CN114167117A - Method for identifying differential protection excitation inrush current of double-winding transformer - Google Patents

Method for identifying differential protection excitation inrush current of double-winding transformer Download PDF

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CN114167117A
CN114167117A CN202111459327.1A CN202111459327A CN114167117A CN 114167117 A CN114167117 A CN 114167117A CN 202111459327 A CN202111459327 A CN 202111459327A CN 114167117 A CN114167117 A CN 114167117A
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transformer
current
differential
double
component
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张莹莹
佘志伟
王海生
鲍冰
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Hefei University of Technology
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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
    • 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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  • Protection Of Transformers (AREA)

Abstract

The invention discloses a method for identifying the excitation inrush current of the differential protection of a double-winding transformer, which comprises the steps of firstly collecting the differential current I (t) of the double-winding transformer and decomposing for n times through wavelet transformation; and calculating the areas of the excitation saturated waveform section and the excitation unsaturated waveform section in each period of the difference current component, and the mean value, the variance and the relative variance of the areas to obtain the excitation inrush current criterion R of the differential protection of the double-winding transformer. The invention enriches the characteristic information of differential flow by collecting the differential flow of the double-winding transformer and carrying out n-layer decomposition, calculates the difference between the front and rear waveform sections of each period of the differential flow component, and realizes the identification of the differential protection excitation inrush current of the double-winding transformer.

