Also referred to as "ingredient". 1. Grading, 2. substances contained.
[Southern Dynasty and Song Dynasty] Luo Han《 Rejuvenation theory 》"If there is a certain number of characters, then we have elements. If there is something that cannot be destroyed, then we can become nothing. If there is something that cannot be destroyed, then it cannot become me." Refers to the various substances or factors that constitute things.
writing reformer 《 History of Chiduxin 》3： "There are also many academic inventions, such as: X-ray, chemical atomic lithium, medical treatment of cancer, etc." Ba Jin Capriccio · The Role of Literature:“《 The Dream of Red Mansion 》Although it is not the author's autobiography, there is always an autobiographical element. " Xie Juezai's On Independent Thinking: "When you eat, you should absorb nutrients into the organs of your body and turn them into strength." Class attribute defined according to the nature of the main source of income of an individual within a certain period of time.
Liu Shaoqi 《 On the Cultivation of Communist Party Members 》7： "People who join our Party not only have different family backgrounds and own composition, but also come with different purposes and motivations." In order to improve the operation management level of thermal power units and achieve energy saving and consumption reduction, the one-sided evaluation of the operation status of thermal power units with a single operation index will be improved Principal component analysis It is applied to the comprehensive evaluation of units. This method improves the limitations of the traditional principal component analysis method in high-dimensional index evaluation, retains the information about the difference in the dispersion of unit operation index data, reduces the dimension of the evaluation index, obtains the principal component of unit operation, and then conducts comprehensive analysis and evaluation. The example analysis verifies the effectiveness of this method. It has reference value for power generation groups on how to implement energy-saving operation optimization, index assessment and competition of thermal power units. [1] Principal component mathematical model
With n Samples, each sample has p Observation indicators, respectively X one ， X two ，…， X p Represent, get the original data matrix X =[ X one ， X two ，…， X p ]Principal component analysis is to analyze p The question of indicators is transformed into a discussion p The linear combination of these new indicators Y one ， Y two ，…， Y m ( m≤p ）, which fully reflects the information of the original indicators and is independent of each other according to the principle of retaining the main amount of information.
Comprehensive indicators determined based on the above conditions Y one ， Y two ，…， Y p They are called the first principal component, the second principal component p Principal components. Among them, the proportion of each comprehensive index in the total variance decreases in turn. In actual research, in order to simplify problem analysis, the first few principal components with the largest variance are usually selected. [1]
Improvement of mean value of principal component analysis
Because the original indicator data contains two parts of information: first, the difference information of the dispersion degree of each indicator is reflected by the variance of each indicator; The second is the information on the degree of interaction between indicators, which is reflected by the correlation coefficient matrix. However, in the above traditional principal component analysis method, when eliminating the impact of indicator dimension and order of magnitude, the standardized method is used to process the original data. After standardization, the variance of each indicator is equal to 1, making the difference of each indicator in the degree of dispersion the same, so that the relationship between each indicator and the principal component tends to be the same, Then the influence of the difference in index dispersion on the principal component is obliterated. Therefore, the principal component extracted from the standardized data cannot accurately reflect all the information contained in the original data. Based on the above reasons, the following data averaging can be considered at this time: after the original indicator data is transformed with the trend X= ( x ij ) n×p 。
From covariance matrix Proceed to principal component analysis. It can be proved that the average processing does not change the correlation coefficient between the indicators, and all the information of the correlation coefficient matrix is reflected in the corresponding covariance matrix. [1] In order to study the pollution flashover characteristics of insulators with different pollution components, XP − 160 standard porcelain insulators were taken as the research object, and the flashover voltage and integral conductivity of insulators with different salt density and different pollution components were measured through artificial pollution tests. The results show that with the decrease of NaCl mass fraction and CaSO four The flashover voltage of insulator string will increase significantly with the increase of mass fraction; When the pollution density of soluble substances is fixed, the concentration of CaSO four With the increase of mass fraction, the integral conductivity value decreases; According to the contribution of different pollution components to conductivity, the mixed salt converted into equivalent NaCl cannot fully explain the impact of pollution components on insulator pollution flashover voltage, so the physical and chemical characteristics of different components and their impact on arc development should be considered when conducting natural pollution tests. The research results can provide reference for the design and selection of external insulation of transmission lines. [2]
Influence of Pollution Components on Flashover Voltage
The conductivity of the polluted layer on the insulator surface is different under different pollution components, so its electrical performance is also different, which will make the flashover voltage of the insulator differ greatly under the same SCD. The flashover voltage of seven XP − 160 insulator strings under different pollution components and SCDs was measured. It can be seen that:
- one
The standard deviations of the test results are all less than 7%, indicating that the dispersion of the pollution flashover voltage measured in this test is small.
- two
When the pollution components are the same, regardless of the mass fraction of NaCl in the soluble salt, the flashover voltage decreases with the increase of salt density. If the mass fraction of NaCl is 50%, when the salt density is 0.05, 0.10, 0.20mg/cm two The flashover voltage is 112.7, 96.6 and 88.2 kV respectively, and gradually decreases.
