Evaluation of Losses in Distribution Networks of Selected Industrial Cities in Nigeria Using ETAP

Distribution losses contribute to energy shortages and therefore power outages in Nigeria’s industries. This work evaluated the technical losses in the distribution networks of selected industrial cities in Nigeria. Power flow simulation of network data collected over the period 2011-2015 from three distribution companies (DisCos) domiciled in these cities was done by Newton-Raphson (N-R) technique using the Electrical Transient and Analysis Program (ETAP) software version 12.6. Results of the power flow simulation showed that between 2011 and 2015 covered by the study, the cities of Lagos, Kano and Port Harcourt recorded a total power loss of 15.8 MW, 36.2 MW and 6.04 MW respectively. The findings also revealed that overloaded power transformers is part of the reasons for high losses in the distribution networks of some of the cities. The outcome of the study provides a guide for system planners and utility companies in providing for prioritization and system upgrade to ensure improved efficiency of their distribution networks. Original Research Article Amadi et al.; BJAST, 17(6): 1-12, 2016; Article no.BJAST.29910 2


INTRODUCTION
The number of power outages in a given locality per year is an indication of the efficiency of power supply even as consumer dissatisfaction with electricity service is often linked to high level of outages [1][2]. Since the more the number of power outages, the less efficient the power system, it follows that given higher system losses (technical and non-technical), there would be more power outages indicating the inefficiency of the system.
The biggest challenge confronting the Nigeria's distribution sector presently is the level of distribution losses namely technical, commercial and collection losses (Fig. 1). Technical losses are due to the nature of the components in use in the network, commercial losses refer to energy not billed for, and collection losses signify energy billed but not paid for. When the distribution companies were privatised as part of the power sector reform process by the Nigeria government, the transactions assumed some particular loss levels. After the asset hand-over, however, it became clear that the losses were much higher than had been estimated. In 2014, ~46% of energy was lost through technical (12%), commercial (6%), and collection losses (28%) [3].
Over the years, scholars and researchers have attributed power outages to: Weak grid and outdated power stations, equipment overloading, inadequate compensation equipment on the system, weather and tree related factors, vandalism, poor maintenance culture, etc. [1,4,5,6]. No researcher known to this study, however, has focused on the effects of distribution losses on electricity supply failures in the Nigeria industrial sector.
It is imperative therefore to undertake an assessment of the losses in the nation's electricity distribution network in order to recommend viable and long-lasting solutions to the perennial problem of system induced power outages among industries in Nigeria. This forms the research gap which the outcome of this work tends to bridge by creating a fresh awareness among stakeholders in the power sector about the need for proactive measures towards minimizing recurrent system induced losses by ensuring improved efficiency of the country's distribution network. The resulting reliable and adequate electricity supply to the industrial sector will make the sector more vibrant thereby growing the country's gross domestic product (GDP) and creating more employment opportunities for the nation's teeming populace.

OVERVIEW
OF THE SAMPLED DISTRIBUTION NETWORKS

Eko Distribution Network
The Eko distribution network shown in Fig. 2 comprises of the Agbara and Badagry Injection substations both of which are supplied from the 2 x 45 MVA, 132/33/11 KV transformer transmission substation at the load centre. The Agbara Injection substation rated 2 x 15 MVA, 33/11 KV feeds Beecham, Evans, OPIC, and other 11 KV outgoing feeders while the Badagry Injection substation rated 15 MVA, 33/11 KV feeds Unilever, P&G, Nestle and Guinness industrial feeders.

Kano Electricity Distribution Network
The Kano Electricity Distribution network shown in Fig. 3

Port Harcourt Distribution Network
The Port Harcourt Electricity Distribution network shown in Fig. 4

METHODOLOGY
Data and diagrams on the sampled distribution networks were collected from the three electricity distribution companies located in Nigeria's three major industrial cities under review. The distribution companies are: Eko Electricity Distribution Company (EKEDP) in Lagos city for

