CN110829371B - Magnetizing inrush current identification method based on waveform similarity of circular current and zero sequence current - Google Patents
Magnetizing inrush current identification method based on waveform similarity of circular current and zero sequence current Download PDFInfo
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- CN110829371B CN110829371B CN201911091285.3A CN201911091285A CN110829371B CN 110829371 B CN110829371 B CN 110829371B CN 201911091285 A CN201911091285 A CN 201911091285A CN 110829371 B CN110829371 B CN 110829371B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
- H02H7/045—Differential protection of transformers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
Abstract
The invention discloses a magnetizing inrush current identification method based on the similarity of the waveforms of a circulating current and a zero sequence current, which comprises the following steps of: collecting angular side internal circulation current of star-delta transformer, and obtaining angular side internal circulation current i reduced to star side by transformer transformation ratioD(ii) a Collecting the current at the star side neutral point of the star-delta transformer to obtain the zero sequence current i at the neutral point0(ii) a Calculating the correlation coefficient of the circular current at the inner angle side of the data window and the zero sequence current waveform of the neutral point; calculating the waveform correlation coefficient of the circular current at the inner angle side of the data window and the zero-sequence current at the neutral point, if the obtained waveform correlation coefficient is larger than a set value, judging that the current is inrush, and locking differential protection; otherwise, the differential protection is opened.
Description
Technical Field
The invention relates to the field of relay protection of a power system, in particular to a method for identifying excitation inrush current when a star-delta transformer is switched on in a no-load mode.
Background
The power transformer is used as an important device in power transmission and distribution links of a power system, the running state of the power transformer seriously influences the power supply reliability of the power system, the demand of people on power energy is increased day by day along with the rapid development of economic construction in China, and the dependence on the power energy is higher and higher. However, the correct operation rate of the main protection of the transformer is always low compared with other elements of the power system, wherein the differential protection malfunction caused by the magnetizing inrush current generated when the transformer is not thrown is an important factor. At present, many researches on the magnetizing inrush current of a transformer are carried out at home and abroad, wherein the principles are mature and applied in practical engineering, such as a second harmonic braking principle, a discontinuous angle principle, a waveform symmetry principle and the like. Therefore, the method and the device have important significance for improving the correct action rate of the transformer by finding a new principle and a new method for identifying the magnetizing inrush current and the fault current.
Disclosure of Invention
The invention aims to provide a method for identifying magnetizing inrush current and ground fault current during no-load closing of a transformer, aiming at the problem that the magnetizing inrush current generated during no-load closing of the transformer easily causes differential protection misoperation. The technical scheme is as follows:
a method for identifying the magnetizing inrush current and the grounding fault of a star-delta transformer based on the correlation degree of zero sequence current and circular current waveforms is characterized in that a waveform correlation coefficient is introduced to judge the magnetizing inrush current and the grounding fault current of the star-delta transformer by utilizing the phase relation between the circular current at the angular side and the zero sequence current at the neutral point at the star side when the star-delta transformer is in idle casting, and the neutral point at the star side of the star-delta transformer is directly grounded or grounded through a small resistor. The method comprises the following steps:
1) collecting angular side internal circulation of star-delta transformer, and obtaining angular side internal circulation i reduced to star side by transformer transformation ratioD；
2) Collecting the current at the star side neutral point of the star-delta transformer to obtain the zero sequence current i at the neutral point0；
3) Calculating the waveform correlation coefficient of the angular side circulation current and the neutral point zero sequence current, wherein the calculation formula is as follows:
wherein, N is a sampling point of a sampling data window, x (i) and y (i) are ith data in the angular side circulation and satellite side zero sequence current sampling data windows respectively, and x and y are data average values in the angular side circulation and satellite side zero sequence current sampling data windows respectively.
Setting a set value according to actual system parameters and a transformer field operation environment, calculating a correlation coefficient of the star-angle transformer angular side circulating current and the star zero sequence current waveform in a data window, if the correlation coefficient obtained by calculation is larger than the set value, judging that the current is inrush, and locking differential protection; otherwise, the differential protection is opened.
The set value may be 0.5.
Drawings
FIG. 1 is a schematic diagram of the connection of a star-delta transformer and an equivalent circuit diagram of phase A
FIG. 2 is a waveform diagram of zero sequence current and circulating current when inrush current is generated by transformer no-load
FIG. 3A is a schematic diagram of a phase-to-ground connection of a star-delta transformer and a single-phase equivalent circuit diagram
FIG. 4A is a zero sequence network equivalent circuit diagram of the phase grounding system
FIG. 5 is a waveform diagram of zero sequence current and circulating current when the transformer is in idle-throw at ground fault
FIG. 6 shows the correlation coefficient between the zero-sequence current and the circular current waveform when the transformer is in inrush current due to air-drop and in earth fault due to air-drop
Detailed Description
The invention provides a method for identifying the magnetizing inrush current and the ground fault of a star-delta transformer based on the correlation degree of zero sequence current and circulating current waveform. Specific embodiments will now be described as follows:
1. fig. 1 shows a schematic wiring diagram of a star-delta transformer and an equivalent circuit diagram of phase a when no fault occurs. The following conclusions can be drawn: when the star-delta transformer is in idle operation to generate excitation inrush current, the neutral zero sequence current i0And angular side internal circulation iDThe relational expression is:
wherein i0Is zero sequence current at neutral point on star side of transformerDFor angular internal circulation, Z, converted to star side1σ、Z2σIs the primary leakage reactance of the transformer and the secondary leakage reactance, Z, converted to the primary side0SIs the equivalent zero sequence impedance of the power supply.
