Abstract: A method for detecting excessive current in a system and interrupting the delivery of further current thereto comprises determining actual system current, obtaining a value of a predetermined system parameter indicative of the time the actual system current can safely exist in the system, creating a dynamic history of the predetermined system parameter by repetitively modifying the predetermined system parameter in accordance with actual system current, and interrupting power to the system if the dynamic history of the predetermined system parameter exceeds a predetermined threshold. The predetermined system parameter may be quadratically extended into an undefined region in order to decrease the response time to an overload or fault condition.

Abstract: A protective means for a series capacitor in a high-voltage network comprises a voltage-dependent resistor (varistor) arranged in parallel with the series capacitor, a spark gap arranged in parallel with the varistor for shunting the latter when it becomes overloaded, a current-sensing member, for example a current transformer, for sensing the current through the varistor, an energy absorption detector for sensing the temperature of the varistor, and a pulse transformer electrically or magnetically connected to the current-sensing member, for triggering the spark gap. During normal operation of the network and the series capacitor the current-sensing member is short-circuited by a normally closed switching device.

Abstract: Separate bargraph displays controlled by the electronic trip unit of a static trip circuit breaker continuously indicate the magnitude of the highest phase current as a percentage of the log-time delay pickup current setting and the timing out of a long-time delay as a percentage of the applicable long-time trip delay interval for a given phase current in excess of the long-time delay pickup setting.

Abstract: An AC transistor switch is provided with simple, accurate and fast overcurrent protection circuitry. A pair of transistors are connected in anti-series across an AC load line, and each transistor has an anti-parallel diode therearound conducting current in the alternate half cycles. Comparator means senses current flow through the diodes and is responsive to given threshold overload current to turn off the transistors. Voltage sensing means is referenced to a common point between the series connected transistors and senses the voltage at each main terminal relative to the common point to thus sense the voltage drop from the common point across each diode to its respective main terminal for sensing current flow through the respective diode.

Abstract: Apparatus for monitoring the fault current in the ground conductor of a polyphase AC electrical power system. When the fault current exceeds a predetermined level, the magnetic field produced causes a magnetic reed switch to close and open at twice the AC frequency. Pulse producing circuitry connected to the reed switch responds to the switch action to produce pulses at the same frequency. The pulses are counted by logic circuitry, and when a predetermined number of pulses have been counted, an output signal triggers circuitry which trips circuit breaker apparatus in the power system. The delay period between first detecting the fault current and tripping of the circuit breaker apparatus can be adjusted by changing the number of pulses to be counted by the logic circuitry before it produces an output signal.

Abstract: A control for an AC circuit protection system which is capable of monitoring either single phase or polyphase current flow. The composite current envelope is periodically sampled and the sample values converted into digital form. Succeeding current signals are tested to determine whether they deviate from previous samples by a given amount. Non-deviant samples increment a first counter, while deviant samples increment a second counter. The ratio of the counts is used to recognize current imbalance and control system parameters are adjusted to compensate for the imbalance.

Abstract: A characteristic timer for a protective relay utilized as part of a system that provides protection for a portion of a high voltage transmission line is disclosed. The characteristic timer provides a time-base for measuring the duration of a signal developed by the protective relay indicative of a normal or an abnormal condition related to the protective portion of the high voltage transmission line. The characteristic timer is comprised of digital devices, such as; programmable counters for preselecting the frequency related limits to which the developed signal is compared, counters that monitor the duration and presence of the developed signal, and a shift register that controls the resetting of the characteristic timer. If the developed signal is disrupted for a predetermined time the shift register resets the digital devices and awaits for the reoccurrence of the developed signal for a revised determination of its time duration.

Abstract: A solid state load protection system whereby the current supplied to a load is monitored enabling a test feature to be used. A current sensing function is utilized so as to produce an output current which is proportional to the current in an electrical circuit. Attached to the current sensing function is a load resistor module which converts the current produced by the current sensing function to a voltage which is also proportional to the current utilized by a load. Attached to the module is an overcurrent and timing function and an output function. The overcurrent and timing function monitors the level of voltage from the load resistor module initiating a timeout sequence when the voltage across the load resistor function, which is proportional to the current utilized by the load exceeds a predetermined level for a predetermined period of time thereby initiating a trip signal to the output function which deenergizes the motor by disconnecting it from its source of power.

