81 results about "Neutral current" patented technology

A high-impedance system that utilizes asynchronous, line-mounted single-phase current and voltage sensors with rolling data logs and a common clock or other event trigger to synchronize the signals to a common time scale whenever a fault event is detected. The use of asynchronous, single-phase current and voltage angle sensors with rolling data logs, along with a common clock to synchronize the signals to common time scale whenever a fault event is detected, avoids the need for simultaneous three-phase current measurement. Integration of information, triggered by the detection of a loss or sufficient change of current on three or four (with a neutral current) devices, is used to determine the presence and direction of high-impedance faults and then report it, typically to a central control center via SCADA or another communication system, which implements fault isolation.

The invention discloses a method for the online detection and total loss determination of the neutral current of a distribution transformer. Four precise split core type current transformers are used for respectively detecting the three-phase current and the neutral current, each harmonic component is obtained by using fast Fourier transform, a fundamental current is calculated, and then the iron loss, the copper loss, the neutral line loss and the earth current loss of the transformer are calculated according to each current, thus obtaining the total loss of the transformer. The method can effectively monitor and acquire the electric signal of the transformer, a DSP high speed central processor performs digital filtering on the electric signal, the anti-interference capability is improved, and the neutral current of the transformer and loss caused thereby are measured on line, realtimely, rapidly and accurately, providing necessary basis for the safe and stable operation of the transformer.

An enclosed metering and protective electrical apparatus includes an enclosure, a meter socket within the enclosure structured to input a power circuit and to engage a power meter, and a circuit interrupter within the enclosure including an operating handle and a trip mechanism. The circuit interrupter is structured to output the power circuit from the meter socket to a load and to interrupt the power circuit. A neutral current sensor within the enclosure is structured to detect a ground fault operatively associated with the power circuit and responsively cause the trip mechanism of the circuit interrupter to interrupt the power circuit. A disconnect handle substantially external to the enclosure includes linkage extending within the enclosure and cooperating with the operating handle of the circuit interrupter to open and close the circuit interrupter.

The invention relates to a hybrid-clamped three-electric-level three-phase four-wired photovoltaic system based on 3D-SPWM (three-dimensional sinusoidal pulse width modulation). By the use of a 3D-SPWM control method, system leak current is reduced effectively, neutral-point potential balance is guaranteed, balance of outputting three-phase voltage by the photovoltaic system in independent operation is guaranteed, and balance of three-phase grid-connecting current in grid-connecting operation is guaranteed. In addition, neutral current can be lowered effectively by controlling zero-sequence component. The photovoltaic system comprises three-phase bridge arms connected in parallel. Each bridge arm comprise four IGBTs (insulated gate bipolar transistors) connected in series, a neutral point of each phase bridge arm is connected with a corresponding resistor through a filter, and the resistors are grounded. A pair of a capacitor C1 and a capacitor C2 in series connection are connected at an input end of each bridge arm in parallel, the capacitors C1 and the capacitors C2 are connected with an acquisition photovoltaic array. A pair of diodes are connected between the first IGBT and the fourth IGBT of each bridge arm in series,and neutral points of the capacitors C1 and the capacitors C2 are grounded. In addition, clamped capacitors Cxi are connected on each pair of diodes in parallel, wherein i is equal to a, b and c. The IGBTs are controlled by a control circuit in a 3D-SPWM manner to balance potential at the neutral points.

The invention discloses a method for calculating stray current and neutral point direct current of transformer caused by stray current in a metro. The method comprises the following steps: 1. The structure of rail-drain network-earth in metro system is equivalent to a three-layer resistance network model, and the resistance network is divided into several sections equally; 2, that flow path of theDC bias magnetic field of the transformer caused by stray current is analyzed, and a current branch of the DC bias magnetic field of the transformer caused by stray current is added into the resistance network model; 3, KVL equations along respective loop are arranged to obtain loop current equations for that built resistance network model; 4, a loop current equation is resolved by using the LU decomposition method, and the stray current of the rail leakage and the neutral point current of the transformer is calculated. This method can be used to calculate the distribution curves of neutral current and stray current of transformer under subway operation, which provides a theoretical basis for evaluating the influence of stray current on DC magnetic bias of transformer.

