17-09-2014, 11:17 AM
PROTECTION OF TRANSMISSION LINE USING GPS
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ABSTRACT:
This is a new technique for the protection of transmission systems by using the global positioning system (GPS) and fault generated transients. In this scheme the relay contains a fault transient detection system together with a communication unit, which is connected to the power line through the high voltage coupling capacitors of the CVT. Relays are installed at each bus bar in a transmission network. These detect the fault generated high frequency voltage transient signals and record the time instant corresponding to when the initial traveling wave generated by the fault arrives at the bus bar.
The decision to trip is based on the components as they propagate through the system. Extensive simulation studies of the technique were carried out to examine the response to different power system and fault condition. The communication unit is used to transmit and receive coded digital signals of the local information to and from associated relays in the system.
At each substation relay determine the location of the fault by comparing the GPS time stay measured locally with those received from the adjacent substations, extensive simulation studies presented here demonstrate feasibility of the scheme.
INTRODUCTION:
Accurate location of faults on power transmission systems can save time and resources for the electric utility industry. Line searches for faults are costly and can be inconclusive. Accurate information needs to be acquired quickly in a form most useful to the power system operator communicating to field personnel.
To achieve this accuracy, a complete system of fault location technology, hardware, communications, and software systems can be designed. Technology is available which can help determine fault location to within a transmission span of 300 meters. Reliable self monitoring hardware can be configured for installation sites with varying geographic and environmental conditions. Communications systems can retrieve fault location information from substations and quickly provide that information to system operators. Other communication systems, such as Supervisory Control and Data Acquisition (SCADA), operate fault sectionalizing circuit breakers and switches remotely and provide a means of fast restoration. Data from SCADA, such as sequence of events, relays, and oscillographs, can be used for fault location selection and verification. Software in a central computer can collect fault information and reduce operator response time by providing only the concise information required for field personnel communications. Fault location systems usually determine “distance to fault” from a transmission line end. Field personnel can use this data to find fault locations from transmission line maps and drawings. Some utilities have automated this process by placing the information in a fault location Geographical Information System (GIS) computer. Since adding transmission line data to the computer can be a large effort, some utilities have further shortened the process by utilizing a transmission structures location database. Several utilities have recently created these
GENERATION TRANSMISSION
Electric power transmission, a process in the delivery of electricity to consumers, is the bulk transfer of electrical power. Typically, power transmission is between the power plant and a substation near a populated area. Electricity distribution is the delivery from the substation to the consumers. Electric power transmission allows distant energy sources (such as hydroelectric power plants) to be connected to consumers in population centers, and may allow exploitation of low-grade fuel resources that would otherwise be too costly to transport to generating facilities. Due to the large amount of power involved, transmission normally takes place at high
WHAT IS TRAVELING WAVE FAULT LOCATION?
Faults on the power transmission system cause transients that propagate along the transmission line as waves. Each wave is a composite of frequencies, ranging from a few kilohertz to several megahertz, having a fast rising front and a slower decaying tail. Composite waves have a propagation velocity and characteristic impedance and travel near the speed of light away from the fault location toward line ends. They continue to travel throughout the power system until they diminish due to impedance and reflection waves and new power system equilibrium is reached. The location of faults is accomplished by precisely time-tagging wave fronts as they cross a known point typically in substations at line ends. With wave’s time tagged to sub microsecond resolution of 30 m, fault location accuracy of 300 m can be obtained. Fault location can then be
BENEFITS OF TRAVELING WAVE FAULT LOCATION
Early fault locators used pulsed radar. This technique uses reflected radar energy to determine the fault location. Radar equipment is typically mobile or located at substations and requires manual operation. This technique is popular for location of permanent faults on cable sections when the cable is de-energized. Impedance-based fault locators are a popular means of transmission line fault locating. They provide algorithm advances that correct for fault resistance and load current inaccuracies. Line length accuracies of ±5% are typical for single-ended locators and 1-2% for two-ended locator systems.
TRAVELING WAVE FAULT LOCATION THEORY
Traveling wave fault locators make use of the transient signals generated by the fault. When a line fault occurs, such as an insulator flashover or fallen conductor, the abrupt change in voltage at the point of the fault generates a high frequency electromagnetic impulse called the traveling wave which propagates along the line in both directions away from the fault point at speeds close to that of light. The fault location is determined by accurately time-tagging the arrival of the traveling wave at each end of the line and comparing the time difference to the total propagation time of the line. Refer to Figure1.0
WHAT IS GPS?
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. GPS Technology allows precise determination of location, velocity, direction, and time. GPS are space-based radio positioning systems that provide time and three-dimensional position and velocity information to suitably equipped users anywhere on or near the surface of the earth (and sometimes off the earth). Concept of satellite navigation was first conceived after the launch of Sputnik 1 in 1957 when scientists realized that by measuring the frequency shifts in the small bleeps emanating from this first space vehicle it was possible to locate a point on the earth's surface. The NAVSTAR system, operated by the US Department of Defense, is the first such system widely available to civilian users. The Russian system, GLONASS, is similar in operation and may prove complimentary to the NAVSTAR system. Current GPS systems enable users to determine their three dimensional differential position, velocity and time. By combining GPS with current and future computer mapping techniques, we will be better able to identify and manage our natural resources. Intelligent vehicle location and navigation systems will let us avoid congested freeways and more efficient routes to our destinations, saving millions of dollars in gasoline and tons of air pollution. Travel aboard ships and aircraft will be safer in all weather conditions. Businesses with large amounts of outside plant (railroads, utilities) will be able to manage their resources more efficiently, reducing consumer costs.
THE GPS SATELLITE SYSTEM
The 24 satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above us. They are constantly moving, making two complete orbits in less than 24 hours. These satellites are traveling at speeds of roughly 7,000 miles an hour. GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.
IMPLEMENTATION AND TESTING
Evaluation of the fault locator involved the installation of GPS timing receivers at four 500kV substations, see Figure 2.0. An especially developed Fault Transient Interface Unit (FTIU) connects to the transmission lines and discriminates for a valid traveling wave. The FTIU produces a TTL-level trigger pulse that is coincident with the leading edge of the traveling wave. A time-tagging input function was provided under special request to the GPS receiver manufacturer. This input accepts the TTL level logic pulse from the FTIU and time tags the arrival of the fault-generated traveling
CONCLUSION:
Thus the use of GPS in protection of transmission systems is beneficial with respect toValue regarding programmatic goals: more reliable monitoring using GPS related technologies.
Technical merit: new fault location algorithm based on new input data.
Emphasis on transfer of technology: CCET partnership aimed at commercialization.
Overall performance: on time, with all goals met so fa