IEC TR 61400-4-2:2026

IEC TR 61400-4-2 ®
Edition 1.0 2026-02
TECHNICAL
REPORT
Wind energy generation systems -
Part 4-2: Lubrication of drivetrain components in wind turbines
ICS 27.180  ISBN 978-2-8327-1068-5

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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, abbreviated terms, units and conventions . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms, units and conventions . 7
4 General information . 8
5 Lubricants . 8
5.1 Type of lubricant . 8
5.2 Lubricant characteristics . 8
5.2.1 General. 8
5.2.2 Viscosity . 9
5.2.3 Viscosity grade . 9
5.2.4 Low temperature characteristics . 9
5.2.5 Performance characteristics . 10
5.2.6 Filterability . 14
5.2.7 Shear stability . 15
5.2.8 Compatibility . 16
6 Lubrication system and components . 17
6.1 General . 17
6.2 Quantity of oil in the lubrication system . 18
6.3 Oil reservoirs . 20
6.4 Filtration systems . 20
6.4.1 General. 20
6.4.2 Inline filter assembly . 21
6.4.3 Offline filter assembly . 21
6.4.4 Pressure strainer . 22
6.4.5 Filter and gear oil compatibility . 22
6.5 Coolers . 22
6.6 Heaters . 23
6.7 Pumps . 23
6.7.1 General. 23
6.7.2 Electrically driven pumps . 23
6.7.3 Mechanically driven pumps . 24
6.8 Breather . 24
6.9 Sensor application and integration in gearbox and lubrication circuit . 24
6.9.1 General. 24
6.9.2 Flow sensor . 24
6.9.3 Oil level sensors and indicators . 24
6.9.4 Additional sensors. 25
6.9.5 Oil condition monitoring sensors . 25
6.9.6 Particle counters (oil cleanliness sensors) . 26
6.9.7 Oil debris monitors . 26
6.10 Auxiliary components . 26
6.10.1 Ports . 26
6.10.2 Magnetic plugs . 26
6.10.3 Fluid lines . 26
6.10.4 Valves . 27
6.11 Serviceability . 27
7 Lubricant life and condition monitoring . 28
7.1 Lubricant condition monitoring . 28
7.2 Offline condition monitoring . 28
7.2.1 Sampling of used oil . 28
7.2.2 Sampling of fresh oil from containers . 29
7.2.3 Analysis parameters . 30
7.2.4 Limit values for used oil analyses . 31
7.2.5 Possible causes for changes of selected oil characteristics . 34
7.2.6 Trend analyses . 35
7.2.7 Remedial actions . 36
7.3 Online condition monitoring . 37
7.3.1 General. 37
7.3.2 Analysis parameters . 37
7.3.3 Limit values . 39
7.3.4 Trending . 40
7.4 Top treat of oil with additive concentrate . 40
7.5 Topping up . 41
7.6 Oil changes . 41
7.6.1 General. 41
7.6.2 First fill . 41
7.6.3 Change intervals and change criteria . 41
7.6.4 Oil change procedures. 42
7.6.5 Application of cleaning and flushing fluids . 42
7.6.6 Cross contamination . 43
Bibliography . 44

Figure 1 – Test apparatus for multi-pass filterability test . 14
Figure 2 – Test apparatus for filterability evaluation . 15
Figure 3 – Example of lubrication system with combined filtration and cooling system . 18
Figure 4 – Gradual trend to iron alarm level . 36
Figure 5 – Rapid change to iron level . 36

Table 1 – Standardized test methods for evaluating wind turbine lubricants . 11
Table 2 – Non-standardized test methods for lubricant performance . 13
Table 3 – Guidelines for used oil characteristics and properties . 33

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Wind energy generation systems -
Part 4-2: Lubrication of drivetrain components in wind turbines

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC TR 61400-4-2 has been prepared by IEC technical committee 88: Wind energy generation
systems, in co-operation with ISO technical committee 60: Gears. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
88/1132/DTR 88/1162/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
INTRODUCTION
The purpose of this IEC Technical Report (TR) is to provide a common reference for lubrication
related matters for wind turbine drive trains. ISO/TR 18792 provides information for lubrication
of industrial gearboxes. Some information is similar or identical to this document.
The contents are non-normative but useful to wind turbine system and component designers,
wind turbine manufacturers, and owners/operators to ensure that lubricant related matters are
addressed in the gearbox design and operation phases.
This current edition of the document covers oil lubricated gearboxes and is developed based
on experience with predominantly gearboxes with rolling bearings. It can be applied to
gearboxes with plain bearings, but possibly does not yet address all aspects of this technology.
The document structure is prepared to receive further content related to other components in
the wind turbine drivetrain and include additional types of lubricants.

