Ratio braking type protection method for bus with voltage class of 35 kV or below

The invention relates to a ratio braking type protection method for a bus with voltage class of 35 kV or below. The ratio braking type protection method comprises the steps that: 1) protection devices of elements in the bus with voltage class of 35 kV or below acquire current/voltage signals and input/output signals of the interval, and outputting the current/voltage signals and input/output signals to a process-level network through network interfaces related with optical cables; 2) and a transformer protection device receives the current/voltage signals and input/output signals of the process-level network, calculates differential currents of all the elements on the bus, and performs bus protective action when the calculation result satisfies an action condition.