An Online Monitoring Method for Low-Frequency Overvoltage of Electromagnetic Voltage Transformer Based on Labview

Abstract

The present invention discloses an online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview. The steps include: 1) Transmitting the denoised secondary-side digital voltage signal to the monitoring system based on Labview; 2) Calculating the inverse digital voltage signal of the primary side of the electromagnetic voltage transformer through the voltage inverse calculation module; 3) The data processing module performs waveform analysis on the calculated inverse digital voltage signal of the primary side of the electromagnetic voltage transformer, and extracts the amplitudes and phase angles of each harmonic; 4) The overlimit module is used to determine whether the low-frequency overvoltage acting on the electromagnetic voltage transformer exceeds the upper limit voltage value, and there is a risk of endangering the power grid; 5) The monitoring system based on Labview has command interaction with the main control system. The monitoring system based on Labview can transmit all the data in the data storage module to the main control system, and the main control system can also remotely control the monitoring system based on Labview. The method of the present invention can effectively monitor the low-frequency overvoltage of electromagnetic voltage transformers online.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic voltage transformers, and specifically to an online monitoring method and system for low-frequency overvoltage of electromagnetic voltage transformers based on Labview. Background Art

[0002] The digital and intelligent development of the power system is an urgent need and an inevitable trend under the background of the global digital era, and is a key development direction of China's energy development strategy. For this reason, the two major power grid companies have further deepened the technological innovation of the power Internet of Things and continuously promoted the digital transformation of the smart grid, which is based on the use of various sensing terminals to real-time sense and process the state of the power grid.

[0003] With the emergence of the new power system, the proportion of a large number of clean energy sources such as wind, light, and water in power generation is gradually increasing. Secondly, in the new power system, the proportion of power electronic devices is also increasing continuously, resulting in a large number of electromagnetic transient processes in the power system. However, the current electrical equipment is difficult to stably and real-time sense the electromagnetic transient information generated in the power grid for a long time, and there is no mature electromagnetic transient monitoring method. It will be more difficult to suppress the electromagnetic transient disturbances in the power grid, and at the same time, it has also caused a huge obstacle to the introduction of clean energy and a large number of power electronic devices.

[0004] There are more than 600 million transformers in the global power system, which are used for real-time sensing of information such as voltage and current measurement and protection. However, under the action of electromagnetic disturbance voltages such as harmonics, transient impulses, and DC bias magnetic fields, it is extremely easy to cause distortion of the secondary waveform of the transformer, and the error even exceeds 100%, becoming a "roadblock" to the development of the digital power system. The electromagnetic voltage transformer is the main sensing terminal for measuring the voltage of the power system measurement system, providing reliable power frequency signals for measurement, protection, and control devices. In addition to power frequency signals, the electromagnetic voltage transformer is also a measurement terminal for harmonics and overvoltages. However, due to the frequency-varying characteristics of the transformer parameters, distributed stray parameters, and the nonlinear characteristics of the iron core, when harmonic aliasing and transient impulses occur in the system, the transmission characteristics of the transformer will show complex variation laws with the change of the excitation voltage frequency and amplitude, resulting in distortion of its output signal and a sharp increase in its harmonic and transient voltage measurement errors. Therefore, the electromagnetic voltage transformer cannot realize the sensing of harmonics and transient voltages, and there is no mature monitoring method based on the electromagnetic voltage transformer that takes into account harmonics and transient voltages, resulting in a long-term lack of electromagnetic transient voltage data in the distribution network, seriously restricting the development of power grid accident traceability, harmonic monitoring, and fault diagnosis work, and becoming one of the key bottlenecks in the digital and intelligent development of the power system. Summary of the Invention

[0005] The object of the present invention is to provide an online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview, including the following steps:

[0006] 1) Build a monitoring and analysis system for the secondary side distortion signal of an electromagnetic voltage transformer, including a secondary side signal measuring device for voltage, a signal isolator, a signal acquisition device, a monitoring and control system based on Labview, and a main control system;

[0007] The monitoring and control system based on Labview includes a voltage back-calculation module, a data processing module, a voltage over-limit module, a parameter input module, and a user permission module;

[0008] The monitoring and control system based on Labview further includes a user permission module;

[0009] The user permission module is used to provide ports for user login and registration;

[0010] The user permission module verifies the user login key. If the verification fails, the user has no right to use the monitoring and control system based on Labview.

[0011] The user permission module is set with a reference level;

[0012] The user permission module assigns an account level to each user. If the user account level is lower than the reference level, the user cannot access the database of the monitoring and control system based on Labview.

