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The Nigerian Independent System Operator (NISO) has attributed recent changes in power allocations to Distribution Companies (DisCos) serving the Lagos, Abuja and Northern corridors to multiple transmission line outages and constraints in the national grid.
NISO, in a statement signed by its Management on Sunday said the affected transmission lines reduced available transfer capacity and altered the configuration of the network at different times, necessitating adjustments to power allocations to keep the interconnected system within safe operating limits.
The system operator explained that the availability of electricity generation does not automatically guarantee that the power can be delivered to a particular load centre, stressing that effective power transfer depends equally on the availability and capacity of transmission infrastructure as well as the prevailing network configuration.
According to NISO, its responsibility as the Independent System Operator includes the real-time monitoring, coordination, control and dispatch of the interconnected Nigerian Electricity Supply Industry (NESI).
It said it continuously assesses available transmission capacity and network configuration to determine safe generation dispatch and load allocation.
NISO said the Lagos complex was affected by successive outages of 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.
It said the cumulative loss of the critical circuits reduced transmission transfer capability into the Lagos axis, forcing a review and curtailment of allocations to Eko Electricity Distribution Company (EKEDC), Ikeja Electric Distribution Company (IE) and the Sakete international supply.
The adjustments, it added, were made in line with the prevailing network configuration and system-security requirements.
On the Northern corridor, NISO said the Shiroro–Mararaba 330kV Line 1 tripped between August 24 and 26, affecting power allocations to Abuja and the Northern part of the country as the load had to be supplied through the remaining circuit.
The situation became more critical at 6:47 a.m. on August 27, when the Shiroro–Mando 330kV Line 2 and Mando–Jos 330kV Line 1 tripped simultaneously.
NISO said the Mando–Jos line was at the time the only available transmission circuit serving Jos and the North-East, while the alternative Apir–Lafia 330kV Lines 1 and 2 had remained out of service for an extended period due to faults.
The simultaneous outage resulted in a significant loss of transmission supply to Jos and the North-East, while the separation of the bus at the Mando Transmission Substation further altered the network configuration and constrained power transfer to affected northern load centres.
Consequently, NISO said power allocations to Kano, Kaduna, Jos, Yola and other affected areas had to be revised and curtailed to keep the remaining network within secure operating limits.
For the Abuja axis, NISO said the Shiroro–Katampe 330kV Line 1 and Gwagwalada–Katampe 330kV Line 1 tripped simultaneously at 3:55 a.m. on August 29.
The two circuits were subsequently restored at 7:25 a.m. and 7:20 a.m., respectively, allowing the affected transmission capacity to be recovered.
The system operator stressed that the incidents demonstrated the interconnected nature of Nigeria's electricity network, where an outage on a critical transmission circuit can affect power transfer to areas beyond the immediate location of the fault.
NISO maintained that generation availability alone could not translate into deliverable power to DisCos without adequate transmission capacity and a secure network configuration.
It said where transmission constraints or changes in network configuration affect the safe transfer of available electricity, it may temporarily redispatch generation, curtail load or revise DisCo allocations to maintain system security and prevent wider network disturbances.
NISO therefore clarified that the recent changes in power allocations were caused by transmission line outages, constrained transmission capacity and prevailing network configurations, rather than generation availability.
The clarification, it said, was issued to put the facts on record and provide the public with a clear understanding of the circumstances surrounding the recent changes in power allocations.