Mathematical Formulation of Newton-Raphson Powerflow Equations for Distribution System
The Newton-Raphson formulates and solves iteratively the following power flow equation: For a system of n buses and bus 1 designated as slack bus, the equations which relate the changes in active and reactive power to changes in bus voltage magnitude and angles take the form [7], The set of equations (4) for all the n-1 buses can be written in the following matrix form, The real and apparent powers at the buses are expressed as: The incremental values of these powers are as follows: The elements of the Jacobian are written as, The Newton-Raphson algorithm for power flow studies [7] is outlined as follows: The flow chart for Newton-Raphson method using polar co-ordinates is given in Fig. 5. Tables 1 -3 shows the maximum power losses due to the injection substations of the sampled distribution networks. During the period 2011-2015 covered by the study, the Agbara/Badagry Injection substation in the Agbara distribution network in the city of Lagos showed a maximum power loss of 15.8 MW (Table 1). During the same period, the Sabon Gari/Dakata Injection substation in Sabon Gari distribution network in Kano City recorded a maximum power loss of 36.2 MW (Table 2) while the Akanni/Trans-Amadi Injection substation in the Port Harcourt distribution network in the Port Harcourt City showed maximum power loss of 6.04 MW (Table  3). It is obvious from the Tables therefore that the power losses in each network increased yearly. This phenomenon is attributable to yearly increases in load and number of overloaded transformers and other distribution components due to lack of regular inspection, preventive maintenance and absence of infrastructure upgrade [4][5][6].

Power Losses in the Distribution Networks
As can be observed from the Tables also, the highest maximum average power losses during the 2011-2015 period occurred on Gezewa feeder in the Kano distribution network, while the least values were reported on the Rumurolu feeder in the Port Harcourt distribution network. The high value of power loss (16.17 MW as shown in Table 2) on the Gezawa feeder is attributable to the significant length of the feeder (405 Km). Recent studies [1,8] have shown that 7 attributable to the significant length of the feeder (405 Km). Recent studies [1,8] have shown that the longer the distribution feeder lines, the more the power that gets dissipated due to I

Fig. 5. Flow chart for load flow studies using Newton-Raphson method in polar co-ordinates [7]
Article no. BJAST.29910 the longer the distribution feeder lines, the more gets dissipated due to I 2 R losses.

method in polar
Other factors that could be responsible for the differences in the power losses in the sampled distribution networks are increase in load, lack of good maintenance culture, aging, pattern of energy use, load density, high rate of illegal connection to the feeder resulting to overloading and then capability and configuration of the distribution system that vary for various system elements [1,9,10,11]. Figs. 6-8 show the average power losses in the respective injection substations during the 2011-2015 period.  As shown in Fig. 9, Transformers T1 and T3 in the Agbara/Badagry injection substation in the Agbara distribution network of Lagos City were loaded to 118% and 104% respectively in 2011 of the rated capacities. Similarly, Transformers T4, T15, T16 and T27 (Fig. 10) in the Sabon Gari/Dakata injection substation of Sabon Gari electricity distribution network in Kano City were loaded to 142%, 239.5%, 159.5% and 120.7% of the rated capacities respectively during the same period. However, as shown in Fig. 11, the transformers in the Akanni/Trans-Amadi injection substation in the Port Harcourt distribution network were loaded within limits of the rated capacities during the period covered by the study. High power losses have been traced to overloaded power transformers [4][5][6]. It is obvious that the relatively low power losses reported in the Port Harcourt distribution network is due to controlled loads on the power transformers.
There is urgent need therefore to reduce the existing loads and ensure balanced loading on the overloaded transformers in the Agbara/ Badagry and Sabon Gari / Dakata injection substations in the Agbara and Sabon Gari distribution networks in Lagos and Kano cities respectively so as to minimise power and energy loss levels and consequently achieve improved electricity supply reliability in the areas covered by the affected distribution network substations. Besides its negative impact on Utility companies turn-over, high distribution losses are known to scare potential investors away from investing in the power sector [1,2,12]. Results of the study showed that between 2011 and 2015 covered by the study, the Eko electricity distribution network in Lagos recorded a total power loss of 15.8 MW, the Sabon Gari electricity distribution network in Kano reported 36.2 MW while the Port Harcourt distribution network reported 6.04 MW. The results of the simulation further reveal that a significant number of power transformers in the Agbara/Badagry and the Sabon Gari/Dakata injection substations are overloaded well beyond their rated values thus contributing to high power losses in the host distribution networks. This paper recommends that weak electrical facilities in the distribution network should be identified and strengthened to make them function better. Shunt capacitors should also be installed at appropriate points in the network in order to improve the system power factor. It is necessary to ensure reduction in the length of low tension transmission lines by relocating the existing distribution substations. Old conductors and distribution lines/cables should be promptly disposed of, only conductors and lines of appropriate sizes should be in use. Lengthy distribution lines cause high technical losses and must be avoided. Efforts should be made to avoid overloading of the feeders by ensuring balanced loads at all times. Transformers are responsible for almost half of network losses, it is advisable therefore to reduce the number of transformers in use. Using fewer but highly efficient transformers can make a significant impact on reduction of technical losses. Besides serving as a guide for utility companies in providing for prioritization and system upgrade to ensure improved efficiency of their distribution networks, the outcome of this research would find relevance among policy makers and researchers especially system planners at the distribution subsystem of power sectors.