A method and system for measuring parameters of a small current grounding system based on harmonic injection

Abstract

A method and system for measuring distribution network system parameters based on harmonic injection, for use in a low-current grounding system containing an arc suppression coil. The system injects currents of multiple frequencies into the neutral point of the low-current grounding system through an injection source and measures the neutral point voltage. The system uses formulas to calculate and obtain the line capacitance, arc suppression coil inductance, and damping resistance parameter values ​​in the distribution network system. This application can accurately measure line capacitance, arc suppression coil damping resistance, and reactance by injecting only two frequencies of current. This method has little impact on grid operation, high measurement accuracy, and broad application prospects.

Description

Technical Field

[0001] The present application belongs to the technical field of power system relay protection, and specifically relates to a method and system for measuring parameters of a distribution network system. Background Art

[0002] In 3kV-66kV low-current grounding systems, accurate system parameters are often required, typically including line capacitance, arc suppression coil damping resistance, and inductive reactance. Several methods exist for calculating these parameters, but these methods generally require multiple frequency injections, significantly impacting the power system, increasing the requirements for injection equipment, and increasing measurement time.

[0003] Reference "New Two-Terminal Resonant Measurement Method for Insulation Parameters of Resonant Grounded Distribution Network", Yu Kun et al. Automation of Electric Power Systems, 2020, 44(12): 154-161. A two-terminal resonant measurement method for insulation parameters of resonant grounded distribution network is proposed. This method uses dual voltage transformers to inject variable frequency constant current characteristic signals into the distribution network through the voltage transformer inside the arc suppression coil or the zero-sequence voltage transformer, and measures the characteristic frequency voltage signal returned from the other voltage transformer. The zero-sequence resonant circuit containing the damping resistor is equivalently transformed to search for the accurate system resonant frequency, thus realizing the accurate measurement of the system capacitance to ground and the leakage conductance to ground. Reference "Improved Resonant Measurement Method for Distribution Network Parameters", Zeng Xiangjun et al. Journal of Electric Power Science and Technology, 2020, 35(03): 3-11. An improved resonance measurement method for distribution network parameters is proposed. By connecting a variable frequency constant current signal source at the neutral point, injecting a characteristic current signal into the distribution network and measuring the characteristic voltage signal at the open triangle of the zero-sequence voltage transformer in real time, the system resonant frequency can be measured; then, the ground parameters of the distribution network can be measured based on the ground parameter expression.

[0004] Chinese patent CN112595896B, "A Method for Detecting Ground Capacitance Parameters," utilizes multiple generalized integrators to form a frequency selector to extract the injected frequency signal. The frequency selector then extracts a specific frequency signal from a zero-sequence voltage signal containing multiple harmonic components. The signal injection method is used to measure the ground capacitance: a frequency generator circuit injects signals of varying frequencies into the ground capacitance with a step size of 0.1 Hz and a duration of 0.2 s. An oscillation frequency detection circuit detects the maximum zero-sequence voltage to obtain the resonant frequency. Finally, based on the principle of LC parallel resonance, the ground capacitance is calculated. Chinese patent application CN112444703A, "A New Method for Measuring Ground Parameter Resonance in Distribution Networks Based on Unknown Arc Suppression Coil Parameters," first injects a small, constant-amplitude, variable-frequency current signal into the distribution network via a transformer inside the neutral arc suppression coil. An external zero-sequence voltage transformer detects the voltage signal returned from the neutral point, first measuring the resonant frequency interval of the distribution network. A discrete heuristic method is then used to accurately measure the resonant frequency and the corresponding peak voltage return value. The arc suppression coil's internal transformer injects a small, constant-amplitude, constant-frequency, and variable-frequency current signal into the distribution network. The corresponding return voltage is recorded. Combining the two injected small current signals and the return zero-sequence voltage signal, a simultaneous equation can be used to complete the measurement.

[0005] All of the above methods require the injection of multiple frequencies, which places high demands on the injection source, has a greater impact on the system, and takes a long time to measure. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems existing in the prior art, the present application discloses a distribution network system parameter measurement method and system based on harmonic injection, which is used in a small current grounding system containing an arc suppression coil. Two frequencies of current are injected into the system neutral point through an injection source, and the neutral point voltage after two injections is measured. The line capacitance, arc suppression coil inductance and damping resistance parameter values ​​in the distribution network system are calculated through a calculation formula.

