Eaton Corporation

Westinghouse Electric Corporation

Raymond W Mackenzie

Joseph C Engel

John A Wafer

Theodore M Heinrich

Steven Christopher Schmalz

Joseph Charles Zuercher

Robert M Oates

A portable tester plugs into a receptacle in a branch circuit of an electric power distribution system to verify protection against arc faults, line to ground faults and neutral to ground faults provided by a circuit breaker located at a remote load center or by ground fault and, or arc fault interrupters in the receptacle, and also checks for proper wiring. The arc fault detector gates phased back rectified half cycles of the ac power to generate step changes in the instantaneous amplitude of current in the branch circuit which mimic the repetitive striking of an arc. Preferably, only half cycles at least 60 ms apart are gated so that the user can verify the time to trip with a watch and can count the gated half cycles to trip by counting pulses generated by a light emitting diode (LED) in the gating circuit.

Plug-in multifunction tester for AC electrical distribution system

A circuit breaker responds to sputtering arc faults by counting the times that a bandwidth limited di/dt signal exceeds a threshold magnitude within a selected time interval. In the exemplary circuit breaker, if the threshold is exceeded twice within a one second interval, a trip solenoid is energized. The di/dt sensor can share a sensing coil with a ground fault detector. Alternatively, the resistance of the neutral lead within the circuit breaker is utilized to sense current which is converted to a bandwidth limited di/dt signal for level detection and counting of sputtering arc events.

Circuit breaker responsive to repeated in-rush currents produced by a

A ground fault circuit breaker includes separable contacts for interrupting current flow in a protected AC electric system when opened. The protected AC electric system includes a ground fault switch, such as a ground fault receptacle having a people protection ground fault trip curve, downstream from the ground fault circuit breaker. A current transformer generates an AC sensor signal representative of AC current flowing from the protected AC electric system to ground. A ground fault controller, connected to the current transformer, generates a ground fault trip signal as a function of the AC sensor signal and an equipment protection ground fault trip curve. A trip means, which is responsive to the ground fault trip signal, opens the separable contacts.

Ground fault electrical switching apparatus for coordinating tripping

A test circuit for arc fault detectors of the type which respond to step changes in ac current over time generated each time an arc is struck includes a low frequency relaxation oscillator which generates a repetitive signal with step changes like those produced by an arc fault. The relaxation oscillator includes a capacitor charged through a resistor and shunted by a voltage breakdown device, preferably a diac. The capacitor is rapidly discharged when its voltage reaches the breakdown voltage of the voltage breakdown device to generate the step change which is input to the arc fault detector. With a repetition rate of the relaxation oscillator not greater than about 15 repetitions per second (rps), and preferably about 5 rps, a user can manually determine the time to trip to verify arc fault detector operation. With the oscillator operating at such a low frequency, a signaling device such as a light emitting diode (LED) placed in series with the voltage breakdown device, permits the user to manually count the number of step changes required to produce a trip thereby providing further verification of detector operability.

Test circuit for verifying operation of an arc fault detector

Arcing faults in an ac current are detected by apparatus which is responsive to a predetermined randomness in step increases in the current to eliminate false tripping caused by regularly occurring discontinuities produced by loads such as dimmers. A signal conditioner generates a bandwidth limited di/dt signal having pulses produced by the step increases in current. In one embodiment, a first tracking circuit tracks the envelope of the di/dt signal with a first time constant. A second tracking circuit also tracks the di/dt envelope, but with a second, shorter time constant. An arcing fault is indicated if the second tracking signal falls to a predetermined fraction of the fist tracking signal. This circuit may be used alone to detect arcing faults or to increase the sensitivity to arcing faults over dimmers of a circuit which responds to a time attenuated integrated valve of the pulses in the di/dt signal. In another embodiment, the di/dt envelope signal is subtracted from the magnitude of the pulses before they are applied to the time attenuated integrator, but with the subtraction time delayed to preclude attenuation of the first pulse.

Apparatus for envelope detection of low current arcs

A motor starter includes separable contacts interconnected between an alternating current (AC) power source and an AC motor for switching an AC load current which flows from the power source and through the separable contacts; a dual-slope analog-to-digital (A/D) conversion circuit for sensing the load current and generating a current value; and a microcomputer with a coil drive circuit for selectively opening the separable contacts as a predetermined function of the current value. The dual-slope A/D conversion circuit includes current transformers for sensing the AC load current and for selectively providing a received current therefrom, a current reference for selectively providing a reference current, a multiplexer for multiplexing the currents, and a class B preamplifier for amplifying and rectifying the multiplexed AC current. The dual-slope A/D conversion circuit also includes a dual-slope integrator which generates an integration value by positively integrating the received current and by negatively integrating the reference current; a comparator which compares the integration value with a predetermined threshold value and generates a comparison signal for the microcomputer; and a bias amplifier for biasing the current transformers with a voltage which is about equal to a bias voltage of the preamplifier. The preamplifier, the dual-slope integrator, and the bias amplifier may each include a Norton amplifier.

