Reliability Worth Assessment of Electric Power Utility in Nigeria: Residential Customer Survey Results

Transcription

1 Reliability Worth Assessment of Electric Power Utility in Nigeria: Residential Customer Survey Results Jide Julius Popoola, Akinlolu Adediran Ponnle 1 and Thomas O. Ale 2 School of Electrical and Information Engineering, University of Witwatersrand Johannesburg, South Africa <jidejulius21@yahoo.com> Abstract This paper presents the results of a customer survey conducted in some selected service areas of the Power Holding Company of Nigeria (PHCN) - the power utility provider in Nigeria. The aim of the study was to quantify the reliability worth of electricity supply in Nigeria. The study was carried out in two phases. In the first phase, primary data were garnered using a well-structured questionnaire about quality of power supply, its failure rate and inconveniences experienced by customers as most impacts of power interruptions to residential users are related to inconveniences. In the second phase, data related to condition of the distribution equipment as well as the distribution network design and planning were obtained by direct inspection of some of the studied areas by the authors. Descriptive statistics such as percentages, means, frequencies and bar chat were used in the analysis of data obtained from the questionnaire. The study showed that the quality of electric power supply in the country is below % and that the power supply is generally unreliable. Also from the responses from the customers survey, it was found that the power supply in Nigeria is seasonal dependent with better power availability in wet season than dry season. In addition, the study also revealed the need for both re-planning and re-designing of the nation s distribution network as the present design gives no room for expansion. The paper was concluded with suggestions on how to improve both the quality and reliability of electricity supply in the country. Keywords: Questionnaire, system adequacy, system security, hierarchical level. Introduction The term reliability has a very wide range of definitions and cannot be associated with a single definition. However, from engineering point of view, reliability can be defined as the probability that a system will perform required function under a given conditions for a stated period, usually a thousand hours or million hours (Abdullahi et al. 27). 1 Department of Electronic Engineering, Tohoku University, Sendai, Japan. <ponnleakinlolu@yahoo.co.uk>. 2 Department of Electrical and Electronic Engineering, Federal University of Technology, Akure, State, Nigeria. E- mail: <aleto4@yahoo.com>. The reliability of a system or equipment as defined by Iresome and Coombs (1998) is the conditional probability at any given confidence level that the system or equipment will perform its intended function at a given age, for a specific length of time when used in the manner and purpose intended while operating under specific environment. The reliability of an electric power system is, therefore, defined as the probability that the power system will perform the function of delivering electric energy to customers on a continuous basis and with acceptable service quality (Bhavaraju et al. 25). The term reliability as used in the context of a power system has a very wide range of connotations. It is therefore being discussed under two general categories namely: system adequacy and system security (Billinton and Allan 1984; Technical Report 217

2 Billinton and Allan 1988). System adequacy relates to the existence of sufficient generation, transmission and distribution facilities within the system to satisfy the customer load demand. System security, on the other hand, relates to the ability of the system to respond to disturbances arising within the system. As the world economy becomes increasely dependent on technology that requires highly reliable electric power, reliable and qualitative electricity has been observed as a sine qua non element for modern living (Ali et al. 24). On a global scale, reliable electric power availability has been observed as effective and indispensable machinery for the rapid industrial and economic growth of any nation (Megbowon and Oyebisi 25). Therefore by its importance in the society and its necessity for national economic growth, electrical energy supply is expected to be available 24 hr a day. Based on this importance, it is expected that electric power utilities throughout the world must ensure they meet customer demands at a reasonable level of service reliability. In order to meet customer demands, power system has been broken down into three functional zones or subsystems known respectively as generation, transmission and distribution. For the purpose of reliability calculation, the three functional zones of a power system (i.e., generation, transmission and distribution) can be grouped into three hierarchical levels (HLs), as shown in Fig. 1, and reliability indices can be calculated at each of these levels (Debnath and Goel 1995). Hierarchical level 1 (HL1) involves the reliability analysis of only the generation system while hierarchical level 2 (HL2) includes the reliability evaluation of both generation and transmission systems, referred to as the bulk power system or the composite power system, and hierarchical level 3 (HL3) consists of a reliability study of the entire power system. Though the reliability evaluation of the entire power system (HL3) is an important requirement in overall power system planning and operation, it is not usually conducted on a complete power system due to its complexity. Rather, the reliability evaluation of each subsystem is usually conducted independently. This kind of analysis generally assumes that the other parts of the system are fully reliable and capable of performing their intended functions (Yang 27). Transmission System Generation System Distribution System Hierarchical Level 3 Fig. 1. Hierarchical levels for power system reliability assessment. Source: Yang (27) In order to assess the reliability of electric power utility at the distribution subsystem, the approach used in this study was to estimate the customer monetary losses as well as other inconveniences resulting from supply interruptions. This was obtained by carrying out customer survey method. The method was used because, it was considered that it will yield the most consistent results based on the assumption that the customer is in the best position to give first hand information on losses incurred and inconveniences experiences whenever there is power interruption. Customer survey costing or monetary losses are of three types: contingent valuation methods, direct costing methods, and indirect costing methods (Tollfson et al. 1991). In this study, indirect costing method was used, as most impacts of power interruptions to residential users are related to inconveniences, disruption of house keeping or leisure activities which are latent variables that cannot be measured physically. In order to provide a lasting solution to these inconveniences, this work was embarked upon with the objective of identifying the characteristics, variables and criteria associated with the worth of electric service reliability and to suggest reliability worth methodologies that can be used by Power Holding Company of Nigeria (PHCN) Technical Report 218