[0007] The present invention specifically adopts the following technical solutions.

[0008] A method for measuring parameters of a small current grounding system based on harmonic injection is used in a small current grounding system containing an arc suppression coil. Two current frequencies are injected into the neutral point of the system, and the neutral point voltage after two injections is measured. The line capacitance, arc suppression coil inductance, and damping resistance parameter values ​​in the distribution network system are calculated using calculation formulas.

[0009] A method for measuring parameters of a low-current grounding system based on harmonic injection, used in a low-current grounding system including an arc suppression coil, is characterized in that the method comprises the following steps:

[0010] Step 1: Set an injection source for injecting current into the neutral point of the low-current grounding system, and control the injection source to inject currents of different frequencies into the neutral point of the low-current grounding system twice in succession;

[0011] Step 2: The current values ​​I injected twice with different frequencies are measured by setting the injection current transformer between the injection source and the neutral point of the low current grounding system, and the bus voltage transformer of the low current grounding system. 0x , and the neutral point voltage U generated by the two injection currents 0x , where x is 1 or 2, representing the order of the two injections of different frequency currents and the corresponding electrical parameters generated before and after;

[0012] Step 3: Define G 0xr , G 0xi When the current I is injected from the neutral point 0x When the equivalent conductance and equivalent susceptance of the port network between the neutral point and the ground are used, the equivalent conductance G under the two injection currents is calculated based on the neutral point injection current value and the neutral point voltage value. 01r , G 02r , and the equivalent susceptance G 01i , G 02i ;

[0013] Step 4: Calculate the resistance-inductance coefficient h of the port network between the neutral point and the ground of the low-current grounding system;

[0014]

[0015] Among them, f1 and f2 are the frequency values ​​of the first and second neutral point injection current respectively;

[0016] Step 5: Calculate the low current grounding system parameters according to the following formula:

[0017]

[0018] Among them, ωC is the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, R is the damping resistance value of the arc suppression coil, and ωL is the reactance value of the arc suppression coil at the power frequency.

[0019] The present invention further includes the following preferred embodiments:

[0020] In step 1, the frequency range of the current injected into the neutral point of the low-current grounding system twice should be between [5,400] Hz, and the amplitude range of the injected current should be between [2,10] A.

[0021] The frequency difference between the two currents injected into the neutral point should not be less than 15Hz.

[0022] In step 3, the equivalent conductance and equivalent susceptance of the port network between the neutral point and the ground are calculated by the following formula:

[0023] in, is the injected current I 0x The phasor value of It is the phasor value of the neutral point voltage generated when a current of frequency x is injected into the neutral point.

[0024] The present application also discloses a small current grounding system parameter measurement system using the aforementioned measurement method, comprising an injection source, an injection current transformer, a bus voltage transformer, an equivalent admittance calculation module, a coefficient calculation module, and a system parameter calculation module;

[0025] An injection source is provided for injecting currents of different frequencies into the neutral point of the low-current grounding system, and an injection current transformer is provided between the injection source and the neutral point of the low-current grounding system;

[0026] The injection source is controlled to inject currents of different frequencies into the neutral point twice in succession;

[0027] The injection current transformer detects the injection current value, and the bus voltage transformer detects the neutral point voltage value;

[0028] The equivalent admittance calculation module calculates the equivalent admittance value of the port network between the neutral point and the ground of the small current grounding system at two different frequencies according to the two injected current values ​​of different frequencies and the neutral point voltage value. The equivalent admittance includes equivalent conductance and equivalent susceptance;

[0029] The coefficient calculation module calculates the ratio of the frequencies of the two injected currents to the rated frequency of the power grid, and the resistance-inductance coefficient of the port network between the neutral point and the ground of the small current grounding system;

[0030] The system parameter calculation module calculates the low-current grounding system parameters according to the equivalent conductance value, the equivalent admittance value, the ratio of the injection current frequency to the rated frequency of the power grid and the resistance-inductance coefficient during the two current injections.

[0031] More preferably,

[0032] The frequency range of the current injected into the neutral point by the injection source should be between [5,400] Hz, and the amplitude range of the primary value of the injected current should be between [2,10] A.

[0033] The frequency difference between the two currents injected into the neutral point should not be less than 15Hz.

