CN107765077B - Magnetizing inrush current identification method and device - Google Patents
Magnetizing inrush current identification method and device Download PDFInfo
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Abstract
The invention provides a method and a device for identifying magnetizing inrush current, wherein the method comprises the steps of setting a time interval reference; calculating the amplitude ratio of the direct current component to the fundamental component of the outlet circuit breaker current of the high-voltage side and the medium-voltage side of the transformer; carrying out logic judgment on the current data of the circuit breaker at the outlet of the transformer, identifying the magnetizing inrush current and the fault current, and ensuring the accuracy of the differential protection action of the transformer; the identification device comprises a current measurement unit, a digital simulation unit, a data discrimination unit, a data processing unit, a criterion formulation unit and a current identification unit. The technical scheme provided by the invention has the advantages of less required measurement data, simplicity and easiness in realization, independent three-phase discrimination, phase braking and no influence of current transformer saturation, ensures high-efficiency and reliable differential protection action of the transformer, and is reliable and effective in an application scene that a switch-on resistor is not additionally arranged on a transformer outlet circuit breaker.
Description
Technical Field
The invention relates to the field of magnetizing inrush current identification, in particular to a magnetizing inrush current identification method and device.
Background
A transformer, which is one of the core elements of an extra-high voltage and extra-high voltage transmission system, puts high demands on the reliability and the quick-action performance of the main protection of the transformer. For a long time, the correct action rate of transformer protection is low, and for the currently commonly used transformer differential protection, magnetizing inrush current is an important reason for incorrect action of the transformer differential protection, and how to prevent the transformer differential protection from causing false action is one of important research subjects of transformer protection.
At present, the differential protection of the transformer operated on site mainly adopts the second harmonic braking principle and the discontinuous angle principle to identify the magnetizing inrush current, wherein the second harmonic braking which is applied most widely has great limitation on the principle: with the development of modern transformers, the conductive performance of ferromagnetic materials is fully utilized, the saturation point of an iron core is advanced, and the characteristics of second harmonic in excitation inrush current become less obvious when residual magnetism is more; in addition, if the end of the transformer is connected with a static compensation capacitor or a long line, the transient current generated by internal faults also contains larger second harmonic; in addition, the current transformer can generate a large second harmonic component when saturated; the second harmonic is therefore no longer a unique feature of the magnetizing inrush current, subject to the above factors.
The limitation of the discontinuous angle principle is that: firstly, the discontinuous angle principle needs a higher sampling rate to improve the sampling precision, and puts higher requirements on the processing speed of a CPU; secondly, transient saturation sometimes occurs in the current transformer, and in order to prevent the secondary side inrush current of the transformer from being distorted or disappeared, corresponding measures must be taken to recover the discontinuous angle, so that a higher requirement is put forward on the protection performance of hardware; and the current of the excitation surge current at the discontinuous angle is very small and is close to zero, if the resolution of the A/D conversion chip is low, a large error is generated during signal conversion, and the data accuracy is reduced.
In the prior art, the accuracy of magnetizing inrush current identification is not sufficient, and a new magnetizing inrush current identification method is needed to improve the accuracy of transformer magnetizing inrush current identification, so that the safe operation of the transformer is guaranteed.
Disclosure of Invention
In order to overcome the defects of insufficient identification accuracy, more secondary harmonic measurement influence factors and high requirement of discontinuous angle measurement on hardware in the existing magnetizing inrush current identification technology, the invention provides a magnetizing inrush current identification method based on the attenuation characteristic of a direct current component of a transformer current, which can accurately distinguish the fault current and the magnetizing inrush current of the transformer and ensure the accuracy of differential protection action of the transformer.
The invention provides a magnetizing inrush current identification method based on attenuation characteristics of direct current components of transformer current, which is improved in that the identification method comprises the following steps:
(1) setting a time interval reference;
(2) calculating the amplitude ratio of the direct current component to the fundamental component of the current of the breaker at the outlet of the transformer;
(3) establishing a criterion for identifying the magnetizing inrush current;
(4) and identifying the magnetizing inrush current according to the established identification criterion.
