CHAPTER ONE

1.1    Background of Study

The power sector is critical to Nigeria’s growing economy. But for several years, the lack of constant electricity supply has driven businesses to rely on expensive and highly polluting off-grid self-generation alternatives which have led to the closure of some businesses in Nigeria.

The Power systems network in Nigeria is unreliable and contributes to a high number of system collapses and regular outages that we do experience.  Some of the factors affecting the network include right of way negotiation and payments, community/security issues, non-performing engineering, procurement, construction and commissioning (EPCC), high costs of grid-extension/inadequate funding, bureaucracy, huge manpower deficits, poor maintenance of existing infrastructures and vandalisationetc.

Considering the huge investment and timeline required to develop power infrastructures from the generation segment to the transmission and distribution segment; there is need to have a defined budget for proper planning and prompt project delivery towards achieving the objective of stable and efficient power supply to the nation that will lead to industrial and economic development.

The Federal Government of Nigeria had taken steps towards the Restructuring of the Nigerian Power Sector to establish an electricity supply that is efficient, reliable and cost-effective throughout the country and which will attract private investment. A Power Sector Reform Act was therefore enacted in 2005[ ], transferring the public monopoly of NEPA to Power Holding Company of Nigeria (PHCN) which was unbundled into 18 Business Units including eleven (11) Distribution companies, six (6) Generation companies and one (1) Transmission company.

This reform led to the privatization of the generation and distribution segment in 2013 while the transmission segment is still 100% controlled by the government.

According to data from Nigeria Bureau of Statistics, only 25% of the 12,522MW installed capacity reaches the end users due to operational inefficiency and other systemic challenges. As at this moment, the Transmission Company of Nigeria (TCN) celebrated transmission of a new generated peak of 5,375MW out of the over 7,000MW that is operational from generating stations. This has left about 2,000MW of the available/generated power stranded as the National Control Center rejects loads sent by the generation companies. There is a need therefore, to provide more transmission infrastructures towards capturing all generated load to the grid.

Transmission line is one of the three stages that is required towards delivery of power to end-users and it is the connecting link between generating stations and distribution companies and also between different transmission networks.

A transmission line transmits electrical energy in bulk from generation segment to the distribution end. The low voltage generated from power plants is stepped-up to a higher value by using step up transformers to reduce the current and power losses during transmission. The transmission voltages in Nigeriapresently are 132kV and 330kV.The national transmission grid has an installed capacity of 5,758 MW, but its effective wheeling capacity lies at about 4,500 MW (Bada A). The transmission network has a total length of 12,300 km (330 kV is about 5,650 km, 132 kV is about 6.687 km) and connects 32 numbers of 330 kV and 105 numbers of 132 kV substations (Bada A). It is managed by the Government owned Transmission Company of Nigeria (TCN).

Transmission lines can be underground or overhead type but because of the high cost of constructing an underground system, the overhead type is more preferred even though it has its own issues.Overhead power transmission lines form the least cost method of transmitting electrical power as in most cases; the medium of insulation is air (Bayliss and Hardy, 2012).According to an article published by the Public Service Commission of Wisconsin, "The estimated cost for constructing underground transmission lines ranges from 4 to 14 times more expensive than overhead lines of the same voltage and same distance( ).

The construction of high voltage transmission line is complex in nature because it transverses communities/cities unlike the generation and distribution segment which are cited in just a location; this account for reasons why it requires huge investment and any delays encountered during the construction will result in underutilisation of the generated power which cannot get to the end-users (distribution).

The main component of an overhead transmission lines are towers, conductors, insulators and ground wires.The towers, also called structures could be in form of Lattice structure or tubular steel pole and they give support to the conductors from one end to another. The weight of every tower is dependent on the voltage level to be transported and the path or topology of the area. In Nigeria, the weights of 330kV double circuit lines is heavier than that of 132kV and also, the weights of angle towers are heavier than the suspension towers. The suspension tower is clearly the cheapest and the most used tower type all over the world. The purpose of the suspension tower is just to sustain the conductors because there link conductors in a straight line. If some forces are affecting the conductor especially if the line has to take a bend or any form of deviation, the tower type must be changed to the angle tower type or to the tension tower. The angle tower is necessary in a situation where the line changes its direction and so, this tower type is used mostly in corners. The forces of the line are so huge in such situations that a normal suspension tower does not fill the requirements and so, angle tower type is intended for this kind of situation. The tension tower type is a form of angle tower that is designed to handle dead-end situations. This means at least two tension towers are used in every line. These towers are placed to the both end of the line. Weight factor for tension tower is three. This weight factor means it is three times more expensive and heavier than suspension tower because of its steel requirements (Juho Y., 2011). Generally, towers are designed to withstand the loads from both the conductors and wind speed and so, its concentrated forces are transferred to the ground through the tower foundation. The foundation is the name given to the system which transfers various loads to the grounddeveloped by the transmission tower and conductors.The selected foundation design for a particular tower must provide an economical, reliable support for the life of the line. The foundation must be compatible with the soil and must not lose strength with age.

The conductor however, carries the current from one end to another and the choice of what type to use is a function of the voltage level or the loading capacity and cost effectiveness. Generally, the Aluminium Conductor Steel Reinforced (ACSR) has been widely used(even in Nigeria), because of its mechanical strength, the widespread manufacturing capacity and cost effectiveness (EEP, 2019).

The insulators helps to provide electrical insulation between the conductor and the steel structure (towers) under live conditions. The ground wire is what is popularly called “earthing” that is always arranged on top of the conductors to help in reducing voltage induction and protection.

Table 1.1 below shows corresponding wind pressures on towers, conductors and insulators which is one of the main parameters required in tower design.