Transverse Magnetic Field (TMF) Contacts: Making the Arc Run Instead of Burning Through the Contact - Blog

Transverse magnetic field contacts generate a transverse magnetic field by controlling current distribution; this field drives the arc to rotate and move at high speed across the contact surface, thereby dispersing heat and preventing localized burn-through. The underlying principles and implementation methods are as follows:

Core Driving Mechanism

Transverse Magnetic Field Action: The transverse magnetic field generated by the contact current interacts with the arc current to produce a Lorentz force, driving the constricted arc to move tangentially or radially across the contact surface.

Energy Dispersion: The high-speed rotation and movement of the arc significantly expand the arcing area, evenly dispersing the immense heat generated by the arc. This prevents excessive heat concentration at any single point on the contact surface, thereby enhancing the circuit breaker's breaking capacity and resistance to arc erosion.

Specific Structural Design Implementation

To enable the arc to "run" effectively, engineers employ various structural designs to optimize the magnetic field and the arc's path:

Multiple Slotted Structure: Multiple pairs of mirror-symmetrical slots (such as straight slots) are evenly spaced around the circumference of the contact segments, creating a spiral or specifically shaped arc path. This design allows the arc path to be selected dynamically based on the arcing point, improving the uniformity of arc movement.

Umbrella-shaped Curved Surface Design: Designing a specific umbrella-shaped curvature for the contact guides current distribution to generate the transverse magnetic field more effectively; combined with the tangential relative motion between moving and fixed contacts during closure, this further prevents localized erosion.

Cup-shaped and Iron Core Designs

Cup-shaped TMF Contact: Utilizes a unique geometric structure to control current distribution and generate a transverse magnetic field. Transverse-magnetic-field (TMF) contacts with an iron core: By incorporating a cylindrical iron core into the interior of a cup-shaped contact, the tangential magnetic field component acting on the arc is increased while the radial component is reduced; this enhances arc control, mitigates molten metal droplet spatter, and stabilizes arc motion.

Currently, magnetic fields are employed in vacuum switches to control arc behavior on contact surfaces. This primarily involves using a transverse magnetic field to drive the vacuum arc to move rapidly in a tangential direction across the contact surface, thereby reducing arc-induced ablation of the electrode surface.

VTZ-12 630A Vacuum Circuit Breaker