In centralized power system transmission networks are built to evacuate bulk power from generating station typically situated away from load centers to points of injection into the distribution network.
For efficient (reduce losses) delivery of this power, it is important that the voltages are increased exponentially in order to reduce loss and to increase the ability of the line to evacuate more power.
For proper administration of the system, you will then require a primary transmission network and secondary transmission network. In Nigeria 330kV is the primary transmission voltage and 132kV the secondary transmission network. This configuration differs in the different countries e.g. 400kV and 220kV in East Africa
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