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
RAISING STABILITY LIMITS IN THE NORDIC POWER TRANSMISSION SYSTEM
The aim of this paper is to present power system stability analyses, which are part of ongoing efforts to raise transmission capabilities in the Nordic power transmission system. The studies focus on the assessment of angle stability limits and the impact of power system stabi- lisers (PSSs). The paper describes applications and testing of prototype devices for on-line power system monitoring (the Voltage Instability Predictor, VIP and Phasor Meas- urement Units, PMUs). Utilisation of phasor measurements as input to power system stabilisers is analysed. Selected results from measurements and computer analyses, using a complete Nordic transmission system model, are shown to illustrate the main benefits from the study. The results indicate that it is possible to raise exist- ing stability limits on important transmission corridors through improved control and better understanding and monitoring of system stability properties. In combination with other ongoing efforts this will enable the system op- erator to raise present operating limits.
Geomagnetic Polarity Epochs: Sierra Nevada Data, 3
Available paleomagnetic and radiometric results for about 60 igneous rocks 3.6 m.y. old or less are consistent with the following geomagnetic polarity epoch time scale: Brunhes normal polarity epoch, 0.0 to 0.85±0.15 million years; Matuyama reversed polarity epoch, 0.85±0.15 to 2.4±0.1 million years; Gauss normal polarity epoch, 2.4±0.1 to 3.35±0.1 million years; Gilbert reversed polarity epoch, 3.35±0.1 million years to (?). A brief interval of normal polarity (the Olduvai event) occurs within the Matuyama reversed epoch at about 1.9 m.y., and a brief interval of reversed polarity (the Mammoth event) occurs within the Gauss normal epoch at about 3.06 m.y. Data for twelve units from eastern California and Nevada, reported here for the first time, are particularly useful in defining the Gauss-Gilbert boundary and for recognizing the Mammoth event.