December 2025: New Standard Elevates DC Gas-Insulated Switchgear Safety in Electrical Engineering

The publication of CLC IEC/TS 62271-318:2025 in December 2025 brings a significant progression for the electrical engineering community, especially those engaged with high-voltage direct current (HVDC) systems. This newly adopted standard sets out rigorous technical specification requirements for DC gas-insulated metal-enclosed switchgear (DC GIS) rated at 100 kV and above, for both indoor and outdoor application. Stakeholders across utilities, manufacturing, EPC contractors, and compliance teams will need to align with these new best practices to ensure enhanced safety, system continuity, and environmental responsibility.

Overview / Introduction

High-voltage switchgear and controlgear are cornerstone technologies in modern power transmission and distribution—enabling safe, reliable, and efficient management of electrical energy at both utility-scale substations and critical industrial sites. With decarbonization and digital transformation driving the spread of HVDC grids globally, the technical complexity and reliability requirements for DC gas-insulated switchgear (DC GIS) have rapidly increased. Standards play a critical role in this field, codifying not only the minimum levels of safety and performance but also introducing internationally harmonized processes to manage risk, maintenance, testing, and environmental impact.

In this article, we provide a specialized analysis of CLC IEC/TS 62271-318:2025—the latest specification from CLC and IEC focused on DC GIS for voltages 100 kV and above. You will learn about its scope, critical requirements, compliance implications, and how it aims to advance both safety and operational resilience in HVDC installations. Whether you are responsible for engineering design, system integration, quality assurance, or procurement, understanding these updates is essential to maintaining competitive, compliant, future-ready infrastructure.

Detailed Standards Coverage

CLC IEC/TS 62271-318:2025 - DC Gas-Insulated Metal-Enclosed Switchgear for Rated Voltages Including and Above 100 kV

High-voltage switchgear and controlgear – Part 318: DC gas-insulated metal-enclosed switchgear for rated voltages including and above 100 kV

Scope & Application

This technical specification sets comprehensive requirements for gas-insulated metal-enclosed switchgear (GIS) operated with direct current at voltages of 100 kV or higher. Designed for both indoor and outdoor settings, the standard addresses all service conditions, defines meaningful ratings, and details functional and safety features for these critical systems.

Its coverage encompasses:

• Service conditions: Normal and special environments (temperature, humidity, pollution, altitude).
• Applicable HVDC technologies: Both Line Commutated Converter (LCC) and Voltage Sourced Converter (VSC) systems, which together form the backbone of advanced HVDC grids and renewable interconnections.
• System topology: Modular switchgear components directly connected and interlocked for integrated operation.

Key Requirements and Specifications

CLC IEC/TS 62271-318:2025 sets out:

• Design and construction rules:
  • Enclosure strength, corrosion resistance, and partitioning for operational continuity and maintenance safety.
  • Gas tightness criteria—addressing environmental leakage via strict limits (≤0.5% per year for typical gases, ≤0.1% for SF₆ and gases with high global warming potential).
  • Pressure coordination, relief, and compartmentalization to mitigate effects of internal arc faults, with detailed criteria for containment and operator safety.
• Ratings:
  • Voltage and current classes, short-circuit withstand capacity, insulation levels, and auxiliary supply standards.
  • Temperature and pressure considerations for both regular and extreme environmental operations.
• Testing regimen:
  • Detailed protocols for type and routine tests, including dielectric, partial discharge, short-circuit, mechanical, and environmental assessments (e.g., salt mist, sealing, EMC, noise, X-ray emission).
  • Special focus on long-term energized tests and composite voltage conditions (combined DC and AC voltages).
• Service and maintenance:
  • Mandated continuous gas density monitoring with dual-alarm thresholds and minimal system downtime during maintenance.
  • Partitioning concepts to ensure safe, reliable service even during partial system shutdowns.
• Environmental objectives:
  • Strict controls on greenhouse gas emissions, including gas selection, leakage limits, and handling requirements per IEC 62271-4.
  • Provisions for end-of-life management and minimum environmental impact over up to 40 years of operation.