[0034] The coefficient calculation module includes an injection frequency coefficient calculation unit and a distribution network resistance and inductance coefficient calculation unit;

[0035] In the injection frequency coefficient calculation unit, the frequencies of the two injection currents are calculated as multiples of the power frequency 50 Hz, that is, the frequency coefficients of the injection currents;

[0036] The distribution network resistance-inductance coefficient calculation unit calculates the resistance-inductance coefficient of the port network between the neutral point and the ground of the small current grounding system according to the frequency coefficient of the two injection currents and the equivalent admittance values ​​under the two injection currents.

[0037] The system parameter calculation module calculates the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, the damping resistance value of the arc suppression coil, and the reactance value of the arc suppression coil based on the equivalent conductance and susceptance value of the distribution network during the two current injections, the frequency coefficient, and the resistance-inductance coefficient.

[0038] Beneficial effects: The technical solution provided in the embodiment of the present application can accurately measure the line capacitance, arc suppression coil damping resistance and reactance by simply injecting two frequency currents. It has little impact on the operation of the power grid, high measurement accuracy, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0040] Figure 1 This is a schematic diagram of a low-current grounding system parameter measurement system based on harmonic injection provided by an embodiment of the present application;

[0041] Figure 2 This is a simplified circuit model diagram provided by an embodiment of the present application;

[0042] Figure 3 This is a flow chart of a method for measuring parameters of a small current grounding system based on harmonic injection in this application. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0044] Figure 1 This is a schematic diagram of a distribution network system parameter measurement system based on harmonic injection provided by an embodiment of the present application, which injects I0 of different frequencies into the neutral point O and generates a voltage U0 according to Figure 1 The simplified circuit model is as follows Figure 2 As shown in Figure 2, the coil resistance of the arc suppression coil and the line impedance are small and are therefore ignored in the analysis and calculation. The system damping can be compensated by calculation or simply ignored.

[0045] As shown in Figure 3, the method for measuring parameters of a low-current grounding system based on harmonic injection includes the following steps:

[0046] Step 1: Set an injection source for injecting current into the neutral point of the low-current grounding system, and control the injection source to inject currents of different frequencies into the neutral point of the low-current grounding system in sequence;

[0047] As a preferred embodiment, the frequency range of the current injected twice into the neutral point of the low-current grounding system should be between [5,400] Hz, and the amplitude range of the injected current should be between [2,10] A. Moreover, the frequency difference of the current injected twice into the neutral point should not be less than 15 Hz.

[0048] Step 2: The current values ​​I injected twice with different frequencies are measured by setting the injection current transformer between the injection source and the neutral point of the low current grounding system, and the bus voltage transformer of the low current grounding system. 0x , and the neutral point voltage U generated by the two injection currents 0x , where x is 1 or 2, representing two different frequencies of injected current; the two frequency current values ​​I 0x And the neutral point voltage value U 0x It can be obtained as a known quantity through measurement.

[0049] Step 3: Define G 0xr , G 0xi When the current I is injected from the neutral point 0x When the equivalent conductance and equivalent susceptance of the port network between the neutral point and the ground are used, the equivalent conductance G under the two injection currents is calculated based on the neutral point injection current value and the neutral point voltage value. 01r , G 02r , and the equivalent susceptance G 01i , G 02i ;

[0050] Assume ω is the system angular velocity at 50Hz, and the line capacitance reactance of the distribution network at 50Hz is Z C =1 / jωC, the arc suppression coil impedance is Z L =R+jωL, where the parameters of line capacitance C, arc suppression coil damping resistance R and inductive reactance L need to be calculated by formula. The two injected current frequencies are f1 and f2, let k x =f x / 50, the subscript x is equal to 1 and 2, indicating frequency 1 and frequency 2. According to the system parameters, the equation is:

[0051]

[0052] For the right side of the above equation, define the system zero-sequence admittance G 0x =I 0x / U 0x -1 / R s , ignoring the system damping R s After that, G 0xr and G 0xi They are defined as the admittance G at frequency x 0x The real and imaginary parts of are calculated as follows:

[0053]

[0054] In the above formula, the subscript x is equal to 1 and 2, representing frequency 1 and frequency 2, and I 0x and U 0x All are known quantities. Ignore R s The latter formula (1) is simplified to:

[0055]

[0056] According to the above formula, G 0x The real and imaginary parts of (subscripts r and i represent the real and imaginary parts respectively, and subscript x is equal to 1 and 2, representing frequency 1 and frequency 2 respectively) are:

[0057]

[0058] Step 4: Calculate the resistance-inductance coefficient h of the port network between the neutral point and the ground of the low-current grounding system;

[0059]

[0060] Among them, f1 and f2 are the frequency values ​​of the first and second neutral point injection currents respectively.

