DC 1500V 2-Pole MCCB Arc Chute Design & MHD Simulation | Technical Guide

DC 1500V photovoltaic (PV) and energy storage system applications place higher demands on DC circuit breakers. Many DC 1500V molded case circuit breakers (MCCB) traditionally adopt a four-pole series scheme, which offers a spacious arc-extinguishing chamber across multiple poles, but increases overall volume and equipment cost.

Internal structure and arc extinguishing principle of the DC circuit breaker

Figure 3 Layout of Arc Chute Structures: (a) Novel two-pole DC MCCB arc chute; (b) Conventional MCCB arc chute

This paper from Xiamen Hongfa investigates achieving DC 1500V breaking capacity using a compact two-pole DC circuit breaker (two-pole DC MCCB).

Although the two-pole DC circuit breaker scheme is compact, each pole must withstand higher voltage. Consequently, the electric arc must leave the contacts within an extremely short timeframe, enter the arc chute splitter plates, and undergo rapid cooling and splitting. In short-circuit breaking capacity tests under DC 1500V / 15kA with a time constant of 10 ms, whether the arc voltage can rise as quickly as possible is the critical factor determining current-limiting and breaking performance.

Figure 6 Comparison of Current-Limiting and Breaking Performance of Two-Pole DC Circuit Breakers

The paper compares the voltage and current waveforms of two prototype units during short-circuit interruption testing:

· Prototype 1: Arc voltage rises to approximately 350V at an earlier timestamp, limiting the peak current to around 8.6 kA.

· Prototype 2: Arc voltage rise is slightly delayed, resulting in a higher peak current of approximately 9.4 kA.

This demonstrates that the earlier the arc enters the arc chute splitter plates, the earlier the arc voltage escalates, allowing short-circuit current to be constrained sooner.

1. Original Splitter Plate Structure

Original Arc Chute Structure with Convex Splitter Plate Arrangement

The paper first analyzes the original arc chute structure. The original design adopts a convex-shaped layout of splitter plates, where the central splitter plates are longer and situated closer to the contact area.

· Plates closer to the contacts can attract the arc at an earlier stage.

· Earlier contact between plates and arc enables quicker cooling and splitting of the arc.

· An earlier rise in arc voltage should theoretically yield superior current-limiting performance.

Figure 7 Temperature Distribution in Original Splitter Plate Structure

Figure 7 illustrates the temperature distribution under the original splitter plate structure. Although the arc moves toward the splitter plates in the initial stage, after reaching them, it fails to smoothly enter the inter-plate gaps. Instead, it stagnates near the entry region, spreads laterally to both sides, and eventually causes restrike near the contacts.

Figure 8 Pressure Distribution in Original Splitter Plate Structure

Figure 8 presents the corresponding pressure distribution:

Because the central long splitter plates are positioned too close to the contacts, a relatively enclosed triangular zone is formed between the chute entrance and the moving/fixed contacts. As the arc burns, high-temperature gas expands and pressure builds up inside this zone, exceeding 5 atm at the entrance.

Conclusion: The arc chute entrance becomes clogged by high-pressure gas, preventing the arc from entering.

2. Staggered Splitter Plate Structure

To resolve this issue, the paper proposes a staggered splitter plate structure:

· Shorten certain splitter plates to enlarge the buffer space between contacts and chute entrance.

· Transition central plates from equal-length to a staggered arrangement, thereby reducing splitter plate density at the entrance.

Figure 9 Temperature Distribution in New Splitter Plate Structure

Figure 9 shows the temperature distribution under the staggered structure. Compared with the original design, the arc travels into the splitter plates much more smoothly and is progressively cut by the plates.

Figure 10 Pressure Distribution in New Splitter Plate Structure

Figure 10 demonstrates the pressure distribution under the new structure. It is evident that a high-pressure blockage zone no longer forms at the chute entrance. Pressure waves propagate freely toward the rear of the plates, keeping the entrance in a lower pressure state and making it easier for the arc to enter.

Figure 11 Simulated Two-Pole Arc Voltage Comparison

Figure 11 shows the simulated arc voltage comparison. Under the staggered structure, the arc voltage rises more smoothly and reaches a higher peak value.

Figure 12 Experimental Arc Voltage Comparison

Figure 12 shows the experimental arc voltage comparison. The experimental trend aligns closely with simulation results, confirming that staggered splitter plates effectively optimize arc entry into the chute.

