In power systems, electricity supply from the utility is usually sufficient to cater for load demand. However, in most cases when there are overload and power losses, matching emergency supply with demand may pose a challenge. To mitigate the dire consequences of insufficient generation and other problems, this thesis presents an efficient load management for Michael Okpara University of Agriculture, Umudike (MOUAU). The load management is the priority load management, and its purpose is to match load demand to supply through load shedding. The major load areas in MOUAU were used as case study. The load management was developed for the individual load areas. The data were collected from the electricity department of Works and Physical Planning Unit, MOUAU using questionnaire and interview. The data were analysed with Electrical Transient and Power Analysis (ETAP) and MATRIX Laboratory (MATLAB) softwares. The method of analysis used is Holistic method: The load of the areas studied is divided into priority and the least priority load is shed first. For the proposed load management, two cases were considered based on synchronization of the three generators used in MOUAU. The first case is where the three generators are synchronized on a common busbar, while the second case is where two of the generators are synchronized on a common busbar, and the remaining generator is connected to a suitable bus. The two cases considered were compared to know the case that will be effective in reducing power losses. The cost involved in running the exiting power plant and the proposed power plant of MOUAU were compared. Results revealed that the fixed demand charge involved in running the existing power plant and the proposed power plant are N576/KVA and N192/KVA respectively. The results indicated that the cost of running the existing power plant is 75% higher than the cost of running the proposed power plant which is 25%. For the existing MOUAU 8-bus network, power losses of 8.4kW and 8.1kVar existed. The result of case 1 showed 30.5kW and 29.5kVar while that of case 2 showed 7.8kW and 7.5kVar power losses. The results obtained when SVCs were installed on the sensitive buses showed 7.2kW and 6.9kVar power losses. This showed 48% and 47.9% reduction of the active and reactive power losses respectively.
TABLE OF CONTENTS
Title page i
Table of Contents vi
List of Tables ix
List of Figures xi
List of Plates xiii
List of abbreviation xiv
CHAPTER 1: INTRODUCTION
1.1 Background of the Study 1
1.2 Problem Statement 3
1.3 Aim and Objective of the Study 5
1.4 Scope of the Study 6
1.5 Significance of the Study 6
1.6 Justification of the Study 7
CHAPTER 2: LITERATURE REVIEW
2.1 Meaning of Load Management 9
2.2 Types of Load Management 9
2.3 Load Management on Supply and Demand Sides 11
2.4 Advantages of Load Management 12
2.5 Concepts of Load and Overload 13
2.6 Reviewed Papers 14
2.7 Summary of Literature Review 61
CHAPTER 3: MATERIALS AND METHODS
3.1 Materials 62
3.2 Methods 62
3.2.1 Study area 62
3.2.2 Load survey 63
3.2.3 Research strategies 64
3.2.4 The existing power system of MOUAU and the load management applied 64
22.214.171.124 Existing power system in MOUAU 64
126.96.36.199 Existing load management in MOUAU 67
3.2.5 The proposed load management of MOUAU 69
188.8.131.52 Case 1 of the proposed load management 69
184.108.40.206.1 The proposed MOUAU network 1 69
220.127.116.11.2 The operation of the proposed MOUAU network 72
18.104.22.168.3 The proposed load prioritization scheme for the load Area 79
22.214.171.124.4 The proposed load prioritization scheme for the appliances used in MOUAU 79
126.96.36.199.5 Sequence for adding and shedding loads based on load area level 80
188.8.131.52.6 The scheme implementation algorithm 80
184.108.40.206 Case II of the Proposed Load Management 83
220.127.116.11 Modelling of the MOUAU 8-bus Networks 84
18.104.22.168.1 The cost model analysis 84
22.214.171.124.2 Load shedding analysis 85
