Patent ID: 6075368
Filing Date: 2000-06-13
Classification: H02H

Abstract:
An electrical circuit for improving fault current measurement accuracy for use with electronic reclosure controls, the electrical circuit comprising:a first input channel connected to receive a first current sample, the first input channel exhibiting a first sensitivity level;a second input channel connected to receive a second current sample, the second input channel exhibiting a second sensitivity level different from the first sensitivity level;a first multiplexer connected to receive the first current sample, the second current sample, and a selector input, and operable to output one of the first or second current samples based on the selector input;a programmable gain amplifier connected to receive a gain selector input and the output of the first multiplexer, and operable to automatically scale the first multiplexer output by a gain based on the gain selector input;an analog-to-digital converter connected to receive the scaled first multiplexer output from the programmable gain amplifier, and operable to convert the scaled first multiplexer output into a digital signal;a digital signal processor connected to receive the digital signal from the analog-to-digital converter, and operable to:generate the selector input for the first multiplexer to obtain a first value of the digital signal corresponding to the first current sample,calculate a first current magnitude from the first digital signal value,compare the first current magnitude to a possible current saturation value,if the first current magnitude is less than the possible current saturation value, scale the first magnitude by a first scale factor to obtain a correct current magnitude,if the first current magnitude is greater than or equal to the possible current saturation value:generate the selector input for the first multiplexer to obtain a second value of the digital signal corresponding to the second current sample,calculate a second current magnitude from the second digital signal value, andscale the second current magnitude by a second scale factor to obtain the correct current magnitude, andprovide the correct current magnitude as a current measurement output.