IEC/DTR 61400-4-2

FINAL DRAFT
Technical
Report
ISO/DTR 61400-4-2
ISO/TC 60
Wind energy generation systems —
Secretariat: ANSI
Part 4-2:
Voting begins on:
2025-10-31
Lubrication of drivetrain
components in wind turbines
Voting terminates on:
2025-12-26
Systèmes de génération d'énergie éolienne —
Partie 4-2: Lubrification des composants de la chaîne
cinématique des éoliennes
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
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IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
This draft is submitted to a parallel vote in ISO and in IEC.
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/DTR 61400-4-2:2025(en) © ISO 2025

FINAL DRAFT
ISO/DTR 61400-4-2:2025(en)
Technical
Report
ISO/DTR 61400-4-2
ISO/TC 60
Wind energy generation systems —
Secretariat: ANSI
Part 4-2:
Voting begins on:
Lubrication of drivetrain 2025-10-31
components in wind turbines
Voting terminates on:
2025-12-26
Systèmes de génération d'énergie éolienne —
Partie 4-2: Lubrification des composants de la chaîne
cinématique des éoliennes
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
This draft is submitted to a parallel vote in ISO and in IEC.
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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Published in Switzerland Reference number
ISO/DTR 61400-4-2:2025(en) © ISO 2025

ii
IEC DTR 61400-4-2 © IEC 2025
1 CONTENTS
3 FOREWORD . 3
4 INTRODUCTION . 5
5 1 Scope . 6
6 2 Normative references . 6
7 3 Terms, definitions, abbreviated terms, units and conventions . 6
8 3.1 Terms and definitions. 6
9 3.2 Abbreviated terms, units and conventions . 7
10 4 General information . 8
11 5 Lubricants . 8
12 5.1 Type of lubricant . 8
13 5.2 Lubricant characteristics . 8
14 5.2.1 General . 8
15 5.2.2 Viscosity . 9
16 5.2.3 Viscosity grade . 9
17 5.2.4 Low temperature characteristics . 9
18 5.2.5 Performance characteristics . 10
19 5.2.6 Filterability . 15
20 5.2.7 Shear stability . 16
21 5.2.8 Compatibility . 17
22 6 Lubrication system and components . 18
23 6.1 General . 18
24 6.2 Quantity of oil in the lubrication system . 19
25 6.3 Oil reservoirs . 20
26 6.4 Filtration systems . 21
27 6.4.1 General . 21
28 6.4.2 Inline filter assembly . 21
29 6.4.3 Offline filter assembly . 22
30 6.4.4 Pressure strainer . 22
31 6.4.5 Filter and gear oil compatibility . 23
32 6.5 Coolers . 23
33 6.6 Heaters . 23
34 6.7 Pumps . 24
35 6.7.1 General . 24
36 6.7.2 Electrically driven pumps . 24
37 6.7.3 Mechanically driven pumps . 24
38 6.8 Breather . 24
39 6.9 Sensor application and integration in gearbox and lubrication circuit . 25
40 6.9.1 General . 25
41 6.9.2 Flow sensor . 25
42 6.9.3 Oil level sensors and indicators . 25
43 6.9.4 Additional sensors . 26
44 6.9.5 Oil condition monitoring sensors . 26
45 6.9.6 Particle counters (oil cleanliness sensors) . 26
46 6.9.7 Oil debris monitors . 26
IEC DTR 61400-4-2 © IEC 2025
47 6.10 Auxiliary components . 27
48 6.10.1 Ports . 27
49 6.10.2 Magnetic plugs . 27
50 6.10.3 Fluid lines . 27
51 6.10.4 Valves . 27
52 6.11 Serviceability . 28
53 7 Lubricant life and condition monitoring . 28
54 7.1 Lubricant condition monitoring . 28
55 7.2 Offline condition monitoring . 29
56 7.2.1 Sampling of used oil . 29
57 7.2.2 Sampling of fresh oil from containers . 30
58 7.2.3 Analysis parameters . 31
59 7.2.4 Limit values for used oil analyses . 32
60 7.2.5 Possible causes for changes of selected oil characteristics . 34
61 7.2.6 Trend analyses . 35
62 7.2.7 Remedial actions . 36
63 7.3 Online condition monitoring . 37
64 7.3.1 General . 37
65 7.3.2 Analysis parameters . 37
66 7.3.3 Limit values . 39
67 7.3.4 Trending . 40
68 7.4 Top treat of oil with additive concentrate . 40
69 7.5 Topping up . 41
70 7.6 Oil changes. 41
71 7.6.1 General . 41
72 7.6.2 First fill . 41
73 7.6.3 Change intervals and change criteria . 41
74 7.6.4 Oil change procedures . 42
75 7.6.5 Application of cleaning and flushing fluids . 42
76 7.6.6 Cross contamination . 43
77 Bibliography . 44
79 Figure 1 – Test apparatus for multi-pass filterability test . 15
80 Figure 2 – Test apparatus for filterability evaluation . 16
81 Figure 3 – Example of lubrication system with combined filtration and cooling system . 19
82 Figure 4 – Gradual trend to iron alarm level . 36
83 Figure 5 – Rapid change to iron level . 36
85 Table 1 – Standardized test methods for evaluating wind turbine lubricants . 12
86 Table 2 – Non-standardized test methods for lubricant performance . 14
87 Table 3 – Guidelines for used oil characteristics and properties . 33
IEC DTR 61400-4-2 © IEC 2025
91 INTERNATIONAL ELECTROTECHNICAL COMMISSION
92 ____________
94 Wind energy generation systems -
95 Wart 4-2: Lubrication of drivetrain components in wind turbines
97 FOREWORD
98 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
99 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
100 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
101 in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
102 Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
103 preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
104 may participate in this preparatory work. International, governmental and non-governmental organizations liaising
105 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
106 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
107 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
108 consensus of opinion on the relevant subjects since each technical committee has representation from all
109 interested IEC National Committees.
110 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
111 Committees in that sense. While all reasonable efforts are made to ensure that the te
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