Why do multiple separate wires need to be used for each phase during ultra-high voltage transmission? What are the reasons for this?
1、 The use of split conductors can improve the transmission capacity of transmission lines
Because compared to a single wire, a split wire can reduce the inductance and capacitance of a transmission line, reduce its impedance to alternating current, and improve the transmission capacity of the line. Research has shown that when the cross-section of each phase conductor is constant, the transmission capacity of the line increases when transitioning from a single conductor to a split conductor. When splitting into two conductors per phase, it increases by 21%, and when splitting into three conductors, it increases by 33%.
2、 Limiting the generation of corona and its associated hazards
Due to the strong electric field generated around ultra-high voltage transmission lines, the main insulation medium for overhead conductors is air. Therefore, when the electric field strength on the wire surface reaches a certain value, the air there may be ionized into a conductor and discharge occurs. At night, a green halo (corona) can sometimes be seen around the high-voltage line, which is actually a tip discharge phenomenon in the high-voltage line.
The appearance of corona will consume electrical power and energy, causing corona loss. The generation of corona not only loses transmission power, but also generates electromagnetic radiation, causing interference to radio stations, navigation equipment, and television, significantly affecting the normal state of the electromagnetic environment. Sometimes corona noise can also cause people to feel restless and restless. In addition, corona will also cause electrical corrosion on the surface of the wire, reducing the service life of the transmission line. Therefore, when designing and operating ultra-high voltage transmission lines, the generation of corona should be avoided as much as possible.
Due to the fact that the generation of corona mainly depends on the strength of the electric field on the surface of the wire, and under the same working voltage, the strength of the electric field on the surface of the wire is related to its cross-section; The larger the cross-section of the wire, the smaller the surface field strength, and vice versa. It can be seen that increasing the cross-section of the wire is a solution. However, for ultra-high voltage lines, simply increasing the cross-section of the conductor to limit the generation of corona is not economical and requires a new approach. Through research, it has been found that the use of split wires can significantly reduce the field strength on the surface of the wires. In slowing down the intensity of the electric field, split wires can achieve the same effect as single wires of the same thickness as split wires. It can be seen that the split wire increases the diameter of each phase of the wire, which can limit the generation of corona and related hazards.
3、 The use of split conductors can improve the economic benefits of power transmission
The use of split conductor technology not only effectively reduces corona losses, but also allows for the use of smaller cross-section conductors on ultra-high voltage transmission lines under the same electric field strength under corona conditions. Therefore, the use of split conductors will reduce transmission costs. In the conclusions of operational economic comparisons conducted in many countries, it has been concluded that using split conductors for ultra-high voltage long-distance transmission lines is more economical and reasonable. In Sweden, the transmission cost of splitting a wire into two is 2% to 14% lower than that of not splitting it.
4、 Improving the reliability of ultra-high voltage transmission lines
The stability requirements of ultra-high voltage transmission lines are high, and the surface conditions and climate of the areas they pass through are often complex. If a single wire is used, if there is a defect somewhere, the probability of causing a problem is high. On the contrary, the possibility of multiple wires having defects at the same location is very low, so the application of split wires can improve the stability of the line. In summary, the use of split conductors in ultra-high voltage transmission does have many advantages, so this technology has been widely adopted by many countries.
