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 control system for a separately excited DC electric traction motor in an electrically powered vehicle incorporates a plurality of current limit functions designed to protect both the motor and control electronics. A time dependent current limit is utilized to permit overcurrent conditions for limited time intervals such that additional power can be obtained for sudden torque requirements without having to design the motor or control electronics to function under continuous high torque conditions. The continuous current limit values based on percent conduction time of a thyristor chopper circuit in the control system is modified in response to overheating of the motor and the main switching thyristor, to overvoltage on the thyristor commutating capacitor and to available voltage for powering the motor.

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. The current representative voltage is sensed through respective dedicated third and fourth diodes connected to the main terminals and having a common anode connection to the voltage sensing means such that the latter senses the more negative of the main terminals regardless of the relative potential therebetween.

Abstract: An overcurrent protection circuit and method therefor for use in a multiple output switched power supply wherein the overcurrent condition accompanying a short circuit or an overload in an output circuit is detected as an undervoltage in a transformer When the undervoltage exceeds a threshold the power supply is switched off and then on again during the cycling of a low frequency oscillator until the short or overload is removed in order to maintain the average power through the output circuit at a safe level

Abstract: This paper describes the protective relaying schemes employed by Georgia Power Company to protect synchronous generators from single-phase- to-ground faults. Three types of relays are connected in the secondary of a distribution grounding transformer. These include a conventional electro- mechanical overcurrent relay with time overcurrent unit and instantaneous overcurrent unit, a solid- state overvoltage relay (with timing module) tuned to reject frequencies near 180 hertz, and a solid-state undervoltage relay (with timer) tuned to reject frequencies near 60 hertz present at the generator neutral. The proper method of selecting the generator grounding components and protective relays is described, and detailed setting instructions for all relays are also included.

Abstract: An overload protection circuit for a semiconductor switch has a control line which can be shorted, via the collector-emitter path of a transistor, to the ground. The base of the transistor is connected to the output of a comparison stage. One input of the comparison stage is connected via a resistor to the control line, via a diode to the lead of the semiconductor switch facing away from the ground potential, and via a capacitor to ground. A fixed reference voltage is applied to the second input of the comparator stage. In this circuit, a control pulse is shorted as soon as the voltage across the semiconductor switch exceeds a given value because of overcurrent. The short circuit of the addressing pulse is cancelled again as soon as the latter goes back to zero.

Abstract: A voltage converter of the transformer type which incorporates at least one switching transistor coupled to control the application of current to the transformer primary and circuitry for switching the transistor off in response to the current drawn through the primary winding and the level of the input line voltage. Overcurrent shutdown may thus be tailored to approximate constant power dissipation within the voltage converter.

Abstract: A short-circuit protection device for a DC control element has at least one transistor which is addressed by timing pulses obtained by comparison of a triangular voltage with a control voltage. Each such transistor is provided with a separate overcurrent protection device which, after a short circuit, blocks the associated transistor until the beginning of a new switching-on pulse. The control voltage assumes values which are above the maximum value of the triangular voltage. In the event of a short circuit, the transistor concerned is switched off very fast, but is switched on again by the next succeeding switching-on pulse and a determination is made as to whether the short circuit is still present. If the control voltage rises to values which are above the maximum value of the triangular voltage because the actual value of the load current deviates heavily from the reference value due to the disconnection of the transistors, the transistors remain switched off until the DC control element is restored to operation by external intervention.

Abstract: An overcurrent display device is described which is suspended directly from a distribution cable for locating the spots of earthing, short-circuiting or other accidents in a distribution line system and is adapted to display the passage of the transient overcurrent due to such accidents through the cable for a predetermined time and to be restored to the original state before the display of the overcurrent condition. The device consists of an overcurrent sensing circuit, a drive unit including a drive element driven by the sensing circuit and a display unit actuated by the drive unit and adapted to achieve a display operation.

Abstract: A MOS type output driver circuit including an output circuit having first and second MOS type output transistors connected between a voltage supply and ground. The gates of the first and second output transistors are respectively, supplied with first and second drive signals that are mutually inverted. The MOS type output driver circuit further includes a protective circuit for preventing the output transistors from being damaged by overcurrent when the output is shorted to ground.

Abstract: PURPOSE:To ensure preservation of pump function by catching abnormal temperature rise of the pump on the surface of a capacitor in a power supply box and opening an electric circuit just before the capacitor temperature reaches the level at which the dielectric loss tangent varies. CONSTITUTION:A capacitor 130 and relay 120 for preventing a motor from seizure are accommodated in a power supply box 3, and a thermo-switch 160 is housed in a thermo switch housing recess 40 located above the capacitor 130. For example, when overcurrent supposed to occur in case of a lock of a motor 1 or the like flows and just before the capacitor 130 temperature reaches the level at which the dielectric loss tangent varies, a relay 120 for preventing the motor from seizure is operated to cut an electric circuit for protecting the pump function. Next, when contacts are not opened because of failure of a pressure switch 19 although the predetermined pressure is reached, and temperature of each portion rises abnormally because of sealed operation or the like, the thermo switch 160 is operated to open the contacts, cut the circuit and stop the operation similarly for ensuring preservation of the pump function.

