Nigerian Independent System Operator
The Nigerian Independent System Operator has attributed recent reductions in electricity allocations to Distribution Companies serving Lagos, Abuja and northern parts of the country to multiple transmission line outages that constrained the capacity of the national grid.
The system operator said the outages forced it to adjust generation dispatch and power allocations to ensure that the remaining transmission network operated within safe limits and to prevent a wider system disturbance.
In a statement signed by its management on Sunday and titled, “Clarification on Recent Changes in Power Allocations Following Transmission Line Outages,” NISO said the changes were caused by transmission constraints and not a shortage of generation.
The clarification came amid concerns over changes in power allocations to DisCos in some parts of the country.
NISO said, “The Nigerian Independent System Operator wishes to provide clarifications on the recent changes in power allocations to Distribution Companies serving the Lagos, Abuja and Northern corridors. The changes in allocations occurred due to multiple transmission line outages that affected available transmission capacity and configuration of the network at different times. Adjustments were made in the course of normal system operations to ensure that the interconnected network remained within secure operating limits.
“The availability of generation does not, by itself, guarantee that the available power can be delivered to a particular load centre. Power transfer is dependent on the availability and capacity of transmission infrastructure and the prevailing configuration of the network.”
NISO, which is responsible for real-time monitoring, coordination, control and dispatch of the interconnected Nigerian Electricity Supply Industry, said it continuously assessed the transmission network before determining how much electricity could safely be delivered to different areas.
The operator 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, while the Osogbo-Ikeja West circuit remained out of service for an extended period.
According to NISO, the cumulative loss of the critical transmission circuits reduced the amount of electricity that could safely be transferred into the Lagos area.
It consequently reviewed and curtailed allocations to Eko Electricity Distribution Company, Ikeja Electric and the Sakete international supply, based on the prevailing network configuration and system-security requirements.
The northern corridor was also affected by transmission failures.Explanation On Reduced Power Allocations To Lagos, Abuja, North ~ NISO
NISO said the Shiroro-Mararaba 330kV Line 1 tripped between August 24 and 26, affecting electricity allocation to Abuja and the northern part of the country because the remaining circuit had to carry the load.
The situation became more critical at 6:47am on August 27, when the Shiroro-Mando 330kV Line 2 and Mando-Jos 330kV Line 1 tripped simultaneously.
NISO said the Mando-Jos circuit was then the only available transmission line 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 outages significantly reduced transmission supply to Jos and the North-East and altered the network configuration following the separation of the bus at the Mando Transmission Substation.
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 was similarly affected on August 29 when the Shiroro-Katampe 330kV Line 1 and Gwagwalada-Katampe 330kV Line 1 tripped simultaneously at 3:55am.
The operator, however, said the two circuits were restored shortly afterwards, at 7:25am and 7:20am, respectively, allowing the affected transmission capacity to be recovered.
NISO said the incidents demonstrated the vulnerability and interconnected nature of the national electricity network, where a fault on a single critical transmission circuit could affect electricity supply far beyond the location of the fault.
It stated, “Generation availability does not automatically translate into deliverable power to Distribution Companies. Adequate transmission capacity and a secure network configuration are equally essential.”
The operator added that where transmission constraints prevented the safe transfer of available generation, it had to temporarily redispatch generation, curtail load or revise DisCo allocations.
It said, “Accordingly, the recent changes in power allocations resulted from transmission line outages, constrained transmission capacity and system configuration prevailing at the respective times, rather than being attributed to generation availability.”
