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This paper proposes a novel transmission network planning method under the background of Transmission and Distribution Price reform. Firstly, a multi-stage transmission network planning model considering the transmission and distribution price is established. The objective function of the planning model is to maximize the profit during the whole planning period. The constraints contains the nodal power balance, AC power flow, construction sequence, construction time, limitation of the total investment cost, and so on. Then, genetic algorithm is applied to solve the planning model. Finally, case studies are carried out on the modified IEEE 24- bus transmission network. And the results show the effectiveness of the proposed method.

As the penetration of RES (renewable energy sources) in large scale grid increases continuously, the inertia support capability and primary frequency regulation of synchronous power grid are both declining. A decrease in inertia is problematic because it negatively influences the dynamic characteristic of the system’s frequency. But its concrete impact is still not clearly distinguished from that caused by the decline of primary frequency regulation. Aiming at the above problem, firstly, the inertia support capability and its physical meaning of synchronous generator are analyzed in depth, and the expression formula of inertia support power of synchronous generator is deduced. Secondly, the distinction between the inertia support capability and primary frequency regulation of synchronous generator is analyzed in detail. Thirdly, the respective impacts of the inertia support and of the primary regulation on the dynamic characteristic of system frequency during power shortage disturbances in large scale synchronous grid are simulated and analyzed. Finally, all the study above points to a conclusion that the large synchronous power grids with increasing penetration of RES require more relatively continuous power support of the primary frequency regulation than the short term inertia support, because the impact brought by the decrease of system inertia support is less serious than that brought by reduction of primary frequency regulation ability in large scale power grid.