GPS in Power Systems full report
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20-04-2010, 01:36 PM
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Fahd Mohamed Adly Hashiesh
Under Supervision of
Prof. Dr. M. M. Mansour
Dr. Hossam Eldin M. Atia
Dr. Abdel-Rahman A. Khatib
Cairo â€œ Egypt
APPLICATIONS OF GPS IN POWER ENGINEERING
What is GPS
GPS or Global Positioning Systems is a highly sophisticated navigation system developed by the United States Department of Defense. This system utilizes satellite technology with receivers and high accuracy clocks to determine the position of an object.
The Global Positioning System
A constellation of 24 high-altitude satellites
A constellation of satellites, which orbit the earth twice a day, transmitting precise time and position (Latitude, Longitude and Altitude) Information.
A complete system of 21 satellites and 3 spares.
GPS at Work
1. Navigation - Where do I want to go
2. Location - Where am I
3. Tracking - Monitoring something as it moves
4. Mapping - Where is everything else
5. Timing - When will it happen
Why do we need GPS
4 Ëœbirdsâ„¢ (as we say) for 3-D fix
Why GPS For power Eng
GPS time synchronization
By synchronizing the sampling processes for different signals â€œ which may be hundreds of kilometers apart â€œ it is possible to put their phasors in the same phasor diagram
Synchronized phasor measurements (SPM) have become a practical proposition.
As such, their potential use in power system applications has not yet been fully realized by many of power system engineers.
Phasor Measurement Units
They are devices which use synchronization signals from the global positioning system (GPS) satellites and provide the phasor voltages and currents measured at a given substation.
The GPS receiver provides the 1 pulse-per-second (pps) signal, and a time tag, which consists of the year, day, hour, minute, and second. The time could be the local time, or the UTC (Universal Time Coordinated).
The l-pps signal is usually divided by a phase-locked oscillator into the required number of pulses per second for sampling of the analog signals. In most systems being used at present, this is 12 times per cycle of the fundamental frequency. The analog signals are derived from the voltage and current transformer secondary's.
Different applications of PMUs in
1. Adaptive relaying
2. Instability prediction
3. State estimation
4. Improved control
5. Fault recording
6. Disturbance recording
7. Transmission and generation modeling verification
8. Wide area Protection
9. Fault location
Adaptive relaying is a protection philosophy which permits and seeks to make adjustments in various protection functions in order to make them more tuned to prevailing power system conditions
Â¢ The instability prediction can be used to adapt load shedding and/or out of step relays.
Â¢ We can actually monitor the progress of the transient in real time, thanks to the technique of synchronized phasor measurements.
Â¢ The state estimator uses various measurements received from different substations, and, through an iterative nonlinear estimation procedure, calculates the power system state.
Â¢ By maintaining a continuous stream of phasor data from the substations to the control center, a state vector that can follow the system dynamics can be constructed.
Â¢ For the first time in history, synchronized phasor measurements have made possible the direct observation of system oscillations following system disturbances
Â¢ Power system control elements use local feedback to achieve the control objective.
Â¢ The PMU was necessary to capture data during the staged testing and accurately display this data and provide comparisons to the system model.
Â¢ The shown figure shows a typical example of one of the output plots from the PMU data
Â¢ They can capture and display actual 60/50 Hz wave form and magnitude data on individual channels during power system fault conditions.
Â¢ Loss of generation, loss of load, or loss of major transmission lines may lead to a power system disturbance, possibly affecting customers and power system operations.
These figures are examples of long-term data used to analyze the effects of power system disturbances on critical transmission system buses.
7-Transmission and Generation Modeling Verification
Â¢ Computerized power system modeling and studies are now the normal and accepted ways of ensuring that power system parameters have been reviewed before large capital expenditures on major system changes.
Â¢ In years past, actual verification of computer models via field tests would have been either impractical or even impossible
Â¢ The PMU class of monitoring equipment can now provide the field verification required
7-Transmission and Generation Modeling Verification
Â¢ The shown figure compares a remote substation 500 kV bus voltage captured by the PMU to the stability program results
8-Wide â€œ Area protection
The introduction of the Phasor Measurement Unit (PMU) has greatly improved the observability of the power system dynamics. Based on PMUs, different kinds of wide area protection, emergency control and optimization systems can be designed
A fault location algorithm based on synchronized sampling. A time domain model of a transmission line is used as a basis for the algorithm development. Samples of voltages and currents at the ends of a transmission line are taken simultaneously (synchronized) and used to calculate fault location.
