The effect of temperature and field strength on the resistivity of transformer oil
Safety operation of total ultra-HVDC transmission system could be directly affected by the operation reliability of converter transformer which is one of the most important equipments in the system. The transformer oil is the main liquid dielectric medium in the converter transformer. Thus, it is significant to study the dielectric properties of the transformer oil. In this paper, the dc resistivity of transformer oil under different conditions has been systematically investigated, and then the temperature and field strength were the test parameter variables. The variation range of temperature was 25~80°C, and under each temperature point the field strength changed ranging from 0.5V/mm to 10kV/mm. Meanwhile, 15 min is selected as the duration of testing resistivity. In this paper, the authors obtained the systematical data points and analysis curves of resistivity under different temperature and field strength, and obtained a empirical equation which describe the relationship between resistivity, temperature and field strength. It enhanced the understanding of the resistivity for transformer oil and provided the theoretical and test basis to expand the engineering application of this transformer oil.
Resistivity of pressboard immersed in mineral insulation oil
The pressboard is an important solid insulation dielectric in AC-DC converter transformers. Thus, it is very significant to understand the dielectric properties of the oil-impregnated pressboard. In this paper, the volume resistivities of oil-impregnated pressboard under different conditions have been systematically investigated. The pressboard was immersed in two kinds of mineral insulation oil, respectively. The measuring device of resistivity was full of oil and isolated from outside. All samples were measured at temperature range of 25-80°C under the field strength range of 1-30kV/mm. The influences of the temperature and the field strength on the resistivity of oil-impregnated pressboard have been investigated. The results of the volume resistivity of oil-impregnated pressboard showed that the resistivity of oil-impregnated pressboard decreased with the increase of temperature, and the activation eneregy increased with the increase of field strength. Meanwhile, with the increase of field strength, the resistivity changed slightly at first and then decreased significantly.
Work, Status, and Income: Men in the American Occupational Structure since the Late Nineteenth Century
The historical record rarely presents researchers with precisely the evidence they desire. This is particularly true for social historians and like-minded scholars, whose subjects left precious few signs of their passing. Consequently, certain data have borne a disproportionate evidentiary load in social-historical research. The occupation a person pursued is one key piece of information on which scholars have come to depend. Our understanding of the historical social structure and where people fit into it is bound up with the interpretation of occupations. But this reliance on occupation as the primary social locator in historical research depends on some largely unexamined premises. Whether scholars group occupations or convert them into numerical status measures, they make assumptions about the nature of the occupational structure. When researchers incorporate change over time into their analyses, they suggest that the meaning of occupations remained stable for the purpose of measuring social mobility, class position, or group status-attainment. This assumption has been the subject of little discussion and even less research. For all the use to which historians have put occupation, there has been little effort to assess systematically its stability as a social or economic indicator.