Experimental characterisation and life data analysis of superior mixed liquid dielectrics for power transformer application

Abstract

Transformer liquid dielectrics play a vital role in safety and reliability of power utility grids under normal and faulty conditions. Liquid dielectrics provide electrical insulation and act as coolant for the power transformer. However, most used dielectrics are made from Mineral Oil (MO) which has low breakdown voltage, flash, and fire point, also posing a risk of contaminating the environment in case of leakage or explosion. Therefore, research explores on potential natural renewable resources to replace the vast use of MO*⁎ Mineral Oil based dielectric. This paper focuses on using Ximenia Oil (XO) and Kalahari Melon Seed Oil (KMS), both being natural esters, for dielectric application. Each of them is mixed at different ratios separately with reclaimed mineral oil to analyse their compatibility with power transformers. Electrical and chemical properties of these esters are tested to find optimal blending ratio for each, and lifetime analysis is applied to further establish their usability. In this study, both XO†† Ximenia Oil and KMS have been identified to be applicable at 75:25 MO: XO ratio and 70:30 for MO: KMS respectively, especially after moisture content reduction. Lifetime analysis has also rendered the two dielectrics applicable as they have a long-estimated lifetime greater than that of MO alone. MO: XO dielectric has been more dominant over KMS, and MO based dielectrics in most property while KMS has shown dominance in the lifetime reliability analysis after 50 kV BDV‡‡ Breakdown Voltage value. Therefore, application of these blends significantly improves the lifetime of the transformer dielectrics hence improving that of the transformer itself.

Keywords

• Power transformer
• Liquid dielectrics
• Ester
• Mineral oil
• Lifetime analysis