An arc detector includes a luminous diode 22 for irradiating the space within a vessel 1 containing an electrical device such as a bus bar 5 and filled with insulating gas such as SF.sub.6. A shielded photo-diode 24 receives light reflected back from a fine powder 12 produced when an arc occurs, and...http://www.google.com.hk/patents/US4685018?utm_source=gb-gplus-share專利 US4685018 - Arc detector for gas insulated electrical apparatus
