•Blackout
The Nigerian Independent System Operator (NISO) has attributed recent reductions in electricity allocations to Distribution Companies (DisCos) serving Lagos, Abuja and northern Nigeria to multiple transmission line outages and constraints on the national grid.
NISO, in a clarification issued on the development, said the disruptions reduced available transmission capacity and forced adjustments to power allocations as part of measures to keep the interconnected electricity network within safe operating limits, reports Daily Independent.
The system operator stressed that the availability of electricity generation does not automatically mean that the power can be delivered to a particular location, noting that the ability to transfer electricity depends significantly on the availability and capacity of transmission infrastructure.
According to NISO, its real-time monitoring, coordination, control and dispatch responsibilities require it to continuously assess transmission capacity and network configuration before determining safe generation dispatch and load allocation.
It said the Lagos axis was particularly affected by successive outages involving the Olorunsogo–Ayede 330kV Line 1, Benin–Egbin 330kV Line 1 and Benin–Omotosho 330kV Line 1, alongside the prolonged outage of the Osogbo–Ikeja West circuit.
“The cumulative loss of these critical circuits reduced the transmission transfer capability into the Lagos axis,” NISO said.
Consequently, the operator reviewed and curtailed load allocations to Eko Electricity Distribution Company (EKEDC), Ikeja Electric Distribution Company (IE) and Sakete international supply, based on the network configuration and prevailing system-security requirements.
The northern corridor also experienced significant transmission constraints following the tripping of the Shiroro–Mararaba 330kV Line 1 between August 24 and 26.
NISO said the outage affected power allocation to Abuja and northern parts of the country because the remaining circuit had to carry the load.
The situation worsened at 6:47am on August 27 when the Shiroro–Mando 330kV Line 2 and Mando–Jos 330kV Line 1 tripped simultaneously.
At the time, NISO said, the Mando–Jos line was the only available transmission circuit serving Jos and the North-East, while the alternative Apir–Lafia 330kV Lines 1 and 2 had been out of service for an extended period because of faults.
The simultaneous outages caused a significant reduction in transmission supply to Jos and the North-East. The subsequent separation of the bus at the Mando Transmission Substation further changed the network configuration and restricted power transfer to affected northern load centres.
As a result, NISO said it had to revise and curtail allocations to Kano, Kaduna, Jos, Yola and other affected areas to keep the remaining network within secure operating limits.
The Abuja axis also experienced a temporary transmission constraint on August 29 after the Shiroro–Katampe 330kV Line 1 and Gwagwalada–Katampe 330kV Line 1 tripped simultaneously at about 3:55am.
According to NISO, both circuits were restored within hours, with the Shiroro–Katampe line returning at 7:25am and the Gwagwalada–Katampe circuit at 7:20am, allowing the affected transmission capacity to be recovered.
The system operator said the incidents underscored the interconnected nature of Nigeria’s electricity network, where an outage involving a critical transmission circuit can affect power supply far beyond the immediate location of the fault.
It explained that when transmission constraints or changes in network configuration limit the safe transfer of available generation, it may have to temporarily redispatch generation, curtail load or revise DisCo allocations.
NISO therefore said the recent changes in electricity allocations should be understood as consequences of transmission line outages, constrained transfer capacity and prevailing network configurations, rather than a shortage of available generation.
The clarification comes amid changes in electricity allocations to DisCos serving major load centres, with NISO seeking to place on record the operational circumstances behind the adjustments.
The operator maintained that adequate generation alone cannot guarantee improved electricity supply to consumers, stressing that sufficient transmission capacity and a secure network configuration are equally necessary to move available power to where it is needed.
