Showing papers on "Fault current limiter published in 1990"

Microcomputer based electronic trip system for circuit breakers

Abstract: A processor-based tripping system uses a precise three phase current detection circuit using a minimal number of components. A set of current sensors is situated adjacent the current path to sense respective phases of current therein. The current sensors provide respective current signals therefrom which are fed to a ground fault transformer. The ground fault transformer includes input inductors connected to respective ones of the current sensors such that current flowing through each respective current sensor also flows through one of the input inductors. An output inductor in the ground fault transformer is coupled with the input inductors for adding the current signals from the current sensors and for producing an output current signal in the presence of a ground fault. The output current signal is then rectified to provide a rectified signal corresponding to the output current. The processor receives the rectified signal to detect the ground fault in the three phase current path and provides a trip signal to a solenoid to break the current path. The ground fault transformer also includes a test input inductor for receiving an external AC signal to simulate a ground fault.

A microprocessor-controlled variable impedance adaptive fault current limiter

Abstract: The design and modeling of a microprocessor-controlled variable-impedance fault current limiter is described. The limiter consists of an LC series circuit tuned to be of minimum impedance at the supply frequency. A thyristor-controlled reactor is shunt connected across the capacitor. By varying the firing angle of a thyristor pair, the impedance of the limiter is varied to allow the necessary current limitation so that the system is protected and all circuit-breaker relays can operate. The fault current limiter is modeled using a digital computer and validated in the laboratory with a prototype test setup. >

Battery-powered fault indicator

Abstract: A fault indicator operable from an internal battery for indicating the occurrence of a fault current in a monitored electrical conductor of an AC power distribution system. Upon occurrence of a fault current a reed switch in magnetic communication with the monitored conductor momentarily closes to connect the internal battery to a capacitor, which is charged by the battery during the switch closure. The capacitor is connected to the display electrodes of a high impedance liquid crystal display, which displays an "F" to indicate fault occurrence. The fault indication may be reset either by the slow discharge of the capacitor, by discharging the capacitor through a second reed switch manually actuated by a magnetic reset tool from outside the fault indicator housing, or automatically upon restoration of power in the conductor.

Insulation monitoring system of a direct current power supply system

Abstract: Insulation monitoring of a direct current power supply system is achieved by application of an alternating current and the detector is constituted by a current transformer and a Hall-effect current sensor. This Hall-effect sensor controls a direct current generator, which supplies a compensation winding of the current transformer, so as to prevent saturation of the toroid of this current transformer. When a ground fault occurs, the alternating current generator generates a fault current detected by the transformer.

High-capacity superconducting current leads of Y1Ba2Cu3O7−x

Abstract: We have fabricated and measured a high-capacity superconducting current lead composed of a Y1Ba2Cu3O7−x cylinder, 20 cm long and 0.9 cm2 cross section. A steady-state, d.c., critical current of 225 A at a temperature of 77 K was measured in this sample, using a voltage criterion of 2×10−7 V/cm (p = 8×10−10 ohm-cm). This current was limited by the currentinduced, self magnetic field. To our knowledge this is the largest d.c. critical current so far reported in a Y1Ba2Cu3O7−x sample and demonstrates the possibility of using hightemperature superconducting HTS materials for current leads to low-temperature superconducting LTS magnets or in power distribution systems.

On the Inductive Method for Maximum Current Testing of Superconducting Cables

Abstract: In order to test superconducting cables at high currents it is convenient to generate the required transport current inductively, i.e. by means of a superconducting transformer. The paper gives a survey of the devices in different laboratories that apply this technique to test cables above 20 kA. An existing test facility at the University of Twente, suitable for 50 to 200 kA, is treated in more detail. Specific aspects of such a facility are discussed, for example the design of the transformer, the methods to measure the current in the superconducting secondary circuit and the fabrication of joints with a sufficiently low electrical resistance.

Performance testing of the Nordon high impedance ground fault detector on a distribution feeder

Abstract: Distribution primary conductors which fault to ground rather than to the neutral conductor or other grounded object are known to result in fault currents which are too low to be detected by conventional overcurrent devices. Such faults, however, are shown to result in distorted currents which can be recognized as distinct from other distribution current distortions. The operating theory of a high-impedance fault alarm system (HIFAS) which can detect these low-current faults is presented. Procedures for safely conducting 13 kV line fault tests to confirm the performance of these new relay operating parameters without jeopardizing customer service are described. Test results that confirm the soundness of the detection principle are given. >

25 kV Superconducting Fault Current Limiter

Abstract: Our technological progress in die field of superconductivity over the last ten years made possible the manufacture of industrial lengths of conductors, consisting of NbTi ultra-fine filaments, embedded in a Cu-30 wt % Ni matrix; 50 Hz losses are greatly reduced, and the electrical resistance beyond the critical current is very large. Such conductors offer numerous new perspectives, through which the design of electrotechnical machines could be reconsidered. This paper describes the main features of a 50 Hz single-phase fault current limiter, constructed in our laboratories, which present some electrical and cryogenic properties: S-N transition limiting the fault current to a value a few percent above the threshold current within a few µs, high voltage insulation capabilities, moderate cryogenic losses during steady state and in transient conditions.

