Ring Main Unit - Transmission and Distribution Electrical Equipment

Ring Main Unit is a group of transmission and distribution electrical equipment (high-voltage switchgear) installed in metal or non-metallic insulated cabinets or electrical equipment made into assembled interval ring network power supply units. The core part adopts load switches and The fuse has the advantages of simple structure, small size, low price, improved power supply parameters and performance, and power supply safety. It is widely used in distribution stations and box-type substations of load centers such as urban residential quarters, high-rise buildings, large public buildings, factories and enterprises.

1. Principle of ring main unit

The ring network refers to the ring distribution network, that is, the main power supply line forms a closed ring, and the power supply supplies power to the ring main line, and then distributes power from the main line through high-voltage switches one by one. The advantage of this is that each power distribution branch can get power from its left main line and from its right main line. When the left main fails, it continues to receive power from the right main, and when the right main fails, it continues to receive power from the left main, so that although the main power supply is single, But from each power distribution branch, it can get benefits similar to dual-circuit power supply, thereby improving the reliability of power supply.

The so-called "ring network cabinet" is to set up a switch cabinet (outgoing switch cabinet) for each power distribution branch, and the busbar of this switch cabinet is also a part of the ring main line. That is to say, the ring trunk line is formed by connecting the busbars of each outgoing cabinet. Each outlet cabinet is called "ring network cabinet". In fact, if you take out a ring network cabinet alone, you can't see the meaning of "ring network".

The rated current of these ring main unit 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 high-voltage load switch with a high-voltage fuse with a simple structure. That is to say, the high-voltage switch in the ring network cabinet is generally a load switch. The ring main unit uses a load switch to operate the normal current, and a fuse to cut off the short-circuit current, and 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 power distribution system, so with the wide application of this switch cabinet, "ring network cabinet" has jumped out of the scope of ring network power distribution and generally refers to load switches. High voltage switchgear for the main switch.

2. Arc extinguishing method of ring main unit

2.1 Direct-acting compressed air type

2.2 Rotary compressed air type

2.3 Rotating magnetic arc extinguishing

2.4 Arc extinguishing with arc chute

2.5 Quartz sand arc extinguishing

3. Ring main unit protection device

3.1 Introduction

On the basis of many years of application experience in the domestic and foreign counterparts of the ring network cabinet microcomputer protection device, combined with the actual characteristics of the domestic comprehensive automation system, the high-tech power automation product that integrates protection, monitoring, control, communication and other functions is developed. Ideal electrical unit for intelligent switchgear. The product has a built-in protection library consisting of more than 20 standard protection programs, and has a complete and powerful acquisition function for the voltage and current analog and switch values of primary equipment (the current measurement is realized through the protection CT).

3.2 Microcomputer protection

Since the ring network cabinet is under high pressure, a protective device is required to protect the ring network cabinet. The use of microcomputer protection devices for ring main unit is becoming more and more popular. Due to the small size and low cost of ring main unit, it is necessary to have a cost-effective and practical microcomputer protection device.

3.3 Requirements

Scope of application: mainly applicable to user projects such as 10KV;

Protection unit: line, main transformer backup, motor, capacitor, reactor, backup self-injection, PT, non-electricity;

Product appearance: The ultra-thin body within 100mm is especially suitable for cabinets such as ring main unit;

Product material: alloy shell, anti-electromagnetic interference test conforms to national standards;

Operation circuit: without anti-jump, can be used with various switches with anti-jump;

Communication: optional with or without RS485 communication interface.

4. Application of ring main unit

The ring network cabinet has not appeared for a long time, but it has been widely used, mainly due to the newly developed buildings of industrial enterprises and institutions. From the perspective of power supply and distribution, among them, small capacity is the most Its distribution transformer generally does not exceed 1250KVA, and the power supply is stable for a long time, and the high-voltage switch is not frequently operated. For such users, although the performance of the ring network cabinet is not perfect, it is competent enough. With the large-scale urban construction, a large number of large high-rise buildings have sprung up, and the substation and distribution station is often located downstairs. According to the fire protection requirements, the substation and distribution equipment must be "oil-free". According to the rational use of the construction area , Transformation and distribution equipment should be "miniaturized", so the ring main unit or vacuum circuit breaker, dry-type transformer, and dry-type transformer have entered the buildings. The structure of the ring network cabinet is simple, reliable and safe in operation, the amount of maintenance is small, and the operating cost is low. Compared with the switch cabinet equipped with circuit breakers, the advantages are very prominent. The ring network cabinet requires the load switch to have higher performance and smaller volume, and a new type of load switch has emerged, which in turn drives the technical progress of the ring network cabinet. Today's ring main unit not only have excellent performance but also are serialized. , which further expands the scope of use of the ring network cabinet.