Abstract: A circuit control device combining the functions of a current sensor, a time delay circuit, an undervoltage sensor, and a lockout such that, once tripped, the device must be reset intentionally. The current sensor includes a coil (16a) surrounding two reed switches (18, 20), the reed elements (18a, 20a) of each of which being perpendicular to those of the other for vibration resistance. The coil is then surrounded by a magnetic shield (28) in order to shield out some of the leakage flux from the main relay coil (14c). The time delay circuit includes a PUT (Q1) which compares a steady voltage from a voltage divider network with the increasing voltage across a capacitor (C3). The undervoltage sensor includes a second PUT (Q3) which compares the voltage of the DC source (10) with the steady voltage across a zener diode (D5).

Abstract: Switching device for the short-circuit and overload protection of a power switching circuit, including an input, an output, a first AND gate, a power amplifier, a current limiter circuit and a current sensor connected in series between the input and output, the first AND gate having an inverting input, a threshold value switch connected to the current sensor for producing a current sensor-shaped signal to be fed to the inverting input of the first AND gate, a digital switch-in retarder for delaying the arrival of the current sensor-shaped signal at the inverting input of the first AND gate by producing a given switch-in time lag for blocking the first AND gate until a given switch-off time lag has run out in case of short-circuits and overloads, the digital switch-in retarder including a second AND gate having a first input, a second input, a third inverting input and an output, and a first counter being after-connected to the second AND gate and having a pulse timing input, a resetting input and an output, t

Abstract: An improvement to fault responsive protective devices, which employ timing capacitors, is provided by controlling the voltage of the timing capacitor by clamping it to a value slightly in excess of the voltage on a master timing capacitor. This allows the master timing capacitor to inhibit the operation of the improved fault responsive device without affecting the input to the timing capacitor. The inherent time constant produced by the timing capacitor is not altered. However, by clamping the voltage level of the timing capacitor only under appropriate conditions, the time current characteristic of the improved fault responsive protective device is altered only when those conditions occur which make it desirable to lengthen the interval before the fault responsive protective device responds to a fault.

Abstract: A motor control circuit for disconnecting the motor's power supply when the motor is stalled but maintaining it connected when it is running comprising a power loop and control loop, the former including a signal sensing means which provides an output sensing signal whose magnitude is a function of the motor's state in series with an ON, OFF switching means' input-output terminals which is responsive to the magnitude of a control signal applied to its control terminal to control its state. The control loop comprises a counter which provides a control output signal in response to a predetermined count and whose input is fed by the output of a voltage controlled oscillator whose frequency is a function of the magnitude of the output sensing signal of the signal sensing means to which it is connected. A resetting means is coupled to the reset terminal of the counter for periodically resetting the counter. The output control signal from the counter is fed to the control terminal of the switching means.

Abstract: Safety apparatus for a motor vehicle electric consumer having a temperature-dependent internal resistance, which includes a temperature indicating circuit for providing a signal which accurately indicates the consumer temperature to a threshold switch which actuates a switching device to interrupt current flow through the consumer whenever the consumer temperature exceeds a predetermined maximum value. The temperature indicating circuit either may be a consumer resistance measuring circuit such as a bridge circuit including the consumer in one leg thereof, or may be a consumer temperature replicating circuit, connected in parallel with the consumer, such as a special RC network. The switching device either may be a switch connected in series with the consumer, or a switch connected in parallel with the consumer, in which case the apparatus also includes an overcurrent device connected in series with the parallel combination of the switch and the consumer.

