Showing papers on "Power-system protection published in 2004"

Development of adaptive protection scheme for distribution systems with high penetration of distributed generation

Abstract: Conventional power distribution system is radial in nature, characterized by a single source feeding a network of downstream feeders. Protection scheme for distribution system, primarily consisting of fuses and reclosers and, in some cases, relays, has traditionally been designed assuming the system to be radial. After connecting distributed generation (DG), part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type, and placement of DG. This paper explores the effect of high DG penetration on protective device coordination and suggests an adaptive protection scheme as a solution to the problems identified. Results of implementation of this scheme on a simulated actual distribution feeder are reported.

A new fault location algorithm using direct circuit analysis for distribution systems

Abstract: The unbalanced nature of distribution systems due to single-phase laterals and loads gives difficulty in the fault location. This paper proposes a new fault location algorithm developed by the direct three-phase circuit analysis for unbalanced distribution systems, which has not been investigated due to high complexity. The proposed algorithm overcomes the limit of the conventional algorithm, which requires the balanced system. It is applicable to any power system, but especially useful for the unbalanced distribution systems. Its effectiveness has been proved through many EMTP simulations.

Fault diagnosis of electric power systems based on fuzzy Petri nets

Abstract: In this paper, Fuzzy Petri Nets (FPN) is used as a modeling tool to build fault diagnosis models aimed to accurately diagnose faults when some incomplete and uncertain alarm information of protective relays and circuit breakers is detected. In order to understand the significance of fault diagnosis models more conveniently, the definition and structure of FPNs are necessarily introduced at first. Then, models of fault diagnosis based on FPN are built, and their corresponding logical testifications are carried out. Finally, the validity and feasibility of this method is illustrated by simulation examples. It is shown from seven cases that the faulted system elements can be diagnosed correctly by use of these models, and a satisfying result can also be achieved even in the situation with large amount of incomplete and uncertain alarm information.

Fundamentals of Power System Protection

Abstract: They may occupy different angular positions, but all machines rotate at the same electrical speed. This close knitting implies an embedded interaction of generators through the transmission network which is governed by the differential and algebraic equations of the apparatus and interconnects. This aspect is referred to as the system behaviour. This system has to be protected from abnormalities which is the task of protection system.

A practical approach for integrated power system vulnerability analysis with protection failures

Abstract: Protection system failure is one of the main causes of cascading outages. This paper proposes an integrated scheme to study power system vulnerability considering protection system failures. In this scheme, both adequacy and security based reliability analysis are conducted. A new protection system reliability model including two major failure modes is established to demonstrate their effects on power system reliability. The mechanism and scheme of protection systems have been analyzed for their contribution to cascading outages as well as system stability after a fault occurs. All contingencies and the responses in the power system are depicted in their inherent stochastic manner. The power system vulnerability is assessed by both adequacy indices, such as Bus Isolation Probability (BIP), Loss of Load Probability (LOLP) and Expected Power Loss (EPL), and the security index Probability of Stability (POS). In addition, a new vulnerability index, Integrated System Vulnerability (ISV), is introduced to give a more comprehensive description of the system vulnerability. A nonsequential Monte Carlo simulation approach is used to implement the stochastic properties of contingencies, protective response and protection system failures. The IEEE Reliability Test System is used to illustrate the methodology and present the results.

Out-of-step protection fundamentals and advancements

Abstract: Power systems are subjected to a wide range of small or larger disturbances during operating conditions. Small changes in loading conditions occur continually. The power system must adjust to these changing conditions and continue to operate satisfactorily and within the desired bounds of voltage and frequency. The power system should be designed to survive larger types of disturbances, such as faults, loss of a large generator, or line switching. Certain system disturbances may cause loss of synchronism between a generator and the rest of the utility system, or between interconnected power systems of neighboring utilities. If such a loss of synchronism occurs, it is imperative that the generator or system areas operating asynchronously are separated immediately to avoid widespread outages and equipment damage. In this paper we describe the philosophy and application fundamentals of out-of-step protection in transmission systems. We also discuss recent enhancements in the design of out-of-step tripping and blocking protection functions that improve the security and reliability of the power system. In addition, we demonstrate the out-of-step phenomena and distance relay element behavior using EMTP and Matlab simulations.

