Study on the mechanism of horizontally striped contamination distribution along the surface of dry-type transformers and its influence on electric field characteristics

• A special contamination distribution of "horizontally striped contamination on high-voltage windings" is observed. • A corresponding phenomenon of “surface discharge along a circular path” of dry-type transformers is discovered. • The mechanism of horizontally striped contamination distribution and surface discharge is proposed based on electric field calculation. • The operating conditions with the most severe electric field distortion have been obtained, serveing transformer design. Dry-type transformers have the advantages of strong anti-short circuit ability, low maintenance workload, and low noise. They are commonly used in places with high performance requirements for fire and explosion prevention. However, due to the direct exposure of its insulation material to air, surface discharge in specific environments poses a threat to the safe operation of transformers. This paper observed a special contamination distribution of “horizontally striped contamination on the surface of high-voltage windings” in engineering practice, and discovered a corresponding new phenomenon of “surface discharge along a circular path”. Therefore, this paper systematically studied this special phenomenon through finite element and micro mechanical analysis. This paper found that a specific winding connection sequence can lead to a larger local electric field. The electric field force exerted on contaminated particles after being charged is the main reason for the formation of “horizontally striped contamination”. The “horizontally striped contamination” further leads to an increase in electric field, ultimately forming a new phenomenon of “surface discharge along a circular path”. In addition, wet contamination can create dry areas, and wet contamination with dry areas can cause more severe distortion of the electric field on the surface of transformers. The surface electric field of wet inorganic salt contamination with dry areas is the most severely distorted. The maximum electric field strength can reach 3.6562 kV/cm. Compared to the maximum electric field strength of 1.1581 kV/cm without pollution, it increases by 215.71 %. The research results of this paper can provide theoretical basis for the optimization design of winding structure of dry-type transformers in polluted regions.