Abstract: An air-core current transducer measurement system is provided for measuring current flow in a high voltage transmission line. The system includes a high voltage end including an electrically conductive case for the circuitry at that end and an isolated low voltage end which is coupled by a fiber optic cable to the high voltage end and which provides a scaled output signal. A current transducer located at the high voltage end includes a coil for sensing current flow in the transmission line and for producing a time derivative output signal. An electrostatic shield connected to the electrically conductive case provides electrostatic shielding of the coil.

Abstract: A single or multiple phase directional harmonic overcurrent relay device suitable for simultaneously monitoring overcurrents at either of two harmonic frequencies in an electric power system is provided which comprises current and voltage input means, upper and lower harmonic current and voltage filters, a trip means which can enable an appropriate protective or diagnostic device when a condition of harmonic overcurrent exists, and a phase detection means which receives signals from the voltage and current filters and transmits a signal to the trip means only when the phase angle between the harmonic voltage and harmonic current is within a specified range. The two harmonics that are to be monitored simultaneously, such as the 5th and 7th harmonics, can be selected by means of a series of simple filter cards which can be inserted into a card cage in an apparatus housing the relay of the present invention.