Showing papers on "Fault current limiter published in 1996"

A new approach to on-line turn fault detection in AC motors

Abstract: Turn fault detection is based on the principal that symmetrical (unfaulted) motors powered by symmetrical multiphase voltage sources will have no negative sequence currents flowing in the leads. A turn-to-turn fault will break that symmetry and give rise to a negative sequence current which may then be used as a measure of fault severity or to initiate protective action such as a circuit breaker trip. A new way of looking at the effects of turn faults has been developed that improves sensitivity and speed while reducing the probability of misdetection, taking into account voltage balance, load or voltage variation and instrument errors. The method has been implemented on a PC and tested, in real time, on a specially prepared small motor. Reliable detection of one shorted turn out of 648 turns per phase (in a Y connected motor) was demonstrated with the fault indicator becoming fully developed in two cycles of line frequency after initiation of the fault.

Principle and characteristics of a fault current limiter with series compensation

Abstract: A power system fault current limiter with series compensation, which is composed of a compensation capacitor and a limiting reactor in series, is proposed. A solid-state switch connected in parallel with the capacitor controls either the ordinal series compensation or fault current limitation. A feasibility study of the current limiter by simulation analysis is presented and the effectiveness of the current limiter is evaluated from the viewpoints of transient stability improvement and device capacity. The current limiter is a useful protection device for large, high power transmission systems.

High Power DC Blocking Device for AC and Fault Current Grounding

Abstract: A high power DC blocking device is provided which blocks DC current, passes AC current, and limits the voltage across it under fault conditions A DC blocking capacitor is used to block the flow of DC current, while allowing the passage of normal AC currents A main bypass path includes switching devices which provide a low impedance path across the capacitor under fault conditions Auxiliary switching devices are used to connect a storage capacitor across the device at the initiation of a fault, thereby charging the storage capacitor to a stored voltage level before the main switching devices are fired After the fault passes, the auxiliary switching devices are fired once again to apply the stored voltage in the storage capacitor to the main switching devices to commutate them off The storage capacitor and auxiliary switching devices also form part of a voltage clamp circuit which dissipates inductive energy stored in a system to which the DC blocking device is connected Multiple backup firing circuits are provided which activate the low impedance bypass path in the event of failure of the main firing circuits or of the blocking device control system The effectiveness of the DC blocking device is continuously monitored using a DC current sensing circuit which is capable of distinguishing small DC currents in the presence of large AC currents

Accurate fault location and protection scheme for power cable using fault generated high frequency voltage transients

Abstract: A new technique for accurate fault location and protection of distribution cable is presented in the paper. A specially designed transient capturing unit is used to extract the fault generated high frequency voltage transient signals from the distribution cable system. The travelling time of the high frequency signal is used to determine the fault position. The scheme is insensitive to fault type, fault resistance, fault inception angle and system source configuration. Studies show that the proposed technique is able to offer a very high accuracy in both fault location and fault detection.

Thyristor controlled ground fault current limiting system for ungrounded power distribution systems

Abstract: A thyristor controlled ground fault current limiting system (TGCL) was proposed to prevent one-line ground fault current rises due to increased capacitance to ground. Basic components of the TGCL are a main ground fault current limiter, which rapidly adjusts a compensating reactor level for the capacitance to ground, and the TGCL's controller. Control is ensured by an in-phase control method for zero-phase sequence voltage and current. The method determines the direction of ground faults and the compensating reactor level. The fast control which can be realized shows the TGCL is a valuable protecting system for high ground fault current distribution systems.

Design and current-limiting simulation of magnetic-shield type superconducting fault current limiter with high Tc superconductors

Abstract: The continuous development of electric power utilities has led to the increase in the problems concerning fault currents. The use of fault current limiters, which suppress fault currents below a prescribed level, has been examined in many places. The authors have studied a superconducting fault current limiter that is based on the magnetic shielding effect of superconductors. In this paper, we derive a requirement for leading to a flux-jumping inside a ceramic superconductor at liquid nitrogen temperature, Next, two kinds of magnetic-shield type superconducting fault current limiters are designed, and their current-limiting simulations are tried using a computer.