[0013] The main control system is used to modify the user's account level.

[0014] The monitoring and control system based on Labview further includes a human-computer interaction module;

[0015] The human-computer interaction module includes a user visualization interface;

[0016] The user visualization interface includes a window for displaying the secondary side voltage signal, a window for the primary side back-calculated digital voltage signal, and a window for the user to input the parameters of the electromagnetic voltage transformer;

[0017] The monitoring and control system based on Labview further includes a data storage module;

[0018] The data storage module is used to store all data of the monitoring and control system based on Labview.

[0019] 2) Use the secondary side signal measuring device for voltage to monitor the secondary side voltage signal of the electromagnetic voltage transformer and input it into the signal isolator;

[0020] 3) The signal isolator denoises the secondary side voltage signal and inputs it into the signal acquisition device;

[0021] 4) The signal acquisition device converts the denoised secondary-side voltage signal into a secondary-side digital voltage signal and inputs it into the monitoring and control system based on Labview;

[0022] 5) The parameter input module obtains the parameters of the electromagnetic voltage transformer and inputs them into the voltage back-calculation module;

[0023] The parameters of the electromagnetic voltage transformer include the resistance values of two nonlinear excitation resistors, the resistances of two primary and secondary windings, one core leakage inductance, two primary and secondary capacitances, two nonlinear inductance magnetic fluxes, and the excitation currents corresponding to the two nonlinear inductances.

[0024] 6) The data processing module receives the secondary-side digital voltage signal, denoises the secondary-side digital voltage signal, and transmits the denoised secondary-side digital voltage signal to the voltage back-calculation module;

[0025] 7) The voltage back-calculation module stores an inversion model of the electromagnetic voltage transformer;

[0026] The voltage back-calculation module inputs the received secondary-side digital voltage signal into the inversion model of the electromagnetic voltage transformer, calculates the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer, and transmits it to the data processing module and the over-limit module;

[0027] The secondary-side voltage inversion model is a forward circuit π model of the electromagnetic voltage transformer considering core nonlinearity and winding stray capacitance;

[0028] The steps for calculating the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer include:

[0029] 7.1) Let the intermediate coefficient k = N / N 2 ; where the number of turns N = N 1 ; N 1 and N 2 are the number of turns of the primary and secondary windings of the electromagnetic voltage transformer;

[0030] 7.2) Calculate the current ic 2 flowing through the inter-turn capacitance on the secondary side of the electromagnetic voltage transformer, that is:

[0031]

[0032] In the formula, C 2 is the inter-turn capacitance of the secondary winding; u 2 is the port secondary-side voltage; t is time;

[0033] 3) Calculate the untransformed voltage u 3 of the ideal transformer on the secondary side, that is:

[0034] u3 = u 2 -(-i c2 R 2s ) = u 2 + i c2 R 2s (2)

[0035] Wherein, i c2 is the inter-turn capacitance current of the secondary winding; R 2s is the resistance of the secondary winding;;

[0036] 7.4) Calculate the node voltage u 4 of the secondary branch, that is:

[0037] u 4 = ku 3 (3)

[0038] 7.5) Calculate the current i C3 of the ideal transformer on the secondary side after reduction, that is:

[0039]

[0040] 7.6) Calculate the current i Ls flowing through the leakage inductance Ls, that is:

[0041] i Ls = i Lm2 + i Rm2+ i C3 (5)

[0042] Among them, the exciting inductance current i Lm2 of the secondary side is as follows:

[0043] i Lm2 = f(λ 2 ) (6)

[0044] Wherein, f() represents the current change function; the secondary magnetic flux indicates that the magnetic flux λ 2 is the integral value of the node voltage u 4 ;

[0045] 7.7) Calculate the exciting resistance current i Rm2 of the secondary side, that is:

[0046] i Rm2 = f(u 4 ) (7)

[0047] 7.8) Calculate the node voltage u 5 of the primary branch, that is:

[0048]

[0049] In the formula, L s is the iron core leakage inductance; i Ls is the iron core leakage inductance current;

[0050] 7.9) Calculate the current i 11 flowing through the node of the primary side branch, that is:

[0051] i 11 = i Ls + i Lm1 + i Rm1 (9)

[0052] Among them, the primary side exciting inductance current i Lm1 is as follows:

[0053] i Lm1＝ f(λ 1 ) (10)

[0054] In the formula, the primary side magnetic flux indicates that λ 1 is the integral value of the node voltage u 5 ;

[0055] 7.10) Calculate the primary side exciting resistance current i Rm1 , that is:

[0056] i Rm1 = f(u 5 ) (11)

[0057] 7.11) Calculate the primary side ideal transformer current i 12 , that is:

[0058] i 12＝ i 11 (12)

[0059] 7.12) Establish the expression of the reverse calculated digital voltage signal u 1 of the primary side of the electromagnetic voltage transformer, that is:

[0060] u 1 = i 12 ·R 1s + u 5 (13)

[0061] 7.13) According to formulas (1)-(13), calculate the reverse calculated digital voltage signal u 1 of the primary side of the electromagnetic voltage transformer, that is:

[0062]

[0063] In the formula, R 1s , R 2sis the resistance of the secondary winding.