Motor starter with dual-slope integrator

Apparatus for generating alarms for a group of circuit interrupters, especially those which respond to arcing faults, includes a device associated with each circuit interrupter providing an indication of a tripped condition and a common alarm generator which generates an alarm when any one, or at least any one of a number of selected circuit interrupters, is in the tripped condition. In one embodiment of the invention, switches indicating that associated circuit interrupters are tripped generate auxiliary trip signals on a common alarm bus. The auxiliary trip signals are latched by a latch on the common alarm bus which energizes a relay to activate a local and/or remote alarm. The latch is reset by a switch on the load center door. In another embodiment of the invention, an IR beam is blocked from reaching a photo-detector whenever a circuit interrupter handle is in the tripped position which also results in energization of a relay to actuate the common alarm. Selected circuit interrupters only can be alarmed by orienting the light beam such that only circuit interrupters selected by adding an extension to the handle block the beam when the associated circuit interrupter is tripped.

Common alarm system for a plurality of circuit interrupters

Ground fault trip units for circuit breakers are tested by a passive test circuit which includes a test conductor passing through the current transformer sensing coil(s), and a test switch which selectively connects the test conductor in a loop which simulates a neutral-to-ground fault. In a dormant oscillator ground fault test circuit, the test conductor loop passes through both sensing coils. When the neutral-to-ground detector is combined with a sputtering are fault detector sharing a common sensing coil, testing of all the components is accomplished by adding an additional test circuit which injects pulses derived from the line conductor into the sensing coil secondary, or which alternatively, connects a capacitor charged from a DC supply across the sensing coil secondary. Either of these alternative test circuits generates the successive events needed to produce a sputtering arc trip.

Self testing circuit breaker ground fault and sputtering arc trip unit

In a ground fault circuit interrupter in which it was found that wide band noise induced by load transients is rectified by an op-amp in the detector circuit, false trips due to the wide band noise are eliminated by only comparing the output of the amplifier with a threshold of opposite polarity to that of the rectified noise signal and by eliminating capacitive coupling between the current sensor and the op amp. This requires an op amp with a low offset, on the order of about five percent or less.

Ground fault circuit interrupter with immunity to wide band noise

A limiter circuit utilizes an RC circuit to provide negative feedback of the average value of the output signal of an amplifier, which may be an op-amp or a comparator, to the inverting input of the amplifier. The midpoint of the amplifier supply voltage is applied to the non-inverting input so that the amplifier operates in the linear range. This, combined with the elimination of the effects of offset produced by the negative feedback, results in a limiter circuit with increased sensitivity to small input signals and therefore extended dynamic range. Where a following circuit would be adversely affected by noise, hysteresis provided by positive feedback applied to the non-inverting input of the amplifier causes the limiter circuit to oscillate, at a frequency determined by the magnitude of the positive feedback and the time constant of the RC circuit providing the negative feedback, for input signals having an amplitude below a threshold set by the magnitude of the positive feedback.

Limiter circuit with means to eliminate offset and an optional selective

An improved circuit is provided for a solid state electrical energy meter having a pair of mutual inductance current transducers, a pulse width modulation circuit, an analog switch, and a voltage-to-frequency converter. The pulse width modulation circuit includes an integrator having a first operational amplifier with a feedback circuit providing a constant DC gain and a variable gain at the power frequency. The pulse width modulation circuit also includes a second operational amplifier configured as a comparator and connected to the first operational amplifier such that the reference level of the comparator is proportional to the average DC output of the first operational amplifier. The summing resistors connected to the input of the integrator are of like value and are formed in a common array.

Electronic circuit for measuring AC electrical energy

A pulse width modulator for an electronic kilowatt-hour meter includes an integrator having its inputs connected to a square wave clock signal and a sine wave signal proportional to the time derivative of current on the metered circuit. A plurality of series-connected inverters are connected to the output of the integrator to function as a comparator which generates a pulse width modulated signal having a duty cycle proportional to metered current. A negative feedback path including a low pass filter is connected between the output of the last inverter and an input to the integrator to compensate for errors produced by the integrator and inverters, thus permitting the use of low cost inverters fabricated on an integrated circuit.

Pulse width modulator for electronic watthour metering

A system is provided for preventing overtemperature of the rotor bars of large squirrel-cage induction motors. A transmitter is mounted on the rotor and supplied with power from the rotor winding itself by a special current transformer. The transmitter is controlled by a temperature sensing element which causes it to transmit a signal in response to excessive temperature, and a slip frequency signal is also transmitted as a reliability check. A stationary receiver picks up the signal from the transmitter and includes circuitry for deenergizing the motor in response to the excessive temperature signal and for preventing energization of the motor if the slip frequency signal is not received.

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Baldwin Borough, PA, United States of America

Raymond W Mackenzie