What are the design principles for 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 number of levels in the distribution system should not exceed two.
(2) Low-voltage electrical equipment on the same production line should be powered from the same busbar or circuit as much as possible. If the equipment is too dispersed, it can be powered by different transformers, but these transformers should be connected to the same high-voltage busbar section. Parallel production lines and standby units should preferably be powered from different busbars or circuits.
(3) The design of the distribution system should facilitate maintenance. If the work sections are relatively fixed, a large workshop can be divided into two sections for power distribution; for multi-story buildings, distribution boxes should be installed 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 as specified by the manufacturer), and the current in any phase must not exceed the rated current value. Impact loads and large-capacity electrical equipment should be separated from other equipment and supplied with power independently.
(5) To allow for the removal of 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 for ease of maintenance and operation.
