CN116973810B - Method and system for identifying excitation surge current and CT saturation of transformer - Google Patents
Method and system for identifying excitation surge current and CT saturation of transformer Download PDFInfo
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- CN116973810B CN116973810B CN202310752498.6A CN202310752498A CN116973810B CN 116973810 B CN116973810 B CN 116973810B CN 202310752498 A CN202310752498 A CN 202310752498A CN 116973810 B CN116973810 B CN 116973810B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/62—Testing of transformers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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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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Abstract
The invention discloses a method and a system for identifying magnetizing inrush current and CT saturation of a transformer, and belongs to the technical field of relay protection. The method of the invention comprises the following steps: sampling three-phase currents on each side of the transformer respectively, and determining three-phase differential currents of the transformer based on transformation ratio parameters on each side of the transformer and the three-phase currents obtained by sampling; performing differential processing on the three-phase differential current and the three-phase currents on each side of the transformer to obtain a differential processing result; performing absolute value processing on the differential processing result to obtain an absolute value processing result, and respectively obtaining the ratio of integral values of the absolute value processing result in a fixed time period; based on the ratio, transformer magnetizing inrush current and CT saturation are identified. The invention can rapidly and accurately identify whether the transformer generates exciting inrush current or CT saturation through the ratio.
Description
Technical Field
The invention relates to the technical field of relay protection, in particular to a method and a system for identifying transformer excitation inrush current and CT saturation.
Background
The transformer is an important electric energy conversion device in an alternating current-direct current system, and the operation safety and reliability of the transformer are crucial to the safe and stable operation of the whole power grid. When the transformer has internal faults, the faults are detected by the relay protection device, and are removed from the power grid, so that the faults are isolated, and fault loops are cut off, so that the safety of equipment and systems is ensured. The existing transformer protection is mainly divided into electric quantity protection and non-electric quantity protection, wherein the electric quantity protection is to extract fault characteristics by utilizing electric quantity information such as voltage, current and the like measured by each side of the transformer, and distinguish faults inside and outside a region. The non-electric quantity protection is to utilize the physical characteristics of temperature, special gas (such as gas) and the like to judge the faults and then remove the isolation faults after the faults occur in the transformer shell. Because the fault position is influenced by a plurality of factors such as the arrangement position of the sensor, signal transmission interference and the like, the sensitivity and the reliability of the non-electric quantity protection are far lower than those of the electric quantity protection in practical application, and therefore, the importance of the electric quantity protection is far higher than that of the non-electric quantity protection.
The main protection of the transformer electric quantity protection is differential protection, and differential current is obtained by summing current phasors or sampling values at each side of the transformer when the transformer fails internally and externally, the differential current is rapidly increased when the transformer fails in a zone, and the differential current is not obviously increased when the transformer fails out of the zone. Meanwhile, the through current is used as the braking quantity of protection, so that the unbalanced differential current of external faults can be ensured not to cause misoperation of differential protection. In addition, since differential currents are also generated when transformer magnetizing inrush current and CT saturation occur, blocking elements, i.e., inrush current blocking and CT saturation blocking, are typically introduced in transformer protection to avoid malfunctions caused by differential currents in these non-internal fault conditions. The overall performance of the transformer protection is thus severely dependent on the impact of the performance of both latching elements. If the identification is inaccurate, false actions under the conditions of inrush current and CT saturation can be caused to be protected, or false locking can cause refusal actions or delay actions during faults, so that the safety of equipment and systems is threatened.
Disclosure of Invention
In view of the above problems, the present invention provides a method for identifying magnetizing inrush current and CT saturation of a transformer, including:
Sampling three-phase currents on each side of the transformer respectively, and determining three-phase differential currents of the transformer based on transformation ratio parameters on each side of the transformer and the three-phase currents obtained by sampling;
performing differential processing on the three-phase differential current and the three-phase currents on each side of the transformer to obtain a differential processing result;
Performing absolute value processing on the differential processing result to obtain an absolute value processing result, and respectively obtaining the ratio of integral values of the absolute value processing result in a fixed time period;
based on the ratio, transformer magnetizing inrush current and CT saturation are identified.
Optionally, each side of the transformer comprises: a transformer high voltage side and a low voltage side.
Optionally, the transformation ratio parameter includes at least one of: transformer transformation ratio and CT transformation ratio.
