What are the design principles of low-voltage distribution systems?
(1) The low-voltage distribution system should meet the requirements of power supply reliability and power quality, and attention should be paid to simple wiring, safe and convenient operation, and a certain degree of flexibility. The hierarchy of the distribution system should not exceed two levels.
(2) Low-voltage electrical equipment on the same production line should be powered by the same busbar or line as much as possible. If the equipment is too scattered, it can be powered by different transformers, but these transformers should be connected to the same high-voltage busbar. Parallel production lines and standby units should be powered by different busbars or lines.
(3) The design of the distribution system should facilitate maintenance. If the work sections are relatively fixed, a large factory building can be divided into two sections for power distribution; multi-story factory buildings should have distribution boxes on each floor, and each independent unit can have a separate power switch.
(4) Single-phase electrical equipment should be properly configured to strive for three-phase balance. The neutral line current caused by unbalanced single-phase loads must not exceed 25% of the rated current of the transformer's low-voltage coil (or according to the manufacturer's regulations), and the current in any phase must not exceed the rated current value. Impact loads and high-capacity equipment should be separated from other equipment and supplied with power independently.
(5) In order to cut off some transformers during holidays or light load periods, tie lines should be laid on the low-voltage side of substations that are far apart.
(6) Lines introduced from outside the building should be equipped with switchgear at the indoor entry point, which is also convenient for maintenance and operation.