126.96.36.199.3 The load flow analysis 85
3.2.6 ROCOF model 86
3.2.7 Model for synchronized generators 93
3.2.8 Power flow method 95
3.2.9 Load model 100
3.2.10 The cost model 103
188.8.131.52 Derivation of pricing policy for generating sets 103
184.108.40.206 Application of the pricing policy to MOUAU’s three generating sets 105
3.2.11 The line model 106
3.2.12 Load shedding optimization problem 109
3.2.13 Line model for SVC performance 114
3.3. Assumption Made in the Work 117
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Results 119
4.2 Discussion 138
4.2.1 Discussion on power consumption 138
4.2.2 Discussion on the cost analysis result 140
4.2.3 Discussion of the electrical loads and load shedding 142
4.2.4 Discussion of the load flow analysis 147
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 151
5.2 Contribution to Knowledge 152
5.3 Recommendations 153
LIST OF TABLES
3.1 Load Add and Load Shed Schedule 82
3.2 Estimated Loads of the Medical Centre (MC) and their Associated Priority Levels 121
3.3 Estimated Loads of Administration Building (AB) and their Associated Priority Levels 122
3.4 Estimated Loads in Afrihub/ICT Centre and their Associated Priority Levels 123
3.5 Estimated Loads of Main Library (ML) Building and their Associated Priority Levels 124
3.6 Estimated Loads of the Offices in College of Engineering and Engineering Technology (CEET) and their Associated Priority Levels 125
3.7 Estimated Loads of College of Applied Food Science and Tourism (CAFST) and their Associated Priority Levels 126
3.8 Estimated Loads of New Female Hostel (NFH) Building and their Associated Priority Levels 127
3.9 Estimated Loads of New Male Hostel (NMH) Building and their Associated Priority Levels 128
3.10 Load Prioritization Scheme of the Load Areas Selected in MOUAU 129
3.11 Determination of Various Feeder ATS Ratings / Supply 129
3.12 Loading Per Phase in MC and AB with respect to the Different Switching Levels 130
3.13 Loading Per Phase in ICT and ML with respect to the Different Switching Levels 130
3.14 Loading Per Phase in CEET and CAFST with Respect to the Different Switching Levels 131
3.15 Loading Per Phase in NFH and NMH with Respect to the Different Switching Levels 131
3.16 Load Shedding Scheme Matric for the Feeders 132
3.17 The Generator Properties 133
3.18 Load Shedding Data 134
3.19 Load Data Per Phase 135
3.20 Generator Starting and Power Consumption 136
3.21 Rate of change of frequency (ROCOF) for the Load Area 137
4.1 Branch losses summary report for existing MOUAU 8-bus network 141
4.2 Equipment cable and heater losses summary report for existing MOUAU 8-bus network 142
4.3 Branch losses summary report for proposed MOUAU 8-bus network without SVC 145
4.4 Equipment cable and heater losses summary report for proposed MOUAU 8-bus network without SVC 146
4.5 Branch losses summary report for proposed MOUAU 8-bus network 1 with SVC 149
4.6 Equipment cable and heater losses summary report for proposed MOUAU 8-bus network 1 with SVC 150
4.7 Branch losses summary report for proposed MOUAU 8-bus network II without SVC 153
4.8 Equipment cable and heater losses summary report for proposed MOUAU 8-bus network II without SVC 154
4.9 Branch losses summary report for proposed MOUAU 8-bus network II with SVC 157
4.10 Equipment cable and heater losses summary report for proposed MOUAU 8-bus network II with SVC 158
4.11: Summary of the Power Losses Result when the network was run without and with SVC 159
4.12: The Result of Comparism for the Existing Network in MOUAU and the Proposed Network 161
LIST OF FIGURES
3.1 Existing MOUAU Power Network 68
3.2 The Proposed MOUAU Power Network 1 72
3.3 System Configuration When Utility is Available 74
3.4 System Configuration When Generator 1 is Powered in Automatic Mode 75
3.5 System Configuration When Generator 2 is Powered in Automatic Mode 76
3.6 System Configuration When Generator 3 Is Powered in Automatic Mode 76
