Abstract: A process for the closed-loop control and thus for the limitation of the maximum allowable force on the primary and secondary closing edges of an automatic door. This object is achieved by conducting a verification of the drive system before each movement of the door panel. During this verification, the actual value of the motor current during the startup phase is verified by means of a stored motor torque characteristic.

Abstract: A safety-assuring control device for an electric blanket which includes a PTC heater includes an integrated circuit microcontroller unit having first and second safety circuit inputs and an output connected to a control input of an electrically controlled heater switch. A neon tube is connected between the primary safety link return conductor of the heater and the first safety circuit input, to indicate whether there is a first type of fault in the PTC heater. A connection between the second safety circuit input and the secondary safety link return conductor of the PTC heater is provided which indicates whether there is a second type of fault in the heater. The microcontroller unit includes a preliminary fault detection circuit for supplying a limited power test signal in a test mode to the heater for a predetermined period of time prior to a full power operation of the heater.

Abstract: Each pole of a multi-pole circuit breaker is equipped to individually separate the circuit breaker contacts within each pole upon overcurrent occurrence. A digital processor within the circuit breaker trip unit determines the occurrence of zero current crossing of phase current within the individual poles and initiates contact separation at zero current values.

Abstract: The invention relates to a differential protective system for electric power transmission paths where measurement quantities obtained from the currents at either end of the section to be monitored are digitized and subjected to digital sine filtering. Sign signals are obtained from auxiliary measured quantities generated from the filtered current measurement values and taken to both ends of the section to be monitored for evaluation with the generation of an exciting signal. To make the system largely unaffected by frequency variations in the currents, further filtered current measurement values are obtained by cosine filtering; from those values and from the individual filtered current measurement values, a measurement quantity is generated by absolute value generation and low-pass filtering. This measurement quantity causes a further exciting quantity to be established using an absolute value comparison quantity. If both exciting signals are present, the sign signals are evaluated.

Abstract: Apparatus for monitoring the functioning of motor driven equipment, including current sensing apparatus connectable to the power input of the motor and producing a current signal; signal correction apparatus receiving as input the current signal and operative to demodulate the current signal, filter the current signal to retain low frequencies thereof, and convert the current signal from analog to digital form and producing a corrected signal; a memory; a controller in operative connection with the memory, receiving the corrected signal, and having a calibration state and an operation state, and operative, when in the calibration state, to compute the calibration norm of the corrected signal based partly on data contained in the memory and to store the calibration norm in the memory and operative, when in the operation state, to compute the operation norm of the corrected signal based partly on data contained in the memory and to compare the operation norm with the stored calibration norm and to produce a fun

Abstract: A relay for monitoring an electrical system to protect the electrical system from an overcurrent condition as a time dependent function of an electrical current level in the electrical system is disclosed. The relay includes a memory which stores a current level count and a current level detector coupled to the electrical system which detects the electrical current level in the electrical system over time. A microprocessor responds to the current level detector by varying the current level count in the memory as a function of the electrical current level over time. The microprocessor also detects an occurrence of the electrical current level falling below a minimum current level. A timer responds to the microprocessor by measuring a period of time during which the electrical current level is less than the minimum current level.

Abstract: A protective circuit for a power field effect transistor, e.g., a power MOSFET, employs a diode-switched pickup circuit, a threshold detector, and a timer. The pickup circuit includes a resistor and diode in series, with the diode connected with the MOSFET drain electrode and the resistor connected with the gate driver for the MOSFET gate electrode. A pickup voltage V.sub.1 appears at the junction of the diode and resistor. When the MOSFET is conducting the pickup voltage is the sum of the channel voltage V.sub.ds-on and the diode forward voltage V.sub.f. When the MOSFET is biased OFF, the pickup voltage is zero. The threshold detector compares the pickup voltage with a reference voltage that is offset some predetermined amount from the source electrode voltage. When threshold circuit goes high, the timer circuit provides a time-out or inhibit signal to an inhibit input of the gate driver circuit. Under high load current or high temperature conditions, the drain-source voltage V.sub.

