A Comparative Electrostatic Analysis of Water Droplet-Induced Electric Field Distortion in Air and Oil Insulation

Chorphaka Plaengpraphan; Nutthaphong Tanthanuch

doi:10.48084/etasr.18522

Authors

Chorphaka Plaengpraphan Department of Electrical Engineering, Faculty of Engineering, Rajamangala University of Technology Thanyaburi, Pathumthani, Thailand
Nutthaphong Tanthanuch Department of Electrical and Computer Engineering, Thammasat School of Engineering, Faculty of Engineering, Thammasat University, Pathumthani, Thailand https://orcid.org/0000-0001-8000-4148

Volume: 16 | Issue: 3 | Pages: 36183-36189 | June 2026 | https://doi.org/10.48084/etasr.18522

Received: 4 March 2026 | Revised: 17 April 2026 | Accepted: 3 May 2026 | Online: 14 May 2026

Corresponding author: Nutthaphong Tanthanuch

Abstract

Moisture reduces insulation strength, but its localized influence on electric field distribution is not always fully understood. This study examines how a single water droplet affects the electric field between two rod electrodes operating under high voltage. A two-dimensional (2D) finite element model is used to evaluate droplet behavior in both air and insulating oil under the same geometric and electrical conditions. The analysis considers how droplet position and size influence field concentration along the gap. The results indicate that the presence of a droplet alters the local electric stress, particularly in regions already experiencing elevated field intensity. The degree of distortion depends on the droplet’s location and on the surrounding medium. A clear difference is observed between air and oil in terms of the magnitude of local field enhancement. While droplet size does affect the response, the trend shows that geometric interaction and positioning play a more dominant role than scale alone, with the Field Enhancement Factor (FEF) in air being approximately 7% higher than in oil under comparable conditions. These findings underline the need to account for localized moisture effects when evaluating insulation reliability. Even a single droplet can generate concentrated electric stress that may promote discharge activity and gradual material degradation. The study offers a consistent electrostatic basis for assessing moisture-related risks in both air- and oil-insulated high-voltage systems.

Keywords:

water droplet, air, oil, electric field, insulation

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