Sigma Instruments, Inc.

Matthew G Dillon

John G Gamble

Joseph R Thibodeau

A sensor in a faulted current indicator includes a coil and a magnetic arrangement passing through the coil and around a current-carrying conductor for coupling the coil to the conductor. The magnetic arrangement has given magnetic reluctance and forms a higher reluctance section, such as a gap, within the coil. Preferably the magnetic arrangement includes a U-shaped laminate and two core laminations joined to the U-shaped laminate by two gaps to allow for installation around the conductor. The ferromagnetic plate outside the coil shields the coil. The sensitivity of the sensor is increased by coating the inner surface of the U-shaped laminate and the core lamination surfaces contacting the U-shaped laminate with a high Ni content ferromagnetic material.

Faulted current indicators with improved signal to noise ratios

An inrush restraint in a fault indicator disables trip in response to the current in the cable being monitored changing from reset to trip values within a predetermined period.

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Hingham, MA, United States of America

Matthew G Dillon