A. NGAOPITAKKUL ET AL.
1046
same as SAIFI. This indicates that utility has still benefit
from employing DG.
The capacity of DG is also considered; it is noticed
that when the capacity of DG is increased, SAIDI tends
to decrease as same as SAIFI. This also indicates that
capacity of DG, location of DG, location of load, and
size of load play an important role for reliability.
The third index, the interruption cost of base case (no
DG) is 147,351 U.S. Dollar /year. Similarly, capacity of
DG and location of DG are also considered; the obtained
results for interruption cost are given in Tabl e 2.
The results show that, when capacity of DG and loca-
tion of DG is considered by installing at bus 1 to bus 3,
the interruption cost is increased and more than the base
case (no DG) due that the size of load is large so average
hours service availability of customer is decreased and
the failure rate of the equipment (λ) in equation 3 will be
increased. Likewise, when the DG is installed at bus 4,
bus 5, bus 6, bus 7 and bus 8, it can be seen that the in-
terruption cost is decreased except for the capacity of DG
is less than 2 MVA. This also indicates the slight mis-
match between DG capacity and size of load. It is clearly
seen for the cases that, when interruption cost is consid-
ered and the capacity of DG is 8 MVA which is installed
at bus 7 and the size of load is 0.58 MW, the interruption
cost is significantly increased.
From Table 3, it can be seen that the reliability index
obtained from the base case as same as case of DG is
installed on any bus will be compared with DG that is
installed between bus. The first index, the SAIFI of base
case (no DG) is still 16.746 times/customer/year and the
SAIFI of PEA regulation is also 17.34 times/customer/
year. The results show that, when location of DG is con-
sidered by installing between bus 1-bus 2, bus 1-bus 3,
the SAIFI is equal to the base case (no DG) and case of
DG installed on any bus. Likewise, when the other case
of DG in Table 3 is considered, it can be seen that the
SAIFI is decreased and less than the base case but has
value nearby the case of DG installed on any bus for the
most cases except for the case that the capacity of DG is
8 MW and DG location is between bus5-bus 7 with load
of 0.58 MW. This also indicates that capacity of DG,
location of DG, location of load, and size of load play an
important role for reliability.
The second index, the SAIDI of base case (no DG) is
still 21.064 hour/customer/year while the SAIDI of PEA
regulation is also 19.55 hour/customer/year. Similarly,
capacity of DG and location of DG are considered and
the behavior of SAIDI is shown in Table 3. The results
show that, when location of DG is considered and in-
stalled at bus 1, 2 and 3, the SAIDI is equal to that of the
base case (no DG). Likewise, when the DG is installed at
bus 4, bus 5, bus 6, bus 7 and bus 8, it can be seen that
the SAIDI is also decreased as same as SAIFI. This indi-
cates that utility has still benefit from employing DG. In
addition, when capacity of DG is considered, it is noticed
that when the capacity of DG is increased, SAIDI tends
to decrease as same as SAIFI.
The third index, the interruption cost of base case (no
DG) is still 147,351 U.S. Dollar/year. Similarly, capacity
of DG and location of DG are also considered and the
obtained results from interruption cost are shown in Ta-
ble 3. The results show that, the interruption cost tends to
decrease as same as the case of DG installed at bus.
However, when the interruption cost is compared be-
tween DG installed at bus and installed between buses, it
can be seen that the interruption cost of DG installed
between buses is lower than that of the DG installed at
bus. This also indicates the slight mismatch between DG
location and size of load.
5. Conclusions
This paper focuses on the analysis of reliability with the
inclusion of DG. The system average interruption fre-
quency index (SAIFI), the system average interruption
duration index (SAIDI), and interruption cost are as-
sessed as index of reliability by comparing the SAIFI,
SAIDI, and interruption cost between the base case (no
DG) and the case that DG connected to the distribution
system. The results can be summarized by focusing on
the location of DG, the capacity of DG, the size of load,
and the distance of load which are factors able to impact
to SAIFI, SAIDI, and interruption cost as shown in Ta-
bles 2-3. Both the location of DG and the capacity of DG
must take into account to reach optimal condition in or-
der to create the suitability and fairness for both utility
and DG.
6. Acknowledgements
The authors wish to gratefully acknowledge financial
support for this research from the King Mongkut’s Insti-
tute of Technology Ladkrabang Research Fund, Thailand
and the energy policy and planning office (EPPO), Min-
istry of Energy, Thailand. They would like also to thank
for the DIgSILENT presented in this paper which is
supported by Provincial Electricity Authority (PEA).
REFERENCES
[1] M. Fotuhi-Firuzabad, “An Analytical Method to Consider
DG Impacts on Distribution System Reliability,”
IEEE/PES Transmission and Distribution Conference and
Exhibition: Asia and Pacific, 2005, pp. 1-6.
[2] I. K. Tarsi, A. Sheikholeslami, T. Barforoushi and S. M.
B. Sadati, “Investigating Impacts of Distributed Genera-
tion on Distribution Networks Reliability: A Mathemati-
cal Model,” Electric Power Quality and Supply Reliabil-
ity Conference (PQ), 2010, pp.117-124.
Copyright © 2013 SciRes. EPE