Further, calculating the data sampling time interval T by the simulation of the set digital simulation system, and obtaining the time interval reference of the step (1).
Further, the step (2) of calculating the amplitude ratio of the direct current component to the fundamental component includes:
(2-1) measuring the current waveform of the circuit breaker at the outlet of the transformer, and detecting and judging that the current amplitude is greater than the action current setting value;
(2-2) calculating the amplitude ratio A of the direct current component to the fundamental component in different time intervals T according to the following formula:
wherein, I0m: a DC component amplitude; i is1m: the fundamental component amplitude.
Further, the criterion for identifying the magnetizing inrush current in the step (3) is a decay rate of a ratio of a direct current component of the transformer outlet breaker current to a fundamental component amplitude.
Further, the method for making the criterion for identifying the magnetizing inrush current comprises the following steps:
(S1) calculating a short-circuit current flowing through the transformer outlet circuit breaker at the time of the short-circuit fault by simulation, and calculating a direct current component and a fundamental component thereof;
(S2) simulating and calculating the magnetizing inrush current flowing through the circuit breaker at the outlet of the transformer when the transformer is switched on and is in no-load main transformer, and calculating the direct current component and the fundamental component of the magnetizing inrush current;
(S3) selecting a minimum data sampling time interval T based on the current data characteristics of steps (S1) and (S2);
(S4) calculating the amplitude ratio A of the direct current component and the fundamental component in the short-circuit current and the magnetizing inrush current at each interval time Tn；
(S5) attenuation rate K according to the calculated amplitude ratio of the direct current component and the fundamental componentnDetermining a decay rate threshold KsetIf K is1<0, the current is the excitation surge current;
if K1>0 and K2>KsetIf the current is the fault current, otherwise, the current is the excitation inrush current;
(S6) correcting the data sampling time interval T and the attenuation rate threshold K of the simulation calculation according to the measured values of the magnetizing inrush current and the short-circuit current in the fault when the no-load main transformer is switched on in the actual engineeringset。
Further, the criterion selection principle is as follows: whether the electrical characteristics of the fault current of the transformer meet the criterion requirements or not and whether the electrical characteristics of the magnetizing inrush current meet the criterion requirements or not.
Further, the direct current component and the fundamental component in the steps (S1) and (S2) are calculated by fourier algorithm, respectively.
Further, the identification process of the magnetizing inrush current in the step (4) includes:
(4-1) rate of decay K of amplitude ratio of direct current component to fundamental componentnAs shown in the following formula:
Kn＝(A0-An)/A0
wherein n is 1, 2; a. the0And An: respectively representing the amplitude ratio of the direct current component to the fundamental component in the 0 th sampling time interval T and the nth sampling time interval T;
(4-2) setting the decay Rate threshold KsetIf K is1<0, the current is the excitation surge current;
if K1>0 and K2>KsetThen is fault powerAnd otherwise, the current is magnetizing inrush current.
A magnetizing inrush current recognition device comprises a current measuring unit, a digital simulation unit, a data discrimination unit, a data processing unit, a criterion making unit and a current recognition unit;
the current measuring unit transmits the obtained current of the transformer outlet circuit breaker to the data judging unit;
the digital simulation unit transmits the calculated action current setting value to the data discrimination unit; and the combination of (a) and (b),
the digital simulation unit transmits the calculated sampling time interval T to the data processing unit;
the data judging unit judges the magnitude of the current amplitude and the action current setting value of the transformer outlet circuit breaker and transmits the magnitude to the data processing unit;
the data processing unit transmits the calculated amplitude ratio of the direct current component and the fundamental component in different time intervals T to the criterion establishing unit;
the criterion establishing unit transmits the defined decay rate and the set threshold value to the current identification unit;
the current identification unit identifies the current output by the transformer outlet circuit breaker.
Further, in the above-mentioned case,
and the digital simulation unit calculates the action current setting value and the sampling time interval T according to the condition of the power grid where the project is located, and corrects the action current setting value and the sampling time interval T according to the field debugging operation result.
Furthermore, the data judging unit judges the magnitude of the current amplitude and the action current setting value of the transformer outlet circuit breaker and determines whether to transmit data to the data processing unit.
