Showing papers on "Power-system protection published in 2016"

Nonunit Protection of HVDC Grids With Inductive DC Cable Termination

Abstract: This paper deals with nonunit protection of HVDC grids by proposing a set of parameters that characterizes the open protection zones together with an efficient method to determine the thresholds on these parameters. Selective HVDC grid protection schemes must detect and discriminate faults within the first milliseconds of the fault transient and consequently differ considerably from existing ac protection schemes. Due to the accompanying speed requirement, primary protection is expected to be based on open protection zones as communication delay impedes fast operation. In this paper, the principles of the nonunit protection scheme are developed based on reflection of a traveling wave at an inductive termination. Next, the method to obtain the protection scheme thresholds is elaborated. The method accurately calculates the thresholds for HVDC grids with an arbitrary topology. A sensitivity analysis of these thresholds toward grid and fault parameters demonstrates the applicability of the proposed protection scheme in cable-based HVDC grids with inductive cable termination. The results obtained with the reduced grid model are validated by comparison against simulations using a detailed model implemented in PSCAD.

Cascading Failure Analysis Considering Interaction Between Power Grids and Communication Networks

Abstract: This paper aims to model interdependencies between power systems and dispatching data networks, and to analyze the intricate impacts on cascading failures. The functions of communication networks are embedded into dispatching data networks in China, thus we use dispatching data networks in the paper. The structures of dispatching data networks are generally categorized into two types: 1) double-star; and 2) mesh. The correlation of nodes in double-star networks and power systems is “degree to degree,” whereas “degree to betweenness” is the correlation for mesh networks. Furthermore, the interactive model between power grids and dispatching data networks is presented by a dynamic power flow model. Taking the IEEE 39-bus system and China’s Guangdong 500-kV system as examples, in the case of random attacks on the interdependent system, simulation results show that the power grid coupled with double-star dispatching data networks has lower probability of catastrophic failures than with the mesh structure, because the double-star dispatching data network has outstanding capability of delivering information even though some communication nodes are out of order. In contrast, under intentional attacks, the decrement of the transmission performance of the double-star network is more serious than that in the mesh network. Therefore, the power system exhibits much higher vulnerability when coupled with the double-star network.

Analysis and Design of DC System Protection Using Z-Source Circuit Breaker

Abstract: A modified Z-source breaker topology is introduced to minimize the reflected fault current drawn from a source while retaining a common return ground path. Conventional Z-source breaker topologies do not provide steady-state overload protection and can only guard against extremely large transient faults. The Z-source breaker can be designed for considerations affecting both rate of fault current rise and absolute fault current level, analogous in some respects to a thermal-magnetic breaker. Detailed analysis and design equations are presented to provide a framework for sizing components in the Z-source breaker topology. In addition, the proposed manual tripping mechanism enables protection against both instantaneous current surges and longer-term overcurrent conditions. The fault operation intervals of the proposed Z-source breaker topologies are both demonstrated in SPICE simulation and validated in experimental characterization.

A Communication-Assisted Overcurrent Protection Scheme for Radial Distribution Systems With Distributed Generation

Abstract: Conventional overcurrent protection schemes for radial distribution systems usually attempt to coordinate a recloser at the beginning of the feeder with the fuses on the laterals. The integration of distributed generation in distribution systems leads to problems related to protection coordination that are difficult to be solved by applying conventional protection techniques. This paper proposes an efficient communication-based protection scheme that implements common directional overcurrent relays instead of reclosers at the line, assisted by intertripping and blocking transfer functions. The proposed protection strategy guarantees selectivity regardless of whether the generating units are connected to the network or not, and can be designed retaining either the fuse-blowing or fuse-saving philosophy. Meaningful conclusions are derived from the application of the scheme on a test distribution system.

