Difference Between DC Cable And AC Cable

Compared with the AC cable, the DC cable has the following characteristics

1. Different systems are used. DC cables are used in rectified DC transmission systems, and AC cables are often used in power frequency (domestic 50Hz) power systems.

2. Compared with the AC cable, the power loss in the transmission process of the DC cable is smaller. The power loss of the DC cable is mainly the DC resistance loss of the conductor, and the insulation loss is small (the size depends on the current fluctuation after rectification); while the AC resistance of the low-voltage AC cable is slightly larger than the DC resistance, and the AC cable is very obvious, mainly because Proximity effect and skin effect, the loss of insulation resistance accounts for a large proportion, mainly the impedance generated by capacitance and inductance.

3. High transmission efficiency and small 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 transformers, the cost of using cable lines is much lower than that of AC cables. The DC cable has positive and negative poles, and the structure is simple; the AC cable is three-phase four-wire or five-wire system, which requires high insulation safety and complex structure, and the cable cost is more than three times that of the DC cable.

6. The safety of the DC cable is high:

1) Due to the inherent characteristics of DC power transmission, it is difficult to generate induced current and leakage current, and it will not cause electric field interference to other cables that are laid in the same way.

2) The single-core laying cable will not affect the transmission performance of the cable due to the hysteresis loss of the steel structure bridge.

3) It has higher current interception capability and over-interruption protection capability than DC cables of the same structure.

4) Direct and alternating electric fields of the same voltage are applied to the insulation, and the direct electric field is much safer than the alternating electric field.

7. The installation and maintenance of the DC cables are simple and the cost is low.

Requirements for the same cable insulation under the same AC and DC voltage and current

When an AC and DC electric field of the same voltage is applied to the insulation, the electric field of the DC cable is much smaller than that of the AC electric field. Due to the large difference in the structure of the two electric fields, the electric field of the cable when the AC cable is energized is concentrated near the conductor, while the electric field of the cable when the DC cable is energized is mainly concentrated within the insulating surface, so it is safer (2.4 times).

Mutual conversion relationship between AC and DC voltage

There are many different understandings on the mutual conversion relationship between AC and DC voltages. However, our company uniformly calculates according to GB12528.1, that is, for the same AC cable, the rated voltage of the DC cable is 1.5 times the phase voltage of the AC cable. But our company's 1500V DC cable is designed according to the voltage of DC3000V, which has safer electrical insulation performance.