Protection device has a communication bus failure diagnosis function, the system and method

The present invention proposes a diagnostic species for delivery regional distribution network selection method on a communication bus fault interlock (the ZSI) signal. The method comprising: an interface that is connected to each of the protective devices with the communication bus (BUS1, BUS2) is in the first diagnosis period (Ts) are configured as an input pin; at each protection means respectively connected to the communication bus detecting which port received the input signal; if the input signal is abnormal is detected, the first protection device to issue an alarm associated with a corresponding interface.