Fault current limiter and alternating current circuit breaker

Abstract: A solid-state circuit breaker and current limiter for a load served by an alternating current source having a source impedance, the solid-state circuit breaker and current limiter comprising a thyristor bridge interposed between the alternating current source and the load, the thyristor bridge having four thyristor legs and four nodes, with a first node connected to the alternating current source, and a second node connected to the load. A coil is connected from a third node to a fourth node, the coil having an impedance of a value calculated to limit the current flowing therethrough to a predetermined value. Control means are connected to the thyristor legs for limiting the alternating current flow to the load under fault conditions to a predetermined level, and for gating the thyristor bridge under fault conditions to quickly reduce alternating current flowing therethrough to zero and thereafter to maintain the thyristor bridge in an electrically open condition preventing the alternating current from flowing therethrough for a predetermined period of time.

Fault powered fault indicator having timed reset

Abstract: A fault indicator is described having a winding disposed on a magnetic pole assembly. The winding delivers energy from a monitored conductor to circuitry of the fault indicator. A series-connected threshold device, such as a four layer bilateral diode or a zener diode, precludes a capacitor from charging during normal current flow in the monitored conductor. The series-connected threshold device, however, breaks down when a fault current flows in the monitored conductor. After break down, the fault current charges the capacitor. A shunt-connected threshold device, such as a zener diode, limits the voltage developed across the capacitor. After its charging phase, the capacitor drives a multivibrator which actuates an LCD, displaying the occurrence of the fault current to an operator. A series-connected threshold device shuts the LCD off when the voltage across the capacitor drops to a sufficiently low level. The arrangement of these electrical components allows the operator to accurately define the duration of time in which the LCD displays the occurrence of the fault current in the monitored conductor.

High temperature superconducting fault current limiter for utility applications

Abstract: One of the most near term High Temperature Superconductor (HTS) applications is the Fault Current Limiter (FCL). It is a device that can provide significant energy benefits and cost savings for the power utility industry. This is especially important when the industry is facing deregulation. The Lockheed Martin team, which also includes ASC, SCE, and LANL, has been developing a 2.4 kV, 2.2 kA HTS FCL since October 1993. This two-year Department of Energy (DoE) cost sharing program is for developing HTS power utility applications. In this paper, a general review of what a FCL is will first be given, followed by a brief description of its requirement definition and underlying working principle. A survey of the recent worldwide progress made in the development of this new utility device will then be given. Description of the salient features of the LMC FCL will be described and compared to other competing FCL concepts. Finally, a status report of this two year program is given and future development plan outlined.

The analysis of the fault currents according to core saturation and fault angles in an inductive high-Tc superconducting fault current limiter

Abstract: In this paper, we investigate the fault currents in an inductive high-Tc superconducting fault current limiter (SFCL). The currents can cause serious damage to the reliability and stability of the power system. To analyze the transient fault characteristics of the SFCL, we fabricated an inductive high-Tc SFCL and tested it under different fault conditions. To simulate a fault condition, a fault angle controller was connected to a load. As the firing angle of the triac in the fault angle controller was controlled, various angles of the fault instant can be selected. An important parameter for the design and the fabrication of the SFCL is the reduction of the fault currents. If abnormally high currents due to low impedance of SFCL do not occur in the network with SFCL, the currents flowing under fault conditions can be limited to a desired value within one cycle. The fault current reduction depends on saturation, normal zone propagation velocity, turns ratio, and the fault angle (the instant of the fault occurrence within a cycle).

Fault current recognition circuitry

Abstract: A circuitry for recognising a fault or leakage current in a supply line (REF) of an electronic circuit contains a current source (IQ; +IG, -IQ) designed for a maximum admissible fault or leakage current (+/- Imax). The current source is supplied by an auxiliary voltage source (UH). The potential in the supply line (REF) when the leakage current causes the supply voltage (UB) to be switched off is determined and evaluated by a potential monitor (PM1).

