Abstract: In a three terminal power line current differential protection system, all three phase current values (IA, IB and IC) are obtained from all three terminals. The current values for each phase are processed in three successive processing operations, using in turn the current values from each terminal as local current values and the combination of the other two terminal current values in each case as the remote current values. The resulting local and remote current values are then processed against preselected values which establish a restrain region in the current ratio (alpha) plane. Current values for each set of local and combined remote currents which result in the ratio being within the restrain region result in a blocking signal while current values which result in a ratio outside of the region result in a tripping signal. If the outputs of the three processing operations agree, then that signal is the system output.

Abstract: A modem with built-in transmission line diagnostic capability is presented. Said built-in line diagnostics are capable of determining said transmission line's length and detecting the presence of any bridge taps. Said built-in diagnostics have an advantage of not requiring any specialized or expensive hardware and can be added to an existing modem without significant redesign work.

Abstract: The method of correcting measurements is intended to limit the risk of unnecessary tripping of a differential phase current protection system that computes the vector sum of the currents of an area to determine the differential current between the inputs and outputs of said area in the course of regular tests. It is based on a statistical balancing method using measured current vectors each obtained from a measurement of the real current vector supplied at the time of each test by a current transformer, and it uses at the time of at least one test an iterative convergence algorithm for determining from the erroneous differential current vector formed by the sum of the measured current vectors the correction vector to be applied to each measured current vector in order to correct statistically the erroneous differential current vector.

Abstract: An AC power interruption detection system is provided which compares an AC signal with a phased AC reference signal to determine the presence or absence of an AC power signal. By comparing the AC power signal with a phased reference signal, power interruption detection occurs within a predetermined minimum time frame, for example, with ½ cycle. In exemplary embodiments, the detection system includes AC power signal frequency multiplying circuitry to improve speed and performance. In other exemplary embodiments, the detection system includes threshold detection circuitry to detect undervoltage (e.g., brownout) and/or overvoltage (e.g., spike) conditions of the AC power.

Abstract: The present invention relates to a method for locating a fault on a power transmission line which is series-compensated with capacitors. The site of the fault is determined with the aid of measured currents and voltages at one of the two ends of the power transmission line before and after the occurrence of the fault and a calculating algorithm based on impedance models of the power transmission line before and after the occurrence of the fault.

Abstract: In a power line current differential protection system, all three phase current values (IA, IB and IC) are obtained from both the local end and the remote end of a power transmission line. The magnitude of the ratio of the remote current values to the local current values are calculated. Also, the angle difference between the local and the remote current values for each phase are calculated. Comparison elements then compare the ratio and angle values against preselected values which establish a restrain region in the current ratio plane. Current values which result in the ratio being within the region do not result in a tripping signal for the circuit breaker on the power transmission line, while current values which result in a ratio outside of the region result in a tripping of the circuit breaker. Similar circuitry is used for negative sequence current quantities, with the negative sequence preselected values being set substantially lower to produce a more sensitive response to possible faults in the line.

Abstract: An apparatus and method for detecting a short in a load which receives power from a transformer having a primary winding and a secondary winding with the load being connected to the secondary winding. The apparatus has a waveform conversion circuit, a phase detector circuit and a filter. The waveform conversion circuit converts voltage and current signals that represent the voltage and current, respectively, of the primary winding into generally squarewave voltage and current signals, respectively. The phase detector circuit outputs a control signal having a first state when the generally squarewave voltage and current signals are substantially in phase and a second state when there is a difference in phase between the generally squarewave voltage and current signals that is greater than a predetermined phase difference. The filter filters the control signal outputted to the phase detector circuit.

Abstract: A short-circuit distance relay has a short-circuit distance relay element that calculates a fault impedance from voltage and current which are introduced from a power system and that compares the fault impedance with a set impedance and uses the fault impedance comparison result within its protection zone. It calculates the amplitudes of the phase-to-phase differences of these voltage amplitudes and a sensitivity constant Vk.

Abstract: The present invention concerns a high throughput electrorotation chip having an array of electrorotation units and methods of use thereof. To make the high throughput electrorotation chip, a plurality of electrorotation units (EU) are fabricated on a substrate or support and each EU is capable of producing a rotating electric field upon the application of an appropriate electrical signal. Exemplary embodiments include a row-column configuration of EUs having four electrode elements realized through two conductive-layers. The electrode elements may be linear, concave, or convex. Thin plates having one or multiple holes are bound to high-throughput electrorotation chips to form assay chambers having one or multiple wells. Particles can be introduced to the wells and electrorotation measurements can be performed on the particles.

