The Scheme Of A Novel On-load Tap Changer And Its Simulation Research

Transformer with on-load tap changer (OLTC) is important equipment for electricity transmission and distribution in the power system, which aims to make the tap changing of the winding without of the interruption of the load current. The turn ratio of the winding, that can also be considered as the voltage ratio is changed via the action of the OLTC and thus the voltage regulation is finished. The traditional mechanical OLTC cannot completely satisfy the requirements of the operation safely and economically of the modern power grid because of the inherent defects exposed by the mechanical OLTC, such as the arc that can be generated in the regulation, slow regulating speed and the high failure rate. In view of the great advantages in changing without arc and response speed, the novel OLTC based on the power electronics gradually required more and more attention from home and abroad. In this paper, a novel hybrid OLTC has been researched and analyzed, the feasibility of the scheme has also been verified. The research work is summarized as follows:Firstly, introduce the function of OLTC in the grid and its development status. On this basis, analyze its components and working principle. Summarize the schemes of the mechanical OLTC (resistance-type and reactance-type) and the novel OLTC (hybrid, auxiliary coil and fully electronic type), then analyze their working process and characteristic. Compare and summarize the advantages and disadvantages of each type OLTC.Secondly, a scheme of novel hybrid OLTC is presented, and its topological structure, working principle as well as advantages are introduced in detail. Then build an 110kV/35kV voltage level single-phase transformer model with the above mentioned hybrid OLTC using MATLAB/SIMULINK software, present the related parameters settings. Observe the transient changing procession of the voltage and current of the model in focus, when the model has made voltage increase and decrease once respectively. Through comparing the simulation results and theoretical analysis, the feasibility of the scheme for its working principle and voltage regulating procession has been validated preliminarily.Then, make detailed simulation research on the model. Observe the transient characteristic of the transformer’s primary side in focus while tap changing. Through researching the influence on the tap changing procession of the model in aspect of load, current limiting component and switching time, the feasibility of the scheme has been validated further. With regard to load, the research should be made in aspect of the load type, size and power factor. Thus, conclude the load operating range for the normal tap changing of the model. Explore the law of the tap changing using resistance and reactor as the current limiting component respectively, and give suggestions about the type and value of the suitable current limiting component. The obtained conclusions can have some reference value in practical application.Lastly, introduce the parametric design basis of the vulnerable thyristor switch branch, which includes the choice of the rated voltage and current for SCR as well as design of the RC snubber circuit. Then present some other protective circuit schemes for the over-voltage depressing for SCR components.