By Aloaye Wilson Alli, PhD MBA FNSE REng
System Collapse is now a familiar term to most Nigerians living in the urban areas, no thanks to the constant grid power outages throwing Nigeria into dark ages. Nigeria is grossly underserved, with the lowest per capita wattage globally.
Nigerian experienced three System Collapses in two weeks, and at the time of the third occurrence, the grid had not been fully restored up to its basic wheeling capacity put at 5.5GW as it was still being progressively loaded with available generated power.
How much do we know about these problems plaguing the grid? What is this concern all about? Why does it occur at all? Is the problem insurmountable? Lots of unanswered questions. This paper is only an attempt to explain this problem to all understanding, and this paper is devoid of any description of power engineering technical terms, phenomena, and associated expressions.
The national grid is the high voltage (HV) wheeling transportation segment of the electrical Power System, an integral part of the Nigeria Electricity Supply Industry (NESI) and a significant aspect of the power sector. The grid comprises all networked power generation systems (thermal or hydro plants) connected by various transmission lines (electrical Conductors) to the transmission substations across the country.
Substations are the electrical power network (grid) points where transmission lines and distribution feeders are connected through circuit breakers (Special HV switches) via various bus bars configurations and Transformers.
These various substations configurations enable the network’s control, grid infrastructure maintenance, and power flow management. Power arriving at any designated Transmission Substations is subjected to transformations or stepped down for distribution through various feeders to the distribution network injection substation. It is further transformed for domestic, commercial, or industrial applications through different local transformers or stepped up to be wheeled to the next Substation.
We now have a fair idea of how the power flow from the generators, stepped and then transported via the HV transmission lines to the transmission substations, down to the DisCo Injection Subsection to various local distribution transformers to our homes commercial centres and industrial or manufacturing setups. All through the power voltage, current and quality are professionally managed to be consistent with the grid and system design. Along each route, varied expertise is required to ensure safe power delivery to our homes.
These connections are likened to the human neurons that convey signals and messages to various body organs and systems. The Electrical Power System is the most complicated of any man’s inventions to date, replete with many phenomena, only second to the human being. Unlike the Human, which can relay feelings, and defects (illness), the electrical transmission system relies on many systems, various relays, switches, etc., to enable it to communicate with the environment and other systems within the grid that enables interpretation of the designated Power System. The power is always controlled and managed until it arrives at our homes, and this process requires a lot of considerable skills and competencies.
Why do we have or experience frequent power System collapse?
Nigeria’s national grid is frail; it has been suffering from poor or inadequate investment (Expansions, Upgrades, and lack of organised maintenance Schedule) over decades until the gradual opening of the sector in 2005 to eventual privatisation in 2013. The expected investment, especially the downstream, is lacking.
The power system engineering is about keeping the grid systems in balance, from generation to load centres, management of power voltages, reactive (for inductive loads) and active powers; it is also about balancing the cost of energy and its environmental impact, the balance between the system reliability and the required investment to develop the system. System Collapse is the term used to describe when all the power generating stations connected to the grid either shut down suddenly or simultaneously, resulting in total darkness.
The sudden shutdown may be as a result of a deliberate action as part of standard operating actions or automatically as a consequence of protective measures by the protective relays reacting to any potentially harmful operational development within the power plant or concerned generator; it could be when the gas supply pressure to the turbines suddenly drop which could perhaps as a consequence of gas pipeline vandalism, electric motors, pump either with mechanical issues or reacting to system low frequency that may trigger relay action to protect the engine and generator from damages.
It may be a result of happenings on the grid that are pretty external to the power generating system, such as sudden load drop or load rejections at the distribution end without bringing the System Operator into focus, vandalisation of transmission infrastructures, and equipment short-circuiting, or any action that induces operational pressures on the generator well beyond its designed capability, one of such occasion is when operating frequency deviates from the nominal operating frequency designed for the generator.
In Nigeria, the nominal operating frequency for electrical equipment and generators is 50Hz; however, sensitivity to frequency fluctuations is dependent on the type of power plants; for example, the thermal stations have many pumps and electric motors undertaking many critical tasks and directly facilitating the operations of the power plant engine/turbine and generators performance, these plant types are more sensitive to low frequency than the hydropower plants. Over time, both plant types eventually shut down, and total darkness ensues if no immediate actions are not taken to arrest the cascading effect of low frequency. This necessitated the need to have more hydropower plants on our grids to serve as our baseload power plants.
What would make the frequency drop?
If loads demands are imposed on the grid that is greater than the summed capacity of all the grid-connected power stations, this will result in the system frequency falling; for example, imagine your home with five 5kw (2hp) Air Conditioning units and other basic units powered by 15KVA generator, as you progressively switch on the Ac units, it gets to a point when you hear you generator sound changing, the governing mechanism releasing more fuel, it will get to an end on other loadings, the plant won’t be able to take a further load, the generator shut down.
This is precisely what happens when the grid is overloaded or demand is placed on it; the engine’s fuel governing system automatically demands fuel to meet our needs; when this demand overwhelms the system, it has no choice but to shut down, and this makes worse in our case, that we do not have effective SCADA, EMS, it is a certainty that the grid will be operating within the realm of low frequencies. It is typical for loads must be weaned off the grid to return to stability; when you observe uncontrolled outages in specific communities and light comes, the generator shutdown becomes imminent when this is not promptly discussed.
Another typical grid low-frequency source is when a network segment is vandalised, resulting in a short-circuit; the power plants recognise this scenario as excessive load demand. The relays subsequently initiate progressive engine shutdown until the lines protection relay automatically isolates the compromised part of the network or equipment. When the relay fails, this problem will be cascaded to the generators, and they have the right to self-protection.
Another heartache in restoring the grid after system collapse is the time required to restart a generator. When the engine shuts down, the engine in the thermal plant loses its steam pressure, and it takes a minimum of six hours to rebuild the steam pressure to the operational stage. The grid must be loaded incrementally; it may take more hours to days to completely restore the grid.
Aside from ageing equipment and inadequate transmission infrastructure, vandalism remains the biggest threat to power generation and transmission in Nigeria through gas pipelines vandalism, transmission tower members, and conductor thefts.
Aloaye Wilson Alli is an Energy & Power System Engineer and the CEO/Lead Consultant of Zaaptron Energy Company/Zaaptron Consulting Company, with outlets in Lagos/Abuja. firstname.lastname@example.org