Abstract: A test system for a evaluating a digital signal link includes a data signal generator, a data signal receiver, a digital signal link to be tested and a test interference signal injection (TISI) network connected as part of the digital signal link. The TISI network includes a data signal input port for receiving digital data signals generated by the data signal generator, a data signal output port for providing the digital data signals to the data signal receiver, and a controlled impedance data signal path carrying the digital data signals between the data signal input port and the data signal output port. An interference signal input port receives interference signals over a range of frequencies from an interference signal generator. One or more directional couplers directionally couple the interference signals into the data signal path toward either the data signal output port or the data signal input port at an impedance that substantially matches the impedance of the digital signal link.

Abstract: Electric arc monitoring is effected by exploiting the discovery that electric arcs are fractal phenomena in that all essential information that signifies an “arc” is contained in each fractal subset. The fractal subsets are logarithmically distributed over the arc spectrum. Monitoring of arcs is most advantageously effected on a fractal subset of low logarithmic order where the amplitude is higher pursuant to the 1/f characteristic of electric arcs, where cross-induction among neighboring circuits is lower, and where travel between the arc and the arc signature pickup is longer that at the high frequency customary for electric arc detection. Fractal subset information reduces the danger of false alarms. Arc signature portions may be processed in out of phase paths or treated as modulated carriers for monitoring.

Abstract: A method for internal fault detection comprises determining whether a local current on a local transmission line terminal exceeds a variable first fault level threshold; if so, determining whether a remote current on a remote transmission line terminal exceeds a variable second fault level threshold; and if so, comparing phases of the local and remote currents. The method can include determining local and remote uncertainty factors for the local and remote currents and using the uncertainty factors to adjust the variable thresholds. The method can further include measuring a current on a local transmission line terminal and bandpass filtering the measured current to obtain the local current.

Abstract: In a measurement system for electric disturbances in a metalen-capsulated high-voltage switchgear having at least one measurement probe for each phase for decoupling of electromagnetic interference signals, both the interference signals and the useful voltage are scanned by the same measurement probe in each phase, and both are made accessible, separately from one another, at a filter arrangement.

Abstract: During a first test phase, the device, after detecting the presence of a load, enables the nature of the load to be identified. For this, a control circuit connects the load to an AC main power system, while limiting the current in the load. The device measures several tens of samples of instantaneous values of the load voltage and current during a limited number of half-waves of an AC sine signal and determines the load impedance and the current/voltage phase shift. These characteristics, possibly with complementary parameters derived from the voltage and current measurements, enable the nature of the load to be identified. During a second test phase, the control circuit applies pulses limited in voltage to the load and detects possible short-circuit, differential or overload faults.

Abstract: A method for producing signals indicating faulty loops in a polyphase electrical power supply network using impedance excitation, in which, after checking for ground faults, by comparing the amounts of the impedance values obtained during the impedance excitation, the signals indicating the faulty loops are formed. In order to eliminate with great certainty all the loops that are actually not faulty, in spite of initial excitation, in ascertaining loops which are exclusively free of ground faults, the actually faulty loops are determined by comparing calculated, virtual impedances, to impedances measured during the impedance excitation; in ascertaining at least one loop having ground faults, fault-free phase-to-ground loops are recognized and eliminated by comparing the amounts of the virtual impedance values, formed with respect to the phase-to-ground loops detected as faulty, to the smallest virtual impedance value, and fault-free phase-to-ground loops are recognized and eliminated.

Abstract: The invention concerns a method for generating a fault indication signal in the event of a fault in an electric power supply network being monitored through a neural network arrangement. In order to rapidly generate fault indication signals capable of distinguishing between permanent metal contact short-circuits and short circuits due to arcing, a neural network (26) is used for each phase of the power supply network being monitored. Each neural network (26) is taught, while being coached through simulated voltages (U.sub.R (t)) of each phase during short-circuits caused by metal contact and arcing, so that the output signal (S) assumes a pre-defined value (0.8) for arcing and another pre-defined value (0.1) for a metal contact short-circuit. At the same time, the sequentially sampled normalized values (U.sub.Rn1 (t) through U.sub.Rn20 (t)) of the respective phase voltages (R.sub.

