Download Protection of Transmission System Using Global Positioning System

MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
33
Protection of Transmission System Using
Global Positioning System
Saurabh Saxena
Maroof Ali
A.P., EE and I Department
MIT, Moradabad
Email: ss_saurabh912@rediffmail.com
A.P., EE and& I Department
MIT, Moradabad
Email: maroofali_ali@yahoo.com
Kapil Gandhi
Nihar Ranjan
A.P., EE and I Department
MIT, Moradabad
Email: kapilkiet@gmail.com
B.Tech. Student (EE)
MIT, Moradabad
Email: ranjannihar991@gmail.com
ABSTRACT
This paper representsthe 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.
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.
Keywords: GPS, GIS, Traveling Waves.
I.
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 to determine fault location to within a transmission
span of 300 meters. Reliable self monitoring hardware can
be configured for installation sits with varying geographic
and environmental conditions. Communications systems
can retrieve fault location information from substations and
quickly provide that information to systems can retrieve fault
location information from substations and quickly provide
that information to system operations. 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 cancollect 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
databases for transmission inventory using GPS location
technology and handheld computers.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
The inventor database probably contains more information
than needed for a fault location system, and a reduced version
would save the large data-collection effort. Using this data, the
power system operator could provide field personnel direct
location information.
Field personnel could use online information to help them
avoid spending valuable times looking for maps and drawings
and possibly even reduce their travel time. With precise
information available, crews can prepare for the geography,
climatic conditions, and means of transport to the faulted
location. Repair time and resources would be optimized by the
collected data before departure. Accurate fault location can also
aid in fast restoration of power, particularly on transmission
lines with distributed loads. Power system operators can
identify and isolate faulted sections on taploaded lines and
remove them by opening circuit breakers or switches remotely
along the line, restoring power to the tap loads serviced by the
unfaulted transmission sections.
34
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.
Generation Transmission Distribution
Due to the large amount of power involved, transmission
normally takes place at high voltage (110 kV or above).
Electricity is usually transmitted over long distance through
overhead power transmission lines. Underground power
transmission is used only in densely populated areas due to its
high cost of installation and maintenance, and because the high
reactive power produces large charging currents and difficulties
in voltage management. A power transmission system is
sometimes referred to colloquially as a “grid”; however, for
reasons of economy, the network is not a mathematical grid.
Redundant paths and lines are provided so that power can be
routed from any power plant to any load center, through a variety
of routes, based on the economics of the transmission path
II. TRANSMISSION SYSTEM
and the cost of power. Much analysis is done by transmission
Electric power transmission, a process in the delivery of companies to determine the maximum reliable capacity of each
electricity to consumers, is the bulk transfer of electrical power. line, which, due to system stability considerations, may be less
Typically, power transmission is between the power plant and than the physical or thermal limit of the line.
Figure 1: Electrical Power System (generation, transmission and distributions)
III. TRANSMISSION LINE PROTECTION
IV.
TRAVELING WAVE FAULT LOCATION
A system including a number of subsystems having dedicated
protection units which are dedicated to the protection of
specific transmission lines and associated power equipment,
each subsystem having stand-alone capability. The subsystems
are interfaced to a central computer through a remote control
communications interface unit. Each subsystem includes
a microprocessor which interfaces with the corresponding
transmission line or associated power equipment to be
protected through converters, sensors, contractors, direct
digital control equipment and the like. The central computer
is capable of performing real time modification by addressing
each subsystem to change local protection parameters thereof
to fit system needs.
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 a new power system
equilibrium is reached.
The location of faults is accomplished by precisely timetagging wave fronts as they cross a known point typically
in substations at line ends. With waves time tagged to sub
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
35
Figure 2: Transmission Line Protection
microsecond resolution of 30 m, fault location accuracy of
300 m can be obtained. Fault location can then be obtained by
multiplying the wave velocity by the time difference in line
ends. This collection and calculation of time data is usually
done at a master station. Master station information polling
time should be fast enough for system operator needs.
V.
