Research On Failure Mechanism And Aging Life Of HVDC Valve Internal Cooling System

The converter valve is one of the core equipment of the converter station,it produces various losses in the operation process,which will cause the junction temperature of thyristor components to rise.Excessively high temperature will lead to the failure of the thyristor,the valve cooling system is required to ensure that the thyristor junction temperature is in the normal range,which ensures the reliable operation of the converter valve.The rubber sealing ring of the internal valve cooling system is one of the key parts for the sealing of the converter valve cooling system,the performance of the rubber sealing ring,especially the service life,directly affects the cooling performance of the valve cooling system.However,as the using time goes on,the using performance and service life of the rubber seal will be greatly reduced,that is so-called “aging”.Therefore,it is necessary to develop deep research on the failure mechanism and aging life of the sealing ring of the HVDC internal valve cooling system,in order to provide theoretical basis for the operation and maintenance of valve cooling system.This paper aims to study the failure mechanism and aging life of the sealing ring in the valve cooling system,which will guide the operation and maintenance of the valve cooling system on site,and help to make the management of the sealing ring more scientific.At the same time,it provides reference for the maintenance and replacement of the sealing ring in the valve cooling system,and it reduces the workload of maintenance and improves the reliability of the HVDC transmission system.The main research contents of this paper are as follows:(1)Firstly,we design the life evaluation test method for the sealing ring of the internal valve cooling system: simulating the actual application environment of the sealing ring,designing the sealing ring aging test tool,choosing the compression set of the sealing ring as the characteristic index and 50% compression set as the critical value.Designing an artificial accelerated thermal aging test scheme,then using the existing EPDM and FKM sealing rings of each DC project to carry out artificial accelerated aging tests.(2)Then the failure mechanism of the sealing ring of the HVDC internal valve cooling system is analyzed,after making some EPDM sealing ring samples,the artificial thermal aging test for 720 h is carried out in the laboratory.Analyzing the samples before and after aging by means of SEM,FTIR,TGA.And identify the main influencing factors of rubber aging,clarify that thermal oxygen aging is the main reason of sealing ring failure.(3)Finally,through the analysis of the artificial accelerated aging test data,the relationship between the compression set of the sealing ring and temperature,time is clear,and establishing the life prediction model of rubber sealing ring by using the Arrhenius equation,which takes the compression set as characteristic parameter.Then predicting the service life of the researched rubber sealing materials.The prediction results are as follows: the service life of the EPDM rubber sealing ring is 29 years,and the service life of the fluorine rubber sealing ring is 5.7 years.The research results in this paper can provide theoretical basis and engineering reference for the operation and maintenance of the internal valve cooling system rubber sealing ring of each converter station of China Southern Power Grid.