Abstract: Arcing faults in an ac current are detected by apparatus which is responsive to a predetermined randomness in step increases in the current to eliminate false tripping caused by regularly occurring discontinuities produced by loads such as dimmers. A signal conditioner generates a bandwidth limited di/dt signal having pulses produced by the step increases in current. In one embodiment, a first tracking circuit tracks the envelope of the di/dt signal with a first time constant. A second tracking circuit also tracks the di/dt envelope, but with a second, shorter time constant. An arcing fault is indicated if the second tracking signal falls to a predetermined fraction of the fist tracking signal. This circuit may be used alone to detect arcing faults or to increase the sensitivity to arcing faults over dimmers of a circuit which responds to a time attenuated integrated valve of the pulses in the di/dt signal.

Abstract: A digital decaying current offset correction method and apparatus, in one aspect, separates the requirements of detecting fault existence from the requirements of detecting fault location. Once the decaying offset removal routine is initiated, current and voltage are sampled and, for each current and voltage sample, current and voltage phasors are generated. The current phasor values, which are not offset corrected, may be used to determine whether to trip a breaker. Once the breaker is tripped, the decaying offsets are removed from the current phasors. The offset corrected current phasors are then used to locate the fault.

Abstract: A quadrilateral characteristic relay system for determining a fault associated with a multiple-phase electric power transmission system is disclosed. The system dynamically adapts one line of the quadrilateral trip region to account for the interaction of load current and fault resistance. As a result of the adaptation, the system exhibits better overreach and underreach performance characteristics. The system employs impedance and voltage plane quadrilateral characteristics using negative sequence current as a proxy for fault current. In the voltage plane, the fault determination is made through a series of comparisons, avoiding computationally inefficient mathematical divisions.

Abstract: A method of and an apparatus for determining an electric wiring state, having the steps of: feeding at least one pulse voltage signal into one of two lines short-circuited at their two source portions; detecting the pulse voltage signal at two end portions corresponding to the two source portions; and discriminating wiring state between the two source portions and the corresponding two end portions upon a comparison of polarities between the fed pulse voltage signal and the detected signal.

Abstract: A process for generating a direction signal indicating the direction of a short-circuit current in a power transmission line to be monitored. To reliably produce a direction signal even in the event of a short-circuit occurring in the proximity of the control point, each derived current and voltage signal (J.sub.R (t)) is separately sampled and normalized to obtain different normalized sample values (J.sub.Rn). Taking the triggering reference values (S.sub.n) into account, difference values (.DELTA.i.sub.R (t), .DELTA.i.sub.R (t-1), .DELTA.i.sub.R (t-2), .DELTA.i.sub.R (t-3)) are formed. The difference values (.DELTA.i.sub.R (t), .DELTA.i.sub.R (t-1), .DELTA.i.sub.R (t-2), .DELTA.i.sub.R (t-3)) of a series (S.sub.iR) are supplied to different input neurons of a suitably trained neural network successively and simultaneously with the difference values corresponding to the same times of the other series (S.sub.iS, S.sub.iT, S.sub.uR, S.sub.uT).

Abstract: A system for automatically detecting whether a power converter or inverter is correctly connected to a three-phase AC power source consisting of first, second, and third phases, the system comprising: a zero-crossing comparator (1) for determining whether the phase of the first-phase voltage (current) is in a positive half cycle or a negative half cycle and generating a first discrimination signal (C.sub.U); a zero-crossing comparator (2, 3) for determining whether the phase of the second- or third-phase voltages (current) is in a positive half cycle or a negative half cycle and generating a second discrimination signal (C.sub.V or C.sub.W); and a D-type flip-flop (5) which detects, in response to the first discrimination signal, that the second discrimination signal is in a predetermined half cycle.

Abstract: When a fault in an energized power distribution cable flashes over, the surge draws charge from both sides of the line. The fault thus produces a pair of current surges that propagate from the fault in opposite directions along the line. These oppositely-directed current surges create pulsed electromagnetic fields of different directions which, in turn, induce voltages of different polarities in a receiving antenna positioned along the line. The polarity of the first such voltage pulse induced in the antenna indicates the direction from the antenna to the fault. In one embodiment, the line is repeatedly "thumped," causing flashovers to recur at the fault. By moving the antenna along the line until the polarity of the initial received pulse inverts, the precise location of the fault can be determined.

