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US 6,218,917 B1Granted
Method and arrangement for calibration of circuit breaker thermal trip unit
AssigneeGeneral Electric Company
InventorsJoseph Criniti, Javier I. Larranaga, Volkman Henschel, Manfred Schulz, Walter Felden
Life of this patent
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Abstract
A thermal trip unit within a multi-pole circuit breaker includes a bimetal element having an off-set end to provide cam function during the calibration of the bimetal element. A calibration screw is threadingly engaged within the bimetal element and is adjusted at various calibration levels by means of a step motor driver element.
Claims16
A thermal trip unit for electric circuit breakers comprising:
- a strap arranged for connection with an electric circuit;
- a trip bar assembly rotatably mounted about a pivot above said strap;
- a bimetal element having a first end and a second end, said bimetal element electrically connected with said strap at said first end and arranged for striking said trip bar assembly at said second end;
- a calibration device having a first end and a second end, said calibration device extending through said trip bar assembly, the second end of said calibration device for contacting said second end of said bimetal element;
- a heater element electrically connecting with said bimetal element and said strap at one end and a circuit breaker contact carrier at an opposite end, said second end of said bimetal element movable towards said second end of said calibration device upon current transfer through said heater element;
- and,
- a drive connected to the first end of said calibration device for automatically moving said calibration device into contact with said second end of said bimetal element when said current transfer through said heater element exceeds a predetermined value.
4 more elements
A circuit breaker comprising:
- an electrically-insulative case attached to an electrically-insulative cover;
- a pair of separable contacts within said case;
- a thermal trip unit within said case, said thermal trip unit comprising a strap arranged for connection with an electric circuit;
- a trip bar assembly rotatably mounted about a pivot above said strap;
- a bimetal element having a first end and a second end, said bimetal element electrically connected with said strap at said first end and arranged for striking said trip bar assembly at said second end;
- a calibration device having a first end and a second end, said calibration device extending through said trip bar assembly, said second end of said calibration device for contacting said second end of said bimetal element;
- a heater element electrically connecting with said bimetal element and said strap at one end and a circuit breaker contact carrier at an opposite end, said second end of said bimetal element movable towards an end of said calibration device upon current transfer through said heater element;
- and,
- a drive connected to the first end of said calibration device for automatically moving said second end of said calibration device into contact with said second end of said bimetal element when said current transfer through said heater element exceeds a predetermined value.
6 more elements
A method for calibrating a circuit breaker thermal trip unit comprising:
- providing a bimetal element having a first end and a second end;
- interfacing said bimetal element between a rotatably-mounted trip bar assembly and a heater element, said trip bar assembly having a calibration screw extending therethrough;
- supplying electric current to said heater element for a predetermined period of time to cause said second end of said bimetal element to move toward said calibration screw;
- attaching an automatic drive unit to a first end of said calibration screw;
- rotating said calibration screw with said automatic drive unit, causing a second end of said calibration screw to contact said second end of said bimetal element;
- and,
- completing an electric circuit between the bimetal, calibration screw, and the automatic drive unit.
4 more elements
Dependencies are inferred from the claim text.