170 results about "Phase line" patented technology

The invention discloses a fault diagnosis comprehensive positioning method for an intelligent distribution network, and belongs to the field of fault monitoring. Based on a fault indicator, a wirelesscommunication technology and a ground fault line selection technology, the method comprises the following steps: monitoring zero-sequence voltage of a transformer neutral point in real time, startingzero-sequence fault diagnosis when detecting that a zero-sequence voltage change value exceeds a preset value, and identifying whether the zero-sequence voltage change value is a single-phase grounding fault; if the zero-sequence voltage change value is single-phase grounding fault, performing grounding line selection through a fault diagnosis device in a station, and positioning the grounding fault on a certain phase of a certain line; when the single-phase earth fault is judged to be a stable fault, recalling the real-time current data of the fault indicators on the fault phase line, comparing the signals collected by the fault indicators, comparing the difference of the real-time current data before and after a fault point, judging the two fault indicators with abrupt changes, and thendetermining the specific section of the fault. The method can be widely applied to the field of power distribution network operation fault monitoring and positioning.

The invention relates to a three-phase three-wire system phase voltage measuring method, in particular to a measuring method by a digital integrated electric parameter measuring system by aiming at phase voltages in a three-phase three-wire system connection method. The invention has the technical scheme that the method comprises the following steps: 1. testing three wire voltages UAB, UBC and UCA; 2. calculating the half L of the algebraic sum of the three wire voltages; 3. calculating the area S of a triangle using the three wire voltages as the lengths of three edges; 4. calculating the sum m of the three phase voltages to be measured; and 5. obtaining the respective phase voltages UA, UB and UC of the three phase wires against the ground through calculation. The invention has the advantages that the measuring method has no theoretical error, is applicable to any electric parameter measuring system with the digital operation function, and can calculate the phase voltages on the basis of the measured wire voltage without increasing any hardware circuit cost.

The invention relates to an energy storage converting control technology, and in particular relates to a control method for realizing passive off-network seamless switching by using an energy storage converter. The method comprises the following steps of: (1) determining that an energy conversion system PCS of an energy storage system is in a grid-connected state; (2) recording the Nth three-phase line voltage sampling value of a power grid, wherein N is a natural number; (3) determining the difference between the Nth three-phase line voltage sampling value of the power grid and the (N-M)th three-phase line voltage sampling value of the power grid; (4) judging whether the difference in the step (3) associated with any one phase of the three phases is greater than 15% of the maximum value of the rated voltage or not; (5) when a counter K is greater than or equal to 3, marking the passive off-network position; and (6) when the passive off-network position is marked, the energy conversion system PCS of the energy storage system enters into the off-network state. The method provided by the invention can be used for realizing seamless switching between the grid-connected network and an independently operated off-network for a micro-network, so that power supply is continuously supplied by voltage and frequency in the micro-network, and the load power supply reliability in the micro-network is improved.

The invention discloses a conductive common-mode / differential-mode noise separation method, belonging to the technical field of conductive electromagnetic compatibility noise measurement. Radiofrequency current probe measurement and software separation calculation are combined, and the method is suitable for conductive interference measurement on a single phase line. The method comprises the following measuring steps: I, directly measuring a phase line, center line and common-mode conducted interference spectrum by using a radiofrequency current probe, connecting the output end of the current probe to a spectrometer through a coaxial line, and driving the spectrometer to work in a peak detection mode; II, calibrating interference spectrum data obtained in the step I, and measuring the transmission admittance of the current probe and the coaxial line used in the step I by using a vector network analyzer; III, putting the corrected data IL, IN and ICM into a formula to obtain a differential-mode current spectrum IDM so as to obtain the interference voltage in a differential mode and a common mode. By adopting a test method, the conducted interference spectrum on each line can be measured rapidly, and separation of common-mode and differential-mode interference is realized. The method is mainly applied to online measurement of electromagnetic compatibility noise.