3.7 System Configuration with System in Manual and Utility Source is Unavailable 77
3.8 Load Shedding Processor Input Interconnection 79
3.9 Load Shedding Processor Output Interconnection 80
3.10 Implementation flowchart 84
3.11 Proposed MOUAU Network II 85
3.12 Flow of mechanical and electrical power in the generator 89
3.13 Synchronizing Generators 95
3.14 Rotation for active and reactive power at bus i 97
3.15 Circuit representation of power consumed by load. 102
3.16 Short Line Model 108
3.17 Two-Port (Block Box) Representation of the Line 110
3.18 A Selection of a Distribution Line 116
4.1a Existing MOUAU 8-bus Network 139
4.1b Load Flow Result for Existing MOUAU 8-bus Network 140
4.2a Proposed MOUAU 8-bus Network without SVC 143
4.2b Load Flow Result for Proposed MOUAU 8-bus Network without SVC 144
4.3a Proposed MOUAU 8-bus Network 1 with SVC 147
4.3b Load Flow Result for Proposed MOUAU 8-bus Network 1 with SVC 148
4.4a Proposed MOUAU 8-bus Network II without SVC 151
4.4b Load Flow Result for Proposed MOUAU 8-bus Network II without SVC 152
4.5a Proposed MOUAU 8-bus Network II with SVC 155
4.5b Load Flow Result for proposed MOUAU 8-bus Network II with SVC 156
4.6 Load consumption (kWh) with Load Area 162
4.7 Plot of Consumption with Generator (Gen) 163
4.8 Plot of Cost (N) Versus Power Plants. 165
4. 9 Plot of Load Versus Load Area 167
4.10 Plot of frequency (Hz) against Time (mins.) 168
4.11 Plot of Load (kW) against Load Area 169
4.12 Plot frequency (Hz) versus Time (mins) 170
4.13 Plot of Phase Load Versus Phase 171
4.14 Plot of Load (A) against Time (Hr) 172
4.15 Plot of Power Loss against Power Types 173
4.16 Plot of Power Loss against Number of Reduction Steps 174
LIST OF PLATES
1: Researcher Interviewing Engineers at the main plant house substation MOUAU 197
2: The Researcher interviewed Engr. Njoku Alphonsus Nnabuike about the appliances used in the Engineering Workshop MOUAU 197
3: The Researcher interviewed Engr. Blessing Ogbonna and Engr. Chukwuka Awazie Nwakudu about the condition of appliances/Loads in the Engineering College of MOUAU 198
4: The Researcher obtained the load ratings of some appliances/machines used in MOUAU 198
5: The Researcher studied the Feeder pillar of the main plant house used in MOUAU through the aid of Engr. K.A. Ike 199
6: The Researcher interviewed female students at the new female hostel about the effect of black out in the area 199
7: The Researcher interviewing a male Computer Operator in the main Library about appliances and their ratings 200
1.1 BACKGROUND OF THE STUDY
A sudden increase in the system load or loss of generation may cause the decrease of line frequency and voltage, and at the end, collapse of the system. The improvement in power system reliability should be of interest to both power companies and customers. However, Montaser and Abdelfatah (2015) reported that since there are no sizeable electrical energy storage element in electrical power system, the generated power should match the load demand at any given time. Failure to meet this balance may cause several system problems such as loss of generation and system blackouts (Rafeal and Urban, 2015). It is generally accepted that the successful method for overcoming such problem is by applying an efficient load management using priority load management (but through automated load shedding) to temporally remove some loads out of the system.
Osuagwu (2015) revealed that the population of MOUAU is sixteen thousand (16,000). This is an evidence to show that electricity consumption is increasing rapidly in the university. The increment in population has caused the problem of overloading in the electricity network of MOUAU. A review of past incidents of blackout in MOUAU power network indicated that overload contributes significantly to most of the system disturbances (Nwaorgu et al., 2015). This has had negative impact in the economy, environment, and academic activities of the university.