Wide area system monitoring and control - terminology, phenomena, and solution implementation strategies

Abstract: This article describes the transition from phasor-based wide area measurement to real time monitoring, control, and protection. The power system phenomena to deal with are reviewed, and key concepts in control and protection are addressed along with different design principles and architectures. Examples of analysis tools, monitoring tools and concepts for control and protection are given. The use of PMU improved the observability of the power system dynamics.

Wavelet fuzzy combined approach for fault classification of a series-compensated transmission line

Abstract: Series capacitor protected by metal-oxide varistor and air-gap arrangement imposes problems to line protection and other online decisions. Discrete wavelet transform integrated with a fuzzy logic system is designed for fault classification of a transmission line possessing a series capacitor at the midpoint. The approach uses information obtained from the wavelet decomposition of current signals for faulty phase selection and section identification. Two different FLSs are designed for the two classification objectives in this paper.

Application of neural-network modules to electric power system fault section estimation

Abstract: This paper presents a neural system intended to aid the control center operator in the task of fault section estimation. Its analysis is based on information about the operation of protection devices and circuit breakers. In order to allow the diagnosis task, the protection system philosophy of busbars, transmission lines, and transformers are modeled with the use of two types of neural networks: the general regression neural network and the multilayer perceptron neural network. The tool described in this paper can be applied to real bulk power systems and is able to deal with topological changes without having to retrain the neural networks.

A new concept of voltage-collapse protection based on local phasors

Abstract: A new algorithm for protection against voltage collapse is proposed. The algorithm makes use of the magnitudes and angles of the local phasors (i.e., bus voltages and load currents). The change in an apparent power-line flow during a time interval is exploited for computing the voltage-collapse criterion. The criterion is based on the fact that the line losses in the vicinity of the voltage collapse increase faster than the delivery of the apparent power and, at the voltage-collapse point, the losses consume all of the increased power. The selected criterion equals 0 when a voltage collapse occurs. The proposed algorithm could be easily implemented in a numerical relay. The information obtained by the relay can be used at two levels-for the coordinated system-wide control action or for automatic action on the local level. The algorithm is simple and computationally very fast. It was tested on the IEEE 118-bus test system.

Investigation of anti-islanding protection of power converter based distributed generators using frequency domain analysis

Abstract: The anti-islanding algorithm proposed by the Sandia national laboratories is analyzed in this study because this scheme, also known as the Sandia scheme, is considered to be effective in detecting islanding of distributed generation systems. Previously, other than heuristic approaches, there has not been any quantitative analysis for tuning the control gains of the algorithm based on the power rating and bandwidth of the distributed generation (DG) power converter. The paper interprets the components of the algorithm that affect the voltage magnitude and frequency into block diagrams that can be linearized and studied using continuous time approximations. This paper uses a frequency domain approach to analyze the range for the gains required by anti-islanding algorithm to effectively determine the disconnection of the mains grid within an acceptable time duration. The analysis provides guidelines for using Sandia's national laboratory schemes under different application conditions. The results are validated using detailed time domain DG and power system simulations.

Wide area protection and emergency control

Abstract: This paper discusses wide area protection and emergency control in power system. System-wide disturbances in power systems are a challenging problem for the utility industry because of the large scale and the complexity of the power system. Addition of nonutility generators and independent power producers, an interchange increase, an increasingly competitive environment, and introduction of FACTS devices make the power system more complex to operate and control, and, thus, more vulnerable to a disturbance. The advanced measurement and communication technology in wide area monitoring and control, FACTS devices and new paradigms (fuzzy logic and neural networks) may provide better ways to detect and control an emergency. The proposed panel presentation will include an overview of causes and risks of wide area disturbances, currently used protective relaying schemes to mitigate them.

