Pagdisenyo og Reliable 24kV Air & Gas-Insulated Gear

Karon, ang mga medium-voltage distribution networks sa China adunay pag-operate sa 10kV. Tungod sa rapidong economic development, ang power loads mibuto, nga nagpakita sa limitations sa existing power supply methods. Ang 24kV high-voltage switchgear, tungod sa iyang outstanding advantages sa pag-meet sa higher load capacity demands, nagsugyot sa industriya. Pagkahuman sa State Grid Corporation's "Notice on Promoting the 20kV Voltage Level," ang 20kV voltage class nagsugyot sa pag-adopt.

Isip usa ka critical product para kini nga voltage level, ang structure ug insulation design sa 24kV high-voltage switchgear naging focal points sa industriya. Sumala sa power industry standard "Common Technical Requirements for High-Voltage Switchgear and Control Equipment" (DL/T 593-2006), ang specific insulation requirements para sa switchgear klaro gisulti. Ang insulation requirements para sa 24kV products mao kini:

Minimum air clearance (phase-to-phase, phase-to-ground): 180mm; Power frequency withstand voltage (phase-to-phase, phase-to-ground): 50/65 kV/min, (across isolation joints): 64/79 kV/min; Lightning impulse withstand voltage (phase-to-phase, phase-to-ground): 95/125 kV/min, (across isolation joints): 115/145 kV/min.

Note: Ang data sa wala sa slash applicable sa solidly grounded neutral systems, ang data sa tuokan applicable sa systems with neutral grounded through an arc suppression coil o ungrounded.

Ang 24kV high-voltage switchgear mahimong icategory batas sa insulation method sa air-insulated metal-enclosed switchgear ug gas-insulated SF6 ring main units. Ang air-insulated metal-enclosed switchgear para sa 24kV, lalo na ang mid-mounted withdrawable type (hereinafter referred to as the 24kV mid-mounted switchgear), naging key design focus. Kini nga article nagdiskubre sa daghang recommendations bahin sa structure ug insulation design sa 24kV mid-mounted switchgear ug gas-insulated SF6 ring main units, offered for reference ug comment.

1. Design of 24kV Mid-Mounted Switchgear

Ang teknolohiya para sa 24kV mid-mounted switchgear gikan sa tulo ka sources: Una, usa ka upgrade gikan sa 12kV KYN28-12 product pinaagi sa direct replacement sa components related sa insulation. Segundo, foreign mid-mounted products molingi sa domestic market, sama sa ABB ug Eaton Senyuan. Tulo, independently developed 24kV mid-mounted switchgear sa China. Ang ikatulong category, designed specifically sa China's existing technical conditions ug requirements, ang pinaka competitive sa market. Busa, sa panahon sa iyang design, ang overall product structure ug insulation design kinahanglan full considered, as detailed below:

1.1 Equal-Height Cabinet Structure ug Triangular Busbar Arrangement

Ang most 12kV mid-mounted switchgear gamit og structure nga mas taas sa front ug mas baba sa rear, ang three-phase busbars arranged sa triangular (delta) configuration, ug ang instrument compartment is removable, independent structure. Kon kini nga method gamiton sa 24kV mid-mounted switchgear, dili kini maka-meet sa minimum air clearance requirement sa 180mm. Busa, ang 24kV mid-mounted switchgear dapat adopt og equal-height cabinet design, ang instrument compartment integrated sa main cabinet.

Ang cabinet height dapat increase sa 2400mm, providing more space sa busbar ug circuit breaker compartments. Ang busbar wall bushings dapat arranged sa triangular configuration. Kini nga approach not only meets ang air clearance requirements apan usab effectively suppress ug withstand electromagnetic forces, improve busbar heat dissipation, ug enhance insulation reliability.

1.2 Rational Design of Switchgear Width

Gikan sa perspective sa insulation reliability, ang air insulation ang pinaka reliable method; as long as guaranteed ang minimum insulation clearance, fully assured ang insulation. Considering a fully air-insulated design, ang theoretical width sa 24kV switchgear dapat 1020mm. Pero, sa actual production, ang majority sa manufacturers choose og cabinet width sa 1000mm, nga necessitates ang use sa composite insulation. Generally, ang heat-shrink tubing applied sa busbars, ug SMC (Sheet Molding Compound) insulating barriers installed between phases ug between phase and ground to enhance insulation.

