Circuit breaker current chopping refers to the phenomenon in which the current flowing through a circuit breaker is abruptly interrupted before it reaches zero. This interruption causes a rapid change in the current waveform, resulting in a discontinuity.
Vacuum Circuit Breakers
Vacuum circuit breakers utilize a vacuum as the insulation medium to extinguish the electric arc during the current interruption. When the circuit breaker operates, a contact separation occurs within a sealed vacuum interrupter, creating a gap where the arc is formed. As the contacts separate, the arc is drawn into the gap, where it is rapidly extinguished due to the absence of any medium for continued ionization.
During this process, the voltage across the contacts increases, causing a high rate of rise of the transient recovery voltage (TRV). This high TRV, coupled with the fast arc extinguishing capability of the vacuum interrupter, leads to a rapid current interruption. The sudden interruption of the current, before it reaches zero, is what characterizes current chopping in vacuum circuit breakers.
Significance of Current Chopping
Current chopping in circuit breakers has important implications. The rapid interruption of the current can generate transient overvoltages, which may affect the connected electrical equipment and the overall system. These overvoltages can stress insulation systems and protective devices, potentially leading to insulation failures or maloperation of other protective equipment.
To mitigate the effects of current chopping, circuit breaker designs incorporate measures such as pre-insertion resistors, pre-insertion inductors, or series capacitors to dampen the transient overvoltages and prevent their harmful consequences.
This post was written by Justin Tidd, Director at Becker/SMC. For nearly a half a century, Becker Mining has been at the forefront of safety, producing the best Vacuum Circuit Breakers in the industry. Becker/SMC is the industry’s leader in increasingly more sophisticated electrical control systems. Most of the major innovations, design features and specialized electrical components have been developed by Becker/SMC