First, DC cables have the following features compared to AC cables:
1. Different systems used
DC cables are often used in rectified DC transmission systems, and AC cables are often used in power frequency (domestic 50Hz) power systems.
2.Compared with AC cable, the power loss of DC cable during transmission is relatively small
The power loss of DC cables 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 cables is slightly higher than the DC resistance. High voltage cables are mainly manifested by proximity and skin effects. Insulation resistance losses account for a large proportion, primarily due to the impedance created 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. The price of converter equipment is higher than that of transformer, but the cost of using cable line is much lower than that of AC cable.
A DC cable has a simple structure with positive and negative poles. AC cables are 3-phase 4-wire or 5-wire systems with higher insulation safety requirements, more complex structures, and more than three times the cost of DC cables.
6. High safety of DC cables:
① Due to the characteristics of DC power transmission, induced currents and leakage currents are less likely to occur, and other cables installed in the same way do not cause electric field interference.
(2) For single-core cables, the hysteresis loss of steel bridges does not affect cable transmission performance.
③ . It has higher current interruption capability and overcurrent protection capability than DC cables with the same structure.
④ DC and AC electric fields of the same voltage are applied to the insulator, and the DC electric field is much safer than the AC electric field.
7. Easy to install and maintain DC cable, low cost.
Second, the same AC and DC voltage and current requirements for the same cable insulation:
When AC and DC electric fields of the same voltage are applied across the insulation, the DC electric field 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 energized in an AC cable is concentrated near the conductor, and the maximum electric field when energized in a DC cable is mainly concentrated in the insulation plane, which is safer ( 2.4 times).
