Global power grids pursue a low-carbon transition, driving the adoption of eco-friendly RMUs filled with low-GWP gas. The strict IAC internal arc test poses great technical challenges for arc quenching and arc protection. As a maker of Chuanli environmental protection switchgear, Chuanli passed full IAC type tests on the CLH-12/24 series. This article analyzes test standards, technical barriers and optimized designs to offer references for engineers and buyers.
Internal arc fault refers to short-circuit discharge caused by insulation aging, foreign body intrusion, and wiring errors in the switch cabinet. At 12 kV/24 kV medium-voltage conditions, the instantaneous temperature of the arc plasma exceeds 10,000°C, generating high-pressure shock waves, molten metal particles, and high-temperature toxic gases in an instant. If there is no reliable arc protection structure, the cabinet door will be blown off, and high-temperature substances will be sprayed into the operation area, causing fatal burns and electric shock risks to the surrounding staff, and even causing secondary fires and power grid collapse accidents. The IAC (Internal Arc Classification) test is a mandatory type test to evaluate the cabinet’s ability to contain and divert arc energy.
| Test Item | 20kA/1s Standard Requirements | Pass/Fail Criteria |
| Enclosure Mechanical Integrity | No through-wall ruptures; no detached bolts; cabinet doors remain securely locked | No structural damage to the enclosure following arc impact |
| Isolation of Hot Objects | No signs of ignition on fire-test cotton fabric surrounding the enclosure | No outward spatter of molten metal |
| Pressure Relief & Venting | Hot gases vented only towards the top or the rear (unoccupied zone) | No venting towards the front (pedestrian area) |
| Arc Containment Capability | Arc cannot penetrate compartment partitions | Fault in a single unit does not propagate to adjacent cabinets |
| Post-Test Gas Tightness | No permanent deformation of the main gas tank; no significant gas leakage | No continuous leakage of low-GWP insulating gas |
The IAC A FL grade represents that the front, left, right, and four sides of the cabinet are all areas that can be reached by humans, requiring comprehensive arc protection verification, and is the highest safety grade for urban public distribution and subway tunnel equipment.
Compared with the traditional SF6 insulated ring network, the nitrogen environmental protection cabinet has three major core test bottlenecks:
Weak arc extinguishing ability: Nitrogen has no self-extinguishing characteristics, and the length of the arc in the fault condition is more likely to be prolonged, and the release of arc energy is greater;
Insulation strength is low: Under the same gas pressure, the insulation performance of nitrogen is only 1/3 of that of SF6, and the risk of arc discharge is higher during testing;
Instantaneous pressure is higher: The expansion coefficient of nitrogen gas is larger, and the arc combustion in the closed gas box produces a higher instantaneous impact pressure than the SF6 cabinet, which is very easy to cause cabinet deformation and the failure of the cabinet lock.
Due to the above three difficulties, most low GWP ring switchgear IAC tests on the market are not qualified, and CLH-12 / 24 from Chuanli solves this problem through integrated design.
In response to the inherent defects of low GWP gases, Chuanli optimized the nitrogen gas filling parameters and the layout of the electric field in the cabinet:
| Structural Level | Arc Protection Design | IAC Test Function |
| Independent Compartment Barriers | 2mm thick steel plates separate the busbar, switchgear, and cable compartments; arc isolation between units | Blocks lateral arc propagation to adjacent modules |
| Top-Mounted Centralized Pressure Relief Channel | Unidirectional pressure relief panel on the cabinet roof; preset weak points for pressure relief | Channels high-temperature gases upward, away from operators at the front |
| Reinforced Cabinet Frame | Perimeter stiffeners and heavy-duty door locking mechanisms | Withstands instantaneous arc impact pressure |
| Auxiliary Exhaust Chamber (Rear of Gas Tank) | Secondary pressure relief cavity at the rear of the gas tank | Reduces peak internal pressure within the gas tank |
The entire cabinet adopts the double logic of layered containment + targeted pressure relief: the internal partition blocks the lateral spread of arcs, and the double channels at the top and back of the cabinet direct the high-pressure gas to non-pedestrian areas, fully meeting the IAC A FL full-facade protection standard.
Three-position isolation switches are equipped with arc shielding covers, insulating arc-blocking plates are installed around the contacts, and arc splashes are blocked during opening and closing;
The vacuum circuit breaker is equipped with a fast tripping coordination mechanism, and the fault signal is tripped instantly, so that the length of the burning arc is controlled within 0.1 seconds;
The structure of the all-copper silver-plated contact is designed to reduce contact resistance and prevent overheating and arcing due to long-term overload.
Strict local discharge control: local discharge ≤20pC at 1.1 times rated voltage, eliminating the risk of arcing caused by insulation defects.
Complete five-protection mechanical interlocking: avoid short-circuit arc fault caused by misoperation from the root.