Supervisory Protection and Automated Event Diagnosis Using PMU Data

Abstract: This paper presents a new framework for supervisory protection and situational awareness to enhance grid operations and protection using modern wide-area monitoring systems. In contrast to earlier approaches dealing with the combined processing of data from multiple phasor measurement units (PMUs), the proposed approach analyzes only the PMU data with the strongest or the most prominent disturbance signature. The specific contributions of this paper are: a) new criteria for identification of PMU with the strongest signature, b) simplified approach for quick detection of faults, c) early classification of eight other disturbances suitable for near real-time response, d) time-frequency transform-based feature extraction techniques for speedy and reliable classifiers, and e) a promising approach to locate disturbances within narrow geographical constraints. The contributions are verified with exhaustive simulation data from the Western Electricity Coordination Council system model and limited real PMU data.

Cascading Failure Analysis for Indian Power Grid

Abstract: Major power grid blackouts in various parts of the world are characterized by voltage collapse. This paper studies the blackout case in the Indian power grid due to voltage collapse in the inter-regional corridor. First, the computer simulation models are tuned to match responses from the phasor measurement units at various locations in the grid. The inter-area mode with the frequency of 0.3 and 0.5 Hz with reduced damping were observed and resulted due to switching actions that occurred during the disturbance. This paper simulates the complex power grid network for various loading conditions of Northern region using power system simulator for engineering. Further, the system variables are analyzed using Prony method to estimate the inter-area mode for different NR loading conditions. The eigen values associated with the 0.3 Hz mode depict the movement from open left half plane into open right half plane with a slight increase in the parameter indicating “hopf bifurcation.” This paper also discusses the maximum loading capacity for the inter-regional lines in-order avoid loss of small signal stability, and highlights the use of real time phasor measurement unit measurements in-order to estimate and track the oscillatory modes.

Adaptive protection scheme for smart microgrid with electronically coupled distributed generations

Abstract: This paper aims at modelling an electronically coupled distributed energy resource with an adaptive protection scheme. The electronically coupled distributed energy resource is a microgrid framework formed by coupling the renewable energy source electronically. Further, the proposed adaptive protection scheme provides a suitable protection to the microgrid for various fault conditions irrespective of the operating mode of the microgrid: namely, grid connected mode and islanded mode. The outstanding aspect of the developed adaptive protection scheme is that it monitors the microgrid and instantly updates relay fault current according to the variations that occur in the system. The proposed adaptive protection scheme also employs auto reclosures, through which the proposed adaptive protection scheme recovers faster from the fault and thereby increases the consistency of the microgrid. The effectiveness of the proposed adaptive protection is studied through the time domain simulations carried out in the PSCAD ⧹ EMTDC software environment.

A Directional Protection Scheme for HVDC Transmission Lines Based on Reactive Energy

Abstract: High-voltage direct-current (HVDC) transmission-line protection is becoming increasingly desirable with the expanding worldwide popularity of HVDC technologies in recent years. This paper proposes a transmission-line backup protection scheme based on the integral of reactive power for HVDC systems. The directional characteristics of reactive power flow are theoretically analyzed for internal and external faults, and these characteristics are used to construct a directional protection scheme. The Hilbert transform is adopted to calculate the reactive power, which ensures a continuous output of calculation results and improves the reliability of the protection. A bipolar 12-pulse HVDC test system based on the CIGRE benchmark is modeled using PSCAD/EMTDC, and extensive simulations of various fault situations are conducted to test the effectiveness of the proposed scheme. The simulation results show that the proposed protection scheme correctly identifies internal and external faults and performs well with different fault distances and fault resistances. Furthermore, the proposed protection is insensitive to the sampling frequency, making it practical for future applications.

Adaptive protection coordination scheme for power networks under penetration of distributed energy resources

Abstract: Integration of distributed energy resources in power networks make them interconnected and active. Depending upon the type, short circuit capability and location of distributed energy resource in transmission and distribution systems, design of protection coordination schemes becomes very challenging. Complexity further increases in the design of protection coordination schemes, when penetration effect of these resources reaches to upstream transmission lines and coordination among the distance and over current relays requires a review. The protection coordination scheme discussed in this article monitors the state of power network continuously. Depending upon the operational topology of the network, time dial settings as well as plug settings of over current relays and zone-2 setting of distance relays are selected from pre-optimsed relay group settings. Whenever there is any change in the network fault level either due to change in line parameters or incoming of new distributed energy resource, new relay group settings are communicated to corresponding relays. The proposed protection coordination scheme is implemented in RSCAD software for modified eight bus test bus and modified IEEE14 bus system. It is observed that the proposed protection approach is highly flexible to maintain the coordination among the over current and distance relays.

