Exploration of Safe Operation and Active Protection Technology for Large-capacity Power Transformers

The existing protection methods for transformer internal faults are still imperfect, and explosion accidents of large-capacity power transformers occur from time to time. In view of the whole evolving process from minor defects to serious defects and finally arc breakdown in the transformer, the paper proposes to build three defensive lines for the safe operation of large-capacity power transformers. The first line is the detection and early warning of minor defects. The paper analyzes the current status of various defect detection methods and preliminarily proposes a thermal defect identification method based on multi-point temperature. The second line is the active protection in the stage of serious discharge defects, which trips before the occurrence of penetrating arc fault. The paper studies the characteristics of pulse current, ultra high frequency and acoustic signal of serious discharge defects through discharge tests, and proposes an active transformer protection scheme based on multiple parameters and a new Bucholz protection scheme. The third line is to improve the sensitivity and rapidity of traditional transformer protection technologies for arc faults. Therefore, the paper proposes core saturation discrimination technique for estimating the main magnetic flux of the transformer, and constructs an inter-turn fault protection scheme with high sensitivity based on the amplitude and symmetry difference in magnetic flux leakage. The exploration of active transformer protection technology and the proposed fault protection system of three defensive lines are of great significance for improving the safe operation level of transformers. © 2023 Automation of Electric Power Systems Press. All rights reserved.