High-energy-consuming metallurgical enterprises, such as electrolytic aluminum and large-scale chemical industries, often have their own power plants due to their high load. In normal operation, the power generated by the captive power plant can meet production requirements. Generally speaking, the power generation price of the captive power plant does not include the cost of long-distance transmission, so the power cost generated is lower. This is the root of many current metallurgical enterprises in China. But this does not mean that these companies can completely separate from the operation of the big grid. Large power grids provide safe backup power for high-energy-consuming enterprises that have captive power plants.
Similar to high-energy-consuming enterprises, newly built industrial parks in many developing countries often have their own rotating power generation equipment due to lack of electricity support. For example, emerging Southeast Asian countries such as Bangladesh and Myanmar, with the increase in the cost of human resources in China's manufacturing industry, many labor-intensive enterprises have moved to these regions. However, due to the long-term lack of infrastructure, power supply in industrial parks is generally a major consideration in the planning stage.
Whether it is due to the company's own cost considerations or the insufficiency of the infrastructure itself, grid companies have provided safe backup power for these high energy-consuming users. What is more important is that the high demands of continuous production by metallurgical and chemical companies determine the necessity of such a standby. When a captive power plant jumps or mass dumps, these users will draw a lot of power from the grid, or, conversely, send large amounts of excess power to the grid. Without the protection of large grids, we know that these microgrid systems will immediately collapse in the event of unbalanced power.
Grid companies certainly do not provide these users with backup free of charge. In China, electric power companies charge fixed fees for enterprises or industrial parks that have captive power plants according to reserve capacity. The greater the reserve capacity, the higher the fee charged, and the proportion of growth is not linear, and it is likely to be of an exponential nature. When the user generates a power supply problem on its own, whether it is a power generation fault or abnormal load removal, if the power grid exceeds the safety reserve capacity, the power grid company will cut off the contact with the user in a very short time. At the same time, the backup of the grid to the users is asymmetrical, that is, the standby for the Internet and the backup for the next network are often different. This is because the grid itself also needs to consider safety and stability issues. Big fluctuations, especially online fluctuations, are a huge and stable risk to the grid.
How to ensure that these high-energy-consuming enterprises or industrial parks balance their power needs? How to reduce the backup demand of these users to the grid as much as possible, so as to further reduce the charges for the reserve capacity of the grid and reduce the cost of energy for the enterprise? These are issues of general concern.
How to achieve energy (power supply) balance?
The private power plant of an enterprise or an industrial park forms a tiny power system in a specific area, which has the same problems as the large power system in many aspects, but it is in a different form.
The balance of the power system generally considers three states: steady state, dynamic, and fault conditions. The difference between dynamic and fault states is that the dynamic is that the system is in a small fluctuation state that can withstand for a short time. For example, a small load switching within the unit's rotating standby range, or the auxiliary unit's own failure, results in a decrease in output. and many more. The fault state is a large load fluctuation outside the standby range of the system, such as accidental tripping, accidental load shedding, and power transmission failures caused by power system failures.
Steady state balance
The electro-hydraulic regulating valve of the power plant unit can control the valve opening of the steam turbine. These minor adjustments are performed in the DCS system of the unit, silently tracking the small changes in the load and keeping the entire microgrid generating power at all times. Consistent with the load. Its control principle is to track system frequency changes and adjust power generation output. In addition, there is the excitation system of the generator and the PSS controller. The voltage and reactive power of the system are constantly adjusted to meet the set value.
dynamic balance
When the steady state balance is broken, often the professionals will call it that the load fluctuation exceeds the scope of the “one frequency modulation”, the dispatch control system of the microgrid will put automatic power generation to control the AGC function and adjust the output of the generator. For example, in electrolytic aluminum, steel or chemical industry, the input of some ore furnaces has a very large instantaneous load impact, and the system frequency drops. At this time, the role of AGC is to issue instructions to increase the output of the unit, and the unit DCS will increase the coal mill accordingly. The supply of powder, or powdered or other forms of fuel, is adjusted on a large scale, not only by the redundant treatment of steam itself. We call this dynamic adjustment "secondary frequency modulation."
Fault balance
In the event of an accidental trip, load shedding or transmission failure, the relative steady state of the system is broken. At this time, rapid response is required. When the power generation capacity disappears in a large scale, we must remove the load corresponding to the approximate matching capacity. When a large amount of load is lost, the corresponding generator set must be removed.
It is very difficult to hope to achieve this kind of fault balancing. It is often necessary to consider possible faults and corresponding countermeasures from the beginning of the micro-grid construction planning.
Fortunately, through recent practice , Nuri Group has completed several cases of successful fault balancing of microgrids and even regional grids. Its main tasks include:
- Systematic Stability Modeling at the Planning Stage
- Formulate system stability strategy (safety plan)
- Installing a microgrid stability controller
- Simulation Test
- Real accident drills
How to achieve economic operation?
Many high-energy-consuming enterprises and industrial parks are concerned about how to pay less to the power company. First of all, it is necessary to minimize the occurrence of the above-mentioned fault conditions and strengthen the management of the operation and maintenance of the equipment; even if a failure occurs, the failure time should be minimized and the operation resumed as soon as possible; some metallurgical or chemical industries that require continuous production need to establish precise stability control. Measures.
In addition, considering the economy, the first is the price factor. In many countries and regions, time-of-use pricing measures are used. During the peak hours of the day, the grid price is high, and there are substantial discounts at night. Industrial parks or enterprises can comprehensively consider that if the cost of power generation is higher than the night power price of the power grid, the general strategy is to generate as much electricity as possible during the day and try not to purchase electricity from the system; at night, use the power grid price advantage to reduce or arrange the maintenance of the unit and many more. It is unrealistic for these tasks to completely rely on manual adjustments and an economic dispatch system is needed.
Another effective measure of economic operation is the use of renewable energy, such as the installation of rooftop photovoltaics, the use of wind power, etc. If the park or enterprise occupies a large enough area, the capacity of these resources may be very large. However, the problems caused by new energy sources are also very significant. They are all intermittent and energy storage is currently very expensive. Therefore, forecasting the generation of new energy sources is also a problem that needs to be paid attention to in the system balance.
The core solution of NARI's weakly connected power grid in high-energy-consuming enterprises / parks
OPEN-3000 Energy Management System EMS
The device can take emergency control measures and corrective control measures to ensure the safe and stable operation of the power grid after the power grid is subjected to large disturbances. It is the key equipment for ensuring the safe and stable operation of the power grid.