Power Reliability Analysis of DC Traction Power Supply System: A Case Study of Addis Ababa Light Rail Transit
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Date
2019-06
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Addis Ababa University
Abstract
DC Railway Traction Power Supply System (TPPS) has been and is still widely used world
over for train propulsion especially in the urban areas and inter- urban regions. With the
evolution of electronic traction control technology giving compact size and reduced weight
of chopper and inverter drives, DC railway traction has become advantageous especially
where we have minimal provision for electrical clearances. Currently, the standard DC
traction voltages are 750V, 1500V and 3000V which require less electrical clearance
compared to AC Railway Traction Power Supply System catenary.
The basic function of an electrical power system is to meet its customer’s expectations
while maintaining the acceptable levels of quality and continuity of supplies. The
reliability level of DC Railway Traction Power Supply System is a major contributor to
the quality of service provided by a railway authority, thus there is a link between
reliability and quality of service. While most of the contingency situations may be
predicted and counteracted on the design stage, only the real-life experience is the ultimate
test for reliability. Reliability is regarded by many researchers as the science of failures
and the work of a reliability engineer is to assess the trend of failure data and determine
the rate of occurrence of failures as accurately as possible.
This research, therefore, addresses the reliability question at AALRT through collection
and analysis of power interruption data. This data is used to compute performance
indicators or indices such as; Basic Reliability Indices (failure rate, MTBF, MTTR and
availability), Customer Orientation Indices (SAIFI, SAIDI, CAIDI, ASAI and ASUI) and
Energy and Cost Indices (EENS, AENS, ECOST and IEAR). From the period of study
(2016, 2017 and 2018), this research finds out that the System Average Interruption Index
SAIFI) is 7.47 interruptions per customer and System Average Interruption Duration Index
(SAIDI) of 58.17 hours per customer. These indices are benchmarked with the those of
other countries. A model of the AALRT TPSS is developed and three cases of potential
reliability improvement alternatives are simulated using an ETAP software. These
improvements gave an overall reduction in EENS of 80.869 MWhr/yr. A cost-benefit
analysis of the reliability improvement alternatives is also done to justify the investment.
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Keywords
DC Railway Traction Power Supply System, Reliability, Power interruption data, Performance Indicators, reliability improvement alternatives