Offshore AC booster substations

as the key construction facility of large offshore wind farm

is the hub of power distribution of offshore wind farm and its design optimization plays an important role for the economy performance

reliability

availability

maintenance and safety etc of the construction and operat

ion of the whole wind farm.The first offshore AC booster substation in China was put into service in 2015 on the site of CGNPC Rudong wind farm

[1]

.Compared to mature onshore AC substations

the offshore AC booster substation in China is still in its initial stage in the aspect of either design or operation.Meanwhile the relevant design standards and technical specifications are also not perfect.Therefore

in case of harsh offshore conditions

the technical specifications and selection of power transformers

&

GIS for an offshore substation become particularly critical.Based on rich delivery experiences in offshore booster substation in Europe

Siemens energy has supplied or is supplying such electrical equipment as power transformers and GIS for dozens of offshore substations in China.Although the application experience on the onshore substation in the past decades makes these products fully meet the application requirement of offshore booster station in the field of electrical design

yet it still faces much harsher challenge from a marine environment regarding mechanical design and environmental adaptation.Moreover

the initial investment for an offshore platform equipment（including substation） is very expensive

at the same time

the subsequent maintenance of the equipment in the offshore booster station is not only difficult but also expensive.Thus

how to reduce the investment and maintenance cost by the prior design selection of the main equipment is also a matter of concern.In this paper

constitution of offshore AC platform and offshore power grid is introduced firstly

then the design and type selection of main power transformer for an offshore booster substation are described based on the actual engineering application experience and also from such aspects as safety

reliability

layout optimization

installation

commissioning

operation and subsequent maintenance and some suggestions are proposed.After that

the main consideration and countermeasures in the design layout and type selection of high voltag

e GIS are given.Finally

both new technology and new requirement of such offshore wind power as OTM offshore substations and 66 kV array systems are given and their application is prospected.If not otherwise stated

all "offshore substations" herein refer to "offshore AC booster substations".