Optionally, the calculation formula of the differential current of the transformer determined by the sampling unit is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the high-voltage side CT transformation ratio.
Optionally, the differential processing unit performs differential processing on the three-phase differential current and three-phase currents on each side of the transformer, and specifically includes:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of A, B, C phase differential current, i aH(k)、ibH(k)、icH (k) is three-phase current at the high voltage side of the transformer, i aL(k)、ibL(k)、icL (k) is three-phase current at the low voltage side of the transformer, N T is transformer transformation ratio, For low-voltage side CT transformation ratio,/>For the high-voltage side CT transformation ratio, i aH(k-1)、ibH(k-1)、icH (k-1) is the previous sampling value of the current sampling value of the high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is the previous sampling value of the current sampling value of the low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is the differential value of the sampling values of the high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is the differential value of the sampling values of the low-voltage side three-phase current.
Optionally, the absolute value processing unit performs absolute value processing on the differential processing result, and specifically includes:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of the three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) is the differential value of the high-voltage side three-phase current sampling values, and di aL(k)、dibL(k)、dicL (k) is the differential value of the low-voltage side three-phase current sampling values.
Optionally, the identifying unit identifies the magnetizing inrush current and the CT saturation of the transformer based on the ratio, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (22) - (24), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (25) - (30), the CT saturation of the transformer can be determined, wherein the formulas (22) - (30) are as follows:
Wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, P set2 is the CT saturation identification constant value, di cd_a(k)、dicd_b(k)、dicd_c (k) are respectively the differential values of three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) are respectively the differential values of the sampling values of three-phase current at the high voltage side, and di aL(k)、dibL(k)、dicL (k) are respectively the differential values of the sampling values of the three-phase current at the low voltage side
In yet another aspect, the present invention further provides a system for identifying magnetizing inrush current and CT saturation of a transformer, including:
The sampling unit is used for sampling three-phase currents at each side of the transformer respectively and determining three-phase differential currents of the transformer based on transformation ratio parameters at each side of the transformer and the three-phase currents obtained by sampling;
The differential processing unit is used for carrying out differential processing on the three-phase differential current and the three-phase currents at each side of the transformer so as to obtain a differential processing result;
an absolute value processing unit, configured to perform absolute value processing on the differential processing result, so as to obtain an absolute value processing result, and respectively calculate a ratio of integral values of the absolute value processing result in a fixed time period;
And the identification unit is used for identifying the transformer excitation inrush current and CT saturation based on the ratio.
Optionally, each side of the transformer comprises: a transformer high voltage side and a low voltage side.
Optionally, the transformation ratio parameter includes at least one of: transformer transformation ratio and CT transformation ratio.
Optionally, the calculation formula of the differential current of the transformer determined by the sampling unit is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the high-voltage side CT transformation ratio.
Optionally, the differential processing unit performs differential processing on the three-phase differential current and three-phase currents on each side of the transformer, and specifically includes:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of A, B, C phase differential current, i aH(k)、ibH(k)、icH (k) is three-phase current at the high voltage side of the transformer, i aL(k)、ibL(k)、icL (k) is three-phase current at the low voltage side of the transformer, N T is transformer transformation ratio, For low-voltage side CT transformation ratio,/>For the high-voltage side CT transformation ratio, i aH(k-1)、ibH(k-1)、icH (k-1) is the previous sampling value of the current sampling value of the high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is the previous sampling value of the current sampling value of the low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is the differential value of the sampling values of the high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is the differential value of the sampling values of the low-voltage side three-phase current.
Optionally, the absolute value processing unit performs absolute value processing on the differential processing result, and specifically includes:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of the three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) is the differential value of the high-voltage side three-phase current sampling values, and di aL(k)、dibL(k)、dicL (k) is the differential value of the low-voltage side three-phase current sampling values.
Optionally, the identifying unit identifies the magnetizing inrush current and the CT saturation of the transformer based on the ratio, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (22) - (24), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (25) - (30), the CT saturation of the transformer can be determined, wherein the formulas (22) - (30) are as follows:
wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, P set2 is the CT saturation identification constant value, di cd_a(k)、dicd_b(k)、dicd_c (k) are respectively the differential values of three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) are respectively the differential values of the sampling values of three-phase current at the high voltage side, and di aL(k)、dibL(k)、dicL (k) are respectively the differential values of the sampling values of the three-phase current at the low voltage side. One or more processors;
a processor for executing one or more programs;
The method as described above is implemented when the one or more programs are executed by the one or more processors.