1 Scope
This document, which is a Technical Report, provides non-binding information regarding the
lubricant, lubrication system layout, and performance for wind turbine gearboxes. This
document covers oil lubricated gearboxes. Additionally, guidance for selected lubricant
parameters as well as for monitoring and maintaining lubricant characteristics is offered.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61400-1, Wind energy generation systems - Part 1: Design requirements
IEC 61400-3 (all parts), Wind energy generation systems - Part 3: Design requirements
IEC 61400-4, Wind energy generation systems - Part 4: Design requirements for wind turbine
gearboxes
3 Terms, definitions, abbreviated terms, units and conventions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61400-1,
IEC 61400-3 series, IEC 61400-4 and the following apply.
NOTE In case of conflict, the definitions in this document take precedence.
3.1.1
lubricant supplier
entity supplying lubricants for the wind turbine gearbox
Note 1 to entry: The lubricant supplier is responsible for the performance of the lubricant and the blending
specifications, but will not necessarily produce any of the components, or blend the final product.
3.1.2
nacelle
turbine structure above the tower that holds the drivetrain, generator, other subcomponents,
and parts of the controls and actuation systems
3.1.3
oil
fluid used to lubricate, flush away debris, and regulate heat transfer in the gearbox
Note 1 to entry: The word oil is ambiguous but is used in this document in addition to other common terms such as:
lubricant, lubricating oil, fluid, gear oil.
3.1.4
line
rigid or flexible means to convey fluids, such as pipes, tubes or hoses, including related fixtures,
fittings, couplings, valves or connectors
3.2 Abbreviated terms, units and conventions
This document uses equations and relationships from several engineering specialties. As a
result, there are, in some cases, conflicting definitions for the same symbol. All the symbols
used in the document are nevertheless listed, but, if there is ambiguity, the specific definition
is presented in the clause where they are used in equations, graphs, or text.
F
flow circulation (or dwell time) min
c
L
basic reference rating life at 50% reliability h
Q
minimum oil flow l/min
min
P
generated mechanical power losses kW
G
power dissipated by natural convection through the gearbox
P
kW
cn
surface
kJ/(kg
C
specific heat capacity of the oil
oil
K)
V
minimum oil volume L
min
ρ oil density
kg/m
temperature difference between oil sump and oil inlet to the
∆T K
gearbox
mass loss of roller caused by wear or fatigue during loading phase
m
mg
w50
in FE8 test
AGMA American Gear Manufacturers Association
ANSI American National Standards Institute
ASTM American Society for Testing and Materials
CEC Commission of the European Communities
DIN Deutsches Institut für Normung
EP extreme pressure, refers to a type of additive
GFT “Graufleckentragfähigkeit”, micropitting resistance
FTIR Fourier transform infrared spectroscopy
FZG “Forschungsstelle für Zahnräder und Getriebebau” TU Munich
IBC international bulk container tote for liquids
IEC International Electrotechnical Commission
IR Infrared
ISO International Organization for Standardization
PAG poly-alkylene-glycol or polyglycol, synthetic lubricants
PAO poly-alpha-olefin, fully paraffinic synthetic lubricant based on synthesized
hydrocarbons
PQ particle quantifier (index)
PTO power take off
VG (ISO) viscosity grade
4 General information
Wind turbines, including their drive trains and gearboxes, operate in extreme environments with
highly variable load conditions, for example:
– temperatures from arctic to hot climates;
– humidity from dry deserts to humid marine conditions;
– sudden load variations, long periods of high loads and long periods under no-load
conditions;
– short start-up and shut-down situations;
– unmanned operation with extended time between service (typically between 6 months and
12 months).
Lubricant and lubrication system elements can be selected and balanced for these sometimes
conflicting needs. Information is provided in Clause 5 for lubricant selection, Clause 6 for
system design, and Clause 7 for maintenance. The following clauses provide information in
addition to IEC 61400-4, which supports designers, manufacturers, end users and service
personnel to develop, manufacture, operate and maintain lubricants and lubrication systems in
wind turbines.
5 Lubricants
5.1 Type of lubricant
Compared to most other gearbox applications, gearboxes in wind turbines are exposed to high
percentage of utilization, though with high variation between periods of partial and full load.
During full load operation, gears operate at low to moderate pitch line velocity with high to very
high contact loads, whereas bearings are exposed to moderate contact loads. Lubricants
fortified with performance enhancing additives and of the highest practical viscosity can be used
to improve operation under these conditions. The base fluids of these lubricants can be chosen
from highly refined mineral oils, full synthetic fluids, or semi-synthetic blends (mixtures of highly
refined mineral oils and synthetic fluids). The choice of a finished lubricant depends on many
factors including viscosity, viscosity index, pour point, additives, and overall lubrication costs.
Site specific operating conditions, wind turbine performance, cold start and operating
temperature within the nacelle as well as serviceability influence the selection of the most cost-
effective gearbox lubricant.
5.2 Lubricant characteristics
5.2.1 General
Most large modern wind turbines are equipped with multistage gearboxes that convert the low
rotor speed to high generator speed for high efficiency. Ideally, each stage of the gearbox would
benefit from a different oil viscosity, but this is not practical. Additionally, the gears and bearings
in each stage would benefit from different performance chemicals such as higher antiscuff (also
known as extreme pressure (EP)) levels and higher antiwear at the input stages. Oxidation
stability is important because of the potential risk of deposit formation such as varnish and
sludge that can clog filters, small oil passages and oil spray nozzles, as well as create deposit
on critical surfaces. Using multiple additives with different characteristics can have synergistic
or antagonistic effects. Therefore, it is common to make some compromise in the choice of
additives and final lubricant characteristics.
The key functions of the lubricant are to minimize friction and wear between surfaces in relative
motion, to remove heat generated by the mechanical action of the system and to protect internal
parts of the gearbox against corrosion. Sufficient viscosity to separate the mating surfaces as
well as appropriate chemical additive systems can help to accomplish these tasks and minimize
thermal and oxidative degradation and promote antiwear performance.
The choice of the appropriate lubricant depends in part on matching its properties to the
application. Therefore, a detailed elastohydrodynamic analysis of the gearbox components with
reference to ISO/TS 6336-20, ISO/TS 6336-21, ISO/TS 6336-22 and ISO 281 has proven
useful.
The following design- or operating characteristics can, amongst others, influence lubricant:
– the type of gearing used in the gearbox;
– selected operating conditions, such as:
• ambient temperature range;
• operating temperature range;
• operating speed range;
– any critical special circumstances, such as:
• low temperature start-up;
• ambient temperatures above 50 °C;
• high transient loads.
5.2.2 Viscosity
Viscosity is the most important physical property of a lubricant, and it has a direct impact on
gearbox performance and its service life. It is the property of a lubricating oil to resist against
flow and contributes to the development of a protective lubricating film.
5.2.3 Viscosity grade
IEC 61400-4 specifies that the correct viscosity grade of the lubricating oil for a gearbox is
selected based on operating, not start-up, conditions. The viscosity grade in the context of this