Abstract: A three wire power supply circuit is provided comprising a circuit for monitoring the integrity of the ground connection of the power supply circuit. A circuit element is provided in the line-to-ground current path which conducts when current flows in the line-to-ground current path and is nonconductive when the ground connection is poor or absent. A microcontroller monitors the output of the circuit element and operates a buzzer or a light emitting diode to indicate when the ground connection is poor or absent.

Abstract: A method of generating a protection-triggering signal using a triggering device of a selective-protective arrangement for an electrical power network to be monitored. In order to produce a protection-triggering signal in a relatively short time after the occurrence of a fault in the power network, a triggering device is provided in which a neural network is associated with each phase conductor in the power network. Successively sampled normalized values of the current in the power network are applied at the same time to the various neurons in the input layer of each neural network and a subsequently sampled normalized value (comparison value) of the current compared with the signal from the output neuron. If the normalized comparison value exceeds the output from the output neuron, a protection-triggering signal is generated.

Abstract: A solid state power controller for switching power on and off to an electrical load which also serves as a circuit protection device protecting the load and/or the wire connected between the load output terminal of the controller and ground from thermal damage due to current overload is shown. When a current overload exists the controller interrupts current to the load in a time inversely proportional to the square of the magnitude of the overload as shown in a trip time vs load current curve. The controller also limits the load current to a selected maximum level by controlling the drain-source resistance of power MOSFETs used for switching the power. A secondary interrupt is provided in the event that the junction temperature of the MOSFETs has risen a selected maximum level. A thermal memory feature is included for both interrupt signals. The controller is controlled by a single on/off input line and provides both a status and trip output line to indicate its state.

Abstract: A protection circuit prevents snapback events in MOS transistors associated with semiconductor or micromechanical structures, such as ink-jet ejectors. A bulk electrode associated with the MOS transistor is monitored for unusual high voltages which are consistent with an impending snapback event. The voltage on the bulk electrode is then used to turn on the control transistor which connects the gate of the MOS transistor to ground and thereby protects the device.

Abstract: A programmable control unit for protecting an appliance connected to a household power source comprises a modular unit plugged into a household power socket. The modular unit presents a socket for plugging a household appliance therein. An internal microprocessor has program logic for analyzing the period of current flow to the household appliance and/or the power consumed thereby. Once the time period of operation and/or rate of energy consumption exceeds preselected values, the program logic of the microprocessor opens a relay so as to cease current flow to the appliance. The maximum threshold values of time and/or energy can be varied by the user according to the utilized appliance. The use of the intermediate unit enables a plurality of appliances to be safely coupled to the household power.

Abstract: A non-dissipative device for protecting an integrated circuit having multiple independent channels against overloading. The non-dissipative device includes an input terminal and an output terminal having an integrated switch connected therebetween which consists of an input portion, a logic gate with two inputs a control portion, and an output portion, all connected in series with one another. The device further includes a generating circuit for generating the on-times and off-times of the integrated switch, the generating circuit is connected between an output of the output portion and an input of the logic gate.

Abstract: In order to obtain an improved operating behavior in the event of short circuits on a high-voltage line having a phase shifter, the phase shifter is used as a current limiter in the event of a fault. A fault signal, which results in an increase in an opposing voltage at an additional transformer of the phase shifter, is produced for this purpose, as a function of a fault current.

Abstract: A motor starter includes separable contacts; an operating mechanism for operating the separable contacts; an overload relay controller including a memory for storing the settings for a plurality of selectable operating features, and a microprocessor for retrieving the settings from the memory and employing the settings at least for controlling the operating mechanism; and a programmer module temporarily engaging the overload relay controller for changing the settings in the memory.

Abstract: A power controller (10) for supplying power to a power distribution network (N) in which power from a polyphase source (G) is routed to using equipment (E) connected to the network through the power controller. A plurality of solid-state power devices (82) switch each separate phase of the polyphase power to the equipment. A firing circuit (14) controls gating of the switches to route the power. Fuses (F) are connected between the switches and the using equipment to interrupt power flow to the equipment if excessive current begins to be drawn. A con, roller (20) controls a shutdown sequence employed by the controller to eliminate current spiking at shutdown. The various components are housed in an enclosure (22) which includes a mounting structure (56) for mounting the aforesaid components. A cooling system (26) employs a fan (88) for directing air flow through the mounting structure to cool the components.