Further, the data processing unit calculates the amplitude ratio of the direct current component to the fundamental component in different time intervals by using Fourier.
Further, the criterion preparation unit sets a decay rate threshold KsetAnd calculating the amplitude of the DC component and the fundamental component according to the following formulaRate of decay K of value ration：
Kn＝(A0-An)/A0
Wherein n is 1, 2.
Further, the current identification unit is used for identifying the current according to the decay rate and a decay rate threshold value KsetJudging whether the output current of the breaker at the outlet of the transformer is magnetizing inrush current or not:
if K1<0, the current is the excitation surge current;
if K1>0 and K2>KsetThen is fault current; if K1>0 and K2<KsetAnd then, the current is the magnetizing inrush current.
Compared with the closest prior art, the technical scheme provided by the invention has the following excellent effects:
1. according to the technical scheme provided by the invention, the specific attenuation rate of the amplitude of the direct current component and the fundamental component of the breaker at the outlet of the transformer is used as a judgment basis for identifying the magnetizing inrush current, so that the defect of delayed action of switching on the fault phase protection in a secondary harmonic braking three-phase or gate braking scheme is overcome, the accuracy of magnetizing inrush current identification is obviously improved, the occurrence of the situations of misoperation and refusal of transformer protection is effectively avoided, the accuracy and reliability of the differential protection action of the transformer are effectively improved, and the method has a good engineering application prospect.
2. The technical scheme provided by the invention can accurately distinguish the fault current and the magnetizing inrush current of the transformer, has the advantages of less measured data, simplicity and easiness in realization, can independently distinguish three phases and brake according to the phases, is not influenced by the saturation of a current transformer, can ensure the correct action of the differential protection of the transformer, and is reliable and effective in an application scene that a breaker at the outlet of the transformer is not additionally provided with a closing resistor.
Drawings
FIG. 1 is a flow chart of a magnetizing inrush current identification method provided by the present invention;
FIG. 2 is a simplified wiring diagram of a dual-port network for research according to the present invention;
FIG. 3 is a schematic diagram of a typical magnetizing inrush current waveform obtained through simulation during closing of an unloaded main transformer;
FIG. 4 is a schematic diagram of a typical waveform of a short-circuit current when an outlet of a transformer fails according to simulation;
FIG. 5 is a schematic diagram illustrating harmonic distortion attenuation of three-phase short-circuit current of a transformer under different conditions;
fig. 6 is a schematic diagram of attenuation of harmonic distortion of transformer magnetizing inrush current under different conditions.
Detailed Description
The technical scheme provided by the invention is explained in detail in a mode of specific embodiments by combining the drawings in the specification.
In an actual electrical signal, two parts are generally included: a direct current component and an alternating current component. In the alternating current component, fundamental waves and harmonics are contained. A sine wave component having a period equal to the oscillation period is referred to as a fundamental wave component, and a frequency corresponding to this period is referred to as a fundamental wave frequency. The amplitude ratio a of the dc component to the fundamental component in the transformer current is given by:
wherein, I0mIs the magnitude of the DC component, I1mIs the fundamental component amplitude.
Under the condition that a closing resistor is not additionally arranged on the circuit breaker, the amplitude of a fundamental component of magnetizing inrush current of the transformer is attenuated, the attenuation speed of a direct current component is low, the amplitude of a fundamental component of fault current is not attenuated, and the attenuation speed of the direct current component is high.
As shown in fig. 1, the magnetizing inrush current identification method based on the attenuation characteristic of the direct current component of the transformer current provided by the invention has the following process:
(1) establishing a digital simulation system for the application scene, obtaining a data sampling time interval T through digital simulation calculation, and taking the data sampling time interval T as an interval reference value of analysis time;
(2) when the current amplitude of the breaker at the outlet of the transformer is larger than the setting value of the action current, measuring and recording the current waveform of the medium-voltage side of the transformer, and solving the amplitude ratio A of 3 groups of direct current components and fundamental wave components in different time intervals T by utilizing Fourier transform0、A1、A2；
(3) And performing logic judgment on 3 groups of data: attenuation rate K of amplitude ratio of direct current component to fundamental componentnAs shown in the following formula:
Kn＝(A0-An)/A0
wherein n is 1, 2; setting a decay rate threshold KsetIf the calculated decay rate K1<0, directly determining the current as an excitation surge current to meet the rapidity as much as possible; then the obtained decay rate K is used2And a decay rate threshold KsetMaking a comparison if K1>0 and K2>KsetIf the current is determined to be fault current, otherwise, the current is magnetizing inrush current, the reliability of the identification result is ensured, and the magnetizing inrush current and the fault current are identified according to the method, so that the accuracy of the differential protection action of the transformer can be ensured.
