Research On The Loss And Temperature Rise Of A Controllable Reactor Of Transformer Type

Controllable reactor of transformer type(CRT),which is suitable for extra high voltage transmission lines of power system,is a reactive power compensation device and has great significance for maintaining voltage level.The concentric CRT and the split magnetic integrated CRT are two typical structures.In this thesis,the calculation of short-circuit impedance,loss and temperature distribution is studied.(1)Firstly,the working principle of the CRT is analyzed.The structural features of the two typical structures from design principle of “high impedance and weak coupling” are compared.The concentric CRT meets capacity requirements through the current limiting inductor series in the control winding and achieves decouple between windings through the control strategy.Using the pancake shape middle core of different magnetic permittivity materials,the split magnetic integration CRT meets capacity requirements and achieves weak coupling between windings,but the complex core structure and difficult material selection of this CRT are difficult to manufacture.Based on the design principle,the structural parameters of the two typical CRTs are given.And a simplified middle core design method of the split structure,which has a rectangular structure with an air gap,is proposed.The design method demands that the middle core uses the same ferromagnetic material.(2)The short-circuit impedance is an important parameter,the reason why is the secondary side is equivalent to a short circuit when CRT is working.The short-circuit reactance is the most part of the short-circuit impedance.This thesis analyzes the calculation principle of three typical methods which are self-mutual reactance method,short-circuit reactance method and finite element method(FEM).Then,the three methods are compared with computational complexity,applicability,accuracy,and calculation error taking the concentric CRT as an example.Short-circuit reactance method is the most concise in terms of computational complexity,but it can only calculate a simplified structure.Although FEM has the longest calculation time,it has wide applicability and high precision.And it can get loss and temperature distribution by FEM.Though self-mutual reactance method is more complicated than the short-circuit reactance method,the short-circuit reactance could be calculated in the engineering calculation of simple structure by the self-mutual reactance,but not the opposite.FEM is adapted in high precision and complex structure.(3)Calculation of loss and study on temperature rise are crucial to the optimum design of CRT and accurate calculation of the current is the premise of loss calculation.A double winding concentric CRT experimental prototype is designed.By comparing the results of experiment and simulation,the correctness of the field-circuit coupling calculation method,used in the transient field of FEM,is confirmed.On the basis of FEM loss analysis,the core loss and winding loss under the rated capacity and stable operation of two kinds of CRTs are calculated.The core loss of the split CRT is higher due to its complex structure and large dosage of the core materials.The winding loss of the concentric CRT is higher,and the total loss would be increased by adding additional devices used for the current limiting reactance.The difference of total loss of two structures under the rated capacity is very small due to the proportion of core loss is small.(4)Based on the heat transfer analysis of the core and windings of two structures,the “electromagnetic-thermal” calculation model is established,and the temperature distribution of all parts is got by using the loss under the rated capacity as the excitation of the temperature field.The simulation results show that the loss and temperature rise of CRT has close relation with the structure,winding arrangement and capacity.Through improving the winding arrangement of the concentric CRT,the winding loss is reduced and the temperature rise of each part is also changed.The optimization of CRT needs to consider various factors.The methods and conclusions in this thesis have a guiding significance for the design and manufacture of CRT.