Showing papers on "Fault current limiter published in 1981"

Solid-state load protection system having ground fault sensing

Abstract: A solid state load protection system whereby the current supplied to a load is monitored enabling ground fault sensing to be used. A current sensor is utilized so as to produce an output current which is proportional to the current in the electrical circuit. Attached to the current sensing function is a resistive load which converts the current produced by the current sensing function to a voltage which is also proportional to the current utilized by the motor. Attached between two resistors which comprise the resistive load is a ground fault resistor which has its remaining end connected to the neutral leg of the current transformers of the current sensing function. The ground fault sensor monitors the voltage across the resistors in the resistive load and the current in the neutral leg of the current sensors. A ground fault condition is indicated when a current in the neutral leg of the current sensor is detected and thereby causes voltages across each of the resistive load resistors to be unequal to each other. If this condition is in excess of a predetermined level, for a predetermined period of time a trip signal to the output function is initiated, in turn causing a light-emitting diode to conduct and indicating a ground fault condition. The output function upon receiving a trip signal causes a second light-emitting diode to conduct and also de-energizes a contactor through which a current source is connected to a load.

A fault isolator for electric utility distribution systems

Abstract: A device (16) for locating faults on the lines (18) of electrical power distribution systems (10), including generally a variable impedance means (26) adapted for connection in series with an electrical power line (18), and means for switching (36) such variable impedance means (26) between a first low impedance value when an initial current I1 of predetermined level flows on the power line (18) for a predetermined period of time to enable detection of a fault condition, and a second high impedance value which limits the flow of current to a low level I2. A meter (46) or other indicating device provides a reading of the current I1 to determine if a fault condition exists. In this fashion, the fault locator device (16) limits both the magnitude and the time duration of the current when testing for a fault, so as not to adversely affect any system components.

Ground fault and fire detector system

Abstract: A ground fault and fire detector system for an A.C. electrical power distribution apparatus including a multi-pole circuit interrupter to disconnect a poly-phase electrical power supply from a load. A single-pole circuit device is operatively connected to the circuit interrupter for controlling its operation. Ground fault sensing circuitry is operatively positioned with respect to at least one wire for initiating a fault current. The single-pole circuit device is responsive to the fault current for activating the circuit interrupter to disconnect the power supply from the load.

Ground fault interrupter circuit

Abstract: A ground fault interrupter (GFI) circuit for interrupting alternating current delivered in a power distribution system whenever a ground fault current exceeding a prescribed level is sensed. The GFI circuit includes a differential current sensing apparatus for sensing the presence of a ground fault current and generating a control signal that assumes a first condition whenever the ground fault current exceeds the prescribed level and for assuming a second condition whenever the ground fault current is less than the prescribed level. A charging circuit is charged with an electrical charge during a fixed portion of each cycle of the alternating current if the control signal has assumed the first condition. If the control signal has assumed the second condition, the charging circuit is discharged during a fixed portion of each cycle of the alternating current, thereby preventing any substantial charge from being stored in the charging circuit. A trigger circuit generates a trigger signal whenever the accumulated charge in the charging circuit exceeds a threshold level, which threshold level is reached within one cycle of the alternating current. Conventional switch means are used to interrupt the current flow in the power distribution system in response to this trigger signal.

Ground fault circuit interrupting device with improved integrated circuit power supply

Abstract: An integrated circuit ground fault signal processor utilizes a power supply having a first, regulated, half-wave rectified supply voltage section and second DC supply voltage section. Operating current for a fault signal amplifier and charging current for a fault signal integrating capacitor are drawn from the second power supply section on a full-cycle basis. Operating current for a trip threshold detector or comparator and a high frequency oscillator circuit is drawn from the first power supply section for operation on an alternate half-cycle basis.

Fault-current control in power-conditioning units using power transistors

Abstract: A modified arrangement of the classic form of inverter ‘leg’ is introduced which automatically limits the rate of rise of current in the event of circuit faults. In particular, it operates when two devices in the same leg are on simultaneously, and if the output terminals are short-circuited. Experimental results for simulated fault conditions show that fault currents are limited in a predictable manner, and that the circuit behaves normally in other respects.

