A hybrid DC circuit breaker
Most DC molded-case circuit breakers use natural air arc extinction, and there are typically two arc extinguishing methods: one is conventional opening and closing, where the contacts axially stretch the arc, while the conductive circuit generates a magnetic field that bends and elongates the arc, pulling it lengthwise perpendicular to the arc axis. This not only increases the arc length but also induces lateral motion, enabling air cooling to achieve arc extinction.
The other method involves the arc being magnetically driven into the arc chute by its own electromagnetic force or the magnetic field from a magnetic blowout coil, causing rapid arc extinction. When the current falls below a certain value (critical load current), during conventional opening, the arc cannot be extinguished effectively. At this point, the magnetic blowout force is weak, providing insufficient driving force for arc movement, preventing the arc from entering the arc chute. Consequently, the arc chute becomes ineffective, causing the arc to stagnate and burn continuously for an extended period, significantly prolonging the breaking time or even leading to breaking failure. Therefore, technical optimization is required during interruption at critical load current to ensure rapid arc extinction.
Utility Model Content
The present utility model aims to overcome the shortcomings of existing technology, particularly the excessively long arcing time during interruption at critical load current, by providing a hybrid DC circuit breaker. This device can autonomously determine whether the load current is at the critical level during breaker interruption and, if so, automatically employ a current commutation technique to rapidly extinguish the arc generated by critical load current.
The present utility model specifically adopts the following technical solution to address the aforementioned problem: A hybrid DC circuit breaker comprising a first mechanical switch connected in series within the main circuit, a commutation circuit connected in parallel with the first mechanical switch, and a drive circuit for activating the commutation circuit when energized. The hybrid DC circuit breaker further comprises:
A switching power supply, whose two input terminals are connected to both ends of the first mechanical switch;
A delay circuit, connected in series between the output of the switching power supply and the input of the drive circuit, implemented via hardware, to delay the output of the switching power supply by a preset first delay time before sending it to the drive circuit; the sum of the first delay time and the establishment time of the switching power supply constitutes the drive delay time, which is greater than the arcing time of the hybrid DC circuit breaker under non-critical load current conditions;
A second mechanical switch, connected in series with the first mechanical switch in the main circuit. The second mechanical switch is mechanically linked to the first mechanical switch but operates with a preset time lag relative to the first switch. This preset time is less than the difference between the drive delay time and the non-critical load current arcing time.
Furthermore, the delay circuit is also used to stop supplying power to the drive circuit after sending the output of the switching power supply to the drive circuit and maintaining it for a second delay time. Preferably, the delay circuit is composed of two RC discharge circuits connected via an optocoupler.
Compared with the prior art, the technical solution of the present utility model has the following beneficial effects: Aiming at the challenge of arc extinction at critical load current in DC circuit breakers, the present utility model adds a commutation circuit to the existing arc extinction scheme, and through a purely hardware-based approach, enables the circuit breaker to autonomously determine whether the load current is at the critical level during interruption. When operating at critical load current, the device autonomously employs the commutation technique to rapidly and selectively extinguish the arc generated under such conditions.
As shown in Figure 3, the operating process and principle of the hybrid DC circuit breaker in this embodiment are as follows:
From time 0 to T₀, the system is in normal operation. The first mechanical switch and the second mechanical switch are closed. The switching power supply circuit is not powered, and the commutation circuit is inactive.
Starting at time T₀, the moving and fixed contacts of the first mechanical switch begin physical separation, generating an arc across its terminals. The switching power supply uses the arc voltage as its input power source and begins establishing its output. If the circuit breaker is interrupting a current that is not at the critical load level at this moment, the arcing duration is from T₀ to T₁, and the arc voltage waveform is Uarc₁. If the circuit breaker is interrupting a critical load current, the arcing duration extends from T₀ to T₂, and the arc voltage waveform is Uarc₂.
The commutation circuit used in this utility model is only activated under low-current critical load conditions. Therefore, it does not require high-rated-current commutation components, resulting in a lower construction cost for the commutation circuit. Moreover, the commutation control is implemented entirely through hardware circuits, eliminating the need for logic control units or complex control algorithms.