Abstract: A solid state load protection system having an inverse time delay circuit. A current sensing function is utilized so as to produce an output current which is proportional to the current in an electrical circuit. Attached to the current sensing function is a load resistor which converts the current produced by the current sensing function to a voltage which is proportional to the current utilized by the load. Attached to the load resistor is an inverse time delay circuit which serves as an overcurrent and timing function. The overcurrent and timing function monitors the level of voltage from the load resistor initiating a time-out sequence when the voltage across the load resistor, which is proportional to the current utilized by the load, exceeds a predetermined level for a predetermined period of time. The overcurrent and timing function utilizes two diode paths for prohibiting the charging or discharging of a capacitor during a normal or overcurrent condition, respectively.

Abstract: A Faraday rotator optical sensor in combination with optical fiber transmission means is employed to monitor overload current conditions in a high voltage electrical load and transmit this information to a low voltage signal processing circuit while providing desired isolation between the high voltage load and the low voltage signal processing circuit.

Abstract: Disclosed herein is a device that detects overcurrents and the loss of one or two phases occurring suddenly in the supply line of electrically operated devices. In both cases, the aforementioned detection is followed by generation of a deenergization signal so as to disconnect the circuits from the electricity mains. The phase loss is detected when, in one or two phases of the line, the line current is below, for a predetermined time, an established value. The overcurrent detection takes place when a line current exceeds, for a predetermined time, a threshold value. In one form or embodiment, the device trips immediately; in another, it operates with a time lag that is a function of the ratio between the line overcurrent and the threshold value, and it again becomes nonoperative when the overcurrent ceases, as a function of the said ratio. According to the invention, when all three phases experience an undercurrent, generation of the deenergization signal is inhibited.

Abstract: An electronic remote control D.C. power control and overload circuit breaker for the cockpit controlled D.C. power system of an aircraft or the like. Electronic sensing of overcurrent conditions provides better accuracy, stability and reliability and easier adjustment or adaptation to specific applications. These are attained by using a combination of a shunt resistor in the D.C. line feeding a transient suppressing input bridge and an instrumentation amplifier with common mode rejection followed by a trip time delay network, a threshold comparator and logic and relay control circuitry, as well as supply voltage regulation plus secondary regulation of the comparator reference voltage. A remote cockpit unit affords control and indication. Modifications afford bidirectional sensing of the D.C. bus overload as well as different trip time delays for the two polarities of overload currents.

Abstract: An A.C. overload current sensing, remote power controller of minimum size and weight and integral construction. Current rate sensing wound toroids are used that are small enough to fit around the line terminal studs without having to enlarge the prior insulator space available therein. The electronic overload current detecting and tripping control circuit is replaced by a pair of modules, detector and control modules, having improved performance and a shape and size such that they fit within the relay housing alongside its operating magnet. The detector module has integrator means for converting current rate of change signals into current magnitude indicative signals thereby enabling use therewith of rate sensing wound toroids of about one-tenth the size of equivalent current transformer wound toroids.

Abstract: A solid state overload relay protective apparatus for electric motors which includes not only the overload feature, but the additional features of underload and single phase protection. Small current transformers for sensing the current flow in each phase of the motor are utilized, like those found in the ground fault sensing art because a current-to-voltage converter circuit reflects a short circuit back to the secondary of the transformers. The signal from the current transformers which is proportional to the sensed current in the motor is fed through the converter, a scaling and summing amplifier adjustable for a wide range of motor full load currents, an ideal diode peak detector, a time integrator amplifier, to one input of a comparator circuit having a trip reference voltage signal at another input. The comparator provides an output signal to a transistorized trip level circuit that deenergizes a coil of an overload relay opening its contacts and interrupting power to the motor.

Abstract: A circuit breaker includes a microprocessor-based trip unit and a power supply for supplying operating power to the trip unit and the trip coil of the circuit breaker from either the internal current transformers of the circuit breaker or a plurality of external sources. The trip unit includes a numeric display for displaying a sequential series of parameter values under normal conditions. Under low-power conditions, the power supply provides pulses of operating power sufficient to enable the trip unit to execute all of its limit check functions and present a flashing display of a single parameter value.