Abstract: A circuit and method for interrupting an AC load current includes a first MOS Controlled Thyristor (MCT) for selectively interrupting the load current. The current through the first MCT is reduced when the load current is to be interrupted by providing a pulse resonant commutation (PRC) current through the first MCT which flows in a direction opposed to the AC load current direction and which has a magnitude reducing the current through the first MCT to an MCT "off" condition (e.g., when a voltage across the MCT is reversed, when there is near zero current through the MCT, or when a current is within the MCT's SOA.) The first MCT turns itself off when MCT gate voltage is an "on" voltage and when reverse voltage is across the MCT. An MCT "off" voltage may then be provided by sensing MCT current and providing an "off" voltage to the MCT gate when the sensed current indicates that the MCT is an "off" condition.

Abstract: The reliability of transformer differential relays is enhanced by providing a method and apparatus which enable improved discrimination between transformer current differentials due to transformer inrush current and current differentials due the occurrence of an internal fault. This improvement in discrimination is provided by generating a first signal representative of currents flowing in at least two windings of the transformer, a second signal representative of a positive portion of the first signal, and a third signal representative of a negative portions of the first signal. A first output signal is generated when the magnitude of the second signal exceeds a first predetermined value, and a second output signal is generated when the magnitude of the third signal exceeds a second predetermined value. A trip signal is generated upon coincidence of the first and second output signals.

Abstract: In a busbar protection method and a corresponding device, the maximum values of the currents in the outgoers are determined. The maximum values Ikmax of the current characteristics are extended by a certain hold time th. Subsequently, these current characteristics are processed further vectorially. With the aid of these current characteristics Ik changed in such a way, a fault signal is calculated by means of a protection algorithm, preferably the current comparison method with current stabilization or the phase comparison algorithm. It can be uniquely determined on the basis of the extension of the maximum according to the invention whether an external fault or an internal one is concerned. The advantage of the method and of the device according to the invention resides, in particular, in that the localization of the fault is possible in a reliable fashion even in the case of strong saturation of the current transformers. Above all, false tripping can be reliably avoided even in the case of external faults.

Abstract: A current sensor has a closed loop magnetic flux concentrating ferromagnetic core with a gap and a central aperture for receiving a conductor. A Hall generator is positioned in the gap and a secondary winding is positioned on a portion of the core. Current flow in the conductor creates magnetic flux in the core which energizes the secondary winding to provide a power output. Magnetic flux concentrated in the gap causes the Hall generator to output a sensing signal that is proportional to the magnetic flux which is proportional to the current flow in the conductor. The single core is used to simultaneously produce a sensing signal proportional to alternating or direct current flow in the conductor.

Abstract: A process for controlling an overcurrent tripping device of a high-speed d.c. circuit breaker. The input voltage can reach a signal evaluation device for current rise rate via two different paths. The tripping of the high-speed d.c. circuit-breaker is no longer fundamentally delayed by the unavoidable delay experienced by signals applied to a filtering device. A path for the input voltage, existing in parallel to the filter path can be designed such that when the current rises very steeply, the unfiltered (and thus also undelayed) signal reaches the signal evaluation device (i.e., the signal bypasses the filter and is applied to the signal evaluation device) whereas, when the current rises more slowly, the filtered signal is evaluated.

Abstract: When the supply current from a pulse width modulation (PWM) inverter drive circuit supplying current to the motor in an electric-powered motor vehicle is an overcurrent exceeding a particular current level, a monitoring circuit outputs a fail signal to disable the PWM inverter drive circuit and lower the current level. When the current level drops to or below said particular current level, the monitoring circuit re-enables the PWM inverter drive circuit to resume supplying current. If the cumulative output time of the fail signal exceeds a particular period, the PWM inverter drive circuit is determined to not be operating normally, and PWM inverter drive circuit operation is therefore interrupted.

Abstract: A computer-implemented method and apparatus for monitoring differentials between a first signal and a second signal. According to a preferred embodiment, the first signal and second signal are sampled for a current sampling interval to provide a current first signal value and to provide a current second signal value. The first signal is compared with the second signal for the current sampling interval to determine a difference indication. At least one of the current first signal value and the current second signal value is repaired if a difference indication is determined and if fewer than a first predetermined number of repairs have been made within a second predetermined number of previous sampling intervals.