document is the kinematic viscosity grade, ISO VG, according to ISO 3448.
Additional operating parameters of importance are the viscosity index of the oil, the viscosity
ratio for rolling bearings and the pitch line velocity of the gears.
If the viscosity of the lubricating oil is too low, the application can suffer from wear. Too high
viscosity can cause excessive losses which can lead to temperature increase, resulting in a
decreased lifetime of the lubricant. Furthermore, too high viscosity can lead to oil starvation
when the oil is cold, e.g. during start-up conditions. Where there is a large difference between
the input and output shaft speeds (as in typical multistage wind turbine gearboxes), it is
beneficial to base the viscosity grade on the low-speed input gear to ensure development of an
adequate lubricant film.
General information on viscosity grade can be found in ISO/TR 18792. The most common
viscosity grade used in wind turbine gearboxes is ISO VG320, but other grades between
ISO VG220 and ISO VG460 are also in use.
5.2.4 Low temperature characteristics
Sufficient lubricant flow to all gear and bearing contacts at the coldest start-up temperature can
help to avoid starvation which could lead to premature damage. There are no published low
temperature requirements for ISO viscosity grades for wind or industrial applications. Oils with
viscosity grade ISO VG320 (ISO 3448) can cope with the typical ambient temperature ranges
in wind turbine applications, if the chosen oils provide a sufficiently low pour point.
NOTE The pour point of oils used in wind turbine gearboxes is typically significantly below the maximum value
specified in ISO 12925-1 for CKMSP lubricants.
Heaters (see 6.6) can be used to adjust sump temperature at start-up. VDMA 23901 provides
additional information regarding cold weather applications.
5.2.5 Performance characteristics
The minimum requirements for gear oils are defined in IEC 61400-4. In addition, as part of the
lubricant selection process, the oil typically satisfies additional selected performance
characteristics to improve long-term reliability of the gearbox. This is primarily a function of the
chemical additive system used in the lubricant. Additives are essential for fulfilling predicted
gearbox design life. Some additives are surface active substances that protect the surface from
specific damage types by building chemical and/or physical reaction layers. However, surface
size and reactivity are limited and can be considered when selecting additional performance
characteristics. For example, measures to increase wear protection can lead to a lower level of
corrosion protection and vice versa. Likewise, measures to improve paint compatibility can
decrease the seal compatibility.
Evaluation of the following characteristics has proven useful to predict lubricant performance in
wind turbine gearboxes:
– gear scuffing;
– gear micropitting;
– bearing wear and bearing fatigue in mixed friction regime;
– oxidation of oil;
– corrosion protection (ferrous and non-ferrous);
– foaming and air release;
– filterability;
– shear stability;
– compatibility with materials (ferrous and non-ferrous metals, elastomers, seals, gaskets,
sealants, paints and coatings, adhesives or plastics);
– compatibility with auxiliary components (e.g. filter media, desiccant used in breather vent
devices, electronic sensors, or connectors);
– compatibility with utilities such as run-in oils or corrosion preservatives.
Acceptance of lubricant performance is commonly based on results from standardized test
methods. For some critical performance characteristics, no standardized test methods exist at
date of publication of this document. Test methods with documented data for repeatability and
reproducibility are preferable.
Table 1 and Table 2 summarize an exemplary and non-exhaustive set of commonly used
standardized and non-standardized test methods and typical performance levels with relevance
for wind turbine gearboxes.
NOTE For elastomer and paint compatibility, the table provides example values since various materials can be
used.
Wind turbines are one of the bearing applications where early premature failures associated
with white etching cracks are observed. IEC 61400-4 discusses potential causes and possible
means to reduce the risk of occurrence. Lubricant interaction is a potential contributor to the
failure mode. However, at the time of publication of this document, there are no test methods
for lubricants which predict the risk of this failure mode, and where test results correlate
consistently with field experience.
Regardless of the method chosen to determine specific lubricant performance, it can be useful
to compare the results with those obtained with a reference oil, preferably one with a positive
field service history.
It has proven useful to demonstrate lubricant performance by field experience of at least 1 to 2
years.
Table 1 – Standardized test methods for evaluating wind turbine lubricants
Property Procedure name Test method Test conditions Typical performance
characteristics
a
Gear – adhesive wear (scuffing) FZG scuffing test ISO 14635-1 A/8,3/90
Fail load stage ≥ 14
A/8,3/60 (additional)
a
Fail load stage ≥ 12
Alternatively: A/16,6/90
Additional: A/8,3/60 bearing Fail load stage ≥ 12
a
Mdf
d
Bearing - antiwear protection DIN 51819-3 D-7,5/100-80 Roller wear:
FE8
c
under extreme mixed friction 7,5 r/min; 100 kN
m ≤ 30 mg
w50
80 h: 80 °C
No microspalled areas according
to ISO 15243
e
Bearing - fatigue under moderate DIN 51819-3 D-75/90-70 Roller wear:
FE8
c
mixed friction 75 r/min
m ≤ 30 mg
w50
90 kN
800 h
No surface damages
a
70 °C
Gear micropitting FZG micropitting test DIN 3990-16 GT-C/8,3 /90 Failure load stage ≥ 10
and GFT-high
GT-C/8,3/60 Failure load stage ≥ 10
and GFT-high
Shear stability Tapered roller bearing shear test ISO 26422 20 h, 60 °C, 5 000 N Stay in ISO VG class
b, c
ISO 1817 Example:
Volume change −5 % to +9 %
Static elastomer compatibility
duration for PAO-oils: 1 008 h
Hardness change ± 10 %
Example:
Elongation change < 50 %
temperature for nitrile butadiene
rubber (NBR) elastomers: 95 °C
Tensile strength change < 60 %
Example:
temperature for fluorocarbon-
based elastomers: 120 °C
Example:
temperature for hydrogenated
nitrile butadiene rubber (HNBR)
elastomers: 120 °C
Property Procedure name Test method Test conditions Typical performance
characteristics
b
Hardness testing ISO 1522 Example for test duration: Visual inspection: No blistering
Compatibility of paint system
ISO 2409 – 168 h for primers
(consisting of primers and top
For film thickness up to 250 µm: Cross-cut ≤ 1
ISO 2812-1 – 504 h for top coat
coat)
cross-cut testing
ISO 2812-3
Pull-off force > 5 MPa
Example for test temperatures:
ISO 16276-1
For film thickness larger than:
– 95 °C for mineral oils;
ISO 16276-2
250 µm: pull-off testing
– 130 °C for synthetic oils
Compatibility of adhesives and Static immersion test ISO 10123 672 h at 80 °C To be specified dependent on
b
product type (different for
sealants
ISO 4587
adhesives and sealants)
Foaming Flender foam test ISO 12152 25 °C ≤ 15 % after 1 min,
≤ 10 % after 5 min
40 °C ≤ 13 % after 1 min,
≤ 9 % after 5 min
60 °C ≤ 10 % after 1 min,
≤ 7 % after 5 min
b
Example:
ISO 2160 Max. 2
Copper Corrosion
100 °C, 24 h
b, f
Collapse burst rating ISO 2943 According to ISO 2943 According to ISO 2943
Filter element compatibility
a
Modified test conditions.
b
To address the needs of the specific applications and/or wind turbine manufacturer requirements, the methods, performance characteristics and test conditions can be modified
considering the lubricant and the material type. The choice of test temperature is dependent upon the stability of the material and/or the stability of the oil.
c
To address specific end user applications, the method can vary depending on the elastomer in use.
d
Sometimes referred to as Schaeffler wind energy 4 stage test stage 1 found in Schaeffler TPI 176.
e
Sometimes referred to as Schaeffler wind energy 4 stage test stage 2 found in Schaeffler TPI 176.
f
This test is typically executed once for a family of filter elements using the same filter media and other materials.