[0064] 8) The data processing module analyzes the secondary digital voltage signal and the primary-side back-calculated digital voltage signal to obtain the maximum relative voltage error, thereby obtaining the distortion rate of the secondary-side voltage signal when a low-frequency overvoltage acts on the electromagnetic voltage transformer.

[0065] The data processing module performs Fourier decomposition on the primary-side back-calculated digital voltage signal to obtain the amplitudes and phase angles of the harmonics of the primary-side back-calculated digital voltage signal.

[0066] 9) The voltage overlimit module stores the upper limit voltage value.

[0067] The voltage overlimit module compares the primary-side back-calculated digital voltage signal with the upper limit voltage value. If the primary-side back-calculated digital voltage signal is greater than the upper limit voltage value, it sends a risk warning prompt to the main control system.

[0068] 10) After receiving the risk warning prompt, the main control system retrieves and displays all the data of the monitoring and control system based on Labview, and performs waveform analysis and fault tracing.

[0069] The technical effect of the present invention is beyond doubt. When the impulse overvoltage generated in the power grid causes significant distortion of the secondary-side voltage of the electromagnetic voltage transformer due to the non-linear and frequency-dependent characteristics of the iron core, the present invention provides a control scheme for the subsequent control system to process the data of the secondary-side voltage distortion of the electromagnetic voltage transformer, so that the main control system of the power grid can monitor the voltage waveform of the impulse overvoltage generated in the power grid in real time.

[0070] The method of the present invention can effectively monitor and regulate the voltage with wide frequency band and wide amplitude caused by electromagnetic transients in the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 is the working flow chart of the monitoring system based on Labview;

[0072] Figure 2 is the structural schematic diagram of the monitoring system based on Labview;

[0073] Figure 3 is the interface of the monitoring system based on Labview

[0074] Figure 4 is the visual voltage waveform display interface; Figure 4 (a)-(b) are respectively the distorted waveform and the true waveform of the primary-side voltage;

[0075] Figure 5 is the circuit diagram of the inversion model of the electromagnetic voltage transformer. Detailed implementation manners

[0076] The present invention will be further described below in conjunction with embodiments, but it should not be understood that the above-mentioned subject matter scope of the present invention is limited to the following embodiments. Without departing from the above technical idea of the present invention, various substitutions and changes made according to ordinary technical knowledge and conventional means in the art shall be included within the protection scope of the present invention.

[0077] Embodiment 1:

[0078] See Figures 1 to 5 , an online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview, including the following steps:

[0079] 1) Build a monitoring and analysis system for the distortion signal on the secondary side of the electromagnetic voltage transformer, including a voltage secondary side signal measuring device, a signal isolator, a signal acquisition device, a monitoring and control system based on Labview, and a main control system;

[0080] The voltage secondary side signal measuring device is used to monitor the secondary side voltage signal of the electromagnetic voltage transformer;

[0081] The signal isolator is used to denoise the secondary side voltage signal;

[0082] The signal acquisition device is used to convert the denoised secondary side voltage signal into a secondary side digital voltage signal;

[0083] The monitoring and control system based on Labview includes a voltage back-calculation module, a data processing module, a voltage overlimit module, a parameter input module, and a user permission module;

[0084] The parameter input module is used to obtain the parameters of the electromagnetic voltage transformer;

[0085] The voltage back-calculation module is used to inversely calculate and obtain the primary side back-calculated digital voltage signal;

[0086] The data processing module is used to process and analyze the secondary side digital voltage signal and the primary side back-calculated digital voltage signal;

[0087] The voltage overlimit module is used to judge whether the primary side back-calculated digital voltage signal exceeds the limit;

[0088] The monitoring and control system based on Labview further includes a user permission module;

[0089] The user permission module is used to provide ports for user login and registration;

[0090] The user permission module verifies the user login key. If the verification fails, the user has no right to use the monitoring and control system based on Labview.

[0091] The user permission module is set with a reference level;

[0092] The user permission module assigns an account level to each user. If the user's account level is lower than the reference level, the user cannot access the database of the Labview-based monitoring and control system.

