(57) On opening of a circuit breaker, an end portion 19 of a pivotable contact arm 12
disengages from fixed contacts 7 such that an arc is drawn therebetween radially across
the pole face of a field coil 9, the end portion 19 moving transversely to the field
coil axis. The arc then transfers from the contacts 7 to a tubular electrode 24 thereby
bringing the field coil 9 into circuit so that a magnetic field is generated which
causes the arc to rotate and become extinguished. In the fully-open position of the
circuit breaker, the end portion 19 lies along the field coil axis. The whole assembly
is disposed in a housing 2 which contains the highly insulating gas sulphur hexafluoride.
A single field coil and electrode can be shared between two such constructions. Arrangements
are also disclosed (Figures 11 to 14) in which the initial arc is drawn directly between
the contact arm 12 and the electrode 24.
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