For the common functional characteristic of microcomputer-based protection and online monitoring for medium voltage distribution circuit breaker

a synthetic monitoring device with the two functions is designed based on dual-CPU structure.This device has the functions of phase-sequence over-current protection

zero-sequence current protection

phase-lack fault and wire-breakage fault detection

and fault recording.It implements the monitoring of the circuit breaker’s mechanical features

electrical endurance

secondary circuit status

ambient humidity

and temperature of conductive connections through collection

storage and process of needed signals

and realizes field display of fault information and the circuit breaker status via large-screen LCD.μC/OS-Ⅱ embedded operating system is used in the software design.The stability

real-time performance

reliability and maintainability of the device are enhanced through reasonable division of tasks and priority assignment.Experimental results show that the precision of state parameters is measured less than 2%

demonstrating the device is reliable.