Novel Remanence Determination for Power Transformers Based on Magnetizing Inductance Measurements

Chen Wei,Ming Yang,Xianqiang Li,Hui Hou,Zhiyuan Ma

doi:10.3390/en12244616

Abstract

The remanence (residual flux) in the core of power transformers needs to be determined in advance to eliminate the inrush current during the process of re-energization. In this paper, a novel method is proposed to determine the residual flux based on the relationship between residual flux and the measured magnetizing inductance. The paper shows physical, numerical, and analytical explanations on the phenomenon that the magnetizing inductance decreases with the increase of residual flux under low excitation. Numerical simulations are performed by EMTP (Electro-Magnetic Transient Program) on a 1 kVA power transformer under different amounts of residual flux. The inductance–remanence curves are nearly the same when testing current changes. Laboratory experiments conducted on the same transformer are in line with the numerical simulations. Furthermore, numerical simulation results on a 240 MVA are reported to demonstrate the effectiveness of the proposed method.

Highlights

Power transformer is the key device of electrical energy system, the performance of transformers directly affects the stability of the power system
The variable frequency constant voltage (VFCV) performs better than the other one. The results show it reduces the residual flux in the core successfully
From the simulation results above, the inductance–remanence curves can be drawn by using excitations on both small and large transformers

Summary

Introduction

Power transformer is the key device of electrical energy system, the performance of transformers directly affects the stability of the power system. When a power transformer is de-energized, there is always a certain amount of remanence (residual flux) left in the iron core due to the hysteresis of the ferromagnetic material [1,2,3,4]. This residual flux may cause negative effects when re-energizing the transformer, such as inrush currents, overvoltages, dynamic stresses, and resonances. Time-controlled switching is an effective method to eliminate inrush currents [5,6,7]. For the method to work, it is essential to know the residual flux

Results

Discussion

Conclusion