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Home Articles CT1000. The switching-off process – function and electric arc processes step by step

CT1000. The switching-off process – function and electric arc processes step by step

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Design of the contact and electric arc extinguishing system

The CT contactor has a symmetrical mirror-image formation. It does not require flexible wires for transmitting power: two fixed contacts and a linearly moved contact bridge form a double-breaking contact system.

Opposingly adjusted permanent-magnetic fields are assigned to the two contacts and their immediate vicinities (figure 1). Small pairs of pole plates with the correspondingly assigned permanent magnets (illustration: red, green) ensure largely homogeneous magnetic conditions in these areas, regardless of current. The electromagnetic blowout areas are arranged adjacent to them: blowout coils, contacted between the fixed contacts assigned to them, and arc modulators generate magnetic fields dependent on the direction of the current with large pole plates (illustration: grey, because it is not activated). The direction of current flow, both in the arc and in the magnetic field of the electromagnetic blowout, work together to create a correctly directed force (Lorentz force) that is constantly exercised on the arc, driving it towards the extinguishing area.

Phase 1: Contact bridge opens

At the moment the contact opens, electric arcs are ignited in both contact points. Due to the varying directions of current flow, the direction of the arc is uniform in the opposing permanent magnetic blowout fields (picture 2, in illustrated example to the left).

Phase 2: Commuting of fixed contact (right) to the arc modulator (right)

Right-hand arc:

Whereas the lower end of the arc on the contact bridge moves to the left under the influence of the permanent-magnetic blowout, the upper end skips to the arc modulator. Thus the right-hand blowout coil is activated for the entire period till the end of the switching procedure. The resulting blowout effect on the arc is independent of the direction of the current (picture 3, illustration: red).

Left-hand arc:

Further movement to the left


 

Phase 3: Commuting of contact bridge to the arc modulator (left)

Right-hand arc:
Commuting of the contact bridge to the arc modulator (left). This activates the left-hand blowout coil and doubles the electromagnetic blowout area (picture 4, illustration: red). The procedure renders the contact bridge potential-free and the left-hand arc is extinguished.


Phase 4: Extinguishing the arc

The situation of the arc has been reduced to an electromagnetically blown-out arc. After passing through the arc chute it is then channelled on to the diverging areas of the arc modulators into the ceramic extinguishing area. Once there, the arc is then efficiently stretched, cooled and extinguished (picture 5).

Due to the mirror-image symmetrical arrangement, the procedure described flows in a changed polarity and therefore opposite arc direction in an identical way.

Thanks to the extremely fast commuting procedures the function of the CT principle has proven itself for frequencies up to 60 Hz.

 

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