Nevertheless, MOUAU has a load management scheme that shed loads from the network in a similar way the other utilities does. The scheme is created for cases such as insufficient generated power, abrupt loss of generator from the power system and system overloading that causes frequency and voltage instabilities. Sujatha (2013) maintained that frequency and voltage instabilities lead to power failure. Thus, the existing load management used in the university is manual operation which involves feeder disconnection in the feeder pillar. It is done by identifying the feeder with overload and then disconnect it. This method provides minimal load control because the university power system is very complex. There are three substations, each consisting of one generator of capacity 800 kVA that operate individually to power MOUAU’s appliances in the university. The feeder disconnection in the feeder pillar coupled with the individual operation of the generators makes the electricity demand outstrips supply, with consequent rolling black outs (Nwaorgu et al., 2015).
Besides, the feeder disconnection in the feeder pillar require expertise, it is time consuming and erroneous due to huge amount of feeders in the electricity network. It does not provide adequate measure for the overload control and hence lead to frequency and voltage reduction. The reduction in frequency and voltage values from their respective standard shows sign of mismatch between load demand and load supply (Nasrudan and Syafiqiuddin 2016).
Conversely, automated load management is considered in this work as the better technique for ensuring matching of the load supply and load demand (Musa et al. 2017). Instead of running the three generators in MOUAU individually, it becomes adequate to use automated synchronization of the generators to obtain maximum control of the overload. Automated synchronization of generators involved connection of the governors to an infinite busbar system (Nasrudan and Syafiqiuddin, 2016), this approach works with identification and arrangement of loads in accordance with their order of priority. However, the method create faster and accurate load shedding schedule. Amin et al.(2014) hints that automated load management bring increase in power system reliability, high efficiency, flexibility, reduction in generating and operating costs. Moreover, it increases load supply, and makes the number of electricity users interrupted to remain minimum. Therefore, this work presents automated synchronization of generators as efficient load management to be applied in MOUAU.
1.2 PROBLEM STATEMENT
In distribution network, a sudden increase in system load, network losses, poor voltage, failure of generator or any other components of the system, may result in some problems such as line overload, inefficient generation, under frequency and voltage collapse (Kaewmanee et al., 2013). Similar problems take place in MOUAU where inefficient load management is applied.
The existing electrical power distribution network in MOUAU suffers from several problems. Osuagwu (2015) affirmed that it suffers from high power losses exceeding 25%. These are technical losses (electrical losses) such as loss of transmission/distribution line, old lines with defects, lines and transformer overloads; and the non-technical losses (non-electrical losses) such as electrical thefts, illegal connections and illegal joints which exist in the transmission lines, poor maintenance and repair of power equipment, drought, poor inventory management, ageing and dilapidated distribution infrastructure. The problem of poor voltage affects the existing power network and the activities that occurs in MOUAU. Various components of the network were affected by poor voltage levels below the allowable limits. The power distribution network suffers voltage fluctuations that exceed the acceptable levels of 10%. This has caused poor supply voltages to consumers in the university, which results in poor performance of electrical equipment for both residential and commercial customers, poor quality of service offered to customers and high reduction in revenue.
Nwaorgu et al. (2015) pointed out that irregular power supply and power outage in MOUAU due to poor load management, has caused the university to spend eight hundred thousand naira (N800,000) for the period of fuelling the standby generators used to power the university loads. Numerous equipment used in the university are powered by electricity. These equipment include x-ray machine and radio therapy machine. Incessant power outages and sometimes near or total collapse have paralyzed the load areas, and also made the equipment not to function properly (Nwaorgu et al., 2015).
Inadequate capacity of the existing feeder lines poses another problem. The network lack suitable capacity to meet present and future demands. The reason is that unspecified existing lines are loaded at firm capacity levels, and some are in fact overloaded. At present MOUAU, suffers from high deficit in the power supply by about 34% (Osuagwu, 2015). Thus no adequate excess capacity is available to meet contingencies and to meet the future demands. Also short circuit problem affect the network too. The existing power network is controlled by manual load shedding through switching. Also the electrical operators in the substations used power house load shedding method and field load shedding method to shed loads using isolators. These methods affect the existing power network, and hence cause adverse effects like blackout. Blackout that results due to power failure in the university adversely affects consumers (Osuagwu, 2015). These include the use of kerosene lamps and burning of wood for cooking. The fume from the kerosene lamps pollute the environment and therefore affect students negatively while reading in the hostel. Again, in many occasions, patients undergoing operations in the medical centre have lost their lives due to unplanned power outage, and inability to change to emergency supply because of manual operation. Poor switch and inability to change to emergency supply damage electrical equipment and also causes death of patience in the hospital (Dike and Uzoma, 2014).
