This document presents a reliability assessment of the Haramaya University distribution system, highlighting the critical issue of frequent power interruptions and their economic impact. It outlines the objectives, reliability metrics, methodologies, results, and cost analysis, concluding that implementing an underground ring distribution system could significantly improve reliability and result in substantial cost savings. Recommendations for future work and preventive maintenance are also provided to enhance system performance.

1. Reliability Assessment of Power
Distribution System
Haramaya University, HiT, SECE
2/16/2024
M.Sc. Thesis Defense Presentation
By: Abdulaziz Adem
Program: Electrical Power Engineering
Major Advisor: Dr. Ramesh Kumar
Co-Advisor: Mr. Wehib Abubeker

2. Outline
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 Introduction
 Literature Review
 Materials and Methods
 Results and Discussions
 Conclusion and Recommendation
 References

3. 1. Introduction
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 The purpose of power systems is to provide an
economic and reliable network for electricity.
 The role of electric utility is to provide reliable electric
power to the customers.
 However, reliability problems in power systems usually
occurs at DS.
 Historical and predictive assessment two methods of RA.
 SAIFI,SAIDI,,CAIDI, ASAI, ASUI, EENS are commonly used
standard reliability metrics.

4. Statement of the problem
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 In Ethiopia, delivering reliable electric power is the role of
EEU, however, power interruptions are becoming a critical
problems.
 Particularly, HU DS usually experiences power interruption.
 The university is using the diesel generators as a backup
supply.
 However, due to high price of fuel, the operating cost of
diesel generator is more.
 Considering the problem an assessment of HU DS reliability
was conducted.

5. Objectives
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General objective
 To assess the reliability of HU DS and propose improvement
technique.
Specific Objectives
 To identify the major causes of power interruptions
 To model and simulate existing and under construction HU
DS
 To compare existing and under construction DS
 To propose improvement technique
 To perform cost analysis

6. 2. Literature Review
6
Power System Reliability
 Reliability
 The probability a system/component performing its
function adequately for a given period time.
 Adequacy
 Sufficient facilities within the power system to satisfy
customer demand.
 Security
 The ability of the system to respond to disturbances
arising within the system.
 RA :- Generation, composite generation&transmission,
Distribution system ,substation

7. Component Model
7
• Failure rate (λ)
• 𝑀𝑇𝑇𝑅 =
total repair time
total no.of int.s
(2.1)
• µ =
8760
𝑀𝑇𝑇𝑅
(2.2)
• MTTF =
1
λ
(2.3)
• MTBF= MTTF +
MTTR
8760
(2.4)
• U =
MTTR
MTTF×8760
(2.5)
Fig.2.12 :Two-state space
diagram
Fig.2.13 : Mean time
Two-state model

8. Series & Parallel Systems
 For n components in series
 λs = i
n
λi (2.6)
 Us = i
n
λi ri (2.7)
 rs =
Us
λs
(2.8)
 For 3 components in parallel
 λp = λ1 λ2λ3 r1r2 + r2r3 +
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9. Reliability Indices
 SAIFI = i λiNi
i Nt
f/yr (2.12)
 SAIDI= i riNi
i Nt
hr/yr (2.13)
 CAIDI =
SAIDI
SAIFI
hr/int (2.14)
 CAIFI = i λiNi
Cn
f/yr (2.15)
 ASAI =
Nt∗8760)− i riNi
Nt∗8760)
(2.16)
 ASUI= 1−𝐴𝑆𝐴𝐼
(2.17)
 EENS = i La i Ui (2.18)
 AENS = i La i)Ui
i Nt
(2.20)
9

10. Reliability Improvement Methods
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 Electrical method
 Protective and switching devices
 Network reconfiguration
 Distributed generation
 Non-electrical method
 Vegetation management
 Installation of lightning arrester
 Animal protection guards

11. 3. Materials and Methods
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Haramaya substation
Fig.3.1: One-line diagram of Haramaya distribution
substation

12. Calculation of Reliability Indices
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 The load point reliability indices have been calculated
using equation (2.6) to (2.8).
 The overall system reliability indices have been
calculated using equations (2.11) to (2.20).
Table 3.11: Calculated system reliability indices of HU DS
SAIFI SAIDI CAIDI ASAI ASUI EENS AENS
198.15 275.39 1.4 0.968
6
0.031
4
2167.4
3
103.21

13. Comparison Reliability Indices
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Table 3.12: Comparison of HU DS reliability indices with
benchmarks
Countries SAIFI
(int./cust.yr)
SAIDI
(hrs./cust.yr)
CAIDI
(hrs./int)
ASAI
(%)
USA 1.5 4 2.05 99.91
Denmark 0.5 0.4 1.67 99.981
France 1 1.03 0.97 99.97
Spain 2.2 1.73 1.9 99.968
Germany 0.5 0.38 0.83 99.999
UK 0.8 1.5 1.67 99.964
Canada 3.4 6.9 2.03 99.95
Netherland 0.3 0.55 1.25 99.97
Italy 2.2 0.97 1.77 99.999
Australia 0.9 1.2 1.87 99.97
Ethiopia 20 25 2.23 99.71
HU 198.15 275.39 1.4 96.86

14. Power Interruption Cost
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 The outage costs have seen by the utility and the
customers.
 Utility side
 Loss of revenue
 Customer side
 Cost of alternative supply

