Abstract: Because of the extensive application of autotransformer in 500 kV power grid, the value of single-phase short-circuit current is generally greater than that of three-phase short-circuit current, or even greater than the maximum rated through current of the breaker. In order to reduce single-phase short-circuit current and avoid implement of bus split, this paper proposes to install small reactors on neutral points of 500 kV autotransformers. By analyzing and calculating the effect on short-circuit current limitation, the most suitable impedance value of small reactor is proposed. In addition，the overvoltage of the neutral point and insulation coordination are particularly discussed.
1609
Authors: Zhi Gang Ding, Jing Tian Ge, Wei Cao, Xiao Qing Qi, Wen Qing Yang
Abstract: The calculations of short-circuit current decrement with PSS/E BKDY and computational curve were compared with the one by the dynamic simulation of PSS/E. Calculation shows that the accuracy of the result by PSS/E BKDY is quite good while the one by computational curve is so conservative that it makes larger errors. The reasons for the above results have been analyzed theoretically.
1126
Authors: Wei Cao, Yong Sheng Wang, Bei Liu, Wei Wang
Abstract: The three-phase short-circuit fault of the 500 kV busbar of Waigaoqiao No.2 Power Plant was described, and the fault recorder data was analyzed for short-circuit current. The RMS of short-circuit current decaying fundamental frequency component, DC component and the attenuation time constant was obtained by Fourier transform, extrapolating with the exponential function. Finally, Corresponding suggestions for grid operation and management were also proposed.
1290
Authors: Guang Lei Li, Shu Min Sun, Yan Cheng, Hong Bo Li, Shuai Yuan
Abstract: To decrease short-circuit current, adjusting the power network operation by breaking transmission lines is the most economic and convenient measure. For large power grid, breaking transmission lines has thousands of combinations, so it's very difficult to find the best combination in a short time. Firstly, this paper formulated the sensitivity relationship between transmission line outage and impedance change. Then preliminary combinations schemes of transmission line outage were selected according to the sensitivity. Index values of factors were given using the fuzzy control evaluation. Finally, this paper determined optimal scheme from maximum priority and accomplished the accessorial intelligent optimize system of limiting short-circuit current. The rapidity and rapidity of the proposed control strategy was verified by calculating the actual power grid.
527
Authors: Xin Huan Wang, Xue Juan Li, Shuo Wang
Abstract: The design scheme of three-phase inverter power which was combined with AT89S52 single-chip microcomputer and three-phase IC chip SA4828 was given in this article and the main power circuit, control circuit, isolation, driven circuit and the software flow chart were introduced. The whole system adopted SA4828 to generate the sine pulse width modulation signal (SPWM), which simplified control circuit, reduced costs and improved the system reliability. At the same time, the interface between SA4828 and single-chip microcomputer was simple and convenient, moreover, the program of SA4828 was simple and the SPWM signal was digital, especially when the output frequency and amplitude remained unchanged, the single-chip microcomputer needn’t intervene in SA4828, which saved computer times and improved the speediness and real-timeliness.
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