Description

Method for identifying differential protection excitation inrush current of double-winding transformer
Technical Field
The invention relates to the field of transformer differential protection, in particular to a method for identifying excitation inrush current of differential protection of a double-winding transformer.
Background
Along with the accelerated development of economy in China, the power generation amount in China is the first in the world, the power grid level is improved, the power grid connection is enhanced, large-area power grids are continuously generated, the power system is more huge and complex, once a fault occurs, the whole power grid can be involved, serious consequences are caused, and the safe operation of the power system is particularly important. The transformer, one of the most important devices in the power system, plays an important role in converting voltage, and whether the transformer is operated safely and stably plays a significant role in the whole power system. Therefore, the reliable transformer protection device can improve the power supply reliability and safety of the power system.
The differential protection is the main protection of the transformer protection, and can quickly and accurately identify and remove various faults occurring inside and outside the transformer area. However, when the voltage of the transformer recovers after the external fault is removed or the transformer is switched on in a no-load mode, a large value of magnetizing inrush current is generated, differential current occurs in the differential protection of the transformer, so that the differential protection malfunctions, and if improper malfunction or operation rejection occurs, irreparable damage may be caused. Therefore, it is necessary to improve differential protection or to identify transformer inrush and fault currents quickly and accurately by other methods.
At present, differential protection of a second harmonic braking principle and a discontinuous angle principle is generally adopted, the protection action speed of the second harmonic braking principle is slow, measures must be taken to recover the discontinuous angle on the discontinuous angle principle, and the protection complexity is increased. The excitation inrush current is considered to contain a large number of non-periodic components, n-layer decomposition is carried out on the collected differential current signals through wavelet transformation, state information of different frequency components is obtained, and the excitation inrush current is comprehensively identified through calculating the area, the relative variance and other various characteristic quantities of the differential current signals. Therefore, the method can identify the magnetizing inrush current signal more reliably, quickly and accurately.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a method for identifying the differential protection magnetizing inrush current of a double-winding transformer, which decomposes a differential current signal for n times through wavelet transformation and combines a differential current component Ii(t) calculating the differential protection excitation inrush current criterion of the double-winding transformer by using the mean, variance and relative variance of the area of the waveform sections of the first half cycle and the second half cycle of each period, wherein the specific method comprises the following steps:
1. a method for identifying the excitation inrush current of the differential protection of a double-winding transformer comprises the following steps:
the method comprises the following steps: collecting a transformer differential current, comprising:
(1) the high-voltage side current transformer end of the transformer collects the high-voltage side current IH(t), collecting N data points and M periods;
(2) low-voltage side current I acquired by low-voltage side current transformer end of transformerL(t), collecting N data points and M periods;
(3) calculating the differential current of the double-winding transformer I (t)
I(t)＝IH(t)-IL(t)
Step two: the differential current characteristic extraction of the double-winding transformer comprises the following steps:
(1) the difference current signal of the transformer is transformed by wavelet to obtain W (i, j)
Figure BDA0003389260830000021
Figure BDA0003389260830000022
In the formula 2ij is a displacement factor, 2iIs a scale factor,. phi.0Is the center frequency
(2) Transformer difference current wavelet transformation reconstruction signal pi(t)
Figure BDA0003389260830000023
In the formula of alphakIs an approximation coefficient, betalkIs a coefficient of detail that is,
Figure BDA0003389260830000024
is a smoothing function, pi(t) is the reconstructed signal of the i-th component wavelet transform of the transformer difference current
(3) Transformer deviceReconstructing approximate signal as difference current component I by difference current wavelet transformi(t)(i＝1,2……n)
Figure BDA0003389260830000025
In the formula Ii(t) is the i-th component of the transformer differential current I (t)
(4) The differential current of the transformer is decomposed for n times through wavelet transformation and reconstruction, and has a differential current component Ii(t) (i ═ 1,2 … … n) up to a threshold ε < 0.8
Figure BDA0003389260830000026
In the formula Ii(t) represents the nth component of the transformer differential current I (t), "Min" is the minimum value, "Max" is the maximum value
Step three: the double-winding transformer differential protection criterion comprises the following steps:
(1) for the difference current component Ii(t) calculated area of the first half cycle and second half cycle waveform segments of each cycle
Figure BDA0003389260830000027
And
Figure BDA0003389260830000028
Figure BDA0003389260830000029
Figure BDA0003389260830000031
in the formula
Figure BDA0003389260830000032
And
Figure BDA0003389260830000033
is the first half-cycle area and the second half-cycle area of the jth component of the differential current, m is the total number of data points collected in one half-cycle
(2) Calculating a difference current component Ii(t) mean value E of the areas of the first half cycle and second half cycle segments of each cyclei(Q) and Ei(H)
Figure BDA0003389260830000034
Figure BDA0003389260830000035
(3) Calculating a difference current component Ii(t) covariance Cov of the area of the first and second half-cycle segments of each cyclei(Q,H)
Figure BDA0003389260830000036
(4) Calculating a difference current component Ii(t) the relative variance e of the area of the waveform segments of the first half cycle and the second half cycle of each cyclei(Q) and ei(H)
Figure BDA0003389260830000037
Figure BDA0003389260830000038
(5) Calculating excitation inrush current criterion R of differential protection of double-winding transformer
Figure BDA0003389260830000039
And if the differential protection criterion R of the double-winding transformer is less than or equal to 0.7, the excitation inrush current is considered.
Compared with the prior art, the invention has the following technical effects:
the invention provides a method for identifying the differential protection excitation inrush current of a duplex winding transformer, which decomposes a differential current signal for n times by wavelet transformation and combines a differential current component IiAnd (t) calculating the mean value, the variance and the relative variance of the areas of the waveform sections of the first half cycle and the second half cycle of each period to obtain the differential protection excitation inrush current criterion of the double-winding transformer. The method can more reliably, quickly and accurately identify the magnetizing inrush current of the transformer.
