118 results about "Self impedance" patented technology

The invention discloses a method for measuring zero-sequence parameters of double-circuit transmission lines. The method comprises the following steps: measuring the zero-sequence parameters of the double-circuit transmission lines in the manner of live line measurement or power cut measurement; by utilizing the global positioning system technology, simultaneously measuring the zero-sequence voltage and the zero-sequence current at the head ends and the tail ends of the double-circuit transmission lines to realize synchronous sampling on the zero-sequence voltage and the zero-sequence current; and then, working out the respective zero-sequence self impedance and zero-sequence self capacitance, and zero-sequence mutual impedance and zero-sequence mutual capacitance between the double-circuit transmission lines. In the method for measuring the zero-sequence parameters of double-circuit transmission lines, the distributed parameter models of the double-circuit transmission lines are established, and the influences of distributed capacitors on measured results are considered, thereby, the accuracy of the measured results of the zero-sequence parameters of the double-circuit transmission lines is greatly improved.

The invention discloses a six-phase-sequence-impedance-based distance protection measurement method of double-circuit lines on the same pole. Two circuit lines are viewed as a whole body. Six single-phase ground impedance measuring elements, six interphase impedance measuring elements and six interline impedance measuring elements are formed by three voltages and six currents in the two circuit lines on the side of the whole body. Totally eighteen measuring impedances are formed. The measurement equation of the distance protection measuring method is as shown as the accompanying drawing, wherein UIAu, UIBu, UICu, UIIAu, UIIBu and UIICu respectively denote voltage drops of A, B and C on the unit length of a circuit line I and a circuit line II, ZS denotes line self-impedance, Zp denotes interphase mutual impedance of the same line, ZM denotes interline mutual impedance, L denotes line length, iIA, iIB, iIC, iIIA, iIIB and iIIC respectively denote A, B and C phase currents, and delta denotes interline zero-sequence mutual inductance compensation coefficient.

The present invention provides a power cable intersect cross connection grounding system grounding current monitoring and evaluating method which is implemented by a power cable grounding current monitoring system. The method comprises the steps of calculating a cable sheath self-impedance, calculating a sheath induction voltage caused by a to-be-tested cable wire core load current, calculating a cable sheath induction voltage caused by a to-be-tested cable sheath grounding current and a large ground leakage current, calculating an induction current of a to-be-tested cable, calculating a cable capacitive current, predicting a grounding current fluctuation value caused by the load change, predicting the grounding current fluctuation caused by the load change, analyzing and determining the current condition of a power cable intersect cross connection grounding system cable sheath, etc. The power cable intersect cross connection grounding system grounding current monitoring and evaluating method of the present invention is different from a method of analyzing and calculating a grounding current from a circuit model purely, introduces the ideas of prediction, analysis and cable parameter characteristic calculation, enables the grounding current monitoring and evaluating accuracy of a power cable intersect cross connection grounding system to be improved effectively, and provides a more effective analysis method for cable external insulation state evaluation.

The invention discloses a method of optimal configuration of a plurality of superconducting fault current limiter based on a sensitivity technology, which comprises the steps of: calculating the three-phase short-circuit current of all nodes in a whole system, and finding b nodes with the short-circuit current exceeding the standard value; determining braches for installation and reliable startup of the SFCLs (superconducting fault current limiter) according to startup conditions of the SFCLs; calculating the sensitivity of self-impedance of each station with the short-circuit current exceeding the standard value, sequencing the stations in a sensitivity descending order, and taking the top a branches as candidate braches for installation of the SFCLs; and taking c candidate braches as optimal branches for a multi-objective optimization algorithm NSGA-II (non-dominated sorting genetic algorithm-II) in next step, determining a scheme with the optimal installation positions of the SFCLs, the number of SFCLs to be installed and the impedance, thereby realizing global optimum configuration. By adopting the method, the search space to be understood is reduced greatly, the speed of calculation is increased, and optimization results are more suitable for actual applications. Meanwhile, the problem of weight selection resulting from conversion of multi-objective optimization to single-objective optimization can be avoided, and a decision-maker can make final decisions according to actual engineering needs.