The Phasor measurement units are installed at both ends of the transmission line. The three phase voltages and three phase currents are measured by PMUs located at both ends of line simultaneously
SPM-based applications in power systems off-line studies
real-time monitoring and visualization
real-time control, protection and emergency control
The conclusions extracted form the present work can be summarized as follows:
1. A technique for estimating the fault location based on synchronized data for an interconnected network is developed and implemented using a modal transform
2. One-bus deployment strategy is more useful than tree search for fault location detection as it gives more system observability
3. 3- The average value of mode 1 and 2 of Karrenbauer transformation is used for 3-phase and line-to-line faults, while the average value of the 3 modes is used for line-to-line-ground and line-to-ground faults
4. 4- The results obtained from applying the developed technique applied to a system depicted from the Egyptian network show acceptable accuracy in detecting the fault and locations of different faults types.
This thesis is to address three issues:
1- Optimal allocation of Phasor Measurement Units (PMUs) using Discrete Particle Swarm Optimization (DPSO) technique.
2- Large scale power system state estimation utilizing the optimal allocation of PMUs based on Global Positioning Systems (GPS).
3- Power system voltage stability monitoring based on the allocated PMUsâ„¢ readings.
Propose a protection system (strategy) to counteract wide area disturbance (instability), through employing adaptive protection relays, and fast broadband communication through wide area measurement.
Configure and adapt the proposed system to be applied on Egypt wide power system network.
A Master Student is Trying to Implement a PMU Lab Prototype in Ain-Shams Univ.
CONCLUSIONS AND FUTURE WORKS
thanks to their multiple advantages, nowadays, the technologies based on synchronized phasor measurements have proliferated in many countries worldwide (USA, Canada, Europe, Brazil, China, Egypt !,..).
up to now most applications based on synchronized phasor measurements have concerned mainly off-line studies, on-line monitoring and visualization, and to a less extent the real-time control, Protection, and the emergency control.
the toughest challenge today is to pass from Wide Area Measurements Systems (WAMS) to Wide Area Control Systems (WACS) and WAP.
Off-line SPM-based applications
software simulation validation
SPM-based technologies can be very useful to help the validation of (dynamic) simulation software
system parameter/model identification (e.g. for loads, lines, generators, etc.)
the identification of accurate model/parameter is a very important and tough task for the power system analysis and control.
difficulty: large number of power system components having time-varying characteristics.
synchronized disturbances record and replay
this task is like that of a digital fault recorder, which can memorize triggered disturbances and replay the recorded data if required.
the use of SPM allows more flexibility and effectiveness.
Real-time monitoring SPM-based applications
fault location monitoring
accurate fault location allows the time reduction of maintenance of the transmission lines under fault and help evaluating protection performance.
power system frequency and its rate of change monitoring
the accurate dynamic wide-area measured frequency is highly desirable especially in the context of disturbances, which may lead to significant frequency variation in time and space.
generators operation status monitoring
this function allows the drawing of generator (P-Q) capability curve. Thus, the generator MVAr reserve, can be supervised.
transmission line temperature monitoring
the thermal limit of a line is generally set in very conservative criteria, which ignores the actual cooling possibilities. The use of SPM allows the higher loading of a line at very low risk.
on-line "hybrid" state estimation
the SPM can be considered, in addition to those from the Remote Terminal Units (RTU) of the traditional SCADA system, in an on-line "hybrid" state estimation.
SPM-based visualization tools used in control centers
display: dynamic power flow, dynamic phase angle separation, dynamic voltage magnitude evolution, real-time frequency and its rate of change, etc.
Real-time (emergency) control SPM-based applications
automatic (secondary and tertiary) voltage control
aim: optimize the var distribution among generators, controllable ratio transformers and shunt elements while keeping all bus voltage within limits.
in the context of WAMS application, the solution of this optimization problem can be used to update settings of those reactive power controllers, every few seconds.
damping of low frequency inter-area oscillations (small-signal angle instability)
low frequency inter-area oscillations (in the range of 0.2 â€œ 1 Hz) are a serious concern in power systems with increasing their size and loadability.
