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Because the phase of the eddy currents in an electrode lags that of the main interruption current, a rather strong axial magnetic field remains at current zero in the space between a pair of electrodes when an interruption current is large. The authors analyzed the magnetic field on a circular conductor which was centered in a coil to stimulate an axial magnetic field type electrode. Because the authors found it difficult to eliminate the residual magnetic field from an electrode, they developed a new type electrode structure which does not generate a residual magnetic field at the center of an axis. An experimental vacuum interrupter equipped with this kind of electrode performed very well at testing voltages from 7.2 kV to 72 kV. Hitachi has applied this new type electrode in the development of a 7.2 kV 63 kA vacuum circuit breaker.
Date of Publication: Nov. 1980