Analysis and Improvement Measures of A Mis-conduction Event of Optocoupler Relay in Converter Station

This paper analyzes a commutation failure event caused by the mis-conduction of the 24V optocoupler relay during the input of the valve group protection outlet platen of Chuxiong-Suidong HVDC. The reason for the mis-conduction is that the output of the optocoupler relay is connected to the capacitor charging at the moment of the input of the outlet platen, and the mis-motivation theory is verified by experiments. Based on this, this paper proposes to replace the original optocoupler relay with a model with a smaller outlet parallel capacitor, and through experiments, the instantaneous output voltage of the contact point is much lower than that of the original relay, which will not lead to misconduction and improve the stability and safety of the DC control and protection system.