In yet another aspect, the present invention also provides a computer readable storage medium having stored thereon a computer program which, when executed, implements a method as described above.
Compared with the prior art, the invention has the beneficial effects that:
The invention provides a method for identifying excitation surge current and CT saturation of a transformer, which comprises the following steps: sampling three-phase currents on each side of the transformer respectively, and determining three-phase differential currents of the transformer based on transformation ratio parameters on each side of the transformer and the three-phase currents obtained by sampling; performing differential processing on the three-phase differential current and the three-phase currents on each side of the transformer to obtain a differential processing result; performing absolute value processing on the differential processing result to obtain an absolute value processing result, and respectively obtaining the ratio of integral values of the absolute value processing result in a fixed time period; based on the ratio, transformer magnetizing inrush current and CT saturation are identified. The invention can rapidly and accurately identify whether the transformer generates exciting inrush current or CT saturation through the ratio.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic diagram of three-phase differential current during inrush current conditions of a transformer in accordance with a preferred embodiment of the present invention;
FIG. 3 is a graph showing the results after differential C phase-contrast flow according to the preferred embodiment of the present invention;
FIG. 4 is a graph showing the absolute value obtained after the difference of the phase difference C current according to the preferred embodiment of the present invention;
FIG. 5 is a schematic diagram showing the calculation result of the inrush current identification ratio formula according to the preferred embodiment of the present invention;
FIG. 6 is a schematic diagram of a result of discriminating a surge current according to a preferred embodiment of the present invention;
FIG. 7 is a schematic diagram of a saturated waveform of the B-phase current on the high side of the transformer in accordance with a preferred embodiment of the present invention;
FIG. 8 is a schematic diagram of the differential results of the B-phase current on the high side of the transformer according to the preferred embodiment of the present invention;
FIG. 9 is a schematic diagram showing absolute values of the B-phase current difference at the high side of the transformer according to the preferred embodiment of the present invention;
FIG. 10 is a schematic diagram showing the calculation result of a CT saturation identification ratio formula according to the preferred embodiment of the present invention;
FIG. 11 is a diagram showing the result of CT saturation identification discrimination according to the preferred embodiment of the present invention;
FIG. 12 is a phase A differential current schematic of a fault phase at turn-to-turn fault in accordance with a preferred embodiment of the present invention;
FIG. 13 is a schematic diagram of the results after A-phase differential flow differencing in accordance with a preferred embodiment of the present invention;
FIG. 14 is a graph showing the absolute value of the difference A phase difference according to the preferred embodiment of the present invention;
FIG. 15 is a schematic view showing the calculation result of the inrush current identification ratio formula according to the preferred embodiment of the present invention;
FIG. 16 is a schematic diagram of a high side phase A current saturation waveform of a transformer in accordance with a preferred embodiment of the present invention;
FIG. 17 is a schematic diagram of the differential results of the high side A-phase current of the transformer according to the preferred embodiment of the present invention;
FIG. 18 is a schematic diagram showing absolute values of the high side A-phase current of the transformer after being differentiated according to the preferred embodiment of the present invention;
FIG. 19 is a graph showing the calculation result of the CT saturation identification ratio formula according to the preferred embodiment of the present invention;
Fig. 20 is a block diagram of a system of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the examples described herein, which are provided to fully and completely disclose the present invention and fully convey the scope of the invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like elements/components are referred to by like reference numerals.
Unless otherwise indicated, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, it will be understood that terms defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Example 1:
the invention provides a method for identifying magnetizing inrush current and CT saturation of a transformer, which is shown in fig. 1 and comprises the following steps:
step 1, sampling three-phase currents on each side of a transformer respectively, and determining three-phase differential currents of the transformer based on transformation ratio parameters on each side of the transformer and the three-phase currents obtained by sampling;
Step 2, carrying out differential processing on the three-phase differential current and the three-phase currents at each side of the transformer to obtain a differential processing result;
step 3, carrying out absolute value processing on the differential processing result to obtain an absolute value processing result, and respectively solving the ratio of integral values of the absolute value processing result in a fixed time period;
And 4, identifying the excitation inrush current and CT saturation of the transformer based on the ratio.