Abstract: A time relay comprising a device (1) arranged to produce an output (F) having a frequency representative of a parameter (I) to be monitored, a comparator (5) responsive to the output (F) for producing an output (IN) when the value of the monitored parameter exceeds a setting value, and relay operating circuitry for operating the relay when the comparator produces an output for a time determined by the relay characteristic for the value of the monitored parameter. The device is suitably a Carrier Domain Magnetometer (C.D.M.) and the operating circuitry suitably includes a digitally addressable memory (8) in which the relay characteristic is stored.

Abstract: A timing circuit for use in an overcurrent relay is disclosed. A plurality of non-interacting R-C circuits whose outputs are summed is provided. The signal representing the summed outputs of the R-C circuits represents one term of the inverse time-current relation it is desired to emulate. Each time the summed signal reaches a predetermined level, a pulse is generated. The frequency of the pulses determines the length of a time delay before the protected circuit is interrupted. When it is necessary to take the second term of the time-current relation into account, this can be done by providing a multivibrator that emits pulses of an adjustable duration responsive to the summed signal and that itself triggers the generation of the pulse train constituting the timing circuit output.

Abstract: A polyphase time overcurrent detector provides a variably delayed control signal wherein the delay is inversely related to both the current magnitude and the number of faulted phases. Current transducers produce input signals representative of the current flowing in each phase of the polyphase system. The input signals are added together to produce a charging signal. If at the end of a predetermined time period the fault has not been cleared, the charging signal will begin to charge a capacitor. If the capacitor charges to a predetermined voltage level within a fixed time period, the control signal is initiated.

Abstract: A solid state trip circuit is disclosed which uses a shunt path saturable transformer comprised of a current transformer having a relatively high resistance shunt which serves to apply input voltage to the transformer primary winding. The larger the input current the higher the voltage drop across the shunt and the more quickly the transformer iron will become saturated. The saturation time during each half cycle then produces a measure of the current flow in the primary line. The output of the secondary winding of the transformer as well as a direct but resistive connection from the input circuit lines are applied to a solid state trip circuit which operates a circuit breaker trip latch. Energy for tripping at lower overload current is derived directly from the applied voltage from the line. At high overload conditions however, direct tripping occurs through energy derived from the transformer rather than directly from the line voltage.

Abstract: The electrical energy flowing between a power source and a furnace blower motor is sensed for controlling the operation of a humidifier. A removable current sensor is connected without damaging or disfiguring the connecting lead being sensed. A solid state switch operatively connects the humidifier to a power source in response to the sensed current and is electrically isolated from the current sensor. The control circuit provides a time delay in the energization and the de-energization of the humidifier and is responsive to the current flow in the sensed lead.

Abstract: A static type circuit breaker in which a transistor is arranged in the current path by which electrical power is supplied to a load from a power source. If short circuit trouble occurs, the fault current flowing in the load circuit is detected so that a luminous diode in a detector circuit is made to cease emitting light. A phototransistor photocoupled to this luminous diode and arranged in the base circuit of the transistor is made non-conductive and produces a short circuit between the base and the emitter of the transistor, whereby the transistor is made non-conductive so that the fault current is cut off.

Abstract: A method and apparatus is disclosed for protecting a circuit from excessive current flow by pulse width modulation of a current sense signal and interrupting the circuit when the width of the pulse is less than a reference period.

Abstract: A current sensing circuit that controls a contactor that connects a load to power lines. The circuit provides an initial momentary delay period after energization of the circuit and before operation of the contactor to permit transients and other short duration anomalies to die out. An immediately succeeding second momentary delay period during which the contactor operation cannot be changed, assures that an initial inrush of current to the load will not cause a fault signal to erroneously operate the contactor. When a fault signal does cause the contactor to be operated, the circuit cannot be set back to its intended operation condition until energization of the sensing circuit is manually interrupted and reestablished. During normal operation of the circuit when current on the power lines is within acceptable limits, the circuit is latched in its proper operating mode.

