10-10-2012, 05:58 PM
Fault classification technique for series compensated transmission line using support vector machine
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Introduction
The series compensated transmission lines are employed in
modern power system to achieve enhancement of transmittable
power, improvement in the system stability, reduction in transmission
losses and more flexibility in power flow control. However,
the distance protection task of a series compensated transmission
line is considered to be more difficult as compared to that of an
uncompensated transmission line due to the following problems
encountered in case of series compensated lines [1,2]:
(a) The steady state current is increased significantly with series
compensation and it may be greater than the line-to-ground
fault current towards the boundary of the line.
(b) In a typical series compensation arrangement, the metal oxide
varistor(MOV) is used to protect the capacitor from over-voltages
during a fault. However, it acts non-linearly during faults
and increases the complexity of the protection problem.
© Voltage and current inversions.
Proposed fault classification technique
In the fault classification scheme proposed in this work, four
SVMs have been used. Out of these four SVMs, one SVM is used
for each phase (termed as phase SVM) to determine whether that
particular phase is involved in the fault or not. The fourth SVM
(henceforth termed as ground SVM), is used to determine the
involvement of the ground in the fault. Each of the phase SVMs receives
samples of one cycle duration of the current of that particular
phase while the ground SVM receives the samples of one
cycle duration of the zero sequence current (I0). At the output of
each SVM, the value ‘1’ and ‘0’ denotes the presence or absence
of the fault, respectively. Table 1 shows the fault classification format
in the proposed work while Fig. 1 depicts the overall fault classification
scheme.
3. Case studies
The feasibility of the proposed SVM based methodology has
been tested on a 400-kV, 50-Hz power system consisting of two
sources representing two areas which are connected by a 300 km
tie line with a series capacitor placed at the middle of the line.
The schematic diagram of the system is shown in Fig. 3. The system
Optimal Separating hyper-plane using SVM.
U.B. Parikh et al. / Electrical Power and Energy Systems 32 (2010) 629–636 631
and line parameters have been adopted from [20] and these
parameters along with the MOV characteristics are given in Appendix
A. For further reference, the source impedance values given in
the Appendix A are denoted as ‘‘base source impedance values
(BSIV)”. The over-voltage protection of the series capacitor is provided
by MOV and the air gap (AG) as shown in Fig. 3. The MOV
is protected by circuit breaker (CB) operation against its energy
dissipation capacity. The MOV conduction level has been chosen
as 2.5 times the rated current and a sampling frequency of 4 kHz
has been used.