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Fuzzy comprehensive state evaluation of housing of silicone rubber insulators based on level difference maximization

Wang Sihua, Chen Long, Zhao Lei, Wang Junjun

Archives of Electrical Engineering

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2022

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Vol. 71, nr 1

57--74

EN

The aging of composite insulators in outdoor operation for a long time has a direct impact on the safe and stable operation of the power grid. To solve this problem, fuzzy comprehensive evaluation of composite insulators based on level difference maximum is proposed. To verify the feasibility of this method, insulators in Xinjiang are sampled and the index evaluation system for composite insulators is established based on electrical, mechanical, hydrophobic and other properties, combined with operational years, geographical environment and other factors; Firstly, different membership functions are established according to index types. It is more likely to determine the grade of insulator by comparing measured data with the boundary value. Then, to solve the problem that weights cannot be effectively integrated in the combination weighting, level difference maximization is proposed (during the operation of insulators, the index which has a greater influence on the performance of insulators takes a higher proportion of the weight). Finally, on the basis of fully considering the clarity and ambiguity of grade division, the grade state of insulators is obtained by using the linear weighting method. The results show that compared with the traditional method, the improved method of the membership function and level difference maximum can realize the dynamic adjustment of the index based on the degree of information change. The method can better evaluate the insulator grade. The case study shows that the model can accurately and quickly judge the state of composite insulators, which can be used as a reference for manufacturing and maintenance departments.

2

Multiphysics simulation and shed structure optimization of catenary icing insulator

Wang Sihua, Wang Junjun, Zhou Lijun, Chen Long, Zhao Lei

Archives of Electrical Engineering

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2021

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Vol. 70, nr 3

675--688

EN

It is not easy to make the insulators of the railway catenary for the dry and cold environment of the icy Qinghai-Tibet plateau, without causing serious ice-related flashover accidents. To study the operating status of catenary icing insulators, a two-dimensional icing model of catenary cantilever insulators was established based on the winter environmental characteristics of the Golmud station on the Qinghai-Tibet Railway. Compared different directions of ice growth, the spatial electric field distribution, and surface temperature distribution characteristics of icing insulators were analyzed by multi-physical field coupling simulation. The results show that as the thickness of the ice layer increases and the length of the icicle increases, the field intensity of the insulator gradually increases, and the surface temperature continues to rise. When the ice edge grows vertically downward, the electric field intensity of the insulator is the smallest, and the electric field intensity is the largest when the ice edge grows horizontally. Although the surface temperature of the insulator will rise with the increase of icing degree, it is lower than the freezing point and will not have a great impact on insulation performance. Secondly, when the cantilever insulator is arranged obliquely, the increase in the inclination angle will cause the electric field to increase and the temperature to rise slightly, so the inclination angle of the oblique cantilever should be reduced as much as possible during installation. Finally, the insulator with better insulation performance is obtained by optimizing the structure of the flat cantilever insulator.

3

A control method of fault current in MT-HVDC grid based on current limiter and circuit breaker

Wang Sihua, Zhao Lei, Zhou Lijun

Archives of Electrical Engineering

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2021

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Vol. 70, nr 4

907--923

EN

In order to realize selective isolation of fault lines in multi-terminal high voltage DC (MT-HVDC) grids, it is necessary to ensure that the sound lines can still transmit power normally after the grounding fault occurs in a DC power network. If the fault line needs to be cut before the converter is blocked, a DC circuit breaker (DCCB) with large switching capacity is often required. At present, the extreme fault over-current and the high cost of DCCBs have become the prominent contradiction in MT-HVDC projects. Reducing the breaking stress of power electronic devices of the circuit breaker and controlling its cutting-off time are the major difficulties in this research field. In this paper, a topology of a hybrid DCCB with an inductive current limiting device is proposed. By analyzing its working principle, the calculation method of key parameters is given, and a four-terminal HVDC grid is built in a PSCAD/EMTDC platform for fault simulation. The results show that compared with the traditional circuit breaker, this topology can effectively limit the rising speed and maximum current of fault current when the system fails, and quickly remove the fault line, so as to meet the suppression requirement of the HVDC system for fault current.

4

Study on the Structure and Properties of Continuous Basalt Fibres

Shi Fengjun, Su Hang, Zhao Lei, Yu Xiuyan, Li Shengxian

Fibres & Textiles in Eastern Europe

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2020

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Vol. 28, no. 4 (142)

52--56

EN

The chemical composition, X-ray diffraction, thermal properties, flammability, mechanical properties and morphology of basalt fibres are investigated in this paper. Chemical analysis and energy dispersive X-ray fluorescence spectrometer experiments showed that basalt fibre is a kind of aluminosillicate fibre which is mainly composed of oxides such as SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, P2O5 and so on. X-ray diffraction indicated that the bulk structure of the fibres is non-crystal with a short range order but no long range order. SEM observation found that basalt fibre is circular in cross-section and smooth in the longitudinal direction. Solubility experiments revealed the superior resistance of the fibre to acids, alkaline and organic solvents. DGA demonstrated there are three weight loss stages in the process of elevating temperature. They are, respectively, evaporation of moisture in the fibre at about 100 °C, decomposition of the residual carbonate minerals between 480 °C and 630 °C, and decomposition of newly generated carbonates between 850~995 °C. On the heat flow curve, there are also three endothermic peaks, where the first and second correspond to the last two stages of weight loss and the third to the melting process of the fibre, whose onset is from 1122.14 °C, reaching a peak value at 1194.96 °C, and ending at 1380 °C. The tensile strength of basalt filaments and staple fibre was measured. Tensile and shear properties of the fibre were also tested.

PL

W pracy zbadano skład chemiczny, dyfrakcję promieniowania rentgenowskiego, właściwości termiczne, łatwopalność, właściwości mechaniczne i morfologię włókien bazaltowych. Analiza chemiczna i eksperymenty ze spektrometrem rentgenowskim z dyspersją energii wykazały, że włókno bazaltowe jest rodzajem włókna glinokrzemianowego, które składa się głównie z tlenków, takich jak SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, P2O5, itd. Dyfrakcja rentgenowska wykazała, że struktura objętościowa włókien jest niekrystaliczna z uporządkowaniem bliskiego zasięgu, ale bez uporządkowania dalekiego zasięgu. Obserwacja SEM wykazała, że włókno bazaltowe ma kołowy przekrój poprzeczny i gładki w kierunku wzdłużnym. Eksperymenty z rozpuszczalnością wykazały lepszą odporność włókna na kwasy, zasady i rozpuszczalniki organiczne. DGA wykazało, że istnieją trzy etapy utraty masy w procesie podwyższania temperatury. Są to, odpowiednio: odparowanie wilgoci we włóknie w temperaturze około 100 °C, rozkład resztkowych minerałów węglanowych w przedziale 480-630 °C oraz rozkład nowo wytworzonych węglanów w przedziale 850-995 °C. Na krzywej przepływu ciepła występują również trzy endotermiczne piki, przy czym pierwszy i drugi odpowiadają ostatnim dwóm etapom utraty masy, a trzeci proces topienia włókna, którego początek wynosi od 1122,14 °C, osiągając wartość szczytową przy 1194,96 °C, a kończąc na 1380 °C. Zbadano także wytrzymałość na rozciąganie włókien bazaltowych.