Design of control and protective switching devices based on inverse time characteristic

According to the GB14048.9,control and protective switching devices(CPS) must have the functions of inverse time characteristics,power failure indication,short protection,electric leakage protection and phase short protection.In order to replace the traditional thermal magnetic release device,a method for a type of control and protective switching devices based on inverse time algorithm with microcontroller was presented.The system was consisted with DC-DC circuit,analog sampling circuit,operational amplifier circuit and tripping circuit.The hardware mode was used to calibrate current,and the detection of three-phase current and leakage current was realized.The two release action modes were proposed,including relay-trip and shunt-trip.After the analysis of inverse time algorithm,the relationship between inverse time over-current algorithm and control and protective switching devices was established.A method was presented to discrete the inverse time over-current algorithm.The inverse time over-current characteristic was tested,and the detail measurement and demonstration of inverse time characteristics in different electrical environment were done.The experimental results show that the analysis lays the foundation for the futher more optimization of control and protective switching devices.