In smart substation

process level equipment and optical fiber virtual terminal connection have been adopted

which leads to the obvious differences in the maintenance and isolation mode of protection equipment. Operation and maintenance personnel are still accustomed to the operation mode of traditional physical circuit

and are not familiar with new technology and equipment

which increases the risk of maloperation. This paper summarizes the status quo of maintenance safety measures for secondary equipment in smart substation. The means of maintenance and isolation of protection and related equipment in smart substation are analyzed. A method of switching the maintenance state of secondary equipment is proposed

which defines the maintenance state of protection and related equipment

such as operation state

signal state

offline state

maintenance state and isolation state

following the working habits of conventional substations. All maintenance operations are simplified as switching between maintenance states. The proposed method reduces the working pressure of operation and maintenance personnel on site

and makes some practical exploration on the modeling and on-line monitoring of secondary circuit in smart substation.