Research on Aluminum Alloy Air Insulated Busway

In the late 1990s, China's coastal areas with rapid economic development and some more developed inland areas widely adopted the switchgear and switch station mode of ring network wiring and multi-circuit distribution to optimize the cable distribution network structure. SF6 fully insulated switchgear has the characteristics of fully enclosed, maintenance-free, small size, excellent performance, safety and reliability, and is very popular among users. The ring network cabinet has developed from the initial air-insulated ring network distribution unit to the compact SF6 ring network distribution unit, and recently developed into an expandable SF6 fully insulated ring network cabinet or multi-circuit distribution cabinet, which has made great progress and development in SF6 fully insulated switch technology. In particular, computer technology, electronic technology, sensor technology, optical fiber communication technology and other technologies are applied to ring network cabinets or multi-circuit distribution cabinets, making the products more miniaturized and intelligent.

Technical features of SF6 fully insulated ring network cabinets or multi-circuit distribution cabinets The

technical features of SF6 fully insulated ring network cabinets or multi-circuit distribution cabinets are mainly reflected in the following aspects:

(1) Modular design, each unit module can be arbitrarily combined and expanded without filling and deflation, which is convenient for scheme combination and high-voltage metering design, and has a wide range of applications. SF6 fully insulated circuit breaker inlet and outlet cabinets (vacuum or SF6 arc extinguishing), load switch inlet and outlet cabinets, busbar cabinets, metering cabinets, load switch-fuse combination cabinets, and TV cabinets (with or without switches). The combination scheme can be a compact combination of single unit, two units, three units, four units, etc., which provides a broad application prospect for SF6 fully insulated ring network cabinets or multi-circuit distribution cabinets.

(2) The cabinet adopts an armored structure, and there are metal partitions between the busbar room and the switch room, and between the switch room and the cable room. The primary part of the fully insulated structure has a protection level of up to IP67. (3

) The load switch with three positions is welded in a sealed stainless steel shell filled with SF6 gas. It has very good air tightness, uses less gas, and can ensure no leakage for 30 years. It meets the requirements of environmental protection. It is suitable for indoor or outdoor use with metal or non-metallic shells, or placed in underground or semi-underground substations.

(4) The operating mechanism is made of corrosion-resistant metal, and the bearings of the rotating parts are all self-lubricating. The product is not affected by the environment, does not require regular maintenance, and is easy to connect to the outside world, which makes the operation work small, the reliability high, and the service life longer.

(5) The extended busbar adopts a plug-in silicone rubber connector, which is fully insulated and shielded to ensure the reliability of conductivity and is not affected by the surrounding environment. It is convenient for combined connection and expansion, which is convenient for future capacity expansion and transformation of users or substations.

(6) The prefabricated silicone rubber insulated cable terminal is plugged in at the front, eliminating the disadvantages of inconvenient cable installation caused by the small size and narrow space of the load switch cabinet. It can be disassembled, quickly restored, and easy to install during maintenance; the outer surface uses a new semiconductor material as a shielding layer, and the outer surface is grounded during operation, which is not affected by moisture, condensation, dust, dirt, etc., and has higher safety; maintenance-free; diverse, novel, and beautiful appearance, can be branched or paralleled; has flood prevention function, and can operate for a short time at 4.5m underwater.

(7) In order to adapt to the requirements of distribution network automation and improve distribution reliability, the new multi-circuit distribution cabinet can be equipped with electric mechanisms, TVs and distribution network control terminal units as needed, and has three remote functions. It can realize remote monitoring of the operating status and faults of the main components, remote meter reading, remote operation, etc.

(8) The cabinet is miniaturized and uses a three-position rotary load switch to effectively reduce the number of parts and realize mechanical five-protection interlocking. The vacuum circuit breaker is filled with SF6 gas insulation, and the respective advantages of vacuum arc extinguishing and SF6 gas insulation are used to make the overall structure more compact; the current limiting fuse is also developing in the direction of miniaturization, large capacity, high breaking capacity, and fast fuse. The combination of the two makes the cabinet smaller and smaller.

(9) The friendly operation interface ensures the safety of operators and maintenance personnel. The primary line simulation single-line diagram and simulation display can display the internal status of the switch, making the operation simple, correct and safe.

SF6 fully insulated load switch-fuse combination

2.1 Technical features

In addition to the above technical features, the SF6 load switch-fuse combination has the following features: (1) The fully insulated SF6 load switch-fuse combination has a double-layer insulation seal of silicone rubber and insulators and is mechanically interlocked. It is safe, reliable, flood-proof, and condensation-proof. The protection level can reach IP67.

(2) The fuse is first installed on the bracket and then automatically introduced into the fuse chamber to ensure reliable contact of the fuse. The fuse directly contacts the left, middle, and right three phases from the front, which is convenient for quick replacement of the fuse. (3) It has fuse overheat protection. When the fuse is seriously heated, it automatically trips, and transformer accidents are discovered in time.

