David G. Hart

Unsynchronized two-terminal fault location estimation

A technique for power system fault location estimation which uses data from both ends of a transmission line and which does not require the data to be synchronized is described. The technique fully utilizes the advantages of digital technology and numerical relaying which are available today and can easily be applied for offline analysis. This technique allows for accurate estimation of the fault location irrespective of the fault type, fault resistance, load currents, and source impedances. Use of two-terminal data allows the algorithm to eliminate previous assumptions in fault location estimation, thus increasing the accuracy of the estimate. The described scheme does not require real-time communications, only offline post-fault analysis. The paper also presents fault analysis techniques utilizing the additional communicated information.

A new frequency tracking and phasor estimation algorithm for generator protection

Digital generator protection is a complex and difficult problem. Analog and solid state methods have been successfully applied to generator protection in the past and implementation of these functions in a digital device is a continuing trend. This paper explores a new method to implement frequency tracking and phasor estimation in a numerical relay. A new algorithm is presented which utilizes a variable window discrete Fourier transform (DFT) for frequency tracking. Use of the DFT to compute the phasor estimates at a frequency other than the assumed frequency is outlined first. Next, a new technique for tracking the frequency is outlined. The paper concludes with testing of the new algorithm.

Algorithms for locating faults on series compensated lines using neural network and deterministic methods

This paper investigates a scheme to improve the reach measurement of distance relays and fault locators for series compensated power lines. A deterministic method and a feedforward neural network method have been implemented for online calculation of the voltage across a nonlinear capacitor installation. These techniques are compared and incorporated into a new relaying scheme which is independent of the series capacitor installation, operation of the capacitor protection, and the surrounding power system elements. The proposed scheme is simple and accurate and requires only local voltage and current at the bus. Detailed testing using EMTP has been done to show the benefits of the new adaptive scheme. The results demonstrate the suitability of the techniques for real world applications.

Fault location using digital relay data

The most accurate and reliable fault location results are obtained using new algorithms that consider the fault data from both ends of the line together. Obviously, the data from the two ends must be brought together via data communications, either from one substation to the other or to a computer at a third site to which both substations can send the data. This might be a control center, relay engineers office, or maintenance depot, which are ideal locations for really accurate fault location displays to be presented. Some two-ended location algorithms require time synchronization of the data from the two ends, which is not widely available. This article presents new calculations that do not require any such synchronization of the records to achieve excellent accuracy. Following an overview of the technical problems in computing fault location from fault voltage and current signals, a sampling of the newest and most accurate techniques that are easily implemented in existing digital devices for calculating location from one-ended or two ended line fault data records is given. >

Automated solutions for distribution feeders

As computers and other electronic equipment become the mainstay of todays businesses, customer awareness and intolerance for power system outages continues to heighten. For these customers, it is important that utilities be able to offer complete solutions to meet their needs. Depending on the customer load requirements, standby generation, uninterruptible power supply, or automatic restoration are possible solutions to improve the system reliability. In addition, utilities are becoming increasingly automated to keep up with the demands of the new business environments. As newly reregulated distribution companies emerge, it is likely that reliability indexes will be one of the key factors for regulators to examine to determine the overall performance of the distribution company. Thus, drivers for distribution automation include: remote control and restoration; targeted regions or customers for improved reliability and operation; performance based rates (PBR); and safety issues for circuit isolation. Whatever the driver for feeder automation, several key issues must be addressed: what automation scheme is required? How are communications implemented? This article addresses these issues with example solutions for overhead feeder automation.

Application of artificial neural networks for series compensated line protection

This paper investigates the feedforward neural network (with a quasi-Newton method for minimization of the error function) for on-line calculation of the voltage across a nonlinear capacitor installation. This technique is incorporated into a new scheme which is independent of the series capacitor installation, operation of the capacitor protection, and the surrounding power system elements. The proposed scheme is simple and accurate and requires only local voltage and current at the bus to improve the reach measurement of distance relays and fault locators. Detailed testing using EMTP has been done to show the benefits, robustness and generalization capabilities of the ANN technique.

Tapping protective relays for power quality information

Protective relays are vital components of power systems. They are deployed on every piece of major equipment and are attached to every circuit breaker in the system. As microprocessor technology continues to expand, microprocessor-based protective relays will enjoy enhanced functionality. Load profiling, fault oscillographic waveform capture, and metering are some of the enhanced functionality available in microprocessor-based protective relays. This article shows how existing signal processing capabilities of protective relays can be used to intelligently monitor power quality (PQ). The definition of power quality, the available functions, and their application to utilities are examined. In particular, it is noted that those PQ events that industrial account managers are interested in (voltage sags, swells, interruptions) and additional events PQ engineers need (waveform capture, harmonics) can be gathered by protective relays. The article concludes with some field results from a microprocessor-based protection unit. While this article discusses the integration of power quality monitoring into protective relaying specifically, PQ monitoring is also integrated into other intelligent electronic devices (IEDs) that have access to the system voltages and currents such as switch controllers and meters.

Methods for electric power measurements

With the advent of electronic meters, a variety of methods are now practical for measuring electrical quantities such as watts, power factor, VA and VARs, which previously were not possible. However, different methods for measuring these quantities may produce different results under certain conditions. This can be of concern since these quantities may be used for billing or tariff purposes, and there may be a question of what is the most equitable approach for the consumer base and existing rates. These concerns must be weighed against the various metering approaches that can help encourage or discourage specific consumer behavior.

Voltage variation analysis for site-level PQ assessment

This paper investigates the challenges in developing a performance index that will reflect the level of power quality at a site based on the actual field data obtained from the site via power-quality (PQ) monitors. For the index, each observed voltage variation is assessed in terms of its potential to impact the customers served from the site. The paper considers the substation level PQ monitoring and adopts a procedure that is similar to one of the methods being proposed in the emerging IEEE guide 1564.

Tapping IED data to find transmission faults

This article describes a data analysis tool that allows electric utility personnel to automatically and accurately compute the location of faults on power transmission lines and analyze fault data without cumbersome manual data retrieval and calculation procedures. When a fault is detected anywhere on the power network, an operator needs only to identify the faulted line, and the data analysis tool will compute the location of the fault as accurately as possible using the information available.