14-09-2013, 03:20 PM
Study on a Series Resistive SFCL to Improve Power System Transient Stability: Modeling, Simulation, and Experimental Verification
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Abstract
This paper presents a study to determine the op-
timal resistive value of a superconducting fault-current limiter
(SFCL) for enhancing the transient stability of a power system
more effectively. A resistive type of SFCL, which provides quick
system protection, is modeled. Then, the optimal resistive value
of the SFCL connected in series with a transmission line during
a short-circuit fault is systematically determined by applying the
equal-area criterion based on the power-angle curves. To verify
the effectiveness of the optimal value of the proposed SFCL for
reducing the value of fault current, several case studies are carried
out by both simulation and experimental tests, particularly in-
cluding the 220-V/300-A-scale laboratory and 13.2-kV/630-A-scale
distribution system hardware tests. The results show that the
optimal resistive value of the SFCL determined by the proposed
method improves effectively the transient stability and damping
performances during a fault over the other values determined by
an ad hoc approach.
INTRODUCTION
DUE to the increase in the scale of power systems with
distributed generation [1], [2] connected to a grid, high-
level fault currents might be caused during a contingency. Until
now, many devices such as split bus bars, transformers with
higher impedance, and fuses have been used in industry to
reduce the peak value of fault currents. However, the use of
these devices has limits, in that they can damage the reliability
of the power system or increase power loss [3]. A fault-current
limiter based on a high-temperature superconductor can be
an alternative to replace the aforementioned conventional de-
vices. In other words, the superconducting fault-current limiter
(SFCL) can improve the transient stability of the power system
by suppressing the level of fault currents in a fast and effective
manner.
Transient Stability Study Based on the
Equal-Area Criterion
During a steady-state condition in the given system, neither
RSFCL nor Rf exists. In this case, the value of Ra in (3) is
small when compared to that of Xd in (4). If it is assumed
that Ra is negligible, then the power-angle equation in (12)
is subject to (13). Its corresponding power-angle curve is
shown in Fig. 4, where the subscript “ss” denotes a steady-state
condition, and the dashed line indicates the initial mechanical
power of 1.0379 p.u.
CONCLUSION
This paper proposed the study to determine the optimal
resistive value (RSFCL ) of a resistive SFCL by analyzing the
transient stability based on the equal-area criterion. The damp-
ing performances of the SFCL during a fault were evaluated
by case studies on both simulation and experimental tests, in-
cluding one test in a practical 13.2-kV/630-A-scale distribution
system.
It was shown from the results that the resistive SFCL with the
optimally selected RSFCL is very effective to reduce the level
of short-circuit current dramatically. Therefore, the reliability
and stability of the power system can be improved by the appli-
cation of the SFCL.
However, the remaining open questions are the selection of
the optimal location of the SFCL in a large-scale power system
and the protection-coordination problem with other existing
protective devices. In other words, existing protective devices,
such as a recloser, may not be operated correctly when the
fault current level is very low by damping that the SFCL can
provide. These issues are being investigated with several case
studies.