- three
Pollution flashover voltage increases with the decrease of NaCl mass fraction in pollution components, such as ρ SCD =0.20mg/cm two When all soluble salt components are NaCl, the flashover voltage is 60. 2kV； When the mass fraction of CaSO4 increased to 20%, 50%, 80% and 100%, the flashover voltage increased by 17.5%, 27.2%, 40.1% and 71.8%, respectively.
- four
By comparing the flashover voltage values under different pollution degrees, it can be seen that the flashover voltage of polluted insulators has an obvious relationship with the content of conductive substances in the polluted layer. Because the conductivity of NaCl and CaSO4 dissolved in the pollution is different, the electrical performance of insulators is also different, that is, the conductivity of the polluted layer has an impact on the flashover voltage. [2]
Influence of Pollution Components on Integrated Conductivity
Apply effective value of U To measure the leakage current flowing through the dirty layer I , then the ratio of power frequency leakage current to applied voltage is the integral conductance G = I / U 。
For the influence of different pollution components on the conductivity of insulator pollution layer, a single XP − 160 insulator is taken as the research object. After the average value of multiple effective integrated conductivity values is obtained, the value corrected to 20 ℃ is taken as the integrated conductivity value under the pollution degree. The integrated conductivity value of XP − 160 insulator measured by the test is taken as the integrated conductivity value. It can be seen that:
- one
The standard deviations of the test results are all less than 7%, indicating that the integral conductivity values obtained from the test have a small dispersion.
- two
When the pollution components are the same, regardless of the content of NaCl in the soluble salt, the integral conductivity increases with the increase of SCD. If NaCl mass fraction is 80%, when ρ SCD 0.05, 0.10, 0.20mg/cm two Its integral conductivity is 6.64 μ S, 10.21 μ S and 21.32 μ S, respectively.
- three
When the SCD is fixed, with the decrease of NaCl mass fraction and the increase of CaSO4 mass fraction in the pollution component, the value of the integrated conductivity of the pollution layer is decreasing. For example, in ρ SCD 0.10mg/cm two When all soluble salts are NaCl, the integrated conductivity of insulator is 12.82 μ S; When the mass fraction of NaCl decreases to 80%, 50%, 20% and 0, the integrated conductivity decreases by 1.71, 3.28, 4.87 and 7.28 μ S respectively. The reason is that NaCl is easily soluble in water to form ions after the dirty layer is saturated and wetted, which significantly increases the conductivity of the dirty layer. CaSO4 is a insoluble substance with poor solubility in water. Because the water absorbed by the dirty layer is limited, only a small amount of ions can be ionized, and the conductivity is relatively weak. Therefore, the higher the NaCl content in the pollution component, the stronger the conductivity of the pollution layer and the greater the integral conductivity. The value of integral conductivity reflects the influence of different pollution components on the electrical performance of insulators.
- four
By comparing the integrated conductivity and flashover voltage of insulators under different pollution levels, it can be concluded that the flashover voltage will decrease significantly with the increase of the integrated conductivity of insulator surface. [2]
Analysis of Influence of Pollution Components on Flashover Characteristics
Under the same SCD, the pollution flashover voltage is significantly different due to the different NaCl mass fraction in the pollution component, but the integrated conductivity value reflects the actual conductivity of some dissolved substances in the pollution, so the integrated conductivity value under different pollution degrees can be used for conversion to obtain the salt density value when the pollution component is equivalent to pure NaCl.
According to the data when the soluble pollution is 100% NaCl, the relationship between integrated conductivity and salt density (SDD) can be obtained.
With the decrease of NaCl mass fraction in the pollutants, the effective salt density value gradually decreases. Due to CaSO four The solubility of CaSO is poor, so under the same salt density value, CaSO four The higher the mass fraction, the smaller the contribution to the conductivity of the contaminated layer. [2]
The effective salt density value under different pollution components can obtain the calculated value of insulator flashover voltage under different pollution components U f *, and the value obtained from the test U f Compare and get the relative error ε =(( U f － U f *)/ U f )×100%。
The flashover voltage calculated according to the effective salt density value through the formula differs greatly from the flashover voltage obtained from the test, with a general error of about 15%, and the maximum error of 30.6%. It can be seen that the impact of pollution components on insulator pollution flashover voltage cannot be fully explained only based on the impact of pollution components on the conductivity of the polluted layer. The reason may be that when measuring the integrated conductivity of insulator pollution layer, the applied voltage is low, and the polluted layer does not form an arc, then the electrolyte dissolves and ionizes in the solution, forming a conductive layer, The conductivity of the dirty layer is greatly affected by the pollution components. NaCl is a strong electrolyte, which can be completely dissolved by a small amount of water, while CaSO four yes Weak electrolyte From the perspective of ion balance, its ionization is a reversible process. During the ionization process, Ca 2+ Or SO four 2- The reduction of ion concentration will also promote its dissolution and ionization. Since the ionic activity coefficient will be affected by the concentration of other ions in the solution, the dissolution and ionization of electrolyte will be affected by the coexisting ions. CaSO four The solubility of will increase with the increase of NaCl concentration. [2]