Voltage recovery of grid-connected wind turbines with DFIG after a short-circuit fault

Abstract: The fast development of wind power generation brings new requirements for wind turbine integration to the network. After the clearance of an external short-circuit fault, the voltage at the wind turbine terminal should be reestablished with minimized power losses. This paper concentrates on voltage recovery of variable speed wind turbines with doubly fed induction generators (DFIG). A simulation model of a MW-level variable speed wind turbine with a DFIG developed in PSCAD/EMTDC is presented, and the control and protection schemes are described. A new control strategy is proposed to reestablish the wind turbine terminal voltage after the clearance of an external short-circuit fault, and then restore the normal operation of the variable speed wind turbine with DFIG, which has been demonstrated by simulation results.

Adaptive over current protection for distribution feeders with distributed generators

Abstract: The connection of distributed generators (DG) to distribution networks influences the performance of the networks. This paper focuses on the impact of DG on the feeder protection, specifically the impact on the overcurrent (OC) relay performance. The paper presents simulation results to show the extent of deterioration a DG can cause on the OC relay performance. The paper then presents an approach to solve this problem and restore the overcurrent relay performance.

HVDC line protection for the proposed future HVDC systems

Abstract: The paper reviews the ability of present protection systems to provide adequate protection for proposed future HVDC systems. This initial study reviews current protection systems used for DC line protection and highlights both the advantages and disadvantages of these systems including the factors that adversely influence their performance. The paper stresses the importance of local fault detection and suggests that telecommunication should, as far as possible, only be used to enhance and optimize the systems. The paper also highlights the major advantages of using the system transients to detect DC line faults in terms of security, reliability, speed of fault clearance and fault recovery as well as the drawbacks and current limitations and possible solutions. The authors finally evaluate the current protection systems and propose ways of enhancing some of the existing protection systems with local supervision and other techniques to improve their performance and capability.

Real time digital simulation for control and protection system testing

Abstract: Today's power system environment is becoming more and more complex. Electrical power networks are being pushed closer to their limits, while at the same time higher reliability and efficiency are demanded. As a result, electrical equipment manufacturers are developing advanced equipment and installations to meet these requirements. Part of the challenge in designing such apparatus is the need to accurately simulate (prove) and test these devices before they are installed in an actual power system. The real time digital simulator (RTDS) allows developers to accurately and efficiently simulate electrical power systems and their ideas to improve them. The RTDS simulator operates in real time, therefore not only allowing the simulation of the power system, but also making it possible to test physical protection and control equipment. This gives developers the means to prove their ideas, prototypes and final products in a realistic environment. This paper will summarize the fundamental design of the RTDS simulator, with particular emphasis on recent developments and enhancements. It will also describe practical applications of the simulator in the various stages of power system design, testing and implementation. A brief description of ongoing development for the real time simulation of voltage source converter (VSC) converters is included.

Recent developments in islanding detection for distributed power generation

Abstract: The aim of this paper is to review recent developments in anti-islanding techniques for distributed resources interconnected with electric power systems. The techniques may be classified as remote and local. Remote techniques are associated with island detection on the utility side while local techniques are associated with island detection on the distributed power generation side. Local techniques may further be classified as passive and active.

Synchronized phasor measurement in protective relays for protection, control, and analysis of electric power systems

Abstract: The advent of satellite-based time-keeping systems and advances in computer technology have made possible protective relay sampling synchronization within 1 /spl mu/s. These relays can now provide synchronized phasor measurements that eliminate the need to have different devices for protection, control, and electric power system analysis for system-wide applications and traditional protection applications. System-wide applications have different sampling and signal processing requirements than do traditional protection applications. This paper proposes combining the aforementioned applications in a single device with a flexible signal processing system.

