Applications & Benefits - Benefits
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Applications & Benefits - Benefits
The power grid of the future must be secure and enable economic power transmission as well as environmental friendly power transmission.
The combination of these three tasks can be provided through new ideas, intelligent solutions and advanced technologies.
HVDC is not only a realistic technical and economic alternative to AC technology, but is also the only solution for power transmission in the case of:
HVDC allows environmental friendly power transmission and offers:
The latest innovative HVDC solutions open the door to a new era in power supply. The DC Compact Switchgear in combination with the HVDC PLUS technology in full-bridge topology enables multi-terminal overlay grids to support and strengthen existing AC transmission systems.
One of the most important HVDC benefits is, that DC transmission offers lower transmission losses than AC transmission at the same capacity, but there are different costs which must also be considered.
The figure shows AC versus DC transmission costs over distance. The break-even distance amounts typically to approx. 600 km for a power transmission level of 1000 MW
The diagram shows a typical cost comparison curve between AC and DC transmission considering:
The DC cost curves are not as steep as the AC cost curves because of considerably lower line costs per kilometer. Additionally, for long AC lines the cost of intermediate reactive power compensation has to be taken into account. The break-even distance is in the range of 500 to 800 km depending on a number of other factors, such as country-specific cost elements, interest rates for project financing, loss evaluation, cost of right of way etc. Therefore feasibility studies must be conducted to identify the most economic power transmission solution.
| Example of relative
| 2000 MW DC
| 2000 MW AC
The cost breakdown for a DC overhead line in comparison with an AC transmission line with the same power capacity demonstrates the differences. The land coverage and the associated right-of-way costs for an HVDC overhead transmission line are much lower than for an AC line.
The HVDC PLUS solution, in a potential combination with DC compact switchgear can be a space-saving solution in urban areas. The Trans Bay Cable project in San Francisco, USA, is an example of a compact HVDC solution (HVDC PLUS; Trans Bay Cable Project).
HVDC transmission can be an attractive solution for enabling power trading by using the controllability for defined power transfers offering benefits for suppliers as well as for consumers, e.g. HVDC Estlink2 (Estonia-Finland) and Britned (UK – Netherland).
The Mundra – Haryana HVDC transmission link in India is an even better example of how CO2 reduction through lower losses in transmission contributes to the return on investment.
Another HVDC benefit is, that an HVDC transmission system enables environmental friendly power transmission, as improved energy transmission possibilities contribute to a more efficient utilization of electrical energy.
It can be an alternative solution:
Compared to AC transmission lines with the same power capacity, as shown in the figure, DC overhead lines require much less space. This offers:
It is also possible to use underground cables which can be a vital alternative in urban areas.
HVDC PLUS, optionally in combination with DC compact switchgear, is one of the most compact HVDC systems today.
Renewable energy sources play an increasingly important role in times of dwindling energy resources. With innovative HVDC solutions Siemens provides:
There are, however, some environmental issues which must be considered during the planning phase for the converter stations, such as for example audible noise, visual impact by the converter station, electromagnetic compatibility, use of ground or sea return path in monopolar operation. In general, it can be said that an HVDC system is highly compatible with any environment and can be integrated into it without the need to compromise on any environmentally important issues of today. Thereby HVDC offers environmental friendly power transmission.
Depending on the converter type used for conversion between AC and DC, two technologies are available for DC transmission:
Both technologies enable Siemens to provide additional HVDC benefits with attractive solutions (Applications) for the most challenging transmission tasks such as:
The total controllability of HVDC systems is a superior feature / function when compared to an HVAC system.
|DC Connection||AC Connection|
|Load flow||fully controlled by the
operator in both directions
depending on actual
|Peak supply||inherent overload
capability, e.g. can
be used actively for peak loads
not controlled by
|stabilising voltage and
frequency by independently
controllable active and
reactive power supply
HVDC Classic with LLC technology is available for the whole power range whereas HVDC PLUS can be used up to 1000 MW per monopole. For higher power ratings HVDC PLUS converters can be connected in parallel and have thereby an additional HVDC benefit. However, HVDC PLUS with VSC technology offers unique advantages for HVDC transmission which become more and more important for applications such as connecting remote renewable energy sources, power in feed for megacities, supply of oil and gas platforms or connecting mines to an existing grid.
Using the latest modular IGBT (Insulated Gate Bipolar Transistor) technology in a pioneering Modular Multilevel Converter (MMC) design, Siemens engineers have developed HVDC PLUS as a landmark product in the evolution of HVDC transmission.
HVDC PLUS provides additional technical and economical features as compared to LCC:
HVDC PLUS is used in applications that require the following capabilities:
Power ratings up to 2 x 1000 MW (INELFE project) have been implemented to date and make HVDC PLUS increasingly attractive also for projects where LCC HVDC could be used from a technical perspective. Converter ratings of 2000 MW are feasible based on DC voltages of +/- 500 kV. By comparing VSC and LCC technology, studies can derive the best solution based on the individual requirements at hand and particular project conditions.