The invention relates to a network voltage sag frequency estimation method and device with a distributed power supply. The method comprises the following steps: calculating a node impedance matrix according to a node admittance matrix of the system; calculating the self-impedance and mutual impedance at the fault point after short circuit occurs in the system; calculating the voltage sag amplitudeof the estimated busbar under different fault types; determining the voltage sag duration of the estimated busbar; performing statistics of the sag frequency of the estimated busbar according to thevoltage sag amplitude and the voltage sag duration of the estimated busbar. According to the method and device provided by the invention, the estimation accuracy of the voltage sag with a distributedpower supply system is improved; by adopting kernel density estimation, the distribution law of the fault occurrence positions better conforms to the practical situation according to the history faultinformation, thus the estimation result of voltage sag is more accurate and conforms to the practice.

The invention relates to a thermal hydro-mechanical drawing forming method for dot matrix self-impedance electrical heating plates, and belongs to the technical field of the thermal hydraulic forming of the plates. The method comprises the following steps of: fully filling liquid into a cavity of a female die serving as a liquid pond; when the plates are driven by a male die to enter the female die, forming the plates by reverse pressure generated when the liquid is compressed; embedding pin type electrodes inside pressure plates according to the distribution of dot matrixes, and performing self-impedance electrical heating on flanges of the plates by using contact resistors between the electrodes and the plates; adjusting the distribution of temperature fields of the flanges by changing the distribution law of the dot matrixes of the electrodes and adjusting the heating current of each heating electrode; adjusting the flow stress of heating points by changing the temperature of each mass point on the flanges so as to control the flow of metal by the asynchronous flow of the metal mass points on the flanges; and coordinating the deformation process of the metal by the asynchronousdeformation of each mass point on the flanges due to the temperature to fulfill the aim of improving the limit drawing ratio of the plates. The method has the advantages that: the heating speed is high, the effect is good, the plates can be heated controllably and flexibly, and the forming limit of the plates is improved.

The invention relates to a composite sensor which is used for measuring the characteristic curve of soil moisture. The composite sensor comprises a sensing unit and a signal processing circuit; the sensing unit consists of a sheathed casing, a porous cup and a pressure sensing element. The sheathed casing is used for transforming the changes of the soil moisture into the change signals of self impedance; the porous cup is closely connected with one end of the sheathed casing and provided with a built-in hollow cylinder; deionized water in the hollow cylinder overflows through the porous cup; the pressure sensing element is arranged at the other end of the sheathed casing and can be used for sensing the change of internal pressure of the hollow cylinder; the signal processing circuit is used for detecting the change signals of self impedance and the pressure changes, and acquiring the signals of soil moisture content and the signals of soil matrix potential, so as to output the characteristic curve of soil moisture.

A direct current detection circuit has a zero-phase current transformer with source lines inserted therethrough for detecting current differences among them and generates a comparison voltage value based on a divided voltage value obtained between the zero-phase current transformer and a voltage divider resistor according to a change in the self-impedance of the zero-phase current transformer. An offset current is passed through the zero-phase current transformer to make it possible to detect on the basis of the comparison voltage value a direct current value in a range which is otherwise difficult to detect accurately on the basis of the comparison voltage value because of influence of hysteresis characteristic of the zero-phase current transformer. A control circuit detects a present direct current value based on the comparison voltage value and the value of the offset current.

A direct current detection circuit has a zero-phase current transformer with source lines inserted therethrough for detecting current differences among them and generates a comparison voltage value based on a divided voltage value obtained between the zero-phase current transformer and a voltage divider resistor according to a change in the self-impedance of the zero-phase current transformer. An offset current is passed through the zero-phase current transformer to make it possible to detect on the basis of the comparison voltage value a direct current value in a range which is otherwise difficult to detect accurately on the basis of the comparison voltage value because of influence of hysteresis characteristic of the zero-phase current transformer. A control circuit detects a present direct current value based on the comparison voltage value and the value of the offset current.

The invention provides an ECPT-based electric energy and signal circuit separated parallel transmission system and a parameter design method. A signal transmission channel composed of a pair of signal transmission pole plates and a signal detection resistor is added on the basis of an ECPT system achieving double-side LC compensation, and the parameter design method is proposed accordingly. According to the system and the method, an additional impedance isolating circuit does not need to be added for reducing electric energy crosstalk, the low-crosstalk and low-attenuation signal transmission channel is constructed through the self impedance characteristic, stable, reliable and parallel transmission of signals is achieved through the channel on the premise that the electric energy transmission power is guaranteed, and meanwhile the channel complexity and the integral system cost are reduced. In addition, the effectiveness of the method is verified through simulation and experiments, and electric energy and signal parallel transmission in the Baud rate range of 1.2 kbps to 115.2 kbps is achieved through built system experiment devices.

