Implementasyon nga Pamaagi Alang sa Pag-install og Lightning Arresters o Voltage Transformers sa Gas-Insulated Ring Main Units

Batas sa tipo sa insulasyon, ang mga ring main units (RMUs) mahimong ma-klasipikar isip gas-insulated o air-insulated. Ang una nga nag-instal sa primary circuit components sa usa ka sealed metal enclosure nga gisuloban og low-pressure gas (primarily SF₆ o mixed gases) isip insulating medium, gamiton ang cable terminals para sa incoming ug outgoing lines. Tungod sa superior insulation, compact size, ug modular design, sila gigamit kasagaran sa 10kV outdoor distribution substations ug prefabricated transformer stations. Pero, ang ilang fully insulated ug compact nature limita ang ilang applicability sa pipila ka typical substation layouts.

​1 Mga Isyu sa Gas-Insulated RMUs​

Figure 1 nagpakita og typical distribution substation design, diin ang load switch-fuse combination cabinet nanginahanglan og lightning arrester, ug ang voltage transformer (VT) cabinet nanginahanglan og duha ka 10/0.1/0.22kV cast resin VTs. Kini nga mga proyekto magpili sa gas-insulated RMUs sama sa Schneider’s RM6 o ABB’s Safenng, ang design requirements dili makompleto.

​1.1 Kadugo sa Pag-install sa Arresters sa Load Switch-Fuse Cabinets​

Para sa load switch incoming/outgoing cabinets, ang tanang brand naghatag og sufficient cable compartment space uban Type-C bushings (IEC 60137-compliant), ngadto sa plug-in T-type cable accessories ug plug-in arresters. Sa load switch-fuse cabinets:

• ​Safenng: Horizontal mounted fuses (Figure 2) preserve cable space, enabling plug-in arrester installation.
• ​RM6: Vertical mounted fuses (Figure 3) occupy cable space, with Type-A bushings limiting accessories to elbow/straight types. No space exists for plug-in arresters, and no market-ready arresters compatible with elbow/straight accessories are available.

​1.2 Kadugo sa Pag-install sa VTs sa VT Cabinets​

Ang standard VT cabinets nanginahanglan og tulo ka HV fuse units ug duha ka single-phase VTs sa V-connected configuration (dual-winding, 10/0.1kV para sa metering, 10/0.22kV para sa power supply; ≥1000VA secondary output). Ang air-insulated RMUs (e.g., Schneider SM6) naghatag og ample space (500×840×950mm). Kontraryo, ang gas-insulated RMUs may compact cable compartments (~400×350×700mm), insufficient for cable accessories, connection cables, exposed fuses, VTs, or 125mm phase-to-phase/ground clearance.

Ang mga manufacturer kasagaran magdugang og empty cabinet sa side sa load switch cabinet aron maputli ang VTs ug fuses, connecting them via cables. Pero, kini kompromiso:

• Safety during VT maintenance tungod sa lack of mechanical interlocks.
• Compactness ug aesthetics sa outdoor stations.

​2 Lightning Arrester Installation Solutions​

​2.1 Omitting Arresters​

DL/T 620-1997 Overvoltage Protection and Insulation Coordination for AC Electrical Installations mandates surge arresters for cables >50m connected to overhead lines. For ≤50m cables, arresters may be installed at one end only. But, the standard does not explicitly require arresters on plug-in cable heads of 10kV gas-insulated RMUs.

Ang modern urban buildings may extensive lightning protection networks, reducing lightning strike risks. Rare na ang overhead cable connections sa cities, making direct lightning surges to cable cores unlikely. International practices (e.g., T-type arrester accessories) are often omitted in urban areas. Ang gas-insulated RMUs sa Zhejiang Province operate reliably for years without arresters. Therefore, ​arresters can be omitted for urban gas-insulated RMU substations.

​2.2 Arrester Selection Criteria​

For suburban/rural grids with overhead-connected cables >50m, arresters must be installed. For pure load switch units, most products suffice. For ​load switch-fuse units, specify ​horizontally arranged fuses​ to reserve arrester space, avoiding retrofitting issues.

​3 Voltage Transformer Installation Solutions​

VT cabinet miniaturization requires resolving ​electrical insulation​ and ​space constraints.

​3.1 Solving Electrical Insulation​

Using standard fuses/VTs from air-insulated RMUs in gas-insulated compartments violates clearance standards. The solution is adopting ​insulation-compliant components, such as the ​JSZV16-10R VT. Features include:

• Integrated American-style cable accessories for full insulation.
• Built-in replaceable fuses at HV terminals.
• Rated voltage: 10/0.1/0.22kV.

​Wiring configuration:

• Load switch side: European-style touchable T-type accessories.
• VT side: American-style 20kV touchable elbow accessories (compatible with VT fuses).
• Figure 4 shows the VT and American-style accessories.

All components are fully insulated and touchable. The limitation is the JSZV16-10R VT’s size (designed for compact outdoor RMUs), restricting 220V output to ≤2×400VA—sufficient for DC battery charging and lighting.

​3.2 Solving Space Constraints​

Validated layouts confirm insufficient space for VTs with cable accessories. Two solutions were tested:

1. ​Top-mounted VT box: External cables and unsafe VT maintenance (violating interlocks).
2. ​Bottom-mounted VT base (implemented)​:
• Extends the cable compartment downward.
• Height: 400mm, compatible with 700mm-high cable compartments.
• Enables mechanical interlocking for maintenance.

​Result: This design ensures safe installation and maintenance while preserving gas-insulated RMU compactness.