The power load calculation method includes: using the coefficient method, the unit product power consumption method, the required coefficient method, and the binomial coefficient method. China generally uses the coefficient method and the binomial coefficient method. The former is suitable for determining the calculation load of the whole plant, the calculation load of the workshop substation and the load calculation of the main line with stable load; the latter is used for the main line or branch line with large load fluctuation. In the actual design and practice, the calculation of the calculation coefficient and the characteristic parameters of the electric load calculation will affect the calculation result of the electric load, making it too large and high.
The correct calculation of the power load is very important. It is the basis for correctly selecting the wires, switchgear and transformers in the power supply system. It is also an important part of ensuring the safe and reliable operation of the power supply system. In the design and preliminary design, the calculation of the electric load is too small or too large, which will cause serious consequences. If the calculation of the electric load is too small, it will cause the power supply line to overheat and accelerate the aging of the insulation. At the same time, it will consume too much energy, causing the electrical circuit to escape fire and causing a major accident. If the calculation of the electric load is too large, the transformer capacity will be excessive, and the cross section of the power supply line will be too large, and the corresponding protection setting value will be set too high, thus reducing the sensitivity of electrical equipment protection; at the same time, the electric load calculation has been calculated. Big also increased investment and reduced the economics of the project.
Generally speaking, when the power load value is greater than 10% of the actual load, the transformer capacity will increase by 11% to 12%, and the consumption of non-ferrous metals such as wires and cables will increase by 20%, and the transformer will be increased. Active power loss caused by power. It can be seen that the electric load calculation is important in the power supply design, especially when determining the transformer capacity. Therefore, the correct selection of the calculation load method and characteristic parameters is of particular importance for electrical design.
Power Load Calculation Method Overview The change in power load is subject to a variety of factors and is difficult to express with a simple calculation formula. In the actual engineering calculation work, the commonly used methods include the coefficient method, the utilization coefficient method, the binomial coefficient method, and the unit product power consumption method to calculate the electric load in the power supply design of industrial enterprises.
1. Using the coefficient method based on the average load, the relationship between the maximum load and the average load is analyzed by probability theory.
2. When the power consumption method of the unit product is compared with the power supply plan in the preliminary design stage, it can be estimated according to the unit power consumption quota of the workshop, the annual output of the product and the number of working hours per year.
3. The binomial coefficient method considers the empirical formula of the number of electrical equipment and the impact of large-capacity equipment on the computational load.
Since there are multiple sets of different types of electrical equipment on a trunk line or a workshop, it should be divided into several groups of power equipment according to the nature of its work (the power consumption of a group is the same). Therefore, the load calculation should be divided into single group calculations, and then the total calculation of multiple groups, the calculation formula is as follows:
(1) The calculation load of a single group of electrical equipment is the same as that of the same group of electrical equipment, and the names and capacities of the machines are not necessarily the same.
(2) Computational load of multiple sets of electrical equipment In a group of electrical equipment, considering the factor of maximum load overlap of the largest x equipment, it is impossible for multiple sets of electrical equipment to overlap the maximum load of all the largest equipments. Generally only consider a set of maximum additional loads.
4. Demand coefficient method The demand coefficient method does not consider the load fluctuation caused by the maximum load of large-capacity equipment and the capacity and number of electrical equipment. It is suitable for determining the calculation load of the whole plant, the calculated load of the substation and the stable calculation of the load of the main line. .
When several sets of electrical equipment with different properties are branched on one trunk line, multiple sets of total load calculations need to be performed on the basis of group calculation.
(1) The calculation load of a single electrical equipment determines the calculation load of a single electrical equipment. The purpose is to provide a basis for selecting the branch line cross-section, and the input power at full load operation should be used as the calculation load.
(2) Calculation load of the power equipment group There are many power equipments in a workshop. When calculating the load, the power equipment should be divided into several groups according to the classification method on the required coefficient table, that is, the process properties are the same. The electrical equipments with similar coefficients are required to be combined into a group, and then the load calculation of each power equipment group is performed.
Several factors affecting the calculation results of electric load are too large and high. The following five problems can be found from the feedback from design to operation.
1. The problem of grouping needs to be selected by the coefficient and the countermeasures. The “required coefficient†of the electrical equipment group recommended by some industries in the current design manual is based on the high level, which is caused by considering the excessive development margin of the enterprise. result.
In another case, the designer lacks the relevant industry grouping needs coefficient, and lacks the necessary research and investigation. When the coefficient is selected by experience, Ningda is not small, and it is often overestimated and the calculation result is too large and high.
