Showing papers on "Power-system protection published in 2000"

Protection cycles in mesh WDM networks

Abstract: A fault recovery system that is fast and reliable is essential to today's networks, as it can be used to minimize the impact of the fault on the operation of the network and the services it provides. This paper proposes a methodology for performing automatic protection switching (APS) in optical networks with arbitrary mesh topologies in order to protect the network from fiber link failures. All fiber links interconnecting the optical switches are assumed to be bidirectional. In the scenario considered, the layout of the protection fibers and the setup of the protection switches is implemented in nonreal time, during the setup of the network. When a fiber link fails, the connections that use that link are automatically restored and their signals are routed to their original destination using the protection fibers and protection switches. The protection process proposed is fast, distributed, and autonomous. It restores the network in real time, without relying on a central manager or a centralized database. It is also independent of the topology and the connection state of the network at the time of the failure.

Predicting islanding operation of grid connected PV inverters

Abstract: Increasing numbers of photovoltaic arrays are being connected to the power utility through power electronic inverters. This has raised potential problems of network protection. If, due to the action of the inverter or inverters, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. Many methods to prevent this have been proposed and a SPICE-based model and analysis of the system are presented. Specifically aimed at predicting the effectiveness of two of these. These are: active frequency drift, which causes the inverter current to be generated slightly lower or higher in frequency than the frequency of the terminal voltage; and slip mode frequency shift, which controls the phase angle of the inverter current as a function of the frequency deviation of the terminal voltage from that of the normal network frequency. Experimental verification of the model is provided. Active frequency drift using frequency speed-up rather than speed-down is shown to be preferable for inductive loads, but conditions that resulted in islanding could be predicted. Slip mode frequency shift proved to be a more robust anti-islanding protection technique.

A novel fuzzy neural network based distance relaying scheme

Abstract: This paper presents a new approach to distance relaying using fuzzy neural network (FNM). The FNN can be viewed either as a fuzzy system, a neural network or fuzzy neural network. The structure is seen as a neural network for training and a fuzzy viewpoint is utilized to gain insight into the system and to simplify the model. The number of rules is determined by the data itself and therefore a smaller number of rules is produced. The network is trained with the backpropagation algorithm. A pruning strategy is applied to eliminate the redundant rules and fuzzification neurons, consequently a compact structure is achieved. The classification and location tasks are accomplished by using different FNN's. Once the fault type is identified by the FNN classifier the selected fault locating FNN estimates the location of the fault accurately. Normalized peaks of fundamental voltage and current waveforms are considered as inputs to all the networks and an additional input derived from the DC component is fed to fault locating networks. The peaks and DC component are extracted from sampled signals by the EKF. Test results show that the new approach provides robust and accurate classification/location of faults for a variety of power system operating conditions even with resistance in the fault path.

On-line fault diagnosis of distribution substations using hybrid cause-effect network and fuzzy rule-based method

Abstract: A correct and rapid inference is required for practical use of an online fault diagnosis in power substations. This paper proposes a novel approach for on-line fault section estimations and fault types identification using the hybrid cause-effect network/fuzzy rule-based method in distribution substations. A cause-effect network, which is well suited to parallel processing, represents the functions of protective relays and circuit breakers for selection of faulted sections. Therefore the inference speed can be improved significantly. In order to deal with the uncertainties involved in the process of clarifying faults, a fuzzy rule-based method is derived. The proposed approach has been practically verified by testing on a typical Taiwan Power Company's (Taipower) secondary substation. The experimental results reveal that the correct and rapid diagnosis is obtained even for the fault domains involving multiple faults and failure operations of protective devices. Moreover, it is easy to implement and transplant into different substations.

Transient based protection for power transmission systems

Abstract: This paper introduces new developments in fault transient based power system protection techniques. A brief review of history of relay development, which outlines the background of the new developments is first given in the paper. The concept of 'transient based protection' is then presented and the advantages of which over conventional techniques are highlighted through the introduction to a number of new transient based protection techniques under development.

An expert system for the back-up protection of a transmission network

Abstract: A back-up protection scheme for a transmission network is described in the paper. The back-up protection uses an action factor-based expert decision system (referred to as the BPES) to provide optimal fault clearance for faults located anywhere on the protected network. To achieve an optimal response, the BPES needs to know the topology of the network and the operating response of existing protection relays. Based on this information, the expert decision system will try to identify the feeder that contains the fault and which circuit breakers need to be tripped to clear the fault.