Table 2 – Non-standardized test methods for lubricant performance
Property Procedure name Test method Test conditions Typical performance
characteristics
a
Corrosion SKF Emcor Distilled water Rating max. 1
ISO 11007
(non-ferrous)
Salt water (0,5 % NaCl) Rating max. 2
Bearing - additive reactions Schaeffler wind energy 4 stage Schaeffler wind energy stage 3 Test bearing: 6 206
L ≥ 550 h
b
under EHD conditions test, stage 3 Test speed: 9 000 r/min
on L11 test rig
Test load: 8,5 kN
Run time: 700 h
No temperature control
Bearing - oil behaviour at Schaeffler wind energy 4 stage Schaeffler wind energy stage 4 Test bearing: 81 212 MPB
Filter blocking < 2
b
increased temperature and with test, stage 4 Test speed: 750 r/min
on FE8 test rig
Roller wear < 30 mg
addition of water Test load: 60 kN
Fatigue damage: no
Run time: >600 h
Preheating system/ water /
Residue at bearing:
Temperature control: 100 °C
moderate/heavy
Residue at preheat system:
moderate/heavy
Chemical and thermal stability SKF roller test SKF 8 weeks at 100 °C Corrosion attack max. 2
Viscosity change max 10 %
No sludge
No incrustation
Filterability Multi-pass with oil analysis and CC Jensen Filter the oil in a test rig through Foam same as fresh oil
foam test the filter 100 to 10 000 times
HYDAC multi-pass HN 30-08 Additive change – define %
Define secondary additive %
change
Filterability Single-pass HYDAC single-pass HN 30-04 Application filter media Filterability index:
a
– ≥ 80 % for stage 1
(ISO 13357-2 )
– ≥ 60 % for stage 2.
a
Modified test conditions.
b
Information on Schaeffler wind energy 4 stage test can be found in Schaeffler TPI 176.