Transformer protective apparatus having semiconductor and mechanical bypass means

Abstract: A power converter protective apparatus for protecting an AC-DC converter against an excess fault current by preventing the fault current of a power system from flowing into the AC-DC converter. The protective apparatus comprises a series transformer, whose primary winding is connected in series with a power system and whose secondary winding is connected to a voltage-type AC-DC converter, first current bypass means of a normally open-type connected in parallel with the primary winding, a current transformer for detecting a fault current in the power system, and a control unit for outputting a bypass control signal to the first current bypass means when the current transformer detects the fault current, whereby when the fault in the power system is detected, a fault current flowing through the primary winding is bypassed by the first current bypass means.

Method of locating a fault in an electric power cable

Abstract: A method of pinpointing the location between manholes of a fault in an electrical cable typically buried underground in an urban environment, the fault being caused by an insulation defect which may be broken down by a high voltage includes the steps of applying the voltage to break down the fault insulation defect to induce a transient fault pulse on the cable on both sides of the fault traveling away from the fault. By the use of a ferrite type transformer coupler producing an output voltage, the direction of the transient fault pulse is determined by relating the polarity of the output voltage to the initial high voltage pulse which was applied.

Recovery time of superconducting non-inductive reactor type fault current limiter

Abstract: A superconducting fault current limiting device for electric power systems has been investigated to determine its feasibility. A noninductive reactor type fault current limiter has been constructed using a metal superconductor. Two bifilar wound solenoids were connected in antiparallel or antiseries. On each connection, a fault current limiting test was performed by suddenly short-circuiting a resistive load. The recovery (normal-to-superconductive state transition) time after the current limiting mode has been studied using a small-scale model of a fault current limiter for an LV power distribution line. The results reveal that the current limiter could be operated under a repetitive fault current accident which was removed within a few cycles of the limiting mode. The recovery time is a function of the dissipated energy under current limiting mode. Test results are presented.

Static and monolithic current limiter and circuit-breaker

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.

A fault control system using solid state circuit breakers and high temperature superconducting fault current limiters

Abstract: High voltage power systems and loads can suffer from extreme peak currents during load fault conditions. Because conventional circuit breakers require several cycles and many milliseconds to open, the large amount of energy deposited into the load during this fault can be destructive to the load as well as disruptive to the power system. A new method of combining a high temperature superconducting fault current limiter in conjunction with a solid-state circuit breaker has been developed to reduce the potential damage of a fault by limiting fault power and energy.

Delayed-action fault current of differential current circuit-breaker

Abstract: A fault of differential current circuit-breaker both hereinafter referred to as a circuit-breaker, which acts with its summation current transformer (1) and its triggering circuit on switch contacts, in which the triggering circuit has a full-wave rectifier circuit (6) with a central tapping and an RC component (7) to form a charging time constant (R1 x C3) between the secondary winding (2, 3) of the summation current transformer (1) and the triggering winding (4) of a trigger (5), in which the RC component (7) is limited in its charging voltage by a voltage limiter (V5). A further RC component (8) is to be connected in parallel with the first RC component (7) for its connection to the secondary winding (2, 3) of the summation current transformer (1). The RC component (7) is designed so that the charging time constant (R2 x C4) of the other RC component (8) is smaller than that of the first (7) so that triggering does not occur at a fault current flow duration of low amplitude of the order of five times the rated fault current.