The 40-/spl Omega/ ground-fault phenomenon

Abstract: Coordination of protective devices on electrical distribution systems always involves the calculation of fault currents. These calculations almost always include a minimum fault current value. This minimum fault current value is not a bolted fault calculation; it includes an assumed impedance. Many utilities have assumed this impedance to be 40 /spl Omega/. This paper examines that assumption and provides some guidance on this issue. This paper is based on a study sponsored by the Cooperative Research Network, a division of the National Rural Electric Cooperative Association, based in Arlington, VA. This original study was completed in 1997.

Network reconfiguration at the power distribution system with dispersed generations for loss reduction

Abstract: This paper discusses the network reconfiguration at the power distribution systems with dispersed generations (DG) for loss reduction. The power distribution systems have a radial network and unidirectional power flows. With the advent of dispersed generations, the power distribution systems have a locally looped network and bidirectional power flows. Therefore, DG into the power distribution system can cause operational problems and impact on existing operational schemes. There are several operational schemes in power distribution systems. One of these operational schemes is network reconfiguration, which is defined as altering the topological structures of distribution feeders by changing the open/closed states of the sectionalization and the switches. However, with the introduction of DG in power distribution systems, this increases the complexity of this problem. In this paper, an operational scheme is presented which uses network reconfiguration at the power distribution systems with DG as real-time operation tool for loss reduction. The solution procedure is illustrated on simple examples.

Power systems of the future. 2

Abstract: The assets and working philosophy of individual utilities will in large measure be reflected by the modernization of their power systems in the next 2 decades. The power system of the future should enable utilities to: be more competitive with their overall strategies; provide better service; better manage their assets; extend equipment life; improve diagnostics; and develop reliability-centered maintenance. In looking ahead at the next 2 decades, we consider various options that are available, point out the less likely, and highlight those that have the potential of achieving major improvements. Although the next 20 years is a little soon for dispersed generation to have a significant impact, some of the implications of dispersed generation are considered. The following topics are covered in this paper: transmission and distribution developments; comparison of overhead and underground power delivery; the pros and cons of underground delivery; superconducting power transmission including cables; and cryoresistive delivery including conventional cryoresistive delivery, hyperconductivity and metal-plated graphite fibres.

Interconnection protection of IPP generators at commercial/industrial facilities

Abstract: Much of the new generation capacity installed during the next millennium will be accomplished through the construction of independent power producer (IPP) generating facilities. These facilities can take the form of small dispersed generating units, or large-capacity plants owned and even operated by nonutility personnel. It is forecasted that many of these dispersed generating units will be at smaller industrial and commercial facilities and operating in parallel with the utility system to reduce energy cost through load sharing or "peak shaving." This paper discusses the protection requirements to interconnect these generators to utility systems, as well as methods to reconnect these generators after interconnect protection tripping.

A busbar protection technique and its performance during CT saturation and CT ratio-mismatch

Abstract: This paper describes a digital technique for protecting busbars. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents are used to detect faults, parameters of the power system are not used. An analysis of the performance of the proposed technique during CT saturation and ratio-mismatch conditions is presented. The performance of the technique was investigated for a variety of operating conditions and for several busbar configurations. Data generated by EMTP simulations of model power systems were used in the investigations. The results indicate that the proposed technique is stable during CT saturation and ratio-mismatch conditions.

Numerical algorithm for overhead lines arcing faults detection and distance and directional protection

Abstract: In this paper, an overhead lines protection numerical algorithm, based on one terminal data and derived in the time domain, is presented. The fault location, direction and its nature (arcing or arcless fault) are estimated using the least error squares technique. The faulted phase voltage is modeled as a serial connection of fault resistance and arc voltage, offering more sophisticated line protection. The algorithm can be applied for both ordinary and the high impedance faults detection, distance protection, intelligent autoreclosure, as well as for the purpose of directional relaying. The approach presented does not require the line zero sequence resistance as an input datum. The algorithm is derived for the case of the most frequent single-phase to ground unsymmetrical faults. The results of algorithm testing through computer simulation are given. The influence of remote infeed, fault resistance, higher order harmonies, power system frequency, network topology, line parameters and other factors are investigated and systematically presented. Finally, an example of real life data processing is given.

AC, DC or hybrid power solutions for today's telecommunications facilities

Abstract: This paper describes alternative design approaches for powering modern telecommunications facilities having both AC- and DC-powered equipment, including the use of a DC plant with inverters for the AC loads, a DC plant for the DC loads and AC UPS for the AC loads, and an AC UPS for the AC loads with rectifiers for the DC loads. The use of standby generators in lieu of long battery backup times is also discussed. Advantages and disadvantages of the various design approaches are presented along with some guidelines as to what circumstances favor one approach over another.