The invention provides a multipoint earth fault detection method, device and system for a secondary current circuit. The method includes the steps that N-phase currents of an N-phase line of a three-phase current circuit and ground line currents of a ground line are collected in real time through a current mutual inductor, and the amplitude and the phase of the 1-kth harmonic of the N-phase currents and the amplitude and the phase of the 1-kth harmonic of the ground line currents are respectively calculated, wherein whether the amplitude of any harmonic, lager than a fault threshold, exists in the amplitude of the 1-kth harmonic of the N-phase currents is judged; if the harmonic exists, whether the amplitude of the harmonic is equal to the amplitude of the corresponding harmonic of the ground line currents and whether the difference between the phase of the harmonic and the phase of the corresponding harmonic of the ground line currents is 180 degrees are further judged; if the amplitude of the harmonic is equal to the amplitude of the corresponding harmonic of the ground line currents and the difference between the phase of the harmonic and the phase of the corresponding harmonic of the ground line currents is 180 degrees, it is judged that multipoint earth faults exist in the secondary current circuit.

The invention discloses a fault line parameter calculation method based on single-phase ground fault record data. The method comprises steps that S1, fault data is acquired, a single-phase ground fault of a line MN occurs, and current and voltage sampling values on both sides of a transmission line are acquired through a fault record device or a relay protection device; S2, a low-pass filter withthe cut-off frequency of 100 Hz is utilized to filter the acquired current and voltage sampling values to remove high-frequency components; S3, the non-fault phase-to-phase line current and voltage onboth sides of the line are calculated; S4, the zero-mode current and the zero-mode voltage on both sides of the line are calculated; S5, fault line parameters are calculated. The method is advantagedin that the fault line parameter calculation problem is solved.

The invention discloses a low-current single-phase earth fault detection method for a 10KV distribution network. The method comprises the steps of (1) data acquisition: tracking and accumulating outgoing line scheduling measurement data and line marketing TTU / load control data of the distribution network line in a normal operation state for a long time so as to calculate the power loss level of each distribution network outgoing line under different loads; (2) establishing a normal loss model of each distribution network outgoing line and an earth fault loss model during single-phase earthingby analyzing correlations among various variables; and (3) judging the fault phase line according to the measurement of the secondary side voltage value of the open triangle PT of each transformer substation bus. According to the invention, the steady-state big data analysis method for automatic operation monitoring of the 10KV distribution network line is realized to perform line selection and fault identification prediction of the small-current earth fault.

A method for monitoring, metering and improving system parameters, including leakage sensitivity and response over a time period in an electrical panel for a single phase system, or a 3-phase system comprising phase lines X, Y and Z, wherein the system reaction and accuracy are critical to a decision to disconnect the line with the malfunction before operation of the leakage breaker to cut off power. Set parameter 1: a leakage threshold in mA that can be changed in system setup mode. Set parameter 2: Allowable deviation in mA for alert; and set parameter 3: Maximum deviation in mA to disconnect currents. Set parameter N for the time to include in an average calculation.

The invention discloses a method and a device for judging overvoltage reasons of a low-voltage transformer area. The method comprises the following steps of: reading hexagonal diagram data every preset time interval from a starting moment; screening the three-phase voltage and the three-phase current at the overvoltage moment; acquiring amplitudes of three-phase line voltages without background factors; judging whether the amplitudes of the three-phase line voltages are equal in a deviation range or not so as to judge whether system-side overvoltage is included in causes of overvoltage or not;and further judging the overvoltage reason caused by the load side according to the three-phase imbalance state index and the grounding resistance state index, and introducing a utility function to evaluate the influence degree. The method and the device for judging the overvoltage reason of the low-voltage transformer area can effectively determine which factor causes the overvoltage problem ofa 380V three-phase four-wire system power distribution network, can evaluate the influence degree of the factor on the overvoltage problem, and are convenient for the research of the overvoltage problem of the power distribution network.

The invention discloses a magnetic induction type current measurement method suitable for parallel three-phase line fault line selection, and relates to the technical field of power grid fault measurement. Magnetic field sensors are annularly arranged at the position away from the center of a wire by the distance R, and the difference between the sensitive directions of the adjacent magnetic fieldsensors on the same wire is 90 degrees; and decoupling calculation is performed on the instantaneous current value of the three-phase wire through the measurement values of the magnetic field sensors, so that a three-phase current measurement value after decoupling compensation can be obtained. According to the method, when magnetic induction type current measurement is carried out on the parallel three-phase wires, measurement errors caused by mutual influence of magnetic fields generated by the parallel three-phase wires are reduced, so that more accurate measurement values are obtained inmeasurement scenes with higher requirements on measurement accuracy, such as small-current grounding fault line selection, and the success rate of line selection is increased. According to the algorithm, many complex quantities in compensation calculation are adaptively simplified, the calculation steps and complexity are reduced, and the requirement for the calculation capability of measurement equipment is reduced.