Prims-Aided Dijkstra Algorithm for Adaptive Protection in Microgrids

Abstract: Decentralization of electric power is possible with the penetration of distributed generators (DGs) in the microgrid (MG) network. Reconfiguration of MG poses a key challenge in identifying suitable protection schemes for varying the topology of the network. In this paper, a central protection center (CPC) is incorporated whose function is to monitor the MG continuously, identify fault occurrence, and locate the exact faulted branch. The proposed Prim-aided Dijkstra algorithm executed continuously in the CPC is responsible for identifying the current topology of the network and aids in identifying the shortest route from the faulted point to the nearest operating source. The CPC is also responsible for adaptively varying the settings of the relays existing in the shortest path identified based on their selectivity levels. This heuristic algorithm is validated on IEEE 21-bus and 40-bus MG test systems for all possible topologies and faults. The proposed algorithm is capable of clearing the fault by disconnecting minimum portion of the network and ensuring continuity of supply to a majority of loads.

Performance of time-domain line protection elements on real-world faults

Abstract: Ultra-high-speed line protection is becoming a reality today, giving the industry a way to trip line faults in a few milliseconds. One relay described in this paper that uses time-domain principles incorporates incremental-quantity (TD32) and traveling-wave (TW32) directional elements in a communications-assisted tripping scheme, incremental-quantity distance element (TD21), and traveling-wave differential element (TW87). This paper introduces these time-domain line protection elements, shares key details of their implementation in hardware, and illustrates their operation using real-world faults and digital simulations. By comparing the performance of the time-domain line protection elements with the traditional phasor-based elements of the in-service relays that captured the fault records, we demonstrate the performance of the time-domain line protection elements.

Improving the performance of power system protection using wide area monitoring systems

Abstract: Wide area monitoring (WAM) offers many opportunities to improve the performance of power system protection. This paper presents some of these opportunities and the motivation for their development. This methods include monitoring the suitability of relay characteristics, supervisory control of backup protection, more adaptive and intelligent system protection and the creation of novel system integrity protection scheme. The speed of response required for primary protection means that the role WAM in enhancing protection is limited to backup and system protection. The opportunities offered by WAM for enhancing protection are attractive because of the emerging challenges faced by the modern power system protection. The increasingly variable operating conditions of power systems are making it ever more difficult to select relay characteristics that will be a suitable compromise for all loading conditions and contingencies. The maloperation of relays has contributed to the inception and evolution of 70 % of blackouts, thus the supervision of the backup protection may prove a valuable tool for preventing or limiting the scale of blackouts. The increasing interconnection and complexity of modern power systems has made them more vulnerable to wide area disturbances and this has contributed to several recent blackouts. The proper management of these wide area disturbances is beyond the scope of most of the existing protection and new, adaptive system integrity protection schemes are needed to protect power system security.

Developments of power system protection and control

Abstract: Synchronized wide area communication has become a mature technology, which makes the real-time interaction between the substations and the wide area protection and control system possible. However, the present protection and control system to handle this real-time data has been recognized to be deficient. This paper begins by reviewing the development history of power system protection, with special attention paid to the recent development in the field of wide-area and integrated protections, in order to look into the future development of protection and control systems. Then the concept of integrated wide area protection and control is introduced, where it can be shown that a hierarchical protection and control system provides the protection and control for wide area or regional power substations/plants and their associated power networks. The system is mainly divided into three levels: the local, the substation/plant, and the wide area/regional. The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between each level. The key element in the proposed system is the wide area real-time protection and control information platform, which not only enables the merger of three lines of defence for power system protection and control, but also provides a perfect tool for the application of cloud computing in substations and power networks.

