Showing papers on "Fault current limiter published in 1998"

Fault-current limiter applications in medium- and high-voltage power distribution systems

Abstract: Electronically triggered fault-current limiters have been used in medium- and high-voltage power distribution systems to limit the available short-circuit current to a lower level, so that the underrated switchgear can be operated safely. However, to insure a safe and proper usage of these devices, the following major operating parameters need to be considered: (1) selection of trigger level; (2) selection of di/dt; (3) effect of the capacitor bank and stray capacitances; and (4) coordination between these devices and phase overcurrent (o/c) relays at the faulted breaker. This paper will examine these major operating parameters, evaluate the performance of the current limiters under various simulated fault conditions, and develop application guidelines for current limiters.

Combination ground fault and arc fault circuit interrupter

Abstract: A combined ground fault and arc fault circuit interrupter includes a differential current transformer, a hot electrical line and a neutral electrical line passing through the current transformer and forming the primary thereof, an asymmetrical current transformer having a core through which the hot and common electrical leads pass, and a secondary wound on the core for producing a signal more strongly responsive to the current in the common line than in the hot line. An arc fault detector is connected to the secondary of the second transformer, while a ground fault detector is connected to the secondary of the first transformer, and the outputs of the ground fault and arc fault detectors are both connected to a circuit interrupter arranged for disconnecting the circuit when either a ground fault or an arc fault is detected.

Insulation and fault current monitoring method for electrical AC network

Abstract: The insulation and fault current monitoring method detects the differential current obtained by vectorial addition between at least 2 conductors of the AC network, for initiating automatic load cut-out when the differential current excedes a threshold value. The AC current component of the differential current is used as a first network variable and the network voltage between 2 network conductors, or between a network conductor and a neutral conductor is used as a second variable, used for calculation of the resistive fault current of the network. compared with a threshold value for automatic cut-out.

1.2 MVA High-Tc Superconducting Fault Current Limiter

Abstract: A 3-phase high Tc superconducting fault current limiter with a rated power of 1.2 MVA has been built, tested, and installed in a power plant for an endurance test. The device is based on the “shielded iron core concept”. The superconducting part consists of a stack of Bi-2212 ceramic rings. They were fabricated by a special partial melt process. The nominal current and voltage of the device are 70 A and 10.5 kV, respectively. In 3-phase short circuit tests with a prospective fault current of 60 kA the current was limited to about 700 A in the first half wave and further to below 250 A after 50 ms.

Inrush current limiter with output voltage detection for control of input current level and activation of current bypass path

Abstract: According to the present disclosure, an inrush current limiter comprises an input (190) for connection to a supply voltage, an output (202) for connection to a load, a current limiter circuit (102), a current bypass circuit (106), and a charge status circuit (104). During the initial charging of capacitors, the current limiter circuit (102) senses a large inrush current and limits the current to a predetermined quantity. The current bypass circuit (106) is switched off during the initial charging of the capacitors. When the capacitors are charged to substantially equal the input voltage, the current bypass circuit (106) is switched on to provide a low-resistance path for the supply current to pass through. In addition, the charge status circuit (104) operates to indicate the supply voltage.

Investigation of the performances of a permanent magnet biased fault current limiting reactor with a steel core

Abstract: There is an increasing need in power system applications for fault current limiter, to limit the fault current in semiconductor devices and switchgear. These fault current limiters must be reliable, compact and inexpensive. This paper reports the result of an investigation of the characteristics of a fault current limiter (FCL) consisting of a steel core and permanent magnet. Design criteria are presented. The FCL characteristics are simulated using a Tableau approach and the simulation results have been compared with experimental results.

Circuit breaker with improved arc interruption function

Abstract: A fault current interrupter is provided by the parallel combination of a polymer current limiter and a voltage dependent resistor connected across a pair of separable contacts to permit the interruption of current without the occurrence of arcing between the contacts when the contacts first become separated. The polymer current limiter is selected to have a relatively low resistance at quiescent operating currents and a substantially higher resistance at short circuit overcurrents. This allows the current to transfer away from the contacts through the polymer current limiter until the voltage across the voltage dependent resistor causes the voltage dependent resistor to become conductive and thereby transfer the current away from the polymer current limiter.

