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The protection of polar flammable liquid storage tanks from fire is an important matter related to the safe production of enterprises and to the safety of people’s lives and property. Although the foam fire-extinguishing system has long been the main means for the fire protection of flammable liquid storage tanks, the influence of the physical properties of polar flammable liquids on the fire-extinguishing characteristics of alcohol-resistant foams has not been well studied, which causes many problems for engineering design. In the present work, 14 kinds of polar flammable liquids were used to carry out non-ignition tests and alcohol-resistant foam fire-extinguishing tests. The results show that water-miscible and water-immiscible polar flammable liquids exhibit significant differences in their interactions with the alcohol-resistant foams under non-ignition conditions. A lower specific gravity and a higher heat of combustion of polar flammable liquids will result in a longer time needed for fire control, and a higher saturated vapor pressure of polar flammable liquids will result in a longer time needed to extinguish the edge fire. In addition, the tests show that the forceful application of alcohol-resistant foams is not conducive to extinguishing fires involving polar flammable liquids and cannot even control the fires.

With the rapid development of the Internet in this era, the traditional power grid is no longer able to meet the growing demand of the people for electricity. In order to realize a new generation of power system with comprehensive sensing, reliable transmission, intelligent processing and interconnection, the State Grid proposes the strategic goal of developing ubiquitous power IoT. Firstly, the concept and basic architecture of ubiquitous power IoT are elaborated, and then the main key technologies of the architecture of power energy consumption monitoring and management system are explained. The power quality parameters are measured and calculated, and the G1 method, which is computationally small and does not require consistency testing, is used to determine the subjective weights in the power quality evaluation process, which can truly reflect the power quality level of power grids in different regions. The information entropy method is used to determine the objective weights in the process of power quality evaluation to solve the error of artificially determined weights, and the combination of subjective weights and objective weights can more truly reflect the influence of each index on the comprehensive level of power quality. The results of the study show that PV is rated between 2 and 3 good when grid-connected and off-grid, and wind turbines are rated between 3 and 4 medium when grid-connected and off-grid. The results of the integrated assessment levels are in line with the actual situation and can meet the growing demand for electricity.

A three-phase three-wire voltage source converter (VSC) can produce third harmonics when it is operated under an unbalanced condition. It is essential to understand the mechanism of the production of this third harmonic and to assess its impact on power systems. Therefore, this paper presents an analytical model of the VSC under the unbalanced condition through mathematical derivations, and the final model is a coupled Thevenin circuit. The proposed model allows for direct computation of the non-characteristic third harmonics through harmonic power flow studies. The results show that VSC under unbalanced conditions emits both positive-sequence and negative-sequence third harmonics, and that the positive-sequence third harmonic is much larger than the negative-sequence third harmonic. It also shows that the unbalanced level and the size of the dc-link capacitor are critical to the level of non-characteristic third harmonics. The correctness of the proposed model and its application on noncharacteristic third harmonic evaluations have been verified using EMT simulations.

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