Cooling Design of HVDC Converter Valve in High Altitude Area

The expansion of high-voltage direct current (HVDC) transmission into high-altitude areas has led to increasingly prominent heat dissipation issues for converter valves. In high-altitude environments, the reduction in air density and the decrease in the heat transfer coefficient on the converter valve surface make heat dissipation difficult, which significantly affects the operation of various components of the converter valve and the temperature inside the valve hall. This article establishes a simulation model for the heat dissipation of the converter valve through theoretical analysis and computational fluid dynamics (CFD) numerical simulation. It analyzes the impact of different altitudes on the temperature of key components such as the thyristor, busbar, and reactor of the converter valve, as well as the impact of the valve tower on the heat dissipation to the valve hall. The patterns of temperature distribution in converter valves under steady-state equilibrium conditions and the variation of temperature with altitude have been obtained. The results show that when the altitude changes from 1500m to 5000m, the natural convection heat transfer coefficient of the valve tower decreases approximately linearly. The impact on the busbar, which relies solely on air for heat dissipation, is the greatest. The highest surface temperature of the busbar increases from 69.4°C to 75.1°C, with a temperature rise of about 29% and a reduction in current-carrying capacity of about 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup>. The impact on the reactor, which uses a combination of air and internal cooling water for heat dissipation, is the next greatest, with the temperature rising from 64.9°C to 69.2°C, an increase of about 28%. The impact on the thyristor, which relies on water cooling for heat dissipation, can be neglected, with a temperature change of less than 1°C. Taking a 12-pulse converter valve tower as an example, for every 500m increase in altitude, the natural convection heat dissipation to the valve hall decreases by about 3kW. The relevant heat dissipation laws can provide important design guidance for the cooling system of converter valves at high altitudes.