By Dr. (Mrs.) Joy Ogaji
Nigerians are now used to the incessant grid collapses in the power sector occurring mostly over the weekend, and public holidays with no clear explanation as to the causes.
Arguably, electricity forms an indispensable part of modern life especially on weekends, when families try to catch up and relax.
The nation is often thrown into relative chaos during these periods with the attendant monetary setbacks as hospitals, airports, train stations etc., are all grounded into a halt. The volatility of the national grid portends serious risk for the Legacy Generating plants, NIPP plants and other IPPs operating in the sector.
The actual reasons which trigger the incessant grid collapses are relatively unknown, and we believe the triggers can only be established if a thorough technical investigation is conducted, and made public to ascertain if these are as a result of human error, negligence or other factors.
Undoubtedly, the transmission networks constitutes the vital channels of the entire power value chain. It goes without saying that the “growth of the power sector is contingent to development of a robust and a non-collapsible transmission network”.
The current transmission network is characterised by such existential conditions such as aging network, obsolete substation equipment, overloading of certain transmission corridors, poor operations and decrepit maintenance culture, etc., all these clearly portend a network plagued with huge infrastructural challenges.
Research has shown that Outages/grid collapses occur when there are system disturbances along the transmission grid. Such disturbances could include a massive drop of load from a sub-station that would cause the grid to become unstable.
This could be solved in most cases with adequate spinning reserve in place. Experts have advised that the Nigerian grid requires up to 400 MW of spinning reserve to be stable. The reality is, there is no spinning reserve procured currently in the market; notwithstanding TCN’s constant reminders to the regulator (NERC) to procure about 260MW which though below the estimated figure, could be a starting point.
One of the main causes of grid instability is Frequency roaming engendered by either load rejection or uninstructed generation/overload. While the first stage solution is compulsory for all GenCos, i.e. operating on “Free Governor Mode (FGM) in accordance with the grid code specification” to enable effective control of the frequency accordingly, the second Stage solution is calling up of “Spinning Reserve” from the incentivized providers.
The non-responsiveness of the regulator to this critical issue is what is unhealthy, given the technical, commercial and economic effects of the frequent grid collapses in a regulated market such as the Nigerian Electricity Supply Industry (NESI).
TECHNICAL AND MECHANICAL EFFECTS OF GRID COLLAPSE
Frequency deviations out of tolerable zones are not only damaging the units but also increasing considerably, the maintenance costs close to three times the normal maintenance costs.
The following are some of the effects:
The intervals between mandatory maintenance will decrease and will need longer time for completion.
The downtime of the generating units will be greater, while damaged units will need extra investment without increasing the power plant capacity.
It causes creep of compressor and turbine blades, as well as cracks on exhaust sleeves,
Irregular heating and cooling cycles of hot gas path components that is fatigue damage;
cracks in ceramic tiles of the combustion chamber; defective gas control valves due to wear and tear; defective instrumentation devices which include thermocouples, RTD’s, pressure transmitters which necessitate purchases in foreign currencies of replacement parts from OEM and, accumulation of large Equivalent Operating Hour (EOH) with corresponding low actual operating hours, which shorten the time to inspect without actually having generated enough income from the gas turbine.
It can also cause resultant wear and tear in the machines mechanical rotating parts and
malfunctioning of electrical controls and protective relays.
Burnt coils, motor contactors, electric motors are observed in the plant. The damaging effect is experienced on Steam Turbine Blades, Hydro and Combustion Turbines, as well as on other Power System Equipment on Active Power flows.
For a Kaplan hydro unit control, guide vanes regulate the flow of water delivered by the penstock. The guide vanes are always responding to the signal from the governor.
Dr. Ogaji is the Executive Secretary, Association of Power Generation Companies,