Three-Phase Transformer Inrush Current Reduction Strategy Based on Prefluxing and Controlled Switching

Yuanlin Pan,Xianggen Yin,Zhe Zhang,Xin Yin,Binyan Liu,Maolin Wang

doi:10.1109/access.2021.3062143

Yuanlin Pan, Xianggen Yin + Show 4 more

Open Access

https://doi.org/10.1109/access.2021.3062143

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Abstract

Inrush current with high amplitude is generated when the transformer is energized. On the one hand, it will have a negative impact on the safety of the transformer itself, and even cause the relay protection to malfunction. On the other hand, it may reduce operation speed of the protection when there is slight fault because of the protection restraint criteria. Both aspects will affect grid security. Based on the generation mechanism of inrush current, this paper proposes an inrush current reduction strategy that combines prefluxing and controlled switching technology. By constructing an equivalent magnetic circuit model of the large-capacity three-phase transformer with a universal core structure, the analytical formulas of the magnetic flux at each stage of implementing the strategy are obtained, and then the parameters design method of this strategy is proposed. The accuracy of the theoretical analysis of magnetic flux is verified through the accurate simulation. Compared with common inrush current reduction strategies, this strategy can reduce the inrush current to 0.5 times rated current below in any situation where the residual flux is unknown and the “core flux equalization” effect are not obvious, avoiding the problem of residual flux measurement. Finally, in the case of the transformer differential protection, the influence of this strategy on the protection is analyzed from the perspective of theory and simulation, and it shows that it can improve the performance of various protections effectively.

Highlights

Power transformer, especially large-capacity transformer plays an important role in power transmission, and its operating characteristics have an important impact on the stable operation of the transformer itself and the power system
There is no research report on the application of controlled switching in inrush current reduction of three phases transformer with five columns core or single phase core
2) TYPICAL RESIDUAL FLUX In the above theoretical analysis, the inrush current reduction strategy proposed in this paper considers the worst case of residual flux when calculating the prefluxing current

Summary

INTRODUCTION

Especially large-capacity transformer plays an important role in power transmission, and its operating characteristics have an important impact on the stable operation of the transformer itself and the power system. In the research of controlled switching strategy, how to avoid the problem of accurate measurement of residual flux, consider the core structure and characteristics of three phases large capacity transformer with five columns core or single phase core, model and analyze the magnetic flux in the process of closing, and put forward the optimal closing strategy are needed to be in-depth research. The magnetic flux solution of large-capacity transformer during prefluxing and controlled switching process is the theoretical basis of inrush current reduction strategy design. The model should be able to consider the different core structures of large-capacity transformers, winding connection modes, core nonlinear characteristics, core residual flux, and the control parameters of the strategy such as prefluxing current and closing angle too.

PRINCIPLE AND STRATEGY OF INRUSH CURRENT REDUCTION

MAGNETIC CIRCUIT MODEL CONSTRUCTION AND MAGNETIC FLUX ANALYSIS

C-PHASE CLOSING TIME

ANALYSIS ON THE IMPROVEMENT OF PROTECTION PERFORMANCE BY STRATEGY

Findings

CONCLUSION