1. For EHV network, the study on normal tide and n-1 tide shows that it is technically practicable for Three Gorges Hydropower Station to apply EHV for power transmission to the East China Grid.2. For the idle balance requirement under different operation mode, the reactors with EHV should be controllable parallel ones.3. To comply with the "n-1" principle for EHV and with reduction in cutting off units, the interconnected transformer should be allocated between EHV line and 500KV line in the station of Three Gorges.4. To restrain line frequency over voltage is a big problem. When a fault happens and reclosing is not in success, it is suggested to break fail-phase and to successively break non-fail phase so that controlled line frequency over voltage can be below 1.25 times. In addition, to apply controllable parallel reactors is also one of important measures.5. If breaker applies closing resistance of 300Ω and MOA with high quality, the operating over voltage in EHV system can be restrained below 1.6 times or so.6. The maximum operating voltage of EHV system is l,200KV. The MOA for power station type and for line type can be allocated to protect equipment respectively. U_r of MOA is 830KV and 860KV respectively. The pressure ratio is 1.6 or so.7. The isolation level of EHV equipment against basic thunder impact is 2,400KV. The isolation level for operating wave is divided into two grades, 1,800KV and 1,950KV respectively.
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