[0061] Step 5: Calculate the low current grounding system parameters according to the following formula:

[0062]

[0063] Among them, ωC is the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, R is the damping resistance value of the arc suppression coil, and ωL is the reactance value of the arc suppression coil.

[0064] The present application also discloses a small current grounding system parameter measurement system using the aforementioned measurement method, comprising an injection source, an injection current transformer, a bus voltage transformer, an equivalent admittance calculation module, a coefficient calculation module, and a system parameter calculation module;

[0065] An injection source is provided for injecting currents of different frequencies into the neutral point of the low-current grounding system, and an injection current transformer is provided between the injection source and the neutral point of the low-current grounding system;

[0066] The injection source is controlled to inject currents of different frequencies into the neutral point twice in succession;

[0067] The injection current transformer detects the injection current value, and the bus voltage transformer detects the neutral point voltage value;

[0068] The equivalent admittance calculation module calculates the equivalent admittance value of the port network between the neutral point and the ground of the small current grounding system at two different frequencies according to the two injected current values ​​of different frequencies and the neutral point voltage value;

[0069] The frequency coefficients of the two injected currents and the resistance-inductance coefficients of the port network between the neutral point and the ground of the low-current grounding system are calculated in the coefficient calculation module;

[0070] The system parameter calculation module calculates the small current grounding system parameters according to the equivalent admittance value, frequency coefficient and resistance-inductance coefficient during the two current injections.

[0071] The frequency range of the current injected into the neutral point of the low-current grounding system should be between [5,400] Hz, and the amplitude range of the injected current should be between [2,10] A. Furthermore, the difference in the frequency of the current injected into the neutral point should not be less than 15 Hz.

[0072] The coefficient calculation module includes an injection frequency coefficient calculation unit and a distribution network resistance and inductance coefficient calculation unit;

[0073] In the injection frequency coefficient calculation unit, the frequencies of the two injection currents are calculated as multiples of the power frequency 50 Hz, that is, the frequency coefficients of the injection currents;

[0074] The distribution network resistance-inductance coefficient calculation unit calculates the resistance-inductance coefficient of the port network between the neutral point and the ground of the small current grounding system according to the frequency coefficient of the two injection currents and the equivalent admittance values ​​under the two injection currents.

[0075] The system parameter calculation module calculates the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, the damping resistance value of the arc suppression coil, and the reactance value of the arc suppression coil based on the equivalent conductance and susceptance value of the distribution network during the two current injections, the frequency coefficient, and the resistance-inductance coefficient.

[0076] The correctness of the formula is verified by simulation below: Assume that in the simulation system, the capacitance ωC = 0.0025Ω -1, arc suppression coil inductance ωL=363.6286Ω, arc suppression coil damping resistance R=94Ω. Three parameter calculations were performed by injecting 1A current with a frequency of 50Hz into the neutral point through a current source, as current 1, and current 2 with an amplitude of 1A and a frequency of 25Hz, 75Hz, and 100Hz, respectively. The calculation results are shown in the following table:

[0077] illustrate Frequency / Hz R / Ω ωL / Ω <![CDATA[ωC / Ω -1 ]]> Current 1 is 50Hz 50 * * * Current 2 is 25Hz 25 94.0310 363.7063 0.0025 Current 2 is 75Hz 75 93.9365 363.5358 0.0025 Current 2 is 100Hz 100 93.9886 363.6298 0.0025

[0078] As can be seen from the above table, the errors of the calculation results are all below 1‰, which can meet the needs of actual applications.