Abstract: A solid state circuit breaker for use in electronic devices which may be connected to an active computer bus. In one embodiment the solid state circuit breaker includes a digital to analog converter by way of which digital control signals are used to set the value at which the circuit breaker determines that a fault condition exists. Fault time is measured from when the fault condition is detected, and when the fault time exceeds a predetermined value, the circuit breaker opens, thereby preventing current flow through the circuit breaker for a second predetermined amount of time. Once this second predetermined amount of time elapses, the circuit breaker again permits current flow, and if a fault condition is determined to continue to exist, the cycle is repeated.The circuit breaker also includes a current limiting portion which restricts current flow to a maximum permissible value should the current flowing through the circuit breaker attempt to exceed this maximum permissible value.

Abstract: An overcurrent detecting circuit provided within a battery pack detects any overcurrent flowing in a circuit electrically connecting the battery and connection terminals. Upon detection of any overcurrent by this overcurrent detecting circuit, a switch circuit intercepts the electric connection between the battery and the terminals, and opens the so far closed circuit.

Abstract: A method for preventing excessive currents in a welding converter that, by use of power semiconductors, generates a two-phase, pulse-width-modulated a.c current from a rectified mains a.c. current supplied to the primary side of a welding transformer. The method includes the following method steps: detecting the current of at least one phase of the primary circuit by a sensor (20); for each detected current signal, forming the time derivation through differentiation according to the time; comparing the time-derived measured signal with a predetermined maximum value; and if the time-derived measured signal exceeds the predetermined maximum value, emitting a signal that leads to deactivation of the power semiconductors (16).

Abstract: A driving circuit for driving a given load based on a load control signal is provided which includes a power transistor, a protective circuit, and a power transistor control circuit. The power transistor is responsive to the load control signal inputted to the driving circuit to be turned on for activating the load. The protective circuit is arranged to be activated by the load control signal to monitor a malfunction of the power transistor caused by overheating or overcurrent flow to restrict an operation of the power transistor. The power transistor control circuit is arranged to prohibit the power transistor from being turned on until the load control signal reaches a preselected level required for operating the protective circuit stably.

Abstract: The method is to detect a fault on a busbar and to specify the faulted point to a specific section of the busbar in order to provide a proper protection. If the fault has occurred, for instance, on a point P of a section between current transformer BCT- and a connecting point thereof to the busbar, or on a point Q of a busbar section between adjacent line outlets, the resulting fault current is expressed as a calculation sum of an output current of the current transformer BCT-. The foregoing current is zero in a normal condition, but in case of a fault, it reaches a definite value other than zero. Noticing this point, the fault current is computed for each section on the basis of the observable output current of the current transformer BCT-, and it is judged that if the foregoing current of a specific section exceeds a predetermined threshold, the fault has occurred on the above section.

Abstract: In an electric circuit supplying AC line current to a load (30, 31) from an AC source (26) of given frequency providing repetitive cycles, arc detection is provided by sensing cycle to cycle changes in the AC line current. The AC line current is sampled with a harmonic notch filter (72) at a plurality of n phases .THETA..sub.1 through .THETA..sub.n during each of a plurality of m cycles of the AC source (26), to provide a plurality of currents I.sub.n,m, where n is the phase and m is the cycle. The differences (I.sub.n,m)-(I.sub.n,m-x), where x is a designated number of cycles, provide a plurality of current difference signals. The absolute values of these current difference signals ID are accumulated in a synchronous summer (94) over the m cycles. An arc indicative signal is generated in response to given conditions and given combinations of conditions (116) of the cumulative absolute current difference signals ID.

