| The Yunnan-Guangzhou Ultra-high Voltage DC Transmission System is the first ± 800 kV UHVDC system of the world.Some typical accidents of the UHVDC transmission system,which is different from those of the ordinary HVDC transmission system,have been happening in the operation and maintenance stage.This paper selects two of the most representative cases for in-depth analysis of the reasons,making the corresponding improvement measures.The first case,with the unique single-pole dual-valve structure of the UHVDC transmission system,the control of the deblocking sequence was out of order as the bypass switch position detection circuit failed when the second valve group deblocks,leading to the 82-BPS protection action and the deblocking sequence failure eventually.Based on the analysis of the causes of the accident,the paper makes a further extended analysis on the other more serious consequences that the fault may lead to,which is verified by a simulation.The logic of valve deblocking control and 82-BPS protection optimization is proposed pertinently,and improvements of the routine operation and maintenance are put forward.The second case,some logical hidden troubles lurk in the DC measurement system adhibit in the Yunnan-Guangzhou UHVDC transmission system which provides measurements for the control and protection system.The measurement bus may not switch correctly when a single measurement channel fails,causing an error response of the control system,and ultimately lead to the block of valve group as the protection actions.After the analysis of the impact of a single measurement on the control and protection system,the related factors causing the measurement bus switching and their rationality are combed emphatically and some corresponding modification suggestions are proposed.The risk in the switch logic of measurement bus in protection system is analyzed and the optimization scheme is put forward meanwhile. |
PDF Full Text Request