Operational Experience with Composite Insulators for HVDC Air Core Reactors in Outdoor Polluted Environments

Air-core dry-type reactors used in HVDC systems are top-heavy structures with a high center of gravity, typically supported by multiple aluminium or steel columns. External insulation to ground is provided by support insulators that also function as mechanical mounting elements.

In polluted environments, increased creepage distances may be required to withstand environmental and electrical stresses. This configuration presents design challenges under external mechanical loads such as seismic events, wind, conductor forces, and short-circuit conditions. Therefore, reactor design must address both dielectric stresses and mechanical stability, which are essential for ensuring long-term performance and reliability in HVDC applications.

This paper presents a comparative analysis of porcelain and composite insulators, with a dedicated focus on their application in air-core dry-type reactors for HVDC systems. The basis for this comparison is a comprehensive review of the relevant literature, the analysis of applicable international standards, and practical input from suppliers and manufacturers with field experience.

The evaluation considers a wide range of performance aspects. These include electrical characteristics such as creepage distance, flashover distance, and behaviour under polluted conditions, as well as magnetic and electrical compatibility, particularly with respect to the design and integration of top and bottom fittings. Mechanical properties are analyzed in terms of cantilever strength, bending moments at interfaces, natural frequencies, and resistance to compression, tension, and torsion. Further, the paper addresses environmental resilience, sustainability factors, service life expectations, and long-term performance under operational stresses and issues related to wildlife interference.

Practical considerations such as weight, handling during assembly, transport and logistics, maintenance requirements, and the insulator’s influence on equipment noise are also examined.

By integrating these multiple dimensions, the paper aims to support informed decision-making regarding the optimal insulator choice for HVDC air-core dry-type reactor applications across varying operational environments.

This paper further provides an updated operational record with composite post and apparatus insulators deployed in various HVDC installations worldwide. Operational experience of composite insulators used in air-core dry-type reactors is revisited.

The collected data indicates a consistently high performance of composite insulators in service as well as applicability of deterministic methods for selection and dimensioning of composite insulators based on operational experience. Based on the authors’ industrial experience, no pollution-related flashovers or ageing-associated failures have been observed for outdoor HTM composite insulators installed in delivered HVDC stations in areas classified under IEC 608151 including very heavy polluted conditions. These findings reinforce the suitability and robustness of composite insulation technology under diverse and demanding service conditions.

The findings of this study highlight the technical and operational advantages of composite insulators in certain HVDC air-core dry-type reactor applications, demonstrating their reliability, mechanical and electrical suitability, and long-term performance even under severe environmental conditions.