Abstract: A control is provided for an AC circuit protection system or the like which is capable of monitoring either single phase or polyphase current flow. The composite current is periodically sampled at a frequency f s which is not a harmonic frequency of circuit current. The current sample values are converted into digital form and processed, then stored in an accumulator stage. When an overcurrent condition occurs the accumulator stage overflows and trips a circuit interrupter.

Abstract: The current in each phase of a multiple phase chopper is sensed and compared to a reference overcurrent value. Any chopper phase reaching overcurrent and any chopper phase on for a longer period of time are turned off immediately. The conduction periods of chopper phases that have been on for a shorter period of time than the overcurrent phase are similarly shortened to maintain balanced phase conduction and minimize the ripple content of the source current. The phase relationship among the various chopper phases is adjusted in response to an overcurrent turn-off to allow the commutation network associated with such phase to be adequately charged before the generation of a current turn-on for another phase.

Abstract: A discharge lamp control circuit comprises a switching circuit 12-17 which is controlled by a control circuit (32-70, Fig. 2) to switch an electrical supply to the lamp on and off, the ratio of on-time to off-time being controlled digitally. The control circuit includes manually-operable switches (32-34, Fig. 2) for setting up binary code elements representing a required brightness level, and an overriding circuit (53-59, Fig. 2) which overrides the manual switch setting during pre-heat and soft start phases of a starting sequence. During the pre-heat phase, the switching frequency is higher than the resonance frequency of the lamp drive circuit 19-22 but the ratio of on-time to off-time is at a maximum. During a first part of the soft start phase, the switching occurs at the resonance frequency so that a high voltage is applied to the lamp, but the ratio is kept low, so that the energy is insufficient to cause the lamp to fire. During a second part of that phase, the ratio is increased, so that the high voltage causes the lamp to fire. The control circuit then steps to a running phase, in which the ratio is controlled by the manual switches. The stepping through the preheat, soft start and running phases is controlled by a low- frequency clock (53, Fig. 2) and a register (54, Fig. 2) which is stepped by the clock. Alternatively both transistors 12, 13 may be driven via opto-couplers. Various protection arrangements are used, e.g. overcurrent, lamp failure, supply voltage failure, etc.

Abstract: A miniature surge protector for use in telephone central offices, or the like which are provided with terminal blocks for communication lines includes an in-line over-current coil arrangement which grounds each communication line if an overcurrent flows therethrough and is additionally provided with a gas tube surge protector and an auxiliary air gap disposed across a pair of communication lines and a common ground terminal, thus providing overvoltage and overcurrent protection to a pair of telephone communication lines.

Abstract: The paper proposes a number of protection methods which can be used with power transistors in power-control units. They give satisfactory protection against simultaneous conduction of the two devices in an inverter leg. The techniques, which are independent of the control electronics and base-drive circuits, are simple and reliable to implement. They include an instantaneous and electrically isolated method of fault indication, a fast-acting crowbar circuit and a means of diverting the current away from the power devices in the event of a fault.

Abstract: A concern that the characteristics and correct application of the generator backup relay are misunderstood is addressed in this report to the Power Systems Protection Committee. It is inherently a secure device, and rarely has the opportunity to operate in its intended capacity. So the question was asked, ``Do generator backup overcurrent relays really protect anything?'' In response a description of the function and operating characteristics of the backup relays, a discussion of generator fault current behavior, examples of relay settings for a typical application, and methods and criteria for determining that the relay both protects the generator and operates selectively with other protective devices are included.

Abstract: Overcurrent protection is obtained in a push-pull network by circuitry repeatedly comparing signals indicative of the instantaneous current flow through the push-pull switching elements with a synchronized reference signal whose value is preferably made to decline during the ON periods of the current switches. Thus, the reference signal may initially be set relatively high to accommodate a moderately high in-rush transient and then to decline to lower levels over the remainder of the time the switching elements are on. At any time that the current signals exceed the compared to reference value, the corresponding current switch is deactivated as a protective measure.

Abstract: For protection of an output switching transistor used in a pulse signal output circuit, the present invention provides a first detector for detecting over-current flowing through the output switching element, a second detection circuit for producing a detection signal in response to detection of over-current by the first detector in excess of a predetermined rate, and a protection circuit protecting the output switching element by suppressing the current flowing therethrough in response to the detection signal. The protection circuit may suppress the current flowing through the output switching element by both the output of the over- current detector and the detection signal.

Abstract: A transistor circuit (18) is series connected with a solid state switching device (14) and a load (4) controlled by that device (14) to protect that device (14) from overcurrents resulting from short circuits such as across the load (4). The transistor circuit (18) detects the overcurrent and switches to a high impedance state in response to that detection. The circuit (18) is self-resettable to restore to the low impedance state each half-cycle of applied voltage, thereby to automatically restore the switching device (14) to normal operation immediately upon removal of the short, and is set to initially respond to a level of current sufficiently high to preclude switching in response to inrush currents. Initial switching of the circuit (18) to its high impedance state latches a reduced level detection circuit (R1-R2-Q4) in the transistor circuitry (18) whereby the latter switches to its high impedance state upon detecting lower overcurrent values for each successive half-cycle until the short is removed. The predictability of the response range for the circuit, especially in the reduced level voltage detection mode, is improved by placing a resistor (R5) in series with the control switching transistor (Q3) for the circuit.

