The Research On The Theory Of Windings Shielding And Its Application In Large Current Transformers

With the development of electrical power system to the large capability and high voltage, the manufacture of Large Current Transformers (LCT) which be wildly used in the measurement and protection of electrical power system has been strongly necessary. LCT has the characteristics of large current, mighty electromagnetic interference and multiphase working, when we design LCT, the effective shielding methods must be taken to shield the stray flux of its adjacent bus. The traditional shielding scheme takes metal shielding cover, which is effective but makes the equipment heavier. In the paper, the author makes diversified research to the LCT with outer shielding windings.After adopting the windings shielded way in the LCT, how to optimal design the shielding windings for the most effectively shielding the loop core from the influence of the stray flux? Aiming at the above problems, the paper author has mainly completed the following tasks:1. Firstly state the development and research status of LCT at present, and successful design 15000/5A LCT.2. Researching in detail the essential electromagnetic theory and the mathematic theory of the coupled magnetic-circuit method, building the 3-dimensions coupled magnetic-circuit finite element method (FEM) mathematic and simulated models. At first using the ANSYS software to build the 3-dimensions FEM model, then establishing the outer circuit model based on the coupled magnetic-circuit theory.3. Analyzing in theory the stray flux how to influence the current transformer core; specially analyzing the theory of how the windings to shield the stray flux; through the equal current method, we can get the result that the middle phase LCT core has been influenced seriously in any case three phases or more phases current transformers, which provides the scientific basics for the effective safe of LCT.4. For getting the most optimal shielding windings, at first introducing the discrete shielding windings ones instead of the successive ones, then thinking of the shielding windings location in the loop core, giving multiform optimal schemes; based on the 3-dimensions FEM model, accurately working out the current in the shielding windings and its distribution, the magnetic induction density and its distribution, the local maximal thermal rise. Through contrasting the computation results alternatively, we finally get the most optimal shielding windings scheme in the...