Three-Coil Permanent Magnet Operating Mechanism: How Does It Simultaneously Address Opening Speed and Closing Bounce? - Blog

Fast enough opening,sufficiently stable closing

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Vacuum circuit breakers impose two hard requirements on the operating mechanism: opening must be fast enough to shorten arcing time, and closing must be stable enough to suppress contact bounce. Insufficient opening speed can aggravate contact electrical wear and even lead to breaking failure, while excessive closing bounce can erode contacts and shorten electrical life. Traditional bistable permanent magnet mechanisms have fast response and few parts, but there is a contradiction between opening acceleration and closing buffering.

Three-coil permanent magnet actuation mechanism

A three-coil permanent magnet operating mechanism is usually based on a bistable permanent magnet mechanism, with a closing coil, an opening coil, and an auxiliary control coil. The permanent magnets are responsible for holding the closing and opening positions, while the three coils are excited in a time-sharing manner according to the control strategy, independently adjusting the magnitude and direction of the electromagnetic force.

During closing, the closing coil drives the moving iron core toward the closing position. When the moving iron core approaches the closing position, the auxiliary coil is supplied with a reverse current, generating controllable electromagnetic damping that reduces the collision speed between the moving iron core and the contact system, thereby reducing closing bounce. This is equivalent to adding an "electromagnetic buffer" in the final stage of motion.

During opening, the opening coil works together with the permanent magnet field to provide a relatively large initial opening force; the auxiliary coil can simultaneously provide a boost, causing the moving iron core to accelerate rapidly. Since the opening process does not require bounce suppression, the electromagnetic force can be concentrated on increasing opening speed and shortening opening time.

shared-time control

Therefore, through time-sharing control of "opening acceleration and closing damping," the three-coil scheme balances opening speed and closing bounce. Its actual effect depends on the magnetic circuit design, coil current waveform, and position detection accuracy. Relevant mechanical characteristic test standards have clear requirements for opening and closing times and bounce time, and this scheme provides a feasible path to meet these requirements.