[0093] The main control system is used to modify the user's account level.

[0094] The Labview-based monitoring and control system further includes a human-computer interaction module;

[0095] The human-computer interaction module includes a user visualization interface;

[0096] The user visualization interface includes a window for displaying the secondary side voltage signal, a window for the primary side back-calculated digital voltage signal, and a window for the user to input the parameters of the electromagnetic voltage transformer;

[0097] The Labview-based monitoring and control system further includes a data storage module;

[0098] The data storage module is used to store all data of the Labview-based monitoring and control system.

[0099] 2) Use a voltage secondary side signal measuring device to monitor the secondary side voltage signal of the electromagnetic voltage transformer and input it into the signal isolator;

[0100] 3) The signal isolator denoises the secondary side voltage signal and inputs it into the signal acquisition device;

[0101] 4) The signal acquisition device converts the denoised secondary side voltage signal into a secondary side digital voltage signal and inputs it into the Labview-based monitoring and control system;

[0102] 5) The parameter input module obtains the parameters of the electromagnetic voltage transformer and inputs them into the voltage back-calculation module;

[0103] The parameters of the electromagnetic voltage transformer include the resistance values of two nonlinear excitation resistors, two primary and secondary winding resistances, one core leakage inductance, two primary and secondary capacitances, two nonlinear inductance magnetic fluxes, and the excitation currents corresponding to the two nonlinear inductances.

[0104] 6) The data processing module receives the secondary side digital voltage signal, denoises the secondary side digital voltage signal, and transmits the denoised secondary side digital voltage signal to the voltage back-calculation module;

[0105] 7) The voltage back-calculation module stores an electromagnetic voltage transformer inversion model, and its circuit structure is shown inFigure 5 ;

[0106] The voltage back-calculation module inputs the received secondary-side digital voltage signal into the electromagnetic voltage transformer inversion model, calculates the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer, and transmits it to the data processing module and the over-limit module;

[0107] The secondary-side voltage inversion model is the forward circuit π model of the electromagnetic voltage transformer considering the core nonlinearity and winding stray capacitance;

[0108] The steps for calculating the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer include:

[0109] 7.1) Let the intermediate coefficient k = N / N 2 ; where the number of turns N = N 1 ; N 1 and N 2 are the number of turns of the primary and secondary windings of the electromagnetic voltage transformer;

[0110] 7.2) Calculate the current ic flowing through the inter-turn capacitance on the secondary side of the electromagnetic voltage transformer 2 , that is:

[0111]

[0112] In the formula, C 2 is the inter-turn capacitance of the secondary winding; u 2 is the port secondary-side voltage; t is time;

[0113] 3) Calculate the un-reduced voltage u 3 of the ideal transformer on the secondary side, that is:

[0114] u 3 = u 2 - (-i c2 R 2s ) = u 2 + i c2 R 2s (2)

[0115] In the formula, i c2 is the inter-turn capacitance current of the secondary winding; R 2s is the secondary winding resistance;;

[0116] 7.4) Calculate the node voltage u 4 of the secondary-side branch, that is:

[0117] u 4 = ku 3 (3)

[0118] 7.5) Calculate the current i after reduction of the ideal transformer on the secondary sideC3 , namely:

[0119]

[0120] 7.6) Calculate the current i flowing through the leakage inductance Ls Ls , namely:

[0121] i Ls = i Lm2 + i Rm2+ i C3 (5)

[0122] wherein, the secondary side exciting inductance current i Lm2 is as follows:

[0123] i Lm2 = f(λ 2 ) (6)

[0124] In the formula, f() represents the current change function; the secondary side magnetic flux indicates that the magnetic flux λ 2 is the integral value of the node voltage u 4 ;

[0125] 7.7) Calculate the secondary side exciting resistance current i Rm2 , namely:

[0126] i Rm2 = f(u 4 ) (7)

[0127] 7.8) Calculate the primary side branch node voltage u 5 , namely:

[0128]

[0129] In the formula, L s is the core leakage inductance; i Ls is the core leakage inductance current;

[0130] 7.9) Calculate the current i flowing through the primary side branch node 11 , namely:

[0131] i 11 = i Ls + i Lm1 + i Rm1 (9)

[0132] wherein, the primary side exciting inductance current i Lm1 is as follows:

[0133] i Lm1＝ f(λ 1 ) (10)

[0134] Wherein, the primary-side magnetic flux linkage indicates λ 1 is the integral value of the node voltage u 5 ;

[0135] 7.10) Calculate the primary-side exciting resistance current i Rm1 , that is:

