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Why we cant use AC circuit breaker for DC ?

AC (alternating current) circuit breakers are designed differently from DC (direct current) circuit breakers due to the distinct characteristics of AC and DC electrical systems. Attempting to use an AC circuit breaker for DC applications can lead to inefficient or unsafe operation for several reasons:

  1. Arc Extinction: AC circuit breakers are designed to extinguish the arc that forms when the circuit is interrupted. In AC circuits, the natural zero-crossing of the current waveform helps in extinguishing the arc. In DC circuits, however, the current remains constant, and extinguishing the arc becomes more challenging. DC arc interruption requires additional mechanisms and considerations not present in AC circuit breakers.
  2. Different Arcing Behavior: The arc produced during the interruption of DC current has different characteristics than that in AC circuits. DC arcs tend to be more stable and persistent, making them harder to extinguish. Special techniques and materials are needed to effectively interrupt DC arcs, which are not part of the design of standard AC circuit breakers.
  3. Contact Erosion: The constant current flow in a DC circuit results in more severe erosion of the contacts in the circuit breaker compared to AC. DC circuit breakers need to be specifically designed to handle the challenges associated with continuous current flow and minimize contact wear.
  4. Voltage Polarity: DC circuits have a specific voltage polarity, and interrupting a DC circuit requires considering the direction of current flow. AC circuit breakers, designed for bidirectional current flow, may not effectively interrupt DC circuits due to their inability to handle polarity considerations.
  5. Magnetic Field Considerations: DC currents create a constant magnetic field, which affects the behavior of the circuit breaker’s arc quenching mechanisms. AC circuit breakers are not optimized for handling the unique magnetic field characteristics associated with DC currents.

In summary, using an AC circuit breaker for DC applications is not recommended due to differences in arc extinction, arcing behavior, contact erosion, voltage polarity, and magnetic field considerations. Specialized DC circuit breakers are designed to address these challenges and ensure safe and efficient interruption of DC circuits.

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