IEEE Power & Energy Magazine - July/August 2019 - 73

These all need to be maintained as part of the overall
operational and maintenance requirements for the offshore topside.

Offshore Platform Electrical Systems
OSS maintenance consists primarily of nonintrusive inspections of topside switchgear and transformers with a requirement of infrequent intrusive services or repairs, depending
on the type of switchgear and transformers installed. It is
typically carried out by the original equipment manufacturer.
More serious repair operations, such as replacing transformers, will require the use of heavy-lift vessels.
Planned maintenance activities are likely to result in a
temporary reduction of available electricity export capacity.
The duration of maintenance is dependent on the type and
design of the transmission infrastructure and the degree of
system redundancy. For the transformers located on the offshore platform topside, generally no intrusive maintenance
will be required. However, there are several real-time monitoring devices attached to the transformer that will require
periodic maintenance.
Typical maintenance tasks for offshore transformers include
✔ transformer oil tests (which analyze water content, carbon, and so on) every five years for the initial 10 years
and then every two years
✔ Buchholz tests (checks for internal faults, such as overheating or arcing, low oil level, or a leak) every three years
✔ periodic checks of the monitoring equipment and the
silica gel breather
✔ protection trip tests from the transformer to the protection system every three years
✔ protection and control tests every three years
✔ general cleaning of the transformer
✔ oil leak checks on every visit to the substation
✔ paint touch-ups.
OSS platform asset operation depends on SCADA monitoring, which is used to optimize performance and, potentially,
identify component faults. In addition to enabling 24/7 monitoring and occasional remote manual intervention (which requires
several dedicated employees per wind farm), data can also be
analyzed in depth offsite for condition monitoring purposes.
GISs are sulfur hexafluoride (SF6) circuit breakers characterized by their simple and robust construction. They have
a long life expectancy. Their operating mechanisms have
a low maintenance requirement, and the interrupters are
maintenance free during their working life. Their servicing
intervals and scope are determined by environmental influences, switching sequences, and the number of short circuit
breaking operations. Under normal operating conditions and
with carefully performed inspections and servicing work, circuit breakers, depending on the type, have a service life of up to
approximately 20,000 operating cycles.
Typical maintenance tasks for GISs include the following:
✔ timing tests for electrical equipment, such as circuit
breakers, disconnectors, and earth switch contacts
july/august 2019

✔ operations testing or cycle testing of the circuit break-

er (spring or pneumatic) and disconnector and earth
switch (motorized)
✔ verification and testing of auxiliary switch positions
and visual position indicators
✔ interlocking mechanisms test
✔ tests of tripping mechanisms, including simulated
trips from the protection relay
✔ electrical integrity testing of the GIS (typically every
two years for a marine environment)
✔ general cleaning of the baffles
✔ protection and control tests (every three years).
There is also a requirement to maintain secondary electrical and ancillary services, such as lighting; navigation lighting; emergency lighting; heating, ventilation, and air-conditioning systems; dc supplies and battery systems; SCADA;
and emergency generators. While most of these secondary
systems will require limited maintenance, the emergency
generator will require regular on-load running, refueling,
and servicing in accordance with the manufacturer's requirements to ensure adequate service when needed. The generator would also require battery replacement during its 20-year
service life.

Offshore Platform Ancillary Assets
The category of ancillary assets is for the allowances associated with additional equipment on the platform that requires
maintenance. This may, for example, cover
✔ meteorological masts mounted on the platform
✔ weather forecasting equipment and software
✔ facilities for use by turbine technicians, such as stores
of spare parts.
There will also be specific maintenance and inspections of
safety equipment, including
✔ fall arrest systems
✔ external evacuation equipment (e.g., lifeboats)
✔ navigational aids.
Inspections must be carried out by qualified personnel,
either as part of the primary turbine maintenance or by a
team of independent inspectors. Inspection frequency will
be annual or biannual, depending on the equipment. Emergency response drills for health and safety incidents should
be a routine part of the operation and maintenance process.
Health and safety equipment, such as first-aid kits and fire
extinguishers, will need to be replenished.

Offshore Transmission Stage
Workboats are an essential part of any shore-based offshore
wind O&M strategy. These vessels transport technicians and
equipment from shore when wave conditions allow and provide
the backbone of logistical services to the turbines and other
elements of the wind farm. For near-shore projects, workboats
are likely to be the sole means of regular access. For more distant projects or where wave conditions are particularly severe,
they may be supplemented by helicopter access. Far offshore
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IEEE Power & Energy Magazine - July/August 2019

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