A new PMU-based fault detection/location technique for transmission lines with consideration of arcing fault discrimination-part II: performance evaluation

Abstract: The theory and algorithms of the proposed technique have been presented in Part I of this two-paper set. In Part II of this two-paper set, the proposed technique is evaluated by considerable simulation cases simulated by the Matlab/Power system Blockset simulator. For the proposed fault detector, the trip time achieved can be up to 3.25 ms and the average value of trip times is about 8 ms for both permanent and arcing faults on transmission lines. For the proposed fault locator, the accuracy can be up to 99.99% and the error does not exceed 0.45%. Moreover, the proposed arcing fault discriminator can discriminate between arcing and permanent faults within four cycles after fault inception. It has proven to be an effective tool to block reclosing on the permanent faults in the computer simulations. The simulation results also demonstrate that the presented extended discrete Fourier transform algorithm eliminates effectively the error caused by exponentially decaying dc offset on fundamental and harmonic phasor computations. Finally, a test case using the real-life measured data proves the feasibility of the proposed technique.

A processing unit for symmetrical components and harmonics estimation based on a new adaptive linear combiner structure

Abstract: Symmetrical components as well as harmonic tracking are of great importance in many applications in power systems such as power quality and protection. This paper introduces a novel Adaptive linear combiner (ADALINE) structure for symmetrical components estimation. This structure is capable of dealing with multi-output systems for parameter tracking/estimation rather than the existing ADALINE, which deals only with single output systems. As the new topology deals with Multi-Output systems, it is called MO-ADALINE. Moreover, the paper presents a new processing unit, which can estimate symmetrical and harmonic components from the measured current signals. The advantages of this proposed unit are its independence of the voltage waveform and its ability to give information about the reactive component of the resolved current. Simulation results are given to validate the proposed algorithms.

Superimposed components based sub-cycle protection of transmission lines

Abstract: Requirements for improvements of system stability and reduction in the effects of shunt type faults in transmission and bulk systems on sensitive industrial loads result in the development of protection relays with sub-cycle operating times. At the same time the relays have to be stable under wide area disturbance conditions. The paper discusses in detail the concept of superimposed components and their application for directional detection, faulted phase selection and power swing detection. Complex distance characteristics can be used to provide sufficient resistive reach to cover the expected range of fault arc resistances, while at the same time are not affected by encroachment of the load impedance in the distance characteristic. Direct relay-to-relay communications allow the implementation of high-speed directional comparison protection.

Performance of Generator protection during major system disturbances

Abstract: Disturbance is an inherent part of any power system during the transition from one steady-state operating condition to the next. Protective relays may experience abnormal operating conditions during this transient period. This paper reviews various control actions that play a part during the transition and provides technical guidance to the industry on the application and setting of generator protective relays that can operate during major system disturbances.

Practical Power System Protection

Abstract: lant operators, electricians, field technicians and engineers will gain a practical understanding of the role and workings of power system protection systems from this work. An understanding of power systems and their optimized management will increase plant efficiency and performance as well as increasing safety levels. This book provides both the underpinning knowledge and basic calculations needed to understand, specify, use and maintain power protection systems, and the practical techniques required on a daily basis.After studying this book you will have an excellent knowledge of the principles of protection. You will also have a better understanding of the possible problems likely to arise in day-to-day work with power protection systems.Key areas of knowledge and expertise developed will include: Fundamentals of electrical power protection and applications Different fault types Perform simple fault and design calculations Practical knowledge of protection system components Apply relay settings Improve the safety of your site with the knowledge gained

A new approach for calculating zone-2 setting of distance relays and its use in an adaptive protection system

Abstract: This paper presents a method for calculating zone-2 setting of distance relays without causing coordination problems. The proposed method is based on the impedance seen by distance relays when faults are simulated on the reach of zone-1 of primary relays for the maximum and minimum generation outputs of the power system. It is shown that the proposed method increases the reach of zone-2 relays without causing coordination problems. The proposed method is modified for use in an adaptive protection system. It is shown that further improvements can be achieved when settings are calculated using the proposed method and the prevailing system conditions. Measures to alleviate the impact of communication failure are discussed. The proposed method and its adaptive version were applied to an existing power system and some results are reported in the paper.

