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
Study on the DC transmission scheme of Xiluodu and Xiangjiaba Hydropower Stations
The main problems associated with the DC transmission scheme of Xiluodu and Xiangjiaba Hydropower Stations are studied. Some problems in the simulation of large-scale AC/DC power systems are discussed, including the applicability of the quasi-steady state model of the HVDC system and the factors causing HVDC converter commutation failure. For the two receiving end systems and one sending end system of the DC transmission scheme for Xiluodu and Xiangjiaba Hydropower Stations, the transient stability of each system is analyzed under various AC and DC disturbances with different stability improving control strategies. The results show the DC transmission scheme for Xiluodu and Xiangjiaba Hydropower Stations is technically sound.
A voltage instability predictor using local area measurements (VIP++)
A smart relay scheme for long term voltage instability phenomena is proposed. The method, called VIP++ is based on local area measurements and seeks to improve observability and robustness of a previously proposed voltage instability predictor (VIP) using measurements only from the bus where the relay is placed. Several strategies can be adopted to deal with the extra set of measurements from neighboring buses, and two such strategies have been explored in the paper. When the system is far from the point of collapse (PoC) the VIP++ gives an approximate distance to PoC and indicate that the distance is quite large. As the system trajectory moves closer to the actual point of collapse the method will become more accurate, and it will be more or less exact at PoC.