Plasma Density Measurements Using a Double Langmuir Probe in a Prototype Vaccuum ARC Fault Current Limiter

Abstract: Electric power systems could benefit from a device that would limit the magnitude of short-circuit current. A switched resistor fault current limiter requires a commutating switch capable of interrupting current without the benefit of a natural current zero. The unstable diffuse plasma discharge between electrodes in a cylindrical geometry might be capable of such a task but the phenomena involved in this discharge is not completely understood. To develop a detailed model of this unstable discharge, measurements of the plasma density as a function of position and time were made using a double probe. A maximum density of 5 x 1020 m-3 was measured 90 mm from the cathode of this diffuse copper vapor discharge in vacuum.

Development of a vacuum arc fault current limiter

Abstract: The primary purpose of this program was to develop an understanding of the operating principles of the vacuum arc devices under development at the State University of New York at Buffalo for fault current limiting applications. The general operating characteristics are given for two basic vacuum arc devices. One is the Vacuum Arc Fault Current Limiter and the other is the Magnetically Controlled Vacuum Arc Switch. The results of detailed studies of the phenomena occurring with the two devices are described. In particular, the repetitive voltage spiking phenomena that occurs in the Vacuum Arc Fault Current Limiter is treated in substantial detail. The mechanism of the voltage spiking (the repetitive formation and collapse of an anode sheath) is described along with measurements that were made of parameters associated with repetitive spiking. Techniques for enhancing current limiting by enhancing spiking development are discussed. Work on the magnetically controlled vacuum arc switch and the cooperative efforts with the industrial partner (Gould-Brown Boveri) are described.

Therminoic fault current limiter and method of current limiting

Abstract: A thermionic fault current limiter utilizes either a vacuum or plasma environment for a plurality of spaced conduction electrodes. The electrode can be supported by insulative spacers with the electrode providing shadow shields for the supporting spacers. Electrode spacing, power density, temperature gradients, and control grids can be utilized for optimum operation and in establishing self-absorption of energy for a desired operating environment. Cesium desorption from the electrode surfaces can be utilized to enhance current termination.

Circuit arrangement for recording a fault current

Abstract: A fault current recording and processing arrangement is specified in which an integrated circuit (14) is used as a device for recording and evaluating a fault current signal produced by the secondary winding (12) of a summing current transformer (10). The device (14) is activated by means of additional elements (15, 90, 44, 63, 64, 82, 84, 90, 94, 96), by which means is provided chatter protection for a trip device (74), driven by a controllable semiconductor valve (54), and a neutral-line monitor, for both a.c. fault currents as well as d.c. fault currents.

Survey osf TRV conditions on the CEGB 400kV system

Abstract: The paper presents results of a survey of transient recovery voltage (TRV) on the CEGB 400 kV system, made by a series of digital-computer calculations, to provide a basis for the preparation of TRV parameters for a revised switchgear purcinising specification. The results are obtained for 3-phase earthed fault and single-phase-to-earth fault conditions. Details of the system represented in the survey are given, together with the method of representation and analysis of results. The relationship between fault current and rate of rise of TRV is discussed, and factors affecting peak voltage are considered

Plasmadensitymeasurementsusinga doublelangmuirprobe ina prototypevacuum arc faultcurrentlimiter

Abstract: Electric power systemscould benefit fromadevice that wouldlimit themagnitude ofshort-circuit current.Aswitched resistor fault current limiter requires a commutating switch capable ofinterrupting current without thebenefit ofanatural currentzero.Theunstable diffuse plasma discharge between electrodes inacylindrical geometrymight becapableofsuch atask butthephenomena involved inthis discharge isnot completely understood. Todevelop a detailed modelofthis unstable discharge, measurementsoftheplasma density asafunction ofposition andtimewere madeusing adouble probe. A maximumdensity of5x 1020m-3was measured 90mm fromthecathode ofthis diffuse copper vapordischarge invacuum.