Kabilarin Yakin Da Kasa a 24kV Eco-Friendly RMUs: Yadda Da Kyau & Yadda A Yi

An samun hanyar inganci da kuma hanyar ingancin hawa mai sauya shi ne abu na gurbin 24 kV ring main units. Tare da hanyar ingancin hawa mai sauya shi, za a iya lalace da ci gaban inganci ko kuma cikakken fase da kyau zuwa rayuwar. Tabbacin pole ya zama yadda ake taimaka da hanyar ingancin hawa mai sauya shi da kuma magana da vacuum interrupter da kuma mafi girman adadin adadin.

Don 24 kV outgoing busbar, idan an rike fase spacing a 110 mm, maka vulcanizing wajen busbar ya zama yadda ake bude dukkan electric field strength da electric field non-uniformity coefficient. Tabular 4 ya kula electric field a kan fase spacing da kuma thickness da aka yi don busbar. Ana iya duba cewa idan an yi karfi fase spacing a 130 mm da kuma 5 mm epoxy vulcanization treatment a round busbar, electric field strength ya zama 2298 kV/m, wanda ya fi dacewa da maximum electric field strength da dry air zai iya sake ta hanyar 3000 kV/m.

Tabular 1 Electric field conditions under different phase spacings and busbar insulation thicknesses

Saboda dielectric strength da ke nan da dry air, ba hanyar ingancin hawa mai sauya shi zan iya taimaka da matsayin masu inganci a lokacin da aka faɗa isolation break. Double-break disconnector ya amfani da gas gaps biyu a tsaye don iya koyar da voltage daidai. Ana kawo electric field shielding da grading rings a wuraren da electric fields suna ciki, kamar stationary contacts da grounding switch, don kudeta electric field intensity da kuma koyar da cikakken air gap. Kamar yadda ake bayyana a Figure 1, double-break mechanism ya samu operational states—working, isolated, da kuma grounded—don enhanced rotation of a nylon main shaft. Grading ring a stationary contact ya zama 60 mm da kuma ana tabbatar da epoxy vulcanization; 100 mm clearance ya zama iya sake ta 150 kV lightning impulse voltage.

Wasu hanyoyi, kamar longitudinal single-phase arrangement using high-strength alloy enclosures for each phase ko kuma moderate increasing the gas pressure, zai iya taimaka da 24 kV dielectric requirements. Amma, ring main units (RMUs) suka buƙata low cost, kuma costs da suka fi karkashin ya ba ake gaji da su. Don haka, tare da optimized design da kuma moderate widening of the RMU cabinet, za a iya samun low-cost da compact 24 kV environmentally friendly gas-insulated RMUs.

Grounding Switch Arrangement in Eco-Friendly Gas RMUs

Akwai hanyoyi biyu a RMUs don samun grounding function a main circuit:

• Outgoing line-side earthing switch (lower earthing switch)

• Busbar-side earthing switch (upper earthing switch)

Busbar-side earthing switch zai iya zama Class E0, wanda ya buƙata coordination with the main switch during operation. Daga Standardized Design Scheme for 12 kV Ring Main Units (Boxes) da State Grid ta fara a 2022, game da three-position switches, an fara cewa three-position switches zai iya amfani da busbar-side arrangement da kuma an redefine them as "busbar-side combined functional earthing switches."

Power safety regulations sun nuna cewa ba zai iya a haɗa circuit breaker ko fuse a kan grounding wires, earthing switches, da kuma equipment under maintenance. Idan, saboda yanayin da aka samu, akwai circuit breaker a kan earthing switch da kuma equipment under maintenance, ya kamata a yi measures to ensure that the circuit breaker cannot open after both the earthing switch and the circuit breaker have been closed.

Saboda haka, line-side earthing switch ita ce wanda yake cikin circuit breaker. Ita ce take haɗa da outgoing cable being grounded, tare da requirement da ke nan da ba zai iya a haɗa circuit breaker ko fuse a kan grounding point, earthing switch, da kuma equipment under maintenance. Amma, busbar-side earthing switch ita ce wanda yake cikin circuit breaker. Akwai vacuum circuit breaker a kan earthing switch da kuma outgoing cable being grounded—it does not connect directly. Saboda akwai circuit breaker a kan earthing switch da kuma equipment under maintenance, ya kamata a yi measures to prevent the circuit breaker from opening once both the earthing switch and the circuit breaker are closed. Misali, trip circuit of the circuit breaker may be disconnected via a link plate, or mechanical means may be used to prevent accidental tripping, thereby avoiding unintended disconnection of the grounding path.

State Grid Standardized Design Scheme ta nuna interlocking requirements for the busbar-side combined functional earthing switch. When the combined functional earthing switch on the busbar side uses closure of the circuit breaker to achieve grounding of the cable side, it must include both mechanical and electrical interlocks to prevent manual or electric opening of the circuit breaker.

State Grid takes into account the short-circuit making (closing) capability in adopting the busbar-side three-position isolation/grounding switch. In SF6-insulated RMUs, the earthing switch benefits from SF6’s dielectric strength being about three times that of air and its arc-quenching capability approximately 100 times greater than air due to superior arc cooling. Thus, the closing capacity of the earthing switch is reliably ensured.

In contrast, eco-friendly gases lack arc-quenching capability and have lower insulation performance. Therefore, very high closing speed is required. However, RMU operating mechanisms have limited energy and cannot provide sufficient force for high-speed closing. Using a line-side earthing switch would require increased closing speed and improved arc resistance and electrodynamic analysis of the contacts, potentially leading to larger operating forces and higher costs. The busbar-side earthing switch, by solving the circuit breaker interlock issue, can still ensure reliable grounding while offering stronger making capacity.

Through technical and product analysis of SF6 versus eco-friendly gases, it can be seen that 12 kV eco-friendly gas-insulated RMUs can meet insulation and temperature rise requirements with only minor increases in size, indicating mature technical solutions.

However, there are few 24 kV eco-friendly gas-insulated products available. The key challenge lies in the higher voltage rating, which leads to significantly increased dimensions. Excessive size and high price will restrict the development of 24 kV eco-friendly gas-insulated RMUs. A balanced approach considering insulating gas type, filling pressure, enclosure volume, and auxiliary insulation cost is needed to design low-cost, compact RMUs. Only then can true SF6 replacement be achieved—enabling not only domestic market dominance but also global export, promoting China's low-carbon, environmentally friendly electrical equipment worldwide.