A layout design of a multilayer printed circuit board (PCB) is provided, which makes use of partial electromagnetic band gap (EBG) structure to constitute a power layer or a ground layer. The EBG structure is mainly used on the linear transmission path from the port of the first integrated circuit to the port of the second integrated circuit on the power layer or the ground layer, so as to overcome the problems concerning self-impedance and transfer-impedance easily occurred in the conventional complete EBG structure.

The invention discloses a calculation method of a single-phase multi-feed-in interaction effect factor based on an impedance matrix, comprising steps of determining a DC converter station to be studied by taking a receiving terminal of the multi-feed-in AC power grid and presuming that the quantity of the DC converter station is N, (2) calculating self-impedance Zii-1, Zii-2, Zii-0 of a converter station i in a positive negative zero sequence impedance matrix of the multi-feed-in AC-DC power grid to be studied and the mutual impedance Zij-1, Zij-2, Zij-0,i=1,2-N, j=1,2-N between the converter station i and the converter station j,calculating the positive-negative zero sequence impedance of the converter station and the sum of the positive-negative zero sequence impedance between the converter station I and the converter station j, and (3) calculating the single-phase multi-feed-in interaction effect factor SMIIFij of the converter station I and the converter station j. The invention can quickly obtain the single-phase multi-feed-in interaction effect factor SMIT between the converter station, and can provide reference to the strongness and weakness.

The invention relates to an antenna for portable wireless equipments which realizes high-gain and broadband, comprising an inverted L-shaped antenna (10), a circuit board (12) and a plate-shaped antenna (14), wherein, the inverted L-shaped antenna (10) is a feeder element, and one end of the feeder element is electrically connected with one surface of the circuit board (12) via a feed point; the circuit board (12) is in the circuit board of the portable wireless equipment, and the circuit components of the inverted L-shaped antenna (10) are connected with the circuit board; the plate-shaped antenna (14) is opposite to the back surface of the circuit board (12) connected with the inverted L-shaped antenna (10); the plate-shaped antenna is a passive element with the electric length in longitudinal direction being about 1 / 2 of the radio wavelength of the portable wireless equipment; the sizes and the mutual distances of the L-shaped antenna (10), the circuit board (12) and the plate-shaped antenna (14) are regulated to be specific values and both the self-impedance of the inverted L-shaped antenna (10) and the plate-shaped antenna (14) and the mutual impedance of the inverted L-shaped antenna (10) and the plate-shaped antenna (14) are changed together.

The invention provides a method for constructing a physical model of double circuit transmission lines on the same tower, which comprises the steps of: reducing the mutual inductance influence of a ground wire to self-impedances of all transmission lines and mutual impedances among phases first, calculating equivalent self-impedances of the phases and equivalent mutual impedances among the phases after the reduction, taking the smallest equivalent mutual impedance as a common resistance Mmin, and calculating a mutual compensating impedance Zik between the i-th phase and the k-th phase of the transmission line of which the mutual impedance is larger than the common resistance, and a self-compensating impedance Zi of the i-th transmission line; and then utilizing the common resistance Mmin, the mutual compensating impedance Zik and the self-compensating impedance Zi of each transmission line to construct the physical model of the transmission lines. The method adopts a strategy of fully simulating the self-inductances of the transmission lines and the mutual inductances among the lines, and considers the influence of a ground return circuit and the ground wire when the self-inductances and the mutual inductances of the transmission lines are calculated. The method can effectively overcome the defects of the prior physical model of the double circuit transmission lines on the same tower, can well simulate transposed or un-transposed double circuit transmission lines on the same tower, and accurately reflect the variation characteristics of electrical quantity when the double circuit transmission lines on the same tower break down.

The invention provides an electromagnetic induction water heater consisting of a shell, a soleplate, a circuit board, a generated electromagnetic induction heating part and an iron-made water container heated part; after a power supply is started to work, the current of an induction heating coil forms a circuit by passing through a gated pipe so as to generate the high-frequency alternating current, thus forming the alternating magnetic field in the heating coil and generating the variational magnetic lines; the magnetic lines magnetize the iron-made water container and induces the electromagnetic eddy; as the self impedance of the water container converts the electric energy into the heat energy which heats the water in the iron-made water container; simultaneously, the induction heating coil symmetrically generates the magnetic lines, thus heating the water in the iron-made water container arranged on two surfaces of the heating coil and leading the heat efficiency to reach the maximum; furthermore, more than one heating coils can be used.