The present invention discloses a measurement loop wiring error determination method and device. The method mainly comprises: emitting voltage / current test signals according a preset period; obtaining the number of cyclic waves of the test signals and the corresponding cyclic wave initial phases of the test signals; receiving feedback signals; obtaining the number of cyclic waves of the feedback signals; screening determination signals located at the same phase lines as the test signals according to the number of cyclic waves of the test signals and the number of cyclic waves of the feedback signals; determining the wiring correctness according to the corresponding cyclic wave initial phases of the test signals and the corresponding cyclic wave initial phases of the determination signals; and outputting a detection result. The measurement loop wiring error determination method and device can effectively solve the problem that a current detection method is low in efficiency.

The invention relates to a method for generating three-phase sine waves, comprising an angle generation step and a phase voltage waveform data generation step. In the method, the range of a phase angle theta in a certain sampling period is judged according to the value of the phase angle theta, data conversion processing is carried out, the duty ratio data u of phase voltage in the sampling period are obtained and transmitted to a PWM generator, and the PWM generator sends out a pulse control signal for controlling the operation of a switching component, so that a phase voltage waveform of a certain phase is output, and a three-phase phase voltage waveform vector with the phase angle phase difference of 120 degrees is synthesized to obtain a three-phase line voltage sine wave; and when the maximum value of phase voltage is U, the maximum value of line voltage is 2U, and the obtained three-phase line voltage is sequentially symmetrical. Compared with a traditional mode that the line voltage is 2 times of the phase voltage when the three-phase phase voltage is a sine wave, the voltage utilization rate of a switching component in a power unit is enhanced, so that the purpose of lowering the power supply voltage of the power unit is realized.

The invention relates to a three-phase voltage measuring method, circuit and equipment. The method comprises the steps: enabling any two phase lines to be connected to the three-phase voltage measurement circuit at the same time through the gating function of a gating device by utilizing three probes to be electrically coupled with a first phase line, a second phase line and a third phase line respectively when each phase voltage of three-phase power is measured. The signal processing device analyzes the aliasing signals at the two ends of the measuring capacitor when any two phase lines are connected, so that each line voltage of the three-phase power to be measured can be correspondingly obtained. Finally, the signal processing device performs analysis and calculation according to each line voltage to obtain each phase voltage of the to-be-measured three-phase power. According to the scheme, when each phase voltage is measured, the insulation layers of the phase lines do not need to be stripped, each phase line is directly connected in an electrical coupling mode, meanwhile, the three-phase power does not need to be provided with a neutral line, each phase voltage of the three-phase power to be measured can be measured, and high measurement reliability is achieved.

The invention discloses a line protection CT disconnection locking method and system under a power flow reverse condition, and a medium. The method comprises the steps: carrying out the fault judgmentaccording to the power flow reverse direction of an A-phase line, a B-phase line and a C-phase line, and obtaining a fault judgment result; performing OR logic operation on the fault judgment result,the monitoring result of the first zero-sequence current monitoring logic and the output fault state self-hold logic judgment result, and performing broadening to obtain an output fault state self-hold logic judgment result; and negating the output fault state self-hold logic judgment result, performing AND logic operation on the negated result and the monitoring result of the second zero-sequence current monitoring logic, and delaying the operation result to serve as a CT disconnection control signal. The self-hold logic for zero-sequence current compensation is included, the locking effectcan be achieved in the whole fault period after power flow is reversed, and it is avoided that line protection is locked by CT when zero-sequence current is between a CT disconnection action value anda zero-sequence overcurrent protection action value under the high-resistance grounding fault.

The invention discloses a single-phase fault phase selection method, device and equipment based on line voltage increment and a medium. The method comprises the following steps: acquiring bus three-phase voltage and line voltage of a transformer substation; calculating bus zero-sequence voltage according to the bus three-phase voltage; judging whether a single-phase earth fault exists or not according to the bus three-phase voltage and the zero-sequence voltage at the current moment; if so, extracting a bus three-phase line voltage before the fault; calculating the increment of the line voltage amplitude according to the bus three-phase line voltage at the current moment and the bus three-phase line voltage before the fault; sorting the increment of the line voltage amplitudes from large to small to obtain an increment maximum value, an increment intermediate value and an increment minimum value in sequence; generating an algorithm criterion according to the maximum value of the increment, the intermediate value of the increment and the minimum value of the increment; and selecting a fault phase in the three phases according to the result of the algorithm criterion. According to the method, the unbalance amount of a neutral point ungrounded power distribution system before the fault is considered, and high phase selection accuracy is achieved in the actual fault.

