01-10-2012, 03:59 PM
A Classification Technique for Recloser-Fuse Coordination in Distribution Systems With Distributed Generation
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Abstract
In this paper, a novel approach is presented to study
the impact of distributed-generation penetration on recloser-fuse
coordination. The main core of this approach is based on an assessment
process using a classification technique to classify the recloser-
fuse coordination status at fault conditions to either coordination
holds or coordination lost. Accordingly, the distribution
system operator can take the proper decision. Then, two complementary
actions are recommended in the proposed approach as a
solution to decrease the number of cases where coordination is lost.
The first one is to search for the bestDGlocations, where such locations
are characterized by the minimum number of cases classified
as coordination lost. The second one is based on changing the recloser
setting in such a way to minimize the cases where coordination
is lost. This new approach has been implemented on the IEEE
37-node test feeder using MATLAB-based developed software and
the obtained results are presented and discussed.
INTRODUCTION
ELECTRIC distribution systems (EDSs) that are usually
designed using a radial structure with protection schemes
mainly depend on reclosers, fuses, and circuit breakers (CBs).
Reclosers are located in the main feeders to protect EDSs
against temporary faults, while fuses are located at the beginning
of laterals and sublaterals to protect the system against
persistent faults. The recloser-fuse coordination is usually
performed based on fuse-saving principles [1], [2].
With the penetration of distributed generation (DG) in EDSs,
recloser-fuse miscoordination problems may appear due to the
unplanned contribution of DGs to fault currents causing a probable
change of temporary faults to permanent faults.
SYSTEM UNDER STUDY
In this paper, the IEEE 37-node 4.8-kV test feeder, which is an
actual feeder in California, has been selected as a study system.
The data of this feeder are obtained from the IEEE’s Distribution
System Analysis Subcommittee [10]. This feeder is shown
in “Fig. 1,” where a single-line diagram of this feeder is shown
after being modified, by removing the regulator, to clearly see
the effect of DG on the system. Also, the nodes are renumbered
for the sake of simplicity. Finally, a protection scheme is implemented
based on the method given in [11], where one recloser
is added at the beginning of the main feeder and 20 fuses are
added at the beginning of each lateral and sublateral feeder.
PROBLEM STATEMENT
Normally, reclosers and fuses are initially selected to achieve
a coordination sequence that is based on the fuse-saving principle.
The coordination process is initially done knowing that
the only current source is the substation current which makes
the current in both devices be approximately the same at fault
conditions. After penetration ofDGin distribution networks, the
current flow will be due to the contribution of the substation current
and the DG current; this makes the current in reclosers and
fuses to be no more the same leading to a probable miscoordination
between both devices.
An example to clarify this problem using the IEEE 37-node
test feeder is presented by assuming a three-phase fault at node
15. The protection devices responsible to clear that fault are
the recloser ® and the fuses (F5, F4, and F1). Based on the
fuse-saving principle, these devices should be coordinated so
that the recloser operates first in the fast mode to give a chance
for the fault to be self cleared. If the fault still exists, then the
nearest fuse (F5) should operate, and in case of fuse failure, the
upstream fuses should then operate in sequence (F4 and F1).
Finally, the recloser in the slow mode should operate as a final
backup step. Fig. 2 shows the coordinated curves for the devices
(R, F5, F4, and F1) along with their operating points based on
the modeling (2) and (3), from which it can be shown that the
required operating sequence is achieved.
CONCLUSION
A novel approach is presented and applied to the IEEE
37-node test feeder to evaluate the effect of the DG penetration
on the protection devices coordination. The approach is
based on two main steps: protection coordination assessment
and protection coordination improvement. In the coordination
assessment step, the coordination status after integrating DG
to the system is classified as either coordination holds or
coordination lost. Different cases are studied by changing DG
penetration levels and locations for each possible fault location.
Applying this step discriminates between the cases that require
an action against DG penetration and the cases where an action
is not required. The coordination improvement step is based
on decreasing the number of cases where coordination is lost.
This is done through two complementary actions: the first is to
search for the best DG locations and the second is to change
the recloser setting. Applying both actions leads to a significant
reduction in the cases classified as coordination lost.