Shielding grids from solar storms [power system protection]

Abstract: The authors describe how geomagnetic disturbances are a real danger to some power grids and detail how being prepared for one requires an assessment of local conditions, as well as monitoring and warning systems.

Adaptive setting of digital relay for transmission line protection

Abstract: The distance relay is the most widely relay used in transmission line protection because it is applicable not only as main protection but also as back-up protection. However, the protection range of the distance relay is always fixed in the unchangeable operating range while the power system varies and therefore the distance relay is the one that is the most highly influenced by the power system changes. In this regard, this paper describes an approach to minimize the maloperation of the distance relay due to the power system changes through changing protection range of the distance relay into optimal condition in response to the load variation and power system condition. Also malfunction of the distance relay in case of high resistance ground faults could be minimized through modeling the protection range into a quadratic function.

Broken conductors protection system using carrier communication

Abstract: This paper presents a detection and signaling system designed to identify and locate high impedance faults caused by broken conductors on distribution primary feeders. Unlike conventional protection systems, which perform current sensing, the working principle of the proposed system consists on monitoring the voltage unbalance along a feeder. This allows the system to detect a fault occurrence even in cases when the conductor touches a high impedance earth surface (for instance asphalt). This system has an additional advantage of giving an indication of the location of a fault since it involves measurements at multiple points on a feeder. In order to detect the voltage unbalance produced by a broken conductor, a new sensor was developed which is sensitive to the electric field generated by primary feeders. A carrier communication channel is associated to each sensor allowing the high impedance fault occurrence information to reach the protection equipment located closer to or at the substation.

A new method for protection zone selection in microprocessor-based bus relays

Abstract: Use of graph theory simplifies representation of complex bus arrangements in power system stations. This paper presents a new method, based upon graph theory, for selecting bus protection zones in microprocessor-based relays. We use a typical bus arrangement to illustrate the graphical representation of station arrangements, graph operations, and associated matrix operations. We also describe an implementation of the zone selection method and use two examples to demonstrate the advantages of the method. Using the status of switching devices in the station, the zone selection method provides the relay with real-time bus arrangement information. The bus relay uses this information to assign input currents to a differential protection zone and to select which breakers to trip for a bus fault or breaker failure.

Low voltage power system surge overvoltage protection

Abstract: The unpredictable threat of transient overvoltages is ever increasing in today's low-voltage power supplies for every aspect of industry. To calculate the magnitude, duration and energy of such transient overvoltages is not an easy task. Some loads are becoming very sensitive to such overvoltages, thereby creating a challenge for the application engineer to design a reliable power supply system. To apply surge overvoltage mitigation devices requires technical knowledge to understand their application limitations and configuration within a power system. A technical overview of the fundamentals of transients and associated noise is presented. The importance of understanding applicable UL, IEEE, and IEC Standards, and a thorough review of manufacturers' data on transient voltage surge suppressors (TVSSs) is included. TVSS testing requirements per the second edition of UL 1449 is presented. An overview of how to design a low-voltage power supply system to suppress transient overvoltages is included.

Investigation of ground-fault protection devices for photovoltaic power system applications

Abstract: Photovoltaic (PV) power systems, like other electrical systems, may be subject to unexpected ground faults. Installed PV systems always have invisible elements other than those indicated by their electrical schematics. Stray inductance, capacitance and resistance are distributed throughout the system. Leakage currents associated with the PV modules, the interconnected array, wires, surge protection devices and conduit add up and can become large enough to look like a ground-fault. PV systems are frequently connected to other sources of power or energy storage such as batteries, standby generators, and the utility grid. This complex arrangement of distributed power and energy sources, distributed impedance and proximity to other sources of power requires sensing of ground faults and proper reaction by the ground-fault protection devices. The different DC grounding requirements (country to country) often add more confusion to the situation. This paper discusses the ground-fault issues associated with both the DC and AC side of PV systems and presents test results and operational impacts of backfeeding commercially available AC ground-fault protection devices under various modes of operation. Further, the measured effects of backfeeding the tripped ground-fault devices for periods of time comparable to anti-islanding allowances for utility interconnection of PV inverters in the United States are reported.

Sub-cycle detection of incipient cable splice faults to prevent cable damage

Abstract: This paper presents an innovative method for subcycle detection of incipient cable failures caused by self-clearing faults occurring in cable splices due to insulation breakdown. Because of their short duration, conventional overcurrent protection will not detect these types of faults. The protection scheme described in this paper has been integrated into a universal relay platform. It is fast enough to operate for sub-cycle faults and has the logic to differentiate them from other types of faults. Imminent cable failure can be detected.

