DEVELOPMENT OF AN ACCURATE TRANSMISSION LINE FAULT LOCATOR USING THE GLOBAL POSITIONING SYSTEM SATELLITES
Abstract
A highly accurate transmission line fault locator based on the traveling-wave principle has
been developed and successfully operated within B.C. Hydro. A transmission tine fault produces a
fast-risetime traveling wave at the fault point which propagates along the transmission line. This
fault locator system consists of traveling wave detectors located at key subsfafions which detect and
time tag the Zeading edge of the fault-generated traveling wave as it passes through. A master
station gathers the time-tagged informution from the remote detectors and determines the location
of the fault. Precise time is a key element to the success of this system. This fault locator system
derives its timing from the Global Positioning System (GPS) satellites. System tests confirmed the
accuracy of locating faults to within the design objective of k 300 meters.
INTRODUCTION
Operating an electric system that includes long transmission lines passing through rugged terrain
poses difficult challenges for operations personnel. The B.C. Hydro system is characterized by
major hydroelectric generation sites that are separated by large distances from load centers.
Confirming the location of transmission line faults typically involve a combination of helicopter
and ground patrols both of which may be difficult or impossible to execute due to adverse
weather conditions - which is usually the time when transmission line faults occur. A method
for quickly and accurately locating transmission line faults has been a much desired tool for
control center operators who must act quickly to determine locations of system disturbances in
order to direct the work of search and repair crews.
Use of commercially available fault location tools such as fault-locating digital relays and digital
fault recorders on the B.C. Hydro 500 kV system have produced limited successful results.
Factors such as high ground resistance, series capacitor banks, etc. reduce the effectiveness
of these fault location systems. To address the problem of accurate fault location under these
conditions, a traveling wave based fault location system has been developed and successfully
operated on the B.C. Hydro 500 kV system.
FAULT LOCATION METHODS
Time Domain Reflectometers
Early fault locators were based on pulse radar techniques. These devices known as time domain
reflectometers (TDRs), are commonly used for locating faults in buried cables where visual
inspection is not possible without excavation. This technique makes use of a "probe" pulse that
is launched into one end of the cable and relies on the pulse being reflected back to the source
due to an electrical discontinuity at the faulted location. The fault location is determined
by measuring the time delay from launching the pulse and receiving its reflection. There is,
however, little interest in applying this method to overhead transmission lines. Several factors
make this technique impracticable:
Unlike cables which are physically and electrically uniform throughout its length, overhead lines
have inherent discontinuities such as tower structures, conductor variations, etc. that cause
unwanted secondary reflections which interfere with detecting the reflected "probe" pulse.
The faulted line must be taken out of service to conduct testing and special precautions must
be taken to ensure mutual inductance effects from healthy adjacent lines and nearby energized
equipment does not pose a safety hazard.
The fault must be permanent (e.g.. solid short or open conductors) to ensure a strong reflected
signal. Difficult to find faults such as ice build-up, galloping conductors, etc., conveniently
disappear by the time the fault location equipment can be mobilized and put into service.
B.C. Hydro has used time domain reflectors on transmission lines for many years before largely
abandoning this technique due to its complexity and small gains.
Impedance-Based Fault Location Methods
The largest area of development on fault location methods are those based on the measurement
of system frequency (6OHz) signals. These methods make use of information from the
transmission lines that are already available for protective relaying purposes (i.e. line voltage
and current). In the most general sense, these techniques analyze the impedance characteristics
of the line to determine the fault location.
Early fault locators were based on the reactance method where fault location is determined by
measuring the ratio of the reactance of the faulted line at the source end to the unfaulted line
reactance, the assumption being that the fault impedance is purely resistive. More complex
algorithms make use of pre- and post-fault conditions to reduce the effects of sources (except
for the virtual source at the fault) and loads. The development of digital fault recorders
and digital protective relays has made it possible to implement better and computationally
more complex algorithms. Many of these methods involve simultaneous solutions of non-linear
equations which can easily be implemented using iterative techniques.
A number of protective relaying manufacturers have incorporated fault location functions as
part of their protective relays. B.C. Hydro has made extensive use of these devices on lower
voltage lines (230 kV and below). Experience with these fault locating relays have shown some
very good results, but occasionally some poor results.

Download full report
http://tycho.usno.navy.mil/ptti/1993/Vol%2025_17.pdf