Abstract: A control circuit utilizes a system voltage monitoring control relay for applying a DC control voltage across a UVR solenoid and a voltage dropping resistor to maintain the UVR in its reset condition in the absence of an undervoltage condition. An RC network maintains the UVR reset condition for momentary dips in the system voltage. If the UVR does drop out to trip its circuit breaker, a second relay temporarily switches out the dropping resistor to render the control voltage capable of electromagnetically resetting the UVR. To accommodate drawout breaker applications, means is provided to sense when the UVR is reconnected to the control circuit pursuant to automatically initiating a UVR reset function via the second relay.

Abstract: A circuit tester is disclosed which automatically open-circuits a main lead to an input circuit in response to an excessive overcurrent. The circuit tester of the present invention will automatically sense the existence of an excessive current which, in turn, open-circuits a main lead to the input circuit, actuates a buzzer and energizes a light-emitting diode. Since the main-lead to the input circuit has been open-circuited, the base voltage at a first transistor drops. This renders this transistor non-conductive and tends to cause the main-lead to the input circuit to short-circuit. This tends to restore the circuit tester to its initial condition. However, if the excessive current is continuing, the above sequence will re-commence, the sequence continuing until the excessive current no longer exists or until the tester is adjusted to a higher range of operation.

Abstract: A network protector relay produces a close signal entirely from sequence components based on the magnitude and phase relationships between the positive sequence component of the phase-to-ground voltages on the network side of the protector and the positive sequence component of the phasing voltages. The close signal may be inhibited by either the presence of the negative sequence component of the phase-to-ground voltages on the network side of the protector or if a trip contact is closed. The trip contact will be closed under certain specified conditions which make it advantageous to prevent manual closing of the contacts.

Abstract: A device for quickly reconnecting two portions of a current carrying line after separation of the line portions through actuation of a circuit breaker includes a second circuit breaker and a serially connected switch connected in parallel with a primary circuit breaker. Closure of the switch reconnects the line portions through the second circuit breaker after actuation of the primary circuit breaker. The switch can include auxiliary contacts for supplying power to an ignition device associated with the second circuit breaker, to render the second circuit breaker operable only when the switch is closed.

Abstract: A method and apparatus for sensing the clearance of a fault current on an ac transmission line and providing a fault cleared signal for closing a current limiter bypass switch includes the technique of successively sensing half cycles of current magnitudes of the system after establishing a predetermined fault current threshold and producing a fault clear signal only when a signal indicating the threshold has been exceeded is followed by two subsequent signals indicating that the threshold has not been exceeded by the two half cycles of current.

Abstract: A trip indicator circuit for a circuit interrupter of an electric power system, which includes an electromagnetic status indicator, having an indicator which is movable between an indicating position and a non-indicating position, a pulse-actuated set coil for moving the indicator to the indicating position, and a pulse-actuated reset coil for moving the indicator to the non-indicating position. An indicator set circuit for energizing the set coil is connected across the trip coil by an electronic switching device which is rendered conductive by an overcurrent sensing circuit whenever a particular abnormal condition occurs in the electric power system, so that the set coil will be energized only when the circuit interrupter is tripped during the occurrence of the particular abnormal condition. A reset circuit is connected across the closing coil to energize the reset coil each time the circuit interrupter is closed.

Abstract: A rapid-response overload protector interposed between a voltage source and a load powered thereby, the protector effectively decoupling the load from the source when the current drawn thereby exceeds a predetermined limit indicative of an overload condition. The protector includes an automatic resetting stage that periodically samples the state of the load and acts to restore the normal supply of current thereto when the current drawn by the load during the sampling interval falls below the limit.

Abstract: DC control voltage derived from the system voltage activates a first relay to apply the control voltage across a dropping resistor and an undervoltage release (UVR) solenoid, thereby holding the UVR solenoid in while the system voltage remains above a minimum level. An energy storage RC network holds the UVR solenoid in for momentary drops in system voltage. In the event of a protracted system undervoltage condition, the first relay drops out to drop out the UVR solenoid and trip a system circuit breaker. When nominal system voltage is restored, the control voltage activates the first relay and, via an RC charging circuit, temporarily actuates a second relay to switch out the dropping resistor, thereby temporarily applying full control voltage across the UVR solenoid to reset it.

Abstract: A circuit which protects a battery powered, pulse controlled, constant current power supply from excessive power dissipation. Voltage controllers disconnect the power supply from an associated battery, a predetermined time after current flows in the power supply, and reconnect the power supply to the battery a predetermined time after current ceases to flow in the power supply.

Abstract: A self-powered solid state overload relay circuit having current transformers energized by conductors supplying current to a multiphase alternating current motor. The transformers have secondary windings connected to charge a capacitor with a voltage indicative of the magnitude of the maximum current in the motor windings. The circuit includes presetable impedance circuits which permit the circuit to be easily programmed to respond to a range of abnormal motor currents in the winding in motors of varying size and service factor ratings, components which are arranged to duplicate the operation of melting alloy and bimetal type overload relays in an automatic or in a trip-free manual reset mode, a light emitting device which visually indicates when the relay is in a tripped state, and components which cause the relay to be insensitive to ambient temperature variations.