3 formerly National Electric Power Authority (NEPA) for better power system planning and operation. Methodology The investigation was conducted in selected cities in the South-West geo-political zone of Nigeria. The zone, which is one of the six geo-political zones in Nigeria, consists of six states (Ekiti,,,, and ) out of the thirty-six states and the Federal Capital Territory that constitute Nigeria. The zone was selected as the true representative model of electric power supply system in the whole country based on the socio - economic development of the zone. The study was carried out in two phases. The first phase was an investigation phase through which relevant primary data were collected from customers using questionnaire. The second phase was field survey carried out directly by the authors by inspecting some of the distribution networks of the PHCN in the studied areas. Customers Survey The investigation begins with the development of the survey questionnaire. The analyses of the obtained data from the survey were later carried out using descriptive statistics such as percentages, frequencies, means and bar chart. Each stage of the study is hereby explained in detail. Structure of Questionnaire: This involved the designing and administering of the well structured research questionnaire to the PHCN customers (domestic and schools) in the studied areas in order to obtain primary data relevant to the study. The questionnaire was divided into two sections. The first section is the introductory part, where the aim of the study was stated for the respondents. The section also contains words of assurance and encouragement, assuring respondents that the information provided by them would be treated with utmost confidentiality. The second section of the questionnaire consists of questions related to objective of the study. The section was divided into three subsections: (i) The first subsection deals with the background information about quality and reliability assessment parameters relevant to the study. In all four questions were asked that were used to determine both the quality and reliability worth of the electric power supply of the zone. (ii) The second subsection extracts information on the effects of power interruption on customers. Four questions were asked in this subsection from which various effects of power failure experienced by customers were revealed. (iii) The third subsection deals with the billing and charging systems of the PHCN. In this subsection, only two questions were asked. The questions revealed the attitude of the staff of PHCN to work as well as the prospect of the body provided the services can be improved. In all, the questionnaire was structured in such a way that one question leads to the next. This is important because it establishes the context for next question. For instance, the first question was asked about the voltage stability usually supplied and number of interruptions they do experience per day. As the respondents begin to reply regarding how many interruptions they normally experience daily, they are also beginning to consider what happens during interruptions. The next set of the questionnaire asks about the specific effects of an interruption. Respondents are asked to rate the negative effects of power interruption on a list of household activities and equipment that are electricity dependent. The essences of these questions are to move the respondent from general thoughts about interruptions to the more specific effects of interruptions. This was followed by questions related to monetary value associated with the effects of the power interruption on the respondents. Administration of the Questionnaire: This phase of the work was carried out in the selected cities of the studied services zone of the country. During this phase of the work, customer surveys using man-to-man interviews and administering of questionnaires were done. Technical Report 219

4 Table 1. Questionnaire distribution. State Study Area Sample Size Ekiti Ado-Ekiti Ikole-Ekiti Ikere-Ekiti Ikeja Ajegunle Abule-Egba Abeokuta Ijebu-Ode Ago-Iwoye Akure Akungba-Akoko Osogbo Ile-Ife Iree Ibadan Ogbomoso Questionnaire Response Size Total Responses Total Responses (%) The purpose was to explain the objective of the study and to gain support of the customers so that the data obtained can be a reliable and true mind of the customers. Nine hundred copies of questionnaires were prepared and divided into six equal parts of 1 each. In each state, most of the towns used are where there are higher institutions so that the two types of customers considered could be well represented. Table 1 shows the detail of how the questionnaires were distributed in each state. Field Study This is the second phase of the study. In this phase of the study, some selected distribution sub-stations in the studied areas were visited by the authors. Observations showed that most of the distribution transformers in the studied areas are aged and needed to be replaced. Similarly, it was observed that nearly all the distribution lines in the studied areas are sagged with numerous numbers of joints. During the inspection, the authors also discovered that, loads on the supplying phases are unevenly distributed. They observed this unevenly load distribution as the major reason causing load in-balancing in almost all the studied areas visited. With these observations, the authors hence suggested that for reliable power supply in Nigeria, not only the generation subsystem of the country s electricity supply needs to be overhauled but the distribution subsystem must be included. The country s power distribution networks need to be redesigned and re-planned as current situation gives no room for expansion. Results and Discussion Questionnaire Analysis This is the final stage of the study. The stage involves data compilation, analysis and interpretation of results obtained. The data generated from customers survey carried out were presented in detail using tables and graphs. All the values used are from the combined customers responses. Though the numbers of customers interviewed were limited to particular service areas of the country, the service areas Technical Report 22