[0136] i Rm1 = f(u 5 ) (11)

[0137] 7.11) Calculate the primary-side ideal transformer current i 12 , that is:

[0138] i 12＝ i 11 (12)

[0139] 7.12) Establish the expression of the back-calculated digital voltage signal u 1 on the primary side of the electromagnetic voltage transformer, that is:

[0140] u 1 = i 12 ·R 1s + u 5 (13)

[0141] 7.13) According to formulas (1)-(13), calculate the back-calculated digital voltage signal u 1 on the primary side of the electromagnetic voltage transformer, that is:

[0142]

[0143] Wherein, R 1s , R 2s are the primary and secondary winding resistances.

[0144] 8) The data processing module analyzes the secondary-side digital voltage signal and the primary-side back-calculated digital voltage signal to obtain the maximum relative voltage error, so as to obtain the distortion rate of the secondary-side voltage signal when a low-frequency overvoltage acts on the electromagnetic voltage transformer;

[0145] The data processing module performs Fourier decomposition on the primary-side digital voltage signal to obtain the amplitudes and phase angles of the harmonics of the primary-side digital voltage signal;

[0146] At this time, the user can clearly feel the distortion rate of the secondary-side voltage signal when a transient impulse voltage in the power grid acts on the electromagnetic voltage transformer;

[0147] The uses of obtaining the amplitudes and phase angles of the harmonics of the primary-side back-calculated digital voltage signal include: the user can clearly observe the harmonic components and phase angle conditions of the impulse voltage, and then monitor the power grid state in real time.

[0148] When abnormal voltage fluctuations occur in the power grid, this part of the data can be called for waveform analysis and fault tracing.

[0149] 9) The voltage over-limit module stores the upper limit voltage value;

[0150] The voltage over-limit module compares the primary-side back-calculated digital voltage signal with the upper limit voltage value. If the primary-side back-calculated digital voltage signal is greater than the upper limit voltage value, a risk warning prompt is sent to the main control system.

[0151] 10) After receiving the risk warning prompt, the main control system retrieves and displays all the data of the monitoring and control system based on Labview, conducts waveform analysis and fault tracing. The main control system conducts waveform analysis and fault tracing through the called data such as voltage waveforms and harmonic characteristics, and quickly takes subsequent actions.

[0152] Embodiment 2:

[0153] See Figures 1 to 5 , an online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview, the content includes:

[0154] First step, reduce the signal interference during transmission of the secondary-side voltage signal of the electromagnetic voltage transformer through a signal isolator;

[0155] Second step, input the processed secondary-side voltage signal of the electromagnetic voltage transformer into the analog input channel of the signal acquisition device and convert it into a digital signal through the internal A / D of the signal acquisition device;

[0156] Third step, transmit the digital signal to the monitoring and control system based on Labview, which includes five modules: voltage back-calculation module, data processing module, user permission module, parameter input module, data storage module, human-computer interaction module, voltage over-limit module;

[0157] Voltage back-calculation module: Based on the existing secondary-side voltage inversion model of the electromagnetic voltage transformer, or through deep learning of BP neural network, after artificially applying typical waveforms of transient voltage, ferromagnetic resonance, lightning overvoltage, etc. to the electromagnetic voltage transformer on a large scale, the voltage transfer function between the primary side and the secondary side of the electromagnetic voltage transformer under transient voltage can be obtained.

[0158] The steps for calculating the primary-side voltage of the electromagnetic voltage transformer are as follows:

[0159] Denote u 1 , u 2 , i 1 , i 2 as the voltage and current of the primary and secondary sides of the port; i12 is the current of the ideal transformer on the primary side; R 1s , R 2s is the resistance of the primary and secondary windings; C 1 , C 2 is the inter-turn capacitance of the primary and secondary windings; i c1 , i c2 is the current of the inter-turn capacitance of the primary and secondary windings; L m1 , L m2 , R m1 , R m2 is the non-linear exciting inductance and non-linear exciting resistance considering the core saturation of the primary and secondary branches; N 1 , N 2 is the number of turns of the primary and secondary windings of the voltage transformer; i 11 , i c3 , u 4 , u 5 are the internal branch current and node voltage; L s is the leakage inductance of the core; Two ideal transformers are used for circuit reduction.

