posifp879 posted an update 1 month ago
Ring main unit is generally divided into air insulation and SF6 insulation. It is used for breaking load current, breaking short-circuit current and transformer no-load current, charging current of overhead line and cable line at a certain distance, which plays a control and protection role. It is an important switch equipment for ring network power supply and terminal power supply. In the cabinet, the load switch equipped with air insulation mainly includes gas producing type, compressed air type and vacuum type. The load switch equipped with SF6 insulation is SF6 type. Because SF6 gas is enclosed in the shell, the partition fracture formed by it is invisible. The load switch in the ring main unit generally requires three positions, i.e. cut off the load, isolate the circuit and be grounded. It is easy to realize three positions for gas production type, air compressor type and SF6 type load switch, while the vacuum interrupter can only be disconnected and cannot be isolated. Therefore, an isolating switch is added in front of the load switch in general vacuum load ring network switch cabinet to form isolation fracture.
Ring network cabinet is commonly known as SF6 load switch and SF6 load switch + fuse combination apparatus used in ring network line or terminal. SF6 load switch is a kind of excellent load switch realized by many users in recent years. In addition to the common advantages of long electrical life and strong breaking force with vacuum load switch, its outstanding advantages are easy to realize three working positions (connection, disconnection and grounding), small current (inductance and capacitance) breaking, and strong ability to resist severe environmental conditions. It is suitable for promotion and application in urban and rural medium voltage distribution network.
Load switch is a kind of switch apparatus with simple arc extinguishing device. The load switch using SF6 gas as insulation and arc extinguishing medium is called SF6 load switch. It can be used as closing and breaking load current and overload current, as well as closing and breaking no-load line, no-load transformer and capacitor bank, etc The switch has the characteristics of simple structure and low price. Only the load switch can not break the short-circuit current.
SF6 load switch + fuse combination apparatus is made by SF6 load switch to undertake the closing and breaking of overload current (the overload current for SF6 load switch is still within the range of rated breaking current of load switch) and normal working current, and it is also required to undertake the breaking of “transfer current”. The short-circuit protection and overload protection of the high-voltage side of the transformer are undertaken by the high-voltage current limiting fuse. At this time, a group of SF6 load switches and three fuses with trigger, as long as any trigger acts, its linkage mechanism will make the three-phase load switch automatically open at the same time. The organic combination of the two can meet the requirements of operation protection of distribution system under various normal and fault conditions.
Ring network cabinet can be divided into indoor ring network and outdoor ring network
Indoor loop network is generally used for high-voltage side power distribution, which is composed of incoming cabinet, metering cabinet, Pt cabinet and transformer outgoing cabinet. For users with high demand for electricity, the incoming line must adopt dual power supply switching cabinet. The seventh floor said that “some people also call the high-voltage switchgear with load switch and fuse as the ring main unit, which is easy to distinguish from the switch cabinet with circuit breaker”. It is not accurate. The ring main unit also has the scheme of installing circuit breaker
The outdoor loop network is generally used in urban power grid. The common box type SF6 ring network cabinet is adopted. The biggest characteristic of this cabinet type is high protection level, which can achieve IP67. It is suitable for outdoor use and can be immersed in water for a short time. The loop network power supply scheme generally adopts one loop in, one loop out, and two to three loops as the outgoing circuit, which forms the loop network power supply mode of hand in hand.
In order to ensure the reliability and continuity of power supply, two incoming lines are used for power supply, which forms a loop. SF6 load switch, 3 positions (closing, opening, grounding), opening line and transformer are adopted.
With the construction of ring network, more and more ring network is adopted. The ring main unit is a new type of complete set of equipment, which is generally composed of three compartments: i.e. The ring main unit (RMU) of outgoing line Bay (or branch unit) and transformer loop Bay (or distribution unit) is one of the most important equipment in the ring line, and its performance directly affects the reliability of the ring network power supply. In order to give full play to its advantages, a perfect loop power supply scheme must have excellent loop network control equipment. Therefore, the selection of 10kV ring network switchgear becomes very important.  Key points for purchasing 10kV ring main switch cabinet:
Technical requirements of 110 kV ring network switchgear
This scheme is characterized by several power supply branch nodes, i.e. 10kV ring network switch or branch unit, power distribution unit (as shown in figure a01a02a03, etc.) and power cables, which are connected into a closed loop network connection through the handle.
In order to better ensure the reliability of urban power supply and improve the power quality, the 10kV ring network switch cabinet should have the following technical performance:
As shown in Fig. When the cable L1 has grounding (or phase to phase short circuit) fault, the ring line can be divided into two situations for fault removal and isolation:
1. The loop network switch a02b01 trips quickly to isolate the faulty cable without affecting the power supply to users or skipping trip. This requires the loop network switch a02b01 to be equipped with longitudinal differential protection device (such as lcd3a or directional over-current protection device); this processing requires a02b01 to be a circuit breaker switch with complete relay protection system, which can meet the requirements of selectivity, rapidity, sensitivity and reliability.
2. The substation switch f01f02 trips quickly, and then the distribution network automation system passes through.China Distribution Box