Modelling of high-power hybrid DC circuit breaker for grid-level studies

Abstract: The modelling principles for hybrid DC circuit breakers (CBs) which is developed to support DC grid protection studies and transient studies involving DC protection are studied. The coordinated control and interlocking of the four subunits (two semiconductor valves and two mechanical switches) are analysed. The model represents accurately the opening sequence, closing sequence and a modified model which includes DC fault current limiting mode (for short duration). The CB self-protection and driver-level valve protection are included in the model. Unidirectional DC CB and bidirectional DC CB are presented. Simulations on EMTP-RV are used to verify the proposed models. The key operating conditions are tested, such as: opening the DC CB under fault current, malfunction of upper layer protection system, re-closing a DC CB under rated DC current, re-closing a DC CB to DC fault and current limiting (for short duration) control of the DC CB.

Improved Fault Classification in Series Compensated Transmission Line: Comparative Evaluation of Chebyshev Neural Network Training Algorithms

Abstract: This paper presents the Chebyshev neural network (ChNN) as an improved artificial intelligence technique for power system protection studies and examines the performances of two ChNN learning algorithms for fault classification of series compensated transmission line. The training algorithms are least-square Levenberg–Marquardt (LSLM) and recursive least-square algorithm with forgetting factor (RLSFF). The performances of these algorithms are assessed based on their generalization capability in relating the fault current parameters with an event of fault in the transmission line. The proposed algorithm is fast in response as it utilizes postfault samples of three phase currents measured at the relaying end corresponding to half-cycle duration only. After being trained with only a small part of the generated fault data, the algorithms have been tested over a large number of fault cases with wide variation of system and fault parameters. Based on the studies carried out in this paper, it has been found that although the RLSFF algorithm is faster for training the ChNN in the fault classification application for series compensated transmission lines, the LSLM algorithm has the best accuracy in testing. The results prove that the proposed ChNN-based method is accurate, fast, easy to design, and immune to the level of compensations. Thus, it is suitable for digital relaying applications.

Implementation and Application of Practical Traveling-Wave-Based Directional Protection in UHV Transmission Lines

Abstract: Traveling-wave-based protection is becoming attractive in ultra-high-voltage (UHV) transmission systems due to the requirement for high-speed protection. However, the poor transfer characteristics of coupling capacitor voltage transformers (CCVTs) for high-frequency voltage have strictly limited its application. A novel traveling-wave-based protection scheme considering the characteristics of CCVTs and current transformers is proposed in this paper. The dyadic wavelet transform is used to extract the polarities of voltage and current traveling waves for fault direction identification. A prototype is further developed for practical applications. Extensive laboratory tests are performed to assess the performance of the developed scheme. The prototype has been applied to the 750-kV substations in China and an external fault was recorded during the operation period, validating the effectiveness and reliability of the proposed protection principle.

Critical aspects on wavelet transforms based fault identification procedures in HV transmission line

Abstract: The fault identification process in transmission systems involves three functions: discrimination, classification and phase selection. The current study classifies the methods that applied for each function. Moreover, this study introduces criticism and assessment study that helps the power system protection engineer to choose the best fault identification scheme at responsible indices. Investigated solutions for the drawbacks appeared with the previous methods are suggested. This study also proposes sensitive and automated fault identification scheme to solve the existing challenges such as high-impedance faults (HIFs), non-linear modelling of arcing etc. Several simulation studies are employed using alternative transients program/electromagnetic transient program (ATP/EMTP) package on a sample 500 kV test system to ensure the performances of the proposed scheme compared with the previous methods. Simulation results concluded that: the proposed identification scheme has the ability to discriminate correctly between HIF and low-impedance faults using current signal captured from one end only. Moreover, the proposed scheme alleviates perfectly the problems associated with load variations by adaptive threshold settings and reduces the impacts on the environmental and external phenomena.

