Long Term Distribution Expansion Planning with the Consideration of Distributed Generation (Case Study; Bishoftu Substation II)
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Date
2020-01
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Addis Ababa University
Abstract
Nowadays, due to economic development of the country the electrical energy demand of Ethiopia
increases by 30% yearly. But in order to satisfy customers’ power demand the planning and expansion of
power must be done using a proper load forecasting method.
This thesis is focused on demand forecasting of Bishoftu town and distribution expansion planning of
Bishoftu substation II with the help of distributed generation. Historical energy demand data, historical
energy growth rate, economic growth rate and distribution system’s reliability related data were assessed
from Ethiopian electric power corporation and Bishoftu city administration. To forecast the load from
2019 to 2029 extrapolation simulation approach is applied. From the results of demand forecasting, it is
found that the energy demand and peak demand in 2028 will be 2,005,457.41 MWH and 401.64 MW
respectively. But the existing peak demand of the town is 54.7MW and the current total capacity of the
distribution system is 43.8 MW. The existing distribution network cannot meet not only the future demand
but also the existing demand. So, improving the reliability of the existing system with the help of
distributed generation is required to expand the system and to meet the future demand. The Substation has
encountered frequent power interruptions. The interruptions are caused mainly by short circuit (SC),
earth fault (EF) and planned outages for operation and maintenance purpose. The substation’s System
Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI)
are 199.92ints/yr and 264.22hrs/yr respectively. The reliability of the substation does not meet the
requirements set by Ethiopian Electric Agency (EEA) which set (SAIFI =20 int/yr and SAIDI= 25hrs/yr).
Then three feeders of Bishoftu substation-II are selected for connecting DG due to high frequency and
long duration of interruptions. Distributed generation is a generation of an electric power close to the
load which has resources like mini hydro, photovoltaic Array (PV), fuel cells, wind generators and micro
turbines. In this thesis, microturbine is selected based on availability of the resource, cost factors, and
utilization area. The size of single DG is 3.71MW but the total capacity of DG 11.13MW is fed to the grid
as backup when there is an interruption. A simulation study for reliability analysis is carried out using
DigSilent software. With the presence of DG, the simulation result shows that the reliability indices
improved SAIFI by 65.16% and SAIDI by 75.62%.
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Keywords
trapolation and simulation, elastic coefficient, distributed generation, reliability assessment, DIGSILENT POWER FACTORY, power demand forecasting, expansion planning