[0160] If the voltage is reduced to the high-voltage side, then let:

[0161] N 1 = N

[0162] k = N / N 2

[0163] The current flowing through the inter-turn capacitance on the secondary side is:

[0164]

[0165] The un-reduced voltage of the ideal transformer on the secondary side is:

[0166] u 3 = u 2 - (-ic 2 R 2s ) = u 2 + ic 2 R 2s

[0167] The node voltage u 4 on the secondary side branch is:

[0168] The current of the rational transformer on the secondary side after reduction is:

[0169]

[0170] The current flowing through the leakage inductance Ls is:

[0171] i Ls = i Lm2 + i Rm2+ iC3

[0172] Wherein:

[0173] i Lm2 = f(λ 2 )

[0174] Wherein the exciting inductance current i Lm2 varies with its secondary magnetic flux linkage λ 2 ;

[0175] i Rm2 = f(u 4 )

[0176] Wherein the secondary exciting resistance current varies with the node voltage u 4 ;

[0177] The node voltage u of the primary side branch 5 is:

[0178]

[0179] The current i flowing through the node voltage u 5 is: 11

[0180]

[0180] i 11 = i Ls + i Lm1 + i Rm1

[0181] Wherein:

[0182] i Lm1＝ f(λ 1 )

[0183] Wherein the exciting inductance current i Lm1 varies with its secondary magnetic flux linkage λ 1 ;

[0184] i Rm1 = f(u 5 )

[0185] Wherein the secondary exciting resistance current varies with the node voltage u 5 ;

[0186] The current of the primary ideal transformer is:

[0187] i 12＝ i 11

[0188] The primary side port voltage is:

[0189] u 1 = i12 ·R 1s +u 5

[0190] Then:

[0191]

[0192] Data processing module: This module includes three functions: First, it performs noise reduction processing on the input voltage digital signal; Second, it inversely calculates the true primary-side voltage of the electromagnetic voltage transformer through the voltage inverse calculation module for the noise-reduced voltage digital signal, and conducts waveform comparison and analysis on the two voltage digital signals to obtain the maximum relative voltage error. Third, it can perform Fourier decomposition on the true primary-side voltage of the electromagnetic voltage transformer inversely calculated by the voltage inverse calculation module, and can use FFT transformation to extract the amplitudes and phase angles of each harmonic, which is convenient for subsequent waveform analysis and diagnosis. Such as Figure 2 。

[0193] User privilege module: Set the usage privileges and data access privileges based on the Labview monitoring and control system. The system usage privileges enable the permitted users to log in and use the system through the set system access account and password. Users can also modify the account password and enable new permitted users to register accounts; The data access privileges limit users below a certain level from accessing the system database by setting a reference level, so as to avoid confidential leakage and improper operations.

[0194] Parameter input module: Due to the non-linear iron core and frequency-dependent characteristics of the electromagnetic voltage transformer, the voltage on its secondary side is distorted. In order to accurately inversely calculate the true voltage waveform of the primary side of the electromagnetic voltage transformer, it is necessary to input the parameters of the electromagnetic voltage transformer into the voltage inverse calculation module.

[0195] Data storage module: Store the original non-noised voltage digital signal, the true primary-side voltage signal of the electromagnetic voltage transformer inversely calculated by the voltage inverse calculation module, the parameters of the electromagnetic voltage transformer, as well as the voltage relative error inside the data processing module, the amplitudes and phase angles of different frequencies obtained by FFT transformation, etc., for subsequent access.

[0196] Human-computer interaction module: It has a user-visualized interface to make it more convenient for users to operate the system. The system interface includes two waveform graph windows, one of which is used to display the secondary-side voltage of the electromagnetic voltage transformer, and the other is used to display the true primary-side voltage of the electromagnetic voltage transformer inversely calculated by the voltage inverse calculation module; A parameter input window for the parameters of the electromagnetic voltage transformer.

[0197] Error analysis is to calculate the primary-side voltage obtained by inverting the secondary-side voltage of the voltage transformer and the voltage of the secondary side of the voltage transformer to the primary side, and then obtain the error caused by the impact voltage on the voltage transformer.

[0198] Voltage overlimit module: A upper limit voltage value is reasonably set according to the voltage level of the bus in the power grid. This voltage value must ensure as much as possible that the insulation of power grid equipment will not break down, resulting in equipment damage and failures. At the same time, it cannot be too low, so as not to exceed the upper limit voltage value due to slight fluctuations in the normal voltage amplitude in the power grid. Compare the true primary-side voltage of the electromagnetic voltage transformer inverted by the voltage back-calculation module with this upper limit voltage value. If it exceeds this upper limit voltage value, this module will issue a system warning prompt.

[0199] In the fourth step, the monitoring and control system based on Labview is interconnected with the main control system through serial port command interaction to monitor the transient voltage of the power grid and risk warnings in real time.