Abstract: An overcurrent signal is replicated by current mirrors for joint processing by a long-time trip mode network and a short-time trip mode network pursuant to initiating a circuit breaker trip function after an adjustably predetermined delay predicated on the overcurrent signal magnitude. The former network measures signal against a sloping I.sup.2 t portion of an established trip time curve, while the latter optionally measures the overcurrent signal against a second I.sup.2 t curve portion terminating in a selected one of plural fixed time delay curve portion. Short-time delay zone selective interlocking between upstream and downstream breakers and long-time delay pickup indication are also disclosed.

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 static instantaneous overcurrent relay with reduced transient overreach is provided for use in protecting an a-c power line from overcurrents. The relay operates on an input signal representative of the magnitude of the current in the a-c power line and develops a relay output signal when the magnitude of the current reaches a predetermined magnitude. In a preferred embodiment, the relay includes a level detector circuit for receiving the input signal which is in the form of a pulsating waveform having the same frequency as the a-c power line. The level detector circuit develops a discrete level detector output signal in response to each pulse of the waveform which attains a magnitude representative of the predetermined magnitude. Output circuit means is coupled to receive the discrete level detector output signals and includes temporary inhibit means for inhibiting the development of the relay output signal until the output circuit has received two of the discrete level detector signals.

Abstract: An electrical device for protecting an alternating current network in which a static inverse time-overcurrent relay obtains network current information and relay circuit operating power from a current transformer having two secondary windings. Low transformer burden and accurate network information signals that are linearly responsive to a wide range of network current magnitudes are achieved through the use of a switching circuit that prevents the simultaneous operation of both secondary windings. The relay circuit employs an RC network with a short, precision time constant for curve shaping and employs digital counting techniques to provide time delay multiplication, precision time scale selection and a variable delay time variable in accordance with the magnitude of system current.

Abstract: Digital overcurrent relay apparatus utilizing sampling, digital conversion and digital comparison techniques is described. The apparatus provides a trip signal after an alternating current in a line being monitored by the apparatus exceeds a preset pick up value for a period of time which is an inverse function of the magnitude of the current expressed in multiples of pick up value.

Abstract: Motor overload current is sensed and coupled to the input of an operational amplifier, causing the amplifier output to invert and charge a plurality of parallel connected capacitors. When the overload condition is present for a predetermined time, the capacitors are sufficiently charged to change the output state of a second operational amplifier. A diode is coupled between the output and the input of the second amplifier and is poled to latch the second amplifier into its inverted state when the capacitors have reached the predetermined charge. A luminous source, such as a light emitting diode, is coupled to the output of the second amplifier and becomes non-luminous in the inverted state of the second amplifier. The diode is photo-coupled to a photo conductive circuit for disabling the power coupling to the motor circuit when the diode is non-luminous.

Abstract: A circuit breaker having an electronic fault sensing and trip initiating unit which provides increased versatility and ability to coordinate the circuit breaker with other interrupting and protective devices in a wide variety of electrical distribution systems. Electronic circuits and components are provided to vary the ampere rating of the breaker, to adjust current carrying capacity, to provide a long time delay trip, a short time delay trip and an instantaneous trip depending on the amplitude of high fault currents, to provide a ground fault trip, to shorten or lengthen the trip time for short time delay faults and for ground faults, and to provide shunt trip capability. The tripping mechanism is magnetic and mechanical, and includes a plunger movable between a trip and non-trip position controlled by an electronic switch in the electronic circuitry, and a toggle mechanism which is unlatched by the plunger when it moves to the trip position.

Abstract: A circuit breaker having an electronic fault sensing and trip initiating unit which provides increased versatility and ability to coordinate the circuit breaker with other interrupting and protective devices in a wide variety of electrical distribution systems. Electronic circuits and components are provided to vary to ampere rating of the breaker, to adjust current carrying capacity, to provide a long time delay trip, a short time delay trip and an instantaneous trip depending on the amplitude of high fault currents, to provide a ground fault trip, to shorten or lengthen the trip time for short time delay faults and for ground faults, and to provide shunt trip capability. The tripping mechanism is magnetic and mechanical, and includes a plunger movable between a trip and non-trip position controlled by an electronic switch in the electronic circuitry, and a toggle mechanism which is unlatched by the plunger when it moves to the trip position.

