Effect of Cooling Medium on LDPE Dielectric Properties.

Yujia Cheng,Zhuohua Duan,Guang Yu

doi:10.3390/polym14030425

Yujia Cheng, Zhuohua Duan + Show 1 more

Open Access

https://doi.org/10.3390/polym14030425

Copy DOI

Abstract

Polyethylene, with its excellent mechanical and dielectric properties is used as an insulator for high-voltage direct current (HVDC) transmission. In ultra-high-voltage direct current (UHVDC) transmission, the ageing of insulation materials caused by space charge under high DC voltage becomes serious. Therefore, restraining the space charge and improving the dielectric properties of HVDC cables is important. In this study, low-density polyethylene (LDPE) was used as the raw material and combined with cooling media in a vulcanizing press. A polarizing microscope was used to observe the samples’ crystal morphologies. The space charge accumulation and dispersion were detected using pulsed electro-acoustic. Additionally, dielectric properties such as electrical conductivity and dielectric frequency spectrum were tested. The grain size in the air-cooled LDPE samples was found to be large and unevenly dispersed. However, the grain sizes in the water and oil cooling LDPE samples were small. The mean charge density of the oil cooling samples was the lowest. Under a short circuit measurement, more space charges were found in the natural and rapid air cooling samples. The mean charge densities of these two samples were high, with a fast decay rate. With an 8 and 50 kV/mm electric field strength, the oil cooling samples’ conductivity was the highest and lowest, respectively.

Highlights

With the development of industry, there must be higher standards for the transmission capacity and operational stability of power systems [1]
To explore the effect of the different cooling mediums on polyethylene space charges and other dielectric properties, the polyethylene samples were melt-pressed by a vulcanizing press for 15 min
20 kV/mm electric field, heteropolarity charges appear around the negative electrode, with a peak value of 1.2425 C/m3

Summary

Introduction

With the development of industry, there must be higher standards for the transmission capacity and operational stability of power systems [1]. Compared with traditional highvoltage AC transmission (HVAC), HVDC possesses several advantages, such as low cost, short line corridor, low electric energy loss, fast power adjustment, and reliable operation. Plastic cables possess some advantages, such as a large transmission capacity, small mass, and long-term operational stability. These cables are widely used in AC transmission systems [9,10,11]. Owing to the effects of a long-term higher electric field, space charges accumulate, which degrade the polyethylene insulation properties [15,16]. During sample preparation, the effects of different cooling processes on the dielectric properties of polyethylene samples need to be explored. The effect of different cooling media on the dielectric constant and dielectric loss factor was explored

Polymer Preparation Process and Crystalline Morphology Analysis

Effect of Different Cooling Media on Material Conductivity and Dielectric

Findings

Conclusions