Abstract: The total hydrocarbon and acetylene content in the oil chromatographic test of a 500 kV power plant transformer was abnormal.Through the power cut, oil extraction, oil filter, demolition annex and hanger inspection, maintainer found the overheating discharge traced at the scene, and determind the cause of the malfunction.The transformer anomaly can be eliminated by sanding the ultra-high block iron, increasing the magnetic shield of the fuel tank, and the top and bottom boxes, along the aluminum and copper lines.