Every day, learn the general requirements of temporary electricity 19 - temporary electricity distribution lines
1. Several types of distribution lines
(1) Radial wiring
The radial wiring is radiated from the power supply to the power point (or electricity load), and each power point can be connected to more than two power points (or power load)
The radial power distribution has good stability, high reliability, each power point basically does not affect each other, the influence range is small after the fault occurs, the switching operation is convenient, the protection is simple, but the cost is high.
For example, the wiring of the low-voltage distribution cabinet is basically radioactive power distribution.
(2) Trunk wiring
Trunk wiring refers to the connection of some independent loads or some concentrated loads to a certain distribution trunk according to their location.
The characteristics of trunk power distribution are that the size of the power supply thousand lines and the branch lines to each electricity is different, the line is simple, the investment is low, and the disadvantage is that when the outgoing line fails, especially when the trunk line fails, the impact range is particularly large, and the power supply reliability is poor.
(3) Chain wiring
Chain wiring is a kind of distribution line similar to the tree type, but the load and the trunk line are not independent branches, but related links.
The chain wiring is suitable for the load places with a small capacity ≤of 3 (KW) that are not important in the switch box that is close to each other, but the number of independent loads of the link cannot exceed 3~4.
For the temporary power project at the construction site, which wiring type is actually used, it is necessary to determine the safety degree and technical and economic analysis and comparison of various types of schemes according to the type of on-site wiring (overhead line or cable line), load distribution and load nature.
2. Distribution line selection
(1) Selection of overhead lines
It is mainly to select the type of overhead line conductor and the cross-section of the conductor, and its selection is mainly based on the requirements of the "Temporary Electricity Safety Technical Specification" for overhead line laying and the calculated current of line load calculation.
The wire must be insulated wire. That is, it is either an insulated copper wire or an insulated aluminum wire. It is strictly forbidden to use bare wires, because bare wires are potentially more dangerous in terms of human contact and electric shock and interline lines.
Insulated wire refers to a wire with good insulation performance. The sign of intact insulation means that the insulation has no aging, no cracks, no damage and bare conductors, and its insulation resistance is not less than 1000Ω per volt, and the rated working voltage is greater than the line working voltage.
Because the conductivity of copper is far better than aluminum, insulated copper wire can be preferred when conditions permit, which has the advantages of good electrical connection, low resistivity, high mechanical strength, and is conducive to reducing line voltage loss compared with aluminum wire.
3. Wire cross-section selection
The selection of the wire cross-section is mainly based on the calculation results of the line load, the primary selection of the wire cross-section according to the allowable temperature rise of the insulated wire, and then the verification according to the line voltage offset and mechanical strength requirements, the approval according to the working system, and finally the comprehensive determination of the wire cross-section. The calculations are more complicated, so I won't repeat them!