Abstract: A method and a device for measuring compensation balance and imbalance in an electrical supply network having a balancing coil. An auxiliary measurement signal is injected into the network's neutral circuit, changes in the homopolar voltage induced by the auxiliary signal injection are measured, and an impedance measurement is obtained by comparing the changes in the hompolar voltage with the injected auxiliary measurement signal, in terms of both amplitude and phase. A parallel current may advantageously be injected into the neutral circuit at the secondary winding of a homopolar transformer placed in the neutral coil.

Abstract: A transmitting box is connected to a first electrical outlet in a building. The phase of the first electrical outlet is used as the reference phase. The transmitter box senses each of the zero-cross-overs of the reference phase and injects a data packet of the data carrier frequency at each zero-cross-over. A receiving box is connected to a second electrical outlet in the building. The second electrical outlet has an unknown phase which may be different from the reference phase. The receiver box receives each data packet and senses each phase zero-cross-over of the unknown phase. The receiver box uses the time between each reception of a data packet and each detection of an unknown phase zero-cross-over to determine the phase angle of the unknown phase relative to the reference phase.

Abstract: A method and a device, after a fault has occurred in a power network, for measuring and recreating the phase currents I.sub.B prior to the occurrence of the fault by determining continuously, starting from sampled measured values of the phase currents up to the time of the fault for each phase, the amplitude I and the phase angle .phi. of the phase currents based on two consecutive sampled measured values, whereupon a comparison is made between the last determined value I.sub.k obtained and the rated current I.sub.n of the power network. If I.sub.k is greater than I.sub.n, it is considered that a fault has occurred and the phase currents prior to the fault are indicated as I.sub.B =I.sub.k-1 .multidot.sin (.phi..sub.k-1 +.omega.(t-t.sub.k-1)).

Abstract: A method of locating a fault point in a parallel two-circuit transmission line in an n-terminal system. When a single fault occurs at one place in one circuit of the transmission line and when a multiple fault occurs at the same place in the two circuits, a distance to the fault may be calculated by the method of this invention.

Abstract: A fault location system comprises voltage/current transducers 10A, 10B located at terminals A and B, respectively; digital relays 12A and 12B respectively coupled to transducer blocks 10A and 10B; and a fault location estimation processor 14, which may comprise a substation controller at substation S.sub.A or substation S.sub.B, a relay at A or B, a stand alone computer at A or B, or a computer at a central location. The digital relays receive analog voltage and current signals (V.sub.A, I.sub.A, V.sub.B, I.sub.B) from the respective transducers and output digital phasor or oscillographic data to the fault location estimation block. The fault location estimation block is programmed to provide the fault location parameter m. The fault location estimation provided by the inventive technique is unaffected by the fault resistance, load current, mutual coupling effects from a parallel line, uncertainties in zero sequence values, shunt elements, and X/R characteristic of the system.

Abstract: A method and a device for determining the fault current which occurs in case of a fault through a short circuit between phases or from phase/phases to ground. A measure of the fault current can be obtained by a linear combination of the sum of measured current samples for each phase at two adjacent points in time and in which each of these sample values is multiplied by a coefficient which is chosen such that the fault current gets into phase with the positive- and negative-sequence current changes.

Abstract: The invention is directed to an arrangement for monitoring an electric consumer in a motor vehicle. The consumer can be actuated by at least one pulse-shaped control signal formed by a control unit with this actuation taking place via a switching device. This arrangement includes a device for detecting electric variables in the region of the consumer and a device for comparing these variables to pregiven limit values as well as a device for recognizing a fault on the basis of this comparison. The device for recognizing faults evaluates the comparison result for recognizing a fault condition pursuant to the actuating state of the electric consumer.

Abstract: The relay includes means for obtaining current and voltage samples on the power transmission line for a particular possible fault type. The current sample is multiplied by the replica impedance of the power transmission line, while the voltage sample is multiplied by a polarizing voltage to provide a first complex expression having a real portion and an imaginary portion. The product of the current sample and the replica impedance is multiplied by the polarizing voltage to produce a second complex expression having a real portion and an imaginary portion. The real portion of the first complex expression is then divided by the real portion of the second complex expression to produce a scale value m which is compared against known reference scale values for each zone, so as to determine underimpedance conditions in any one of the zones.

