Abstract:Since the planning and construction of the UHVAC transmission project in China, there has been considerable controversy over the transmission capacity, economy, and implementation effects of UHVAC transmission. This article compares UHVAC with EHVAC in terms of transmission capability and economy applying both theorical and simulation analysis. Model the point-to-grid and grid-to-grid transmission simulation system for both UHVAC and EHVAC, and for the different tranmission distance and system strength, analyze the transmission capability of UHVAC and EHVAC according to thermal stability and transient stability constraints. In addition, the economy of UHVAC and EHVAC are studied under the assumption of same system strength for sending end and receiving end, as well as same transmission capability per kilometer. Research shows that the maximum transmission capacity of UHVAC transmission is 2~4 times of EHVAC transmission under the same transmission distance, and EHVAC transmission is superior to UHVAC transmission in the same transmission capacity with medium and short range transmission.