Linear and nonlinear filters suppressing UWB pulses

Abstract: In order to protect electronic systems against natural or man-made electromagnetic interferences with high energies and amplitudes nonlinear protection elements like spark gaps, varistors or Z-diodes are state-of-the-art countermeasures. Most of these protection circuits are designed for well studied transient interferences like lightning electromagnetic pulse, nuclear electromagnetic pulse or electrostatic discharge pulses. It is of special interest to investigate the response of common nonlinear protection elements at ultrawideband (UWB) pulses with significant amplitudes, rise times in the picosecond range and pulse durations of a few nanoseconds. It is discussed whether traditional protection concepts provide a sufficient protection against such extremely fast pulses. Furthermore the possibility of linear filtering is presented with focus on the protection of high frequency datalines.

Multi-agents based protection for distributed generation systems

Abstract: As a result of deregulation, distributed generation (DG) systems with distributed generators installed in the middle or low voltage networks become popular in distribution systems. Traditional protections developed in radial systems are difficult in coordination and in protecting against high impedance fault (HIF), sometimes it may cause nuisance tripping in the DG systems. A decentralized multi-agent based protection with capability of HIF detection, fault location and load shedding for the DG systems is proposed in the paper. Digital relay is designed as a relay agent which is capable of searching for information from other relay agents, interacting with other relay agents and performing tasks of protection with autonomy and cooperating. The agent based protection scheme is also presented. EMTP simulation results show that the proposed agent based protection scheme can remove the influence of load switching operations, protect against HIF, electric shock. The prototype of relay agent is developed, the research is now in progress on testing the prototype in dynamic power system.

Alarm processing in electrical power systems through a neuro-fuzzy approach

Abstract: This work presents a methodology that combines the use of artificial neural networks and fuzzy logic for alarm processing and identification of faulted components in electrical power systems. Fuzzy relations are established and form a database employed to train artificial neural networks. The artificial neural networks inputs are alarm patterns, while each output neuron is responsible for estimating the degree of membership of a specific system component into the class of faulted components. The proposed method allows good interpretation of the results, even in the presence of difficult corrupted alarm patterns. Tests are performed with a test system and with part of a real Brazilian system.

Analysis of angle stability problems: a transmission protection systems perspective

Abstract: Postfault rotor angle oscillations lead to power swings. Both unstable and stable swings can induce distance relay tripping. For unstable swings, a new computational procedure to locate all of the electrical centers is developed. It simplifies the work associated with visual screening of all the R-X plots. For stable swings, a generic three-tier hierarchy of stability-related norms defined by branch norm, fault norm, and system norm is proposed. Ranking by branch norm leads to ranking of power swings. Ranking by fault norm leads to ranking of faults or contingencies. Magnitude and rate of change of system norm can be used to detect an out-of-step condition. Results on a ten-machine system and a utility system with detailed models are also presented.

Systems and methods for fault-based power signal interruption

Abstract: Systems, methods, and apparatus for fault detection and interruption in power lines are provided. Circuitry is implemented via software and hardware that is configured to sense an operational aspect of a power line and apply signal processing to the sensed operational aspect to detect faults including different types of faults such as transient and steady state faults and can also be configured to identify the type of fault. Information on the fault and the identification of the type of fault can be displayed, stored, or some other output operation can be implemented. Circuitry can be implemented to provide digital signal processing and analog signal processing to, for example, independently and in parallel (e.g., redundant operation) detect faults and respond to faults as they occur (i.e., in real time). The types of faults can include transient type faults that can include ground, arc, line-to-line, and imbalance type faults and can also include steady state type faults (e.g., those showing wear in the machinery of a load).