Moisture determination of the main insulation in a transformer by frequency‐domain spectroscopy

The XY model is a simplified insulation model for transformers that aims to connect the frequency spectrum of major insulation, insulation paper, and oil. It enables the calculation of the paper's frequency spectrum, facilitating a quantitative evaluation of the transformer's insulation status. Given the scarcity of research addressing the accuracy of the XY model and its corresponding equivalent circuit, this paper investigates the accuracy of the XY model and conducts an in‐depth analysis of the error associated with its equivalent circuit. Firstly, the frequency spectrum of oil‐paper insulations based on the XY model with varying moisture content and structure configurations were measured, followed by the simulation of both the corresponding 2D‐coaxial and XY models. By comparing the results obtained from these simulations with experimental data on oil‐paper insulation, the accuracy of XY model is verified. Subsequently, two variants of the equivalent circuit of the XY model are derived by combining the oil, spacer, and paper differently, which denoted as Type I and II circuits. Finally, we analyzed and explained the errors present in these equivalent circuits compared with the XY model. Our findings show that the width‐thickness ratio of oil‐paper insulation is the most critical influencing factor, while moisture content and insulation structure have a less decisive impact. Notably, for general transformers, as the width‐thickness ratio is between 30 and 70, the relative error of the Type I circuit remains consistently below 0.3% across different frequencies. Consequently, the Type I circuit proves to be a more suitable representation of the equivalent circuit for the XY model in the context of general transformers. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Section: Introductionmentioning

confidence: 99%

“…FDS can be applied to analyze the insulation status of electrical equipment. Notably, FDS allows the quantification of moisture levels and the aging status of transformer insulation paper, facilitating the quantitative evaluation of moisture and aging of the transformers [4–8].…”

Section: Introductionmentioning

confidence: 99%

Error Analysis of XY Model Equivalent Circuit Based on Finite Element Simulation

Tu,

Xu,

Jiang

et al. 2024

“…During long‐term operation, oil‐paper insulation bears mechanical, chemical, electrical, and thermal stresses, causing the degree of polymerization (DP) to decrease [3]. Among them, the moisture can greatly accelerate the degradation process, seriously affecting the insulation performance [4,5]. Therefore, it is of great significance to accurately evaluate moisture content of oil‐paper insulation [6].…”

Section: Introductionmentioning

confidence: 99%

“…Among them, the moisture can greatly accelerate the degradation process, a Correspondence to: Shengkang Wang. E-mail: wsk@hust.edu.cn seriously affecting the insulation performance [4,5]. Therefore, it is of great significance to accurately evaluate moisture content of oil-paper insulation [6].…”

Section: Introductionmentioning

confidence: 99%

Frequency‐Domain Dielectric Response of Insulating Paper with High Humidity

Tu,

Wang,

Chen

et al. 2023

The frequency‐domain dielectric spectroscopy (FDS) of humid insulating paper has been measured at different temperatures. The data show three independent dielectric processes: electrode polarization, hopping conductivity and interfacial polarization. The dielectric properties of humid insulating paper are composed of hopping conductivity and interfacial polarization, and its equivalent dielectric model can be represented by a Havriliak‐Negami (HN) relaxation branch parallel hopping conductivity. At high temperatures and low frequencies, the measured dielectric spectroscopy bends downward, which is caused by the electrode polarization. In this case, the equivalent dielectric model is composed of the body impedance of insulating paper and the electrode polarization in series. According to the equivalent dielectric model, the components of electrode polarization, hopping conductivity, and interface polarization can be separated, thereby eliminating the parasitic effect of electrode polarization on the dielectric properties of insulating paper. Both of hopping conductivity and interface polarization of insulating paper move toward high‐frequency direction with temperature increasing. For humid insulating paper with a moisture content of 5.9%, the activation energies of hopping conductivity and interface polarization are 1.18 and 0.99 eV, respectively. This difference in activation energies results in the inability of the spectrums of insulating paper to overlap with each other at different temperatures. Based on the insulating paper without oil immersion, the results obtained in this article are not affected by oil or oil‐immersion operations. This provides a reference for exploring the dielectric properties and physical mechanisms of oil‐paper composite insulation materials widely used in high‐voltage equipment. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

“…The equivalent circuit of XY model has two forms for selection: "Series to Parallel" and "Parallel to Series" [12]. At present, the commonly used form is the "Series to Parallel" circuit [13][14][15]. However, the specific selection basis and the comparative study of the two circuit forms have not been investigated yet.…”

Section: Introductionmentioning

confidence: 99%

Study on XY Model and Its Equivalent Circuit of Oil‐Paper Insulation

Tu¹,

Wang

et al. 2022

The XY model of oil‐paper insulation connects the dielectric properties of oil, paper and oil‐paper system. Its equivalent circuit is the basis of the application of dielectric response technology in the state diagnosis of transformer oil‐paper insulation. To better apply the XY model to the study of the dielectric properties of oil‐paper insulation, the dielectric properties of the coaxial oil‐paper insulation system built in the laboratory, XY model and its equivalent circuits are compared. Then an improved circuit of XY model which can reflect the properties of the oil‐paper insulation more truly is proposed. The results show that there is no difference between the XY model and the coaxial model, and both can well characterize the oil‐paper insulation system. The two equivalent circuits of XY model, “Series to Parallel” circuit and “Parallel to Series” circuit, ignore the current tangential component and the electric field distortion in oil‐paper insulation, respectively, resulting in deviations from the XY model. By introducing a new branch C*XY, the improved circuit can reflect the tangential current and electric field distortion in oil‐paper insulation, which can be completely equivalent to XY model. In addition, there is a characteristic frequency point in the oil‐paper insulation system, where the dielectric loss factor tan δ of oil, paper and oil‐paper system are the same. There is no difference between the XY model and its two equivalent circuits at this point. The characteristic frequency is determined by the dielectric properties of oil and paper, and not affected by the insulation structure. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.