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HEI-24 Eco-Gas (SF₆-Free) Gas-Insulated Metal-Enclosed Ring Main Unit
The HEI-24 is Huanghua Group's next-generation eco-gas insulated metal-enclosed ring main unit (SF₆-free RMU) for 24 kV medium-voltage distribution networks. Nitrogen (N₂) or dry air replaces conventional SF₆ as the insulating medium, with a global warming potential (GWP) below 1, eliminating SF₆ emissions and end-of-life recovery obligations.
Send Inquiry Product Overview
The HEI-24 is Huanghua Group’s next-generation eco-gas insulated metal-enclosed ring main unit (SF₆-free RMU) for 24 kV medium-voltage distribution networks. Nitrogen (N₂) or dry air replaces conventional SF₆ as the insulating medium, with a global warming potential (GWP) below 1, eliminating SF₆ emissions and end-of-life recovery obligations. It fully complies with the EU F-Gas Regulation (EU 517/2014 as revised in 2019/2024) for SF₆-free new MV switchgear. Rated voltage 24 kV, rated current 630 A / 1,250 A, internal arc classification IAC A FLR 25 kA 1 s, gas tank protection IP67, annual leakage rate ≤0.1% — ideal for urban distribution grids, renewable stations, rail transit, data centres and ESG-driven EPC projects.
Type Designation
Key Highlights
| Highlight | Description |
| Zero SF₆ · GWP < 1 | Nitrogen (N₂) / dry air insulation with GWP < 1, no PFCs and no SF₆, removing F-Gas reporting, recovery and carbon-accounting obligations. |
| EU F-Gas Regulation Compliant | Meets EU 517/2014 (as revised 2019/2024) SF₆-free requirements for new MV switchgear, qualifying for EU public tenders mandating SF₆-free equipment from 2026. |
| Sealed Stainless Tank, IP67 | 304L laser-welded stainless steel tank, IP67 main tank protection, ≤0.1% annual leakage, ≥30-year sealing life; immune to humidity, dust, condensation and pollution. |
| Internal Arc Class IAC A FLR | Internal arc classification IAC A FLR 25 kA 1 s, with a non-rupturable pressure-relief diaphragm and top-vented duct, providing verified protection for personnel at the front, sides and rear. |
| Insulation Level 65 kV / 125 kV | Rated power-frequency withstand 65 kV and lightning impulse withstand 125 kV (BIL), complying with IEC 62271-1 for 24 kV equipment and coordinated with 24 kV transformer insulation levels. |
| VCB-Centric V-Module Design | VCB module breaking capacity 25 kA / 31.5 kA, making current 63 kA / 80 kA, mechanical endurance 10,000 operations (C2). As N₂ has weaker arc-quenching than SF₆, the V-module (VCB) is recommended for transformer protection. |
| Compact 600 mm Footprint | Only 600 mm wide (incomer / outgoing / sectionalising / disconnector), 1,500 mm deep and 2,400 mm high — a major space saving for urban underground substations and compact substation retrofits. |
| Extensible & Maintenance-Free | Extensible via silver-plated finger contacts with bellows sealing — field extension without de-gassing adjacent bays; hermetically sealed tank requires essentially no maintenance over its service life. |
Scope of Application
Suitable for urban ring and terminal distribution networks, renewable (PV / wind / BESS) collection and step-up, industrial plants and campuses, hospitals and data centres, rail transit and municipal works, as well as EU public procurement and ESG-driven packaged substation projects.