Development of Superconducting AC Fault Current Limiter

Abstract: The authors have developed a new superconducting fault current limiter whose impedance during normal operation is very small. During fault conditions, the limiter behaves as a superconducting reactor. The limiter consist of a superconducting limiting coil and a superconducting trigger coil. The former coil has a larger critical curent than the latter coil. These coils are wound non-inductively on coaxial cylindrical formers and are parallel connected to each other. They are wound with AC superconductor having ultra-fine NbTi filaments. The limiter has a very little impedance because both coils are in superconducting state during normal operation. On the other hand, in the case of fault conditions, the trigger coil quenches at a critical current. After the’ trigger coil quenching, the limiter becomes a superconducting reactor because current in the coil decreases very rapidly with rapidly developing resistive normal zone. The fault current is, therefore, limited by the superconducting limiting coil to a certain value determined by the coil inductance. In experiments, the authors have succeed in limiting a fault current level to 200A, with a limiter whose terminal voltage under limiting conditions was 54V.

D.C. current network insulation monitoring system

Abstract: The insulation of a DC network is monitored by injecting an alternating current into the network. The detector consists of a current transformer (38) and a Hall effect current sensor (28). The Hall effect sensor controls a DC generator (46) which supplies a current to a compensation winding (42) on the current transformer (38) in such a way as to avoid saturating the core (36) of the current transformer (38). When an earthing fault (24) occurs, the AC generator (22) produces a fault current which is detected by the transformer (38).

Basic Test of A 3-Phase Superconducting Fault Current Limiting Reactor

Abstract: A novel 3-phase superconducting fault current limiting reactor (SCFCLR) for power system is presented. It has 3-phase superconducting windings on single iron core. Small experimental devices are fabricated and tested. Through some experiments, the fundamental behavior of the limiter is confirmed. In the experiment, two SCFCLRs are inserted in the sending and the receiving ends of the model power-transmission line. In a normal operation, the SCFCLR exhibits very small impedance for balanced three-phase current. In the case of single-line-to-ground fault, the fault current is limited to very small value by the large zero-phase-sequence reactance of the SCFCLR. In this case, the superconducting windings do not quench. In the case of two-phase or three-phase short circuit, the superconducting winding of the SCFCLR quenches, and the short circuit current is limited by the normal conducting resistance of the winding. It is experimentally confirmed that the SCFCLR can limit the fault current in all fault conditions.

Limiter circuit for alternating voltages

Abstract: A limiter circuit for alternating voltages includes a pair of zener diodes arranged in series but in opposite sense. Each zener diode forms an additional current mirror with a respective further transistor so that for each of the two possible directions of the limiter current it is possible to derive a limiter signal current which is decoupled from the actual limited current and which, unlike the actual limiter current, always flows in the same direction. Such a limiter circuit can be used in the input circuit of a bridge rectifier for ringing-current detection in electronic telephone sets connected to two-wire lines.

Fault current limiter

Abstract: PURPOSE: To get current limiter property dependent on currents by connecting is series current limiting elements, where the critical current density go up. CONSTITUTION: To convert a current limiting element with a critical current, conditions on the sectional area and the dimension of superconductive material, or the sectional area and the length of usual conductive material, the temperature rise, the generated power, and the necessity of a refrigerant are decided by the property of the material at manufacture and the generated current. On a supporting insulator 1 rectangular in section, a first resistor 2 of superconductive material is attached to its one side by sputtering or the like, and thereon a second resistor 3 of lower-resistance material is attached by deposition or plasma flame-coating or the like, and this is provided with connection means 4 and 5. Since this consists of two resistors this way, the superconductor is broken due to temperature rise is case of partial defect, but the current is transmitted into the second resistance layer. Then, the energy produced in the resistance of the second resistor 3 is absorbed by the amplitude and the duration of this current. Though this energy causes temperature rise, it is removed with a refrigerant.

Integrated limiting circuit for AC-voltages

Abstract: An integrated limiting circuit for alternating voltages, comprising Zener diodes connected in series in opposite directions. … Due to the fact that a current balancing circuit is inserted into the circuit for each of the two possible directions of the limiter current, a limiter signal current can be derived which is decoupled from the actual limiter current and which, differently from the latter, always flows in the same direction. Such a circuit can be used in the input circuit of a bridge rectifier for ringing current detection in electronic telephone sets on two-wire lines. … …

Test on superconducting ac fault current limiter

Abstract: The authors have developed a new superconducting fault current limiter whose impedance during normal operation is very small. During fault conditions, the limiter behaves as a superconducting reactor. The limiter consists of a superconducting limiting coil and a superconducting trigger coil. The former coil has a larger critical current than the latter coil. These coils are wound non-inductively on coaxial cylindrical formers and are connected in parallel to each other. They are wound with AC superconductor having ultra-fine NbTi filaments. The limiter has a very little impedance, because both coils are wound non-inductively and in superconducting state during normal operation. On the other hand, in the case of fault conditions, the trigger coil quenches at a critical current. After the trigger coil quenching, the limiter becomes a superconducting reactor, because non-inductiveness is broken by trigger coil current. The fault current is, therefore, limited by the superconducting limiting coil to a certain value determined by the coil inductance. In experiments, the authors have succeeded in limiting a fault current level to 200A, with a limiter whose terminal voltage under limiting conditions was 54V.