Abstract: A low voltage equipment ground fault protection system for solidly grounded radial systems is described. The protection provides primary protection for source substation buses. It is capable of providing selective operation with downstream ground fault trip devices or phase-overcurrent devices set to detect ground faults. It also provides source transformer protection for phase-to-ground through faults to supplement transformer primary phase-to-phase and three-phase through-fault overcurrent protection.

Abstract: Overcurrent protective device coordination is defined, and the advantages of computerizing this process are explained. A computer program written by the authors, who are engineers responsible for performing coordination studies, is discussed. The program was written with emphasis on engineering flexibility. It can select settings for overcurrent protective devices to satisfy loading and protection requirements and to achieve the greatest possible degree of selective operation. Since complete selectivity is seldom possible, a means is provided whereby the engineer can indicate where compromises in coordination should be made. The data used by the program is discussed, as well as the setting process and the program output.

Abstract: PURPOSE:To improve operability by enabling manual operation when a momentary switch SW is operated once and automatic operation when it is operated twice within a prescribed time. CONSTITUTION:In a window regulator, pushing an SWA outputs a signal H from a terminal A1. When FFs A8 and B8 are both reset, a circuit A2 is opened because a signal H is being sent from the terminal Q' of the FFB8 to an AND circuit A2, and contacts A12 and A13 are connected by energizing a relay A11 with the signal H passed through an OR circuit A9 and an amplifier A10 so as to turn a motor M normally, thereby enabling the manual operation of closing a window. The output of the circuit A2 is differentiated A3 to trigger a monostable multivibrator A5, which outputs a signal H, which is inputted to an AND circuit A7 via a delay circuit A6. When the SWA is freed and then pushed again within a delay time, the circuit A7 is opened to set the FFA8, and the signal H is outputted from a terminal Q to put the motor M in automatic operation through the relay A11. When the window is closed, an overcurrent detecting circuit D outputs a signal H to reset the FFA8.

Abstract: The invention relates to a digital electronic overcurrent trip device for a switching apparatus, having a microprocessor for evaluating the measurement voltage and having a device for adjusting the tripping parameters, there being allocated to the microprocessor an electrically erasable, programmable read only memory (EEPROM) for storing the tripping parameters, and an interface for connection of a data input and erasing apparatus for access to the read only memory (Figure 1).

Abstract: PURPOSE:To avoid a breakdown of a laser diode caused by an overcurrent by a method wherein the current of the laser diode is observed and when the current is going to exceed a specified value, the impedance of the circuit connected to the laser diode in parallel is reduced, so that the surge current is by-passed. CONSTITUTION:A transistor TR17 is connected to a circuit of a laser diode 2 in parallel and the emitter circuit of the TR17 is connected to a resistor 19. When a current begins to flow through the diode 2 by some reason, a voltage is produced between the both ends of an emitter resistor 13 of a compound TR3 by the surge current and the voltage is applied to the TR17 through a base resistor 18. If the circuit is so designed that a base voltage produced by the surge current is saturate enough by the TR17, most of the surge current will flow through the TR17. With the above method the diode 2 is protected from deterioration or breakdown caused by the surge current.

Abstract: In the last decade there has been renewed interest in fault-current-limiting devices and various concepts are under active consideration. The paper describes the principle, design, manufacture and testing of a device based on one of these concepts. The possible areas of application of the device are indicated.

Abstract: A current limiting device comprises a current limiting element 36 normally of good electrical conductivity but having high resistance to overcurrents, a switching element 44 serially connected to the former, and an impedance element 46 in parallel with both When an overcurrent is limited, a current detector 48, 50 detects a current flowing through another impedance element 18 connected across the current limiting element to open the switching element through a trip coil 44a A closing coil 44b closes the switching element with a predetermined delay timed out by a delay element 52 connected to the current detector 50 Alternatively the switching element 44 may be closed upon the disappearance of the overcurrent as determined by another current detector 54, or an indicator rod 58 may be connected to a piston 24 in a pressure buffering cylinder operatively coupled to the current limiting element and provided at the free end located outside of the element with two movable contacts 60 arranged to separably engage respectively stationary contacts connected across the trip coil 44a

Abstract: In order to drive current loads locally in a railway signalling system in a fail safe manner in terms of signalling technology, an electronic power inverter (3, 4) is provided, via which the current load (7, 8) draws the power necessary to operate it from an intermediate direct current circuit (11, 12) which is fed via a rectifier (2). The power inverter can be driven by a redundantly constructed control circuit (5, 6) from a common data line (10). Connected upstream of the current load are inhibiting means (9) and/or interruption means (14, 15; 16, 17) which prevent a flow of direct current across the current load and/or ensure that the power supply is cut off when overcurrent occurs.