Assemble the 4-unit standard CLH-12 test cabinet according to the actual engineering layout;
Nitrogen is filled to the standard of 0.02 MPa, and a 24-hour gas tightness test is carried out to confirm that the leakage rate meets the standard;
Special short-circuit wiring for IAC test is laid in the cable room, and a 20kA / 1s short-circuit current source is calibrated;
The front, left, right, and rear of the cabinet are arranged with temperature-measuring paper and fire-proof test cotton cloth according to the standard;
Check all cabinet locks, pressure relief plates, and partition steel plates to ensure there are no assembly defects.
Isolate the test area, set up a safety barrier, and install surveillance cameras from all directions;
In the cable room, a man-made short-circuit point is triggered to produce an arc, generating a rated 20kA internal arc for 1 second;
Through monitoring equipment, real-time recording of pressure changes, gas jet direction, and cabinet deformation;
Observe whether the surrounding cotton cloth is ignited and whether molten metal is flying out;
After the arc is extinguished, the cabinet should be cooled for 30 minutes before entering the test area for inspection.
Visual inspection: The cabinet frame, cabinet door, and divider are intact, and all locks are still closed;
Air tightness re-test: the nitrogen gas box has no permanent deformation, and the leakage rate is still ≤0.01%;
Insulation re-measurement: the re-measurement of the withstand voltage test of the working frequency and lightning impulse is qualified;
Arc spread inspection: there are no signs of arc penetration on the partitioned steel plates;
The full set of test records and imaging materials are archived, and an official IAC A FL2kA/1s type test report is issued.
Pedestrians are densely packed around the urban residential area, commercial complex, and municipal road ring network switchgear, requiring full-direction IAC A FL arc protection. The CLH-12 low GWP nitrogen ring network has no SF6 greenhouse gas emissions, outstanding environmental protection properties, reliable arc containment performance, and is the mainstream equipment for the low-carbon urban power grid.
The wind and solar photovoltaic base is located in the scenic area, with strict environmental control, and there is a risk of random personnel approaching the outdoor cabinet. The low GWP gas meets the requirements of carbon neutrality, and the high-grade IAC arc protection prevents safety accidents caused by arcs in unmanned equipment.
The tunnel and underground subway distribution space are closed and poorly ventilated, and once an internal arc occurs, the high-temperature toxic gas cannot spread quickly. The CLH-12 cabinet top centralized pressure relief design avoids the accumulation of gas in underground closed spaces, and fully meets the mandatory IAC network standard for rail transit projects.
Optimize the core logic: from gas medium matching, mechanical structure reinforcement, directional pressure relief, and active arc warning multi-dimensional integrated design, completely eliminate the typical defects in the IAC test of low GWP gas cabinets.
| Typical Non-compliant Defects | Root Causes | Chuanli Optimization Solutions |
| Cabinet door blown open by arc pressure | Door panel too thin; insufficient lock strength | Thicker door panel + multi-point reinforced locking assembly |
| Forward ejection of molten metal | No top-side pressure relief; arc gases blast directly outward | Top-mounted unidirectional burst-type pressure relief panel |
| Arc penetration into adjacent compartments | Thin partition plate; lack of stiffeners | 2mm reinforced all-steel isolation partition |
| Permanent deformation of nitrogen gas tank | Low inflation pressure; weak arc energy suppression | Standardized 0.02 MPa nitrogen filling + rear auxiliary pressure relief chamber |
| Partial discharge (PD) exceeding limits triggering arcing | Uneven electric field distribution within the cabinet | Full-section equipotential shielding and equipotential electrode configuration |
The IAC internal arc test is essential certification for eco-friendly RMU. Chuanli’s CLH-12/24 environmental protection switchgear solves bottlenecks of low GWP gas and delivers reliable arc protection. Prioritize products with complete IAC test reports to eliminate hidden safety risks in engineering procurement.
Q1: What is the IAC arc rating of the CLH-12/24 low GWP environmental gas ring cabinet?
A1: It conforms to the IEC 62311-200 standard and reaches the internal arc protection level of IAC A FLR20kA/ 1s.
Q2: Why can a low-GWP nitrogen gas still pass the stringent IAC internal arc test?
A2: By optimizing the inflation pressure, equalizing the electric field, and designing multiple structures for directional pressure relief, the arc control and explosion suppression capabilities are enhanced.
Q3: Where is the pressure relief channel located after an internal arc occurs in the CLH-12/ 24 ring network cabinet?
A3: The top-centralized pressure relief design is adopted to prevent high-temperature gas from being sprayed into the operating and pedestrian areas.
Q4: What are the core anti-arc components inside the environmental network cabinet of Chuanyi Environmental Protection?
A4: Vacuum interrupter chamber, three-position isolation switch, independent partition multi-chamber cabinet structure.
Q5: Which projects must use IAC-certified low GWP environmental network cabinets?
A5: Urban residents’ ring network, subway tunnel power supply, wind and solar new energy power station, small switch station in public places.