The invention provides a method for making a magnetizing inrush current identification criterion based on the attenuation characteristic of a direct current component of a breaker at an outlet of a transformer, which comprises the following steps:
(1) and (3) a principle for formulating action criteria is provided, namely: whether the electrical characteristics of the fault current of the transformer meet the criterion requirements or not and whether the electrical characteristics of the magnetizing inrush current meet the criterion requirements or not are ensured;
(2) establishing a digital simulation model based on system conditions of an engineering place, considering different fault time factors, carrying out simulation calculation on short-circuit current flowing through a breaker at an outlet of the transformer when the transformer has single-phase or multi-phase short-circuit fault, and calculating a direct-current component and a fundamental component of the short-circuit current by adopting Fourier transform;
(3) establishing a digital simulation model based on system conditions of an engineering place, taking different closing moments and different remanence conditions into consideration, performing simulation calculation on excitation inrush current flowing through a circuit breaker at an outlet of a transformer when the transformer is closed and a no-load main transformer is switched on, and calculating a direct current component and a fundamental component of the excitation inrush current by adopting Fourier transform;
(4) according to the short-circuit current and excitation surge current data characteristics obtained by simulation calculation, on the premise of ensuring reliability, analyzing and screening out the minimum data sampling time interval T so as to meet the requirement of rapidity;
(5) analyzing the amplitude ratio A of the direct current component and the fundamental component in the transformer excitation inrush current and the short-circuit current at intervals of 0, T and 2T aiming at the selected data sampling time interval T0、A1、A2；
(6) Calculating the attenuation rate K of the amplitude ratio of the direct current component and the fundamental componentn＝(A0-An)/A0(n-1, 2), determining the decay rate threshold K with sufficient marginset；
(7) If K1<0, directly determining the current as the excitation inrush current; then K is put2And KsetMaking a comparison if K2＞KsetIf the current is determined to be fault current, otherwise, the current is determined to be magnetizing inrush current;
(8) according to the test results of the magnetizing inrush current when the no-load main transformer is switched on in the actual engineering field and the short-circuit current when the main transformer outlet is in fault, the data sampling time interval T and the attenuation rate threshold K provided by the simulation calculation are subjected tosetAnd (6) correcting.
According to the simulation and the verification of the measured data, 2 data can be selected by considering the problem of the action speed.
The invention provides an identification device applying an identification method, which comprises a digital simulation unit, a current measurement unit, a data processing unit, a criterion formulation unit and an identification unit;
the digital simulation unit and the current measurement unit transmit data to the data processing unit;
the data processing unit transmits a processing result to the criterion formulation unit and the identification unit;
the criterion formulating unit calls the digital simulation unit and the data processing unit to formulate a criterion and transmits the criterion to the identification unit;
and the identification unit transmits the judgment result to the criterion formulation unit.
The digital simulation unit simulates and calculates the data sampling time interval by using a set digital simulation system and obtains a time interval reference value.