5 investigated, however, are considerable in terms of countrywide coverage, development and electric service areas and not in terms of population size. It is therefore assumed that the results are good representative of the customers in the country. Discussion Responses Regarding Quality of Service and Reliability: In the first section of the questionnaire, the customers were asked to give their opinions regarding the quality of power provided by Power Holding Company of Nigeria PLC, the number of power failure they do experience per day and the duration of power failure as well as the season of the year they do experience frequent power failure. In determining the quality of service supply to the public, the questions asked include voltage stability of the power supply, voltage surges and frequency of interruption. This is because power quality has to do with the supply voltage meeting the needs of the customer and is measured in terms of voltage stability, frequency stability, and absence of measurable voltage sags, voltage surges and very short interruptions (Schienbein and Desteese 22). Response from this section of the questionnaire showed that quality of power supply in Ekiti state is the worst while that of state is the best as shown in Fig. 1. The overall calculated quality of service mean showed that 64.2% considered the service quality to be poor in the six states. Only 22.6% of the respondents considered it to be good while the last 13.2% of the respondents considered it to be excellent. Percentage of Respondent Poor Good Excellent Customer Respond Fig. 1. Graph of quality of service. Fig. 2 and Table 2 show the customers responses to the frequency of failure experience. From Fig. 2, it was observed that daily power outage ranges from 13.9% to 84.8% with the highest outages in Ekiti state and the lowest in state. The frequency of power outages in other four states considered fall in between these extreme values Frequently Occassionally Customer Response Fig. 2. Graph of frequency of power failure per day. In estimating the reliability worth of the nation s distribution system, both the failure rate and the mean time between failures were calculated. The failure rate according to Megbowon and Oyebisi (25) is defined as a measure of the frequency at which faults occur. For a repairable items or systems, the failure rate is expressed as the number of failure which occurs per unit-hour of operation. It is denoted by FR(N) and expressed as: FR Number of time that failure occurred Number of unit hour of operation (1) ( N ) =. According to Megbowon and Oyebisi (25), high value of FR(N) is an indicative of low reliability. From Table 2, the daily, weekly and monthly calculated failure rates are 1.46, 1.59 and 1.55, respectively. This confirmed that Nigeria s power distribution system is unreliable. Similarly, the mean time between failures which is another index of reliability that expresses the average time, elapses between consecutive failures of a repairable system or Technical Report 221

6 Table 2. Reliability indices estimated value. Average Estimated Failure Rate (FR) and Mean Time Between Failure (MTBF) State Daily Weekly Monthly Failures FR MTBF Failures FR MTBF Failures FR MTBF Ekiti Total equipment was estimated for the nation s distribution system. It is denoted by MTBF and expressed as: Numberof unit hours of operations MTBF =. Numberof failures (2) MTBF being a reciprocal of FR(N), the longer its value the more reliable is the system. However, for the Nigeria power distribution network considered, it was found that its MTBF values;.68 (daily),.63 (weekly) and.65 (monthly) were shorter. These also confirmed that Nigeria power distribution network system is unreliable as shown in Table 2. In addition, it was found that the power outages in the zone vary with seasonal variations. Fig. 3 reveals the frequency of power outages during the two seasonal periods of the year with higher power outages during the drying season than the raining season. The average percentage power outages calculated using Fig. 3 gives 69.5% in drying season and.5% in wet season. Indicating that power supply in the country is seasonal dependent. This indicates better power supply during the wet or raining season than drying season. Responses Regarding Interruption Effect: This is the second section of the questionnaire. The result of this section is shown in Fig. 4. The respondents were asked to rate the undesirable effects of power interruption on several household activities that are electricity dependent. Loss of lighting was rated as the most undesirable effect in all the states 6 2 Dry Season Wet Season Seasonal Period Fig. 3. Graph of power failure with seasonal variation. considered with 6.8% dislike darkness. This was followed closely by adverse effect of equipment not usable (16.9%) and fear of crime (13.8%). The fear of accident at home (3%); especially fire outbreak when using lanterns or kerosene stove was not all that pronounced. Responses Regarding Authority s Monthly Charging: In this third section of the questionnaire, the customers were asked to give their views about the authority billing system whether the authority monthly bill is commensurate with the number of unit consumed or not. Also, in the section, questions were asked on the relationship between the power interruption and their monthly billing. In all the service areas considered, the responses as shown in Fig. 5 indicate that bills to customers are not commensurate with electricity used. In addition, in the section, questions were asked to find out whether the authoritycharging rate is better or not when compare Technical Report 222

