The Evolution of Trapping Parameters on Three-Layer Oil-Paper of Partial Discharge Degradation for On-Board Traction Transformers

Quanfu Li,Yan Yang,Guangning Wu,Xiaonan Li,Yixuan Li

doi:10.1109/access.2020.3024774

Quanfu Li, Yan Yang + Show 3 more

Open Access

https://doi.org/10.1109/access.2020.3024774

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Abstract

Trap plays an important role in the charge transportation of three-layer oil-paper and the investigation of trap parameters at different degradation degree is of great significance for further research of the partial discharge (PD) mechanism. This article considers the turn-to-turn structure of on-board traction transformer. A defect model of three-layer oil-paper insulation was designed for PD test. The PD degradation samples are selected from the inception of PD to the breakdown of PD to study the characteristics of surface potential decay on degradation samples by using isothermal surface potential decay method. Given that, the trap distribution at different degradation stages was calculated and its influence on PD characteristics was investigated. The result shows that AC fluctuation voltages caused by inter-harmonic has a great influence on PD distribution, surface charge distribution and trap distribution. With the increase of degradation, the decay rate of surface potential increases and the decay rate of AC fluctuation voltages is larger than that pure AC. And also, the number of shallow trap with AC fluctuation voltages is larger than that with pure AC. The rate of free charge increases with the number of shallow trap increasing. More free electrons involves in the process of PD, accelerating the aging rate of three-layer oil paper samples. Therefore, it can be concluded that surface charge and trap distribution are helpful to clarify PD mechanism.

Highlights

On-board traction transformer is an important equipment of energy change in electric locomotives and electric multiple units (EMUs) [1]
It can be observed that the similar properties of Partial discharge (PD) with AC fluctuation voltages and pure AC are shown from PDIV (PD inception voltage) to PD breakdown
The conclusions are obtained as follows: (1) The decay of surface potential for the three-layer oilpaper samples increases with the increase of PD degradation under AC fluctuation voltages and AC fluctuation voltages

Summary

Introduction

On-board traction transformer is an important equipment of energy change in electric locomotives and electric multiple units (EMUs) [1]. Oil-paper insulation plays an important role in insulation of on-board traction transformer [1], which consist of mineral oil and Nomex papers. These interturn insulation due to the electric stress, thermal stress and mechanical stress are prone to appear insulation defects [3], including fracture, metal tip, cavity and so on. They will cause the unevenness of electric field and the concentration of the local electric field. The local irregular electric field may result in charge accumulation on the surface of oil-paper insulation. It is of great significance to investigate the evolution law of trap parameters and its influence mechanism on partial discharge

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