Maximum transmission power
The maximum transmission power is an indicator reflecting the determined transmission capacity of each transmission scheme, and embodies the power transmission margin of the determined AC and DC transmission schemes, which plays an important role in the long-distance transmission planning.
Annual fee
Economics is the main consideration in engineering construction. The annual cost indicator is used to measure the economics of transmission schemes, mainly involving construction economy and grid operation economy. As mentioned above, it mainly consists of three parts: investment cost (year value), transmission loss cost, and operation and maintenance cost.
Forced outage time
The reliability of the new transmission project affects the normal operation of the power system and the normal power supply to the users. The forced outage time indicator is used to reflect the reliability of the transmission system. To investigate and analyze the reliability data of various power grids in the ITU, and to calculate the average number of hours of forced and de-energized power transmission and transformation facilities caused by faults in transmission and transmission equipment in each year. The forced outage time of the HVDC transmission scheme.
Transmission corridor
The transmission corridor indicators are used to reflect the occupation of land resources by various transmission schemes and the impact on the environment. As the contradiction of power corridor corridor resources becomes more and more prominent, this indicator also has greater influence in the selection of transmission schemes. The value is determined by calculating the line width corresponding to the standard limit portion of the power frequency electric field, the power frequency magnetic field, and the radio interference field strength, respectively, and taking the maximum value. For the single-return or multi-circuit transmission schemes and DC transmission schemes in this paper, the values ​​are mainly based on engineering experience.
Reactive loss
The reactive power will cause the loss of active power during the transportation process, resulting in a huge waste of power resources, and whether the balance of reactive power is directly related to the voltage stability of the system. In DC transmission, the reactive power loss of the converter station is very large, accounting for 40% to 60% of the transmission power, which not only increases the investment of reactive power compensation, but also may cause more problems in the case of AC grid failure or DC transmission system failure. Large voltage stability problems. The UHV AC transmission line also generates a large charging power, which is about 4.4 times that of the 500 kV line. At the same time, depending on the transmission power, some reactive power is consumed on the line. Therefore, the problem of reactive power loss should be considered in the decision-making of transmission schemes.
Fault loss power
The fault loss power is the impact of the power lost in the system on the grid when the transmission line is faulty, which threatens the safety and stability of the system. Therefore, it should be considered comprehensively in the scheme selection. In the DC transmission line, the poles are independently regulated and operated, and have no effect on each other. Therefore, when one pole fails, it is only necessary to stop the fault pole, and the other pole can still deliver not less than half of the power. In the case of a permanent failure of a phase in an AC transmission line, the line must be completely powered off. The power loss caused by the fault will cause the power imbalance of the grid and cause harm to the system.
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