[0079] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core ideas of the present application. At the same time, changes or modifications made by those skilled in the art based on the ideas of the present application, the specific implementation methods, and the scope of application of the present application, all fall within the scope of protection of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A method for measuring parameters of a small current grounding system based on harmonic injection, used in a small current grounding system containing an arc suppression coil, characterized in that: The method comprises the following steps: Step 1: Set an injection source for injecting current into the neutral point of the low-current grounding system, and control the injection source to inject currents of different frequencies into the neutral point of the low-current grounding system twice in succession; Step 2: The current values ​​I injected twice with different frequencies are measured by setting the injection current transformer between the injection source and the neutral point of the low current grounding system, and the bus voltage transformer of the low current grounding system. 0x , and the neutral point voltage U generated by the two injection currents 0x , where x is 1 or 2, representing the order of the two injections of different frequency currents and the corresponding electrical parameters generated before and after; Step 3: Define G 0xr , G 0xi When the current I is injected from the neutral point 0x When the equivalent conductance and equivalent susceptance of the port network between the neutral point and the ground are used, the equivalent conductance G under the two injection currents is calculated based on the neutral point injection current value and the neutral point voltage value. 01r , G 02r , and the equivalent susceptance G 01i , G 02i ; Step 4: Calculate the resistance-inductance coefficient h of the port network between the neutral point and the ground of the low-current grounding system; Among them, f1 and f2 are the frequency values ​​of the first and second neutral point injection current respectively; Step 5: Calculate the low current grounding system parameters according to the following formula: Among them, ωC is the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, R is the damping resistance value of the arc suppression coil, and ωL is the reactance value of the arc suppression coil at the power frequency.

2. The method for measuring parameters of a low-current grounding system based on harmonic injection according to claim 1, wherein: In step 1, the frequency range of the current injected into the neutral point of the low-current grounding system twice should be between [5,400] Hz, and the amplitude range of the injected current should be between [2,10] A.

3. The method for measuring parameters of a low-current grounding system based on harmonic injection according to claim 2, wherein: The frequency difference between the two currents injected into the neutral point should not be less than 15Hz.

4. The method for measuring parameters of a low-current grounding system based on harmonic injection according to claim 1, wherein: In step 3, the equivalent conductance and equivalent susceptance of the port network between the neutral point and the ground are calculated by the following formula: in, is the injected current I 0x The phasor value of It is the phasor value of the neutral point voltage generated when a current of frequency x is injected into the neutral point.

5. A low-current grounding system parameter measurement system using the measurement method according to any one of claims 1 to 4, comprising an injection source, an injection current transformer, a bus voltage transformer, an equivalent admittance calculation module, a coefficient calculation module, and a system parameter calculation module, characterized in that: An injection source is provided for injecting currents of different frequencies into the neutral point of the low-current grounding system, and an injection current transformer is provided between the injection source and the neutral point of the low-current grounding system; The injection source is controlled to inject currents of different frequencies into the neutral point twice in succession; The injection current transformer detects the injection current value, and the bus voltage transformer detects the neutral point voltage value; The equivalent admittance calculation module calculates the equivalent admittance value of the port network between the neutral point and the ground of the small current grounding system at two different frequencies according to the two injected current values ​​of different frequencies and the neutral point voltage value. The equivalent admittance includes equivalent conductance and equivalent susceptance; The coefficient calculation module calculates the ratio of the frequencies of the two injected currents to the rated frequency of the power grid, and the resistance-inductance coefficient of the port network between the neutral point and the ground of the small current grounding system; The system parameter calculation module calculates the low-current grounding system parameters according to the equivalent conductance value, the equivalent admittance value, the ratio of the injection current frequency to the rated frequency of the power grid and the resistance-inductance coefficient during the two current injections.

6. The low-current grounding system parameter measurement system according to claim 5, characterized in that: The frequency range of the current injected into the neutral point by the injection source should be between [5,400] Hz, and the amplitude range of the primary value of the injected current should be between [2,10] A.

7. The low-current grounding system parameter measurement system according to claim 6, characterized in that: The frequency difference between the two currents injected into the neutral point should not be less than 15Hz.

8. The low-current grounding system parameter measurement system according to claim 5, characterized in that: The coefficient calculation module includes an injection frequency coefficient calculation unit and a distribution network resistance and inductance coefficient calculation unit; In the injection frequency coefficient calculation unit, the frequencies of the two injection currents are calculated as multiples of the power frequency 50 Hz, that is, the frequency coefficients of the injection currents; The distribution network resistance-inductance coefficient calculation unit calculates the resistance-inductance coefficient of the port network between the neutral point and the ground of the small current grounding system according to the frequency coefficient of the two injection currents and the equivalent admittance values ​​under the two injection currents.

9. The low-current grounding system parameter measurement system according to claim 8, characterized in that: The system parameter calculation module calculates the capacitive reactance value of the distribution network of the small current grounding system at the power frequency, the damping resistance value of the arc suppression coil, and the reactance value of the arc suppression coil based on the equivalent conductance and susceptance value of the distribution network during the two current injections, the frequency coefficient, and the resistance-inductance coefficient.

Images