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US 4,737,878 AGranted
Overload switch
AssigneeRTE Corporation
InventorHarvey W. Mikulecky
Life of this patent
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AssigneeRTE Corporation
InventorHarvey W. Mikulecky
Estimating the term…
In a transformer primary circuit breaker having a primary switch for opening and closing the transformer primary circuit, an operating handle mounted exteriorly of the transformer for opening and closing the primary switch, a trip mechanism operatively connected to open the primary switch under fault current conditions, the trip mechanism including a conductive metallic sensor element connected in the primary circuit and having a predetermined Curie temperature and a magnet mounted for movement into engagement with the sensor element and biased to open the primary switch when the temperature of the sensor element approaches the Curie temperature, the improvement comprising a shunt circuit connected to the primary circuit in parallel with the sensor element, a normally closed switch in the shunt circuit, a resistance element for limiting the current passing through the shunt circuit, and a tab mounted on the operating handle for opening the shunt circuit switch, a spring mounted in the operating handle for limiting the motion of the operating handle to thereby close the shunt switch, whereby a portion of the primary current will flow through the shunt circuit when the switch is closed. A bimetal switch can be included in the shunt circuit to open the shunt circuit at predetermined oil temperatures or excessive currents.
In a primary circuit breaker for a transformer, said circuit breaker including a frame, a primary switch mounted on said frame for opening and closing the primary circuit, an operating handle mounted exteriorly of the transformer for opening and closing the primary switch, a trip mechanism operatively connected to open the primary switch under fault current conditions, the trip mechanism including a conductive metallic sensor element connected in the primary circuit and having a predetermined Curie temperature and a magnet mounted for movement into engagement with the sensor element and biased to open the primary switch when the temperature of the sensor element approaches the Curie temperature, the improvement comprising a shunt circuit connected to the primary circuit in parallel with said sensor element, a normally closed switch in said shunt circuit and means mounted in said operating handle for selectively opening said shunt circuit switch whereby a portion of said primary current will flow through said shunt circuit when said switch is closed.
In an underoil primary circuit breaker for a transformer, the circuit breaker including a magnetic, heat sensitive trip assembly for opening the circuit breaker, the assembly including a sensor element having a predetermined Curie temperature, the improvement comprising a shunt circuit assembly for bypassing a portion of the primary current passing through the sensor element for the trip assembly for emergency overload service, said shunt circuit assembly including a resistance element for controlling the proportion of current passing through the shunt circuit assembly and a shunt switch for opening and closing the shunt circuit assembly.
In a primary circuit breaker for a transformer of the type having a crank for opening and closing the primary circuit breaker and an operating handle mounted on said crank external to the transformer, a trip mechanism operatively connected to open the circuit breaker under fault current conditions, the trip mechanism including a sensor element connected in the primary circuit and a magnet mounted for movement into engagement with said element and biased to actuate the trip mechanism when the temperature of sensor element approaches the Curie temperature, the improvement comprising a shunt circuit connected across the sensor element, a switch in said shunt circuit, means in said shunt circuit for controlling the proportion of primary current bypassed through said shunt circuit, and means mounted in the operating handle for selectively opening and closing said shunt circuit switch.
Dependencies are inferred from the claim text.