Drawings
FIG. 1 is a block flow diagram of the method of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The invention is described in further detail below with reference to the following figures and specific examples:
example 1
FIG. 1 is a flow chart of a method for identifying the differential protection magnetizing inrush current of a duplex winding transformer, which is characterized in that the acquired differential current signals are decomposed n times through wavelet transformation, and differential current components I are respectively calculatediEach week of (t)The method comprises the following steps of calculating the mean value, the variance and the relative variance of the area of waveform sections of the first half cycle and the second half cycle in the period by combining, and obtaining the differential protection excitation inrush current criterion of the double-winding transformer:
1. a method for identifying the excitation inrush current of the differential protection of a double-winding transformer comprises the following steps:
the method comprises the following steps: collecting a transformer differential current, comprising:
(1) the high-voltage side current transformer end of the transformer collects the high-voltage side current IH(t), collecting N data points and M periods;
(2) low-voltage side current I acquired by low-voltage side current transformer end of transformerL(t), collecting N data points and M periods;
(3) calculating the differential current of the double-winding transformer I (t)
I(t)＝IH(t)-IL(t)
Step two: the differential current characteristic extraction of the double-winding transformer comprises the following steps:
(1) transformer differential current wavelet transform W (i, j)
Figure BDA0003389260830000041
Figure BDA0003389260830000042
In the formula 2ij is a displacement factor, 2iIs a scale factor,. phi.0Is the center frequency
(2) Transformer difference current wavelet transformation reconstruction signal pi(t)
Figure BDA0003389260830000043
In the formula of alphakIs an approximation coefficient, betalkIs a coefficient of detail that is,
Figure BDA0003389260830000051
is a smoothing function, pi(t) is the reconstructed signal of the i-th component wavelet transform of the transformer difference current
(3) Transformer difference current wavelet transformation reconstruction approximate signal as difference current component Ii(t)(i＝1,2……n)
Figure BDA0003389260830000052
In the formula Ii(t) is the i-th component of the transformer differential current I (t)
(4) The differential current of the transformer is decomposed for n times through wavelet transformation and reconstruction, and has a differential current component Ii(t) (i ═ 1,2 … … n) up to a threshold ε < 0.8
Figure BDA0003389260830000053
In the formula Ii(t) represents the nth component of the transformer differential current I (t), "Min" is the minimum value, "Max" is the maximum value
Step three: the double-winding transformer differential protection criterion comprises the following steps:
(1) for the difference current component Ii(t) calculated area of the first half cycle and second half cycle waveform segments of each cycle
Figure BDA0003389260830000054
And
Figure BDA0003389260830000055
Figure BDA0003389260830000056
Figure BDA0003389260830000057
in the formula
Figure BDA0003389260830000058
And
Figure BDA0003389260830000059
is the first half-cycle area and the second half-cycle area of the jth component of the differential current, m is the total number of data points collected in one half-cycle
(2) Calculating a difference current component Ii(t) mean value E of the areas of the first half cycle and second half cycle segments of each cyclei(Q) and Ei(H)
Figure BDA00033892608300000510
Figure BDA00033892608300000511
(3) Calculating a difference current component Ii(t) covariance Cov of the area of the first and second half-cycle segments of each cyclei(Q,H)
Figure BDA00033892608300000512
(4) Calculating a difference current component Ii(t) the relative variance e of the area of the waveform segments of the first half cycle and the second half cycle of each cyclei(Q) and ei(H)
Figure BDA0003389260830000061
Figure BDA0003389260830000062
(5) Calculating excitation inrush current criterion R of differential protection of double-winding transformer
Figure BDA0003389260830000063
And if the differential protection criterion R of the double-winding transformer is less than or equal to 0.7, the excitation inrush current is considered.
Any numerical value recited herein includes all values from the lower value to the upper value that are incremented by one unit, provided that there is a separation of at least two units between any lower value and any higher value. For example, if it is stated that the number of a component or a value of a process variable (e.g., temperature, pressure, time, etc.) is from 1 to 90, preferably from 20 to 80, and more preferably from 30 to 70, it is intended that equivalents such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also expressly enumerated in this specification. For values less than 1, one unit is suitably considered to be 0.0001, 0.001, 0.01, 0.1. These are only examples of what is intended to be explicitly recited, and all possible combinations of numerical values between the lowest value and the highest value that are explicitly recited in the specification in a similar manner are to be considered.
Unless otherwise indicated, all ranges include the endpoints and all numbers between the endpoints. The use of "about" or "approximately" with a range applies to both endpoints of the range. Thus, "about 20 to about 30" is intended to cover "about 20 to about 30", including at least the endpoints specified.
All articles and references disclosed, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of …" describing a combination shall include the identified element, ingredient, component or step as well as other elements, ingredients, components or steps that do not materially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, components, or steps herein also contemplates embodiments that consist essentially of such elements, components, or steps. By using the term "may" herein, it is intended to indicate that any of the described attributes that "may" include are optional.
A plurality of elements, components, parts or steps can be provided by a single integrated element, component, part or step. Alternatively, a single integrated element, component, part or step may be divided into separate plural elements, components, parts or steps. The disclosure of "a" or "an" to describe an element, ingredient, component or step is not intended to foreclose other elements, ingredients, components or steps.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Many embodiments and many applications other than the examples provided will be apparent to those of skill in the art upon reading the above description. The scope of the present teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes. The omission in the foregoing claims of any aspect of subject matter that is disclosed herein is not intended to forego such subject matter, nor should the inventors be construed as having contemplated such subject matter as being part of the disclosed subject matter.

