Koƙari na Ƙaunsi 24kV na Tana Iya Mai Tsabta Daji

A cikin ɗaya da take da Solid Insulation Assist + Dry Air Insulation yana nuna hanyar zama na RMUs na 24kV. Ta haka, tana iya kula da al'amuran insulation da kuma gudummawa, ta haka za a iya tabbatar da ci gaba da insulation tests ba zan iya karfin ƙarin inganci daga phase-to-phase da phase-to-ground. An fi pole column fitowa don samun insulation masu vacuum interrupter da connecting conductors.

Tare da ƙarfin ɗaya da take da 24kV outgoing busbar phase spacing a 110mm, za a iya kula da electric field intensity da non-uniformity coefficient tare da fitowa a busbar surface. Table 4 ya kula electric field under different phase spacings da busbar insulation thicknesses. Ya bayyana cewa in yi karfi ko ƙarin phase spacing zuwa 130mm da kuma ɗaukan 5mm epoxy encapsulation a round bar busbar, za ta haɗa electric field strength zuwa 2298 kV/m. Wannan zai ɗauka ƙarin tushen dry air (3000 kV/m).

Table 4: Electric Field Conditions under Different Phase Spacing and Busbar Insulation Thicknesses

Saboda low insulation strength of dry air, solid insulation alone ba zan iya kula da voltage withstand issue for the isolating gap. A dual-isolation-break configuration yana kula da voltage across two gas gaps. Grading rings (field shields) an sanar da su a concentrated field areas like the isolation and earthing stationary contacts don kula da field strength da kuma kara ƙarin air gap dimensions. Kamar yadda aka baka a Figure 3, reinforced nylon main shaft yana jirgin dual-break mechanism don samun operational, isolation, and grounding states. Grading rings a stationary contacts, with a 60mm diameter da kuma epoxy encapsulation, suna ɗauka 100mm clearance don kula da 150kV lightning impulse withstand voltage.

Wasu hanyoyi, kamar longitudinal phase-segregated layouts, using high-strength single-phase alloy tanks, ko moderately increasing gas pressure, zai iya kula da 24kV withstand requirements. Amma, RMUs sun buƙata low cost, kuma costs mai yawan daidai ba zan ɗauka users. Tare da optimized design, kamar moderately increasing RMU width, za a iya samun goal of low cost and miniaturization don 24kV eco-friendly gas-insulated RMUs.

1. Arrangement of Earth Switches in Eco-Gas RMUs
Biye hanyoyi ne zai iya kula da grounding functions:

• Outgoing side earth switch (lower earth switch)
• Busbar side earth switch (upper earth switch), optionally E0 rated, requiring main switch coordination for earthing operations.

State Grid's "12kV RMU (Cabinet) Standardized Design Scheme" 2022 Edition specifies that all three-position switches (isolate, connect, earth) should utilize the busbar side arrangement, termed the "Busbar Side Combined Function Earth Switch".

Power safety regulations mandate that no circuit breaker (CB) or fuse can exist between the earth conductor/earth switch and the equipment under maintenance. If a CB exists between the earth switch and the equipment due to design constraints, measures must ensure the CB cannot open after both the earth switch and CB are closed. Therefore:

• A Line Side Earth Switch, located downstream of the CB, connects directly to the earthed outgoing cable, naturally meeting the regulation as no CB exists between it and the equipment.
• A Busbar Side Earth Switch, located upstream of the CB, has the vacuum CB between it and the earthed outgoing cable, violating the direct connection requirement. After closing the earth switch and CB, measures preventing CB opening must be implemented. Examples include disconnecting the CB trip circuit via a blocking plate or using mechanical interlocks to prevent accidental CB opening and consequent loss of earthing.

The National Grid standard also mandates mechanical and electrical interlocks to prevent manual or electrical opening of the CB when the combined function earth switch is using the CB (closed) to ground the cable side.

The primary reason for choosing the Busbar Side Isolating-Earthing Three-Position Switch in the National Grid standard is earthing/grounding making capacity:

• SF6 RMUs: SF6 has ~3x the insulation strength of air and ~100x greater arc-quenching capability due to superior cooling, ensuring adequate earth switch making capacity.
• Eco-Gas RMUs: Eco-gases lack inherent arc-quenching ability and have poorer insulation. Achieving the required making capacity thus demands very high closing speeds. However, standard RMU operating mechanisms lack the energy for such speeds. Using a line-side earth switch necessitates expensive higher-speed mechanisms, robust arc-resistant contacts, and force analysis, increasing cost and complexity. Busbar Side Earth Switches, while requiring CB interlocking solutions, offer stronger making capacity and can ensure earthing reliability.

Analysis of SF6 vs. Eco-Gas Technology and Products indicates that 12kV Eco-Gas RMUs can meet insulation and temperature rise requirements with minimal size increase, representing a mature technical solution.

Conversely, 24kV Eco-Gas Insulated products are still limited. The key challenge is the significantly higher voltage level leading to much larger dimensions and higher costs, impeding development. Balancing factors like insulating gas type, filling pressure, gas tank volume, and auxiliary insulation cost is crucial to designing low-cost, compact RMUs. Successfully replacing SF6 will not only capture the domestic market but also enable global outreach, promoting China's low-carbon, eco-friendly products worldwide.