Abatement of Electromagnetic Noise of Vaccum Interrupters

When a 3000A alternating current of commercial frequency (50 or 60Hz) flows to the central conductor in a vacuum interrupter (VI), a magnetostrictive noise of about 77dB(A) is generated on account of a magnetostrictive vibration of the metallic seal rings. From environmental considerations, the elimination of the VI noise is a pressing problem to be solved. In the newly developed low noise VI reported here, magnets have been bonded to the metallic seal rings. They produce a powerful magnetic field to saturate always the magnetic flux density in the ring so as to reduce or almost suppress a magnetostriction change. Repeating many experiments by this method, we have found an optimum condition and developed a 38dB(A) low noise vacuum interrupter at 3kA, 12kV.