On using the solid state breaker in distribution systems

Abstract: The paper demonstrates, through the use of electromagnetic transient simulations, the key issues in the application of solid state devices for fault control and protection in the distribution systems. Three types of topologies have been considered, viz. a bus tie breaker, a transfer switch, a fault current limiter, but only two have been discussed in detail; the bus tie breaker is taken to be a special case of the fault current limiter. The control scheme for each topology has been designed and studied, with emphasis on the detection schemes and the responses to various system and load parameters. All simulations have been carried out using the PSCAD/EMTDC program.

Safety-enhanced transformer circuit

Abstract: A transformer control circuit (10) which includes a ground fault detection circuit (52) that detects ground fault currents in the transformer secondary (42, 44) and delivers a ground fault detection signal to the primary circuit. This circuit derives power from the secondary winding (42, 44) and transmits the ground fault detection signal through an optical isolation barrier (54), thus avoiding the use of an auxiliary transformer. The ground fault detection circuit further includes safety features for detecting whether AC power is being supplied without earth ground being connected, and/or whether there is an undesired electrical connection between a transformer output connection and earth ground, which would defeat the ground fault detection circuit.

Arcing fault and ground fault interrupting device for branch circuits and extensions

Abstract: A fault detection device for an electrical distribution system comprises a single arcing fault detection device which can be shared among a plurality of branch circuits. A scanning device is connected to the arcing fault detection device. A line conductor from each of the branch circuits is provided to the arcing fault detection device. A current transformer is provided for each branch circuit to monitor its line conductor and to provide an output signal to the scanning device. the scanning device polls each current transformer for an output signal for a selected number of cycles and provides the output signal to the arcing fault detection device. The arcing fault detection device analyzes the output signals and, upon detection of an arcing fault condition in a branch circuit, shunts the line conductor of that branch circuit to ground via a resistance to induce ground fault condition in the ground fault interrupting device for that branch circuit.

Reconstruction of output currents and fault detection in a B4-inverter with only one current sensor

Abstract: A three-phase inverter with four switches and four free-wheeling diodes (B4) is an alternative to the classical B6-inverter in order to reduce cost and complexity. This paper proposes a method to reduce the number of current sensors in a B4-inverter to one but still keep the knowledge of the three output currents. Different current sensing topologies are proposed and one is selected for implementation which protects the inverter. The current is only sensed in the DC-link fault protection. Practical problems are discussed and solved. An implementation is done in a hardware setup and experimental work validate that the proposed method can identify the output phase currents by only measuring the DC-link current.

A numerical method for analyzing a passive fault current limiter considering hysteresis

Abstract: Fast transient analysis of a passive fault current limiter (FCL) using permanent magnets can be done by direct numerical solution of a single non-linear differential equation. The non-linear B-H excursion that is caused by hysteresis is incorporated in the computation using a transient hysteresis model. Rational fractions are used to represent the parent hysteresis loop curves. Since the method uses preconstructed expressions as applicable to FCL schemes only, computation time required is less.

Resonance phenomena on line-to-ground fault current harmonics in MV networks

Abstract: High levels of harmonic components measured on MV line fault currents have prompted a detailed investigation of the phenomena in order to develop models to accurately reproduce the observed harmonic currents and clarify the resonance characteristics of the system under line-to-ground fault conditions. A procedure which can predict the fault current wave-form of a whatsoever complex distribution system supplying a variety of loads, enabling identification of potentially harmonic resonance conditions, is presented. It may be applied, for instance, to verify the performance of networks adopting suppressing coil (which is normally tuned on the fundamental frequency) or zero-sequence protection relays. A parametric analysis on typical MV distribution systems shows how it is possible to identify critical fault locations which may give rise to very high harmonic currents.

A fault current limiter

Abstract: An inductive fault current limiter 30 comprises a core 12 surrounded by a superconducting magnetic shield device 11 and a winding 14. The winding 14 is formed from a cable having at least one conducting means 72 which is surrounded by solid material 75 including electrical insulating means and means to confine the electric field within the cable when the fault current limiter 30 is in use. The superconductive shield device 11 includes appropriate cooling means. The solid material 75 of the cable may comprise inner and outer semiconductive layers which are separated by an electric insulating layer. The cable may have a number of coaxial conductors 72, 73, 74 which are each surrounded and separated by solid material layers 75, 76, 77. The conductor means 72, 73, 74 may be formed from conductive or superconductive material and the cable may include cooling channels to hold the conductors at the required temperature. The cooling means for the shield device 11 may be combined or separate from that possibly used for the cable. The voltage levels may be distributed across the cable's conductive elements and the outermost semiconductive layer may be earthed.