Wherein, the transformer each side includes: a transformer high voltage side and a low voltage side.
Wherein the transformation ratio parameter comprises at least one of the following: transformer transformation ratio and CT transformation ratio.
The calculation formula for determining the differential current of the transformer is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the high-voltage side CT transformation ratio.
The differential processing is performed on the three-phase differential current and the three-phase current at each side of the transformer, and specifically includes:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of A, B, C three-phase differential current, i aH(k)、ibH(k)、icH (k) is the high-voltage side three-phase current of the transformer, i aL(k)、ibL(k)、icL (k) is the low-voltage side three-phase current of the transformer, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>For the high-voltage side CT transformation ratio, i aH(k-1)、ibH(k-1)、icH (k-1) is the previous sampling value of the current sampling value of the high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is the previous sampling value of the current sampling value of the low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is the differential value of the sampling values of the high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is the differential value of the sampling values of the low-voltage side three-phase current.
The absolute value processing of the differential processing result specifically comprises the following steps:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of the three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) is the differential value of the high-voltage side three-phase current sampling values, and di aL(k)、dibL(k)、dicL (k) is the differential value of the low-voltage side three-phase current sampling values.
Based on the ratio, the excitation inrush current and CT saturation of the transformer are identified, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (22) - (24), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (25) - (30), the CT saturation of the transformer can be determined, wherein the formulas (22) - (30) are as follows:
Wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, P set2 is the CT saturation identification constant value, di cd_a(k)、dicd_b(k)、dicd_c (k) are respectively the differential values of three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) are respectively the differential values of the sampling values of the three-phase current at the high voltage side, and di aL(k)、dibL(k)、dicL (k) are respectively the differential values of the sampling values of the three-phase current at the low voltage side.
The following description is made with reference to the accompanying drawings and specific examples:
excitation surge current identification case:
a certain double-winding transformer is closed on the system from the high-voltage side in an idle mode.
Calculating differential current by using the current sampling values of each side of the transformer, the transformer transformation ratio and the CT transformation ratio of each side;
Fig. 2 is a three-phase differential current sampling value calculated by using the formulas (1) to (3).
Differential operation is carried out on the differential current:
Fig. 3 is a result of calculating the C phase difference current difference calculated by the formula (6). The inrush current maximum phase, i.e., the differential current maximum phase C, is described as an example. The other two phases have small differential flow, so that the differential action threshold is not reached, and the false action of differential protection is not caused, so that the inrush current judgment result can be not considered.
Taking absolute value operation for differential current after differential:
Fig. 4 is an absolute value processing of the calculation result in the step b by using the formula (15).
And carrying out sectional integral ratio operation on the absolute value of the differential post-differential stream:
Fig. 5 shows the result of the absolute value processing in the previous step c, and the result of the piecewise integral ratio is obtained by using the formula (24).
And finally, comparing the result of d with a fixed value to obtain a criterion result.
Fig. 6 shows the distinguishing result signals of the phase difference current and the inrush current, and it can be seen from the figure that the method provided by the patent can quickly identify the excitation inrush current 12ms after the inrush current occurs.
CT saturation recognition case:
And after a three-phase short circuit occurs outside a certain double-winding transformer, the phase B is saturated by CT.
Sampling the original waveform of the current at each side of the transformer;
fig. 7 is an original high side B-phase current sample.
And carrying out differential operation on the phase current sampling value:
fig. 8 is a B-phase current difference calculation result calculated by using the formula (8). Here, a CT saturated phase will be described as an example. The other two phases have small differential flow, so that the differential action threshold is not reached, and the false action of differential protection is not caused, so that the CT saturation judgment result can be not considered.
And (3) taking absolute value operation on the phase current after the difference:
Fig. 8 is an absolute value processing of the calculation result in the step b by using the formula (17).
And carrying out sectional integral ratio operation on the absolute value of the differential post-phase current:
Fig. 9 shows the result of the absolute value processing in the previous step c, and the result of the piecewise integral ratio is obtained by using the formula (26).
And finally, comparing the result of d with a fixed value to obtain a criterion result.
