New DC grid access solution
The high potential of wind power far offshore calls for
cost-effective solutions for grid connection.
Our experience along the supply chain from generation to
the grid access of wind power, including references for
DC offshore grid access projects, AC platforms, and wind
turbines, enables us to meet this challenge by creating
the next generation of DC grid access solutions.
New DC grid access solution –
saving weight, space, and costs with
• Encapsulated, rugged equipment
• Biodegradable and flame-retardant insulation
• Simple and robust power electronics
The new second-generation DC grid access solution is a
breakthrough in simplifying today’s offshore AC/DC converters, making them smaller and easier to install and to
maintain in an offshore environment. Combined with the
benefits of DC cables like their high power density, the
new DC grid access becomes the most cost-effective
solution for large-power offshore wind farms. The breakeven distance versus AC is reduced to about 80 km.
• Easy transport and installation
The new innovation uses compact, robust, encapsulated
power electronic devices. It is the simplest and most
robust AC/DC converter the electrical engineer can imagine at all: a diode rectifier. The insulation liquid used is
flame retardant and biodegradable. The DC switchgear
is encapsulated as well, so there is no longer any high
voltage in open air.
• Flexible offshore installation options due to
modular rectifier concept
This allows us to reduce platform size and weight sub­
stantially and to provide small, modular, and flexible
DC platforms easy to install and maintain.
• High reliability, minimal maintenance
• No offshore DC converter as single point of failure
• Shorter delivery times
• Stepwise offshore installation feasible
• Fast commissioning of WTG aux power
• Up to 1,200 MW DC
Best solution for long distances and high rated power
The new DC grid access concept does not require any
AC offshore substations. The turbine strings can be connected directly to one of three DC platforms. These are
of similar size to today’s AC offshore substations. The
total topside volume is reduced by 80 percent. The
weight is reduced from approximately 26,000 tons to
only 9,000 tons.
siemens.com/energy/grid-access-solutions
Current status
New concept
Distributed small DC
platforms
OSS
Large central
DC platform
Onshore HVDC
converter station
Onshore HVDC
converter station
Siemens’ new and cost-efficient DC grid access solution basically relies on distributed transformers and diode rectifiers.
They are located on small, distributed DC platforms and connected in series by a DC cable. A central DC transmission
platform is not required. The system can also operate with a reduced number of DC platforms, and a platform can even
be bypassed. This feature ensures outstanding availability and enables the stepwise construction and commissioning
of the power transmission system following the progress of installed turbine capacity.
The operation costs are reduced as well, since there is
no complex control and no maintenance-intensive
auxiliary equipment like seawater cooling and large air
conditioning.
DC grid access, general data
Finally, the small platform size allows fast erection:
approximately 28 months till first power transmission.
Auxiliary power supply for the turbines can be commissioned even faster, if the cables are in place.
According to Siemens analysis, the 2nd generation DC
grid access is the largest single lever to achieve the target
of reducing the cost of energy to €0.10/kilowatt hour
commonly set by the industry for the levelized cost of
electricity (LCoE) of offshore wind in 2020.
Rated power
Up to 1,200 MW (3 x 400 MW)
Rated DC voltage
+/– 320 kV
Distance
Up to 250 km
Rated AC voltage
66 kV (or 33 kV)
Platform weight
Approx. 3,000 t per platform
The new DC grid access solution will be open to all wind
turbine suppliers.
Remark:
The wind turbine control has to be modified to ensure proper power flow
control and stability of the weak offshore AC grid with high cable capacitances
present. For full converter machines this is a software update only.
Siemens is ready to support all interested turbine manufacturers.
Published by and copyright 2015:
Siemens AG
Energy Management Sector
Freyeslebenstrasse 1
91056 Erlangen, Germany
For more information, please contact
our Customer Support Center.
Phone: +49 180/524 70 00
Fax:
+49 180/524 24 71
(Charges depending on provider)
E-mail: support.energy@siemens.com
200 MW di-rectifier unit
Power Transmission Solutions
Order No.: E50001-G610-A139-X-7600
Dispo: 30003, fb6627 MA 473222 WS 03151.0
Printed in Germany
siemens.com/energy/grid-access-solutions