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 locators are becoming popular
where higher accuracy is important. Long lines, difficult
accessibility lines, high voltage direct current (HVDC), and
series-compensated liens are popular applications. Accuracies
of <300 meters have been achieved on 50 kV transmission lines
with this technique. Hewlett-Packard has developed a GPSbased sub microsecond timing system that has proven reliable
in several utility traveling wave projects. This low-cost system
can also be used as the substation master clock.
VI.
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 the of light.
Unlike impedance-based fault location systems, the
traveling wave fault locator is unaffected by load conditions,
high ground resistance and most notably, series capacitor banks.
This fault locating technique relies on precisely synchronized
clocks at the line terminals which can accurately time-tag the
arrival of the traveling wave. The propagation velocity of the
traveling wave is roughly 300 meters per microsecond which
in turn requires the clocks to be synchronized with respect to
each other by less than one microsecond.
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.
The voltage and current at any point x obey the partial
differential
∂e
∂i
∂i
∂e
= -L
and
= -C
∂x
∂t
∂x
∂t
where L and C are the inductance and capacitance of the line
per unit length. The resistance is assumed to be negligible. The
solutions of these equations are
e( x , t ) = e r ( x - vt ) + e r ( x + vt ) l( x, t )
1
1
e r ( x - vt ) - e r ( x + vt )
x
z
where Z = (L/C) is the characteristic impedance of the
transmission line and v = 1/(LC) is the velocity of propagation.
Forward (ef and if) and reverse (er and ir) waves, as shown
in Figure 1, leave the disturbed area “x” traveling in different
directions at “v”, which is a little less than the speed of
light, toward transmission line ends. Transmission line ends
represent a discontinuity or impedance change where some
of the wave’s energy will reflect back to the disturbance. The
remaining energy will travel to other power system elements
or transmission lines. Figure 2, a Bewley lattice diagram,
illustrates the multiple waves (represented by subscripts 2
and 3) generated at line ends. Wave amplitudes are represented
by reflection coefficients ka and kb which are determined by
characteristic impedance ratios at the discontinuities. ta and
tb represent the travel time from the fault to the discontinuity.
=
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
36
With GPS technology, ta and tb can be determined very
precisely.
By knowing the length (l) of the line and the time of arrival
difference
(ta – tb), one can calculate the distance (x) to the fault from
substation A by:
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.
GPS satellites circle the earth twice a day in a very precise
orbit and transmit signal information to earth. GPS receivers
take this information and use triangulation to calculate the
1 - c( t a - t b )
user’s exact location. Essentially, the GPS receiver compares
x=
2
the time a signal was transmitted by a satellite with the time it
where c = the wave propagation of 299.79 km/microsec was received. The time difference tells the GPS receiver how
(1ft/ns).
far away the satellite is. Now, with distance measurements from
a few more satellites, the receiver can determine the user’s
position and display it on the unit’s electronic map. By knowing
the distance from another satellite, the possible positions of the
location are narrowed down to two points (Two intersecting
circles have two points in common). A GPS receiver must be
locked on to the signal of at least three satellites to calculate
a 2D position (latitude and longitude) and track movement.
With four or more satellites in view, the receiver can determine
the user’s 3D position (latitude, longitude and altitude). Once
the user’s position has been determined, the GPS unit can
calculate other information, such as speed, bearing, track, trip
distance, distance to destination, sunrise and sunset time and
Figure 3: Bewley Lattice Diagram.
more. Accurate 3-D measurements require four satellites. To
achieve 3-D real time measurements, the receivers need at
least four channels.
VIII. THE GLOBAL POSITIONING
SYSTEM
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
1. The Gps Satellite System
The 24 satellites that make up the GPS space segment are
orbiting the earth about 142,000 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.
Here are some other interesting facts about the GPS
satellites (also called NAVSTAR, the official U.S. Department
of Defense name for GPS :
The first GPS satellite was launched in 1978.
A full constellation of 24 satellites was achieved in 1994.
Each satellite is built to last about 10 years. Replacements
are constantly being built and launched into orbit.
A GPS satellite weights approximately 2,000 pounds and is
about 17 feet across with the solar panels extended.
Transmitter power is only 50 watts or less.
