Abstract: Expanded inner bridge connection is widely used in new and rebuild station. However there are design defects in voltage switching circuit,which may cause bus voltage parallelling through voltage switching circuit,and lead to the hidden dangers of reverse power transmission from live busbar to non-live busbar.To solve this problem,this article analyzes the reasons for its formation,and proposes an optimized design scheme for voltage switching circuit,solving the problem of parallel connection of bus voltage through switching circuits.