novel distance protection which can operate rapidly during power swings. The necessary issues on the implementation of the proposed criterion are discussed. Based on the result of the discussion, complete self-adaptive distance protection is put forward. On the basis of the aforementioned analysis, the availability and the feasibility of this novel scheme are verified with the results of EMTDC simulations.