Test device for a fault current circuit breaker

Abstract: There is described a device for testing a fault current circuit breaker, which formed a summation current transformer (10) whose primary winding through the phase conductors (L, N) and whose secondary winding (11) are connected to a tripping relay (12). The residual current circuit breaker further comprises a switching mechanism (15) is unlatched by the tripping relay (12) upon occurrence of a fault current, so that the power conductors to contact points (L, N) situated (17, 18) are opened to change. The fault current protective switch is still a test circuit (19) associated with the simmuliert between a phase conductor (L) and neutral (N) an error current when the test contact (20) is closed, and a test resistor (22). The test circuit (19) is zugeorndet a timer (23) to which a predetermined time period after closing of said contact probes (20), an actuator (26, 39) is actuated, which causes the permanent, possibly irreversible turning off the fault current circuit breaker.

Apparatus for measuring line constant of nongrounding system line and apparatus for monitoring ground fault

Abstract: PROBLEM TO BE SOLVED: To early detect a ground fault current of a protecting range with high accuracy without being influenced by a ground fault outside the protecting range by measuring in an active state an element of a line generating a zero-phase current, a zero-phase voltage when no ground fault occurs as a line constant and operating with the use of the element. SOLUTION: A line constant operation means 13 calculates line constants Y, Yf from zero-phase currents I0 , I01 calculated by a zero-phase current detection means (zero-phase current transformer) 4, zero-phase voltages V0 , V01 detected by a zerophase voltage detection means 5 before and after a line is changed, and a reference voltage E. A ground fault current operation means 7 calculates a ground fault current Ig from the line constants Y, Yf , and a ground fault phase voltage formation means 9 compares the current in phase with the reference voltage E and obtains a phase voltage Eg with a zero component of a ground fault phase removed. Thereafter, a ground fault impedance operation means 10 calculates a ground fault impedance Zg from the phase voltage Eg , zero-phase voltage V0 and ground fault current Ig . A ground fault Judgment means 11 compares the impedance with a reference value and outputs a line interruption command signal, a warning signal, a measured value record control signal when the impendance is lower than the reference value.

Electrically stabilized thin film high temperature superconductor, useful as a fault current limiter, comprises a superconducting layer in interrupted contact with a metal substrate to avoid hot spots

Abstract: An electrically stabilized thin film high temperature superconductor (30), comprises a superconducting layer (32) in interrupted contact with an underlying flat metallic substrate (31). An Independent claim is also included for production of the thin film high temperature superconductor. Preferred Features: The superconducting layer (32) consists of YBCO and is locally separated from the metallic substrate (31) by a buffer layer (33) of yttrium-stabilized zirconia, CeO2 or Y2O3.

Computer modelling of superconductive fault current limiters

Abstract: Investigations are being carried out on the use of superconductors for fault current limiting applications. A number of computer programs are being developed to predict the behavior of different ‘resistive’ fault current limiter designs under a variety of fault conditions. The programs achieve solution by iterative methods based around real measured data rather than theoretical models in order to achieve accuracy at high current densities.

Using a fault detecting circuit for parallel connected DC/DC converters

Abstract: In applications that demand high power consumption, there is a trend to use several standard DC/DC power converters working in parallel. The goal of this work is to develop a fault detecting scheme for every individual module in such parallel system. Together with the fault detecting scheme, a control circuit is used in order to achieve a proper response of the system in the presence of faults. To evaluate the behavior of the fault detection scheme, simulation and laboratory tests were made with one single buck power converter. Experimental results are given that validate the scheme.

Static and monolithic current limiter and circuit-breaker component

Abstract: The present invention relates to a static and monolithic current limiter and circuit-breaker component including, between two terminals, a one-way conduction current limiter, a sensor of the voltage between the terminals, and a mechanism for inhibiting the conduction of the current limiter when the voltage sensed exceeds a given threshold.