Claims (1)

1. A method for identifying the excitation inrush current of the differential protection of a duplex winding transformer is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: collecting a transformer differential current, comprising:
(1) the high-voltage side current transformer end of the transformer collects the high-voltage side current IH(t), collecting N data points and M periods;
(2) low-voltage side current I acquired by low-voltage side current transformer end of transformerL(t), collecting N data points and M periods;
(3) calculating the differential current of the double-winding transformer I (t)
I(t)＝IH(t)-IL(t)
Step two: the differential current characteristic extraction of the double-winding transformer comprises the following steps:
(1) wavelet transform of transformer differential current to obtain W (i, j)
Figure FDA0003389260820000011
In the formula 2ij is a displacement factor, 2iIs a scale factor,. phi.
(2) Transformer difference current wavelet transformation reconstruction calculation difference current component Ii(t)
Figure FDA0003389260820000012
In the formula of alphakAre the coefficients of the approximation to be used,
Figure FDA0003389260820000013
is a smoothing function, Ii(t) is the i-th component of the transformer differential current I (t)
(3) The differential current of the transformer is decomposed for n times through wavelet transformation and reconstruction, and has a differential current component Ii(t) (i ═ 1,2 … … n) until a threshold epsilon < 0.8;
Figure FDA0003389260820000014
in the formula Ii(t) represents the nth component of the transformer differential current I (t), "Min" is the minimum value, "Max" is the maximum value step three: the double-winding transformer differential protection criterion comprises the following steps:
(1) for the difference current component Ii(t) calculated area of the first half cycle and second half cycle waveform segments of each cycle
Figure FDA0003389260820000015
And
Figure FDA0003389260820000016
Figure FDA0003389260820000017
Figure FDA0003389260820000018
in the formula
Figure FDA0003389260820000019
And
Figure FDA00033892608200000110
the area of the first half cycle and the area of the second half cycle of the jth component of the differential current are shown, and m is the total number of data points collected in the half cycle;
(2) calculating a difference current component Ii(t) mean value E of the areas of the first half cycle and second half cycle segments of each cyclei(Q)、Ei(H) Sum covariance Covi(Q,H)；
Figure FDA0003389260820000021
Figure FDA0003389260820000022
Figure FDA0003389260820000023
(3) Calculating a difference current component Ii(t) the relative variance e of the area of the waveform segments of the first half cycle and the second half cycle of each cyclei(Q) and ei(H)；
Figure FDA0003389260820000024
Figure FDA0003389260820000025
(4) Calculating a differential protection excitation inrush current criterion R of the double-winding transformer;
Figure FDA0003389260820000026
and if the differential protection criterion R of the double-winding transformer is less than or equal to 0.7, the excitation inrush current is considered.
CN202111459327.1A 2021-12-02 2021-12-02 Method for identifying differential protection excitation inrush current of double-winding transformer Pending CN114167117A (en)

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