Figure 13 Comparison of Arc Motion Captured by High-Speed Camera

Figure 13 displays high-speed camera recordings. In the original structure, the arc fails to enter the arc chute smoothly, leading to back-strike breakdown. In the staggered structure, the arc enters the chute successfully and is extinguished by plate cutting.

Key Takeaway: Longer splitter plates and closer proximity to contacts are not inherently better. Without pressure relief space at the entrance, the arc will be blocked outside.

3. Flow Guiding Cone Structure: Preventing Turbulence at the Bottom

While staggered splitter plates are effective, they increase assembly complexity and may not suit fully automated production.

Therefore, the paper proposes another optimization scheme: adding a flow guiding cone at the bottom of the arc chute.

In two-pole DC MCCBs, the arc chute is arranged along the length direction. After entering the chute, the arc and hot gas flow must redirect at the bottom before discharging toward the bilateral exhaust ports.

In other words, the gas flow does not travel straight through—it must turn corner, where pressure accumulation is most likely to occur.

Figure 14 Temperature Distribution in Arc Chute with Flow Guiding Cone

Figure 14 shows the temperature distribution after incorporating the flow guiding cone. Overall arc movement becomes smoother, allowing proper entry and cutting by splitter plates.

Figure 15 Pressure Distribution in Arc Chute with Flow Guiding Cone

Figure 15 shows the pressure distribution with the flow guiding cone. The cone directs gas flow from the plate outlets toward both sides, eliminating severe pressure accumulation at the chute bottom and achieving a more uniform pressure distribution.

This prevents high-temperature gas from piling up or repeatedly changing direction at the bottom, guiding it steadily outward along both sides.

4. Flow Velocity Comparison Before and After Flow Guiding Cone

Figure 16 Comparison of Flow Velocity at Arc Chute Bottom Before and After Flow Guiding Cone

Figure 16 compares gas velocity at the bottom of the arc chute before and after adding the flow guiding cone.

· Without Flow Guiding Cone: Gas velocity rises rapidly, drops, and then reverses, indicating repeated flow reversal at the bottom. Flow reversal causes localized pressure build-up and impedes arc movement.

· With Flow Guiding Cone: Although initial velocity rises more slowly, the flow direction remains significantly more stable. Once high speed is reached, uni-directional flow is maintained over a longer period.

Figure 17 Comparison of Simulated Arc Voltage Before and After Flow Guiding Cone

Figure 17 compares simulated arc voltage. Without the cone, arc voltage rises fast initially but drops sharply later due to abnormal arc behavior. With the cone, voltage rises moderately in early stages but continues climbing steadily, favoring final arc extinction.

Figure 18 Comparison of Experimental Arc Voltage Before and After Flow Guiding Cone

Figure 18 compares experimental arc voltage. Consistent with simulation, adding the flow guiding cone produces a more pronounced voltage rise in later stages, demonstrating continuous elongation, cooling, and cutting of the arc.

Figure 19 Comparison of Arc Motion Captured by High-Speed Camera Before and After Flow Guiding Cone

Figure 19 presents high-speed camera observations. Without the flow guiding cone, arc and hot gas concentrate locally and fail to diffuse throughout the chute, sometimes reversing direction and blowing out near the rotating shaft. With the cone, thermal gas distribution is far more uniform, enabling prompt arc entry and extinction.

Core Principle: Transforming turbulent flow into directed flow, converting localized pressure buildup into uniform exhaust.

5. Conclusion

· The arc extinguishing capacity of DC 1500V two-pole DC MCCBs depends heavily on whether the arc can smoothly enter the arc chute splitter plates during early stages.

· The original convex splitter plate layout brings plates closer to contacts but induces severe pressure accumulation at the entrance, blocking arc entry.

· Staggered splitter plates reduce entrance plate density, providing crucial pressure-relief space that facilitates arc entry and cutting.

· The flow guiding cone redirects gas flow at the arc chute bottom, reducing pressure buildup and flow reversal to ensure stable arc motion.

References

CHEN Mo, LU Ningyi, ZHAI Guofu. Optimal Design of Gas Passages for DC 1500V Two-Pole Molded Case Circuit Breaker Based on Arc Magnetohydrodynamics Simulation [J]. Transactions of China Electrotechnical Society.