Product Features
| Feature | Detailed Description |
| N₂ Insulation · Zero SF₆ | Nitrogen (N₂) or dry air serves as the primary dielectric with GWP < 1 and negligible greenhouse effect; free of PFCs and SF₆, with no F-Gas reporting, annual leakage auditing or end-of-life recovery obligations. |
| Laser-Welded Stainless Gas Tank | The tank is laser-welded from 304L stainless steel on longitudinal and circumferential seams, with helium mass-spectrometer leak testing on every unit; welds are ground and NDT-inspected to guarantee ≥30-year sealing life. |
| Gas Density Monitoring | A temperature-compensated gas density monitor alarms at low pressure and blocks operation on further decline. Since N₂ dielectric strength is directly density-dependent, monitoring is even more critical than on SF₆ units. |
| Non-Rupturable Pressure Relief | A non-rupturable relief diaphragm vents hot, high-pressure gas from an internal arc through a dedicated duct to the cabinet top, preventing secondary injury to personnel and adjacent equipment. |
| Three-Position Load Break Switch | Close – Open – Earth is achieved with a single operating handle and mandatory mechanical interlocking, preventing energising onto an earthed circuit and earthing a live circuit; mechanical endurance 5,000 operations (M2). |
| Vacuum Circuit Breaker Module | The V-module uses a vacuum circuit breaker with 25 kA / 31.5 kA breaking, 63 kA / 80 kA making, rated operating sequence O-0.3 s-CO-180 s-CO and 10,000-operation mechanical endurance (C2). |
| Fully Insulated & Fully Sealed | All live HV parts — busbars, LBS and VCB — are sealed inside the stainless tank, immune to condensation, pollution, salt mist and vermin; suitable for basements, coastal and high-humidity sites. |
| Extensible Modular Design | Plug-in silver-plated finger contacts with bellows sealing enable common-busbar extension; bays can be added or removed on site without de-gassing adjacent units. Flexible V / De module combinations. |
| Compact Enclosure & Installation | Standard units are 600 mm wide (metering panel 800 mm), 1,500 mm deep and 2,400 mm high; front operation with bottom cable entry and generous termination space — ideal for space-constrained switchrooms and compact substations. |
| Smart Distribution Interface | The LV control compartment accommodates numerical protection relays, energy meters, live-line indicators and SCADA interfaces, supporting telemetry, remote signalling and control for distribution automation and unattended operation. |
| Lifecycle Green Compliance | LCA (Life Cycle Assessment) declaration and a GWP < 1 certificate are available on request, supporting ESG bids, carbon-footprint accounting and green-procurement scoring; no special SF₆ disposal process at end of life. |
Technical Parameters
1.RMU Assembly Parameters
| Parameter | Unit | Data |
| Product type | — | Eco-gas insulated metal-enclosed RMU (SF₆-free) |
| Rated voltage (Ur) | kV | 24 |
| Rated frequency | Hz | 50 / 60 |
| Rated insulation level | kV | PF 65；BIL 125 |
| Rated short-duration power-frequency withstand voltage | kV | 65 |
| Rated lightning impulse withstand voltage | kV | 125 |
| Internal arc classification | — | IAC A FLR 25kA 1s |
| Type of insulating gas | — | N₂/ Dry air |
| Global warming potential (GWP) | — | ＜1 |
| Insulation gas pressure (absolute, at 20 °C) | MPa | 0.02 |
| Annual gas leakage rate | %/per year | ≤0.1 |
| Sealing life | years | ≥30 |
| Degree of protection — main tank body | — | IP67 |
| Degree of protection — operation mechanism & LV control cubicle | — | IP4X |
| Creepage distance | mm | ≥720 |
| Gas tank material & process | — | 304L stainless steel, laser-welded |
| Cabinet enclosure material | — | Galvanised steel, powder-coated RAL 7035 |
| Pressure relief | — | Non-rupturable diaphragm, vented to cabinet top |
| Gas monitoring | — | Temperature-compensated density monitor, alarm + lockout |
| Extensibility | — | Extensible / non-extensible |
| Cable entry | — | Bottom entry |
| Operating temperature — gas tank | ℃ | -40 ~ +70 |
2.AC Load Break Switch Parameters
| Parameter | Unit | Data |
| Rated voltage | kV | 24 |
| Rated current / rated busbar current | A | 630 |
| Rated frequency | Hz | 50 / 60 |
| Rated short-time withstand current (4 s) | kA | 25 / 31.5 |
| Rated short-circuit making current | kA | 63 / 80 |
| Rated mainly active load-breaking current | A | 630 |
| Mechanical endurance class | ops | 5000（M2） |
