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The little investigation I conducted into the recent nationwide power outage on Sunday March 7, 2021 clearly indicates an ineffective Automatic Under-Frequency Load Shedding (AUFLS) control system on generation and generation systems. transmission of electricity from Ghana.
In power generation and transmission systems, one of the most important protective measures used to avoid a sudden and complete power outage is the use of the AUFLS (Auto Under Frequency Load Shedding) scheme.
This control system is exactly what Ghana’s power system lacks and needs to be installed with haste to prevent the last Sunday back from happening again.
The purpose of AUFLS is to balance power generation and load in situations where a sudden loss of generation capacity on a system results in a significant drop in the frequency of an interconnect or island area. . In other words, AUFLS serves as a defense mechanism for power plants, particularly effective in stopping the grid frequency collapse in the event of a sudden large loss of production. Exact situation, we are told this happened in Ghana last Sunday which led to the total blackout of electricity across the country. It was preventable but failed.
The Electricity Industry Participation Code specifies that electricity generators must remain securely connected to the grid within a certain frequency range. This, any generator operating outside the frequency range will have to disconnect to protect itself.
In industry, blackout or blackout is considered a prohibited circumstance for generation governors who never want to dream of a power outage, as its repercussion comes at a cost to the country in terms of money and loss of reputation.
Last Sunday afternoon, Ghana Grid Company Limited (GRIDCo) announced a nationwide power outage following a challenge in the power system. In a press release issued by management, GRIDCo said the challenge led to a complete shutdown of their systems, which in turn cut off power across the country.
The information I have gathered so far since this incident occurred indicates that a transient fault has occurred on one of GRIDCo’s critical transmission lines somewhere between Prestea and Obuasi.
This transient fault caused the tripping of Karpower and other thermal power plants in and around the environment of Takoradi. In this case, these factories detected the fault on the system and decided to shut down to protect themselves.
This means that Karpower’s 450 MW plus the power generated by other thermal power plants in the Takoradi region passing through Anwomaso in Kumasi have plummeted, causing a sudden and colossal disruption of the power transmission system.
This situation resulted in putting a very large portion of the additional load on the operating factories being shipped resulting from the significant capacity loss in the system, forcing the active factories to shed the entire load across the country.
Removing this huge load on operating plants has become problematic and unbearable for distributed active generators to cope with sudden and stressful demand, as each plant has its adjustable maximum threshold designed to accelerate in situations where a sudden surge is acceptable. of demand forces them to produce a supplement in order to meet the increased demand. Rather, this situation was an extraordinary different case for the factory to face.
This means that these factories sent online had to spontaneously adjust their production yields to meet the large increase in load due to the loss of production capacity in the Takoradi region.
However, as this expected additional load from the factories being shipped was unbearable, the frequency of the system became a free fall, until it collapsed totally. Blackout!! No way to stop the fall frequency.
Now what should have happened is that if the system had the AUFLS installed and was functioning efficiently, as soon as some power plants were tripped in the Takoradi area causing a painful disturbance in the system, the automatic load shedding of the underfrequency load in place would have served as the police force to stop the falling frequency before it collapsed to the factory trip level.
The AUFLS control system stops the collapse frequency by instantly disconnecting a designated load block / clients from the grid to avoid collapse or blackout.
During the Ghana Black Sunday incident, nothing was in place to effectively disconnect the bulk loads from the national grid until the collapse frequency became stable within the operating range.
AUFLS in Ghana, if at all, was completely unsuccessful in doing its job as planned when the sudden loss of much of the production capacity emerged.
It also means that the same disaster will happen in Ghana next time, if, for example, the thermal power plants in Tema or Akosombo / Kpong were unexpectedly triggered under similar conditions, with any incident in the power system resulting in a similar oppressive disruption. in the transport system. will lead to a blackout because the cannot withstand the strain.
