07-01-2011, 02:41 PM
[attachment=7996]
by:
satyajyoti dash
OVER VIEW
INTRODUCTION
TRANSMISSION SYSTEM
FAULT LOCATION
CAUSES OF FAULTS
GPS TECHNIQUE
INTRODUCTION
A new technique for the protection of transmission systems.
Relays are installed at each bus bar in a transmission network.
Relay contains a fault detection system together with a communication unit.
Relay determine the location of the fault.
LOCATION OF FAULT
Save time and resources for the electric utility industry.
Determine “distance to fault” from a transmission line end.
Aid in fast restoration of power.
Communication systems can retrieve fault location information.
WHAT IS TRAVELING WAVE
FAULT LOCATION?
Faults on the power transmission system cause transients
that propagate along the transmission line as waves.
Fault location can then be obtained by multiplying
the wave velocity by the time difference in line ends.
BENEFITS OF TRAVELING WAVE FAULT LOCATION
Early fault locators used pulsed radar.
Radar equipment is typically mobile or located at substations and requires manual operation.
Impedance-based fault locators are a popular means of
transmission line fault locating.
Traveling wave fault locators are becoming popular where higher accuracy is important.
GPS-based sub microsecond timing system has proven reliable in several utility traveling wave projects.
TRAVELING WAVE FAULT LOCATION THEORY
Traveling wave fault locators make use of the transient
signals generated by the fault.
Unlike impedance-based fault location systems, the traveling wave fault locator is unaffected by load conditions.
Precisely synchronized clocks are the key element in the implementation of this fault location technique.
The required level of clock accuracy has only recently been available at reasonable cost with the introduction of the Global Positioning System.
WHAT IS GPS?
Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit.
originally intended for military applications
allows precise determination of location, velocity, direction and time.
HOW GPS WOKS?
GPS satellites circle the earth twice a day .
Transmit signal information to earth.
Receivers take this information and calculate the user's exact location.
Accurate 3-D location require four satellites.
THE GPS SATELLITE SYSTEM
24 satellites that make up the GPS space segment
are orbiting the earth about 12,000 miles above us.
WHAT’S THE SIGNAL?
GPS satellites transmit two low power radio signals.
A GPS signal contains three different bits of information.
- a pseudorandom code,
-ephemeris data,
- almanac data.
HOW ACCURATE IS GPS?
Today's GPS receivers are extremely accurate.
GPS receivers are accurate to within 15 meters on
average.
Newer GPS receivers with WAAS
(Wide Area Augmentation System) capability can
Improve accuracy to less than three meters on average.
Increased accuracy to within an average of three to five
meters.
SOURCES OF GPS SIGNAL ERRORS
Ionosphere and troposphere delays.
Signal multipath.
Receiver clock errors.
Number of satellites visible.
Satellite geometry/shading.
Intentional degradation of the satellite signal.
CONCLUSION
Thus the use of GPS in protection of transmission systems is
beneficial in the respects like
-Value regarding programmatic goals
-Technical merit
-Overall performance