| Positions | — | Close – Open – Earth |
3.AC Circuit Breaker (VCB Module) Parameters
| Parameter | Unit | Data |
| Rated voltage | kV | 24 |
| Max. rated continuous current | A | 630 / 1250 |
| Rated frequency | Hz | 50 / 60 |
| Rated short-circuit breaking current | kA | 25 / 31.5 |
| Rated short-circuit making current | kA | 63 / 80 |
| Rated short-time withstand current (4 s) | kA | 25 / 31.5 |
| Rated operating sequence | — | O-0.3s-CO-180s-CO |
| Mechanical endurance class | ops | 10000（C2） |
| Operating mechanism | — | Spring mechanism |
4.Dimensions (24 kV, Main Busbar Current up to 1250 A)
| Panel Type | Width (mm) | Depth (mm) | Height (mm) |
| Incoming, Segmented, Disconnect, Outgoing | 600 | 1500 | 2400 |
| PT panel | 600 | 1500 | 2400 |
| Measurement (metering) panel | 800 | 1500 | 2400 |
5.Applicable Standards & Eco Compliance
| Standard / Regulation | Code | Scope |
| Gas-insulated metal-enclosed switchgear with alternative gases | IEC 62271-214 | Primary standard for 24 kV eco-gas RMU |
| High-voltage alternating-current circuit breakers | IEC 62271-100 | VCB in the V-module |
| High-voltage alternating-current load break switches | IEC 62271-103 | Three-position LBS |
| Internal arc test method | IEC 62271-200 | IAC A FLR verification |
| Common specifications for HV switchgear | IEC 62271-1 | Ratings and insulation co-ordination |
| Degrees of protection provided by enclosures | IEC 60529 | IP67 / IP4X verification |
| EU F-Gas Regulation | EU 517/2014（2019 / 2024 修订） | SF₆-free compliance |
| GWP & carbon footprint | GWP ＜ 1；LCA | ESG bid support |
| Quality management system | ISO 9001 | Manufacturing & inspection |
6.Type Tests & Routine Tests
| Test Item | Type | Test Condition | Remark |
| Dielectric test | Type | Power-frequency 65 kV / 1 min; lightning impulse 125 kV (peak) | Applied to earth, between phases and across the open break as required by the standard |
| Short-circuit making and breaking test | Type | VCB 25 kA / 31.5 kA breaking; LBS+fuse combination 31.5 kA making (symmetrical) | IEC 62271-100 / 62271-103； Carried out with the rated operating sequence O-0.3 s-CO-180 s-CO |
| Short-time and peak withstand current test | Type | 25 kA / 31.5 kA for 4 s (busbars and joints inside the tank) | Verifies dynamic (peak) and thermal withstand of main and earthing circuits |
| Temperature-rise test | Type | Full-load cyclic duty; temperature rise at contacts and joints ≤65 K | Confirms continuous current-carrying capability with stable contact resistance |
| Mechanical endurance (mechanical operation) test | Type | LBS 5,000 operations (M2); VCB 10,000 operations (C2) | IEC 62271-103 / 62271-100 |
| Internal arc test | Type (on request) | IAC A FLR, 25 kA / 1 s | IEC 62271-200 Annex AA; assesses accessibility type for front, lateral and rear |
| Gas tightness test (helium leak detection) | Type | Helium mass-spectrometer leak test, ≤0.1% / year | N₂ leakage causes an immediate dielectric drop — more critical than on SF₆ units |
| Verification of the degree of protection (IP code) | Type | Main tank IP67; mechanism and LV compartment IP4X | IEC 60529 |
| Gas composition stability test | Type | Thermal cycling -40 °C → +70 °C; no condensation, no decomposition products | Unlike SF₆, N₂ produces no toxic SOF₂ / SO₂ decomposition under arcing |
| Helium leak check (per tank) | Routine | Sniffer helium test on every tank | Performed on every unit; stricter than the SF₆ equivalent |
| Power-frequency withstand voltage test (tank-internal) | Routine | As specified in the product specification, 1 min | Performed on every cubicle before delivery |
| Measurement of the resistance of main and earthing circuits | Routine | DC voltage-drop method; measured value not exceeding the design limit | Verifies contacts and joints |
| VCB timing and travel test | Routine | Opening / closing times, pole synchronism, travel and clearance | Performed on every cubicle; characteristic curves retained |
| Three-position switch and interlock function check | Routine | Close – Open – Earth positions; door and earthing-switch interlocks | Includes five-prevention interlock verification |
| Calibration of the gas density monitor | Routine | Calibration of alarm and lockout thresholds | Performed on every cubicle before delivery |
| Cable terminator torque and visual inspection | Routine | Tightening torque, phase identification and overall finish | Performed on every cubicle before delivery |
