From the technical point of view, adopting ±800 kV UHV DC transmission, the middle of the line does not need to drop point, which can send a large amount of power directly to the large load center; in the case of AC/DC parallel transmission, it can use bilateral frequency modulation to effectively inhibit the regional low-frequency oscillation, and improve the limit of temporary (dynamic) stability of the cross-section; and solve the problem of exceeding the short-circuit current of large receiving end of the power grid. Adopting 1000kV AC transmission, the middle can be dropped with grid function; strengthening the grid to support large-scale DC power transmission; fundamentally solving the problems of short-circuit current exceeding the standard of large receiving end grid and the low transmission capacity of 500kV line, and optimizing the structure of power grid.
In terms of transmission capacity and stability performance, using ±800 kV UHV DC transmission, transmission stability depends on the effective short circuit ratio (ESCR) and effective inertia constant (Hdc) of the grid at the receiving end, as well as the structure of the grid at the sending end. Adopting 1000 kV AC transmission, the transmission capacity depends on the short-circuit capacity of each support point of the line and the distance of the transmission line (the distance between the drop points of two adjacent substations); the transmission stability (synchronization capacity) depends on the magnitude of the power angle at the operating point (the difference between the power angles at the two ends of the line).
From the perspective of key technical issues that need attention, the use of ±800 kV UHV DC transmission should focus on the static reactive power balance and dynamic reactive power backup and voltage stability of the receiving end of the grid, and should focus on the system voltage security issues caused by simultaneous failure of phase switching in the multi-drop DC feeder system. The use of 1000 kV AC transmission should pay attention to the AC system phase adjustment and voltage regulation problems when the operation mode is changed; to pay attention to the problems such as the transfer of high power in relatively weak sections under serious fault conditions; and to pay attention to the hidden dangers of large-area blackout accidents and their preventive measures.
Post time: Oct-16-2023