The invention discloses a phase current acquisition method, device, equipment and system and a storage medium. The method comprises the following steps: acquiring equivalent electrical parameters of a transformer sampling and conditioning circuit, wherein the transformer sampling and conditioning circuit is used for acquiring a current signal of a secondary side of a current transformer arranged on a phase line of a motor; determining a phase shift angle of the current transformer based on the equivalent electrical parameters and the electrical angular velocity of the motor rotor; and performing phase shift compensation on the current signal acquired by the mutual inductor sampling conditioning circuit based on the phase shift angle to obtain the phase current of the phase line. Therefore, the phase current in the phase line of the motor can be acquired based on the current transformer, and especially in an overmodulation area, acquisition of the phase current can be realized on the basis of satisfying an effective voltage vector, so that the output torque of the motor can be increased and the utilization rate of the power supply voltage can be improved under the condition that the bus voltage is not changed.

The invention relates to a correction dielectric constant-based voltage measurement method and device, computer equipment and a storage medium. The method comprises the steps of constructing a three-phase line for a three-phase power line scene, correcting an electric field coupling model of a harmonic source and a sensor, and determining model parameters corresponding to the electric field coupling model; displacement current flowing into a sensor measurement loop is obtained, and the corresponding relation between sensor output voltage and field source conductor potential is established; performing spectral decomposition on the output voltage of the sensor to obtain a first frequency point and a second frequency point, and correcting the dielectric constant by adopting the first frequency point to obtain a corrected dielectric constant; and on the basis of the second frequency point, according to the corrected dielectric constant and the corresponding relationship between the sensor output voltage and the field source conductor potential, determining the ground potential corresponding to each field source conductor, and obtaining voltage measurement data by adopting the ground potential corresponding to each field source conductor. By adopting the method, the voltage measurement error can be reduced, and the voltage measurement precision is improved.

The invention provides a metering device wire misconnection analysis method and system based on internal data of an electric energy meter, and the method comprises the steps: obtaining original data collected by the electric energy meter, and classifying the original data according to an access phase line mode of the electric energy meter; and judging a voltage access mode of the classified data according to a voltage phase sequence, respectively listing a correct expression of a power factor angle and an expression under the current real wiring according to the relationship between the voltage and the current of each element in space, and realizing wire misconnection analysis through the distribution of vectors in the space. Based on the method, the invention further provides the meteringdevice wire misconnection line analysis system based on the internal data of the electric energy meter. According to the invention, strong voltage is not required to be contacted in the operation process, and work contents such as wiring condition analysis, vector diagram drawing, power expression calculation, correction coefficient calculation, electric quantity compensation and electric chargecompensation calculation of an electric energy metering device are completed through database and software analysis by acquiring internal data of the electric energy meter; therefore, electric shock danger is avoided and the working efficiency is improved.

The invention discloses a synchronous signal obtaining system and method. The system comprises a phase-line conversion module, a 3 / 2 conversion module, a band-pass filter, a line-phase conversion module and a signal generation module. The method comprises the following steps: converting the three-phase voltage into a three-phase line voltage; converting the three-phase line voltage into a line voltage in a two-phase static coordinate system; filtering the disturbing signals in a power grid, obtaining the sine wave with the same frequency as the power grid, and ensuring that the output signal has the same phase as the input signal; converting the line voltage in the two-phase static coordinate system into a phase voltage in the two-phase static coordinate system; and obtaining a synchronous signal based on the phase voltage in the two-phase static coordinate system. According to the synchronous signal obtaining system and method provided by the invention, due to line-phase conversion and phase-line conversion, high-performance extraction of synchronous signals can be realized in the case of unbalance or disturbance of the power grid. Moreover, as phase shift does not exist in the output and input of the band-pass filter, the filtering performance is good.