The invention discloses a linear filter-based harmonic current detection method in a three-phase four-wire system. According to the method, a structural characteristic of the three-phase four-wire system is considered; according to the idea of an adaptive notch filter (ANF), a two-dimensional linear sine filter is obtained after rotation transformation on the basis of a minimum variance principleand a gradient decent method; fundamental currents of all phases are respectively separated from an actual measured current by the two-dimensional linear sine filter; and then a symmetrical fundamental wave positive sequence component is obtained by utilizing a modified instantaneous symmetric component calculation method; after calculation of the fundamental wave positive sequence component withthe original actual measured current, a harmonic component of a load current, a fundamental negative sequence component and a zero sequence component are drawn off. Compared with the prior art, a technique employed in the linear filter-based harmonic current detection method in the three-phase four-wire system provided of the invention enables the method to have the following advantages that: themethod is simple with a small amount of computation and it is not needed to carry out complicated rotation transformation and trigonometric function calculation; the method has a good real-time performance and high detection precision; and a harmonic current and a reactive current and a neutral current in the three-phase four-wire system can be detected on the condition of unsymmetrical nonlinearload and nonideal voltage.

A system for cancelling fundamental neutral current on a multi-phase power distribution grid. The system includes a controller coupled to the power distribution grid responsive to a neutral current signal configured to determine a first corrective current based on at least the neutral current signal. A power module responsive to the controller is configured to generate the first corrective current. A transformer subsystem includes primary windings coupled to the power distribution grid and a zero sequence voltage point coupled to the power module. The transformer subsystem is configured to transform the first corrective current into a second corrective current coupled to the power distribution grid such that the second corrective current cancels all or part of a fundamental neutral current. The power module is configured as a four-quadrant power module which provides real power flow in either direction between the power module and the transformer subsystem at the zero sequence voltage point.

The invention provides a technical scheme of a power distribution system equivalent ground distributed capacitor measuring method, comprising the following steps: 1) injecting signal current with constant frequency into a power distribution system; 2) measuring neutral current of primary side of an arc suppression coil and busbar voltage of a busbar in the power distribution system, filtering the measured neutral current and busbar voltage, and filtering out power frequency quality to obtain current injected into the power distribution system and pressure drop generated by the current on an equivalent ground distributed capacitor; 3) modeling the power distribution system based on a lumped parameter model, and calculating a complex functional equation of the injected signal current, voltage and power distribution system equivalent ground distributed capacitance according to Ohm's law; and 4) calculating equivalent ground distributed capacitance value of the power distribution system and ground insulation resistance value of the power distribution system according to the equation in the step 3). The method provided by the invention is clear in principle, is easy to implement, and has a wide application range and high accuracy in computation.

An apparatus and method for determining, in real time, the key parameters of a three phase system electrical generator's output. A pair of reference vectors in quadrature (orthogonal) is phase-locked to a selected input open delta line to line voltage vector. Preferably, the cosine reference vector is locked 45 DEG out of phase from the selected input vector whereby a best projection of the input vector onto the quadrature pair is provided and increases accuracy in subsequent magnitude and phase calculations. The phase-locked reference vectors provide a basis for computing the magnitude and phase angle for the remaining open delta line to line voltage vectors and three line to neutral current vectors. Instantaneous measurement of magnitude and phase angle for the three line to line voltages and three line to neutral currents, the generator's real power (watts), volt-amperes reactive (VARS), apparent power (VA), power factor (PF) and, as a result of the phase locking, the precise frequency of the generator are possible.

The invention provides a three-level four-leg active filter compensation distribution network neutral current control method. The method includes the steps of extracting harmonic waves and the sum of negative sequence components and zero sequence components of a line current as a command current of the controlling; setting the alternating current side three-phase current of an active filter and a neutral current as feedback currents, and performing feedforward decoupling control and dq0-abc conversion on each current component of dq0 axis for outputting three-phase voltage after respectively performing abc-dq0 conversion on the command current and the feedback currents; separately performing compensation control on the neutral current. The purpose of direct current side voltage balance and stability can be achieved through direct current side voltage stability and balance control. The three-level four-leg active filter compensation distribution network neutral current control method can effectively solve the problems such as overcurrent of a neutral line due to load imbalance in a three-phase four-wire system and is quick in response of a control system, capable of achieving dynamic real-time compensation and good in control effects.

