IEC/IEEE 61886-2:2025

Subsea equipment - Part 2: Power transformers

IEC/IEEE 61886-2:2025 is applicable to three-phase and single-phase liquid immersed subsea power transformers (including auto-transformers) with at least one winding with rated voltages in the range 3,6 ≤ Um ≤ 245 kV and with rated power in the range 50 kVA to 300 MVA. The intention is to specify additional requirements that are not covered by the IEC 60076 series and IEEE Std C57.12TM series.
This document is published as an IEC/IEEE Dual Logo standard.
This publication contains attached files in the form of a Microsoft Excel file. This file is intended to be used as a complement and does not form an integral part of the publication.

General Information

• Status: Published
• Publication Date: 25-Aug-2025
• ICS: 29.180 - Transformers. Reactors
• ICS: 47.020.60 - Electrical equipment of ships and of marine structures
• Technical Committee: TC 18 - Electrical installations of ships and of mobile and fixed offshore units
• Drafting Committee: JWG 31 - TC 18/JWG 31
• Current Stage: PPUB - Publication issued
• Start Date: 26-Aug-2025
• Completion Date: 22-Aug-2025

Standards Content (Sample)

IEC/IEEE 61886-2 ®
Edition 1.0 2025-08
INTERNATIONAL
STANDARD
Subsea equipment -
Part 2: Power transformers
ICS 47.020.60; 29.180  ISBN 978-2-8327-0601-5

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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, abbreviated terms and symbols . 10
3.1 Terms and definitions. 10
3.2 Abbreviated terms and symbols . 13
4 Profiles and use of normative references . 14
5 Service, transportation and storage conditions . 14
5.1 Normal service conditions . 14
5.2 Transportation, handling and installation requirements. 14
5.3 Storage . 15
6 Design analyses . 15
7 Design requirements. 16
7.1 Design lifetime . 16
7.2 Rated power . 17
7.3 Highest voltage for equipment . 17
7.4 Winding insulation . 17
7.5 Neutral terminal . 17
7.6 Tappings . 17
7.7 Neutral grounding resistors . 17
7.8 Penetrators and connectors . 18
7.9 Transfer of over-voltages and transients . 18
7.10 Cooling and temperature limits guaranteed at the rated conditions. 18
7.11 Transformer magnetic core . 19
7.12 Tolerances . 19
7.13 Service and maintenance . 19
7.14 Mechanical stresses . 19
7.15 Tank design . 20
7.16 Pressure compensators . 20
7.17 Seals . 21
8 Material requirements . 22
8.1 General material requirements . 22
8.2 Material certification . 22
8.3 Tank material . 23
8.4 Dielectric liquid . 23
9 Instrumentation and monitoring. 23
9.1 General requirements . 23
9.2 Pressure compensator position . 24
9.3 Top liquid temperature measurement . 24
9.4 Winding temperature measurement . 24
9.5 Water penetration monitoring . 24
9.6 Pressure monitoring . 24
9.7 Insulation monitoring system . 24
9.8 Instrument transformers . 24
9.9 Monitoring of cathodic protection . 25
10 Rating plate . 25
11 Testing . 26
11.1 General requirements . 26
11.2 Artificial seawater requirements . 26
11.3 Test voltage levels . 26
11.4 Liquid samples . 27
11.5 Type tests for new transformer designs . 27
11.6 Routine tests for all transformers . 28
11.7 Additional type and routine tests for transformers with U > 72,5 kV . 29
m
11.8 Special tests . 29
11.9 Test procedures . 30
11.9.1 General . 30
11.9.2 Material and component testing . 31
11.9.3 Fabrication and welding . 32
11.9.4 Liquid sample tests . 33
11.9.5 Helium leakage control test . 33
11.9.6 Leak testing with pressure for liquid immersed transformers . 34
11.9.7 Pressure deflection test . 35
11.9.8 Vacuum tightness test . 35
11.9.9 Vacuum deflection test . 35
11.9.10 Long term pressure cycling of pressure compensators . 35
11.9.11 Measurement of winding resistance . 36
11.9.12 Measurement of DC insulation resistance between each winding to
earth and between windings . 37
11.9.13 Measurement of polarization index . 37
11.9.14 Measurement of boost factor . 37
11.9.15 Dielectric routine tests . 38
11.9.16 Extended routine tests . 39
11.9.17 Temperature rise test in water . 40
11.9.18 Temperature rise test in air . 41
11.9.19 Partial discharge tests . 42
11.9.20 Tests of neutral grounding resistors . 42
11.9.21 Temperature cycle test . 42
11.9.22 Dismantling and examination . 43
Annex A (normative) Subsea power transformer data sheet . 45
Bibliography . 52

Figure 1 – Definition of saturation . 38
Figure 2 – Indirect measurement of winding resistance . 41
Figure A.1 – Subsea power transformer data sheet . 51

Table 1 – Temperature rise limits for transformers with insulation system in class
105 °C . 18
Table 2 – Test voltage levels . 26
Table 3 – Pressure cycles . 36
Table 4 – Test classification overview . 39
Table 5 – NGR tests . 42
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Subsea equipment -
Part 2: Power transformers
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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