Reliability Assessment of Radial Distribution System With Distributed Generation”: (A Case Study of Cottebe Substations)
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Date
2016-06
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Addis Ababa University
Abstract
The utility company, EEP and EEU mission is to transmit, distribute and supply electricity in
reliable and efficient manner. The problem facing electric power utilities is that the power
demand is increasingly but, power problem in distribution system occurs several times, due to
over loading, short circuit, improper allocated distribution transformers, poor maintenance,
limited protective devices. Therefore the substation need for more extensive justifications of the
system facilities, and improvements in production and use of electricity.
This thesis presents reliability assessment of the 132/15 kV transformer through five 15 kV
outgoing feeders. The 15 kV network is operated as radials and the total capacity of 132/15 kV
transformer is 31.5 MVA supplying to five 15 kV outgoing feeders and the total connected load
to the 15 kV feeders between 14.5 and 19.5 MW. The distribution system consists of 45, 33, 15
and 0.4 kV systems but the case study considered 15 and 0.4 kV outgoing feeders of the
distribution system with distributed generation providing support to the system adequacy and
security for reliability improvement. The distributed generation (DG) units considered for this
assessment are any possible DG units installed at optimal place and size at their site to the
customers satisfactions. DG systems have received more attention recently due to their high
overall efficiency and increase in reliability. A composite system adequacy assessment, which
includes the two main components of the power grid viz., generation and distribution, is done
using Monte Carlo simulation. The analytical approach is system reliability using direct
numerical solutions. The basic data and the topology used in the analysis are based on the
Institution of Electrical and Electronics Engineers - Reliability Test System (IEEE-RTS) and
IEEE-Reliability Bus bar Test System (IEEE-RBTS). Integrating DG units in 0.4 kV bus of
distribution system improve the overall system reliability indices SAIDI from 206.56 to 2.532,
SAIFI form 188.8 to 1.9575, ASAI from 97.64% to 99.971%, ASUI from 2.36% to 0.0289%
and also EENS, and EIC of the overall distribution system improved by 97.3%. Therefore a base
Cotebe distribution system reliability index is very poor according to the reliability standards.
KEY WORDS: Adequacy, DIgSILENT, ETAP, Distribution system, Expected Energy not
supplied, Expected Interruption cost, Failure rate, Forced outage, Indices, Interruptions,
Reliability, Security.
M.Sc. Thesis by Amache Jara in Electrical Power Engineering, SECE AAiT Page iv
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Keywords
Adequacy, DIgSILENT, ETAP, Distribution system, Expected Energy not supplied, Expected Interruption cost, Failure rate, Forced outage, Indices, Interruptions, Reliability, Security