When the current measuring unit measures that the current amplitude of the circuit breaker at the outlet of the transformer is larger than the action current setting value, the current measuring unit measures and records the current waveform at the medium-voltage side of the transformer
The data processing unit is used for calculating the amplitude ratio and the attenuation rate of the direct current component and the fundamental component in different time intervals T by Fourier transform;
the criterion making unit makes the criterion according to the principle that the electrical characteristics of the fault current of the transformer meet the criterion requirement, and the electrical characteristics of the magnetizing inrush current do not meet the criterion requirement;
the function of the criterion formulating unit comprises:
(1) simulating and calculating the short-circuit current flowing through a breaker at the outlet of the transformer when the transformer has a short-circuit fault by using a digital simulation system, and calculating the ratio of the direct-current component to the fundamental component in different time intervals;
(2) simulating and calculating the magnetizing inrush current flowing through a circuit breaker at the outlet of the transformer when the transformer is switched on and is in no-load main transformer by using a digital simulation system, and calculating the ratio of the direct current component to the fundamental wave component in different time intervals;
(3) calculating the attenuation rate of the ratio of the direct current component to the fundamental wave component according to the ratio of the direct current component to the fundamental wave component in different time intervals, and setting an attenuation rate threshold Kset。
(4) According to the test results of the magnetizing inrush current when the no-load main transformer is switched on in the actual engineering field and the short-circuit current when the outlet of the main transformer fails, the data sampling time interval T and the attenuation rate threshold K provided by simulation calculation are correctedset。
The identification unit judges the magnetizing inrush current or the magnetizing inrush fault output by the outlet circuit breaker of the transformer according to the attenuation rate and the attenuation rate threshold valueBarrier current: if K1<0, the current is the excitation surge current;
if K1>0 and K2>KsetThe current is a fault current, otherwise, the current is a magnetizing inrush current.
The data processing unit calculates the amplitude ratio of the direct current component to the fundamental component according to the current waveform recorded by the current measuring unit;
the identification unit identifies the current of the breaker at the outlet of the transformer according to the criterion formulated by the criterion formulation unit;
the criterion making unit makes a criterion and corrects the data according to the data of the digital simulation unit, the current measurement unit and the data processing unit and the judgment result of the identification unit
Examples
The two-terminal simplified wiring diagram shown in FIG. 2 is for a rated voltage of
The ultra-high voltage three-winding transformer carries out simulation calculation on the characteristic difference between the short-circuit current when a three-phase short-circuit fault occurs on the 500kV side and the magnetizing inrush current when the no-load main transformer is switched on the 500kV side, and analyzes the application effect of the magnetizing inrush current identification method based on the attenuation characteristic of the direct-current component of the transformer current, and the circuit breakers on the 1000kV side and the 500kV side of the transformer are not provided with a switching-on resistor.
Typical waveforms of magnetizing inrush current when a main transformer is switched on and no-load and short-circuit current when an outlet of a transformer fails, which are obtained through simulation of a digital simulation unit, are shown in fig. 4 and 5.
Taking phase a as an example, taking the previous zero crossing point of the waveform as 0 moment when the amplitude of the transformer current judged by the data judging unit is greater than the action current setting value, table 1 lists the calculation results of the attenuation condition of the amplitude ratio of the three-phase short-circuit current, the magnetizing inrush current direct current component and the fundamental component of the transformer under different conditions calculated by the data processing unit.
TABLE 1 amplitude ratio of three-phase short-circuit current to DC component to fundamental component of transformer in different cases (A phase)
As shown in table 1, in the case of a three-phase short-circuit fault, the amplitude ratio of the dc component to the fundamental component in the current tends to decay, while the amplitude ratio of the dc component to the fundamental component in the magnetizing inrush current tends to increase or slowly decay, but the decay rate is significantly slower than the short-circuit current. The line graphs plotted according to the data of the table are shown in fig. 5 and 6, and it is apparent from the line graphs that the attenuation of the amplitude ratio of the three-phase short-circuit current direct-current component to the fundamental component is large, and the attenuation of the amplitude ratio of the magnetizing inrush current direct-current component to the fundamental component is small or increased.
To facilitate quantification and analysis, K is now definedn＝(A0-An)/A0(n is 1, 2) is the attenuation ratio of the amplitude of the direct current component to the amplitude of the fundamental wave component, and the statistical results are shown in table 2.