Compliance & Implementation

Targeted at electrical utilities, switchgear manufacturers, EPC contractors, and asset managers responsible for large HVDC nodes and substations, this specification is intended to:

• Supersede or supplement national standards for DC GIS above 100 kV where applicable.
• Serve as an implementation benchmark for new projects and as a risk analysis tool for upgrades or retrofits.
• Ensure sustained safe operations, occupational safety compliance, and environmental stewardship through robust specifications covering both day-to-day and emergency scenarios.

Key highlights:

• Establishes harmonized requirements for DC GIS in HVDC applications (100 kV and above)
• Strict environmental and gas-leakage benchmarks aligned with international best practice
• Advances maintenance safety, arc-fault mitigation, and service continuity

Access the full standard:View CLC IEC/TS 62271-318:2025 on iTeh Standards

Industry Impact & Compliance

The adoption of CLC IEC/TS 62271-318:2025 is expected to reshape risk management, compliance, and operational strategies for organizations deploying high-voltage DC GIS. Key industry impacts include:

• Accelerated HVDC project standardization: Harmonized technical criteria simplify international tendering and supply chains, reducing time-to-market for advanced grid projects.
• Enhanced occupational safety: Partitioning, arc-fault protection, and mandatory alarm systems minimize risks to operational teams during maintenance, installation, and fault handling.
• Compliance readiness: Early adoption will help organizations preempt regulatory challenges, particularly around environmental and functional safety, throughout the asset lifecycle.

Compliance considerations for stakeholders:

• All new HVDC projects above 100 kV, and retrofits involving GIS installations, will require conformity with these technical requirements—either by contractual mandate or as due diligence.
• Quality assurance, engineering, and procurement teams must update design checklists, sourcing requirements, and audit protocols to reflect the new performance, gas management, and safety expectations.
• Organizations should review the standard’s guidance for documentation, site testing, and maintenance manuals, ensuring that all relevant processes and records are fully aligned.

Benefits of adopting this standard:

• Reduced environmental footprint via minimized leakage and improved gas handling
• Increased asset availability and safety during both normal operation and maintenance
• Easier global market access through standardized design and reporting conventions

Risks of non-compliance:

• Exposure to legal, financial, and operational penalties from non-conforming installations
• Compromised safety and production continuity, particularly during unforeseen incidents (e.g., arc faults, enclosure leaks)
• Ineligibility for international projects or grid codes embracing IEC CLC requirements

Technical Insights

This standard introduces several complex yet critical technical requirements that savvy professionals should note:

• Common requirements across DC GIS:
  • Sealed or closed gas systems with continuous leak-tightness verification
  • Modular, compartmentalized architectures for optimal resilience and minimum service interruption
  • Integration of automated density monitoring and alarm response, including temperature compensation
• Implementation best practices:
  • Early systems engineering to assure compatibility with both LCC and VSC HVDC converter schemes
  • Use of standardized documentation and naming conventions for device identification and mass/gas tracking
  • Adoption of proven calculation procedures (such as those for internal arc energy and enclosure pressure coordination) to guide both equipment selection and incident response readiness
• Testing and certification:
  • Prioritize manufacturer testing facilities capable of complying with type and routine tests as outlined (including dielectric, short-circuit, environmental, mechanical, and EMC assessment)
  • Ensure supporting documentation for all delivered components, plus a quality trail linking type/routine test outcomes to installation asset records
  • Encourage on-site dielectric and gas integrity tests post-installation, in accordance with guidance in the standard (Annex B)

Conclusion / Next Steps

CLC IEC/TS 62271-318:2025 establishes a rigorous, forward-looking benchmark for the deployment of DC gas-insulated metal-enclosed switchgear in complex HVDC applications above 100 kV. By aligning your organization’s engineering and procurement processes to this new specification, you unlock:

• Robust safety management for both system assets and operational personnel
• Improved system uptime, maintainability, and future upgradeability
• Assured environmental compliance, now and in the decades ahead

Recommendations:

1. Review and communicate the core technical requirements of this standard across all engineering, quality, and procurement teams
2. Audit current and planned HVDC projects to benchmark compliance gaps
3. Engage early with suppliers and service partners who can demonstrate conformity
4. Utilize the full-text standard as a foundational document for operational manuals, procurement specifications, and compliance audits

Stay ahead of regulatory and market evolution—explore the latest standards in electrical engineering on iTeh Standards and make your assets ready for the future of the power industry.