1.3 Design for Uniform Electric Field Distribution

Testing proves nga ang mas taas ang voltage level, ang mas taas ang local electric field strength during power frequency withstand voltage tests, sometimes accompanied sa noticeable corona discharge sounds. Sumala sa regulations, as long as no disruptive discharge occurs, ang test considered passed. Pero, ang high local electric field strength can affect ang product's ability sa pag-withstand overvoltages during normal operation. 

Busa, ang product design kinahanglan prioritize sa achieving as uniform electric field distribution as possible, avoiding localized field concentration. Gikan sa practical experience, shaping conductors sa achieving a uniform field effective. Para sa cut ends sa busbars, use og forming milling cutter sa machining sa ends sa rounded corners. Para sa busbar ends inside the contact box, first form sila sa semi-circular shape, then mill sila sa rounded corner. Where conditions allow, install og metal shielding cover outside the circuit breaker's plum blossom contacts, o embed og metal shielding mesh during the casting sa contact box. Kini nga measures can effectively uniform ang electric field distribution, suppress field peaks, ug further improve insulation levels.

1.4 Use of Insulating Materials with Long Creepage Distance

Ang insulating materials sama sa wall bushings, contact boxes, ug support insulators kinahanglan enlarged sheds ug sufficient creepage distance sa pag-meet sa insulation requirements sa 24kV. Especially sa design sa contact boxes, kinahanglan add og metal shielding mesh, ug ang inner cavity dapat use og tongue-like structure sa avoidance sa problems inherent sa ring structures, nga dili effective sa suppression sa condensation ug resulting pollution accumulation during operation.

2. Design of 24kV Gas-Insulated SF6 Ring Main Units

Ang foreign 24kV gas-insulated SF6 ring main units nagsugyot early; companies sama sa Siemens ug ABB introduce sila sa early 1980s. Busa niini kay ang daghang foreign countries use 24kV isip primary medium-voltage distribution voltage. Ang ilang products technologically advanced, high-performing, ug highly reliable. Ang domestic 24kV gas-insulated SF6 ring main units nagsugyot lang sa recent years. Limited sa various conditions, ang products still sa research, development, ug testing stages.

Tungod sa advanced nature sa 24kV gas-insulated SF6 ring main unit technology, ang ilang structure ug insulation design kinahanglan draw sa mature foreign experience. Ang following mao ang daghang recommendations bahin sa product structure ug insulation design:

2.1 Focus on Structural Rationality

Tungod kay tanang live parts ug switches sa 24kV gas-insulated SF6 ring main units sealed sa stainless-steel enclosure filled sa SF6 gas, compact sila. Sa structural design, ang insulation strength ug humidity sa insulating gas kinahanglan full considered sa rational design sa cabinet's dimensions. Ang unit dapat have complete functionality, easy to operate, ug simple structure.

2.2 Expandability of Configurations

Ang configuration design kinahanglan expandability. Sa certain extent, ang quality sa product ug potential sa widespread adoption depend sa configurational flexibility. Standardized, modular design allows flexible left ug right expansion.

2.3 Reliability of Insulation Design

Ang primary risk sa 24kV gas-insulated SF6 ring main units mao ang degradation sa insulation performance. Ang factors causing insulation degradation include: SF6 gas leakage; polymeric insulation or sealing materials may permeability sa different gases (such as water vapor), leading sa unacceptable condensation sa container's inner walls; control sa moisture content sa SF6 gas; ug cracks sa insulating components.

Para ma-prevent ang insulation degradation, corresponding measures kinahanglan, sama sa: manufacturing sa gas container gikan sa stainless steel pinaagi sa full welding, leaving no sealed openings; making cable connection bushings gikan sa epoxy cast resin ug welding sila integrally sa container; enhancing sa gas container's seal sa minimization sa water vapor permeation; regularly measuring sa moisture content pinaagi sa SF6 moisture tester, placing appropriate amount sa desiccant sa sealed enclosure, ug strictly baking all components sumala sa specified temperature ug time; when evacuating ug charging sa SF6 switchgear, cleaning sa charging lines pinaagi sa high-purity N2 or SF6 gas; ug minimizing internal mechanical stress sa insulating components sa prevention sa aging ug cracking. Kini nga measures will effectively improve insulation reliability.

3. Conclusion

Tungod kay ang structure ug insulation design sa 24kV high-voltage switchgear based sa 12kV switchgear, ang requirements far higher. Furthermore, tungod kay insufficient practical operating experience, ang tanang influencing factors kinahanglan full considered sa design process sa pag-meet sa product standards.