In Europe, in particular, many research studies have been performed to reveal such oscillations as well as provide best remedial actions to damp them out.
transient angle instability
since such instability form develops very quickly, nowadays, Special Protection Systems (SPS), also known as Remedial Action Schemes (RAS), are designed to act against predefined contingencies identified in off-line studies while being less effective against unforeseen disturbances.
Real-time (emergency) control SPM-based applications (contâ„¢d)
short- or long-term voltage instability
a responde-based (feedback) Wide-Area stability and voltage Control System (WACS) is presently in use by BPA.
this control system uses powerful discontinuous actions (switching on/off of shunt elements) for power system stabilization.
the underfrequency load shedding has its thresholds set for worst events and may lead to excessive load shedding.
new predictive SPM-based approaches are proposed aiming to avoid the drawbacks of the conventional protection.
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Have you ever been lost and wished there was an easy way to find out which way you needed to go? How about finding your self out hiking and then not knowing how to get back to your camp or car? Ever been flying and wanted to know the nearest airport?
Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.
GPS is a satellite based radio navigation system which provides continuous, all weather, worldwide navigation capability for sea, land and air applications. So things are much, much easier today. For less than $100, you can get a pocket sized gadget that will tell you exactly where you are on Earth at any moment. As long as you have a GPS receiver and a clear view of the sky, you'll never be lost again.
Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals. Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers. Surveying, geodetic control, and plate tectonic studies are examples. Time and frequency dissemination, based on the precise clocks on board the SVS and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
THE GPS EVOLUTION
GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime. The Global Positioning System is a constellation of satellites that orbit the earth twice a day, transmitting precise time and position (latitude, longitude and altitude) information.
Cavemen probably used stones and twigs to mark a trail when they set out hunting for food. The earliest mariners followed the coast closely to keep from getting lost. When navigators first sailed into the open ocean, they discovered they could chart their course by the stars. The next major developments in the quest for the perfect method of navigation were the magnetic compass and the sextant. The needle of a compass always points north, so it is always possible to know in what direction you are going. The sextant uses adjustable mirrors to measure the exact angle of the stars, moon, and sun above the horizon.
GPS is one of the most fantastic utilities ever devised by man. GPS will figure in history alongside the development of the sea-going chronometer. This device enabled seafarers to plot their course to an accuracy that greatly encouraged maritime activity, and led to the migration explosion of the nineteenth century. GPS will affect mankind in the same way. There are myriad applications that will benefit us individually and collectively.
The technology evolved from, Mr. Marconi’s transmission of radio waves. This was applied for society during the 1920's by the establishment of radio stations, for which you only needed a receiver. The same applies for GPS- you only need a rather special radio receiver. Significant advances in radio were bolstered by large sums of money during and after the Second World War, and were even more advanced by the need for communications with early satellites and rockets, and general space exploration. The technology to receive radio signals in a small hand-held, from 20,000kms away, is indeed amazing.
Throughout the 1960s the U.S. Navy and Air Force worked on a number of systems that would provide navigation capability for a variety of applications.
Disadvantages of other navigation systems
Landmark: Only work in local area. Subject to movement or destruction by environmental factors.
Dead Reckoning: Very complicated. Accuracy depends on measurement tools which are usually relatively crude. Errors accumulate quickly.
Celestial: Complicated. Only works at night in good weather. Limited precision.
OMEGA: Based on relatively few radio direction beacons. Accuracy limited and subject to radio interference.
LORAN: Limited coverage (mostly coastal).Accuracy variable, affected by geographic situation. Easy to jam or disturb.
SatNav: Based on low-frequency doppler measurements so it is sensitive to small movements at receiver. Few satellites so updates are infrequent.
Many of these systems were incompatible with one another. In 1973 finally, the U.S. Department of Defense decided that the military had to have a super precise form of worldwide positioning. And fortunately they had the kind of money ($12 billion!) it took to build something really good. In short, development of the GPS satellite navigation system was begun in the 1970s by the US Department of Defense. The basis for the new system was atomic clocks carried on satellites, a concept successfully tested in an earlier Navy program called TIMATION. The Air Force operated the new system, which it called the Navstar Global Positioning System. It has since come to be known simply as GPS.