15. Sizing of Solar DG for HU
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 PV Syst 7.2 software has been used to size the system.
 Data required:-
 Load data
 Meteorological data

16. 4. Results and Discussions
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 The simulation was performed for the following cases.
Reliability
indices
Base
case
Case 1 Case
2
Case
3
Case 4 Case 5
SAIFI 196.38 196.50 1.18 176.8
0
168.53 80.57
SAIDI 277.78 191.98 20.77 123.5
7
118.64 78.44
CAIDI 1.41 0.98 17.60 0.69 0.70 0.97
ASAI (%) 96.83 97.81 99.76 98.59 98.65 99.1
ASUI (%) 3.17 2.19 0.24 1.41 1.35 0.9
EENS 2186.5
7
1509.2
0
290.1
9
981.4
2
958.81 671.33
AENS 104.12 71.87 13.82 46.73 45.66 31.97

17. Cost Analysis
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 The reliability of a system can be increased by increasing
investment cost.
 Payback Period =
Investment Cost
Annual Revenue Saved
(4.1)

18. …Cost Analysis
18
Table 4.8: Summary of cost analysis for all cases
 Case (3)and (4) are profitable for both utility and HU.
 Case 5 and 2 are profitable only for HU.
Study
Utility side HU side
Revenue
saved (ETB/yr)
Payback
period
(yr)
Money
saved
(ETB/yr)
Payback
period
(yr)
Case 3 1,414,909.93 1.11 3,297,306 0.48
Case 4 1,141,883.66 2.05 3,423,349.
3
0.7
Case 5 1,784,847.3 34.38 4,328,113.
6
14.17
Case 2 2,239,549.9 77.7 5,762,746.
4
30.2

19. 5. Summary and Conclusion
19
Conclusion:
 HU DS is out of service due to unplanned and planned
interruptions.
 There are serious reliability problems in HU DS.
 The reliability problem in existing system has a negative
impact on economy of utility and customers.
 Fuses, reclosers, solar DG, and UG ring network can all
improve DS reliability.
 UG ring HU DS has improved system reliability indices.
 HU can save 5,762,746.38ETB/yr by constructing an UG
ring DS and the payback period will be 30.2 yr.

20. Recommendations/Future Work
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 The next researcher will work on power quality issues
raised when DG is connected to grid.
 Case 3&4 are recommended for the utility to implement
(in terms cost).
 UG ring DS is recommended for HU to get improved
reliability performance.
 Preventive maintenance of existing distribution line are
required on a regular basis.
 I recommend Haramaya substation and EEU to enhance
data record experiences.

21. References
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Abrha H. and Teshome G. 2020. Reliability Assessment of Electrical Distribution Network
using Analytical Method: A Case Study of Maychew City Distribution System.
International Journal of Engineering Research & Technology (IJERT), 9(08): 977-985.
 Akhikpemelo A., Eyibo N. R and Adeyi A.,2016. Reliability Analysis of Power Distribution
Network. Wilolud Journals of Continental J. Engineering Sciences, 11 (2): 53 - 63
 Amache Jara, 2016. Reliability Assessment of Radial Distribution System with Distributed
Generation: A Case Study of Cottebe Substations. Master’s Thesis, Addis Ababa University,
Addis Ababa, Ethiopia.
 Balogun M. O., Ahmed M. O., Ajani A. A., and Olaoye H. 2019. Reliability Assessment of
33KV Feeder: A Case Study of Transmission Company of Nigeria, Ganmo Work Centre.
World Journal of Innovative Research, 6(1): 77-83.
 Chemdi M. 2020. Reliability Analysis of 15kv Distribution System Network. (Case Study:
Addis Alem Substation Network, Master’s Thesis, Addis Ababa University, Addis Ababa,
Ethiopia.
 Degarege Anteneh. 2020. Reliability Assessment of Distribution System Using Analytical
Method: A Case Study of Debre Berhan Distribution Network. Journal of Informatics
Electrical and Electronics Engineering, 1(1): 1-9.

22. …References
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 Eyasu B, 2017. Studies on Power Distribution System Reliability Assessment and improvement,
Master’s thesis, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia.
 G. Sengi and E. Ntagwirumugara. 2021. Improving reliability of the power distribution system
in Goma (DRC) using solar distributed generation, Journal of Energy in Southern Africa 32(4):
84–101.
 Khaidir A, Rama O, and Ramadoni S, 2017. Reliability Analysis of Power Distribution System, Journal
of Electrical Technology UMY (JET-UMY), 1(2).
 M. Wadi, M. Baysal, A. Shobole, and M.R. Tur, 2020. Historical and Monte Carlo Simulation-Based
Reliability Assessment of Power Distribution Systems, Sigma Journal of Engineering and Natural
Sciences, 38(3): 1527-1540
 S. L. Braide and E. O. Kenneth, 2018. Improved Reliability Analysis of Electricity Power Supply to
Port Harcourt Distribution Network. International Journal of Engineering Science Invention, 7(7): 2319
– 6734
 Vishalini Divaka, B. K. Keshavan and M. S. Raviprakasha. 2016. A Survey on Methods of Evaluation
of Reliability of Distribution Systems with Distributed Generation. International Journal of Engineering
Research & Technology, 5(08): 220-226.
 Z. Hoosain Khan,2015, Improving the reliability performance of medium voltage networks, Master’s
dissertation, University of Cape Town, Cape Town

23. Thank You!
2/16/2024
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Haramaya University, HiT, SECE