The influence of loading conditions and network topology on voltage sags

Abstract: The paper presents the results of the analysis of the voltage sag propagation in distribution networks. Two different networks are used in the study. Voltage sags resulting from the symmetrical and asymmetrical faults in the system are calculated. Different network topologies (radial, semi-meshed and meshed) of a generic distribution network are examined. The influence of the loading conditions of the network and pre-fault voltages is assessed. The contribution of the embedded generation to voltage sag propagation is also investigated.

Design optimization and performance evaluation of the relaying algorithms, relays and protective systems using advanced testing tools

Abstract: This paper defines underlying performance quality measures for designing, optimizing, setting and evaluating the protective relaying algorithms and equipment. The paper starts with evaluation of digital measuring algorithms, and gradually introduces the performance indices for the operating principles, relays and protection systems. Multi-objective formal ranking methods based on fuzzy set theory are used to combine diverse measures into composite performance indices enabling evaluating and optimizing various functions of protective equipment.

A smart relaying scheme for high impedance faults in distribution and utilization networks

Abstract: The paper presents a novel transient time domain relaying scheme for distribution/utilization networks. The scheme is based on graphical image feature extraction of a diagnostic feature vector x/sub f/ that carries information about the fault types. The relaying algorithm is capable of detecting low current impedance type faults (HIF).

Selective power control with active link protection for combined rate and power management

Abstract: In wireless multimedia services, the system can provide a user with multiple data rates. This paper focuses on the combined control of rates and powers for the system, in which a finite number of transmission rates are available. This problem was first addressed by Kim, Rosberg and Zander (see Proc. IEEE VTC Fall, p.1653-57 1999) and two distributed power control algorithms were suggested. One of the suggested algorithms there is called selective power control (SPC). In this paper, we extend SPC by combining it with the active link protection (ALP) scheme. The main purpose of such an extension is trying to guarantee the minimum rate to users and to minimize the number of rate changes by smoothing the realized CIRs. Computational experiments are carried out on a DS-CDMA system. The results indicate that the modified SPC achieves smaller outages and less rate changes while giving the same or slightly higher system throughput, compared with SPC.

Prevention of underground cable splice failures

Abstract: The failure of underground medium-voltage cable splices produces many undesired events. When water invades an underground cable splice, a series of self-clearing faults ensues. These self-clearing faults continue until complete splice failure occurs. This paper discusses the nature of medium-voltage cable splice failure in underground installations. In addition, a new methodology is described which will predict the occurrence of cable splice failures before they happen.

A primer on capacitor bank protection

Abstract: Capacitor banks are applied in power systems to provide reactive power. The reactive power results in lower current in lines upstream of the bank improving system voltage and power factor and reducing line losses. Capacitor banks can be configured as filters for harmonic reduction. The protection systems for capacitor banks include fuses, surge arresters, and protective relays. This paper focuses on protective relaying philosophies of grounded and ungrounded Y connected shunt capacitor banks, which are commonly applied on industrial and utility power systems.

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

Abstract: Voltage instability is strongly influenced by unsuitable allocation or insufficient production of reactive power. It is basically a dynamic phenomenon, but system-oriented approaches are mostly used for the analysis. These approaches are time consuming and therefore not appropriate for on-line monitoring. There is also no clear path to the physical interpretation of the process. Since the phenomenon is of local nature, the goal of this research was to derive a simple method that would yield a voltage collapse proximity indicator with physical meaning. The paper presents a new scheme for protection against voltage collapse based on local phasors. Detection of critical lines instead of critical nodes is used. The difference between apparent power flows at the receiving and the sending end of the line is used for computation of voltage collapse indicator. According to the developed protection scheme, the relay sends a triggering signal to reactive power sources to increase reactive power production. Because of the computational simplicity the proposed protection scheme can be used for on-line system monitoring as well as for off-line analyses.

Power transformer protection based on transient detection using discrete wavelet transform (DWT)

Abstract: This paper addresses a new relaying scheme for power transformer protection. In principle, the new technique implements the wavelet transform to extract the transient components from the captured transform currents. The powerful function of a discrete wavelet transform (DWT) in analysing nonstatic signals is capable of extracting those predominant transient signals energised by transformer internal fault. With the aid of spectrum analysis of extracted transients, the high selectivity of the proposed relay can be achieved. The new relay possesses the advantages of high speed response, immunity to the CT saturation, ability of detecting low level internal faults and inrush current, etc. The study in this paper evaluates the performance of the proposed relaying scheme and proves its feasibility.