Over-current protective apparatus for a power circuit

Claim 2

A protective apparatus for actuating a switching device in response to abnormal alternating current flow in a power circuit comprising: a storage device, circuit means energized by the current in the power circuit for charging the storage device at a non-linear timed rate in response to the magnitude of current in the power circuit, a bistable switching device, a direct current source activated by the presence of current in the power circuit, a timing capacitor energized by the direct current source during periods of current flow in the power circuit, a level detecting circuit means having an input responsive to the charge on the storage device and providing an output to the switching device for switching the switching device from a second to a first of its bistable states when the charge on the storage device reaches a predetermined level, and a timing circuit means having an input responsive to the charge on the timing capacitor and providing an output to the switching device for switching the device to the second of its bistable states when the charge on the timing capacitor decreases to a predetermined level a predetermined time after the switching device is switched to the first bistable state.

Claim 3

The combination of claim 1 in which the switching device is included in a discharge circuit for the timing capacitor.

Claim 4

The combination of claim 1 in which the switching device includes a solenoid having a stationary magnetizable part, a movable magnet part and a coil winding connected in circuits with the level detecting means and the timing circuit means to cause the movable magnet part to move from a first position to a second position in response to the output from the level detecting circuit means and from the second position to the first position in response to the output from the timing circuit means.

Claim 5

The combination of claim 3 in which the magnet part is maintained in its first position by magnetic retention between the movable magnet part and the stationary part.

Claim 6

The combination as recited in claim 1 including circuit means providing an input to the level detecting circuit in response to a ground fault in the power circuit for causing the level detecting circuit means to provide an output to the switching device when the magnitude of the ground fault exceeds a predetermined value.

Claim 7

The combination as recited in claim 1 wherein the power circuit includes three conductors connected between a three phase source and a three phase motor and the apparatus includes a first current transformer, a second current transformer, said first transformer providing an output voltage signal that is 180* out of phase with the current flow in a first of the three conductors, said second transformer providing an output voltage signal that is in phase with the current in a second of the three conductors, means including a phase shift network for shifting the output signal of the first transformer so that the output voltage signal of the first transformer is equal in magnitude and in phase with the output voltage signal of the second transformer, and means for summing the voltage signal of the second transformer and phase shifted signal of the first transformer and providing an output to the storage device for charging the storage device at a rate dependent oN the magnitude of an unbalance between the summed voltage signals.

Claim 8

The combination as recited in claim 1 wherein the level detecting circuit means includes a temperature responsive resistive network for varying the response of the level detecting circuit means to variations in ambient temperature or internal temperature of a motor supplied by the power circuit.

Claim 9

The combination as recited in claim 6 wherein the direct current source includes a full wave three phase rectifying bridge network having inputs connected to the three phase source, a capacitor connected between a pair of outputs of the bridge network, and a means for limiting the charge on the capacitor to a level which will permit operation of the apparatus in the event of a complete loss of one of the phases of the source.

Claim 10

The combination as recited in claim 1 wherein the power circuit includes three conductors connected between a three phase source and a three phase motor and the apparatus includes three current transformers each having a primary winding energized by current in one of the conductors and a secondary winding providing an output through a three phase rectifier to the storage device for charging the storage device at a rate dependent upon the current in the conductors.

Claim 11

A protective apparatus for actuating a switching device in response to abnormal current in a three phase motor circuit comprising: a storage device, circuit means including a first current transformer energized by current in a first conductor to the motor and providing an output voltage signal for charging the storage device at a non-linear timed rate in response to the magnitude of current in the first conductor, a bistable switch device, a direct current source, a timing capacitor energized by the direct current source, a level detecting circuit having an input responsive to the charge on the storage device and providing an output to the switching device for switching the switching device from a second to a first of its bistable states when the charge on the storage device reaches a predetermined level, a timing circuit responsive to the charge on the capacitor and providing an output to the switching device for switching the switching device to the second of its bistable states when the charge on the capacitor decreases to a predetermined level a predetermined time after the switching device is switched to the first bistable state, a second circuit means including a second current transformer energized by current in a second conductor to the motor and providing an output voltage signal that is in phase with the current in the second conductor, means including a phase shift network for causing the output signals of the first and the second transformers to be equal in magnitude and in phase with respect to each other, and means for summing the signals of the first and the second transformers and providing an output to the storage device for charging storage device at a rate dependent upon the magnitude of an unbalance between the summed signals.

Claim 12

A protective apparatus for actuating a switching device in response to abnormal current in a three phase motor circuit comprising: a storage device, circuit means including a first current transformer energized by current in a first conductor to the motor and providing an output voltage signal for charging the storage device at a non-linear timed rate in response to the magnitude of current in the first conductor, a bistable switch device, a direct current source, a timing capacitor energized by the direct current source, a level detecting circuit having an input responsive to the charge on the storage device and providing an output to the switching device for switching the switching device from a second to a first of its bistable states when the charge on the storage device reaches a predetermined level, a timing circuit responsive to the charge on the capacitor and providing an output to the switching device for switching the switching device to the second of its bistable states when the charge on the capacitor decreases to a predetermined level a predetermined time after the switching device is switched to the first bistable state, a second circuit means including a second current transformer energized by current in a second conductor to the motor and providing an output voltage signal that is in phase with the current in the second conductor, means including a phase shift network for causing the output signals of the first and the second transformers to be equal in magnitude and in phase with respect to each other, and means for summing the signals of the first and the second transformers and providing an output to the storage device for charging storage device at a rate dependent upon the magnitude of an unbalance between the summed signals.

Claim 13

The combination as recited in claim 10 including circuit means providing an input to the level detecting circuit in response to a ground fault in the power circuit for causing the level detecting circuit means to provide an output to the switching device when the magnitude of the ground fault exceeds a predetermined value.