Fuzzy logic based on-line fault detection and classification in transmission line

Abstract: This study presents fuzzy logic based online fault detection and classification of transmission line using Programmable Automation and Control technology based National Instrument Compact Reconfigurable i/o (CRIO) devices. The LabVIEW software combined with CRIO can perform real time data acquisition of transmission line. When fault occurs in the system current waveforms are distorted due to transients and their pattern changes according to the type of fault in the system. The three phase alternating current, zero sequence and positive sequence current data generated by LabVIEW through CRIO-9067 are processed directly for relaying. The result shows that proposed technique is capable of right tripping action and classification of type of fault at high speed therefore can be employed in practical application.

Modified Z-Source DC Circuit Breaker Topologies

Abstract: The Z-source dc circuit breaker has been introduced as a new circuit for quickly and automatically switching off in response to faults. A modified Z-source breaker design is introduced for the operation at medium-voltage dc with future applications in naval ship power systems. Compared to existing designs, the respective design will allow for greater control of step changes in load. This new design also limits capacitor current in the circuit and can be easily modified for fault detection. Analysis of the breaker operation is presented during both the fault and step changes in load. Low-voltage laboratory validation of the breaker was carried out on two different versions of the proposed circuit.

Enhanced Protection Security Using the System Integrity Protection Scheme (SIPS)

Abstract: Events, such as faults, loss of load, or generation may cause unwanted relay operations which initiate cascade tripping leading to system collapse. Security of power system protection is a major concern for utilities. A system integrated protection scheme-based approach is proposed for improving the security of protection operations. Identification of vulnerable points, which may maloperate during a stressed condition and initiation of preventive strategy, is proposed in this paper. Synchronized measurements obtained from strategic locations in the system are used for this purpose. It includes two algorithms; the first of which changes the operating characteristic of relays in accordance with system condition. The second one identifies nodes in the system where load reduction can reduce the risk of maloperation. The proposed method is tested for the New England 39-bus system and is found to be accurate.

A multi-agent based technique for fault location, isolation and service restoration

Abstract: This paper presents a communication-assisted fault localization, isolation and restoration method for microgrids based on a multiagent system (MAS). The proposed system comprises distributed agents, located in the middle and at the two ends of a protection section, which will detect a fault through phase angle comparison of current signals at both sides of a given distribution line. The agents then send trip signal to corresponding circuit breakers accordingly. The importance of the proposed protection technique is twofold: first, it eliminates the use of voltage transformers and thus reduces costs. Second, it does not require transfer of data along long distances which decreases the delay time for fault isolation. Power restoration processes following the fault clearance considering voltage, frequency and power flow constraints in the microgrid under study was also performed. Simulation of the proposed protection methodology was presented followed by experimental verification. The experimental results showed excellent agreement with the simulated protection scheme.

A Local Backup Protection Algorithm for HVDC Grids

Abstract: DC faults in HVDC grids lead to quickly increasing currents which should be interrupted sufficiently fast to prevent damage to power-electronics components. Although several primary relaying algorithms for HVDC grids have been proposed, fast backup relaying algorithms are needed to ensure system reliability when primary protection fails. This paper proposes a local backup relaying algorithm for HVDC grids, which leads to a short delay between primary and backup protective actions. The proposed algorithm, consisting of breaker and relay failure subsystems, uses classifiers which detect primary protection malfunctions based on the voltage and current waveforms associated with dc breaker operation. The algorithm initiates the detection of uncleared faults during primary protection operation, which results in accelerated actions by the backup protection after primary protection failure. The proposed algorithm is applied to a four-terminal HVDC grid. Study results show that the proposed algorithm accurately detects uncleared faults, identifies the source of primary protection malfunction, and expedites backup protective actions by operating during the fault current interruption interval of the primary protection.