2. Implementation and Testing
Evaluation of the fault locator involved the installation
of GPS timing receivers at four 500 kV substations, see
Figure 11.1. A especially developed Fault Transient
Interface Unit (FTIU) connects to the transmission lines
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
37
Fault Locator Response to Traveling Waves Generated by
and discriminates for a valid traveling wave. The FTIU
produces a TTL-level trigger pulse that is coincident with Routine Switching of Substation Equipment.
the leading edge of the traveling wave. A time-tagging input
Line Estimated
Measured
function was provided under special request to the GPS
Tp (µ sec)
Tp (µ sec)
receiver manufacturer. This input accepts the TTL level logic
501
499
pulse from the FTIU and time tags the arrival of the fault66
67
generated traveling wave. The time tag function is accurate
to within 300 nanoseconds of UTC–well within the
850
851
overall performance requirement of timing to within 1
900
896
microsecond.
901
901
3. Distortion and Attenuation of Traveling Waves
The accuracy of fault location depends on the ability to
accurately time tagging the arrival of the traveling wave at
each line terminal. The traveling wave once generated, is
subject to attenuation and distortion as it propagates along
the transmission line. Attenuation occurs due to resistive
and radiated losses. Distortion of the waveform occurs due
to a variety of factors including bandwidth limitations of
the transmission line, dispersion from different propagation
constants of phase-to-phase and phase-to-ground components,
etc. These effects combine to degrade the quality of the
“leading edge” of he traveling wave at large distances from
the fault inception point. The accuracy of time tagging the
traveling wave diminishes for the substations far away from
the fault. Experience with the evaluation system has shown that
the traveling wave is relatively “undistorted” for distances less
than 350 km. To effectively reduce the effects of attenuation
and distortion requires traveling wave detector installations
spaced at regular intervals. For B.C. Hydro, this translates to
installing fault location equipment at fourteen out of nineteen
500 kV substations.
The distance to the fault from the line terminals is given by:
Where Vp is the velocity of propagation for the line and
Fault Locator System Test
Calculated cumulative are length from NIC substation to the
fault = 13 1,694.5 meters.
Test
Fault Locator Output
(meters)
1
2
3
4
131,725
131,819
131,721
131,803
131,800
131,834
131,730
131,697
130,829
131,806
131,810
131,814
5
6
7
8
9
10
11
12
Difference from Est.
Value (meters)
30
124
26
108
105
139
35
2
134
111
115
119
Figure 4: Fault Locator Installations and Testing
4. What’s The Signal?
GPS satellites transmit two low power radio signals, designated
L1 and L2. Civilian GPS uses the L1 frequency of 1575.42
MHz in the UHF band. The signals travel by line of sight,
meaning the will pass through clouds, glass and plastic but
will not go through most solid objects such as buildings
and mountains. A GPS signal contains three different bits
of information – a pseudorandom code, ephemeris data and
almanac data. The pseudorandom code is simply an I.D. code
that identifies which satellite is transmitting information. You
can view this number on your GPS unit’s satellite page, as it
identifies which satellites it’s receiving. Ephemeris data tells
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
the GPS receiver where each GPS satellite should be at any
time throughout the day. Each satellite transmits ephemeris
data showing the orbital information for that satellite and for
every other satellite in the system. Almanac data, which is
constantly transmitted by each satellite, contains important
information about the status of the satellite (healthy or
unhealthy), current date and time. This part of the signal is
essential for determining a position.
5. How Accurate is GPS?
Today’s GPS receivers are extremely accurate, thanks to their
parallel multi-channel design. 12 parallel channel receivers
are quick to lock onto satellites when first turned on and they
maintain strong locks, even in dense foliage or urban settings
with tall buildings. Certain atmospheric factors and other
sources of error can affect the accuracy of GPS receivers.
GPS receivers are accurate to within 15 meters on average.
Newer GPS receivers with WAAS (Wide Area Augmentation
System) capacity can improve accuracy to less than three
meters on average. No additional equipment or fees are
required to take advantage of WAAS. Users can also get better
accuracy with Differential GPS (DGPS), which corrects GPS
signals to within an average of three to five meters. The U.S.