The following countermeasures can be taken for the above phenomenon.
1) When using the value recommended in the design manual, it is advisable to use the “average value†or the “lower limit†according to the specific situation. Generally, the “upper limit†should not be adopted.
2) When there is a lack of industry calculation factors, the same type or approximate industry survey results should be conducted to correctly select the value of the value.
2. The value of the load factor calculated by a single device in the coefficient method has the following differences:
1) The motor that runs continuously, which is the rated power specified on the nameplate.
2) Intermittent repetitive working motor, the power of the rated power should be calculated according to the actual situation.
3) For the rated power of electric welders, electric furnaces, electric heaters and electric lamps, it is the input power.
3. The problem of selecting the maximum simultaneous use factor is to determine the sum of the calculated capacity of the workshop substation or the total substation of the whole plant, that is, when there are multiple power plants or groups of electrical equipment. Consider multiplying the active and reactive maximums by using the coefficients k:w and k:.
According to the data, the coefficient is basically quoted from foreign materials, and these countries are often more developed in the power industry, and the energy is relatively rich, so the coefficient of use is often high.
Therefore, when using the "simultaneous use factor", the simultaneous use factor can be reduced as appropriate according to the characteristics of different industries.
0.9 to 0.75, which can reduce the calculation load by 5% to 15%. It can be seen that reducing the "co-use coefficient" is the key to reducing the total calculation load.
4. Selection Principles Appropriate use of calculation methods is a fundamental measure to reduce the computational load. The specific selection principles are as follows:
1) As mentioned above, in the actual engineering calculation, the two methods of using the coefficient method and the unit product power consumption method are generally not used.
Although the coefficient method has a certain theoretical basis, the calculation steps are complicated because of the large number of coefficients to be determined, and the data of “maximum coefficient gas†and “utilization coefficient k†in the formula are currently lacking, so usually work at work. This calculation method is not used in many cases.
The load of the electrical equipment obtained by the unit product power consumption method may be quite different from the actual load. Therefore, in the absence of the formal power equipment capacity, the calculation is performed according to the “required coefficient methodâ€. In order to achieve a more realistic calculation load as much as possible, as the basis for selecting power distribution equipment and wires.
2) The coefficient method is relatively simple and therefore widely used. However, when the number of electrical equipment is small and the power difference is very different, the calculation result of the coefficient method is often too small, so it is not suitable for low-voltage distribution line calculation, but suitable for calculation. , the load of the power distribution station.
3) The binomial method considers two factors: 1 average load. The additional load caused by the overlap of the maximum load of the 2x maximum equipment is used to make up for the lack of the calculation result of the coefficient method in the above case.
Because the binomial coefficient method not only considers the average power of the maximum load of the electrical equipment, but also considers the additional impact of the equipment with the largest capacity on the total computing load. Therefore, the binomial method is more suitable for determining the load calculation of low-voltage trunk lines and branch lines with fewer equipments and larger capacity differences. However, the binomial calculation coefficient (experience coefficient) b, c and x values ​​lack sufficient theoretical basis, and these coefficients are only suitable for the machining industry. Other industries lack this data, which limits their citation.
Therefore, it is more accurate to use the binomial coefficient method to determine the calculation load for the main line or branch line with large load fluctuation. When determining the calculation of the workshop substation and the total load of the whole plant, it is usually not used, or the "required coefficient method" is closer to the actual power consumption than the "binomial method".
5. The problem that the electrical equipment is separated from the actual and high and large is found to be solved by the craftsman. Otherwise, in the load calculation, the calculation coefficient should be reduced when selecting the group “required coefficient†or “simultaneous use factorâ€. The method is to lower the load calculation value to ensure reasonable selection of transformers and other power supply and distribution equipment, so as to be safe and applicable and save energy.
Conclusion In summary, in the electrical design practice, the power consumption method and the utilization coefficient method of the unit product are usually not used in the calculation load method, and the coefficient method is required to calculate the load of the transformer and the power distribution. The binomial coefficient The method is in accordance with the load calculation of the traversing main line or branch line, so the correct selection of the calculation load method is fundamental and directly affects the result of the load calculation. At the same time, whether the characteristic parameters in the load calculation are reasonably selected will also make the calculation load too large or too small.
Therefore, selecting appropriate calculation methods for various types of electric power loads and correcting them with corresponding countermeasures can significantly reduce the calculation results, ensuring safety and reliability, and obtaining economic benefits of energy saving and capital saving.
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