Overview of ring main unit

 Ring main unit is a set of high-voltage switchgear installed in a steel plate metal cabinet or made into an assembled and partitioned ring network power supply unit. Its core part uses load switches and fuses. It has a simple structure, small size, low price, and can be used. Improve power supply parameters and performance as well as power supply security and other advantages

In fact, the so-called ring network refers to a ring-shaped power distribution network, which is a closed ring formed by the power supply trunk line. The power supply supplies power to the entire ring trunk line, and then distributes power from the trunk line all the way through the high-voltage switch cabinet. The advantage of this is that each distribution branch can take power from the main line on its left side and the main line on its right side. When one side of the main line fails, it continues to receive power from the other right main line. In this way, although the total power supply is a single-channel power supply, each distribution branch gets a similar dual-circuit power supply. Affordable, thus improving the reliability of power supply.

The ring main unit is generally composed of four parts: switch room, fuse room, operating mechanism room and cable room (chassis). 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 circuit breaker with a complex structure but a simple-structured high-voltage load switch with a high-voltage fuse. In other words, the high-voltage switch in the ring main unit is generally a load switch. The ring main unit uses a load switch to operate normal current and a fuse to cut off short-circuit current. The two are combined to replace the circuit breaker. Of course this can only be limited to a certain capacity.          

Ring main unit is divided into common box type and unit type according to the air box structure; they are divided into American style and European style according to the overall structure; they are divided into solid insulation type, air insulation type and SF6 gas insulation type according to the insulation material; they are divided into indoor and outdoor according to indoor and outdoor nets and outdoor ring nets. Ventilation needs to be considered for outdoor ring main units. At least the ring main units need air flow to avoid condensation. In addition, ventilation needs to consider the entry of wind and sand, which may cause damage to the mechanism. At the same time, high temperature needs to be considered. If the top plate of the outdoor box is too close to the top of the switch cabinet, it will cause the switch to overheat and affect the overall service life.

Due to the requirement of miniaturization, the height of the ring main unit must be low. On the one hand, it is easy to maintain and on the other hand, it is convenient for container transportation. In this way, the width of the ring main unit is generally not limited. The arrangement of circuit breakers and three-station switches in the circuit breaker cabinet cannot be Vertically arranged, the position is changed to horizontal arrangement, the overall height is reduced, and the height is reserved for a dedicated secondary automation compartment. The overall layout is reasonable, high strength and good reliability.

The ring main unit have not been around for a long time. From the perspective of power supply and distribution, small and medium-sized capacity generally does not exceed 1250KVA. The power supply is stable for a long time and the high-voltage switch operation is infrequent. The ring network cabinet is simple to install and the box occupies a small area. It can be conveniently placed on both sides of the street, residential areas, and urban green belts. Therefore, it is widely used in industrial parks, streets, residential areas, bustling commercial centers, etc. as a receiving and distribution center. Use of electrical energy.