Performance Enhancement of GPS based Line Fault Location Using Radial Basis Function Neural Network M. R. Mosavi Assistant Professor, Department of Electrical Engineering Behshahr University of Science and Technology, Behshahr 48518-78413, Iran M_Mosavi@iust.ac.ir Abstract: GPS, well known as a versatile, global tool for positioning, has also become the primary system for distributing time and frequency. Fault locator systems measure the time of arrival of a fault-generated traveling wave at the time terminals using the precise timing signals from the GPS. Therefore, GPS timing accuracy is very important. In this paper, a Radial Basis Function Neural Network (RBF NN) is proposed for GPS receivers timing error modeling and perdition. It uses successive approximation, first obtaining a number of coarse approximations, and then optimally linearly combining the coarsely defined functions to achieve an accurate end result. The method is particularly very useful for modeling and prediction of GPS receivers timing error in the presence of Selective Availability (SA) noise. The experimental results on the collected real data using a low cost GPS engine are presented. It is shown that proposed RBF NN can improve GPS timing accuracy from 340nsec and 200nsec to less than 170nsec and 40nsec, before and after SA, respectively. 1. Introduction The Global Positioning System (GPS) is an earth-orbiting-satellite based navigation system. GPS is an operational system, providing users worldwide twenty-four hour a day precise position in three dimensions and precise time traceable to global time standards. GPS is operated by the United States Air Force under the direction of the Department of Defense (DOD) and was designed for, and remains under the control of, the United States military. While there are now many thousands of commercial and recreational civil users worldwide, DOD control still impacts many aspects of GPS planning, operation, and use [1]. Primarily designed as a land, marine, and aviation navigation system, GPS applications have expanded to include surveying, space navigation, automatic vehicle monitoring, emergency services dispatching, mapping, and geographic information system georeferencing. Because the dissemination of precise time is an integral part of GPS, a large community of precise time, time interval, and frequency standard users has come to depend on GPS as a primary source of control traceable through the United States Naval Observatory to global time and frequency standards [2]. The need to determine the location of faults is industry wide. Equipment based on traveling wave theory has been used for many years for this purpose and also for relaying. The application to fault location, however, dos not give adequate accuracy because such systems usually rely on measuring the impedance of the line (or its voltage); a quantity which is affected by load conditions, high grounding resistance, and most notably series capacitor banks. The mentioned problems would be eliminated if the measured quantity was the time of arrival of the traveling wave rather than the encountered impedance or the produced voltage. This, however, requires that highly accurate time signals produced by a single source (i.e. having the same reference) be available at all power system locations. Traveling wave fault locator systems use the time signals available (via satellite) from the GPS [3]. Since GPS is a military navigation system of U. S., a limited access to the total system accuracy is made available to the civilian users. The service available to the civilians is called Standard Positioning System (GPS) while the service available to the authorized users is called the Precise Positioning Service (PPS). User current policy the time accuracy available to SPS users is 340nsec and for PPS users it is 200nsec. Additional limitation Anti-Spoofing (AS), and Selective Availability (SA) was further imposed for civilian users. Under AS, only authorized users will have the means to get access to the P-code. By imposing SA condition, timing accuracy was randomly offset for SPS users. Since May 1, 2000 according to declaration of U. S. President, SA is switched off for all users. To make effective use of GPS timing information, it is essential to model these errors and to reduce these effects [4-8].
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