ABB eVD4, Installation And Service Instructions Manual, Page: 12 / 72

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5.3.2. Poles
The eVD4 series vacuum circuit-breaker has poles with the
vacuum interrupter embedded in resin or thermoplastic
material. Embedding the interrupter makes the circuit-breaker
poles particularly sturdy and protects the interrupter against
shocks, dust deposits and humidity.
The vacuum interrupter houses the contacts and forms the
interruption chamber.
The vacuum circuit-breaker does not require any interruption
and insulating means. In fact, the interrupter does not contain
ionisable material.
When the contacts separate, an electric arc formed only by
fusion and vaporization of the contact material is generated
in any case. The electric arc is sustained by the external
energy until the current is nullified near its natural zero. At
that instant, the sharp reduction in the density of the charge
conveyed and rapid condensation of the metallic vapour very
rapidly leads to the dielectric properties being restored.
1 Upper terminal
2 Vacuum interrupter
3 Housing/pole
4 Stem of moving contact
5 Lower terminal
6 Flexible connection
7 Tie-rod spring fork
8 Tie-rod
9 Pole fixing
10 Connection to operating
mechanism
Vacuum interrupter embedded in the pole.
1 Terminal
2 Protection
3 Metal bellows
4 Interrupter housing
5 Shield
6 Ceramic insulator
7 Shield
8 Contacts
9 Terminal
10 Interrupter housing
Vacuum interrupter.
Embedded pole with vacuum interrupter.
The vacuum interrupter therefore recovers its insulating
capacity and the capacity to sustain the transient return
voltage, definitively extinguishing the arc.
Since a high dielectric strength can be reached in the vacuum
even with minimum distances, circuit breaking is guaranteed
even when separation of the contacts takes place a few
milliseconds before the current passes through natural zero.
The particular geometry of the contacts and of the material
used, together with reduced duration of the arc and the
low arcing voltage, ensure minimum contact wear and a
long life. Moreover, the vacuum prevents their oxidation and
contamination.
For the trip curves, see paragraph 7.2.3.