A set of dynamo transformer for 667 thousand KVA, 500KV impregnated three phase double ring water composition has passed all the factory test of Xi’an Xi Bian Electric Group and the technologic index has reached the international and domestic leading level. This kind of transformer adopts the double concentric and low voltage outgoing structure. Comparing to the traditional single concentric structure, this kind of transformer has limited load loss, 10% reduce of open circuit losses, 8% decrease of transportation volume. This structure has successfully solved the partial overheating problems caused by large capacity, high voltage dynamo transformer.