Study On Heat Transfer Performance Of The HVDC Outdoor Water Cooling System In Cold Area

As the electronic engineering facility in High-voltage Direct Current Transmission System to switch direct power, HVDC utilizes its function using Inverter. Thyristor valve is the most basic component in Inverter and is recognized as the heart of HVDC project.To operate the Inverter normally, the temperature of thyristor must be in the normal interval.Now, the cooling system to the thyristor valve includes water cooling and air cooling, and the main component of water cooling is traditional closed cooling tower. The outdoor cooling system of HVDC converter station must operate all the year round. Nowadays, traditional closed cooling tower operates facing the problems of condensation、freezing and anti-freezing in winter in cold areas, which makes the HVDC converter most in northern area applying air cooling and usage of the more effective heating system—water cooling is limited.This paper states a new outdoor water cooling system of HVDC converter station in cold weather. Based on the traditional closed cooling tower as the core, this article designs a new cooling tower that could operating all the year in cold areas to make sure the outdoor water system of HVDC converter station could safely and long lasting operate. At the same time,the article applies numerical simulation method to conduct research on the new cooling tower,to provide the theoretical support to apply and promote the new outdoor water cooling system in cold weather areas.This paper builds the simplified physical model to get the structure 、 designing assumption and heating theory in the new cooling tower. Fluent is used to conduct the numerical simulation to test the new cooling tower in cold area in winter and manipulates the data to get the velocity field and the temperature field of spray water. According to the result,it can be concluded:(1)The new cooling tower applies to the outdoor water cooling system of HVDC converter station in cold area by analyzing the temperature field of spray water in winter. It could solve the problems of condensation、freezing and anti-freezing,and make sure the new cooling tower it can be used in cold weather.(2)Sprays water of the new cooling tower through the water collection plate and then well-distributed on the heat exchange coil from the research of the velocity field and temperature field in cold area in winter. The water apron device in the center of water collection plate would resist the water spraying and affect the water-spraying density of central area in the coils. The density is relative small comparing to outside area of the center,but the effect is under control.(3)From the analysis of new cooling tower cooling water supply and return water temperature,the cooling water load borne by the spray of water, hardly affected by the air when the constant spray of water temperature.,So draining water content has a great influence on the heat transfer effects.On the condition of structural parameters permission,new cooling tower winter operation requires increased draining water content to ensure DC converter station operated safely and efficiently.This numerical simulating model could be used in the type selection design in the outdoor water cooling system of HVDC converter station in cold areas in reality.