(4) The fuse support is placed in the SF6 gas and arranged horizontally, which greatly uniformizes the electric field and reduces the volume.

(5) The microcomputer can be configured to implement overcurrent protection. The overcurrent fault of the transformer is interrupted by the load switch, and the short-circuit fault is interrupted by the fuse. The protection of the transformer is more reasonable and can replace the circuit breaker to provide full-range protection for transformers of 1250kVA and below.

2.2 Application of transformer protection

The load switch-fuse combination electrical appliance can limit the short-circuit current value to protect the transformer from sudden short-circuit fault current, and quickly cut off the internal short-circuit fault of the transformer within 10ms to prevent the transformer oil tank from deforming and cracking due to the pressure increase caused by the internal arc, so that the transformer can be protected more reliably and reasonably. For the short circuit at the end of the low-voltage side of the transformer, the high-voltage fuse is reasonably selected, and the short-circuit fault at the end of the low-voltage side is cut off by the high-voltage side fuse, which can effectively protect the transformer.

Whether the structure of SF6 load switch-fuse combination or circuit breaker is adopted, it can protect the transformer. However, load switch-fuse combination has its unique advantages in transformer protection:

(1) SF6 load switch-fuse combination is cheaper than circuit breaker. If the price of circuit breaker is 100%, the price of SF6 load switch-fuse combination is only 20%. The price of imported SF6 load switch-fuse combination is only about 1/3 of that of domestic circuit breaker cabinet. (2

) The manufacturing structure of SF6 load switch-fuse combination is simpler than that of circuit breaker, with less material consumption and high reliability. Its key manufacturing process is shell welding sealing technology and leakage detection technology. The transformer is more reliably and reasonably protected. For the short circuit at the low-voltage end of the transformer, the high-voltage fuse can be reasonably selected, and the high-voltage side fuse can cut off the short circuit fault at the low-voltage end, which can effectively protect the transformer.

Whether the structure of SF6 load switch-fuse combination device or circuit breaker structure is adopted, both can play a protective role for transformers. However, in comparison, load switch-fuse combination device has its own unique aspects in protecting transformers:

(1) SF6 load switch-fuse combination device is cheaper than circuit breaker structure; if the price of circuit breaker is 100%, the price of SF6 load switch-fuse combination device is only 20%, and the price of imported SF6 load switch-fuse combination device is only about 1/3 of that of domestic circuit breaker cabinet.

(2) The manufacturing of SF6 load switch-fuse combination device is simpler than that of circuit breaker, with less material consumption and high reliability. Its key manufacturing processes are shell welding sealing technology and leakage detection technology.

(3) According to the practice of some European power companies, the characteristics of load switch-fuse combination devices for protecting transformers are better than those of circuit breakers. The breaking time of circuit breakers with relay protection is more than 60ms, while fuses can be quickly blown in 10ms at high currents. In addition, the increase of short-circuit current is limited, thus preventing the transformer from being damaged by sudden short circuits.

(4) SF6 load switch-fuse combination electrical appliances with power-free relay protection devices make up for the defect of fuses without protection in the overcurrent part of the transformer. Compared with the relay protection device of the circuit breaker, the power-free relay protection device of the load switch-fuse combination electrical appliances does not require an external power supply, eliminating the TV cabinet or DC screen that provides power for the relay protection of the circuit breaker. The protection is simpler and the cost is cheaper. A load switch incoming line, a meter, and a load switch-fuse combination electrical cabinet can complete the protection of the user's transformer without an external power supply. The traditional circuit breaker design requires a circuit breaker incoming line cabinet, a meter cabinet, a TV cabinet, and a circuit breaker outgoing line cabinet. Both circuit breakers require relay protection and high-performance TA, and each switch cabinet requires a heater. Therefore, the cost and energy consumption are high, and there are many fault links.

(5) In actual operation, the capacity of transformers is 1250kVA or less, and most of their rated currents are below 72A. The rated current of circuit breakers is generally designed to be in the range of 1250A to 3150A. It is obviously a big horse pulling a small cart to protect transformers of 1250kVA or less, and the structure is not very reasonable. Using the load switch-fuse combination electrical structure, high-voltage fuses protect the transformers under their respective jurisdiction, simplifying the coordination relationship with the upper circuit breaker, and making commissioning and maintenance much more convenient.

Conclusion

It is completely feasible to replace the circuit breaker with the SF6 load switch-fuse combination electrical appliance to protect transformers of 1250kVA or less. It can provide comprehensive and reasonable protection for the transformer, and the cost is reasonable and the protection is simple. Under the same conditions, users can afford to buy maintenance-free products with higher performance grades. Therefore, the technical characteristics of SF6 fully insulated ring network cabinets or multi-circuit distribution cabinets are very obvious, and the load switch factory fuse combination electrical appliance is an ideal product for protecting distribution transformers.