IEC/IEEE 61886-2:2025 PDF

Overview

IEC/IEEE 61886-2:2025 - Subsea equipment, Part 2: Power transformers is a dual-logo IEC/IEEE standard that defines additional requirements for liquid‑immersed subsea power transformers (including auto‑transformers). It applies to single‑ and three‑phase units with at least one winding rated between 3.6 kV and 245 kV and rated power from 50 kVA to 300 MVA. The standard supplements-but does not replace-requirements in the IEC 60076 and IEEE Std C57.12 series and includes guidance on design, materials, seals, monitoring and testing specific to the subsea environment. An attached Microsoft Excel file is published as a complementary aid (not an integral part of the standard).

Key topics and technical requirements

The standard addresses subsea‑specific technical topics that affect reliability, safety and maintainability:

• Design and lifetime: design analyses, guaranteed lifetime, rated power and highest equipment voltage.
• Insulation and windings: winding insulation requirements, tap changers, neutral terminals and neutral grounding resistors (NGR).
• Materials and fluids: tank materials, dielectric liquid selection and material certification.
• Mechanical and pressure design: tank design, pressure compensators, seals, mechanical stress and pressure/deflection limits.
• Penetrators and connectors: electrical penetrators, subsea connectors and interfaces for cables and instrumentation.
• Instrumentation & monitoring: temperature sensors (top liquid and winding), pressure monitoring, water‑penetration detection, insulation monitoring systems and cathodic protection monitoring.
• Testing and quality assurance: extensive type and routine tests including dielectric tests, helium leakage, vacuum tightness, pressure cycling, temperature‑rise (in water and air), partial discharge and specific tests for U > 72.5 kV. Test voltages, artificial seawater requirements and liquid sampling are specified.
• Service, transport and storage: environmental profiles for normal service, handling, transportation and storage requirements.
• Documentation: mandatory rating plate information and a normative subsea power transformer data sheet (annex).

Practical applications and users

This standard is intended for organizations involved in subsea power systems and offshore electrification:

• Transformer OEMs designing and manufacturing subsea liquid‑immersed transformers and auto‑transformers.
• Subsea system integrators and EPC contractors specifying transformer equipment for umbilicals, platforms, floating wind, offshore grids and tie‑backs.
• Operators and asset owners seeking robust reliability, monitoring and maintenance criteria for subsea power equipment.
• Testing laboratories, certification bodies and classification societies conducting type and routine tests and certifying subsea electrical equipment.
• Consultants and regulators preparing technical specifications and procurement documents for offshore projects.

Related standards

• IEC 60076 series (power transformer general standards)
• IEEE Std C57.12 series (transformer standards) IEC/IEEE 61886-2:2025 is explicitly intended to provide the subsea‑specific supplements to these mainstream transformer standards.

Keywords: IEC/IEEE 61886-2:2025, subsea power transformer, liquid‑immersed transformer, subsea equipment standard, pressure compensator, dielectric liquid, penetrator, testing, insulation monitoring.