[0200] The main control system can remotely control the monitoring and control system based on Labview, including: the main control system can remotely log in to the system and remotely operate the system; the main control system can access the user permission module to modify the permission access level; the main control system can call the data storage module in the monitoring and control system based on Labview, and transmit the required data to the main control system for display through the serial port or export the data.

[0201] The voltage overlimit module inside the monitoring and control system based on Labview determines whether the voltage exceeds the limit. If an overlimit occurs, the monitoring and control system based on Labview will transmit a risk warning prompt to the main control system to facilitate the main control system to make a faster and more rapid response. Figure 3 It is the interface of the monitoring system based on Labview.

[0202] The present invention discloses an online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview. The steps include: 1) The data processing module receives the secondary-side digital voltage signal, denoises the secondary-side digital voltage signal, and transmits the denoised secondary-side digital voltage signal to the Labview-based monitoring system; 2) After receiving the secondary-side digital voltage signal, the Labview-based monitoring system calculates the inverse digital voltage signal of the primary side of the electromagnetic voltage transformer through the voltage inverse calculation module, and transmits it to the data processing module and the overlimit module; 3) The data processing module performs waveform analysis on the calculated inverse digital voltage signal of the primary side of the electromagnetic voltage transformer, and extracts the amplitudes and phase angles of each harmonic; 4) The overlimit module is used to determine whether the low-frequency overvoltage acting on the electromagnetic voltage transformer exceeds the upper limit voltage value, posing a risk to the power grid; 5) The Labview-based monitoring system has command interaction with the main control system. The Labview-based monitoring system can transmit all the data in the data storage module to the main control system, and the main control system can also remotely control the Labview-based monitoring system. The method of the present invention can effectively monitor the low-frequency overvoltage of electromagnetic voltage transformers online.

[0203] Embodiment 3:

[0204] A case of monitoring the secondary-side voltage signal of an electromagnetic voltage transformer using the online monitoring method for low-frequency overvoltage of an electromagnetic voltage transformer based on Labview:

[0205] When an electromagnetic transient occurs in the power grid, due to the highly non-linear iron core and winding frequency dependence characteristics of the electromagnetic voltage transformer, the secondary-side voltage of the electromagnetic voltage transformer is distorted. At this time, the voltage signal will first be processed by digital noise reduction, and then the distorted waveform will be displayed on the visualization interface of the Labview-based detection system ( Figure 4 a). Then, the waveform is inversely calculated through the voltage inverse calculation module to obtain the true voltage waveform of the primary side of the electromagnetic voltage transformer ( Figure 4 b).

Claims

1. An online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview, characterized in that, it includes the following steps: 1) Build a secondary-side distortion signal monitoring and analysis system for electromagnetic voltage transformers, including a secondary-side voltage signal measuring device, a signal isolator, a signal acquisition device, a monitoring and control system based on Labview, and a main control system; The monitoring and control system based on Labview includes a voltage back-calculation module, a data processing module, a voltage over-limit module, a parameter input module, and a user permission module; the user permission module is used to verify the logged-in user; 2) Use the secondary-side voltage signal measuring device to monitor the secondary-side voltage signal of the electromagnetic voltage transformer and input it into the signal isolator; 3) The signal isolator denoises the secondary-side voltage signal and inputs it into the signal acquisition device; 4) The signal acquisition device converts the denoised secondary-side voltage signal into a secondary-side digital voltage signal and inputs it into the monitoring and control system based on Labview; 5) The parameter input module obtains the parameters of the electromagnetic voltage transformer and inputs them into the voltage back-calculation module; 6) The data processing module receives the secondary-side digital voltage signal, denoises the secondary-side digital voltage signal, and transmits the denoised secondary-side digital voltage signal to the voltage back-calculation module; 7) The voltage back-calculation module stores an inversion model of the electromagnetic voltage transformer; The voltage back-calculation module inputs the received secondary-side digital voltage signal into the inversion model of the electromagnetic voltage transformer, calculates the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer, and transmits it to the data processing module and the over-limit module; 8) The data processing module analyzes the secondary-side digital voltage signal and the primary-side back-calculated digital voltage signal to obtain the maximum relative error of the voltage, so as to obtain the distortion rate of the secondary-side voltage signal when low-frequency overvoltage acts on the electromagnetic voltage transformer; The data processing module performs Fourier decomposition on the primary-side back-calculated digital voltage signal to obtain the amplitude and phase angle of each harmonic of the primary-side back-calculated digital voltage signal; 9) The voltage over-limit module stores an upper limit voltage value; The voltage over-limit module compares the primary-side back-calculated digital voltage signal with the upper limit voltage value. If the primary-side back-calculated digital voltage signal is greater than the upper limit voltage value, it sends a risk warning prompt to the main control system.