Neglecting the resistance part in the leakage inductance at the two sides of the transformer and the equivalent zero sequence impedance of the power supply, when the star-delta transformer is switched on in no-load to generate excitation inrush current, the neutral zero sequence current and the internal circulation current at the angular side basically have a linear relationship, the two currents have the same waveform trend, and the simulation waveform diagram is shown in fig. 2.
2. Fig. 3 is a schematic diagram of a connection of a phase a grounded time star-delta transformer and a single-phase equivalent circuit diagram; fig. 4 shows an equivalent circuit diagram of the zero sequence network of the phase a grounding system. The following conclusions can be drawn: when the star-delta transformer is airdropped in a single-phase earth fault, the phases of the zero-sequence current and the circulating current are opposite, namely the wave trends are opposite, and the relational expression is as follows:
wherein i0Is zero sequence current at neutral point on star side of transformerDFor angular internal circulation, Z, converted to star side1σ、Z2σIs the primary leakage reactance of the transformer and the secondary leakage reactance, Z, converted to the primary sideTIs equivalent zero-sequence impedance of the transformer and satisfies ZT>Z1σ。
Similarly, when the star-delta transformer is in no-load closing and ground fault, the change trend of the waveforms of the neutral zero-sequence current and the angular side inner loop current is opposite, and the two current simulation oscillograms are shown in fig. 5.
3. Calculating the zero sequence current and circulation waveform correlation coefficient, wherein the calculation formula is as follows:
wherein N is the number of sampling points of the data window, x (i) and y (i) are respectively zero sequence current and ith data of circulating current in the sampling data window,
the data mean values in the zero sequence current and the circulation sampling data window are respectively.
4. Calculating the correlation coefficient between the zero sequence current and the circulation waveform in the data window, wherein when the transformer is switched on in no-load to generate magnetizing inrush current, the correlation coefficient is very close to 1, and the correlation coefficient is calculated to be greater than a set value (0.5), so that the magnetizing inrush current is judged, and differential protection is locked; when the transformer is switched on in no-load and has ground fault, the correlation coefficient is close to-1, the correlation coefficient obtained by calculation is smaller than-1, and the differential protection is opened.
Because the actual operation environment of the transformer is complex, the real value of the correlation coefficient can be calculated according to data collected on site, and the threshold value (0.5) can be properly adjusted.
Claims (2)
1. A magnetizing inrush current identification method based on the similarity of the circular current and the zero sequence current waveform is characterized in that a waveform correlation coefficient is introduced to judge the magnetizing inrush current and the grounding fault current of a star-delta transformer by utilizing the phase relation between the circular current in the star-delta transformer on the air-drop time angle side and the zero sequence current at the star-delta neutral point, and the star-delta transformer star-delta neutral point is directly grounded or grounded through a small resistor, and the method comprises the following steps:
1) collecting angular side internal circulation current of star-delta transformer, and obtaining angular side internal circulation current i reduced to star side by transformer transformation ratioD；
2) Collecting the current at the star side neutral point of the star-delta transformer to obtain the zero sequence current i at the neutral point0；
3) Calculating the waveform correlation coefficient of the inner circular current at the angular side and the zero sequence current at the neutral point, wherein the calculation formula is as follows:
wherein, N is a sampling point of a sampling data window, x (i) and y (i) are the ith data in the sampling data window of the circulating current in the angular side and the zero sequence current at the neutral point of the star side respectively,
respectively obtaining the average values of data in the zero sequence current sampling data windows at the corner side internal circulation point and the star side neutral point;
setting a set value according to actual system parameters and a transformer field operation environment, calculating a correlation coefficient of a circular current and a zero sequence current waveform at a neutral point in the angular side of the star-angle transformer in a data window, and if the correlation coefficient is calculated to be larger than the set value, judging that the current is inrush, and locking differential protection; otherwise, the differential protection is opened.
2. The identification method according to claim 1, wherein the set value is 0.5.
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Citations (4)
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| CN101257208A (en) * | 2007-12-21 | 2008-09-03 | 清华大学 | Method for identifying transformer excitation surge current |
| CN103675415A (en) * | 2012-08-31 | 2014-03-26 | 西门子公司 | Excitation surge current detection method, excitation surge current brake method and excitation surge current detection device |
| CN104078933A (en) * | 2014-07-04 | 2014-10-01 | 国家电网公司 | Method for calculating delta side loop current of Y/delta connection transformer |
| CN105552838A (en) * | 2016-02-26 | 2016-05-04 | 三峡大学 | Standardized graphic similarity matching identification-based zero-sequence differential protection algorithm for transformer |
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2019
- 2019-11-09 CN CN201911091285.3A patent/CN110829371B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101257208A (en) * | 2007-12-21 | 2008-09-03 | 清华大学 | Method for identifying transformer excitation surge current |
| CN103675415A (en) * | 2012-08-31 | 2014-03-26 | 西门子公司 | Excitation surge current detection method, excitation surge current brake method and excitation surge current detection device |
| CN104078933A (en) * | 2014-07-04 | 2014-10-01 | 国家电网公司 | Method for calculating delta side loop current of Y/delta connection transformer |
| CN104078933B (en) * | 2014-07-04 | 2017-01-18 | 国家电网公司 | Method for calculating delta side loop current of Y/delta connection transformer |
| CN105552838A (en) * | 2016-02-26 | 2016-05-04 | 三峡大学 | Standardized graphic similarity matching identification-based zero-sequence differential protection algorithm for transformer |
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| 基于波形上下对称系数识别励磁涌流的新原理;姚斌等;《电力系统及其自动化学报》;20040430;第16卷(第2期);第32-35页 * |
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