5.2.6 Filterability
5.2.6.1 General
The filterability test according to ISO 13357-1:2017 is not applicable for the oils of the ISO VGs
typically used in wind turbines . Non standardized test procedures can be applied instead as
described in the following subclauses.
5.2.6.2 Multi-pass filterability test
The filterability of the oil and its additive package can be tested by means of an accelerated
multi-pass filterability test. In this test, a small oil volume passes through the test filter multiple
times to assess the filterability. The intention of the test is to investigate the compatibility of the
gear oil with the filter media. A filterability test is usually carried out with a fresh oil sample.
Used oil, preferably from the field, can also be considered. As an example, the Hydac
Filterability Test HN 30-8 (schematically shown in Figure 1) is based on a test rig design with
an integrated Flender Foam Tester, which serves as an oil reservoir. The test oil is pumped
through a test filter typically 1 000 passes of the oil over the filter (also 100 or 10 000 times can
be considered). Before and after filtration, a Flender Foam Test, ISO 12152 is carried out to
assess the foaming tendencies of the oil. Before and after filtration (0, 10, 100, 1 000 cycles),
an oil sample is taken to provide oil analysis data such as viscosity (ISO 3104) and additive
elements (ASTM D5185). The foam test is commenced after the pump has been stopped, the
foam has settled, and the oil is de-aerated. The pressure drop at the filter is measured as a
function of testing time to allow detection of any change. Other multi-pass filterability test rigs
can be designed to address offline filtration or other specific field conditions, for example higher
or lower test temperatures or flow rates.

