Low power solid state three-phase overcurrent/undercurrent protection circuit
AssigneeThe United States of America as represented by the Secretary of the Air Force
InventorJoseph M. Hudak
Life of this patent
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Abstract
Each phase of the power input circuit in a three-phase electrical system is coupled to a sensor by means of a pick-off transformer. Each sensor has an overcurrent detection circuit comprising a slow response filter, an operational amplifier, and a comparator and an undercurrent detection circuit comprising a fast response filter, an operational amplifier and a comparator. A fourth overcurrent detecting sensor is coupled to a selected system feed circuit. A C/MOS logic circuit responds with a "high" state output when any number of sensor network outputs go to the high state. The output of the C/MOS logic circuit is filtered by a slow response filter and is used to trigger an actuating circuit that operates a standby breaker in the system input circuit.
Claims3
A protection circuit for a three-phase electrical system comprising
- a pick-off transformer connected to each phase of the system power input circuit,
- an overcurrent/undercurrent sensing means connected to the secondary of each said pick-off transformer, each said overcurrent-undercurrent sensing means comprising a rectifier bridge, a slow response filter connected to the output of said rectifier bridge, a first operational amplifier connected to receive the output of said slow response filter, a first comparator means connected to the output of said first operational amplifier, a fast response filter connected to the output of said rectifier bridge, a second operational amplifier connected to receive the output of said fast response filter, and a second comparator means connected to the output of said second operational amplifier,
- a pick-off transformer connected to a selected system feed line,
- an overcurrent sensing means connected to the secondary of the feed line pick-off transformer, said overcurrent sensing means comprising a rectifier bridge, a slow response filter connected to the output of said rectifier bridge, an operational amplifier connected to receive the output of said slow response filter, and a comparator means connected to the output of said operational amplifier,
- a logic circuit having an output responsive to the outputs of said overcurrent/undercurrent and overcurrent sensing means,
- a standby breaker connected in said system power input circuit,
- actuator means responsive to the output of said logic circuit for operating said standby breaker and,
- a slow response filter connected to filter the output of said logic circuit.
Dependencies are inferred from the claim text.