（a） （b） （c）
Typical opening shapes at the inlet of deionization grids in low-voltage circuit breaker arc chutes control the path of arc entry, elongation, and splitting through geometric design. The three diagrams correspond to common AC and DC configurations respectively:
(a) Standard U-shaped or V-shaped Notch (Commonly Used for AC)
The grid inlet is designed with a U-shaped or V-shaped notch, serving the following purposes:
● Arc Capture: Facilitates arc attachment to the edge of the grid inlet, forming stable attachment points.
● Initial Arc Elongation: When the arc is pushed from the contact area by magnetic or pneumatic blowing, it extends along the notch edge, increasing its length.
● Splitting Between Grids: As the arc advances deeper, it splits into multiple segments between adjacent grids.
(b) Central Groove
On the basis of (a), a longitudinal central groove is added at the inlet center. Key effects include:
● Arc Guidance: The arc tends to form cathode and anode spots along the groove edges.
● Elongation Before Splitting: The arc is forced to extend upward along the central groove first before splitting between grids.
● Improved Entry Consistency: Enhances "capture robustness" for arcs with different current amplitudes and positions.
(c) Staggered Grooves (Commonly Used for DC)
The inlet features two staggered (offset) diagonal or forked grooves. This is a typical DC arc extinguishing design: since DC current has no zero-crossing point, the arc must be rapidly elongated, segmented, and its voltage increased to exceed the system voltage for extinguishment. Main effects:
● Forced Z-shaped Path: The arc is forced to change attachment points and direction at the inlet, equivalent to folding several times before entry, significantly increasing its length.
● Promoted Early Splitting: Staggered grooves enable the arc to jump between adjacent grids more easily, forming multiple series arcs earlier.
● Suppressed Arc Backflow: DC arcs have high stability; the staggered structure increases path complexity, reducing the probability of sustained arcing along a straight path.
When the contacts just separate and the arc root forms, the arc is subjected to a distinct resultant force F directed upward toward the grid inlet.
● Blue Coil-like Curves: Magnetic field lines around the arc current, indicating that the magnetic field around the arc is unevenly distributed but biased by conductor geometry and ferromagnetic components.
● Color Gradation: Represents magnetic flux density—higher at conductor bends, near coils, and grid inlets.
● Red Arrows: Direction of the resultant force on the arc calculated by ANSYS.
The force direction is derived from F = I × B (Lorentz force law). The arc current direction follows the arc channel, and magnetic field lines form asymmetric closed loops in the arc region with a clear local B direction and gradient. Thus, the I×B effect pushes the arc toward the grid inlet, denoted by the red F in the diagram.
Variations at Different Positions
When the equivalent arc current channel is at different positions at the grid inlet, the magnetic flux density distribution at the ferromagnetic grids and V-shaped opening changes, altering the arc-driving force vector. However, the overall trend is that the arc is pushed deeper into the V-shaped notch and further splits between grids.
● Arc Outside the Inlet
Short-circuit breaking tests were conducted on miniature circuit breaker prototypes to record short-circuit current and recovery voltage waveforms, which were correlated with arc chute ablation marks after disassembly.
● Blue (CH2): Short-circuit current waveform
● Orange (CH1): Recovery voltage/TRV waveform
(a) Breaking Time: 3.0 ms, Breaking Current: 3670 A (Maximum)
The waveform is more intense with obvious ringing after truncation. The arc chute shows severe blackening and molten accumulation.
(b) Breaking Time: 3.0 ms, Breaking Current: 2790 A
Sharp peaks and clear ringing near the truncation point reflect frequent splitting and switching. Photos show concentrated ablation in the upper area.
(c) Breaking Time: 2.8 ms, Breaking Current: 2820 A
Current suppression and truncation are smoother with continuous splitting. Ablation is uniform, and excessive single-point nodulation is avoided.
(d) Breaking Time: 3.0 ms, Breaking Current: 2810 A
Typical process of entering the splitting zone and completing truncation with almost no TRV. The arc attaches stably in the upper area, resulting in obvious nodulation in the upper part but no excessive overall ablation.
The geometric shape of the arc chute inlet determines the initial path of the arc after entering the arc chamber:
● U-shaped/V-shaped notches: For arc capture and guidance.
● Central groove: Enhances guidance consistency.
● Staggered grooves: For early elongation and multi-segment splitting under DC conditions.
ANSYS simulation results are mutually verified with actual test data, reducing the difficulty and time required for development to a certain extent.
At XUCKY, our MCCBs/MCBs/ACBs rely on optimized arc chute design to deliver industry-leading safety.
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