TABLE 2 attenuation ratio of three-phase short-circuit current to amplitude ratio of direct current component to fundamental component of transformer in different cases
As can be seen from table 2, when the current amplitude of the transformer outlet circuit breaker is greater than the action current setting value, the previous zero crossing point of the waveform is 0 time, the attenuation ratios of the amplitude ratios of the three-phase short-circuit current direct current component and the fundamental wave component are all above 10% at 5ms, and the attenuation ratio of the amplitude ratio of the magnetizing inrush current direct current component and the fundamental wave component is below 10% or is increased; by 10ms, the difference between the attenuation ratios is more pronounced. For this example, the digital simulation unit may take the time interval T as 5ms, and the criterion-making unit may set the decay rate threshold KsetThe value is 10-15%.
Therefore, according to the technical scheme provided by the invention, under the application scene that the circuit breaker is not additionally provided with the closing resistor, the current identification unit can accurately distinguish the fault current and the excitation inrush current of the transformer, so that the reliability and effectiveness of the differential protection action of the transformer are ensured.
Finally, it should be noted that the above-mentioned embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above-mentioned embodiments, a person skilled in the art can make modifications or equivalent substitutions to the specific embodiments of the present invention, and any modifications or equivalent substitutions which do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention as filed.
Claims (12)
1. A magnetizing inrush current identification method is characterized by comprising the following steps:
(1) setting a time interval reference;
(2) calculating the amplitude ratio of the direct current component to the fundamental component of the current of the breaker at the outlet of the transformer;
(3) establishing a criterion for identifying the magnetizing inrush current;
(4) identifying the magnetizing inrush current according to the established identification criterion;
the identification process of the magnetizing inrush current in the step (4) comprises the following steps:
(4-1) rate of decay K of amplitude ratio of direct current component to fundamental componentnAs shown in the following formula:
Kn＝(A0-An)/A0
wherein n is 1, 2; a. the0And An: respectively representing the amplitude ratio of the direct current component to the fundamental component in the 0 th sampling time interval T and the nth sampling time interval T;
(4-2) setting the decay Rate threshold KsetIf K is1If the current is less than 0, the current is excitation surge current;
if K1> 0 and K2＞KsetThe current is a fault current, otherwise, the current is a magnetizing inrush current.
2. The identification method according to claim 1, wherein the data sampling time interval T is calculated by simulation of a digital simulation system set up to obtain the time interval reference of said step (1).
3. The identification method of claim 1, wherein the step (2) of calculating the ratio of the magnitudes of the dc component and the fundamental component comprises:
(2-1) measuring the current waveform of the circuit breaker at the outlet of the transformer, and detecting and judging that the current amplitude is greater than the action current setting value;
(2-2) when the current amplitude of the breaker at the outlet of the transformer is larger than the action current setting value, measuring and recording the current waveform of the medium-voltage side of the transformer, and calculating the amplitude ratio A of the direct current component to the fundamental component in different time intervals T according to the following formula:
wherein, I0m: a DC component amplitude; i is1m: the fundamental component amplitude.
4. The identification method according to claim 1, wherein the criterion for identifying the magnetizing inrush current in the step (3) is a decay rate of a magnitude ratio of a direct current component to a fundamental component of the transformer outlet breaker current.
5. The identification method according to claim 4, wherein the criterion for identifying a magnetizing inrush current is formulated by:
(S1) calculating a short-circuit current flowing through the transformer outlet circuit breaker at the time of the short-circuit fault by simulation, and calculating a direct current component and a fundamental component thereof;
(S2) simulating and calculating the magnetizing inrush current flowing through the circuit breaker at the outlet of the transformer when the transformer is switched on and is in no-load main transformer, and calculating the direct current component and the fundamental component of the magnetizing inrush current;
(S3) selecting a minimum data sampling time interval T based on the current data characteristics of steps (S1) and (S2);
(S4) calculating the amplitude ratio A of the direct current component and the fundamental component in the short-circuit current and the magnetizing inrush current at each interval time Tn；
(S5) attenuation rate K according to the calculated amplitude ratio of the direct current component and the fundamental componentnDetermining a decay rate threshold KsetIf K is1If the current is less than 0, the current is excitation surge current;
if K1> 0 and K2＞KsetIf the current is the fault current, otherwise, the current is the excitation inrush current;
(S6) correcting the data sampling time interval T and the attenuation rate threshold K of the simulation calculation according to the measured values of the magnetizing inrush current and the short-circuit current in the fault when the no-load main transformer is switched on in the actual engineeringset。
6. An identification method as claimed in claim 5, characterized in that said criterion is selected on the basis of: the electrical characteristics of the fault current of the transformer meet the criterion requirement, and the electrical characteristics of the magnetizing inrush current do not meet the criterion requirement.
