Secondary Gas-Insulated Switchgear & RMU (12–40.5kV) Engineering Guide

1. Executive Summary & Architectural Overview

Secondary gas-insulated switchgear (Secondary GIS) and compact ring main units (RMU) represent the core infrastructure of modern urban, coastal, and industrial medium-voltage power distribution networks. Designed to operate across 12kV, 24kV, 36kV, and 40.5kV voltage classes, these assemblies house all primary medium-voltage busbars, rotary disconnectors, and vacuum circuit breakers inside a hermetically sealed gas envelope.

By isolating all high-voltage conductors from ambient atmospheric conditions, secondary GIS delivers an operational footprint up to 70% smaller than traditional air-insulated switchgear (AIS) while providing complete immunity against humidity, salt spray, airborne chemical pollution, and floodwater submersion.

2. Physical Construction: The 3.0mm Laser-Welded Hermetic Stainless Steel Tank

The cornerstone of secondary GIS reliability is the gas vessel. RW Energy manufactures its secondary GIS tanks from heavy-gauge 3.0mm corrosion-resistant stainless steel utilizing computer-controlled robotic laser welding.

Key engineering benchmarks of this construction include:

• Ingress Protection Degree: Rated IP65, the gas tank can withstand temporary flood submersion in underground vaults without moisture ingress or dielectric tracking.
• Vacuum Mass-Spectrometry Leak Detection: Every fabricated tank is tested in a vacuum chamber using helium tracer gas before gas filling, certifying an annual gas leakage rate below 0.1% across a 30-year sealed-for-life design duration.
• Maintenance-Free High-Voltage Core: Because primary switching contacts and busbars operate in an inert, oxygen-free gas environment, internal contact oxidation and partial discharge inception are completely eliminated.

3. Decarbonization Roadmap: Eco-Friendly Nitrogen-Insulated Switchgear

In response to global greenhouse gas phase-out mandates and European F-gas regulations, RW Energy delivers eco-friendly nitrogen-insulated secondary switchgear (such as Product 3426).

Technical highlights of the clean-air alternative include:

• Pure Nitrogen Gas Medium: Utilizing pure nitrogen (N2) with zero global warming potential (GWP = 0) and zero ozone depletion potential (ODP = 0).
• Vacuum Circuit Breaker Core: Current interruption is executed entirely within hermetically sealed ceramic vacuum interrupters, ensuring safe load, fault, and transformer inrush breaking.
• Zero Regulatory Reporting: Eliminates mandatory SF6 mass inventory logging, gas leakage emission taxation, and specialized decommissioning recovery contractor expenses.

4. Modular Functional Units & System Configuration (C, V, F Schemes)

Secondary GIS lineups can be delivered as compact monolithic multi-way tanks or modular expandable assemblies joined by shielded solid-insulated busbar extensions:

• Code C (Cable Switch Unit): Features a 3-position rotary load break switch (Closed, Open, Earthed) with capacitive voltage indicators and integral earthing switch rated for full making capacity.
• Code V (Vacuum Circuit Breaker Unit): Houses high-endurance vacuum circuit breakers rated up to 2500A and 31.5kA short-circuit breaking, equipped with CT-powered autonomous digital protection relays requiring zero external potential transformers.
• Code F (Switch-Fuse Combination): Provides transformer feeder protection utilizing fast-acting current-limiting fuses with striker-pin mechanical trip linkages conforming to IEC 62271-105.

5. International Standards Compliance & Safety Interlocking

RW Energy secondary gas-insulated switchgear is type-tested and certified by accredited international testing authorities:

• AC Metal-Enclosed Switchgear: Fully certified to IEC 62271-200.
• Vacuum Circuit Breakers: Conforms to IEC 62271-100.
• Disconnectors & Earthing Switches: Conforms to IEC 62271-102.
• Internal Arc Classification: Certified IAC AFLR up to 31.5kA for 1.0 second, directing arc-flash pressure waves upward through rear blast channels.
• Mechanical Five-Prevention Interlocking: Enforces strict operational sequencing, preventing operator access to energized cable rooms and disallowing switching between live and earthed states under load.

6. Substation Automation & Telemetry Integration

All secondary GIS units can be equipped with factory-fitted motorized operating mechanisms, auxiliary contacts, and feeder terminal units (FTUs). Supporting standardized industrial protocols including Modbus, DNP3.0, and IEC 61850, the switchgear enables real-time SCADA telemetry, automated fault detection, and rapid FLISR feeder reconfiguration across smart grid architectures.

Technical Inquiries & Global EPC Support

• Direct Engineering Desk: jaylen@rw-relay.com
• WhatsApp Technical Line: +86 13867748881
• Official Manufacturer Portal: https://www.energy-rw.com