The invention discloses relay protection device and system, realizing plug-and-play, of a transformer station. The protection device comprises a line protector, a transformer protector, a bus connection protector and a bus separation protector relying on one another and associated with one another; required current and switching amount information are connected to the line protector, the transformer protector and the bus connection protector directly via secondary cables; opening/closing control is output directly via the secondary cables, and the protectors directly act on a switching mechanism of a bay level; the bus voltage collected by a voltage transformer is connected to the bus separator protector in the analog form; and the bus separator protector is directly connected to the line protector, the transformer protector and the bus connection protector via two optical cables in a point-to-point manner. On the premise that faults of the electric network can be overcome rapidly, the relay protection device system of the invention can further reduce the operation risk of the electrical network as well as the labor intensity of maintenance staff, and it is ensured that the electrical network operates safely, reliably and stably.