Electronic processing unit, and circuit breaker including such a unit
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United States of America Patent
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May 6, 1997
Grant Date -
N/A
app pub date -
Dec 28, 1994
filing date -
Dec 28, 1994
priority date (Note) -
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Abstract
Digital processing of current signals allows close matching of arbitrary time delay curves for a circuit breaker. An analog signal proportional to the current is sampled and digitized. Digital samples, with or without further processing, are used to select increment values from a look-up table for accumulation in a counter. The counter is decremented periodically to simulate cooling of the circuit being protected. The values in the look-up table are determined according to the desired time delay curve. Processing of the digital samples may include squaring samples, accumulating the squared values to form a subtotal which is compared with an instantaneous trip threshold, accumulating the subtotals for a time period equal to half a cycle of AC line voltage, taking the square root of the accumulated subtotals, and using that square root as the address for looking up the increment value.
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