Superconducting fault current limiter for utility applications

Abstract: The capacity of an electric power system to supply high short circuit current is an essential characteristic of a robust and stable system.This capability is necessary for the system to meet large or new load demands without excessive voltage or frequency drops. However, high current surges caused by short circuits, if not handled by appropriately rated equipment can result in severe damage to utility and user installations with serious economic and safety consequences. Traditionally, large resistors or series reactors have been used to limit short circuit currents to safe levels. Unfortunately these brute-force fixes limit current not only during disturbances, but also under normal operating conditions causing unnecessary losses and voltage drops, thus weakening the system. To date, utilities have been lacking an affordable fault current limiter which can not only automatically detect and limit fault currents, but also intelligently disconnect itself anytime current flows do not exceed those required for normal operation of the loads. By reducing fault current to a desired level lower than those reached by uncontrolled current surges, a utility can potentially achieve: significant savings due to deferred or avoided equipment upgrades; increased reliability as expensive transmission and distribution will be less stressed; and increased powermore » quality. These benefits are directly in line with the today`s utility industry`s goal of enhancing their competitive position under a deregulated market in the immediate future.« less

A passive current limiter for power semiconductor protection

Abstract: Static power converters are being used increasingly in power system applications. The power semiconductor switches within these converter systems accommodate power system fault overvoltages. Significant cost reductions can be attained by reducing the magnitude of power system fault currents. In this paper, the authors propose the use of a novel passive current limiter to accomplish this task. The limiter consists of two magnetic devices connected in series and in magnetic counter opposition to each other. Each magnetic device consists of three slices of NdFeB permanent magnet material sandwiched between the three end poles of two ferrite E cores. Experimental and finite element results are presented and are found to be in good agreement with each other. The need for 3D modeling in the future is demonstrated. The operating characteristics of the current limiter are experimentally verified using a scaled down version of a power system.

AC loss reduction of a 6.6 kV superconducting fault current limiter

Abstract: The authors have been investigating a 6.6 kV superconducting fault current limiter (SCFCL) for use in power distribution systems. For practical application, heat load at 4.2 K must be reduced to a level which can be compensated by a small refrigerator. This paper describes AC loss reduction of a SCFCL coil, which is comprised of a conductor and junctions. The conductor is a cable of double-twisted multi-filament NbTi strands in a high-resistivity CuNi matrix. The filament diameter in strands and the filament twist pitch were reduced for AC loss reduction. Current junctions made of copper generate eddy current loss because an alternating magnetic field is applied on them by the conductor. It was confirmed experimentally that cylindrical-shaped junctions effectively reduced the loss. A total coil loss of 0.8 W at 1 kA has been achieved, which value is sufficiently low for the development of a closed cryostat of superconducting fault current limiter compensated by a small refrigerator.

Limitations of current limiting protectors for expansion of electrical distribution systems

Abstract: Application of current limiting protectors (CLPs) has been recommended in the existing literature to retain underrated medium voltage circuit breakers of lower short-circuit ratings in service, when the distribution systems are expanded and the short-circuit currents increase. However, the existing published literature does not describe the limitations of CLPs from system separation and loss of protective device coordination conditions, nor does it provide an analysis of short-circuit duties of medium voltage circuit breakers used with CLPs. The paper shows how these evaluations can be carried out. Considerations of high cost of replacements, the far greater loss of production due to lack of coordination and availability of a proven alternate solution should be included in an informed decision to use CLPs. 'CLP', 'triggered fault current limiter (TCL)', 'CLIP', and 'I/sub s/ Limiter' are synonymous.

Current limiter for electrical transmission/distribution protection systems

Abstract: A current limiter arrangement particularly adapted to be positioned at a substation of an electrical power system for limiting the fault current for a predetermined period of time to permit protective devices positioned downstream in the network to clear the fault. If the fault is not cleared and the fault persists for a predetermined period of time the current limiting arrangement acts as a circuit breaker to open the load circuit. The arrangement includes an SCR bridge having a superconducting coil connected across two nodes. A novel gate pulse firing circuit generates two pulses per ac cycle for application to the gates of the SCR's of the bridge at 90° and 270° of each 360° cycle and is ON at all times to provide for prompt dc charging of the super conducting coil with no ac load current and non-fault conduction of ac current at less than the maximum current limit. The gate pulse firing circuit by staying ON at all times also provides current limiting under the fault condition and recovery of the dc superconducting coil current after the fault is cleared by a downstream protective device and is turned OFF only after a predetermined period of time for opening of the load circuit.

