Abstract: Failure of converter transformer will directly affect the safe service of the entire DC system. The selection of converter transformer is of great importance. Discussions about the structure, technical parameters and insulation tests are made. It is suggested that two-winding converter transformer of 296MVA, 550kV be applied for Three Gorges Project. Other issues related to transformer specification are also pointed out.
Key words: converter transformer, structure, technical parameters, insulation test
The converter transformer serves as a bridge between AC system and DC system, the secondary side of which is connected with converter valves. How the converter valve works determines that high-order harmonic wave component and DC component exist in the converter valve, which will cause loss, noise and an increase in no-load current. On the other hand, the deviation in short circuit impedance of converter transformer also has an effect on harmonic wave component and DC component. The electrical stress and thermal stress converter transformer bears are far higher than AC transformer. Hence, the insulation problem of converter transformer is more prominent.Discussions about the formulation of code for converter transformer are made through combining the experience in the operation of Genan DC system and actual condition of Three Gorges DC project. According to the results of electrical field calculation, present insulation test is evaluated and proposals for test conduction method and extra test items are put forward.