The invention provides a novel zero-sequence current compensator. An inverter bridge is connected between a neutral point and a neutral line of a zigzag transformer; and a current output by the inverter bridge is injected into a system through a low-impedance zero-sequence current channel which is provided by the zigzag transformer so as to compensate for a neutral current. A controllable rectifier module is connected with the secondary side of the zigzag transformer to supply a direct-current power supply to the inverter bridge, and thus, the two-way flow of energy is realized and the problem of direct-current voltage rise caused when the compensator absorbs active power is solved. The novel zero-sequence current compensator has a series of advantages of good compensation effect, low direct-current voltage, small switching stress, few influences of system parameters, flexible control, few influences on system operation and the like.

The invention provides a potential compensation method for eliminating and weakening the DC current of a transformer neutral point in high voltage power network. The method adds a controllable potential compensation device between the neutral point of grounding transformer in power station and a ground pole in series, the DC current of the transformer neutral point is measured by a transformer neutral point DC monitor, and a control unit controls the current output of a bipolar current source based on the measured DC current of the transformer neutral point, and then the potential compensation device generates a compensation potential which partly or fully compensates the potential variety of each grounding pole in AC grid generated by neutral current thereby making the potentials of each grounding transformer neutral point in the AC grid similar to or close to each other, thus the DC current of the transformer neutral point in high voltage power network can be effectively restrained. The provided method can conquer the weaknesses existing in current engineering application methods such as capacitor DC blocking method, small resistance current limiting method, neutral point injecting reverse current limiting method.

The invention discloses a three-phase circuit tester. The tester comprises a sinusoidal oscillator, a voltmeter, an ammeter and a three-phase load, wherein the signal output terminal of the tester is connected with a non-shift-phase power amplifier and a two-circuit shift-phase power amplifier separately, and a work power supply provides a stabilized voltage direct current power supply for the above circuits. The stable low voltage three-phase alternating current with the equal three-phase voltage and 120 degrees of phase difference of three-phase voltage can be outputted, wherein the common ground wire is the neutral line of the three-phase alternating power supply. The detects of the existing three-phase alternating current experimental instrument, like unbalanced three-phase voltage and phase difference, instability, unsafety, large power consumption and volume and the like can be well solved. The tester can be used to conveniently observe the neutral current generation phenomenon caused by the unbalanced three-phase voltage or phase difference. The tester can be single used as the experimental instrument and can be combined with the common electrotechnics and electronic engineering practice rig. The tester can be used in the three-phase alternating current experimental project of various colleges and universities, thus greatly improving the experimental accuracy and effect and avoiding the risk of electric shock in experiments.

The invention discloses a control method for three-level neutral-point potential balance zone verification and correction based on zero sequence voltage injection, and the method comprises the steps: measuring a voltage across two ends of an upper DC capacitor and a voltage across two ends of a lower DC capacitor in each control period, and calculating the voltage bias; calculating a mean neutral current according to the DC voltage bias of the upper and lower capacitors; pre-estimating a zero sequence voltage v0; carrying out the verification and correction of a pre-estimated calculation result: limiting an output result. The method adds a verification-correction link, carries out the analysis and verification according to a calculation result, and finally corrects a control instruction. The method reflects the essence of a problem of neutral point potential fluctuation, is suitable for a carrier modulation mode, and also suitable for an SVM method.

An apparatus for reducing a neutral current using a load switching method in accordance with the present invention includes a phase current detection unit for detecting a phase current in each of a top stage power line and a bottom stage power line, a load switching unit for changing an arrangement of a load connected each phase of at least one among the top stage power line and the bottom stage power line and a control unit for controlling the load switching unit so as to compare a strength of the detected phase current of the top stage power line with a strength of the detected phase current of the bottom stage power line and to change the arrangement of the load connected to each phase of at least one among the top stage power line and the bottom stage power line according to the comparison result.

The invention relates to a control method of a hybrid four-leg shunt active power filter. In the method provided by the invention, a space vector control method is utilized as a core for calculation to obtain the base quantity of the output voltage reference value of legs, and a current hysteresis control method is utilized as a core for calculation to obtain the regulating quantity of the outputvoltage reference value of the legs. When the error of the reference current of the legs of the active power filter and the actual output current is smaller, the current hysteresis control is of no avail, and the active power filter is ensured to have higher control accuracy when the load harmonic content is small; when the error is larger, the regulating quantity obtained by calculation adds thebase quantity, and the active power filter is ensured to have quicker response speed when the load harmonic content is large. By utilizing the method, the adaptive ability of the four-leg active power filter can be improved, and the four-leg active power filter is ensured to well compensate the harmonic current and neutral current in the system under different harmonic conditions.