Computer controlled fault current limiter (ccfcl)

Abstract: A computer-controlled fault-current limiter is proposed. The design of the CCFCL provides an effective reduction in the short-circuit current during the fault. It is controlled by a microprocessor which guaranties an accurate adjustment of the short-circuit impedance to be inserted under fault. The transient behavior of the CCFCL is studied by the EMTP. In general, the CCFCL is inexpensive, reliable and can be modified to accommodate future changes or expansions.

Monolithic and static current limiter and circuit breaker

Abstract: The static monolithic current limiter and circuit breaker comprises two terminals (A,K), between which there is a uni-directional current limiter (1), and a detector (2) sensing the voltage between the terminals. A switch device (3) is arranged to inhibit conduction through the current limiter when the detected voltage exceeds a given threshold. The voltage detector is formed by a potential divider (2) connected between the terminals, with its mid-point providing the output indication. This potential divider may be constructed from two MOS transistors with N-type depletion channels connected in series. The current limiter may also be an MOS transistor with an N-type depletion channel of vertical format. Alternatively this limiter may be a vertical IGBT type transistor with a depletion channel, and in yet another configuration may be a bipolar transistor used in conjunction with an N-type depletion MOS transistor.

Method for short-circuit current limiting on an electrical power transmission line and configuration for short-circuit limiting

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.

Quench current degradation in superconducting coil for 6.6 kV/2 kA fault current limiter

Abstract: A 6.6 kV/2 kA class fault current limiter that consists of noninductive superconducting windings was developed and tested. The limiter can deliver continuous power at 2 kArms and limit fault current of more than 20 kA to 4 kA in 6 kV. The limiter recovers to the superconducting state within a few seconds and can perform a fault current limiting operation in 60 seconds after the last limiting operation. After high-voltage operation, however, the quench current of the limiter dropped significantly. This quench current degradation is related to the coil bobbin strain due to helium pressure raised by large ohmic heating in quenching. The degradation is a fatal problem for a fault current limited if the quench current falls below the operating current because the limiter cannot revert to the normal operation. High Young's modulus bobbin is effective to remove the coil degradation. The authors have obtained a fault current limiter without any degradation after repeated limiting operations.

Estimating system fault level from naturally occurring disturbances

Abstract: An essential requirement in all aspects of power system design is an evaluation of the fault levels at a particular switching or control point on the network. This evaluation is covered in IEC 909. The fault level can vary according to the supply configuration and load, particularly where rotating plant is involved. Little work has been done in the past to justify the calculated values of circuit fault levels and there is some belief that the values obtained could be unduly pessimistic. At present there is no easy method of measuring the fault level at a particular point on a network. In theory an assessment of the supply impedance can be made from naturally occurring disturbances. Here, the author describes an instrument based on this principle which is being developed at EA Technology, which uses power system disturbances to make an estimate of both the source impedance, and also the contribution from induction motors downstream of the measuring point.

Coil and HTS Development for Fault Current Limiters

Abstract: Fault current limiters are being developed to limit peak currents in transmission and distribution systems. The authors company* has developed a large, robust, high temperature superconducting (HTS) coil for this application. The development included the design of a composite superconductor and a coil configuration specifically for high transient currents and the resulting high transient forces. The results of the testing of the coil including critical current, transient impedance and ac loss data will be described.

Application of Hi-Tc superconducting current fault limiters to utility distribution networks

Abstract: A new classification of superconducting current fault limiter (SCFL) is described which is a non-quenching, variable-inductance-mode VIM current limiter with characteristics matched to utility distribution line parameters. A major application of this device is for replacement of fixed-inductance air-core reactors used in impedance and short-circuit levels from sub-transmission to distribution. The secondary application of the SCFL is for protection of distribution substation transformers in the 5--40 MVA range, as a replacement for current limiting fuses and air-blast circuit breakers. The SCFL devices have the unique characteristic of producing minimal or no transient recovery voltage (TRV) as is typical of conventional interruption technologies.