Cable issues on Xi’an Metro Line 3
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These past two days, while reading the news, there has been a lot of coverage regarding the cable issues on Xi’an Metro Line 3. The cable manufacturer is Xi’an Aokai Cable Company. The incident started when a user with the online username “Aokai Employee” posted a message alleging that the cables used on Xi’an Metro Line 3 had quality problems and posed a risk of accidents. Then the relevant departments got involved and began an investigation; the main issue found was that the resistance value of the cable conductors did not meet the national standards. For 3-core cables, the resistance per core per kilometer is higher than the national standard, by at least 0.046 ohms and at most 0.048 ohms. The news didn’t specify the specifications of the cable. Personally, I think 0.048 ohms is a very low value. Could someone who knows about this explain what specific hazards might arise from it?
If the resistance is high, the loss will be high as well, and heating will be much more severe than in normal cables; accordingly, the current-carrying capacity of such cables is lower. It’s not just the absolute value of the high resistance that matters, but also the magnitude of the current. For example, the resistance value required for lightning protection downconductors is very low; if it is even slightly higher, a high voltage difference will be generated under the influence of high currents.
This post was last edited by jizhanwei22 on 2017-3-22 at 10:56. I’ll try to share some casual insights: In science, the amount of electric charge that passes through any cross-section of a conductor per unit of time is called current intensity, commonly referred to as current, and is denoted by the symbol I. Ohm’s law: I=U/R ； Assuming the voltage U remains constant, the greater the resistance of the conductor, the smaller the current. In other words, the greater the resistance, the more electrical charge is consumed per unit area. At the same voltage, the amount of electricity received by users (the stations along the subway line) varies; the farther away from the power source, the smaller the current, and thus the less electricity available. It increases by 0.046Ω per kilometer, but how long are the wires used in the subway? They stretch back and forth and wind around, so it is likely that under the same voltage, this will affect the power supply for users at the various stations along the subway line. I don’t know if the rumors are true or not; what’s next below?~~~
I just checked – according to the national standards, the resistance per kilometer for wires with cross-sectional areas of 4 square millimeters, 95 square millimeters, and 150 square millimeters is 4.61 ohms, 0.193 ohms, and 0.121 ohms respectively. Based on the excess value of 0.048 ohms, the excess percentages are 1%, 24.8%, and 39.6% respectively. Considering the national conditions, I think that a 4-square wire is still considered normal. If it’s a 95-square meter wire, it’s definitely a scoundrel. If it’s a 150-square meter wire, it’s absolutely criminal.
Ah, yes. . . . . . I don’t know where all the bribes go. .
This problem exists in all state-owned enterprises and institutions in the country at present, though to varying degrees. Now, aside from private enterprise owners who are more responsible for their own money, how many people who don’t use their own money to carry out tasks can act honestly and in accordance with the rules? In the country, whenever a project is implemented or a policy is put into effect, there are always some clever opportunists who try to find ways to gain benefits from it.