Tashin Kalmomin 24kV Air da Gas-Insulated Gear

Yanzu, tushen medium-voltage distribution networks na China suna da 10kV. Wajen fadada tattalin arzikin kasuwanci, tashin kawo kyautar zafi ya rage, wanda yake sa shi a duba cikakken hanyoyin kawo kyau da ke dace. Saboda muhimmancin 24kV high-voltage switchgear wajen samun kyau da inganci masu kawo kyautar zafi, an yi nasara a kan industry. Ba aiki da "Notice on Promoting the 20kV Voltage Level" na State Grid Corporation, an yi amfani da 20kV voltage class ta hanyar rage.

A matsayin babban abincin wannan voltage level, structure da insulation design na 24kV high-voltage switchgear suka zama manyan nuna a kan industry. Daga bayanan power industry standard "Common Technical Requirements for High-Voltage Switchgear and Control Equipment" (DL/T 593-2006), ana bayyana cewa insulation requirements na switchgear su ne. Insulation requirements na 24kV products sun haɗa:

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: Data a zuwa na farko na slash yana iya a gina a kan solidly grounded neutral systems, domin data a zuwa na biyu yana iya a gina a kan systems with neutral grounded through an arc suppression coil or ungrounded.

24kV high-voltage switchgear zai iya faɗinsu a kan insulation method saboda air-insulated metal-enclosed switchgear da gas-insulated SF6 ring main units. Air-insulated metal-enclosed switchgear na 24kV, musamman mid-mounted withdrawable type (da aka sani a matsayin 24kV mid-mounted switchgear), ta zama baka mai mahimmanci a kan design. Wannan rubutu yana magana game da wasu recommendations game da structure da insulation design na 24kV mid-mounted switchgear da gas-insulated SF6 ring main units, don tabbataccen bayanai da lura.

1. Design of 24kV Mid-Mounted Switchgear

Technology na 24kV mid-mounted switchgear sun fito da uku masu asalin: Kima, upgrade daga 12kV KYN28-12 product tare da koyarwa components related to insulation. Buka, foreign mid-mounted products ta shiga domestic market, kamar ABB da Eaton Senyuan. Uku, independently developed 24kV mid-mounted switchgear na China. Uku, wanda ake design saboda tushen technology da abubuwan da ke dace a China, ce mafi nasara a kan market. Saboda haka, a lokacin da ake design, yana buƙata a yi tasiri ga overall product structure da insulation design, kamar yadda aka bayyana:

1.1 Equal-Height Cabinet Structure and Triangular Busbar Arrangement

Duk 12kV mid-mounted switchgear suna da structure da take faru a kan front da kuma lafiya a kan rear, da three-phase busbars suna da triangular (delta) arrangement, da instrument compartment yana iya a kawo ta hanyar removable, independent structure. Idan wannan hanyar yana amfani a kan 24kV mid-mounted switchgear, ba zan iya a tabbatar da minimum air clearance requirement na 180mm. Saboda haka, 24kV mid-mounted switchgear yana buƙata a yi amfani da equal-height cabinet design, da instrument compartment yana aji tsaya a kan main cabinet.

Cabinet height yana buƙata a yi karɓe ta hanyar 2400mm, don bayyana masu space masu busbar da circuit breaker compartments. Busbar wall bushings suna buƙata a yi arrangement a kan triangular configuration. Wannan hanyar yana iya a tabbatar da air clearance requirements, kuma yana iya a yi nasara a kan electromagnetic forces, improves busbar heat dissipation, da kuma enhances insulation reliability.

1.2 Rational Design of Switchgear Width

Daga riyoyin insulation reliability, air insulation ce mafi nasara; idan minimum insulation clearance an tabbatar, insulation za a tabbatar da ita. Amma a lokacin da ake design saboda fully air-insulated, theoretical width na 24kV switchgear yana iya a haɗa 1020mm. Amma, a cikin production, duk manufacturers suna zaba cabinet width na 1000mm, wanda yana buƙata a yi amfani da composite insulation. Generally, heat-shrink tubing suna amfani a kan busbars, da SMC (Sheet Molding Compound) insulating barriers suna zama a kan phases da kuma between phase and ground don enhance insulation.

