A Study On Control And Protection Strategy Of The De-ice Mode In UHVDC Converter Station

The ice crust on the transmission line in winter serious threat to the safety and stabilization of power system.As DC line is longer than AC line,and greater in transmission capacity,it is more susceptible to the influence of icing.The De-ice Mode is a special operating mode developed for melting ice covered on the DC line of HVDC system,which is still in experimental stage.The control and protection strategy of De-ice Mode are studied in this paper,providing further improvements for the application.Compared some present de-icing technologies of UHVDC system,the method of increasing the thermal current by changing the operating mode of system is considered to be the most suitable way for long-distance DC line.By analyzing the UHVDC converter station operating mode,and in accordance with the control and protection requirements needed for de-iceing,we propose two programs for different degrees of the ice crust:De-ice Mode Round and De-ice Mode Hybrid.De-ice Mode Round is a mode specially for mild icing problem,the control mechanism and operational processe are studied and simulated with the parameters of Long-Zheng HVDC system to demonstrate the availability of the mode.De-ice Mode Hybrid is a special mode for sevre icing problem,which has two parallel converters in each other ploe.The paper conclued a new control and protection program for this mode by amending the existing protection and control mechanisms of the normal mode.The program was tested in field trials for three times,proved to be feasible.But through calculating the parameters of the tests,we found De-ice Mode Hybrid can not reach it’s theoretical maximum current, predicting the limitations by equipment conditions at present.