Abstract: With the increase of urban electric load,improving the transmission capacity of existing city network has become extremely urgent.In order to solve this problem,a compact transmission scheme for increasing capacity is proposed,in which the sending and receiving ends connect to the original three transmission lines through half-bridge modular multilevel converters and inter-pole current transfer switches.Secondly,the current modulation strategy is modified to serve this topology and the ability of power increases is calculated.Thirdly,the steady-state operation mechanism and the system start-up procedure are analyzed,while the start-up strategy is designed.Finally,through the simulation based on PSCAD/EMTDC,the scheme is verified in terms of start-up and steady-state operation.The results show that the scheme proposed has good performance in increasing capacity while contributing to stable and reliable operation.