Study on the pure DC transmission scheme for China's future power transmission from the West to the East
In the year after 2015, China's national power grid interconnection will have been completed. Most likely, there will be four synchronous power systems, that is, big East China power grids, central China power grids, South China power grids and Northwest China power grids. For the long distance (more than 1000 km) bulk power (more than 50 GW) transmission from the West to the East, if the pure DC transmission scheme is adopted, there will be more and more HVDC links feeding power to different points in the same synchronous AC network. An important issue arising in such a situation is the influence of the multiinfeed HVDC links on the security of the AC systems. This paper analyzes the transient stability of each system under various AC and DC disturbances. The recovery characteristics of the multiinfeed HVDC links are also investigated. The results show that pure DC power transmission from the West to the East of China is technically feasible
The effect research on transformers and protections under HVDC monopole ground operation mode
The neutral point potential of the grounding transformer will be changed when HVDC system operates in a dc monopole ground return mode and dc bias may be generated. Dc bias will change exciting currentdasias waveform. Then large quantity of even and odd harmonics will be produced. The harmonics will do harm to the transformer and its protection. This paper uses PSCAD/EMTDC to create a simulation model. It emulates exciting current of a practical 750 kV single-phase transformer in variant cases under dc bias. It studies the distortion of exciting current, harmonic distribution, the peak value of the exciting current under dc bias. Meanwhile, the performance of transformer protection in this harmonic environment is analyzed. The loss made by exciting currentpsilas distortion and elevated temperature rise of core tie-plate are quantitative calculated.
Continuous calibration of a vacuum ultraviolet system from 65 to 125 nm by a cascade arc and comparison with the calibrated line radiation of a hollow cathode.
A high-power stationary helium cascade arc has been developed as a standard source for continuum radiation in the VUV spectral range from 65 to 125 nm. The calibration of the VUV system response was based on the calculated and measured continuum radiation of a 2-mmphi pure He arc. Diagnostics of the arc plasma in partial thermal equilibrium yielded the electron density and the temperature that were inserted in the calculations of the continuous radiation. The results were compared with the helium, argon, and krypton radiation lines of a high-current hollow cathode lamp. This lamp was built according to the construction drawings of a hollow cathode, which was calibrated by means of the electron synchrotron radiation at the Physikalisch Technische Bundesanstalt Berlin.