In order to improve the reliability of power supply and enable users to obtain power from two directions, the power supply network is usually connected in a ring. This power supply method is referred to as ring network power supply. In the AC 10KV distribution system of industrial and mining enterprises, residential areas, ports and high-rise buildings, due to the small load capacity, the high-voltage circuit is usually controlled by load switches or vacuum contactors and equipped with high-voltage fuse protection. The system usually adopts ring network power supply, and the high-voltage switch cabinet used is generally called ring network cabinet.
Ring network refers to a ring distribution network, that is, the power supply trunk forms a closed ring, the power supply supplies power to this ring trunk, and then distributes power to the outside through high-voltage switches from the trunk. The advantage of this is that each distribution branch can get power from both its left trunk and its right trunk. When the left trunk fails, it continues to get power from the right trunk, and when the right trunk fails, it continues to get power from the left trunk. In this way, although the total power supply is single-circuit power supply, each distribution branch gets benefits similar to dual-circuit power supply, thereby improving the reliability of power supply. The so-called "ring network cabinet" means that each distribution branch is equipped with a switch cabinet (outgoing line switch cabinet), and the busbar of this switch cabinet is also part of the ring trunk. That is to say, the ring trunk is composed of the busbars of each outgoing line cabinet connected together. Each outgoing line cabinet is called a "ring network cabinet". In fact, the meaning of "ring network" cannot be seen from a single ring network cabinet. The rated current of these ring network cabinets is not large, so the high-voltage switch of the ring network cabinet generally does not use a complex circuit breaker but a simple high-voltage load switch with a high-voltage fuse. In other words, the high-voltage switch in the ring network cabinet is generally a load switch. The ring network cabinet uses a load switch to operate the normal current and a fuse to cut off the short-circuit current. The combination of the two replaces the circuit breaker. Of course, this can only be limited to a certain capacity. Such a switch cabinet can also be used in a non-ring network structure distribution system. Therefore, with the widespread application of this switch cabinet, the "ring network cabinet" has jumped out of the scope of ring network distribution and generally refers to a high-voltage switch cabinet with a load switch as the main switch.
Ring main unit has not been around for long, but it has been widely used in recent years. This is mainly because the buildings of newly developed industrial enterprises and institutions, from the perspective of power supply and distribution, are mostly small and medium-sized. The distribution transformers generally do not exceed 1250KVA, long-term stable power supply, and high-voltage switches are not frequently operated. For such users, the performance of the ring main unit is not perfect, but it is sufficient and competent. With large-scale urban construction, a large number of large high-rise buildings have sprung up, and substations are often located downstairs. According to fire protection requirements, substations and distribution equipment must be "oil-free". According to the reasonable use of construction area, substations and distribution equipment should be "miniaturized", so ring main units or vacuum circuit breakers, dry transformers, and dry mutual inductors have entered the buildings. The ring main unit has a simple structure, reliable and safe operation, small maintenance, and low operating costs. Compared with switch cabinets equipped with circuit breakers, it has outstanding advantages. Ring main unit requires load switches to have higher performance and smaller size, so new load switches came into being, which in turn promoted the technological progress of ring main unit. Today's ring main unit not only has excellent performance but also is serialized, which further expands the scope of use of ring main unit.