The invention provides a visualization method and device for electrical distance of a power system. The method comprises the steps of calculating a self-impedance matrix of a node according to a power grid topology and a running parameter, which are acquired in advance, of the power system by a node admittance matrix inversion method; mapping high-dimensional space data to a low-dimensional space by a t-SNE algorithm according to the self-impedance matrix to calculate the electrical distance; and drawing a pattern relevant to the electrical distance of the power system according to node coordinates obtained by calculation of the low-dimensional space. The device comprises a matrix building unit, a dimension reduction unit and a drawing unit. With the technical scheme provided by the invention, the tightness degree among different equipment can be fully displayed, and an intuitive object can be given to an operator.

The invention discloses an online measurement method for impedance parameter of a three-phase asymmetric power transmission line, which comprises the steps of: a first step, mounting synchronous measurement devices at two ends of a measured three-phase asymmetric power transmission line, and synchronously measuring the three-phase voltage and current signals at two ends of the measured three-phase asymmetric power transmission line through the synchronous measurement devices at n times; a second step, perform quick Fourier transform on n sets of three-phase voltages and current signals which are acquired in the first step, thereby calculating n sets of three-phase voltage industrial frequency vectors at two ends of the measured three-phase asymmetric power transmission line and n sets of three-phase current industrial frequency vectors at the first end of the measured three-phase asymmetric power transmission line; a third step, calculating the self impedance parameter of each phase and mutual impedance parameters among different phases; and a fourth step, calculating a positive sequence impedance, a negative sequence parameter, a zero sequence parameter and coupling impedance parameters among the phases. The online measurement method realizes online measurement for the impedance parameter of the three-phase asymmetric power transmission line, and furthermore has a relatively high measurement precision.

The invention discloses a mixed-pressure bipolar direct-current power transmission line zero-sequence parameter precisely measuring method. Bipolar head ends and tail ends of direct power transmission lines different in voltage level are respectively connected, zero-sequence voltages and zero-sequence currents on head and tail ends of the mixed-pressure bipolar direct-current power transmission lines are simultaneously measured, and a global satellite positioning system is utilized to realize synchronous sampling of voltages and currents on double ends of the mixed-pressure bipolar direct-current power transmission lines; and then zero-sequence self-impedance, zero-sequence mutual-impedance, zero-sequence self-capacitive-reactance and zero sequence mutual-capacitive-reactance of the mixed-pressure bipolar direct-current power transmission lines are obtained by means of calculation. According to the invention, a distributed constant model of the mixed-pressure bipolar direct-current power transmission lines is established, and the influences of distributed capacitance on the measuring result are considered, so that the precision of mixed-pressure bipolar direct-current power transmission line zero-sequence parameter measurement is substantially improved.

A power transmission line thunderbolt electromagnetic transient dynamic simulating test system is based on a power transmission line and overhead ground wire model, a pole and tower and pole and tower grounding body model and an insulator model to divide a pole and tower into a diagonal member section, a cross arm section and a principal member section, factors of an insulator, a power transmission line and an overhead ground wire are taken into consideration, and a lighting stroke transient equivalent circuit is simulated and constructed through corresponding wave impedance, self-impedance, mutual impedance, self-admittance, mutual admittance, inductance and the like. The power transmission line thunderbolt electromagnetic transient dynamic simulating test system provides a physical testing platform for collecting a power transmission line lighting stroke current and voltage data. Surge currents are added into different positions of the system, signals of a far-end overhead ground wire and a far-end wire are measured, the transmitting process of a lighting wave in the whole power transmission line can be analyzed, and according to an analyzing result, lighting protection of a lighting protection weak section of the power transmission line and substation equipment is optimized. The characteristic quantity analysis is carried out according to a wave form obtained by the measurement, a pattern recognition method of power transmission line direct stroke and shielding failure flashover can be provided.