Abstract: A solid-state circuit breaker with fault current conduction is described. The circuit includes a power sensor connected to a power line having an up-stream side and a down-stream side. The output of the power sensor is conveyed to a switch selection circuit that identifies a line disturbance on the power line. In response to a line disturbance, the switch selection circuit generates a set of output signals. The output signals force the opening of a fault current interruption circuit including a set of turn-off thyristors. The turn-off thyristors respond to the line disturbance within a fraction of a power signal cycle to provide isolation between the up-stream side and downstream side of the power line. An alternate power source may then be applied to the down-stream side of the power line. If the line disturbance exists on the down-stream side of the power line, the output signals force the closing of a fault current conduction circuit including a set of thyristors connected in series with a reactor.

Abstract: A circuit interrupter with a digital trip unit automatically sets the sampling interval appropriate for the 50 Hz or 60 Hz distribution system to which the interrupter is connected. In order to avoid falsely shifting the interval in response to distorted currents, the trip unit only changes the interval if the number of zero crossings of the current within a fixed number of samples is within two zero crossings of the number of zero crossings for an undistorted current of the other frequency for two consecutive time periods in which the fixed number of samples are taken. Furthermore, changes in the interval are only written into an EEPROM for use on power-up a fixed number of times to preclude disabling the EEPROM. In one embodiment, a 2 pole filter is utilized in the zero crossing counting circuit to eliminate false counts from noise originating in a chopper used in the trip unit power supply.

Abstract: A fault sensor device which can detect and distinguish abnormal current and voltage events on an alternating current overhead and underground power transmission or distribution line. The abnormal current events are momentary outage, sustained outage, normal overload, and inrush on transmission or distribution lines. The sensor can further distinguish whether the momentary or sustained fault is a line to ground fault, line to line fault or a three phase fault. It can also identify the faulted phase(s). In the overload scenario, the sensor can identify if the overload has occurred on all three phases or only on one or two phases of the power line in an unbalanced situation. The voltage events are open line(s) on one, or two of the phases with a possibility of a fallen live wire and voltage sag. The sensor can identify which of the three phases or if all three phases of the power line are open or on the ground.

Abstract: A low-voltage drop current regulator regulates the current in a data interchange circuit. In one embodiment, the low-voltage drop current regulator couples a positive power supply voltage to the power supply pin of a driver integrated circuit. In another form of the invention, the low-voltage drop current regulator is placed in series with the individual output leads of a driver integrated circuit to couple the respective output signals to respective pins of the data interchange circuit.

Abstract: The fault latch and filter circuit used in a MOSgated driver for a high side power MOSgated device to turn off the MOSgated device high side output in response to a given fault condition is located in the high side of the circuit and in a floating well of a semiconductor chip containing the driver circuit. The fault latch and filter are connected to the output driver circuit through a gate which also receives the high side filter and latch which are operated by the input control logic circuits through a level-shift up circuit. The fault latch circuit has an output which is level-shifted down by a single PMOS device to a fault reporting latch circuit on the low side of the device.

Abstract: A fast reacting ground fault interrupter circuit particularly suited for use with high current, high voltage DC pulses generated by transistor switched magnet pulsers driving pulsed electromagnets used with electromagnetic acoustic transducers (EMATs). Whenever a ground fault is detected, a digital shut off signal is sent to the transistor switched magnet pulser to shut it off and prevent transmission of the DC pulse. Additionally, the shut off signal is also provided to a DC current interrupter which shuts off power supplied to the transistor switched magnet pulser itself.

Abstract: A system of protection for an AC/DC hybrid electric power generation and distribution system having an AC portion comprising at least one source of AC power producing AC current coupled by first power feeders to a DC portion comprising at least one AC to DC converter producing DC current, the DC current being coupled by second power feeders to utilization equipment, comprises AC current sensors producing current sense signals proportional in magnitude to the AC current and DC current sensors producing current sense signals proportional in magnitude to the DC current. The AC current sensors define an entrance to a zone of protection, and the DC current sensors define an exit from the zone of protection. The AC and DC current sense signals are relationally compared to detect the presence of a differential current fault within the zone of protection.

Abstract: An electric vehicle control device including a collector for extracting power from an overhead wire and a circuit breaker for breaking the power. The power includes first AC power in AC power source zone and first DC power in DC power source zone. The device also includes a changeover device for changing over the power to apply the first AC power to an AC side or the first DC power to a DC side, a transformer connected to the AC side of the changeover device for transforming the first AC power into second AC power, a first opening/closing device, a power converter for converting the second AC power to second DC power and an inverter for converting the second DC power into third AC power. The third AC power is supplied to drive an electric motor. The device further includes a second opening/closing device, a filter inductor and a filter capacitor connected between positive and negative terminals of the DC input side of the inverter.