The invention discloses a method for locating a fault point of an operation failure of a residual current protection device in a low-voltage distribution line, which improves fault point location efficiency and shortens location time. The method comprises the following steps: judging whether the residual current protection device is at fault; if not, judging whether a phase line and a neutral line of a low-voltage distribution line are at fault; and carrying out rapid judgment and location on the fault point according to the golden section method. The method disclosed by the method takes fulluse of the function of a residual current clamp meter.

The invention relates to a three-phase load imbalance adjustment method and device, distribution transformer side monitoring equipment, a three-phase load imbalance adjustment system and a storage medium. The method comprises the following steps that: the phase current of each phase line on the outgoing line side of a distribution transformer and the current of each branch are acquired, and the current three-phase unbalance degree iscalculated according to the phase current of each phase line; if the condition that the current three-phase unbalance degree meets an adjustment condition, an optimal target load branch is determined according to the minimum value in the pre-judged three-phase unbalance degree, and a current commutation instruction is generated according to a commutation mode corresponding to the optimal target load branch, the pre-judged three-phase unbalance degree refers to the three-phase unbalance degree which is obtained after each target load branch is connected to the phase line with the minimum phase current in a commutation mode and is calculated according to the phase current of each phase line and the current of each branch. With the method adopted, excessive commutation in a three-phase load imbalance adjustment process can be avoided, so that the service lives of a commutation switch and electric equipment are prolonged.

The invention discloses a single-phase high-resistance line break fault identification method and device of a power distribution network. A wide area measurement system is used to synchronously measure three phases of voltages in the downstream load side of a fault, the voltage amplitude of the fault phase in the load side is calculated and analyzed, and high-resistance single-phase line break fault identification is carried out on the basis of the voltage amplitude of the fault phase in the load side. Compared with a traditional identification method, a load-side equivalent circuit model under different grounding conditions and different grounding transitional resistances is analyzed and calculated, the fault identification method has a higher identification accuracy and wider applicationrange, and a feasible effective new scheme is provided for overcoming difficulty in single-phase high-resistance line break fault identification of the power distribution network.

The invention relates to a power distribution network single-phase earth fault detection method and system. The power distribution network single-phase earth fault detection method comprises steps that S1, a plurality of detection devices send detected three-phase current sampling data to a detection collection terminal, and the detection collection terminal filters all the three-phase current sampling data; and S2, the detection collection terminal calculates three-phase abrupt change current effective values and three groups of correlation coefficients between every two phase lines accordingto the three-phase current sampling data sent by each detection device. The metod is advantaged in that the single-phase earth fault identification is carried out based on three-phase current sampling data, the single-phase earth fault detection method provided by the invention does not need to additionally acquire a zero-sequence voltage signal, improves fault detection efficiency, is convenientand quick in configuration of the detection topology, even does not need to update hardware equipment, can finish updating only by replacing the detection method with the single-phase earth fault detection method provided by the invention, and has great progress.

The invention discloses a transformer area multi-layer topological structure identification method based on data driving, and the method comprises the steps: S1, converting the identification problem of a multi-layer topological structure into the solution of an adjacent matrix in a graph theory according to the characteristic that a low-voltage distribution network presents a radial tree structure; s2, performing frequency domain filtering on the active power time sequence of the feeder unit and the branch unit for feature extraction; s3, obtaining the upstream and downstream and parallel relation of the units by adopting a correlation analysis method based on the highlighted features; s4, in combination with the voltage amplitude characteristics of the nodes, realizing identification of adjacent units of the user, and determining the corresponding relation between the user and the isolated sub-network; and S5, carrying out linear transformation on the line section of the isolated sub-network and the active power sequence of the user while considering the data error, and determining the line section to which the user belongs through regression analysis to achieve the construction of a multi-layer topological structure. According to the method, the identification of a feeder-branch-phase line-user multilayer topological structure is realized, so that the investment for deploying a large number of monitoring equipment or changing an equipment communication mode is greatly reduced.

The invention provides a phase-splitting identification method and device for an electric energy meter in a transformer area, a terminal and a storage medium. The method comprises the steps of obtaining first power consumption and second power consumption in the transformer area through metering equipment in the transformer area, and in combination with a phase-splitting correlation coefficient of the electric energy meter and a fixed loss rate of a line segment, establishing a phase-splitting energy relation model based on an energy conservation law, and resolving the phase-splitting energy relation model through a least square estimation solution algorithm according to a linear algebraic theory, so as to determine a phase line hung on a single-phase user electric energy meter according to an electric energy meter phase-splitting correlation coefficient obtained through model resolving. The technical problems that the manual synchronization efficiency of the existing low-voltage transformer area electric energy meter phase line is low, and the increasingly refined management requirement is difficult to meet are solved.

