05-09-2012, 10:21 AM
Real-Time Multiterminal Fault Location System for Transmission Networks
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Abstract
Fault location information is critical for operating
and maintaining transmission networks. Some of the challenges
in calculating accurate fault location include fault resistance,
zero-sequence mutual coupling, load, system nonhomogeneity,
and transmission lines composed of multiple sections with
considerably different characteristics. This paper presents a fully
automated real-time fault location system that provides accurate
fault location information for multiple transmission lines and
makes the results available to system operators and maintenance
personnel.
INTRODUCTION
Fault location in protective relays has been available for
over 20 years. These relays use impedance-based fault
location algorithms, typically from one terminal of the
transmission line [1] [2]. While these relays have been very
useful in locating the majority of faults, the following
conditions can affect their fault location accuracy:
• High-resistance faults
• Heavy load conditions
• Zero-sequence mutual coupling
Two-end fault location methods minimize these errors.
Reference [3] describes a two-end method based on negativesequence
quantities that can be implemented within line
protection relays using the relay programming abilities.
Reference [4] describes an implementation of this algorithm
using two line relays with relay-to-relay communication to
calculate the fault location in real time.
CONSIDERATIONS FOR VARIABLE FAULT RESISTANCE
Variable fault resistance affects the voltages and currents
that the relays at each terminal measure. Fig. 3 shows the sum
of the local and remote residual currents (total residual
current) and the estimated fault resistance for a B-phase-toground
fault. The total residual current is approximately equal
to the total fault current at the fault location. The fault
occurred on a 400 kV transmission line with a line length of
225 kilometers; wildfires close to the transmission line caused
the fault condition. Observe that the fault current starts with a
peak value lower than 828 A that increases to a peak value of
3,860 A in 4 cycles at a rate of 758 A per cycle. The
corresponding resistance that we calculate according to (2)
changes at the beginning of the fault and settles to
approximately 3 Ω after 4 cycles [1].
AUTOMATED FAULT LOCATION SYSTEM
Most of the existing multiterminal fault location methods
are mainly for post-event analysis. To perform this analysis,
we need to collect event reports from all line terminals, align
these data, and estimate the fault location, which is timeconsuming
and inefficient. The automated fault location
system (AFLS) that we present in this paper can monitor
hundreds of transmission lines in the utility and provide fault
location information in real time without human intervention.
The AFLS includes protective relays connected to an IRIG-B
time source and fault location software running on a computer.
This software automatically retrieves event reports from the
relays, calculates the fault location, and presents the results to
the user. Fig. 16 shows the AFLS architecture to monitor three
lines of a power system. This architecture uses Ethernet-based
communication between the protective relays and the
computer running the fault location software. The software
accommodates serial and Ethernet communications.
CONCLUSION
This paper presents an automated fault location system for
transmission networks. The system uses a new multi-end fault
location algorithm that is suitable for composite transmission
lines. The fault location algorithm and the automated system
have the following characteristics:
• The algorithm uses the negative-sequence voltage
profile along the transmission line to identify the
faulted section, makes a network reduction, and
estimates the fault location.
• A field case validates the accuracy of the algorithm for
a phase-to-ground fault on a 26.3-mile 230 kV
composite line. In this case, the fault location
estimation is off by 475 feet.
• After the user configures the system, the system
reports fault location information in less than 1 minute
when using Ethernet-based communication without
human intervention.