Converter valve cooling system is an important equipment of HVDC transmission system. For avoiding damage of the converter valve due to high PN junction temperature of the thyristor

it is equipped with inlet valve temperature protection. The formula for calculating the junction temperature of thyristor valve is derived in combination of the loss calculation principle of thyristor valve and a kind of calculation and correction formula of junction temperature considering loss calculation error of thyristor. On this basis

the protection setting method of the inlet valve of the valve cooling system is systematically proposed. This method calculates the permissible maximum junction temperature of the thyristor and reversely deduces the maximum allowable inlet valve temperature through junction temperature calculation and correction formula

so to determine the temperature protection setting of the inlet valve of the valve cooling system. The effectiveness of the method is verified by an example analysis of the setting of the temperature protection of the incoming valve of Luxi converter station of southern power grid. This method has been applied in the field of Luxi station and Jinguan station of southern power grid with good result

which can provide referenceforprotectiondesignandsettingofvalvecoolingsystemfornewproject.