6.2. VSC-Based HVDC Transmission Cost Calculation
Regarding VSC-based HVDC transmission, the calculation performed to gain an idea of the overall cost of
KVSC consists of
Kcap(VSC) for capital expenditures,
Kopex(VSC) for operation and maintenance, and
Kloss(VSC) for less cost
[63][101].
6.2.1. Capital Costs
Kcap(VSC) is made up of two costs:
Kstation(VSC) for the foundation of the converter station and
Kcable(VSC).
6.2.2. Operation and Maintenance Costs
Equation (3), which is used in the study, yields the
Kopex(VSC); the B of the DC submarine cable equals 0.5%, I is 5%, and n is 240 months.
6.2.3. Cost of Losses
The converter station loss
Ksub(loss)
and line loss
Kline(loss) make up the loss expenses for the
Kloss(VSC) loss rate for converter stations. Psub loss measures how much of the transmitted power is lost at the station. Two converter stations’
Psub(loss) ranges from 1.6 to 2.4%, and Zhen notes that
Psub(loss)
is between 1 and 2 percent
[64][102].
6.2.4. Foundation Costs for Converter Stations
The entire infrastructure investment for each converter station is the VSC-based converter station cost. In addition, the expected additional expenses for IGBT technology are the converter station layout’s civil construction costs, the converter station’s DC capacitor and AC filter costs, and the converter station’s converter controller and reactor costs. The cost of a converter station based on VSC is then calculated as a percentage of the capacity of each converter station, denoted by P.
6.2.5. Cost of Cable Installation and Foundation
The DC cable’s VSC-based cost is determined by transmission distance, much like the cost for the HVAC cable is.
where
P1 and
P2 represent the cost and installation expenses for a DC cable per kilometer
[19][17]. Since the DC voltage waveform is not susceptible to peak/effective ratio underutilization, the cost of the cables in the VSC-HVDC option is significantly lower than that of AC alternatives. The transmission capability ratio of DC cables to AC cables can be calculated using Equation (6).
As observed in (6), DC solutions only require two polar wires for a given power transmission, but AC solutions require three. Compared to AC choices, the cost of the cable would be substantially lower with VSC-HVDC. This benefit might be more apparent if the reactive power and skin impact are factored, as in the work of Xiang
[65][103].
6.3. An Economic Comparison of HVAC and HVDC Systems
Since every project has unique situations and features, including line distance, rated power, topography, and utilized technology, it is challenging to estimate the accurate price of HVDC. On the other hand, a broad estimate can be derived using the information from earlier initiatives. The DC grid interconnection back-to-back plan of Chongqing-Hubei in China was the first clarified VSC HVDC line, encompassing a total distance of 1711 km with a maximum voltage capability of 420,000 V and a main power transmission capacity of
5000×106 W
[66][104].
Three cost factors come into play when comparing HVAC and HVDC economically:
-
Cost of line;
-
Cost of losses;
-
Cost of terminal.
The overall cost is split into two parts: the expense of building the infrastructure and the expense of maintaining the system once it is operational. This considers the cost of the investment, the cost of the poles, wires, insulation, converter stations, and the use of the right of way. Financial losses are specifically included in the operating cost. Given that both AC and DC use the same types of insulation and conductors, AC requires three conductors while DC just requires two
[67][109]. DC poles become a less costly route as a result, using less conductor and insulator material
[68][110]. Calculations for AC and DC transmission line losses look like this:
By combining Equations (9) and (10) we obtain Equation (11).
If three-phase AC is substituted with DC, the same power transfer, conductor size, and power loss are assumed
[69][70][24,111].
7. Summary
Offshore wind farms must comply with safety limits to ensure the stable operation of the system. The IEC and IEEE have established standards for the integration of offshore wind farms into electrical power systems. These standards cover a range of topics including design, installation, operation, and maintenance of OWFs. Additionally, the safe distance between WTs and the coast, shipping lanes, and other infrastructure are considered in the design process.
Some specific safety and performance standards for offshore wind farms include:
-
IEC 61400-3
[71][112], which provides guidelines for the design, installation, operation, and maintenance of WT generators and WF control systems.
-
IEEE 1547
[72][113], which covers the interconnection and interoperation of distributed energy resources within the electric power system.
-
IEEE P2450
[73][114], which provides guidelines for the planning, design, installation, operation, and maintenance of WT generator systems, including the wind turbine, electrical equipment, and the wind farm control system.
-
IEC 62271-110
[74][115], which covers the HVDC systems used to transmit power from OWFs to the onshore electrical grid.
It is important to note that compliance with these standards is not mandatory, but it is highly recommended as it ensures the safety of the equipment and the people who operate it, and also helps in the integration of the WFs into the existing power grid.