The difference between DC cables and AC cables. DC cables are used in rectified DC transmission systems, while AC cables are commonly used in industrial frequency (domestic 50 Hz) power systems.
I. DC cable has the following characteristics compared with AC cable
1. The systems used are different. DC cable is used in the rectified DC transmission system, AC cable is commonly used in the power system of industrial frequency (domestic 50Hz).
2. Compared with AC cables, DC cables have less power loss in the transmission process. DC cable power loss is mainly conductor DC resistance loss, insulation loss part is smaller (size depending on the size of the current fluctuations after rectification). While the AC resistance of low-voltage AC cables is slightly larger than the DC resistance. High-voltage cables are very obvious, mainly because of the proximity effect and skin effect. The loss of insulation resistance accounts for a larger proportion of the impedance generated mainly by capacitance and inductance.
3. High transmission efficiency and low line losses.
4. It is convenient to adjust the current and change the direction of the power transmission.
5. Although the price of the converter equipment is higher than the transformer, the cable line use cost is much lower than the AC cable. DC cable for positive and negative poles, simple structure. AC cable for three-phase four-wire or five-wire system, insulation safety requirements are high, the structure is more complex, and the cost of the cable is more than three times the DC cable.
6. DC cables are safe to use.
6.1 DC transmission inherent characteristics, it is difficult to generate induction currents and leakage currents, the same laying of other cables will not produce electric field interference.
6.2 Single-core laying cable will not affect the cable transmission performance due to the hysteresis loss of the steel structure bridge.
6.3 With the same structure as the DC cable higher interception capacity and over-cut protection capacity.
6.4 the same voltage of direct, AC electric field applied to the insulation, DC electric field is much safer than AC electric field.
7. DC cables are easy to install and maintain, and they are less expensive
Ⅱ. The same AC and DC voltage and current when the same cable insulation requirements
The same voltage AC and DC electric field applied to the insulation, DC cable 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 the AC cable is energized is concentrated near the conductor. While the maximum electric field when DC cables are energized is mainly concentrated within the surface layer of the insulation, thus making it more secure (2.4 times).
Ⅲ. Mutual conversion relationship between AC and DC voltages
In the mutual conversion of AC and DC voltage relationship, there are many different understandings. Uniform calculation according to GB12528.1, that is, the same AC cable, DC cable voltage rating of 1.5 times the phase voltage of the AC cable.