HDG stands for Hot Dip Galvanized, which is a method of coating steel with a layer of zinc to protect it from corrosion. In the context of a transformer radiator, HDG refers to a radiator that has been hot dip galvanized to provide additional protection against rust and other forms of corrosion. Transformer radiators are used to dissipate heat generated by the transformer during operation. They consist of a series of tubes or fins that allow air to flow through and cool the transformer. By hot dip galvanizing the radiator, it becomes more resistant to corrosion, ensuring its longevity and performance.