Planning and Operation of Electricity Distribution Networks Speaker: Engr. Ezonfade, Percy Speaker: Engr. Ezonfade, Percy Project M anager, Lilleker Bros. Nig. Ltd At the NEF2017 Annual Conference/ Exhibition
Table of Contents 1.0 Introduction and General Overview of an Interconnected Power System as it Applies to Nigeria 2.0 Features of Planned Power Distribution System 3.0 Basic Problems and Challenges in a Typical Overhead Line Distribution system 4.0 Recommendations for Improved Distribution Practice 5.0 Conclusion/ Remarks 2
1.0 Brief Introduction and General Overview of Power System 1.1 The power system in Nigeria that is of a distributed generation system interconnected in a National Grid 1.2 The generating stations generate at 11kv or 33kV 50Hz or any other similar generator specs as the case maybe, depending on the unit size of the generator and the Genco busbar specs 1.3 The generating stations connect to Transmission or the National grid at 330kV or 132kV 1.4 Transmission connects Distribution at 33kV as standard in Nigeria 1.5 Distribution connects consumers at 33kV (for some industrial consumers), 11kV (for many commercial off-takers with dedicated transformer greater that 500kVA). 1.6 Residential or other type consumers with substation capacities less than 500kVA are presently connected at 415/ 240volts 50Hz in a system largely described as overhead Low Voltage Distribution System. Some distributions concerns are now upgrading to M V distribution system at 11kV to reduce tech losses. These systems have much smaller substation unit capacities typically at 50kVA to 100kVA max. 1.7 Our National grid code specified 11kV or 33kV 50Hz at generation, 132/ 330kV 50Hz at transmission and 11kV / 415/ 240volts 50Hz at distribution/ consumer level. 1.8 The unbundled power sector in Nigeria comprises the Generation Companies (Gencos), the Transmission Company (TCN) and the Distribution Companies (Discos) 3
1.9 Typical Power System Arrangement – Illustration 1 Typically Coal, gas or hydro turbine stations are available in Nigeria. Several of these are connected together in the National Grid System 4
1.10 Typical Power System Arrangement – Illustration 2 D T T T I 5
2.0 Features of A Planned Power Distribution System 2.1 Distribution in an unbundled power system is the technical and commercial activities of the business entity saddled with the responsibility of receiving power from the grid, connecting consumers and billing. 2.2 Distribution must work or carry out this task in the most efficient manner that reduces losses (commercial and technical) to the barest minimum such that a planned distribution system is a designed distribution system. 2.3 Distribution sells the power generated by the Gencos that they would have received via Transmission and pays everyone through the market operator. 2.4 Effective planning of distribution system is required at the onset for the business thereof to be profitable and mutually beneficial to the power off-takers/ consumers as well the Discos. 2.5 A planned distribution system is system where the consumers are metered with operative vending system for the prepaid consumers. 2.6 A planned distribution system should deliver on the grid code, i.e. deliver the authorized and specified supply voltage to consumer meter board. Anything less is a technical gamble. A distribution system that does not achieve this singular objective is a failed system that would also have impact on its overall profitability. 2.7 A planed distribution system should therefore afford the Disco the opportunity to carry out tech and commercial evaluation of any off-taker’s request for connection before deciding on how best to connect them. 6
2.0 Features of A Planned Power Distribution System Cont’d. 2.8 In the planning or design of overhead distribution systems like we have in Nigeria, it is necessary to tropicalize and derate the aluminum conductors in use due to heavy sagging occasioned by the high currents and temperatures within the tropics. A 20-30% derating factor is typical for most practical purposes. Some Nigerian wires and cables may already be tropicalized. 2.9 Distribution planning engineers should therefore consult data sheets of the cables and wires they are given to use on them projects. 2.10 M ost of the low voltage problems experienced at the distribution outlets are traceable to operators negligence for not checking what they are receiving from the network and making adjustments at the power transformers to compensate for any significant drops in voltage. 2.11 A properly planned distribution system should also then be efficiently supervised and manned and provided with sufficient logistics support to respond to emergencies especially in our overhead line system. 7
3.0 Challenges in our Present day Distribution System 3.1 A major drawback of overhead distribution system is the attendant low reliability index. 3.2 In an unbundled system there are clear cut responsibilities amongst the major players in the sector namely the Discos, Gencos and Transmission. 3.3 Due this split in management responsibilities, a Disco may be called upon to receive power for their districts and they would say no as they are not bound to take your power either, and in most cases without giving any reasons. The reality however is that they don’t have the capacity to evacuate or distribute the power due to the general decay in distribution infrastructure. 3.4 Unbundled power sector has led to less integration in the system. The unbundled management style places more emphasis on the services they offer and getting paid for those services in the end and at a price they agree with. 3.5 Exorbitant Tariffs. Discos have been having running battles with the sector regulators on tariff issues. While I do not think the problems of the sector can be resolved by charging higher tariff structures, I believe that the Discos are not earning enough money due to their inability to expand or maintain their facilities; occasioned by low revenue base on account of reduced quality of services. 8
3.0 Challenges in our Present day Distribution System cont’d 3.6 Lack of sound maintenance. M ain distribution facilities such as transformers are not being replaced as and when due or when they fail. The only visible maintenance efforts you probably see is fault tracing and restoration of supplies. So if your transformer fails you will have to replace it by yourself is a common thing in the industry. 3.7 There is a general decay in electricity distribution infrastructure in the country that need urgent attention and the federal and state governments who are still major stake holders should be prepared to address this problem for the sector to survive the times. This is because Investors didn’t inherit much in the first place, though equipment failures have gone worse under their watch. 3.8 Today distribution is being funded by a few consumers who can afford the high tariffs compared to buying diesel for their generating sets; and through estimated bills, the rest is paid by the general public, though they may have no idea how much electricity they consumed during the month. 3.9 Lack of meters. M etering is below 50% with most Discos and this gap needs to be reduced and eventually erased. 3.10 There is pervasive unemployment in the sector with the Discos retrenching most of the staff they inherited at the onset. Some say the wage bill is too high and so they want down sizing to shed weight and survive or they just employ less experienced staff which cost them much less. This high level of unemployment created by retrenchments in the last two years is unacceptable and portends danger for the sector which shows that it is not a healthy sector. 3.11 Another good performance indicator is the thriving diesel genset sales and maintenance business in the country. An equally thriving power sector can erase this extremely high cost of power in the country . 9
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