Abstract
To optimize the operating temperature and flow velocity of cooling water in a high voltage direct current (HVDC) thyristor valve cooling system, the erosion corrosion characteristics of aluminum electrodes in deionized water at various temperatures were studied. With increasing water temperature, the corrosion current of the aluminum electrode gradually increases and the charge transfer impedance gradually decreases, thus, the corrosion of aluminum tends to become serious. The aluminum electrode in 50 °C deionized water has the most negative corrosion potential (−0.930 V), the maximum corrosion current (1.115 × 10−6 A cm−2) and the minimum charge transfer impedance (8.828 × 10−6 Ω), thus, the aluminum corrosion at this temperature is the most serious. When the temperature of deionized water increases, the thermodynamic activity of the ions and dissolved oxygen in the deionized water increases, and the mass transfer process accelerates. Therefore, the electrochemical corrosion reaction of the aluminum surface will be accelerated. The corrosion products covering the aluminum electrode surface are mainly Al(OH)3. With increasing water temperature, the number of pits and grooves formed by corrosion on the aluminum surface increased. In this paper, the molar activation energy Ea and the equilibrium constant K of the aluminum corrosion reaction with various temperatures are calculated. This clarifies the effect of temperature on the aluminum corrosion reaction, which provides a basis for protecting aluminum from corrosion. The results of this study will contribute to research that is focused on the improvement of production techniques used for HVDC thyristor valve cooling systems.
Highlights
When a high voltage direct current (HVDC) converter works, a large amount of heat is transferred to an aluminum radiator that is in direct contact with the thyristor
The corrosion products that covered the surface of the aluminum electrode were mainly Al(OH)3
The aluminum corrosion at this temperature was the most serious, and the reasons were the thermodynamic activity of the ions and dissolved oxygen in the deionized water increased
Summary
When a high voltage direct current (HVDC) converter works, a large amount of heat is transferred to an aluminum radiator that is in direct contact with the thyristor. The heat is conducted out of the system by the cooling water flowing in the inner hole of the aluminum radiator to maintain the normal operating temperature of the converter. The cooling water is deionized water with very low conductivity. The scaling that forms on grading electrodes in HVDC cooling circuits that use deionized water is a long-known and unsolved problem and has a great impact on the safe operation of an HVDC cooling system [1,2]. The primary cause of scaling on a platinum grading electrode scaling is corrosion of the aluminum radiator [3,4]. Some researchers had studied the corrosion behavior in Materials 2020, 13, 779; doi:10.3390/ma13030779 www.mdpi.com/journal/materials
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