PROTECTOIN OF TRANSMISSION LINES USING

GPS

SUBMITTED by: MONALISHA DASH BRANCH: ELECTRICAL Regd no: 0701208143

CONTENTSINTRODUCTIONTRANSMISSION SYSTEMTRAVELLING WAVE FAULT LOCATIONTRAVELLING WAVE FAULT THEORYCAUSES OF FAULTWHAT IS SIGNALFAULT LOCATION USING GPSSOURCES OF GPS SIGNAL ERRORSADVANTAGES & DISADVANTAGESCONCLUSION

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 busbar. 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. Power companies and utilities have fundamental requirements for time and frequency to enable efficient power transmission and distribution.Repeated power blackouts have demonstrated to power companies the need for improved time synchronization throughout the power grid. Analyses of blackouts have led many companies to place GPS-based time synchronization devices in power plants and substations.

INTRODUCTION

GENERATION         TRANSMISSION            DISTRIBUTION

TRANSMISSION SYSTEM  

WHAT IS TRAVELLING WAVE FAULT LOCATION?

Faults on the power transmission system cause transients that propagate along the transmission line as waves.These waves have a propagation velocity & characteristic impedance , travel from fault location towards line ends

The location of faults is accomplished by precisely time-tagging wave fronts as they cross a known point typically in substations at line ends.

Fault location can then be obtained by

multiplying the wave velocity by the time difference in line ends.

TRAVELLING WAVE FAULT LOCATION THEORY

Travelling wave fault locators make use of the transient signals generated by the fault.

Unlike other fault location systems,the travelling wave fault locator is unaffected by load conditions.

Precisely synchronised 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.

BENEFITS OF TRAVELLING WAVE FAULT LOCATION

Early fault locators used pulsed radar.

Radar equipment is typically mobile or located at substations and requires manual operation.

Travelling wave fault locators are becoming popular where higher accuracy is important.

GPS-based sub microsecond timing system has proven reliable in several utility travelling wave projects.

POSSIBLE CAUSES OF FAULT

FAULT LOCATION USING GPSGlobal 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 WORKS?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 and 2-D position can be tracked using two satellites.

WHAT’S THE SIGNAL?

GPS satellites transmit two low power radio signals. A GPS signal contains three different bits of information. -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.12 parallel channel receivers are quick enough to lock onto the satellites and maintain strong locks even in dense foilage or urban settings with tall buildings. 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 can be achieved with DGPS.

OPERATION OF THE FAULT LOCATION SYSTEM(FLS) USING GPS

A fault locator remote is coupled to each end of line via CPT.

FL, a fancy electronic stop watch is synchronized to the common timing standard of UTC from GPS.

Fault resulting produces

traveling waves(transients).

The FL remote time tag the

transient arrival times.

By knowing the line length L and the time-of –arrival difference (tb - ta ) distance X can be calculated from the FL equation:

X=[L-C(tb -

ta )]/2

ta & tb are end A

and end B arrival time

c-velocity of light

SOURCES OF GPS SIGNAL ERRORS

Ionosphere and troposphere delays.

Signal multipath.

Receiver clock errors.

Number of satellites visible. 

Satellite geometry/shading.

ADVANTAGES

Protection of transmission line using GPS is extremely accurate.

Economical.

Fast response.

Reliability & availability

DISADVANTAGES

GPS SIGNAL ERRORSo Ionosphere and troposphere delays.o Receiver clock errors.

Distortion in travelling wave causes fault location error. Climate dependant.

CONCLUSION

Uses a dedicated fault detector to extract transient signal and GPS system to time tag these signals.

Traveling time of the transient signal from the point of fault to the adjacent substation is used to determine the fault position.

Proposed technique is able to offer a high accuracy in fault location.

Unlike traditional protection schemes , this technique offers a new concept in network protection.

REFERENCES

Zhiqian Q Bo Weller, Tom Lomas and Miles A, Redfern “Positional Protection of Transmission system Using global Positioning System” IEEE Trans. On Power delivery, vol 15 no 4 oct 2008

http://www.howstuffworks.com/gps

http://www.gisdevelopment.net/technology/gps