The invention provides a system for testing the property of a thunder and lightning traveling wave of a power transmission line. The system consists of a power transmission line thunder and lightning electromagnetic transient movable mold device and an intelligent monitoring device; and on the basis of a power transmission line and lightning conductor model, a pole tower and pole tower grounding body model and an insulator model, the pole tower is divided into a slantwise material section, a cross arm section and a main material section, and in consideration of factors of the insulator, the power transmission line and the lightning conductor, a lightning stroke transient equivalent circuit is built in a simulation way by the corresponding wave impedance, self-impedance, mutual impedance, self-admittance, mutual impedance, inductance and the like. The intelligent monitoring device is formed by the means that a current or voltage sensor is sequentially cascaded with an A / D (analog to digital) convertor, a singlechip, and a display or an oscilloscope. Impact current is added into different positions of the system, so that signals of the lightning conductor and the conductor wire arranged at a far end can be measured, the propagation process of the lightning wave at the whole power transmission line can be analyzed, and the anti-thunder weak section of the power transmission line can be optimized and the lightning protection of substation equipment can be carried out according to an analysis result.

The invention discloses an impedance calculation method of a return-wire direct feeding mode tunnel traction network. The impedance calculation method is applied in a return-wire direct feeding mode traction power supply system inside an electric railway tunnel; all conductors participating in transmission and backflow of the traction power supply system including the earth inside the tunnel are taken into consideration; after the conductors inside the traction network system are classified according to the transmission and backflow functions, every two different conductors participating in transmission and backflow form a loop; and the self impedance of each loop and mutual impedance among different loops are deduced and calculated according to the radius of each conductor forming the loop and space relative distance parameters, an impedance matrix is solved to obtain the current distribution coefficient of each loop, then the system comprehensive impedance is obtained, and finally the return-wire direct feeding mode impedance parameter is obtained. The method is based on the subsistent loops of the system, the complex conditions caused by a model constructed with the earth as the reference conductor in the prior art are avoided, the calculation complexity is reduced, and the current distribution coefficient of each loop of the traction network can be obtained.

The invention provides a radio frequency matching system and a method of realizing radio frequency matching automation. The radio frequency matching system comprises a debugging terminal, a radio-frequency integrated measuring instrument and a matched network chip, wherein the debugging terminal is installed with debugging software; the debugging terminal is connected to the radio-frequency integrated measuring instrument and the matched network chip respectively and is used for collecting a test result of the radio-frequency integrated measuring instrument and sending an impedance expectation value to the matched network chip; the debugging software is used for processing the test result and generating the impedance expectation value; one end of the radio-frequency integrated measuring instrument is connected to a radio frequency input source, and the other end is connected to a load output terminal, and the radio-frequency integrated measuring instrument establishes connection with the debugging terminal and is used for testing radio frequency pathway performance and acquiring the test result; and the matched network chip is arranged between the radio frequency input source and the load output terminal and is used for receiving the impedance expectation value, adjusting a self impedance according to the impedance expectation value and acquiring an optimum matching value. Through the technical scheme of the invention, based on calculating and an apparatus, radio frequency matching is automatically completed, and manual welding matching is replaced so that precision of radio frequency debugging is increased and a workload of a radio frequency engineer is reduced.

The invention discloses a method for modeling of an electromechanical transient simulation system based on three-sequence equivalent impedance and belongs to the field of electric power system simulation. On the basis of an electric power system load flow and transient algorithm, first interface nodes are set single-phase earth faults, three-phase voltage prior to the faults of each interface node and three-phase voltage at the starting time of the faults are recorded, and the self-impedance and mutual impedance of the interface nodes are solved according to the fault calculation principle. The mature electromechanical transient short-circuit calculation is utilized to solve each-sequence equivalent impedance of an external system. According to the method, existing data of a power grid are utilized directly, data conversion is not performed, the development of a data interface program is avoided; the secondary development is avoided, so that the solving error caused by load flow calculation and model modeling inaccuracy is avoided, the working intensity is relieved, and the research efficiency is improved.

The invention discloses a multi-target decision method for limiting short circuit currents in the receiving-end electrical network. The method comprises steps that, an impedance matrix of a breaking line for the receiving-end electrical network is monitored, and self impedance sensitivity of a breaking m back line having n exceeding standard sites is figured out; according to short circuit current exceeding standard degrees of the various exceeding standard sites, weighted self impedance sensitivity of limit short circuit currents of any breaking line for all exceeding standard sites in the receiving-end electrical network is acquired; a power flow equation of the receiving-end electrical network is solved through utilizing a Newton Laphson algorithm to acquire Thevenin equivalent parameters; sensitivity indexes of the breaking line for system safety is acquired according to the Thevenin equivalent parameters and boundary conditions for static state voltage stabilization margin; a multi-target model is established, the Pareto optimal solution set is figured out, and optimal broken line combination for limiting short circuit currents of the various exceeding standard sites is acquired. The method can satisfy multi-target decision requirements for integrated optimum effects of short circuit current limit and integrity and safety of the system.