Fig. 10 shows the discrimination result signals of the B-phase current and the CT saturation, and as can be seen from fig. 11, the method provided by the present patent can rapidly and accurately identify the CT saturation 4.6ms after the CT saturation.
Inter-zone turn-to-turn fault case:
a double-winding transformer generates an inter-turn short circuit in the A-phase region.
Calculating differential current by using the current sampling values of each side of the transformer, the transformer transformation ratio and the CT transformation ratio of each side;
Fig. 12 is a three-phase differential current sampling value calculated by using the formula (1).
Differential operation is carried out on the differential current:
Fig. 13 is a result of a phase a differential current difference calculation calculated by the formula (4). The inter-turn fault phase a is described as an example. The other two phases have small differential flow, so that the differential action threshold is not reached, and the false action of differential protection is not caused, so that the inrush current judgment result can be not considered.
Taking absolute value operation for differential current after differential:
Fig. 14 is an absolute value processing of the calculation result in step b using formula (13).
And carrying out sectional integral ratio operation on the absolute value of the differential post-differential stream:
Fig. 15 shows the result of the absolute value processing in the previous step c, and the result of the piecewise integral ratio is obtained by using the formula (22).
As can be seen from the graph, the criterion condition is not satisfied in the whole fault process, so that the fault is not misjudged as the surge.
Sampling the original waveform of the current at each side of the transformer;
fig. 16 is an original high side a-phase current sample.
And carrying out differential operation on the phase current sampling value:
Fig. 17 is a result of the a-phase current difference calculation calculated by the formula (7). Here, a fault phase will be described as an example. The other two phases have small differential flow, so that the differential action threshold is not reached, and the false action of differential protection is not caused, so that the CT saturation judgment result can be not considered.
And (3) taking absolute value operation on the phase current after the difference:
Fig. 18 is an absolute value processing of the calculation result in the step b using the formula (16).
And carrying out sectional integral ratio operation on the absolute value of the differential post-phase current:
Fig. 19 shows the result of the absolute value processing in the previous step c, and the result of the piecewise integral ratio is obtained by using the formula (25).
As can be seen from the figure, the criterion condition is not satisfied in the whole fault process, so that the CT saturation is not misjudged.
The three embodiments show that the method provided by the invention can accurately identify the current and CT saturation, can not be erroneously distinguished as the current or CT saturation when the fault occurs in the area, and has simple and clear principle and convenient realization.
Example 2:
The invention also proposes a system 200 for identifying transformer magnetizing inrush current and CT saturation, as shown in fig. 20, comprising:
The sampling unit 201 is configured to sample three-phase currents on each side of the transformer, and determine three-phase differential currents of the transformer based on the transformation ratio parameters on each side of the transformer and the three-phase currents obtained by the sampling;
The differential processing unit 202 is configured to perform differential processing on the three-phase differential current and the three-phase currents on each side of the transformer, so as to obtain a differential processing result;
an absolute value processing unit 203, configured to perform an absolute value processing on the differential processing result, so as to obtain an absolute value processing result, and respectively calculate a ratio of integral values of the absolute value processing result in a fixed period of time;
And an identification unit 204, configured to identify transformer magnetizing inrush current and CT saturation based on the ratio.
Wherein, the transformer each side includes: a transformer high voltage side and a low voltage side.
Wherein the transformation ratio parameter comprises at least one of the following: transformer transformation ratio and CT transformation ratio.
The calculation formula of the differential current of the transformer determined by the sampling unit is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the high-voltage side CT transformation ratio.
The differential processing unit 202 performs differential processing on the three-phase differential current and the three-phase currents on each side of the transformer, and specifically includes:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of A, B, C three-phase differential current, i aH(k)、ibH(k)、icH (k) is the high-voltage side three-phase current of the transformer, i aL(k)、ibL(k)、icL (k) is the low-voltage side three-phase current of the transformer, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>For the high-voltage side CT transformation ratio, i aH(k-1)、ibH(k-1)、icH (k-1) is the previous sampling value of the current sampling value of the high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is the previous sampling value of the current sampling value of the low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is the differential value of the sampling values of the high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is the differential value of the sampling values of the low-voltage side three-phase current.
The absolute value processing unit 203 performs absolute value processing on the differential processing result, and specifically includes:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is the differential value of the three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) is the differential value of the high-voltage side three-phase current sampling values, and di aL(k)、dibL(k)、dicL (k) is the differential value of the low-voltage side three-phase current sampling values.
