Analysis And Prediction Of Magnetic Field Of Dry-type Air-core Reactors Based On Scaling And Simplification

With the continuous development of power system, dry-type air-core reactor were widely used because of its initial uniform voltage distribution, the advantages of high linearity, and low noise etc. Air-core reactors play an important role in reactive power compensation, current limiting, filtering and overvoltage protection. However, the extensive use of air-core reactor in power system also bring many problems. Due to the lack of a closed ferromagnetic pathway, the air-core reactor would produce strong power frequency magnetic field (MF) in its outer space, not only interfere the operation of sensitive electric equipment but affect the staff’s health in power station. Inter turn short-circuit was one of the most common failure of air-core reactor, which will change reactance value, resulting in current increases, local temperature anomaly and even burnt, threating the reliability of power system operation.The accurate prediction of the MF before the installation is an important mean to the reasonable design of reactor structure and solution to the electromagnetic pollution of the surrounding environment and inter turn short-circuit fault. However, limited by the large size and complex structure, there are many difficulties in the field measurement and direct calculation of MF distribution of the air-core reactor. Therefore, this paper carries on the related research to the model scaling and simplification of the air-core reactor. The research contents cover several aspects as follows:a) Scaling rules derivation based on the similarity theory; b) Study on simplified-model for multi coating air-core reactor; c) Structural optimization for circular simplified-model; d) The inductance and MF distribution characteristic research of inter turn short-circuit based on the scaling experimental method.In this paper, the scale-model was established based on the similarity theory and in combination with the structure characteristics of air-core reactor. On the basis of geometric similarity, the scale-model was expanded to the electrical parameters and MF distribution similarity. The similarity of electrical parameters and MF distribution between scale-model and air-core reactor was verified through formula deduction, numerical calculation and real scale-model measurement in the laboratory. The scale-model can be widely used in the structure design, parameter determination and MF prediction of air-core reactor, the results consistent with original model conclusions.Aiming at the problem existing in the two kinds of simplified model, improvement measures were put forward. First, put forward a single-coating model based on the principle of equal ampere windings, which improved the accuracy of simplified model, and explored the influence of airway width on the MF distribution. The optimal structure of circular simplified model are obtained, through structural optimization for two-loop model and three-loop model in the key direction. Finally, the feasibility of MF prediction was verified through the simulation or experimental methods.Scale-model was set up to study the variation of the reactance and MF distribution in the inter turn short-circuit fault. According to the similarity theory, the conclusion of scale-model also applies to the air-core reactor. The equivalent simulation model was established based on the voltage balance equation of inter turn short-circuit to study the influence of the fault location and severity on the inductance and MF distribution. Proposed an on-line monitoring system based on MF distribution variation, and the feasibility of the system was analyzed through an example.