Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Patent
1986-10-16
1989-01-03
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
361 31, 361 94, 361100, 364483, H02H 308
Patent
active
047961422
ABSTRACT:
A thermal overload detector and interrupter has a current transformer for monitoring load current and providing a current value signal, a microprocessor for calculating values related to load current and the thermal characteristics of a load, and an interrupter for selectively conducting and interrupting load current. The microprocessor computes a square current value from the current value signal and multiplies the square current value by a predetermined constant to obtain a multiplied square current value. The predetermined constant is related to the heat transfer characteristics of the load. A present running sum is computed in the microprocessor by adding the multiplied square current value to a past test value. The microprocessor then computes a proportionate present running sum by multiplying the present running sum by the predetermined constant. A present test value is computed by subtracting the proportionate present running sum from the present running sum. If the present test value exceeds a trip value, the microprocessor causes the interrupter to trip and interrupt the load current.
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De Boer Todd E.
Guttman Richard T.
Johnston A. Sidney
Pellinen A. D.
Square D Company
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