The identifying unit 204 identifies the magnetizing inrush current and the CT saturation of the transformer based on the ratio, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (22) - (24), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (25) - (30), the CT saturation of the transformer can be determined, wherein the formulas (22) - (30) are as follows:
Wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, P set2 is the CT saturation identification constant value, di cd_a(k)、dicd_b(k)、dicd_c (k) are respectively the differential values of three-phase differential current sampling values, di aH(k)、dibH(k)、dicH (k) are respectively the differential values of the sampling values of the three-phase current at the high voltage side, and di aL(k)、dibL(k)、dicL (k) are respectively the differential values of the sampling values of the three-phase current at the low voltage side.
Under the condition that excitation surge current occurs to the transformer, the calculated ratio result is quite large (more than 20) and is far more than a fixed value P set1; when the transformer is saturated by CT, the calculated ratio is far greater than the fixed value P set2 in the discrimination formulas corresponding to the saturated phase of CT in the formulas (25) to (30). In the case of an intra-zone fault, the ratio obtained by both criteria is less than the fixed values P set1 and P set2.
Example 3:
Based on the same inventive concept, the invention also provides a computer device comprising a processor and a memory for storing a computer program comprising program instructions, the processor for executing the program instructions stored by the computer storage medium. The processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processor, digital signal processor (DIGITAL SIGNAL Processor, DSP), application specific integrated circuit (Application SpecificIntegrated Circuit, ASIC), off-the-shelf Programmable gate array (Field-Programmable GATEARRAY, FPGA) or other Programmable logic device, discrete gate or transistor logic device, discrete hardware components, etc., which are the computational core and control core of the terminal adapted to implement one or more instructions, in particular to load and execute one or more instructions within a computer storage medium to implement the corresponding method flow or corresponding functions to implement the steps of the method in the embodiments described above.
Example 4:
based on the same inventive concept, the present invention also provides a storage medium, in particular, a computer readable storage medium (Memory), which is a Memory device in a computer device, for storing programs and data. It is understood that the computer readable storage medium herein may include both built-in storage media in a computer device and extended storage media supported by the computer device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also stored in the memory space are one or more instructions, which may be one or more computer programs (including program code), adapted to be loaded and executed by the processor. The computer readable storage medium herein may be a high-speed RAM memory or a non-volatile memory (non-volatile memory), such as at least one magnetic disk memory. One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the steps of the methods in the above-described embodiments.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java, an transliteration script language JavaScript and the like.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (10)
1. A method for identifying transformer magnetizing inrush current and CT saturation, the method comprising:
Sampling three-phase currents on each side of the transformer respectively, and determining three-phase differential currents of the transformer based on transformation ratio parameters on each side of the transformer and the three-phase currents obtained by sampling;
the calculation formula for determining the three-phase differential current of the transformer is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the CT transformation ratio of the high-voltage side;
performing differential processing on the three-phase differential current and the three-phase currents on each side of the transformer to obtain a differential processing result;
the differential processing for the three-phase differential current and the three-phase current at each side of the transformer specifically comprises the following steps:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is a differential value of A, B, C phase differential current, i aH(k-1)、ibH(k-1)、icH (k-1) is a previous sample value of a current sample value of high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is a previous sample value of a current sample value of low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is a differential value of a sample value of high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is a differential value of a sample value of low-voltage side three-phase current;
Performing absolute value processing on the differential processing result to obtain an absolute value processing result, and respectively obtaining the ratio of integral values of the absolute value processing result in a fixed time period;
identifying transformer magnetizing inrush current and CT saturation based on the ratio;
Based on the ratio, the transformer excitation inrush current and CT saturation are identified, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (13) - (15), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (16) - (21), the CT saturation of the transformer can be determined, wherein the formulas (13) - (21) are as follows:
Wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, and P set2 is the CT saturation identification constant value.
2. The method of claim 1, wherein the transformer sides comprise: a transformer high voltage side and a low voltage side.
3. The method of claim 1, wherein the transformation ratio parameters comprise at least one of: transformer transformation ratio and CT transformation ratio.
