The Research On Filtering Theory Integrated In Transformer And Its Application

Because of a large number of nonlinear loads connected to the grid, harmonic pollution is getting worse, and the power filtering must be imp lemented. The inductive filtering is one of effective filtering methods which can stimulate the transformer’s potential electromagnetic ability, and to implement inductive filtering technology, a necessary filtering winding must be integrated in the transf ormer. In addition, in some fields where the space is strictly limited such as the ship and prefabricated substation, the filtering reactor integrated in the transformer is also needed. In this paper the above two methods are collectively referred to as the filtering technology integrated in the transformer which can achieve good filtering effect or save the space. The filtering theory integrated in the transformer and its application is researched in detail. The emphasis and achievement of the paper mainly manifests in the following aspects:(1) For suppressing harmonic currents of the load windings of the transformer to transfer to the grid winding, the impedance condition and the winding layout scheme of the inductive filtering winding integrated in the multi-transformer are described. And, the design method of the full-tuned inductive filters connected in the inductive filtering winding is obtained. Furthermore, the essence of eliminating core’s harmonic magnetic flux is revealed through analyzing the harmonics’ electromagnetic induction process of the multi-winding transformer with inductive filtering winding. What is more, the mathematical model and the equivalent circuit are established of multi-winding transformer with inductive filtering winding. Then, by analyzing the harmonic responsive factor’s trends when the power grid impedance parameters or filter’s parameters change, that the inductive filtering scheme has more advantages than the passive filtering scheme at the grid side in resisting disturban ce capability is revealed. At last, the conclusion that the inductive reactive power compensation capacity almost has no effect on the transformer’s short-circuit current is obtained.(2) A novel filtering reactor integrated in the transformer is proposed so as to reduce the volume. Firstly, the special windings’ wiring and layout scheme of the filtering reactor integrated in the transformer are introduced. Secondly, three adopted decoupling techniques are analyzed for its implementation. That the filtering reactor integrated in the transformer has linear leakage inductance characteristics is explained. In addition, based on its structural features the design method of the filtering reactor integrated in the transformer is given. At the same time, a method based on the reduced-order inductance matrix of checking the inductance values and the coupling degree of the filtering reactor is derived, and using this method, the effects of mutual inductance on the operating performance of the filtering reactor integrated in the transformer are studied. Finally, the simulation model based on the controlled voltage sources of the filtering reactor integrated in the transformer is established.(3) Based on the inductive filtering winding theory integrated in the multi-winding transformer, the twelve-pulse rectifier transformer and 220 k V power transformer with inductive filtering winding are proposed. The main parameters and wiring scheme of the two new transformers are introduced. For the twelve-pulse rectifier transformer, the filtering performance by phase-shifting and the energy-saving measures used are analyzed. Then, for 220 k V four-winding inductive filtering power transformer, the zero-sequence equivalent circuit and load distribution characteristic when parallel operating with three-winding transformer are studied. Finally, the test results of the two engineering prototypes verify the correctness of inductive filtering winding integrated in the multi-winding transformer in this paper.(4) Based on the filtering reactor theory integrated in the transformer, a filtering reactor integrated in the 10 k V distribution transformer is proposed. Firstly, the finite element simulation model and the controlled voltage sources simulation model of the filtering reactors integrated in the 10 k V distribution transformer are established. Next, using the finite element model the inductance values and the coupling degree is simulated, and the simulation verify the correctness of the design method and the decoupling technique. Using the controlled voltage sources model, the good filtering effect is verified. At last, the prototype is tested, and the results show its superiority in high linearity, low coupling, small volume and low noise.(5) The inductive filtering winding and filtering reactor both integrated in the transformer are discussed. Firstly, the implementation scheme is discussed. Then, in this case the analyzing methods of the harmonic current and the core harmonic flux when considering mutual inductance are given.This thesis performs the systematical research on the theory of inductive filtering winding and the filtering reactor integrated in the transformer, and constructs a set of relative complete filtering theory integrated in the transformer and its application research system. The research achievement has the scientific significance for the improvement of technical development of both power filtering and the new electrical power equipment.