Aiming at inadequate mechanical properties of Glass ionomer cement (GIC) commonly used in dental clinic, commercial and melt quenched GIC powders as control groups, homemade GIC powder was prepared by sol–gel route and modified by Nb2O5. The GIC samples were characterized by X-ray Diffraction (XRD), particle size analysis, Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR). The compressive strength, Vickers hardness, working and net setting time were tested. The data was analyzed by one-way ANOVA. The XRD results showed that commercial, melt quenched and sol gel GIC powders were similar amorphous. D90 of three GIC powders and Nb2O5 powder were 26 μm, 17 μm, 29 μm and 19 μm respectively. 5% Nb2O5-GIC exhibited the highest values of compressive strength and Vickers hardness, which were 112.93 Mpa, 139.48 MPa and 142.25 MPa respectively, increased 19.11%, 30.56% and 16.51% (P <0.05); the Vickers hardness were 35.15 MPa, 36.23 MPa and 37.62 MPa, increased 18.03%, 29.95% and 16.32% (P <0.05) compared to those of unmodified GICs as well. There was no significant change of the FT-IR characteristic peaks of modified GIC. The working time of three kinds of GIC were 4'58 ", 3'28" and 4'10 ", the net setting time were 5'16", 3'15 "and 4'38" (standard is 1.5-6 minutes). It was concluded that the dispersion stiffened effect of niobium oxide could improve the mechanical properties of the filling GIC without affecting the clinical operating performance.
With the application of FACTS devices in large-scale new energy base, in the light of FACTS devices installed in each wind farm in Gansu Jiuquan, which can supply reactive compensation for the power transmission system and stable the grid voltage, in this paper the magnetic controllable reactor (MCR) type static var compensator (SVC) is studied deeply. The paper introduces the working principle and characteristics of the MCR-SVC. In connection with MCR equivalent circuit, the simulation model is built in MATLAB/SPS, the simulation results and field tests verify the reactive power compensation effect of MCR-SVC during wind farms.
Recently, the static synchronous compensator (STATCOM) device has been installed in Jiuquan wind farm in Gansu Province. To study its ability to support voltage, this paper presents a study of the mathematical model of the steady state and transient state of STATCOM and then uses the power system analysis software package (PSASP) to establish a user-defined model of STATCOM. In addition, the model is added into the power system example (CEPRI 7). After that, the power flow calculation and transient stability calculation are carried out to simulate and analyze. At last the STATCOM device is field tested in Jiuquan wind power base. Test results verify that STATCOM effectively supports the grid voltage.
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