The invention discloses a metering system secondary circuit monitoring method and device based on fundamental wave zero sequence characteristics. The method comprises the steps as follows: acquiring three-phase voltage in a voltage circuit of a high-voltage metering system, three-phase current in a current circuit and neutral current; obtaining a zero sequence voltage component and a zero sequencecurrent component through vector superposition; extracting amplitude and phase of a fundamental wave zero sequence component; establishing a classifier based in the depth belief network with amplitude and phase of fundamental wave voltage, amplitude and phase of fundamental zero sequence point current and the absolute value of the difference between the fundamental wave zero sequence current andneutral current as input variables and various faults as output variables to realize classification and recognition of faults. Secondary circuit fault characteristics of the high-voltage metering system can be extracted accurately, various faults can be classified and recognized accurately, so that faults are effectively eliminated, secondary circuits are monitored in real time, and the safety, stability and accuracy of electric energy metering are guaranteed.

This invention aims to provide an electric rotating machine which is free from the procedure of selecting different preset neutral current values for different types of machines, and which can detect a ground fault in a phase coil of the armature winding without suffering any erroneous operation. An electric rotating machine having an armature winding including three phase coils, which has been provided to attain the object of this invention, comprises a grounding resistor connected at a neutral of the armature winding, and current measuring apparatuses furnished for at least two phase coils, wherein phase currents through the phase coils are compared with each other, and the detection of a coil ground fault is determined when harmonic components of the phase currents differ from each other.

The invention discloses a quintuple harmonic excitation brushless synchronous generator, which is characterized in that: the generator consists of a main generator and an alternating current exciter, which are arranged coaxially; the direct current excitation source of a stator pole winding of the alternating current exciter is taken from a direct current source; wherein a triphase quintuple harmonic winding in a stator core of the main generator is rectified into the direct current power supply by a rectifier; the generator has 60 stators, 4 poles and three phases; and the rotor of the main generator is made into an integral salient pole type. The quintuple harmonic excitation brushless synchronous generator overcomes the shortcoming that the fundamental harmonic excitation has low short circuit current ratio and electromagnetic interference, and also overcomes the shortcoming that when the triple harmonic exciters are connected in parallel, the neutral current has great demagnetizing effect on triple harmonic excitation magnetic field. Therefore, the quintuple harmonic excitation brushless synchronous generator has the characteristic of better electrical property than that of the fundamental harmonic excitation and the triple harmonic excitation brushless synchronous generator.

A secondary neutral point multipoint grounding monitoring deivce of a voltage transformer of a transformer substation comprises a one-point grounding loop connected with a secondary neutral point of the voltage transformer, wherein a single-turn through current sensor is connected onto the one-point grounding loop. The secondary neutral point multipoint grounding monitoring deivce is characterized in that an analog / digital (A / D) data conversion module is connected onto a current sensing coil; the output end of the A / D data conversion module is connected into a micro-programmed control unit (MCU) microprocessor; and an alarming circuit, an internal memory, a communication module, a power supply processing module, a liquid crystal display (LCD) module, a key operation module and a time clock signal control module are connected onto the MCU microprocessor. Compared with the prior art, the secondary neutral point multipoint grounding monitoring deivce can store current values, give alarms and transmit the current values to a remote monitoring platform when the current values surpass the preset value by monitoring and judging secondary neutral current. In addition, compared with the traditional monitoring method, unattended operation is achieved, and a large amount of time and labor force wasted in the existing monitoring process is saved.

The invention discloses a controllable interphase power transfer method and system which are implemented through the following steps that: a digital signal processor (DSP) acquires four paths of voltage / current signals, calculates the balance degree of loads of three phases, and carries out comparative analysis on the balance degree of loads of three phases, the imbalance degree of a load current set by the system, and the upper and lower thresholds of a neutral current so as to obtain the optimal interphase power transfer control decision scheme at the moment; through controlling a fling-cut switch to extract power from a phase line with the lightest load in A, B and C phases, after boosting, rectifying and filtering by an isolation transformer, the DSP realizes the dynamic allocation of power transmission among the A, B and C phases so as to reduce the electric energy loss of neutral lines and power transmission lines as far as possible through controlling the output power of a BUCK converter and an inverter, controlling the fling-cut switch to transfer the output power to the phase line with the lightest load, then carrying out acquisition and analysis on the four paths of voltage / current signals again, and carrying out dynamic control on the output power of the inverter; and related control information such as the dynamic allocation of power transfer among the A, B and C phases and the like can be subjected to remote transmission through a wireless GPRS (general packet radio service) network.

