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By Oluseye Ojo
The Nigerian Independent System Operator (NISO) has dismissed claims by the Association of Power Generation Companies (APGC) that the June 25 power disturbance amounted to a national grid failure.
It insisted that the incident was a localised voltage instability confined to the Lagos axis and not a total system collapse.
In a statement made available to journalists, yesterday, NISO described APGC’s publication on the incident as misleading and technically inaccurate
It argued that the information presented did not reflect the actual operational realities of the power system or the provisions of the Nigerian Grid Code.
According to the system operator, the disturbance was detected early and contained through coordinated interventions by its operators, supported by network protection systems and emergency procedures.
It said the prompt response prevented the fault from spreading to other parts of the national grid, while electricity supply in the affected Lagos area was progressively restored.
NISO also aligned its position with an earlier explanation by the Transmission Company of Nigeria (TCN), maintaining that the incident was a localised voltage instability rather than a nationwide grid collapse.
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Responding to APGC’s interpretation of system frequency, voltage and generation data, NISO said quoting isolated minimum and maximum values recorded during a disturbance without the appropriate operational context created a misleading impression of system failure.
The operator explained that under the Nigerian Grid Code, the national grid normally operates within a frequency range of 49.75Hz to 50.25Hz, while the acceptable operating voltage for the 330kV transmission network ranges between 280.5kV and 346.5kV.
It added that the code anticipates temporary deviations from these limits during faults or other stressed operating conditions before corrective actions restore stability.
According to NISO, the Grid Code also provides that, under severe system disturbances, frequency may temporarily fall below 48.75Hz or rise above 51.25Hz.
The operator explained that during such transient events, generating units are required to remain connected to the grid for frequency excursions between 47.50Hz and 51.50Hz for up to 15 seconds to help stabilise the system.
It further stated that the temporary reduction in electricity generation highlighted by APGC formed part of deliberate operational measures taken by the System Operator to protect the integrity of the grid and prevent a cascading nationwide outage.
Reaffirming its statutory responsibility for operating, monitoring and safeguarding the national grid, NISO said it welcomed constructive engagement from stakeholders but stressed that real-time operational information should come from authorised sources.
It urged market participants, policymakers and members of the public to rely on its official communications for verified information on grid operations.
The operator also pledged to continue implementing the Nigerian Grid Code and international operational standards to strengthen the reliability, stability and efficiency of electricity supply across the country.
