Abstract: the economic operation mode of power grid is based on ensuring the safe operation and power supply quality of power grid and meeting the power supply demand. By comparing and optimizing the operation modes with the least loss between transformers and power lines, under the condition of ensuring technical safety, economy and rationality, we can make full use of existing equipment and components, and through relevant technical argumentation, choose the best operation mode, adjust the load, improve the power factor, adjust or replace transformers, transform the power grid, and reduce the system loss on the basis of transmitting the same amount of electric energy.
Paper Keywords: energy-saving measures; Analysis; transformer loss
Because the power grid loss is mainly composed of transformer loss and power line loss, saving electricity and reducing consumption in power grid transformation is to select and optimize all transformers and power lines in the power grid to form a "safe and economical power grid". There are many loss reduction measures in power grid operation. According to various experiences and theories, the main technical measures to reduce losses are discussed only from several main aspects of economic operation of power grid.
First, rationally transform the power grid and reduce the power loss.
Due to various reasons, the power transmission and transformation capacity of the power grid is insufficient, resulting in "stuck neck" and long power supply radius. These problems not only affect the safety and quality of power supply, but also affect the line loss. On the basis of the transformation of the existing power grid, on the premise of improving power supply capacity and ensuring power supply quality, the line loss of urban and rural power grids is reduced by using optimized quantification technology. For example, old transformers should be eliminated with inferior ones, and new transformers should be selected with superior ones. According to the characteristics of load distribution in urban and rural power grids, the operation positions of transformers and power supply lines should be adjusted to achieve optimal combination, and the economic distribution of loads and the economic operation mode of power grids should be optimized according to the distribution of transformers and power supply lines in power grids. Relying on scientific and technological progress, we should popularize advanced technology with computer application as the main content, and improve the management level of safe and economical power supply in power grid. In the process of urban and rural power grid construction and transformation, it is necessary to optimize and adjust the power supply structure of urban and rural power grids, improve the technical content in the power grid structure, and lay a good foundation for safe power supply of power grids.
(A) Power line loss
According to the principle of economic current density optimization and rationality, two lines can be run in parallel or the cross-sectional area of conductor can be increased (and the cost of power grid can also be increased to some extent). Heavy line load, long power supply radius and circuitous power supply are one of the reasons for the increase of line loss. In this regard, we can add a conductor to the line to make the two lines run in parallel. Increasing the cross-sectional area of the conductor also reduces the resistance of the line, thus reducing the active loss of the line.
(2) Reasonable selection of transformer capacity
Power consumption load in some rural areas in rural power network transformation. The peak load time is short and the light load time is long, so the capacity of distribution transformer should be reasonably selected according to the actual situation of rural power load to avoid the phenomenon of "big horse-drawn car" and reduce the active loss of transformer. According to the single-ended power supply situation of distribution transformer, the distribution transformer should be properly installed in the load center, so that the low-voltage line can be changed from one output to multiple outputs, thus improving the voltage quality and reducing the low-voltage line loss. By adjusting the installation position of the transformer, the voltage quality can be improved and the line loss can be reduced. Choosing energy-saving transformers to eliminate high-energy transformers can minimize the active and reactive losses in transformer operation.
(3) Type and structure of power grid
1, adjust the unreasonable network structure. Reasonable design and improvement of power grid layout and structure can avoid or reduce the staggered, overlapping and circuitous power supply of urban and rural power grids and reduce the phenomenon of excessive power supply radius. Simplify the voltage level of the power grid and reduce the network loss. Each simplification can reduce the first-class equipment, reduce the operation management and maintenance work, and reduce the line loss.
2. Actively apply energy-saving equipment. Most of the distribution transformers in rural power grid provide mixed power supply for domestic electricity and rural power supply, and there are some problems, such as wide peak-valley load, high secondary voltage of distribution transformers in low valley time, and low actual power conversion efficiency of distribution transformers. If the energy-saving distribution transformer phase number automatic transfer switch is installed, the above problems can be solved, thus effectively reducing the no-load and light-load losses of transformers and lines. There are many problems in the distribution transformer, which mainly supplies power for civil life and factories, such as the disparity of peak-valley load, the rise of secondary voltage of distribution transformer and the low efficiency of actual power conversion of distribution transformer. If the energy-saving automatic phase-to-digital conversion switch is installed, the above problems can be solved, thus effectively reducing the no-load and light-load losses of transformers and lines.
3. Simplify the voltage level of the power grid and reduce the power loss. If the voltage can be simplified by one level, the level of equipment can be reduced, the operation management and maintenance work can be reduced, and the line loss can be reduced. The urban load center should introduce high voltage as much as possible, which can shorten the power supply distance of distribution lines. If you have the economic and technical conditions to deal with the boosting transformation of the line, you should reasonably choose the boosting scheme according to the transmission capacity and distance of the line and the development requirements. The boosting investment can be recovered quickly, and it is feasible to properly consider the boosting power supply.
4, choose energy-saving transformer, eliminate high energy consumption transformer. S9 series transformers are low-loss products of domestic 10kV and 35kV power transformers. The transformers with high energy consumption still in use should be reformed, rationally planned, eliminated or updated. In the design of power grid reconstruction, the capacity selection of new transformer should consider not only the capacity utilization rate of transformer, but also the operation efficiency of transformer. The active loss and reactive loss in transformer operation are minimized.
Second, reasonably arrange the operation mode of the transformer to ensure the economic operation of the transformer.
On the basis of ensuring the safe operation and power supply quality of the transformer, the economic operation of the transformer should make full use of the existing equipment, and take technical measures such as selecting the best operation mode of the transformer, optimizing the load adjustment, optimizing the operation position combination of the transformer, improving the operation conditions of the transformer, etc., so as to minimize the power loss of the transformer and improve the power factor of the power supply side. Therefore, the essence of economic operation of transformer is power-saving operation of transformer. Power-saving technology of transformer economic operation is an application technology that closely combines the optimization theory and quantitative calculation method of transformer economic operation with various actual operating conditions of transformer. This power-saving technology does not require investment, and in some cases it can also save investment (saving capacitor investment and reducing transformer investment). Therefore, the power-saving technology of transformer economic operation belongs to the category of knowledge economy, and it is a scientific method to tap the potential of intelligence and management and implement connotative power-saving.
(1) Reasonably calculate the economic load rate of the transformer, so that the transformer is in the best economic operation zone.
Transformer is not the most economical when rated, but the most economical when the copper loss and iron loss of the load are equal, that is, the highest efficiency. For substations with more than two main transformers, the economic operation curve of main transformers should be drawn to determine its economic operation area. When the load is less than the critical load, a transformer will run. When the load is greater than the critical load, two machines will run.
(2) Balance the three-phase load of the transformer and reduce the transformer loss.
The greater the transformer imbalance, the greater the loss. Therefore, it is generally required that the unbalance of low-voltage current of power transformer should not exceed 10%, and the unbalance of initial current of low-voltage trunk line and main transformer branch line should not exceed 20%.
(3) Reasonably configure the economic operation mode of parallel connection and separation of transformers, and optimize the selection of transformer operating voltage taps.
According to the spare transformer, load change law and quantity combination, the transformer operation mode with excellent technical characteristics, parallel and discrete economy is preferred. On the premise of meeting the voltage demand of transformer load side, according to the voltage and load of power supply side in working state, the operating voltage tap of transformer is optimized by quantitative calculation method, so as to reduce transformer loss and improve its operating efficiency.