Download Accurate Fault Location Algorithm for Series Compensated

IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 15, NO. 3, JULY 2000
1027
Accurate Fault Location Algorithm for Series
Compensated Transmission Lines
Javad Sadeh, N. Hadjsaid, A. M. Ranjbar, and R. Feuillet
Abstract—In this paper, an accurate fault location algorithm
for series compensated power transmission lines is presented. Distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance—one for faults behind the series capacitors and another one for faults in front of the series capacitors.
Then a special procedure to select the correct solution is utilized.
Samples of voltages and currents at both ends of the line are taken
synchronously and used to calculate the location of the fault. The
proposed algorithm is independent of fault resistance and does not
require any knowledge of source impedance. The proposed method
has been tested using the EMTP/ATP model of a 400 kV, 300 km
transmission line, which is compensated, by a three-phase capacitor bank in the middle. The results of computer simulation confirm the accuracy of the proposed method.
Index Terms—Distributed line model, fault location, MOV-protected series capacitor, series compensated line.
I. INTRODUCTION
A
CONTINUOUS and reliable electric energy supply is the
objective of any power system operation. Nevertheless,
faults do occur in power system. A transmission line is the part
of the power system where faults are most likely to happen. Determination of the fault point is vital for economic operation
of power systems and quality of power supply. The faults are
in the form of a short circuit between the conductors or to the
ground. The location of permanent faults will facilitate quickly
repair and restoration, while accurate location of transient (temporary) faults will aid in preventive maintenance. A fault locator is used for pinpointing transmission line faults, and it allows the reduction of maintenance time and hence improves the
system availability. Several fault location algorithms have been
proposed and applied for determining the point of fault on transmission lines [1]–[10]. These algorithms can be classified in two
categories. In the first category voltages and currents measured
at one line terminal are used [1]–[5]. Under such conditions, it
may become difficult to determine the fault location accurately,
since data from other transmission line ends are required for
more precise computation. In the absence of data from the other
end, existing algorithms have accuracy problem under several
Manuscript received July 19, 1999.
J. Sadeh is with Laboratoire d’Electrotechnique de Grenoble, BP. 46, 38402
Saint Martin d’Hères cedex, France. He is also with Sharif University of Technology, Department of Electrical Engineering, P.O. Box 11365–9363, Tehran,
Iran (e-mail: Javad.Sadeh@leg.ensieg.inpg.fr).
N. Hadjsaid and R. Feuillet are with Laboratoire d’Electrotechnique de
Grenoble, BP. 46, 38402 Saint Martin d’Hères cedex, France.
A. M. Ranjbar is with Sharif University of Technology, Department of Electrical Engineering, P.O. Box 11365-9363, Tehran, Iran.
Publisher Item Identifier S 0885-8977(00)08133-4.
circumstances. The algorithms of the second category use voltages and currents measured at both line terminals [6]–[10]. In
the later category, synchronized [7], [9] and nonsynchronized
[6], [8], [10] sampling techniques are used.
The series capacitor (SC) is widely used in long transmission
systems to improve power transfer capability. It also increases
transient stability margins, optimizes load sharing between parallel transmission lines and reduces system losses. One of the
main considerations in the design and application of series capacitors is their protection against overvoltage. In modern installations, the traditional gap type scheme, which bypasses the
series capacitor to avoid overvoltage, is replaced by Metal Oxide
Varistor (MOV) protection. However, location of fault point and
protection of systems with series compensated lines is considered as one of the most difficult tasks for relay manufacturers
and utility engineers. The problem is not in the inclusion of capacitance in the series path but in the operation of the MOV in
parallel with the capacitor. Series capacitors together with their
MOV create a nonlinear and current dependent circuit. This nonlinear circuit must be taken into consideration in accurate fault
location algorithm.
Recently some research efforts have been focused on fault location in series compensated lines [11]–[13]. In [11], the voltage
drop across the series capacitor is estimated and subtracted from
the voltage measured in the substation. The corrected signals
have been proposed for relaying and fault location purposes.
Reference [12] proposed two subroutines for calculation of the
fault point, one for faults in back of the series capacitor and another one for faults ahead of the series capacitor. Moreover, it
proposed a special selecting procedure to pick-up the correct alternative. In these references, for determining fault location, the
lumped model of the transmission line is used. In [13], a new
approach based on calculation of voltage and current profiles is
proposed. In this algorithm, distributed time-domain model of
transmission line is used. The latest three references are considered as a one-end algorithm, which need only the voltages and
currents samples at one line terminal.
In this paper, we introduce a new and accurate fault location algorithm for series compensated transmission lines. Samples of voltages and currents at both ends of the line are taken
synchronously and used to estimate the location of fault. The
over-voltage protection of the series capacitor (MOV) is taken
into consideration and for algorithm development, the partial
differential equations are used as a model of transmission line
[14]. The proposed fault location algorithm is composed from
two subroutines. One of them is for faults behind the series
capacitors and another one for faults in front of the series capacitors. With applying these subroutines, we will obtain two
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