…Records 5 system collapses in 4 months
By Ediri Ejoh
EXCEPT the Federal Government addresses the deficiency in its spinning reserve, volatile loads and poor investment from the Distribution Companies, DISCOs, the power sector may never escape the continuous system collapse and outages, Energy Vanguard has gathered. This follows the five system collapses in four months witnessed in the country between February and April, 2022. This was confirmed in report – Spinning Reserve to do or not to do? NESI Conundrum: Save our Machines – obtained by Energy Vanguard, weekend.
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Specifcally, the report, stated: “Outages/grid collapses occur when there are system disturbances along the transmission line and the ready solution, which is calling up of ‘spinning reserve’ is not readily available and this is because there few or no incentivized providers of this service. International best practice recommends that 10 percent of the total generating capacity should be allowed for spinning reserve. Thus, the Nigerian grid requires up to 600MW.
“The Instability in the grid over the years has led to several forced outages of the power system and the consequent impact on the economic growth of the country due to unreliable power network. The grid disturbances primarily hinge around variations between generation and demand leading to frequency excursions. Often these frequency excursions are well outside the Grid Code operational limits of 50Hz ± 0.25Hz, and often exceed the ‘system stress’ limits of ±1.25Hz as shown by the snapshot of Nigerian grid frequency excursions.
“The Grid Code Version 02 Titled Frequency Control and Operating Reserve provides in Section 15(1-3) the need for Operating Reserve (additional active power output provided from generating units), which must be realisable in real-time operation to contain and correct any potential power system frequency deviation to an acceptable level. It is imperative to state that an operating reserve or spinning reserve is required to secure capacity that will be available for reliable and secure balancing of supply and demand. Section 15.8.1 states that the Operating Reserves are mandatory and shall be concluded by a contract.
“Nigerian power system requires a minimum spinning reserve that is enough to cover the largest credible trip to secure the network. This is because the grid operators find it nearly impossible to keep the frequency within the Grid code required narrow band. Daily, the frequency varies from 51.5 Hz to 48.5 Hz as against Section 15.3.1 of the grid code, which states that the Frequency shall be maintained at 50 Hz.
“The National Control Centre will endeavour to control the System Frequency within a narrow operating band of +/- 0.5% (49.75 – 50.25 Hz) from 50 Hz, at least 97 % of the time during Normal Conditions. Under System Stress the Frequency Control on the Power System will be exercised within the limits of 50 Hz +/- 2.5% (48.75 – 51.25 Hz).”
The report also noted that the inability of the system operator to maintain grid stability to acceptable technical limits has exposed generator units to perform beyond factory-rated capability. “Frequency deviations out of technical tolerable limits are not only damaging to the units but also are increasing both the machines fixed maintenance cost and variable maintenance costs.”
It said that steel mills form a large chunk of funds both for the DISCOs and the TCN but is detrimental to the generation machines, adding: “It is trite that steel mills create harmonics and cause voltage fluctuations at a very high level. These harmonics create lots of stress on the rotors of the turbines. They create inverse torques on the blades of the rotors producing cracks and distortions.
“The GENCOs have, due to this menace, been saddled with continuously adjusting their AVR. There are too much amount of volatile loads mostly brought by steel mills. Research shows that close to 50 Steel Mills are connected to the Nigeria electric grid. The loads for the Steel Mills vary from 3 to 35 MW depending on the Steel Mills, going from minimum to maximum to minimum in continuous cycles varying within 6 to 10 minutes.”
On low investment from the DISCOs, the report noted that, “the GENCOs do not believe that the DISCOs are significantly improving the quality of their Distribution feeders this will be further buttressed during the upcoming raining season as a high quantity of feeders’ trip during the next raining season.
“Hence, in addition to procuring spinning reserve, there is a need for adequate monitoring and sanctioning of all participants who go outside the grid code specification.”
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