7 6 2 Darkness Crime Fear Equipment Unuse Effects of power interruption Domes tic Accident Low Moderate High Fig. 4. Graph of frequency of power failure per day No Yes Customer Response Fig. 5. Graph of monthly bill commensuration with utility usage. with other source of energy fuel s price (kerosene, petrol and diesel). The responses of the customers were shown in Fig. 6. From the figure (Fig. 6), it is obvious that despise the poor electric supply situation in the country, the customers still prefer the PHCN charges to other sources of power in the country. Conclusion and Recommendation This study illustrates the application of customer survey method in determining the reliability worth of electric power utility. The method was used specifically to study the reliability worth of Nigeria s electricity distribution functional zone or subsystem. The study presents the summary of an investigation of interruption costs experienced by the electricity customers in Nigeria. The result of the study shows that the electric power supply situation varied in all the six states considered. Customer Respond Fig. 6. Graph of electricity charge compared with other sources of energy. The overall result of the study reveals that power supply in the country is unreliable. Based on the above findings, the following recommendations should be put into practice to ameliorate the observed defects: The utility body (PHCN) and the government at the three tiers (federal, state and local) in Nigeria should help in general renovation of the power distribution networks in Nigeria. The current overhauling in the generation subsystem of the country power system be extended to the nation s distribution subsystem in order to ensure overall reliability of power supply in the country. The power distribution networks of the country should be both re-planned and redesigned to enhance load balancing at the distribution substations as well as to give room for future expansions. To eradicate the seasonal dependent nature of the power supply, the hydropower generation stations in the country should be overhauled to enhance all round power availability throughout the year. References Abdullahi, M.I.; Akinsanmi, O.; Muazu, M.B. and Jubril, Y. 27. Reliability assessment of an electronic system: A case study of a British siren in Nigeria. J. Appl. Sci. Res..3: 1, Technical Report 223

8 Ali, N.A.; Achinanya, U.D.; and Nuhu, M.S. 24. Frequency failures of equipment in power system network the Nigeria experience. Proc. 8 th IEE Int. Conf. Devel. Power Syst. Protect..2(5 8): Bhavaraju, M.P.; Billinton, R.; Brown, R.E.; Endrenyi, J.; Li, W.;Meliopoulos, A.P.; and Singh, C. 25. IEEE Tutorial on Electric Delivery System Reliability Evaluation. IEEE Power Engineering Society (PES), Publication 5TP175: Billinton, R.; and Allan, R.N Powersystem Reliability in Perspective. IEE J. Electron. Power.: Billinton, R.; and Allan, R.N Reliability Assessment of Larger Electric Power Systems. Kluwer Academic Publishers, Boston, MA, USA. Dednath, K.; and Goel, L Power system llanning a reliability perspective. Electric Power Syst.Res. 34: Gouen, T Electric Power Transmission System Engineering. John Wiley, New York, NY, USA Ireson, W.G.; and Coombs, C.F A Handbook of Reliability Engineering and Management, 2 nd ed. McGraw-Hill, New York, NY, USA. Megbowon, I.O.; and Oyebisi, T.O. 25. A reliability assessment of the south western transmission lines of the Nigerian National Grid. FUTAJEET 4: Schienbein, L.A; and Desteese, J.G. 22. Distributed Energy Resources, Power Quality and Reliability Background. Pacific Northwest National Laboratory, U.S Department of Energy, DE-AC6-76RL18, pp 1-, [Online Available]: < Tollefson, G.; Billinton, R.; and Wacker, G Comprehensive bibliography on reliability worth and electrical service interruption costs: IEEE Trans. Power Syst. 6: 1,8-14. Yang, F. 27. A Comprehensive Approach for Bulk Power System Reliability Assessment. PhD Thesis, Georgia Institute of Technology, Atlanta, Georgia, USA, March, 27, [Online Available]: < /unrestricted/yang_fang_ 25phd.pdf>. Technical Report 224