Means for indicating the passage of a fault current along a conductor

1,029,141. Automatic fault indication, electromagnetic relays. FERRANTI Ltd. Jan. 6, 1965 [Jan. 10, 1964], No. 1144/64. Headings H2B and H2K. [Also in Division G4] A device for indicating fault current in a power line conductor 12 comprises a magnetic vane 15 secured to a rotatable spindle 14, means to constrain the spindle in each of two or more positions of the vane, a clamp 11 for securing the housing 10 of the device to the conductor so that in one position the vane is substantially tangential to the magnetic field produced around the conductor, the vane being rotated from a non-tangential position to the tangential position when fault current exists. The vane may be constrained in each of its positions by a ceramic permanent magnet 16 secured to the spindle 14 and co-operating with polepieces 18, 19 formed on a magnetic yoke 17. Resetting may be effected by a winding (not shown) on the polepieces, the winding being energized after a delay by the discharge of a capacitor C 2 through a gas-filled discharge tube or semiconductor device S. The capacitor C 2 is slowly charged by a circuit including diodes D1, D2 and a capacitor formed by a coating 22 and earth. Alternatively the device may be reset by the use of a permanent magnet secured to a pole. Contacts may be operated on rotation of the spindle and the vane may be embedded in a cylinder of plastic foam highly coloured to give a visible indication, the housing 10 being wholly or partly transparent.