Key
1 Flender foam test apparatus
2 test filter
3 circulation pump
4 pressure relief valve
Figure 1 – Test apparatus for multi-pass filterability test
___________
A new edition of this document exists but the cited edition applies.
The methods described in ISO 13357-1:2017 and ISO 13357-2:2017 are designed for mineral oils up to
ISO VG 100 and can be applied for mineral oils up to ISO VG 220. Future revisions of these standards can include
methods for higher viscosity grades.
5.2.6.3 Single-pass filterability test
This test serves to evaluate the general ability of the oil to pass through the filter media in a
reasonable time and to evaluate premature filter blockage caused by components of the oil.
The test rig is similar to the apparatus described in ISO 13357-2:2017 (see Figure 2).

Key
1 source of compressed air or nitrogen
2 pressure regulator
3 pressure gauge
4 ball valve
5 pressure vessel with membrane support
6 measuring cylinder
Figure 2 – Test apparatus for filterability evaluation
Compared to ISO 13357-2:2017, test procedures, parameters, and interpretation can be
adapted for gear oils of higher ISO VG (e.g. the use of coarser filter media can be used in the
in-house test procedure).
5.2.7 Shear stability
In order to maintain the functionality of the lubricant, it has proven useful to evaluate the
potential for viscosity loss due to breakdown of polymeric components. ISO 26422 has proven
suitable to evaluate this characteristic in other applications and can be used. From experience,
a wind turbine lubricant works well when its viscosity is maintained within the initial ISO VG
class. Maintaining proper viscosity by using shear stable lubricant over the entire operating
temperature range of the gearbox can also help to minimize the potential for foaming and air
entrainment.
5.2.8 Compatibility
5.2.8.1 General
Wind turbine gearboxes use many different materials that come in contact with the lubricant.
These materials can be laboratory tested for compatibility. These tests typically include:
– compatibility with materials of construction (e.g. ferrous and non-ferrous metals, paints,
coatings, elastomers, seals, sealants, and adhesives);
– compatibility with auxiliary and peripheral components (e.g. filter media, desiccant used in
breathers, electronic sensors, or connectors);
– compatibility of process media used during manufacturing and assembly (e.g. run-in oils,
test oils, corrosion inhibitors), if they remain inside the gearbox in relevant quantity.
Individual test procedure and acceptance limits can be defined and specified.
Although each method specifies certain materials and test conditions, these can be modified to
accommodate specific end user applications. Regardless of the method chosen to determine
compatibility, the results are typically compared to a standard or to results obtained with a
reference oil with a positive field service history.
5.2.8.2 Elastomer compatibility
Lubricant compatibility with elastomers can be measured in different ways depending on the
sealing system and its requirements. Two primary methods are static immersion testing and
dynamic testing.
Static immersion tests are popular and relatively simple to conduct. ISO 1817 and ASTM D5662
are examples of such test methods. The test usually consists of suspending samples of the
elastomer in a glass test tube containing the oil to be assessed. The test tube is placed in a
controlled heated bath for a specified length of time. At the end of the specified time, the
elastomer samples are removed and rinsed with a hydrocarbon solvent to remove the oil. The
elastomer is then evaluated for changes in volume, hardness, and elongation.
Dynamic tests, such as ISO 6194-4, use special rigs and are often conducted to an equipment
manufacturer's preferred duty cycle. Typically, such tests last between 240 h and 1 008 h, or
even longer. Dynamic testing is usually assessed by quantifying the amount of leakage that
occurs during the test. When complete, the seal itself is usually analysed.
5.2.8.3 Filter compatibility
Appropriate sizing of filter assemblies is beneficial, as there can be detrimental effects on the
long-term performance of the lubricant or lubrication system such as:
– hardening, softening, or degradation of the filter media or sealing components;
– reduced filterability;
– removal or alteration of additives such as antifoam agents;
– filter contribution to electrophoresis (static electricity b
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