Abstract: The operation of energized substation circuit breakers in electrical power distribution systems is directly monitored. For each circuit breaker in a multi-phase breaker arrangement, the flow of electrical current is sensed. A signal is then formed for each phase representative of the sensed current flow. The signals so formed for the multi-phases are combined into a composite waveform for monitoring and diagnostic purposes. In the composite waveform, the signal for each phase of the circuit breaker is identifiable by its time relationship to others and by a distinctive voltage level.

Abstract: In order to detect if there is a fault in a cable (6), three signals are applied to the cable (6) by a suitable transmitter (FIG. 1). Two of the signals are of high frequency and the other signal is of low frequency equal to an integer multiple of the difference between the frequencies of the high frequency signals. Aerials (10a, 10b) of a receiver (FIG. 2) detect the high frequency signals and the receiver processes those high frequency signals to determine a frequency signal. This is then compared in a comparison circuit (31) with the low frequency signal detected by ground probes (22,23) of the receiver (FIG. 2). At a fault in the cable (6), e.g. where the outer insulation is damaged, the conductor of the cable (6) is shorted to ground and this causes a change in a phase between the signals. Thus by moving the receiver along the cable (6), there will be a change in place at or adjacent the fault which will be detected by the receiver (FIG. 2) allowing the fault to be located.

Abstract: A method for determining the spacial relationship between concealed elongated conductors wherein a test signal is coupled to a first concealed conductor and conductively coupled to a second adjacent concealed conductor. The relative direction of the current of the test signal on the second conductor is measured on opposite sides of the first conductor. An indication of the relative directions of the current of the test signal on opposite sides of the first conductor can be used to determine if the two conductors are separated or in contact with each other. If the relative direction of the test signal radiated from the second conductor is the same on opposite sides of the first conductor, then the two conductors are separated from each other. If the relative direction of the test signal radiated from the second conductor is opposite on opposite sides of the first conductor, then the two conductors are in contact with each other.

Abstract: A digital isolation monitor comprises a signal processor operating in conjunction with a measuring circuit to perform a first no-load measurement and a second load measurement of a zero sequence signal delivery by a toroid of a differential transformer, followed by synchronous demodulation, A microcontroller computes the tangent of the angle of phase difference introduced by the toroid by computing the relationship between the load and no-load components, and determines the true values of the leakage resistance and stray capacitance of the power system.

Abstract: A system for detecting an arcing fault in a telephone central office DC power distribution conductor repeatedly measures the current flow in the distribution line, as with an inductive coupling, and derives a Fourier transform analysis spectrum from such measurements. The power values at intervals across the frequency spectrum are compared with recorded threshold template values encompassing the spectrum typical of an arcing event and an alarm condition is established when such threshold levels are exceeded.

Abstract: In order to detect interlamination shorts (8 ) in the case of laminated core stacks, the core stack (1) is magnetized with an auxiliary winding. The iron surface (15) is scanned with a measuring coil arrangement (5) comprising two electrically separated, mechanically interlinked coils (6, 7). The output signals from the coils are compared with each other in a downstream measuring instrument (9); in the case of an interlamination short, the fault current through the short-circuited laminations will induce in the coils different, phase-shifted voltages which make it possible to infer the position and size of the interlamination shorts.

Abstract: A variable speed, constant frequency aircraft power system uses current sensing diodes to rectify the power generator output. The current flow through pairs of diodes is compared to generate phase currents to detect feeder faults.

Abstract: A method of and apparatus for the detection of insulation deterioration in an electrical power supply system utilizes the detection of a progressive wave generated by a corona discharge or partial discharge due to such insulation deterioration. Sensing of said progressive wave may be effected by an apparatus comprising: a first coil having two primary windings, wound with the same number of turns and in the same direction, and a secondary winding, the primary and secondary windings being wound on a core whose magnetomotive force and magnetic flux density are roughly proportional to each other; a second coil composed of a primary winding and a secondary winding both wound on a core whose magnetomotive force and magnetic flux density are roughly proportional to each other; and an impedance circuit.

