Analysis of By-products from Crosslinked Polyethylene using Gas Chromatography

Abstract

Introduction: During the crosslinking process of high voltage cables, by-products are formed that affect the electrical properties of the cables, therefore these must be detected and quantified to improve manufacturing of high voltage cables.

Background: Understanding conduction mechanism and insulation systems is essential for improving cable performance and preventing failures in high voltage direct current (HVDC) cables. The crosslinking process produces by-products that affect conductivity and electrical performance. This thesis will therefore focus on examining semiconductive and insulation crosslinked polyethylene (XLPE) materials and compare by-products due to their impact on performance. The results may provide valuable insights to optimize cable design and production parameters.

Aims: The objective of this thesis is to compare by-products in various XLPE materials under different activation energies, where the temperature and time will be varied. The relationship and impact of crosslinking temperature and time on by-product quantity will be analyzed using gas chromatography (GC). Variations in by-product quantity will also be examined.

Methods: To fulfill the aim of this thesis a GC with a flame ionization detector (FID) will be used to analyze and quantify the by-products in XLPE materials. The experimental design involves varying crosslinking temperatures and times to study their influence on the by-product formation.

Results: Analyses conducted on insulation material, material A, show that the amount of alpha-methylstyrene and acetophenone increases with increasing temperature while the amount of 2-phenyl-2-propanol decreases with increasing temperature. The amount of alpha-methylstyrene increases during longer durations while acetophenone and 2-phenyl-2-propanol amounts decrease. For semiconductive material B, more by-products are formed at lower temperatures and shorter durations. For material C it is not possible to determine a clear pattern.

Conclusion: Based on this thesis work it can be concluded that the amount of by-products is affected by both temperature and time. The results contribute to further optimization of cable manufacturing in the future.

Popular Abstract

Uncovering Chemical Traces - Investigating By-products in Crosslinked Polyethylene with Gas Chromatography

High voltage cables play a key role in the green transition by enabling electricity transmission between continents or countries, between power plants such as wind farms or hydro power plants and consumers such as industries, large cities and offshore platforms. They are especially used over long distances on land or under water. The insulation in these cables are typically made of polyethylene which must undergo crosslinking to improve heat resistance as well as electrical insulation and mechanical strength. In its original form polyethylene melts at high temperatures, but crosslinking alters its chemical structure, making it more durable.

During the crosslinking process various by-products are formed. Increased by-product content correlates with higher conductivity and reduced breakdown strength. Additionally, these by-products can accumulate within the material and potentially weaken the cable’s ability to withstand high electrical fields over time. Controlling by-products is crucial for reliable DC cable operation. One common by-product is alpha-methylstyrene which can increase the electrical conductivity and raise the risk of electrical current leakage. To further understand and improve cable performance and reliability, these by-products need more research. To do this, a set of test samples of cable materials are exposed to different temperatures and durations to allow assessment of different parameters’ effects on crosslinking by-products. Gas chromatography is then used to analyze the types and amounts of by-products present. This technique vaporizes the sample and separates its chemical components within the instrument, allowing precise detection and quantification of by-products. The results are presented as a chromatogram and provide valuable insights contributing to improving the manufacturing process and thereby enhancing high voltage cables quality.

The results showed that the amount of by-products is affected by temperature and time. For the insulation material the amount of the by-products alpha-methylstyrene and acetophenone increased with increasing temperature, while the by-product 2-phenyl-2-propanol decreased. The amount of alpha-methylstyrene increased with longer durations while the other two by-products decreased. For one of the semiconductive materials more by-products were formed at lower temperatures and shorter durations. The results provide valuable information for further optimizing parameters in cable extrusion.

• author: Antonischki, Elin
• supervisor: Sabina Strand; Svetlana Zlatkovic
• organization: Department of Chemistry
• course: KEML10 20251
• year: 2025
• type: M2 - Bachelor Degree
• subject: Chemistry
• keywords: By-products, Cables, Alpha-methylstyrene, GC, XLPE, Analytical chemistry
• language: English
• id: 9197682
• date added to LUP: 2025-06-12 13:49:06
• date last changed: 2025-06-12 13:49:06