The United States of America As Represented by the Secretary of

The United States of America, As Represented by the Secretary of the Interior

Philip L Atwater

Malin L Jacobs

James M Dehaan

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. A low pass filter, connected to the transducer and to the input of the electrically conductive case, filters out electrical noise while an integrating and scaling circuit, located in the case, receives the output of the low pass filter and converts the time derivative signal into a scaled signal corresponding to the scaled output signal provided at the low voltage end.

High current measurement system incorporating an air-core transducer

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. The relay of the present invention also employs adjustable taps for conveniently setting the minimum level of harmonic current corresponding to a condition of overcurrent, and provides a selection of time-overcurrent characteristic operating curves to delay the operation of the trip means once a condition of harmonic overcurrent has been detected. The relay is advantageous in that extremely low levels of harmonic overcurrent can be monitored so as to or prevent damage to a power system, and in that two harmonic currents may be monitored simultaneously.

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Golden, CO, United States of America

Philip L Atwater