Timing is everything, and not just in show business. With less than perfect timing, jokes fall flat, and an actor’s lines are less than convincing. In the power business, customers can be inconvenienced at home and at work by service disruptions. Some situations may even be life-threatening. Then the show does not go on.
To ensure efficient electric power delivery to customers, utilities depend on global positioning system (GPS) technology. Bonneville Power Administration in the state of Washington incorporated GPS timing as a reliable component of its switching substations and pioneered the technology’s use for power outage isolation. Other power suppliers use GPS as an indispensable tool to maintain their power distribution system assets.
The Role of GPS in Timing and Location
GPS supplies the means to determine precise latitude, longitude, altitude, velocity and timing through a worldwide system of 24 satellites, providing 24-hour coverage without charge to users. As a broadcast-only radio system, GPS can support an unlimited number of receivers. Position is calculated based on the time it takes radio signals from each satellite in view to reach the GPS receiver’s antenna. GPS technology is sensitive enough to measure the Earth’s minute motions near fault lines, as well as the speed of jet aircraft. Depending on the type of GPS receiver used, timing is typically to 50 nanoseconds (billionths of a second) accuracy or greater. GPS is the only technology to provide this high level of accuracy everywhere on Earth.
GPS receivers with their sophisticated algorithms are particularly useful in today’s timing applications. Investment bankers use GPS to precision time-stamp trades on international networks to ensure that interest income and calculations are based on proper dates and time. GPS is also used in communications for synchronizing wireless networks. The latest digital cellular phone systems allow several users to share a frequency simultaneously, thus providing service to more users. A unique time signal tags each call to ensure that it is routed and transmitted properly.
In addition, GPS timing synchronizes power plant generators to provide electrical phase matching and fault detection throughout the U.S. power grids. Timing and synchronization are critical in the electrical power business to control the generation and distribution loop within the grid, to share power with adjacent grids, and to quickly identify the location of short circuits within the system. To accomplish these tasks, utilities turn to manufacturers of precision time and frequency products. The most precise products use satellite transmissions from GPS.
GPS on the Grid
In terms of the electrical transmission grid system’s efficiency, more is less. That is, access to more generators and transmission paths between grids means less chance of an outage. Thus, synchronization among the nine major power generating and transmission grids in the United States is vital to make power sharing work.
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Because electricity must be used as it is generated, power usage, or load, must equal power generation. The speed of the alternator that generates electricity determines the frequency, which increases when the load on the system decreases. System loads constantly change in other ways. Generators trip off when load drops. Capacitors switch in when lines break. These controls must operate precisely in milliseconds to strike a balance between load and generation and to keep the grid in synchronization with neighboring systems to share power. Keeping the system in sync allows more frequent power sharing and reduces instances of power outages.
To keep the system in sync, a central timing system at one location can provide a time code via microwave to field locations, such as to the controllers at smaller switching substations, often at remote locations. A time code generator running on its internal oscillator can provide timing to synchronize switching at the area controller at less cost, but it must be reset manually at regular intervals. GPS timing requires no adjustment by the user to keep accurate time.
GPS provides one of the most cost-effective, reliable and accurate time standards, which is why Bonneville Power Administration selected it. GPS satellite broadcasts are easily received at remote locations without the considerable expense of microwave communications. Microwave communication can also distort the time code, causing code readers to register the incorrect time. GPS provides reliability from interference that is a problem with other broadcast services.
Bonneville also uses GPS timing technology for power outage repair. A short circuit caused by a downed high-voltage transmission line is easy to trace. But what about the disruptions that are difficult to detect, like those produced by a shorted insulator?
When a short occurs, a high-frequency wave propagates in both directions on the transmission line. At substations on both sides of the short, the arrival times of the traveling waves are precisely time-stamped and compared to calculate the distance to the fault. Microsecond accuracy pinpoints fault location within 1,000 feet. In the seconds it takes for an electric power circuit to go down, GPS timing can determine where the short occurred or which breaker first tripped to cause the others to go down.
Management on the Map
Keeping accurate records of the various assets in an electric distribution system is a challenge, especially when a utility experiences dynamic changes. Even rural electric companies near high-growth urban areas can experience changes so rapidly that maps are outdated before they are printed. Rapid updating of road, subdivision and utility assets solves this problem, when GPS location information is stored on a computer. GPS receivers are equipped to record location and detailed information about each asset. The figure shows some attributes of typical utility assets that can be collected for inventory with a GPS unit.
The GPS data collector, a small handheld unit, records the geographic location in latitude, longitude and elevation with whatever attributes the operator identifies. Then, this information is fed into geographic information system (GIS) software for mapmaking. The accuracy and speed of GPS mapping makes the update process efficient at a very low cost, saving crew time and mileage. At the same time, operators can collect information about right-of-way width, state highways, city streets, rural roads and even areas with no roads.
The wilderness areas of eastern Utah and western Colorado provide a good example of the electric industry’s GPS use. The Moon Lake Electric Association cooperative delivers power to farms, ranches, oil fields and mines over 6,500 square miles of high-altitude desert and rugged mountains. Asset inventory represents a large part of the association’s GPS use, but the utility also maps roads in remote areas. To do this, the operator simply drives down the road while capturing position and elevation data with the GPS receiver and data collector, both of which are compact units for easy traveling.
Other situations are closer to urban growth areas, like Denton County Electric Cooperative in Texas and White River Valley Electric Cooperative in Missouri. Their challenges are to provide power to rapidly growing areas. With constant growth in Denton County, the manually generated paper map systems were overwhelmed and constantly out of date. By attaching the GPS antenna to the roof of a vehicle, crews drive both sides of a road to map it. For subdivisions, surveyors set up on the four corners to establish control points, from which they map the locations of pole lines, trenches and mounting pads. The significant advantage of GPS is that a person can survey more territory in less time and input changes quickly. Other utilities using GPS mapping include the Public Service Company of New Mexico and Duke Power in the Southeastern United States.
A Win-Win Situation
Agricultural implementations of GPS technology are also useful for utilities, such as aerial herbicide spraying to control vegetation growth on remote power line rights-of-way. Herbicide application from the air is most economical in remote areas that are inaccessible from the ground. To comply with environmental impact regulations that protect waterways and wildlife habitat, herbicide application must be precise to prevent overspray and drift. Hydro-Quebec uses GPS to precisely guide the helicopter pilot applying herbicides, minimizing both overspraying and untreated strips of vegetation that must be cut later by a ground crew. These GPS products provide the pilot with a display that indicates any deviation from the correct line of flight. Over time, the elimination of trees that threaten power lines provides space for lower vegetation to become established. The low growth of these grasses and shrubs reduces by half the time required between cutting or herbicide application in the right-of-way. Such herbaceous plants do not threaten the power lines and provide habitat for small animals. In this way, GPS can promote a win-win situation by reducing both utility expense and environmental impact.
The Skilled GPS Operator from the Start
Just as a surgeon brings skill to the operating room, a skilled GPS operator brings precision to utilities. Thus, the importance of GPS training cannot be overstressed. Whether formal training occurs on the job, in a classroom setting or a mix of both, it will foster efficient use of the equipment and dramatically improve field productivity from the start. Like computer software and other technology, GPS has its simple tricks of the trade-simple once they’re learned. GPS equipment training should be a requirement from the start to save time and expense. A proper understanding by a trained user can inspire even more applications than those already in use in the electric power industry, guaranteeing that the show will go on for millions of electric customers.
Norman Martello is an editorial writer for Trimble Navigation in Sunnyvale, Calif. For more information about Mobile and Timing Technology applications, contact Doug Merrill at 800-874-6722.