Flux distribution of passive fault current limiter based on saturable core and permanent magnet

Abstract: From the point of view concerned with the development of the information, oriented functions in social activities, recently power consumption has rapidly increased. On the other hand, ability of power supply has not been increased to follow this increasing consumption, because it is difficult to construct new power generation plants. Therefore, reserve capacity of power supply is going to be decreased and power down has become a serious problem. To prevent the serious power down and to maintain a stable power supply, we had already proposed a passive fault current limiter using a permanent magnet with high coercive force, high remanent magnetic flux density and a ferrite core with high permeability, low saturated flux density compared to that of a permanent magnet. In this paper, the flux distribution of the limiter is investigated using the three dimensional finite element method.

Toroidal inductively coupled superconducting fault current limiter with interleaved windings

Abstract: The characteristics and performance of a small prototype inductively-coupled fault current limiter (FCL) are described. The FCL in question has an unusual toroidal geometry in which primary and secondary coils are interleaved to minimise leakage fields and leakage inductance and maximise the effective utilisation of superconducting material. The paper investigates the effect of winding configurations and geometry on the electromagnetic properties of the FCL. The construction of the prototype uses superconducting secondary coils made from double-sided YBCO thick film layers on ring shaped zirconia substrates. The primary windings were made of planar coils of copper wire. An interleaved winding structure produces a leakage inductance that is less than one-tenth of that obtained with an equivalent 'E' core transformer. Computed and measured leakage impedance are shown to be in good agreement. Transient and current limiting measurements demonstrate that the proposed FCL displays typical characteristics. The advantages of interleaved winding configurations are demonstrated directly by varying the degree of interleaving of the windings on the prototype FCL.

Characteristics and Possibilities of Superconducting FCLs Fabricated with High-Tc Tapes

Abstract: The current-limiting properties of high-Tc tapes were examined in order to investigate the possibility of using these tapes as superconducting fault current limiters. The short samples studied comprised two types of Bi-2223 tape having different sheath resistances, and two types of YBCO thin-film tape having different silver coating thicknesses on the YBCO surface. The relationships between the current- limiting performance of these samples and the characteristics of the tapes were clarified through experiments. Fault current limiter models were then fabricated with non-inductively wound high-Tc tapes, and their characteristics and current-limiting properties were evaluated.

On-line fault level measurement

Abstract: The fault level represents the maximum short circuit current that a power system causes to flow to the point of short circuit. Due to change of network configuration, the fault level at any point of the power system network changes accordingly. It is not practical to apply full short circuit on the system in order to determine the fault level. This paper describes scheme for continuous measuring of the fault level at any point of the power system network. This scheme is composed of an antiparallel thyristor pair. The thyristor current, which is controlled by the firing angle, can be used to perform the on-line fault level measurement. However, problems are associated with such measurement. These are mainly the complexity of the current waveform and its dependence on the system impedance. The effect of the system X/R ratio on the measurement is also analyzed.

Power distribution network incorporating a voltage support transformer and process of use

Abstract: A power distribution network including a voltage support transformer (1A,B) is disclosed which uses the fault current from a line (A or B) of the power distribution network in which a fault condition exists to support or stabilize the voltage across one or more other lines of the network connected to the same bus and seeing the same source impedance, to maintain the voltage in those lines substantially at the pre-fault levels. The voltage support or stabilization in the unfaulted line is based upon a current change due to the impedance change in the faulted line caused by the fault.

Discussion of "Fault-current limiter applications in medium- and high-voltage power distribution systems" [and reply]

Abstract: The author makes five comments on the paper by A.Y. Wu and Y. Yin (see ibid., vol.34, p.236-42, 1998). The author points out that there are no fault current limiters available for applications above 38 kV, discusses two sensing modes for current limiters, zero current crossings for fault currents, coordination between the current limiter and the phase overcurrent relays, and briefly mentions reactor bypass schemes. The original authors reply to the comments.

Fault current limiter using bulk oxides superconductors

Abstract: We study the limitation possibilities of bulk Bi high T c materials. For this we test these materials with a.c. or d.c. currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3 4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current.