Abstract: An electrical device such as an electrical contactor interfaces at least one alternating current transformer having an output providing a signal proportional to changes in alternating current and includes at least one filter for filtering the output signal of the transformer. Each of the filters have an input connected to the transformer and an output having a signal proportional to the transformer output signal and inversely proportional to selected frequencies of the alternating current. The electrical device also has means for determining a value related to the alternating current using the output of each of the filters. The filter may have a resistor and a capacitor for filtering the transformer output signal in order that the filter is a low-pass filter. Alternatively, the filter may be a band-pass filter.

Abstract: A solid state overload relay utilizes an apparatus that converts the current of a polyphase electrical load to a voltage signal approximately proportional to the RMS current of the load. In addition to providing the overload function, the voltage signal is used to provide an improved phase current unbalance protection. Conventional current transformers sense the current flow in each phase of the load. The current waveform for each phase is converted to a voltage by rectification and the peak value and the average value of the resultant voltage is determined. A summing circuit combines the two values at a predetermined ratio to create a DC voltage that is approximately equal to the rms value of the input phase current. A combination of the approximation circuit with a time integrating circuit and a level detecting circuit produces a low cost solid state overload relay in one embodiment of the invention.

Abstract: A method and a device, after a fault has occurred in a power network, for measuring and recreating the phase currents I.sub.B prior to the occurrence of the fault by determining continuously, starting from sampled measured values of the phase currents up to the time of the fault for each phase, the amplitude I and the phase angle .phi. of the phase currents based on two consecutive sampled measured values, whereupon a comparison is made between the last determined value I.sub.k obtained and the rated current I.sub.n of the power network. If I.sub.k is greater than I.sub.n, it is considered that a fault has occurred and the phase currents prior to the fault are indicated as I.sub.B =I.sub.k-1 .multidot.sin (.phi..sub.k-1 +.omega.(t-t.sub.k-1)).

Abstract: A system of protection for an electric power distribution system which has at least two parallel power feeders for each electrical phase coupling a source of electrical energy through a contactor device to a load distribution bus comprises a controller, and a parallel feeder current sensor for each parallel power feeder which sense electrical current conducted therein. The parallel feeder current sensors produce output parallel current sense signals proportional to the magnitude of the parallel feeder current sensed, and are coupled to the controller by conductors which communicate the output parallel current sense signals thereto. The controller comprises circuitry which compares the magnitudes of the output parallel current sense signals for each electrical phase.

Abstract: A branch protection circuit is provided to isolate a power network from a faulty load such as an overcurrent condition. The circuit employs a current-sense field effect transistor formed from two power field effect transistors integrated onto the same silicon substrate. The current-sense-FET is provided to detect if the electrical current in the larger FET has exceeded a predetermined threshold level. The circuit does not measure the specific current flowing through the transistors, and the circuitry employed to detect if the threshold current level is exceeded is significantly less complex than circuitry otherwise required to determine a specific current flow through one of the transistors.

Abstract: The operating parameters of a proximity switch can differ depending on the type of switch and also because of manufacturing tolerances. To make it possible for one to react to new developments in ultrasonic transducers and to customer-specific solutions without requiring additional space, data such as operating parameters are able to be input into a microprocessor of a prefabricated proximity switch with little expenditure of time and energy. A proximity switch may contain an enabling input and an overcurrent-detection device including a microprocessor. An overcurrent across the switching output can be identified by a pulse provided to a first input of the microprocessor. A programming device is provided through which such an overcurrent condition is simulated and the corresponding pulse is generated which represents information about an operating parameter in the form of a bit pattern. The microprocessor is loaded with this bit pattern.