1.3 Design for Uniform Electric Field Distribution

Testing ya tabbatar cewa, mara da voltage level, local electric field strength a lokacin da power frequency withstand voltage tests yana rage, kuma yana iya a duba corona discharge sounds. Daga cikin regulations, idan ba a samu disruptive discharge, test yana tabbatar da ita. Amma, high local electric field strength yana iya a duba product's ability to withstand overvoltages during normal operation. 

Saboda haka, product design yana buƙata a yi tasiri ga achieving as uniform an electric field distribution as possible, avoiding localized field concentration. Daga riyoyin experience, shaping conductors to achieve a uniform field yana iya a tabbatar da ita. For the cut ends of busbars, use a forming milling cutter to machine the ends into rounded corners. For the busbar ends inside the contact box, first form them into a semi-circular shape, then mill them into a rounded corner. Where conditions allow, install a metal shielding cover outside the circuit breaker's plum blossom contacts, or embed a metal shielding mesh during the casting of the contact box. These measures can effectively uniform the electric field distribution, suppress field peaks, and further improve insulation levels.

1.4 Use of Insulating Materials with Long Creepage Distance

Insulating materials such as wall bushings, contact boxes, and support insulators must have enlarged sheds and sufficient creepage distance to meet the insulation requirements of 24kV. Especially in the design of contact boxes, a metal shielding mesh must be added, and the inner cavity should use a tongue-like structure to avoid the problems inherent in ring structures, which cannot effectively suppress condensation and the resulting pollution accumulation during operation.

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

Foreign 24kV gas-insulated SF6 ring main units sun faru ne a kafin; companies like Siemens and ABB suna faru a kan early 1980s. Wannan shine saboda duk countries suna amfani da 24kV as primary medium-voltage distribution voltage. Their products are technologically advanced, high-performing, and highly reliable. Domestic 24kV gas-insulated SF6 ring main units sun faru ne a nan. Limited by various conditions, products are still in the research, development, and testing stages.

Due to the advanced nature of 24kV gas-insulated SF6 ring main unit technology, their structure and insulation design must draw on mature foreign experience. The following are several recommendations on product structure and insulation design:

2.1 Focus on Structural Rationality

Since all live parts and switches in 24kV gas-insulated SF6 ring main units are sealed within a stainless-steel enclosure filled with SF6 gas, they are compact. In structural design, the insulation strength and humidity of the insulating gas must be fully considered to rationally design the cabinet's dimensions. The unit should have complete functionality, be easy to operate, and have a simple structure.

2.2 Expandability of Configurations

Configuration design must have expandability. To a certain extent, the quality of a product and its potential for widespread adoption depend on its configurational flexibility. A standardized, modular design allows for flexible left and right expansion.

2.3 Reliability of Insulation Design

The primary risk for 24kV gas-insulated SF6 ring main units is the degradation of insulation performance. Factors causing insulation degradation include: SF6 gas leakage; polymeric insulation or sealing materials having certain permeability to different gases (such as water vapor), leading to unacceptable condensation on the container's inner walls; control of moisture content in the SF6 gas; and cracks in insulating components.

To prevent insulation degradation, corresponding measures must be taken, such as: manufacturing the gas container from stainless steel using full welding, leaving no sealed openings; making cable connection bushings from epoxy cast resin and welding them integrally to the container; enhancing the gas container's seal to minimize water vapor permeation; regularly measuring moisture content with an SF6 moisture tester, placing an appropriate amount of desiccant in the sealed enclosure, and strictly baking all components according to specified temperature and time; when evacuating and charging SF6 switchgear, cleaning the charging lines with high-purity N2 or SF6 gas; and minimizing internal mechanical stress in insulating components to prevent aging and cracking. These measures will effectively improve insulation reliability.

3. Conclusion

Although the structure and insulation design of 24kV high-voltage switchgear are based on 12kV switchgear, the requirements are far higher. Furthermore, due to insufficient practical operating experience, all influencing factors must be fully considered during the design process to meet product standards.