4. The method according to claim 1, wherein said performing an absolute value processing on said differential processing result specifically comprises:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
5. A system for identifying transformer magnetizing inrush current and CT saturation, the system comprising:
The sampling unit is used for sampling three-phase currents at each side of the transformer respectively and determining three-phase differential currents of the transformer based on transformation ratio parameters at each side of the transformer and the three-phase currents obtained by sampling;
the calculation formula for determining the three-phase differential current of the transformer is as follows:
Wherein i cd_a(k)、icd_b(k)、icd_c (k) is the differential current of the transformer A, B and the C phase respectively, i aH(k)、ibH(k)、icH (k) is the high-side three-phase current of the transformer respectively, i aL(k)、ibL(k)、icL (k) is the low-side three-phase current of the transformer respectively, N T is the transformer transformation ratio, For low-voltage side CT transformation ratio,/>Is the CT transformation ratio of the high-voltage side;
The differential processing unit is used for carrying out differential processing on the three-phase differential current and the three-phase currents at each side of the transformer so as to obtain a differential processing result;
the differential processing for the three-phase differential current and the three-phase current at each side of the transformer specifically comprises the following steps:
And carrying out differential processing on the three-phase differential current, wherein the formula is as follows:
and carrying out differential processing on the three-phase current at the high voltage side of the transformer, wherein the formula is as follows:
diaH(k)＝iaH(k)-iaH(k-1) (7)
dibH(k)＝ibH(k)-ibH(k-1) (8)
dicH(k)＝icH(k)-icH(k-1) (9)
and carrying out differential processing on the three-phase current at the low-voltage side of the transformer, wherein the formula is as follows:
diaL(k)＝iaL(k)-iaL(k-1) (10)
dibL(k)＝ibL(k)-ibL(k-1) (11)
dicL(k)＝icL(k)-icL(k-1) (12)
Wherein di cd_a(k)、dicd_b(k)、dicd_c (k) is a differential value of A, B, C phase differential current, i aH(k-1)、ibH(k-1)、icH (k-1) is a previous sample value of a current sample value of high-voltage side three-phase current, i aL(k-1)、ibL(k-1)、icL (k-1) is a previous sample value of a current sample value of low-voltage side three-phase current, di aH(k)、dibH(k)、dicH (k) is a differential value of a sample value of high-voltage side three-phase current, and di aL(k)、dibL(k)、dicL (k) is a differential value of a sample value of low-voltage side three-phase current;
an absolute value processing unit, configured to perform absolute value processing on the differential processing result, so as to obtain an absolute value processing result, and respectively calculate a ratio of integral values of the absolute value processing result in a fixed time period;
the identification unit is used for identifying the excitation inrush current and CT saturation of the transformer based on the ratio;
Based on the ratio, the transformer excitation inrush current and CT saturation are identified, specifically: when the excitation surge current of the transformer is identified, the ratio satisfies any one of the following formulas (13) - (15), the excitation surge current of the transformer can be determined, and when the CT saturation identification is carried out, the ratio satisfies any one of the following formulas (16) - (21), the CT saturation of the transformer can be determined, wherein the formulas (13) - (21) are as follows:
Wherein t 0 is the current sampling time, t 0-5 is the sampling time when the current sampling point is pushed forward for 5ms, t 0-10 is the sampling time when the current sampling point is pushed forward for 10ms, t 0-15 is the sampling time when the current sampling point is pushed forward for 15ms, P set1 is the inrush current identification constant value, and P set2 is the CT saturation identification constant value.
6. The system of claim 5, wherein each side of the transformer comprises: a transformer high voltage side and a low voltage side.
7. The system of claim 5, wherein the transformation ratio parameters comprise at least one of: transformer transformation ratio and CT transformation ratio.
8. The system according to claim 5, wherein the absolute value processing unit performs absolute value processing on the differential processing result, specifically comprising:
The three-phase differential current after difference is subjected to absolute value processing, and the formula is as follows:
and carrying out absolute value processing on the three-phase current at the high voltage side after the difference, wherein the formula is as follows:
and carrying out absolute value processing on the low-voltage side three-phase current after the difference, wherein the formula is as follows:
9. a computer device, comprising:
One or more processors;
a processor for executing one or more programs;
The method of any of claims 1-4 is implemented when the one or more programs are executed by the one or more processors.
10. A computer readable storage medium, characterized in that a computer program is stored thereon, which computer program, when executed, implements the method according to any of claims 1-4.
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