An impedance frequency equivalence new method for designing alternating current filter for establishing a generator, a transformer, lines or the like electric elements, impedance frequency models of filter element parameters plunged by neighbouring other converter station, but the parameters are simplied in power system routine calculation, each impedance frequency model are established based on diffferent characteristics of the nodes, the generator, the transformer, the lines, filters or the like electric elements, resistance parameters of the generator, the transformer and the lines are added for determining to be used for alternating current-direct current system operating mode of the harmonic impedance equivalence calculation and to perform statistical sectorization for the equivalence result by the harmonic impedance equivalence. The abstract figure is an impedance fan diagram performing harmonic impedance equivalence sectorization with the new method.

The invention discloses a distance protection method for non-transposition double-circuit lines on the same tower. The method comprises the following steps of firstly, according to the existing fault phase selection method, accurately identifying the fault phase of the non-transposition double-circuit lines on the same tower; then, utilizing a six-phase impedance matrix obtained by an actual pole tower structure to calculate the average self-impedance, inter-phase mutual impedance, inter-line mutual impedance, and positive sequence impedance and zero sequence impedance of a virtual line; performing the fault calculation on the occurred fault type, and performing phase division and rectification on the protection area of each fault phase. The method has the advantage that the distance protection work of the non-transposition double-circuit lines on the same tower is controlled in the excellent state, and the important realistic meaning is realized for guaranteeing the safe and stable running of power systems.

The invention discloses an internal heating method suitable for a power battery pack and relates to the technical field of lithium ion power battery heating. The invention solves the problems that anexterior preheating mode which is commonly used for a conventional power battery for preheating needs an additional preheating circuit and is not uniform in preheating. Through the large self-impedance of a lithium battery at low temperature, an alternating excitation current with adjustable frequency is generated between the two groups of power batteries through a bidirectional DC / DC, so that theinterior of the lithium battery is self-heated to a proper working temperature. Thus, an external heating device is not needed, an excitation source does not need to be additionally arranged, and only the bidirectional DC / DC converter needs to be arranged between the two sets of batteries. By controlling the switching frequency, namely the alternating excitation frequency, of the conduction direction of the bidirectional DC / DC converter, the two batteries are excited and heated at the same time. The optimal alternating excitation frequency for heating is calculated by establishing an equivalent circuit model of the battery to control the switching frequency of the bidirectional DC / DC converter. The preheating method is suitable for preheating the lithium ion power battery.

The invention provides a measuring system and method for self-impedance and mutual impedance of a three-phase grid-connected converter. The measuring system comprises a disturbance source unit, a volt-ampere characteristic collecting unit, a data processing unit and a data analysis unit; the output end of the disturbance source unit is connected with a common connection point; the input end of thevolt-ampere characteristic collecting unit is connected with common connection points of a disturbance source and the grid-connected converter; the input end of the data processing unit is connectedwith the output end of the volt-ampere characteristic collecting unit; the input end of the data analysis unit is connected with the output end of the data processing unit, and the self-impedance andthe mutual impedance of the three-phase grid-connected converter are calculated based on voltage-current data provided by the data processing unit. According to the measuring system and method, the influence of the frequency coupling effect on impedance measuring of the three-phase converter under the static coordinates is fully considered, when the internal resistance of a power grid is non-negligible, the self-impedance and the mutual impedance of the converter can be accurately measured, and the accuracy of power grid stability analysis based on impedance criteria is improved.

The invention provides a method and system for locating a fault independent from a parameter of a multi-branch overhead line circuit of a power distribution network. Voltage and current measuring values and the total circuit length are obtained after a tail-end fault of the circuit, fundamental waves of voltages and currents of different ends are extracted, it is supposed that the faults occur indifferent sections, a proper range finding equation set is listed for each supposed fault section according to the Kirchhoff's current law and relation between the voltage and current of each phase and line impedance, fault positions and tapping point positions of different groups as well as the self-impedance and mutual impedance in unit length of each line are solved, and a fault point is located direction according to solutions of different sets. The method and system are higher in precision, and basically not influenced by the circuit parameters, fault position, transitional resistance andasymmetric fault type.