2、 ? Compared with AC cable, DC cable has less power loss during transmission. The power loss of DC cable is mainly the conductor DC resistance loss, and the insulation loss is small (depending on the current fluctuation after rectification);
The AC resistance of low-voltage AC cable is slightly larger than that of DC cable, while the AC resistance of high-voltage cable is obvious, mainly due to proximity effect and skin effect, and the loss of insulation resistance accounts for a large proportion, mainly due to the impedance generated by capacitance and inductance.
3、 ? Although the price of converter equipment is higher than that of transformer, the cost of cable is much lower than that of AC cable. DC cable has positive and negative poles and simple structure; Ac cable is made of three-phase, four-wire or five-wire system, which requires high insulation safety and complicated structure. The cable cost is more than three times that of DC cable.
4. The installation and maintenance of 4.DC cable are simple and the cost is low.
When AC and DC voltages and currents are the same, what are the requirements for the same cable insulation?
When the same voltage AC /DC electric field is applied to the insulation, the electric field of DC cable is much smaller than that of AC. Because of the great difference between the electric fields, the maximum electric field of AC cable is concentrated near the conductor, while the maximum electric field of DC cable is mainly concentrated on the insulation surface, so it is safer (2.4 times).
What is the conversion relationship between AC voltage and DC voltage?
At present, there are many different understandings of the conversion relationship between AC voltage and DC voltage. However, our company uniformly calculates according to GB 12528. 1, that is, the rated voltage of the same AC cable and DC cable is 1.5 times of the phase voltage of AC cable. However, our company's 1500V DC cable is designed according to the DC voltage of 3000 V, which has relatively safe electrical insulation performance.
Extended data:
The rated current-carrying capacity of cables can be determined according to IEC60287 standard formulated by the International Electrotechnical Commission, and a lot of research results of relevant personnel at home and abroad can be used as a supplement and perfection of this standard. The short-circuit current that the cable bears in a very short time (a few seconds) due to ground fault can be determined according to IEC-949( 1988) and IEC-986( 1989).
In actual operation, due to various reasons, there is no mature standard for determining the short-term load current of cables, and it is too complicated to calculate with strict mathematical methods, and its formula can not meet the requirements of daily calculation. The existing calculation methods of cable short-term load current I2 under simple laying conditions are studied and synthesized, and the related problems in the calculation process are studied, and I2 under complex laying conditions is popularized.
The calculation method and empirical formula of I2 under ordinary cable laying are given, which can be used as a reference for power line design and operation departments to meet the needs of practical engineering application. Because the heat capacity of air can be generally ignored when laying cables in air, the cable body can be expressed by concentrated thermal resistance TT and concentrated heat capacity CT, and I2 of laying cables in air is
Where TT = t1+(1+λ1) T4 and CT=CTc+k(CTi? +CTs), τ=TTCT, where T 1 and T4 are the thermal resistances of the insulation layer and the cable surface to the surrounding medium, respectively, t ω cm; λ 1 is the ratio of sheath to core loss; CTc, CTi and CTs are the heat capacities of wire core, insulation layer and sheath, respectively, J/cm3 c; K is a constant, taking 0.5; T is the short-term load time allowed by the cable,
s； τ is the equivalent time constant of cable, s; I 1 is the current flowing through the iron core before overload, a; θc 1 and θc2 are the allowable temperatures of the core before overload and the core under short-term load, respectively, c; R 1 and R2 are the resistances of the wire core per unit length at θc 1 and θc2, respectively, ω/cm.
Reference: Baidu Encyclopedia -DC Cable