Ghana’s power system does not have a robust protection mechanism capable of automatically disconnecting load blocks from the grid in the event of a loss of a large portion of generation capacity. This is not a good situation. This situation should never happen again.
From the footage, the avalanche of cascading factory failures from Karpower’s factories in Tema, Akosombo yo Kpong continued unabated because the currently installed frequency automatic load shedding is not designed for disconnect the load to balance the voltage and the load, but only communicate with the generating stations to adjust their outputs to meet the changing acceptable demand, but not to connect the loads. It’s not enough.
On Ghana’s recent Black Sunday, Takoradi and Karpower thermal power plants tripped on fault, followed by Tema power plants which also identified the frequency drop as a fault and tripped on frequency collapse. , leaving the Akosombo and Kpong factories alone in the system to transport the whole load across the country.
Akosombo and Kpong factories also saw the situation associated with a sudden drop in frequency as a system fault and ultimately decided to do the same to shut down to protect themselves as well. Hence the nationwide blackout.
This situation can be avoided with an improved and better protection control system.
Question: Could Ghana Black Sunday have been avoided anyway?
The answer is yes, if there was an efficient, robust and comprehensive AUFLS system in place to remove load blocks from the grid when the system identified a significant loss in generating capacity.
Could reserved plants help prevent this blackout?
The answer is no. Reserved installations, even shipped on demand, should start up and achieve synchronous speed before connecting to the national grid. The AUFLS scheme works in microseconds as a protection mechanism. Therefore, there is no time to wait for the reserved facilities to start to meet the demand under the AUFLS trigger. The alleged black Sunday transient fault led to the sudden outbreak of Karpower and others, instantly creating the series of tripping of all other factories within seconds.
At the time the Ghana Black Sunday incident occurred, Akosombo was running on four turbines, generating almost 600 MW and Kpong was also producing around 130 MW. The only thing that could have given the factories shipped enough time to automatically adjust their outputs to minimize the impact of the outage was the AUFLS trigger alone. Unfortunately, this protective mechanism did not exist when the fault occurred.
What happened to the excess installed capacity? This catastrophic outage, as explained in detail above, has nothing to do with excess installed capacity.
Could this have been avoided if the Bui power plant produced substantial power? The answer is, maybe yes, maybe no, depending on the total loss of production capacity compared to the total factories distributed online at that time. It should be noted that by design thermal power plants are very susceptible to transmission system failures and sharp for protection.
Currently, the 400 MW power plant in Bui is experiencing a low inflow which has forced the authority to stop active production.
As we know, the Bui factory is strategically positioned to increase tension levels in Kumasi and beyond. Already with the current situation, there is unbearable stress at the tension levels in Kumasi due to the disabilities of the Bui Dam.
Recommendations.
To avoid the future recurrence of the power outage nationwide in the event of an unexpected large loss in the production system or in the event of a faulty situation, the production regulators and the grid authority should embark on the installation. complete AUFLS control system both at the point of production and at bulk feed substations to activate quickly. Priority load block disconnections until the system is stable Total failure should be avoided.
The maintenance history and test regime of installed AUFLS controls, as performed by qualified control engineers, must be carefully inspected to perform their task when intended.
Large and medium-sized production companies should be encouraged or use other means to get them to install capacitor banks at their point of entry in order to reduce reactive power losses.
Since the Bui Power Plant is not readily available to help increase and control voltage levels in and around Kumasi, the Electricity Authority needs to aggressively engage in battery installation. capacitors in its substations to strengthen voltage level control, to reduce unnecessary load shedding, especially in the Ashanti region.
The authority should encourage independent power producers to see at least one 100 MW power plant in the central part of Ghana, to help maintain the voltage level across Kumasi in the northern part of Ghana.
The authority should also consider encouraging Ghanaians to adopt smart grid, benefit from solar power generation in private homes during the day, with the aim of reducing demand on the grid and controlling the level of electricity. voltage.
Ing. Peter Antwi Boasiako.
London, UK.
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