MOUAU has its own standby power system which is made up of three generators that run individually, and operated manually. In case if any of the generators becomes out of order, the relevant area faces total blackout. Manual load shedding applied in the power network is inefficient, time consuming, erroneous, yield minimal load control, and leads to load mismatch. Therefore to provide continuous supply to all the load areas, it is better to apply efficient load management method called priority load management. The proposed load management will assist to minimize losses, ensure fast load shedding, facilitate automated operation, match load demand to load supply, and reduce the huge cost used in running and maintenance of generators in MOUAU. Parallel operation of generators improved system efficiency and reduced number of personnel needed (Amin et al., 2014).
1.3 AIM AND OBJECTIVES OF THE STUDY
The aim of the study is to develop efficient load management for MOUAU. The specific objectives are:
i. To review literatures relating to the study of load management systems.
ii. To obtain correct data from field survey and MOUAU electrical department.
iii. To determine and compare the cost of running and operation of the existing and proposed load management for MOUAU.
iv. To carry out load flow analysis of MOUAU power distribution network using ETAP.
v. To reduce power losses with Static Var Compensator (SVC).
1.4 SCOPE OF THE STUDY
The study dealt with load management and its activities. It overlaps with current literature review on load management. The study goes beyond to cover an overview of existing load management method in MOUAU, paying attention to priority load management (that is automated and involves synchronization of generators) as efficient load management for MOUAU’s power network. The research also covers a description of component required for circuit implementation, and simulation of the proposed networks. The work also covers an algorithm that gives details of how load is shed. It covers load flow analysis carried out to determine active loss and reactive loss of the existing and proposed MOUAU networks. SVC was applied for power losses reduction. The analysis of cost for both existing and the proposed MOUAU’s power distribution system was also made.
However, load shedding is not considered during supply from the utility. Transmission lines and its associated parameters were not put into consideration as the thesis focuses on generation in distribution system.
1.5 SIGNIFICANCE OF THE STUDY
The findings of this research will:
1. Enable electric utilities to ensure reduction in maximum demand, minimization of losses or reduction in power losses.
2. Enable power companies and electric utilities to ensure better equipment utilization and savings through reduced maximum demand charges.
3. Sensitize the government on the need and urgency to have good electrical equipment to ensure reliable power supply.
4. Assist in the reduction of high cost involved in running and maintenance of generators in MOUAU and the society at large.
5. Provide a better understanding to energy stakeholders on the linkages and impact of electricity services.
6. Help to prevent overloading and damage of the power generators.
7. The outcome of this study will serve as a warning to the utility hence, forcing them to increase capacity and efficiency so as to meet the demand.
1.6 JUSTIFICATION OF THE STUDY
The priority load management has been proposed such that firms that deal with more than one standby generator can apply the system on their standby generators. This will help to shed loads successfully when there is problem of overload, and therefore keep the standby generator in normal operations. Scope of the work with the ongoing state of energy crisis worldwide and especially in MOUAU, are often at the kindness of rural electricity authorities. Therefore the mismatch between load demand and load supply stand as the issue. Nwaorgu et al. (2015) opined that many factors such as network losses contribute to make the situation worse in MOUAU.
Most firms decide to carry out their activities with backup generators coupled with Electricity Distribution Companies (EDC) supply. Shedding of loads is crucial since it does not allow the power system to collapse. The least priority load is often shed first based on the prioritization scheme formed after observing the situation of the power system (Dike and Uzoma, 2014). The priority load management is required to be applied in MOUAU power system to help in synchronization of the generators, assist fast load shedding, aid in reducing overload, power losses and unbalancing issues. It will help on good communication, on energy matter, control and protect the power network equipment. It will also help in high speed switching, permit reliability and easy maintenance system.
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