2. The online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, after receiving the risk warning prompt, the main control system retrieves and displays all the data of the monitoring and control system based on Labview, and performs waveform analysis and fault source tracing.

3. The online monitoring method for low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, the secondary-side voltage inversion model is a forward circuit π model of an electromagnetic voltage transformer considering core nonlinearity and winding stray capacitance; The steps of calculating the primary-side back-calculated digital voltage signal of the electromagnetic voltage transformer include: 1) Let the intermediate coefficient k = N / N 2 ; where the number of turns N = N 1 ; N 1 , N 2 are the number of turns of the primary and secondary windings of the electromagnetic voltage transformer; 2) Calculate the current ic flowing through the inter-turn capacitance on the secondary side of the electromagnetic voltage transformer, i.e.: 2 , namely: Where C 2 is the inter-turn capacitance of the secondary winding; u 2 is the secondary-side voltage at the port; t is time; 3) Calculate the untransformed voltage u of the ideal transformer on the secondary side 3 , that is: u 3 = u 2 -(-i c2 R 2s ) = u 2 + i c2 R 2s (2) Where, i c2 is the inter-turn capacitance current of the secondary winding; R 2s is the resistance of the secondary winding; 4) Calculate the node voltage u of the secondary side branch 4 , that is: u 4 = ku 3 (3) 5) Calculate the current i after reduction of the secondary ideal transformer C3 , that is: 6) Calculate the current i flowing through the leakage inductor Ls Ls , that is: i Ls = i Lm2 + i Rm2 + i C3 (5) Among them, the secondary side exciting inductance current i Lm2 is as follows: i Lm2 = f(λ 2 ) (6) where f() represents the current change function; the secondary side magnetic flux linkage indicates the magnetic flux linkage λ 2 which is the integral value of the node voltage u 4 ; 7) Calculate the secondary side exciting resistance current i Rm2 , namely: i Rm2 = f(u 4 ) (7) 8) Calculate the node voltage u of the primary side branch, i.e.: 5 That is: Where, L s is the leakage inductance of the iron core; i Ls is the leakage inductance current of the iron core; 9) Calculate the current i flowing through the nodes of the primary side branch, i.e.: 11 , namely: i 11 = i Ls + i Lm1 + i Rm1 (9) Among them, the primary side exciting inductor current i Lm1 is as follows: i Lm1 = f(λ 1 ) (10) In the formula, the primary-side magnetic flux linkage indicates λ 1 is the integral value of the node voltage u 5 ; 10) Calculate the primary side exciting resistance current i Rm1 , that is: i Rm1 = f(u 5 ) (11) 11) Calculate the primary-side ideal transformer current i 12 , namely: i 12 = i 11 (12) 12) Establish the expression of the inverse-calculated digital voltage signal u on the primary side of the electromagnetic voltage transformer, i.e.: 1 That is: u 1 = i 12 ·R 1s + u 5 (13) 13) According to formulas (1)-(13), the inverse-calculated digital voltage signal u of the primary side of the electromagnetic voltage transformer is obtained, that is: 1 Namely: wherein, R 1s , R 2s is the primary and secondary winding resistance.

4. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, the parameters of the electromagnetic voltage transformer include two non-linear exciting resistance values, two primary and secondary winding resistances, one core leakage inductance, two primary and secondary capacitances, two non-linear inductance magnetic fluxes, and exciting currents corresponding to the two non-linear inductances.

5. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, the user privilege module is used to provide ports for user login and registration; the user privilege module verifies the user login key. If the verification fails, the user has no right to use the monitoring and control system based on Labview.

6. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 5, characterized in that, the user privilege module is provided with a reference level; the user privilege module assigns an account level to each user. If the user account level is lower than the reference level, the user cannot access the database of the monitoring and control system based on Labview.

7. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 6, characterized in that, the main control system is used to modify the user's account level.

8. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, the monitoring and control system based on Labview further includes a human-computer interaction module; the human-computer interaction module includes a user visualization interface; the user visualization interface includes a window for displaying the secondary-side voltage signal, a window for displaying the primary-side inverse-calculated digital voltage signal, and a window for the user to input the parameters of the electromagnetic voltage transformer.

9. A method for on-line monitoring of low-frequency overvoltage of electromagnetic voltage transformers based on Labview according to claim 1, characterized in that, the monitoring and control system based on Labview further includes a data storage module; the data storage module is used to store all data of the monitoring and control system based on Labview.

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