Abstract: A circuit breaker having an electronic fault sensing and trip initiating unit which provides increased versatility and ability to coordinate the circuit breaker with other interrupting and protective devices in a wide variety of electrical distribution systems. Electronic circuits and components are provided to vary the ampere rating of the breaker, to adjust current carrying capacity, to provide a long time delay trip, a short time delay trip and an instantaneous trip depending on the amplitude of high fault currents, to provide a ground fault trip, to shorten or lengthen the trip time for short time delay faults and for ground faults, and to provide shunt trip capability. The tripping mechanism is magnetic and mechanical, and includes a plunger movable between a trip and non-trip position controlled by an electronic switch in the electronic circuitry, and a toggle mechanism which is unlatched by the plunger when it moves to the trip position.

Abstract: A circuit for protecting a ballast in a high pressure metal vapor, such as sodium, lamp system which includes means for interrupting the power supply to the ballast in the event that no current is flowing through the lamp, once the system has been energized. The circuit has automatic compensation for short interruptions and for the time which it normally requires for the lamp to ignite. The absence of current flow through the lamp is sensed and this information used to provide the protection.

Abstract: A current regulator for a pulse code modulated (PCM) transmission line is interposed between a voltage potential and a load (consisting of repeater amplifiers along the PCM transmission line) for limiting the current flow to the load. During normal operation, the regulator provides a relatively low impedance path from the voltage potential to the load through a series pass transistor and a sensing resistor. During an overload condition, which is sensed by the sensing resistor, the series pass transistor is deprived of base drive thereby providing a high impedance path with an accompanying increased voltage drop across the series pass transistor of the series regulator. This voltage drop is used to drive a timer which turns the series pass transistor off and on, with a low on time or duty cycle, in order to minimize power dissipation during the overload condition.

Abstract: The timer circuit includes ramping circuit means for producing a substantially linear ramping voltage output signal. Control circuit means is provided for receiving a timer input signal and controlling the ramping circuit means wherein the presence of the timer input signal causes the ramping voltage output signal to ramp with a positive slope. Level detector circuit means is coupled to the ramping voltage circuit means to receive the ramping voltage output signal and to produce a level detector output signal when the positively ramping voltage output signal is of a predetermined threshold. The level detector output signal continues as long as the timer input signal continues and is coupled back to the control circuit means. The presence of the level detector signal develops a truncating signal which causes the positively ramping voltage output signal to truncate. When the timer input signal terminates, the ramping voltage output signal ramps negatively and the level detector signal terminates.

Abstract: The minimum instantaneous voltage output of a phase resistor connected to receive the rectified phase and neutral currents of three wye-connected current transformers, magnetically coupled to respective phase conductors of a three phase electric power circuit, is proportional to the peak current of the phase conductor carrying the center magnitude phase current. A voltage proportional to this minimum instantaneous voltage is measured and stored by a capacitor each cycle. The peak instantaneous voltage output of a ground resistor connected to receive the full wave rectified output of three, parallel-connected current transformers, also coupled to respective phase conductors of the power circuit, is proportional to the peak ground current of the electric power circuit.

Abstract: A charge-sensitive switch is described sensitive to the adjacency of, or transfer of charge from a person, for controlling lamps, appliances, motors, etc. The switch contains an over-current sensor for detecting excess load current, and takes action to shut off the current. It can also switch successive loads, as would be required in a tri-light lamp. The input sensitivity of the switch is adjustable so as to be able to switch in the presence of an adjacent charge, as would be required for proximity detection in a burglar alarm.

Abstract: An automatic current overload protection circuit for electrostatic precipitator power supplies of the type utilizing a ferroresonant transformer. A low voltage tertiary winding in association with the transformer provides an output voltage to a sensing circuit for inhibiting current flow into the primary of the transformer when the tertiary voltage falls below a predetermined threshold. Another output voltage developed in association with the high voltage secondary winding of the transformer is also utilized to independently inhibit current flow into the primary of the transformer when the secondary voltage falls below a predetermined threshold. A time delay may be provided to permit operation of the overload protection circuit only in the event of a sustained overload current condition.

