Physicochemical Characteristics and Dynamic Charge Mapping in Thermally Aged Two-Layered Polymer Considering Surface States: Experiment and Simulation.

Xiongwei Jiang,Potao Sun,George Chen,Qingjun Peng,Wenxia Sima

doi:10.3390/polym12030634

Abstract

Under operational conditions of high electric fields and elevated temperatures, the accumulation of space charges at multilayer insulation interfaces is often considered as an important factor affecting insulation performance. This study experimentally explored the influence of different thermal aging degrees (110 °C for 0, 720, 1600, 2100, and 2900 h) on physicochemical characteristics. The space charge dynamics in two-layered thermally aged PET-PET films were measured using the pulsed electro-acoustic (PEA) method and simulated on the basis of a one-dimensional modified bipolar charge transport model. The parameterization for key parameters involved in the model was analyzed through parameter sensitivity. Results indicated that the molecular structure, crystallinity, and dielectric spectra of the PET films are affected by thermal aging. The thermalization process also has noticeable effect on the surface state characteristics, which are characterized by deeper trap depth and larger trap density. Several experimental phenomena measured by the PEA method were observed on the basis of numerical simulation.

Highlights

Multilayered polymeric insulation has been widely used to meet specific requirements in electrical equipment, such as dry-type reactors and gas-insulated transformers
With the increase in thermal aging time, the reflection intensities at 1018 and 1097 cm−1 wavenumbers weakened, which corresponded to the symmetrical aromatic C–O and asymmetrical aliphatic C–O stretching, respectively [17]
When the electrons and holes passed through the interface via drift and diffusion, they could be captured and had more difficulty escaping on the second layer surface due to the asymmetrical surface state (F2 > F1, n2 > n1 )

Summary

Introduction

Multilayered polymeric insulation has been widely used to meet specific requirements in electrical equipment, such as dry-type reactors and gas-insulated transformers. Layered insulation hinders the breakdown process by providing localized states at layer interfaces to the propagation of the breakdown pathway. Insulation performance degrades under combined thermal, electrical, and mechanical stresses during long-term operation. Under a high DC field, dielectric–dielectric and metal–polymer interfaces combine a potentially mechanically weak boundary with substantial interface (surface) charges and a corresponding large field gradient [1,2,3,4,5]. Electrical failure likely occurs at these particular positions. The way in which space charge trapping/detrapping occurs at the interface must be investigated. The majority of studies investigated the effects of thermalization [1], electrical aging [5], voltage polarity reversal [4], temperature [3], and moisture [2]

Methods

Results

Conclusion