7. The identification method of claim 5, wherein the DC component and the fundamental component in the steps (S1) and (S2) are calculated by Fourier algorithm, respectively.
8. A magnetizing inrush current identification device applying the identification method of any one of claims 1 to 7, wherein the device comprises a current measurement unit, a digital simulation unit, a data discrimination unit, a data processing unit, a criterion formulation unit and a current identification unit;
the current measuring unit transmits the obtained current of the transformer outlet circuit breaker to the data judging unit;
the digital simulation unit transmits the calculated action current setting value to the data discrimination unit;
the digital simulation unit transmits the calculated sampling time interval T to the data processing unit;
the data judging unit judges the magnitude of the current amplitude and the action current setting value of the transformer outlet circuit breaker and transmits the magnitude to the data processing unit;
the data processing unit transmits the calculated amplitude ratio of the direct current component and the fundamental component in different time intervals T to the criterion establishing unit;
the criterion establishing unit transmits the defined decay rate and the set threshold value to the current identification unit;
the current identification unit identifies the current output by the transformer outlet circuit breaker;
the criterion formulating unit sets an attenuation rate threshold KsetAnd calculating the attenuation rate K of the amplitude ratio of the DC component to the fundamental component according to the following formulan：
Kn＝(A0-An)/A0
Wherein n is 1, 2; a. the0And An: respectively, the dc component to fundamental component amplitude ratios in the 0 th and nth sampling time intervals T are shown.
9. The identification device according to claim 8, wherein the digital simulation unit calculates the action current setting value and the sampling time interval T according to the condition of the power grid where the project is located, and corrects the action current setting value and the sampling time interval T according to the field debugging operation result.
10. The identification device of claim 8, wherein the determination of whether to transmit data to the data processing unit is based on the determination by the data determination unit of the magnitude of the transformer outlet circuit breaker current magnitude and the action current setting.
11. The identification device of claim 8 wherein the data processing unit fourier computes the ratio of the magnitude of the dc component to the fundamental component over different time intervals.
12. The identification device of claim 8, wherein the current identification unit is based on a decay rate and a decay rate threshold KsetJudging whether the output current of the breaker at the outlet of the transformer is magnetizing inrush current or not:
if K1If the current is less than 0, the current is excitation surge current;
if K1> 0 and K2＞KsetThen is fault current; if K1> 0 and K2＜KsetAnd then, the current is the magnetizing inrush current.
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| CN111525508B (en) * | 2020-04-03 | 2022-08-30 | 中国电力科学研究院有限公司 | High-voltage shunt reactor turn-to-turn protection anti-saturation misoperation method and device |
| CN111463751A (en) * | 2020-04-27 | 2020-07-28 | 国网陕西省电力公司西安供电公司 | Transformer protection method based on equivalent excitation impedance characteristics |
| CN111668819B (en) * | 2020-06-22 | 2022-07-29 | 广东韶钢松山股份有限公司 | Line protection control method and microcomputer protection device |
| CN111969556B (en) * | 2020-08-13 | 2022-07-26 | 广东电网有限责任公司 | Excitation inrush current judgment method and judgment device |
| CN112147396B (en) * | 2020-09-09 | 2023-01-31 | 中国电力科学研究院有限公司 | Method and system for calculating percentage of direct current component of short-circuit current |
| CN113176439B (en) * | 2021-04-29 | 2022-08-16 | 四川虹美智能科技有限公司 | Single-phase alternating-current voltage detection circuit and detection method thereof |
| CN116404612B (en) * | 2023-06-06 | 2023-09-15 | 三峡智能工程有限公司 | Method and system for preventing generator differential protection misoperation caused by emergency current |
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| CN101820166B (en) * | 2010-02-10 | 2012-08-15 | 江苏金智科技股份有限公司 | Magnetizing inrush current discrimination method based on equivalent excitation impedance frequency domain character of transformer |
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