First, compared with AC cable, DC cable has the following characteristics:
1. The system used is different
DC cable is used in the rectified DC transmission system, and AC cable is often used in the power system with power frequency (domestic 50Hz).
2. Compared with AC cable, the power loss of DC cable during transmission is relatively small
The power loss of DC cable is mainly the loss of conductor DC resistance, and the insulation loss is relatively small (the size is related to the current fluctuation after rectification); The AC resistance of low-voltage AC cable is slightly larger than DC resistance; High voltage cable is obvious, mainly due to proximity effect and skin effect. The loss of insulation resistance accounts for a large proportion, mainly due to the impedance generated by capacitance and inductance.
3. High transmission efficiency and low line loss.
4. It is convenient to adjust the current and change the direction of power transmission.
5. Although the price of converter equipment is higher than that of transformer, the use cost of cable line is much lower than that of AC cable
DC cable is of positive and negative poles, with simple structure; AC cable is of three-phase four-wire or five-wire system, with high insulation safety requirements, complex structure, and more than three times the cost of DC cable.
6. High safety of DC cable:
① Due to the inherent characteristics of DC transmission, it is difficult to generate induced current and leakage current, and it will not produce electric field interference to other cables laid in the same way.
② The single-core cable will not affect the cable transmission performance due to the hysteresis loss of the steel structure bridge.
③ It has higher current interception capacity and overcurrent protection capacity than DC cables of the same structure.
④ The DC and AC electric fields of the same voltage are applied to the insulation, and the DC electric field is much safer than the AC electric field.
7. The installation and maintenance of DC cable is simple and the cost is low.
Second, the same AC and DC voltage and current requirements for the same cable insulation:
When the AC and DC electric fields of the same voltage are applied to the insulation, the electric field of the DC cable is much smaller than the AC electric field. Due to the large difference in the structure of the two electric fields, the maximum electric field when the AC cable is energized is concentrated near the conductor, while the maximum electric field when the DC cable is energized is mainly concentrated within the insulation surface, so it is more safe (2.4 times).