Abstract: An overcurrent protection circuit for a power transistor for generating a main current in response to a gate drive voltage generated by a gate circuit. The overcurrent protection circuit includes a current detection circuit for detecting the main current flowing in the power transistor to generate a detection voltage corresponding to the main current, and a level detection circuit connected to receive the detection voltage for generating a control current corresponding to a difference between the detection voltage and a prescribed value when the detection voltage exceeds the prescribed value. The overcurrent protection circuit further includes a current control circuit connected to receive the control current for limiting the main current by regulating the gate drive voltage based on the control current, and a drive instruction control circuit connected to receive the control current for making the main current zero by controlling the gate drive voltage to an OFF condition based on the control current.

Abstract: In a circuit arrangement having a semiconductor switch for the switching of a load, in particular of a setting member in manual or automatic control devices, as a function of a switch signal which is fed, a device for disconnect in the event of a short-circuit being adapted to be controlled by a current sensor over a filter, the device for the disconnecting can furthermore be actuated via a logic circuit by the switch signal and by an output signal of a detector for an overvoltage at the semiconductor switch in such a manner that disconnect takes place when an overvoltage is present and the switch signal assumes a level intended for connection.

Abstract: The system includes a blocking counter which is set to 255 quarter cycles and the output contacts of the protective relay are blocked for five quarter cycles if the first order difference between two successive quarter-cycle samples of current is above a selected threshold, referred to as the last previous and the first samples. The first order difference between the first and the next successive (second) samples is compared against a second threshold and the instantaneous value of the current sample is compared against the second threshold. If both comparisons are above the second threshold, then the output contacts are unblocked. If not, such that a constant DC A/D converter output or an A/D spike is indicated, then the outputs remain blocked for the full five quarter cycles, which is sufficient time to permit the A/D spike to disappear and to recognize a constant DC output from the A/D converter.

Abstract: An apparatus for detecting differences between zero-sequence current caused by load unbalance and fault current caused by fallen distribution conductors. The apparatus makes it possible to readily check a high impedance fault. The apparatus includes analog-to-digital converters for converting analog A-, B-, C- and neutral phase current signals to digital data, respectively. The apparatus further includes a data processing system for computing even order power, rate of the even order to odd order power, and incremental variance of even order power. The apparatus analyzes the digital data and determines the fault when the computed information is compared with respective setting values and is greater than the setting values.

Abstract: In an electric circuit supplying AC line current rent to a load (30, 31) from an AC source (26) of given frequency providing repetitive cycles, arc detection is provided by sensing cycle to cycle changes in the AC line current. The AC line current is sampled with a harmonic notch filter (72) at a plurality of n phases .THETA..sub.1 through .THETA..sub.n during each of a plurality of m cycles of the AC source (26), to provide a plurality of currents I.sub.n,m, where n is the phase and m is the cycle. The differences (I.sub.n,m)-(I.sub.n,m-x), where x is a designated number of cycles, provide a plurality of current difference signals. The absolute values of these current difference signals ID are accumulated in a synchronous summer (94) over the m cycles. An arc indicative signal is generated in response to given conditions and given combinations of conditions (116) of the cumulative absolute current difference signals ID.

Abstract: A load drive apparatus is used in a vehicle direction indicating apparatus operable free from overcurrents and overvoltage. The load drive apparatus includes: a charging/recharging capacitor; a charging/recharging circuit for charging/recharging the capacitor at a preselected time constant in such a manner that a voltage across the capacitor is varied between a preset upper limit voltage and a preset lower limit voltage; a drive circuit for turning ON a power transistor series-connected to a current path employed to supply a current from a DC power source to a load, thereby driving the load when the charging/discharging circuit causes the capacitor to be charged, or the voltage across the capacitor is higher than, or equal to a predetermined voltage defined between the upper limit voltage and the lower limit voltage; overcurrent judging means for judging whether or not a voltage across terminals of the power transistor connected to the above-described current path exceed an overcurrent judging voltage.

Abstract: The terminals of a test circuit are directly connected to outputs of the transformer secondary windings and to the input of the rectifying circuit so that the test current checks operation of the trip device. A sign detection circuit supplies a processing circuit with the values of the polarities of the rectified currents. The processing circuit comprises means for determining the presence of a test current when the sign of the rectified current comprising the test current remains continuously in the same polarity. A differentiation of the continuous polarity, positive or negative, of the test current enables testing to be carried out with or without earth protection tripping.