Innovations - DC Compact Switchgear (DC CS)
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Innovations - DC Compact Switchgear (DC CS)
The changing generation and load structure in existing power grids requires increased transmission capacity. Longer transmission distances and increased loading tend to reduce the AC grid’s static and dynamic stability. To amend this, HVDC systems can be integrated into existing AC grids to provide the required transmission capacity and at the same time increase grid stability.
What is more, the global trend towards decarbonization of power generation calls for an increased use of renewable energy sources (RES). While RES like offshore wind are typically found at great distances from the load centers, HVDC provides an effective (and in some cases the only) technical solution for power transmission.
The compact 320 kV DC switchgear DC CS is needed for HVDC cable connections to remote offshore wind farms as well as for onshore HVDC projects. Thanks to its compact design, the DC CS helps to reduce the HVDC system’s space requirements. Hence it is predestinated for applications where space is limited or expensive, e.g. offshore HVDC platforms for remote wind farms as well as close to city centers. Using the DC CS outdoors even in rough climates adds to this effect. In the near future, DC compact switchgear and transmission solutions facilitate the realization of multi-terminal arrangements or DC grids, backing up the existing AC networks.
The 320 kV Direct Current Compact Switchgear (DC CS) (without circuit breaker) is the next generation of DC switchgear. It is developed based on proven 8DQ1-1 550 kV AC gas insulated switchgear design and a new DC insulator following the well-established Resin-impregnated-paper design which is used in wall bushings for decades.
The DC CS is a highly modularized product line, with standardized and predefined modules which minimize the required interface engineering complexity between the DC CS modules as well as interfaces to e.g. control and protection systems. An example of a 320 kV converter pole feeder is given in the figure.
The range of modules like 0°/90° disconnector and earthing switch modules, 45°/90° angle modules grant flexibility to adapt to complex arrangements such as designs with a single or double busbar.
The module catalogue is completed by an RC divider for voltage measurement, the zero flux compensated current measurement system, surge arrester and compensation modules required for service access and both axial and lateral heat dilatation.
|Switchgear type||320 kV DC CS|
|Nominal voltage||320 kV|
|Rated current||4000 A|
|Rated short-time withstand current, 1 second||50 kA|
|Max. continuous operating voltage||336 kV|
|Rated lightning impulse withstand voltage (1.2/50 µs)
- to earth
- across the isolating distance at the power frequency
1175 kV + 336 kV
|Ambient temperature||-30 to +50 °C|
|Application||indoor / outdoor|
DC compact switchgear can be applied at various locations within an HVDC system. An important application option for DC CS is between the converter transformer and the converter valves. With bipolar arrangements where 2 or more converters are arranged in a line with neutral in between, the section between the secondary connection of a converter transformer and the respective converter valves is stressed with a DC voltage offset resulting in a mixed voltage stress AC/DC requiring dedicated DC equipment. On the DC terminal, the DC switchyard, transition stations (enabling compact transition from cable to overhead line) along the line and finally future multi-terminal stations can be planned with DC CS.
The most important benefit of 320 kV DC Compact Switchgear is its inherent size advantage compared to air-insulated DC switchyard equipment.
Further the option for outdoor installation, even under extreme environmental conditions is an advantage of DC CS.
If for technical reasons, like temperature below -30°C, a housing is required, the DC CS fits into pre-fabricated, containerized building modules. Containerized arrangements further have the advantage to pre-assemble and test whole switchyard/substation layouts locally at the manufacturer or container builder’s plant, cutting short remote erection and commissioning efforts and costs as well as simplifying the interface to civil works. Layouts with identical design which are repetitive used in an HVDC scheme can be planned and executed likewise, e.g. cable transition stations. Building and foundation costs can therefore be greatly reduced.
Finally an underground installation hidden from view and public access is possible thanks to the encapsulation and compact design.
Regarding planned projects in densely populated areas, with critical points which are already occupied by traffic junctions and AC overhead-lines as well as natural barriers like rivers, huge potential for compact DC transmission solutions is existent. Learn more about HVDC applications for DC CS from Siemens.
Phone: +49 (9131) 7-44510