A Wide-Area Backup Protection Algorithm Based on Distance Protection Fitting Factor

Abstract: In view of the time delay and potential information loss problem in wide-area data acquisition, a wide-area backup protection algorithm based on the distance protection fitting factor is proposed in this paper. First, the contribution of the distance protection operating information to fault identification is defined as the distance protection contribution degree. Second, the protection fitness function and protection fitness expectation function are constructed using the distance protection contribution degree as the weight. And then, the distance protection fitting factor is gained by calculating the division of the protection fitness function by the protection fitness expectation function. Thus, the fault line can be identified. Finally, simulation tests on the IEEE 10-machine 39-bus system and Guizhou Duyun real-time digital simulator verify that the proposed method is not affected by the time delay in wide-area data acquisition and is able to identify the fault line correctly even when a large amount of distance protection operating information is lost or in error. Meanwhile, the uncertainty problem in traditional weight setting due to reliance on subjective experience is avoided. Besides, being small in computation amount, the proposed method is easy to implement in engineering practice.

A New Protection Scheme for Multi-Bus DC Power Systems Using an Event Classification Approach

Abstract: DC microgrid systems with hybrid energy resources are of significant interest in shipboard and spacecraft applications. In such a system, coordinated operation of circuit breakers (CBs) and disconnecting switches (DSs) can rapidly isolate short-circuit faults and restore the system very fast. In this paper, we investigate a new protection scheme for a Multi-Bus dc systems based on an event classification approach. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods and does not require high-speed communication and synchronization. The results show that the developed protection scheme is able to identify the type of fault accurately, isolate the faulted area, and restore the system very quickly while maintaining continuous power to the loads.

Fault Section Identification Protection Algorithm for Modular Multilevel Converter-Based High Voltage DC With a Hybrid Transmission Corridor

Abstract: This paper addresses the protection of a high voltage direct current (HVDC) transmission system, utilizing the modular multilevel converter (MMC) topology in addition to incorporating a hybrid transmission corridor (transmission line including overhead line and cable sections). A solution is proposed for identifying the section within which a dc fault is located for the purpose of maintaining power delivery. A detailed model of the MMC-HVDC system is simulated using PSCAD and an in depth fault analysis is performed. A characteristic signal is discovered and then implemented into a novel solution. The end result is a fault section identification protection algorithm, implementing protective relay coordination to protect the system from false circuit breaker reclose as well as enabling fast system restart for nonpermanent faults. This restart protection algorithm is implemented without the use of a communications channel between converter stations, introducing novelty and quick restart response.

Traveling-wave-based protection of parallel transmission lines using Teager energy operator and fuzzy systems

Abstract: This study proposes an intelligent traveling-wave (TW)-based protection algorithm for parallel transmission lines. In the proposed algorithm, Karenbauer's phase to modal transform is applied on three phase current signals. Teager energy operator is then applied on the modal components to extract TWs. First extracted TW of each modal component along with well-designed fuzzy systems are used for internal fault identification and fault type classification. In order to find the fault location, the time difference between the first and the second TWs and the TW propagation speed are utilised. Test signals are generated in PSCAD/EMTDC software and the algorithm is implemented in MATLAB. Results show that the proposed algorithm is an ultra-high-speed algorithm for the reliable protection of parallel transmission lines.

General Analysis of Vacuum Circuit Breaker Switching Overvoltages in Offshore Wind Farms

Abstract: Understanding mechanisms of switching transient overvoltages in modern electrical power systems is a necessity to ensure a proper design of power plants and switchgear and the required level of reliable and secure system operation. High fidelity plant modelling and accurate transient analysis is a prerequisite for understanding the mechanisms of how overvoltages are created and whether or not the voltage withstand capabilities of system components will be exceeded. This research is focused on switching overvoltages typical for an offshore wind farm power collection grid configuration that comprises vacuum circuit breakers (VCBs), cables and transformers. An in-depth understanding of the prestrike effects in VCBs is a prerequisite for studying switching transient overvoltages. In this paper, the impact of VCB parameters (e.g., stray capacitance and withstand voltage ability)and cable length on the transformer terminal voltage during closing operation was studied. A wind farm power collection system was modelled in ATP-EMTP environment. To validate the results obtained through computer simulation, field measurements from an actual system were used.