A New Approach With Sequential Waveform Characteristics To Monitor Electrical Life Of Switch Contacts

The power switches are widely used in electrical system to make and break electrical current. Monitoring and prediction on residual electrical endurance of power switch is an important work for the reliable performance of power switches and stabilization of electrical system. The previous techniques of contact life prediction are summarized such as time-integrated current, comprehensive diagnosis with fuzzy theory and double-variable life prediction with super-path time and pick-up time. A new idea is presented to monitor and predict the residual life of contact, which is with the waveform characteristics in making and breaking current and voltage. The waveform characteristics or indexes of breaking and making arcing current and voltage are used to reveal the effect of contact surface change on electrical life of switch contact. Few papers about this work have been reported by now. In this thesis, a PC-DAQ data acquisition system is built with the technique of LabVIEW virtual instrument. The system is applied to sample, display and store the current and voltage waveforms obtained from the contact endurance tests. The electrical contact endurance tests were performed under the resistive, lamp and inductive load at 14VDC respectively with the contact materials AgSnO2, AgNi10 and AgNi0.15. Comparing with some waveform analysis methods like SOM, the breaking arc duration analysis method is adopted. According to the dynamic behavior of the breaking current, breaking arc duration is extract from the breaking current waveform by using the concept of moving average of statistics. As a result, using the diagnosis technique of electrical contact life with the waveform of making and breaking current and voltage, it is easy to observe the occurrence of continuous arcing phenomena during the contact breaking operations. And this is available for the synthetical diagnosis on the reliability and the residual electrical life of the contact. And the breaking arc duration is irrespective with the number of contact operations regardless of the loads. Furthermore, it is found that the electrical contact life and the occurrence of continuous arcing phenomena are deeply related to contact surface condition with the number of contact operations.