Abstract: An overload-protection circuit for an electric motor has a current transformer whose primary winding is connected in series with the windings of the motor to be protected while two secondary windings are provided. The first secondary winding is connected to an actual-value current-monitoring circuit while the second secondary winding forms part of a voltage-supply network for the circuit. The primary winding is subdivided into a plurality of winding sections having respective taps for different nominal values of the overload current. The product of the number of turns of each winding section and the nominal-current value of the respective tap (ampere-turns) is the same for each winding and the respective tap.

Abstract: An inrush current restraint circuit, for use with a typical overcurrent minimum pickup circuit of a power system switching device, such as a recloser or sectionalizer, for raising the initial overcurrent minimum pickup value upon closure of the switching device to a selected value, then linearly returning this pickup value to normal within a selected period of time. The minimum pickup circuit is actuated by the voltage drop across a current sensing resistor, through which a current signal proportional to current in the power system is passed. The initial pickup overcurrent value is increased by providing another current path in parallel with the current sensing resistor when the switching device is closed. A timing capacitor is discharged each time the switching device is open, then charged from a constant current source each time the switching device is closed.

Abstract: The primary winding of a saturable transformer, coupled to an a.c. circuit, drives the core of the transformer into saturation during at least a portion of the cycle of an a.c. current flowing through the circuit. A plurality of rise-time indicator pulses, having a duration inversely proportional to the rate of rise of the a.c. current being monitored, is induced in the secondary winding of the saturable transformer. The rise-time indicator pulses appearing in the secondary winding of the saturable transformer are applied to a pick-up circuit which generates a plurality of rectangular pulses whenever the a.c. current exceeds the normal rated value of the circuit. The pulses generated by the pick-up circuit each have a duty cycle inversely proportional to the rate of rise of the a.c. current being monitored. An inverter circuit, responsive to the pulses generated by the pick-up circuit, generates a second series of rectangular pulses having a duty cycle proportional to the rate of rise of the a.c.

Abstract: A thyristor fault-detecting apparatus comprises a thyristor bridge with A.C. terminals connected to a three-phase A.C. power supply and having six thyristor arms, and an inductive load connected to D.C. terminals of the bridge. Each of the A.C. paths has a saturable reactor with an output winding so set as to be excited by the line current within the range from .pi./3 to 2.pi./3 (rad). Output voltages of the reactors are rectified and added, so that a fault in the thyristor is detected by the disappearance of the added output.

Abstract: An overload circuit for a loudspeaker system which indicates the overload and also automatically reduces the load on the speaker system to prevent damage in which a rectifier followed by a smoothing circuit is connected in parallel with the speaker and supplies an output to a magnetic coil for energizing a magnetic switch on overload so as to place a load dropping means in series with the speaker during overload. The load dropping means might be a lamp which visually indicates the overload condition.

Abstract: A field test set for static trip circuit breakers is electrically connected to the static trip unit and to the circuit breaker trip coil and phase current sensor transformers. The test set, powered from a low voltage source, is equipped to shunt feed the trip unit power supply, bringing the trip unit up to power preparatory to the injection of selected levels of overcurrent and ground fault simulating test signal current for verifying the time-current characteristics and current pickup calibrations of the various trip functions of the trip unit. A lockout circuit automatically terminates a test signal current whose magnitude and duration represents potential harm to the trip unit. The test set is also equipped to test the trip coil energization level developed by the trip unit and also the continuity of the breaker current transformers.

Abstract: Electronic control means for a paper handling and counting machine. An LED array provides a visual display of the number of paper documents counted during either normal counting or "batching" operations. The LED display is utilized to the exclusion of additional display devices for providing an indication of a jam condition in the event of a jam by "flashing" the zero decimal digit. A similar indication is artificially created upon turn-on of the machine. When operating in the "batching" mode the LED array, in addition to providing a visual display of a completed batch count, will display a partially completed batch count in a flashing manner. The "jam-type" display is also activated whenever the batch control selector switch is switched from the "count" mode position to any batching mode position.