"Strong Strong and Strong Straight" is the Development Direction of UHV

The adjustment of China's energy strategic structure has already kicked off, and the trans-regional transmission will gradually be transformed from the small role of auxiliary power distribution in the past to the “aorta” to solve the energy supply in the eastern region in the future. Therefore, the driving mechanism and growth scale of trans-regional transmission will all undergo tremendous changes in the past, and historical experience data cannot be copied.

The primary criterion for judging the merits of transmission schemes should be the transmission capacity, that is, whether the scheme can meet the large-scale power transmission needs in the future. The high-redundancy scheme will provide sufficient space for future power deployment and reduce the occurrence of upgrades, make-ups, and reconstructions. If the construction of transmissions is not sufficient to save money, it may affect social production activities and lead to greater economic losses. On the basis of satisfying the transmission of electricity, the second is economic and other factors.

In terms of transmission capacity, UHV transmissions naturally adapt to greater natural power than ordinary high pressures. Because when the resistance is fixed, the transmission power is proportional to the square of the transmission voltage. If the transmission voltage is increased by 1 time, the transmission power will be increased by 4 times. Compared with the existing ultra-high voltage transmission, the natural power of UHV under the same conditions is 4-5 times before, which is far more economical and convenient than repeating construction of EHV lines. Moreover, from the point of view of the development of the entire power grid, the transmission voltage level is approximately doubled. When the demand for power is increased to 4 times, a higher voltage level will naturally appear, and the UHV can better meet the requirements. Large-scale long-distance transmission of Western Electric Power, to solve the urgent problem of "coal burning" in the eastern electricity.

UHV is naturally suitable for longer delivery distances than other high voltage transmissions. The rated capacity of 500 kV and 1000 kV AC transmission at a transmission distance of 300 km is 100%. With the increase of the transmission distance, the attenuation of UHV transmission capacity is obviously less than that of ultra-high voltage transmission, and the distance of its transmission capacity. Extensibility is better.

The construction of UHV power grids can fundamentally solve the problem of poor power grid security caused by weak 500 kV AC interconnections across large regions, and provide strong grid support for the recipient power grid in the eastern region of China, which can solve short-circuit currents in 500 kV power grids in load-intensive regions. Exceeding the problem.

In respect of construction costs, taking the Ximeng-Nanjing UHV AC project as an example, the project is a twin-circuit network on the same tower. It plans to deliver 9.4 million kilowatts of transmission lines with a total length of 1,450 kilometers, a total investment of 32.2 billion yuan, and a unit construction cost of about 20 million yuan. / Kilometer. With the same delivery capacity, UHV construction costs about 70% of ultra-high pressure. For reference, the highway construction cost is about 120 million yuan/km, the railway is about 20 million yuan/km, and the national highway is about 2000-50 million yuan/km. On the whole, UHV is not astronomical in terms of construction costs, but is in the normal range of infrastructure investment.

In addition, UHV can reduce the number of corridor circuits, thereby saving a lot of land resources. With the same transmission capacity, compared with 500kV UHV DC transmission technology, the 800kV UHV DC transmission line can be reduced from 10 to 6 cycles. For AC transmission, 500kV AC requires 8-10 lines, while 1000kV AC requires only 2 lines, saving about 50% of the width of the transmission corridor. Therefore, UHV will significantly increase the power density of the unit corridors, and there are significant advantages in environmental protection.

Overall speaking, the overall construction costs of the UHV AC and DC schemes are not significantly different. The respective advantages and disadvantages of the two are mainly at the technical level.

The main advantage of UHVDC is ultra-long-distance transmission. Three wires are required for AC transmission, and DC transmission uses the ground as a neutral wire, requiring only one wire. Under the same conditions, HVDC has very little investment in cables. However, the cost of DC transmission at both ends of the transmission is high, which is mainly reflected in the fixed cost of the converter station. Therefore, the longer the transmission distance, the lower the average construction cost of DC transmission. Foreign experience shows that UHV DC transmission is more economical than AC transmission when the transmission distance exceeds 1000 kilometers.

The main drawback of UHV DC is that DC only has a transmission function and can not form a network, similar to a "direct flight", and can not be placed in the middle, and is located in ultra-long distance, large capacity "point-to-point" transmission. DC transmission can reduce or avoid a large number of over-the-wave flows, and the direction and size of the current can be easily controlled. However, HVDC power transmission must be attached to a strong AC grid to function.

The advantage of UHV AC is that it has the dual functions of power transmission and network construction. Similar to the “highway traffic network”, it can constitute a power grid based on the actual needs of power distribution, load distribution, transmission power, and power exchange. The middle point can be set, the access, transmission and consumption of electricity is very flexible. It is positioned to build a strong transmission network at all levels and large-capacity, long-distance transmission at economic distance. It is widely used in the transmission of power and provides important for DC transmission. support.

UHV DC and AC transmission can only complement each other and cannot be replaced by each other. The "strong and strong" mashup model will be the development direction of UHV construction in the future.