A three-phase line mutual feedback power balance control method is provided. By controlling the mutual feedback power of a three-phase line, bidirectional tide flow of the mutual feedback power of thethree-phase line is achieved at the same time, and three-phase balance at the tail end of a power grid is achieved. The method comprises the following steps: 1, respectively comparing three-phase line voltages Ua, Ub and Uc with a national standard voltage lower limit Ulgb and a national standard voltage upper limit Uugb, and identifying a phase line with the highest voltage, a phase line with the second highest voltage and a phase line with the lowest voltage in the three-phase line; meanwhile, calculating the difference value Udiff between the voltage value Uac_max of the highest-voltage phase and the voltage value Uac_min of the lowest-voltage phase; 2, calculating feed power values Pdiff under different conditions according to the impedance rmin of the lowest-voltage phase line and the optimized power coefficient epsilon; and 3, when Ulgb < = (Ua, Ub, Uc) < = Uugb or Uac_max > = Uugb or Uac_min < = Ulgb, controlling the controllable rectification of a power module corresponding tothe highest-voltage phase line, inverting the output of a power module corresponding to the lowest-voltage phase line according to the feed power value, and feeding the power of the highest-voltage phase line to the lowest-voltage phase line to reduce the voltage difference of the lines, wherein Uac_max is the voltage value of the highest-voltage phase line, and Uac_min is the voltage value of the lowest-voltage phase line.

The invention relates to a low-voltage transformer area topology identification method, which comprises the following steps: classifying equipment into different phase line areas (A, B and C) by utilizing a density-based clustering algorithm DBSCAN according to the voltage similarity of the equipment on a same-phase feeder line, and excluding the equipment which does not belong to the transformer area; secondly, based on the basic law of energy conservation and the characteristic that the input power of the upstream equipment is equal to the sum of the power of the downstream equipment, judging the connectivity between the upstream equipment and the downstream equipment jointly by combining two factors including a power Pearson's correlation coefficient and a residual sum of squares; and finally, adjusting the connectivity of the equipment, and establishing an optimal transformer area topological structure. According to the invention, topology identification of the low-voltage transformer area can be accurately and efficiently realized, so that fine management of a power distribution network side is facilitated.

The invention discloses a topology identification method of a low-voltage power distribution network topology identification system. A main station and a concentrator are in wireless communication orwired network communication, implementation is simple and convenient, the concentrator and the node information collector adopt power line carrier communication, and the concentrator and the node information collector which can communicate with each other are ensured to belong to the same transformer area, so that the comparison of voltage zero crossing point time in the same transformer area in the step 2 is facilitated, and the problem of confusion of data among different transformer areas is avoided. Besides, according to the topology identification method, the voltage zero-crossing time ofeach node is compared with the voltage zero-crossing time of an A-phase line, a B-phase line and a C-phase line in the same transformer area to identify an in-phase line node group; and the identification method is simple and easy, and is beneficial to determining that the nodes in the correlation comparison in the step 3 are the nodes connected to the same phase line, and is beneficial to improving the correlation comparison efficiency in the step 3.

The invention discloses a voltage sag event normalization method based on waveform characteristics. The voltage sag event normalization method comprises the following steps of S1, acquiring A, B and Cthree-phase voltage amplitudes by utilizing a voltage monitoring device; S2, filtering zero-sequence voltage of A, B and C three-phase voltage amplitudes to obtain A, B and C three-phase voltage andA, B and C three-phase line voltage; S3, judging a sag type according to the A, B and C three-phase voltage and the A, B and C three-phase line voltage; S4, according to the A, B and C three-phase voltage amplitudes, calculating the segment similarity of events of the same sag type; S5, obtaining an initial similarity set according to the segment similarity of the events of the same sag type; andmining and correcting the influence of the transformer based on the association rule, outputting a normalization identification result, and completing normalization processing of the voltage sag event. According to the method, the influence of the monitoring device on the time error is overcome, the method does not completely depend on the criterion of the voltage sag occurrence moment, the sag waveform characteristics are considered, normalization identification is carried out by taking the sag waveform characteristics as the criterion, and the accuracy is high.