The invention discloses a current and voltage state monitoring method and device based on fundamental wave zero sequence characteristics. The current and voltage state monitoring method comprises the following steps: obtaining three input variables, that is, a three-phase voltage fundamental wave zero sequence value, a three-phase current fundamental wave zero sequence value, and a zero-sequence current and neutral current difference absolute value; inputting the three input variables into a preset fuzzy inference system, wherein the fuzzy inference system comprises a mapping relation between the three input variables and fault type diagnosis results serving as output variables; and finally, obtaining the fault type diagnosis results. The current and voltage state monitoring device comprises an input variable obtaining program unit and a fuzzy inference program unit in full correspondence to the steps of the method. The current and voltage state monitoring method and device based on the fundamental wave zero sequence characteristics can accurately judge various faults under different conditions, are high in detection accuracy, do not cause false alarm, and can realize fault alarm and effective fault removal, thereby ensuring safety and stability of the power supply system.

The invention aims to provide a method for suppressing the neutral current of a transformer. In the method provided by the invention, a neutral current suppression model is constructed aiming at the influence of a compensation range of reactive power compensation on compensation effects based on the relation among interphase reactive power compensation, relative reactive power compensation and the second side current and load side current of the transformer by leading an optimization theory; and on the premise of ensuring the stability and reliability of compensation, the neutral current suppression is realized by setting constraint conditions and target function weight coefficients in the model. The method provided by the invention determines the optimal reactive power compensation quantity by solving the neutral current suppression model, thereby enabling the compensation effects and the reactive power compensation configuration to be optimal.

The invention relates to a capacitive switching control method for inhibiting zero sequence and negative sequence current of a distribution transformer. An electric power quality acquisition unit acquires a three-phase voltage current and neutral current signals; a central processing unit calculates voltage, current and power factor parameters according to the acquired signals, and determines an actual switching amount; a capacitor is switched by the control of an intelligent combination switch; current load state and capacity regulation conditions are transmitted to an upper computer through a GPRS (General Packet Radio Service) module; and background software realizes the functions of data recording, analysis and the like. According to the method provided by the invention, the influence of overcompensation on a distribution transformer can be considered according to the acquired electric power quality signals, so that the capacitor can be reasonably regulated, thereby effectively inhibiting zero sequence and negative sequence current of the distribution transformer and improving the electric power quality of the distribution transformer.

The invention discloses a safety detecting circuit for an intelligent electric energy meter. The safety detecting circuit for the intelligent electric energy meter comprises a sampling conversion module, a safety detecting module, a main control module, and an uplink communication module. The sampling conversion module detects a live current, a neutral current, and the voltage between the neutralline and the live line to generate a live current digital signal, a neutral current digital signal, and a zero-live line voltage digital signal, and calculates a first electrical parameter. The safetydetecting module calculates a second electrical parameter according to the live current digital signal, the neutral current digital signal, and the zero-live line voltage digital signal, and obtainsearly warning information according to the second electrical parameter and a pre-stored load characteristic database. The main control module stores and displays the first electrical parameter and thewarning information. The uplink communication module forwards the early warning information. Therefore, it is judged whether there are electrical safety hazards such as leakage, overload, and illegalload on the line, and the warning information is transmitted, which can effectively eliminate the electrical safety hazards of the load.

The invention discloses a single-phase meter shunt accurate judging method for analyzing electricity stealing, which relates to an electricity stealing analysis method. At present, the electricity theft analysis is not comprehensive, and there are misjudgments and misjudgments of sharing the neutral line. The present invention includes the following steps: 1) calling the A-phase current and zero line current of the low-voltage single-phase user smart meter once a month; 2) judging whether the single-phase meter is shunting; If it is suspected that there is a shared neutral line, it will not be generated as an exception; 4) For all users who suspect that there is a shared neutral line, call again on the next day. If there are changes compared with the previous day and still meet the diversion Judgment conditions, judge again whether there is a shared neutral line; 5) For electric energy meters that do not have a shared neutral line, call through again after a period of time. An exception is generated. The technical solution removes the situation of sharing the zero line, and prevents misjudgment and misjudgment.