Coast Guard operates the most common DGPS correction
service. This system consists of a net work of towers that
receive GPS signals and transmit a corrected signal by beacon
transmitters. In order to get the corrected signal, users must
have a differential beacon receiver and beacon antenna in
addition to their GPS.
6. Sources of GPS Signal Errors
Factors that can degrade the GPS signal and thus affect
accuracy include the following:
1. Ionosphere and troposphere delays: The satellite
signal slows as it passes through the atmosphere.
The GPS system uses a built-in model that calculates
an average amount of delay to partially correct for
this type of error.
2. Signal multipath: This occurs when the GPS signal
is reflected off objects such as tall buildings or
large rock surfaces before it reaches the receiver.
This increases the travel time of the signal, thereby
causing errors.
3. Receiver clock errors: A receiver’s built-in clock is
not as accurate as the atomic clocks onboard the
GPS satellites. Therefore, it may have very slight
timing errors.
4. Number of satellites visible: The more satellites a GPS
receiver can “see,” the better the accuracy Buildings,
terrain, electronic interference, or sometimes even
dense foliage can block signal reception, causing
position errors or possibly no position reading at
38
all. GPS units typically will not work indoors,
underwater or underground.
5. Satellite geometry/shading: This refers to the relative
position of the satellites at any given time. Ideal
satellite geometry exists when the satellites are
located at wide angles relative to each other. Poor
geometry results when the satellites are located in a
line or in a tight grouping.
6. International degradation of the satellite signal:
Selective Availability (SA) is an intentional
degradation of the signal once imposed by the U.S.
Department of Defense. SA was intended to prevent
military adversaries from using the highly accurate
GPS signals. The government turned off SA in May
2000, which significantly improved the accuracy of
civilian GPS receivers.
VIII.
CONCLUSION
Thus the use of GPS in protection of transmission systems is
beneficial with respect to Value 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 far.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 databases for transmission
inventory using GPS location technology and handheld
computers.
The inventory database probably contains more information
than needed for a fault location system, and a reduced version
would save the large data-collection effort. Using this data, the
power system operator could provide field personnel direct
location information.
Field personnel could use online information to help them
avoid spending valuable time looking for maps and drawings
and possibly even reduce their travel time. With precise
information available, crews can prepare for the geography,
climatic conditions, and means of transport to the faulted
location. Repair time and resources would be optimized by the
collected data before departure. Accurate fault location can also
aid in fast restoration of power, particularly on transmission
lines with distributed loads. Power system operators can
identify and isolate faulted sections on taploaded lines and
remove them by opening circuit breakers or switches remotely
along the line, restoring power to the tap loads serviced by the
unfaulted transmission sections.
MIT International Journal of Electrical and Instrumentation Engineering Vol. 3, No. 1, Jan. 2013, pp. 33–39
ISSN 2230-7656 (c) MIT Publications
REFERENCES
[1]
[2]
39
El-Rabbany, Edition: illustrated, Published by Artech House,
2002.
Electric power transmission system engineering: analysis [5]
and design, By TuranGonen, Edition: illustrated, Published
by J. Wiley, 1988, Original from the University of Michigan,
Digitized Dec. 15, 2006.
[6]
Electric power systems. By Birron Mathew Weedy, Edition:
2, illustrated, Published by J. Wiley, 1972, Original from the
University of California, Digitized 10 Oct, 2008.
[3]
Global Positioning System, By Institute of Navigation,
[7]
Published by Inst of Navigation, 1980.
[4]
Introduction to GPS: the Global Positioning System, By Ahmed
[8]
Protective Relaying: Principles and Applications, By J. Lewis
Blackburn, Edition: 2, illustrated, revised, Published by CRC
Press, 1997.
Communication and Control in Electric Power Systems:
Applications of Parallel and Distributed Processing, By
M. Shahidehpour, Yaoyu Wang, Institute of Electrical and
Electronics Engineers, Edition: illustrated, Published by WileyIEEE, 2003.
www.autherstream.com
www.jamiamilliaislamia.com