The transformers are in accordance with National Standards GB1094 Power Trans- formers and GB/T6451 Technical Specifi- cations and Requirements for Three Phase Oil-immersed Power Transformers. The vol- tage regulation range is 10±4×2.5% kV for 10 kV class and 5±3×2.5% kV for 35 kV class. Voltage regulation is effected by adj- usting the on-load tap changer on the high voltage side. Adjustment can be made manually or motor-operated, the output voltage on the secondary side at a required stable level. Therefore they are widely used in places where requirement of voltage quality is emphasized, such as institutes, building, hotels, hospital and factories. These transformers are new products and have better economy in operation