Abstract: A device for determining the location of a fault at a fault position (F) on a power transmission line between two stations (P, Q), and in which the power transmission line has an unknown conduction impedance (Z.sub.PQ), wherein, at one of the stations (P), capacitive voltage measuring transformers measure the phase voltage (U.sub.PM) and the phase currents (I.sub.P) or changes in the phase currents (.DELTA.I.sub.P) are measured on the occurrence of a fault. The phase voltage, phase currents or changes in the phase currents are low pass filtered; and the filtered phase voltage, phase currents or the change in the phase currents are converted from an analog to instantaneous digitized phase voltage, phase currents or changes in phase current values, respectively.The fault distance .alpha. and a value of an apparent fault resistance R.sub.F at the fault location are calculated, using linear regression, on the basis of the relationship:U.sub.PM =.alpha.Z.sub.PQ I.sub.P +R.sub.F I.sub.P +.DELTA.U.sub.CVT ;where .

Abstract: A system and method is disclosed for detecting an abnormality in a network for distributing or transmitting electric power at a predetermined fundamental frequency. The system produces a signal representing the fundamental frequency and another signal representing a harmonic current occurring in the network. The phasor relation between the fundamental voltage and harmonic current representing signal are compared. The system produces a signal indicating the occurrence of a high impedance fault in response to a predetermined change in the compared phasor relationship. Embodiments are disclosed utilizing expression of signals within the network in polar coordinates, as well as embodiments utilizing signals expressed in rectangular coordinates. Such embodiments include circuitry for detecting zero crossing phenomena, as well as circuitry for producing representation of signal products.

Abstract: In order to test conductors on substrates for current constricting defects, such as cracks, narrow conductors, line breaks and intermittent opens, a test signal combining two alternating current signals at different frequencies and direct current offset signal is applied to the conductor. Upon encountering a defect, intermodulation signals are generated and detected. The phase of the detected signal and the phase of a reference signal are compared. The difference between the phase of the two signals is indicative of the presence of a defect in the conductor. The invention has particular application for testing thin conductors.

Abstract: A method for measuring an insulation resistance of an electric line is disclosed. A low frequency signal, which has the same frequency as a signal applied to the electric line and is in phase with the line applied signal or shifted by 90 degrees therefrom, is applied with the amplitude value being varied with a period T. A leakage current sent to synchronous detector is adjusted with respect to its phase or a reference signal is adjusted with respect to its phase to minimize (make zero) or maximize one of induced effective components or induced ineffective or reactive components of the leakage current having a frequency of 1/T.

Abstract: An apparatus for visually indicating abnormal phase relationships between incoming or outgoing phases for a plural phase device, comprised of a plurality of light emitting means interconnected between phases by a logic circuit arrangement whereby the various combinations of on/off indicators present a coded, visual presentation representing the specific mismatch condition of the network. The invention encompasses the concept of incorporating the indicating circuitry within the multiple phase device enclosure and providing an aperture in the enclosure so that the indicators may be viewed without the necessity of gaining access to the interior of the device and exposing individuals to the danger of high voltage/current circuits.

Abstract: According to the present invention, a sampled value of a reference voltage V.sub.p which is a voltage (in general, a relative voltage to ground, an interphase voltage or a positive sequence voltage) prior to the occurrence of a fault in an electric-power system and a sampled value of the quantity of electricity E (a voltage or current in each phase or a symmetrical component voltage or current) during a fault time period or after the recovery of a fault are used to compute a plurality of functional values capable of specifying the phase angle .theta. or the value of .theta. of said quantity of electricity E in relation to said reference voltage V.sub.p and deliver them as information data. When the relative phase angle between the quantity of electricity E during a fault or after the recovery of a fault and a voltage (reference voltage) V.sub.p prior to the occurrence of a fault is clarified in this manner, the relative phase angles of reference voltages V.sub.

Abstract: Faults in a three-phase power transmission line are identified by vectorially subtracting from the postfault current for each phase, the zero sequence current and the prefault current. The resultant currents which are the vectorial sums of the postfault positive and negative sequence currents are then compared. If the magnitude of the resultant current in one phase exceeds that in each of the other two phases by a preselected factor, than one phase is identified as the phase to ground faulted phase. If the magnitudes of the resultant currents of two phases exceed that of the third, those two phases are involved in either a phase to phase or a phase to phase to ground fault with the distinction being made by the presence of zero sequence current in the later case.