Hitachi, Ltd.

Yoshiaki Inui

Yukio Kurosawa

Tokio Yamagiwa

Tadashi Sato

Akira Hashimoto

Youichi Oshita

Genji Takahashi

A contact abnormality detection system for use in a gas-insulated switchgear or other power transmission or distribution apparatus. A gas-insulated switchgear includes a hermetic housing, an insulating gas sealed in the housing, and conductors in the housing having contacts for providing a path for a large current and being electrically insulated from the housing. An abnormality in the contacts causes the contacts to generate vibrations when a large current flows through them. A vibration detector detects vibrations generated by the switchgear including the vibrations generated by the contacts. The frequency spectrum of the vibrations detected by the vibration detector is analyzed to detect if the vibrations contain frequency components in the range of 200 to 500 Hz which meet predetermined criteria. If the vibrations do contain such frequency components, a contact abnormality decision unit decides that the contacts exhibit a contact abnormality, thereby permitting the abnormality to be identified before the contacts fail.

Contact abnormality detecting system

A current is measured by making use of a rotation of polarization plane in a magnetic field, that is, a Faraday effect. A conductor under measurement is transversely inserted into a center opening of a Faraday effect glass which has at least two total reflection areas on a periphery thereof so that a light directed into the Faraday effect glass is circulated around the conductor and emitted externally. The light emitted from the Faraday effect glass is split into at least two light beams, which are converted to electric signals by photoelectric elements, and A.C. components contained in the electric signals are extracted and compared. The electric signals are corrected based on the comparison result. The present measuring apparatus and method attain high precision current measurement in a stable manner over an extended period.

Method and apparatus for optically measuring a current

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Ibaraki, Japan

Yoshiaki Inui