Why did the Department of Defense develop GPS? In the latter days of the arms race the targeting of ICBMs became such a fine art that they could be expected to land right on an enemy's missile silos. Such a direct hit would destroy the silo and any missile in it. The ability to take out your opponent's missiles had a profound effect on the balance of power but you could only expect to hit a silo if you knew exactly where you were launching from. That's not hard if your missiles are on land, as most of them were in the Soviet Union. But most of the U.S. nuclear arsenal was at sea on subs. To maintain the balance of power the U.S. had to come up with a way to allow those subs to surface and fix their exact position in a matter of minutes anywhere in the world.
The first GPS satellite was launched in 1978 and a second-generation set of satellites ("Block II") was launched beginning in 1989. Today's GPS constellation consists of at least 24 Block II satellites. A full constellation of 24 satellites was achieved in 1994. The U.S. Air Force Space Command (AFSC) formally declared the GPS satellite constellation as having met the requirement for Full Operational Capability (FOC) as of April 27, 1995. Since then, the system has been taken into full use. In 1995 an agreement was made between the US-DOD and the US Department of Transportation regarding wide area broadcasts. With the modernized Block IIF satellites nearing launch—and the GPS III program now in its planning stages—the technology is poised to reach new levels of sophistication unimagined just a few years ago. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. After the downing of Korean Flight 007 in 1983 -a tragedy that might have been prevented if its crew had access to better navigational tools- President Ronald Reagan issued a directive that guaranteed that GPS signals would be available at no charge to the world. That directive helped open up a commercial market. Deployment of GPS continued at a steady pace through the 1990s, with growing numbers of civilian and military users. GPS burst into public awareness during the Persian Gulf War in 1991. GPS was used extensively during that conflict, so much so that not enough military-equipped GPS receivers were available. To satisfy demand, the Department of Defense acquired civilian GPS units and temporarily changed GPS transmissions to give civilian receivers access to higher-accuracy military signals.
When the system was created, timing errors were inserted into GPS transmissions to limit the accuracy of non-military GPS receivers to about 100 meters. This part of GPS operations, called Selective Availability, was eliminated in May 2000.
The system's dominant roles are in intelligent transportation systems, telecommunications, and precision delivery of military munitions. Moreover, its use in supporting both critical civil infrastructure and military operations has received new attention since September 2001. The GPS signals are available to an unlimited number of users simultaneously, and there is no charge for using the GPS Satellites either. The Soviet Union also developed a satellite-based navigation system, called GLONASS, which is in operation today.
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 by the U.S. Department of Defense that continuously transmit coded information, which makes it possible to precisely identify locations on earth by measuring the distance from the satellites. The satellites transmit very low power specially coded radio signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time thus allowing anyone one with a GPS receiver to determine their location on earth. Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock. The system was designed so that receivers did not require atomic clocks, and so could be made small and inexpensively.
The GPS system consists of three pieces. There are the satellites that transmit the position information, there are the ground stations that are used to control the satellites and update the information, and finally there is the receiver that you purchased. It is the receiver that collects data from the satellites and computes its location anywhere in the world based on information it gets from the satellites. There is a popular misconception that a gps receiver somehow sends information to the satellites but this is not true, it only receives data.
PRINCIPLE OF GPS
The principle behind GPS is the measurement of distance (or "range") between the receiver and the satellites. The satellites also tell us exactly where they are in their orbits above the Earth. It works something like this-If we know our exact distance from a satellite in space, we know we are somewhere on the surface of an imaginary sphere with radius equal to the distance to the satellite radius. By measuring its distance from a second satellite, the receiver knows it is also somewhere on the surface of a second sphere with radius equal to its distance from the second satellite. Therefore, the receiver must be somewhere along a circle which is formed from the intersection of the two spheres. Measurement from a third satellite introduces a third sphere. Now there are only two points which are consistent with being at the intersection of all three spheres. One of these is usually impossible, and the GPS receivers have mathematical methods of eliminating the impossible location. Measurement from a fourth satellite now resolves the ambiguity as to which of the two points is the location of the receiver. The fourth satellite point also helps eliminate certain errors in the measured distance due to uncertanties in the GPS receiver’s timing as well.