In all Power Systems, voltage is a localized issue, while voltage may be low at heavily loaded points of the system, it can simultaneously be high at another point where the same system is lightly loaded. 
In Nigeria grid, the Operational Procedure stipulates that the acceptable limits of the nominal value of our highest voltage in the grid which is 330kV ranges between +5% & -15% of the nominal i.e 346.5kV and 280.5kV .

The voltage problem in Lagos was as a result of inadequate generation from Egbin Power Station sequel to gas inadequacy. Egbin, with a capacity of 1,320 MW came into existence to cater for Lagos load which is a commercial Centre (heavy loaded area) and to simultaneously improve the voltage in that axis of the grid.

Effective voltage control is that which regulates voltage with resources closest to the point of voltage problem, since ideally VAR deficiency is best met at point of need. Generator AVRs are the most important means of voltage control in power systems. Due to insufficient gas at Egbin, only 2 units are fired and these could not generate enough VARs to meet up with the voltage requirements in the area hence the manifestation of the low voltage. As it stands, Egbin daily average generation is just 350MW, while the Lagos daily average consumption from the grid in recent times is 1,100 MW. At least, 800MW has to be imported from other parts of the grid to meet this power demand.

Before the gas issue is fully addressed, which will permit Egbin Power Station to play its double of providing adequate power supply to Lagos axis and stabilizing the voltage, Eko/Ikeja DISCOS should deploy power factor correction devices to maintain 0.95 power factor in accordance with grid code. 

Egbin Power Station