IEEE Power & Energy Magazine - July/August 2019 - 72

Preenergization Commissioning
This stage defines the situation where the OSS has been
transported to and installed at the final offshore site with
array power cables as well as export power cables connected.
At this stage, final tests and inspections take place before
the grid connection is established and the WTGs are set
into operation. Outstanding items that still remain from the
onshore commissioning stage are subject to clarification.
Typical tasks related to this stage are
✔ a visual inspection
✔ checks of the following:
* low voltage and safety systems
* communication systems [e.g., supervisory control
and data acquisition (SCADA) as well as very high
frequency/ultrahigh frequency radio]
* insulation resistance of primary electrical equipment
* transformer tap changer operation
* transformer auxiliaries
* helideck readiness for operation
* the readiness of davits and lifeboats for operation
* platform cranes' readiness for operation
✔ HV tests for power cables.

Postenergization Commissioning
Postenergization commissioning defines the situation of the
OSS once the grid connection is established or the WTGs
have been successfully commissioned and put into operation.
Typical tasks related to this stage are
✔ monitoring
* the transformer operation as well as additional tests
and checks, including oil sampling
* the switchgear operation as well as additional checks
on cable connections and auxiliary systems
✔ checking the control and cable marshaling panels and
the emergency generator set.

O&M of an OSS System
The OSS contains the electrical equipment and also often
provides some maintenance facilities for the electrical works
and turbines, such as spare parts and technician workshops.
O&M requirements for the different elements of an OSS
platform are as follows.
Offshore Platform Structures

The offshore topside and foundation of the OSS are generally considered separately, distinguishing the subsea
and splash-zone inspections needed for the foundation.
Foundation Structural Integrity
For the jacket foundation, specialist surveys are required
to ensure structural integrity. Routine surveys are likely to
be undertaken in the first two years. Once the site has been
characterized, subsequent surveys are very infrequent, with
many required on a five- or ten-year cycle. It is unlikely that
structural repairs will be needed.
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Subsea Operations
Surveying the status of the scour protection installed to prevent sediment erosion where the jacket meets the seabed
can be carried out by remotely operated underwater vehicles (ROVs) from a survey vessel or, in exceptional cases,
by divers. Activity requiring subsea operations may include
infrequent inspections of the structure and J-tube cathodic
protection, and it can generally be carried out using ROVs.
Diving, although currently relatively commonplace, is labor
intensive and relatively expensive and required only in
exceptional circumstances. Efforts are being made to maximize the use of safer remote techniques.
Topside Paints and Coatings
OSS topsides and splash zones are expected to have highspecification paint to prevent corrosion. While the integrity
of the paint may be suitable for 10 -15 years, paint guarantees
are shorter, and areas of corrosion will need to be addressed
regularly based on visual inspections. Over the 20-year life
of the assets, at least one major repainting program would
be expected.
Topside Structures
The topside structure will need regular surveys of the integrity of the steelwork, welds and joints, and equipment modules. It is unlikely that major structural repairs will be needed.
Maintenance will include boat landings and ladders, walkways, external gates, and railings. This will include annual
cleaning and the removal of bird guano.
The davit crane on the topside will require periodic
maintenance in accordance with the manufacturer's O&M
manual. The crane will require some form of maintenance
or recertification every three years through its lifetime. The
topside structure may include a helipad or helihoist platform,
depending on the strategy for operation and maintenance
of the wind farm as well as for the OSS. If present, it will
need to be inspected and maintained. The maintenance and
inspection information of specific safety equipment, such as
fall-arrest systems and lifeboats, is included in the "Offshore
Platform Ancillary Assets" section.
Fire Safety
For passive fire protection, walls and decks must meet minimum fire integrity standards. In terms of active fire protection, a fixed water mist, gaseous system, or deluge system
is installed to cover the following areas and equipment
as applicable:
✔ HV equipment, such as main transformer(s), switchgear, and semiconductor converters, require a water
mist or gaseous system.
✔ Emergency generators need a water mist or gaseous
system.
✔ Areas of storage of cylinders with compressed gas
(e.g., oxygen and acetylene) use a deluge system.
✔ Helicopter decks (if present) use a foam system.
july/august 2019

IEEE Power & Energy Magazine - July/August 2019

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2019