CN113848421A - Voltage sag acquisition method and device considering transformer impedance voltage sag - Google Patents
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Abstract
The invention discloses a voltage sag acquisition method and a voltage sag acquisition device considering voltage sag of transformer impedance, wherein the method comprises the following steps: acquiring three-phase voltage signals and three-phase current signals in voltage sag event recording data of a high-voltage side of a distribution transformer; obtaining the amplitude and the phase of three-phase fundamental wave voltage and the amplitude and the phase of three-phase fundamental wave current in the voltage sag event process; calculating three-sequence components of A-phase fundamental wave voltage and A-phase fundamental wave current; obtaining the equivalent impedance sequence voltage drop of the transformer; acquiring voltage sequence components actually transmitted to the secondary side of the transformer; synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage after voltage sag passes through the transformer; the invention has the advantages that: the voltage sag obtaining method considering the voltage sag of the transformer impedance is high in calculation accuracy, and is beneficial to obtaining the sag characteristic of a target point according to the existing monitoring point data, and data are provided for user access point selection, voltage sag evaluation, positioning and the like.
Description
Technical Field
The invention relates to the technical field of power quality analysis methods, in particular to a voltage sag acquisition method and device considering transformer impedance voltage sag.
Background
Due to the influence of factors such as natural environment, weather and human factors, the problem of voltage sag caused by short-circuit faults and other factors is inevitable, which is in contradiction with the current situation that industrial equipment tends to be integrated and precise, high-tech precision equipment taking digitization and informatization technology as the core is very sensitive to voltage sag, and the contradiction between the two causes the problem of voltage sag to be further concerned by power consumers, power grid companies and more research institutions and students.
The propagation of the voltage sag mainly comprises two links, namely the propagation through a line and the propagation through a transformer, wherein the propagation through the transformer is relatively complex and closely related to the sag types, the transformer connection modes and the like, the voltage sag characteristics caused by different short-circuit fault types under different system neutral point grounding modes are greatly different, and the transmission of the voltage sag is influenced by different transformer winding wiring modes. The electrical engineering technical newspaper, volume 9, 9 th and 22 th of 2007 discloses documents of voltage sag types under different grounding modes of neutral points and transmission (one) among transformers, which mainly illustrate that the grounding modes of the neutral points of a system are different, and the characteristics of phase voltage and line voltage sag of the voltage class caused by short-circuit faults are greatly different, phase voltage and line voltage sag expressions and the characteristics thereof of a neutral point effective grounding system and a non-effective grounding system are analyzed by taking single-phase grounding as an example, the characteristics and types of phase voltage and line voltage sag caused by two-phase grounding, two-phase short-circuit and three-phase short-circuit faults are summarized, the effectiveness of the voltage sag type characteristic expressions is discussed when voltage phase jump is considered, and the transmission rules of the sag types in the transformers of different winding connection modes are further researched to be laid.
The expert and scholars also analyze the transmission rules of different sag types through a primary transformer and a multi-stage transformer in detail, deduce the voltage sag amplitudes of different fault types after being transmitted through the multi-stage transformer with different types, perform linear fitting on the voltage sag amplitudes, analyze the influence of different transformer winding connection groups on the voltage sag transmission rules, but are only limited to theoretical research, and do not verify the combination of theory and practice. The above-mentioned transfer law takes an ideal transformer as a research object, and does not consider the action of the load current, but the literature recognizes that the load current has a certain influence on the voltage sag transfer characteristic, but does not deeply analyze the mechanism of the influence of the load current on the voltage sag transfer characteristic. In addition, the existing power quality monitoring system utilizes a power quality monitoring terminal installed on a power grid side or a user side to monitor the power quality of a monitoring point, however, the installation quantity of power quality monitoring terminals of a power grid in China is limited, and a voltage sag observable area cannot cover the whole power grid, so that the research is based on the voltage sag transfer characteristic, a voltage sag calculation method of a secondary side power grid of a transformer is designed, the target point sag characteristic is obtained according to the existing monitoring point data, data are provided for user access point selection, voltage sag evaluation, positioning and the like, and the basic significance is great.
Disclosure of Invention
The invention aims to solve the technical problem of providing a voltage sag acquisition method considering the voltage sag of the impedance of a transformer, which has high calculation accuracy, is beneficial to obtaining the sag characteristic of a target point according to the data of the existing monitoring point, and provides data for user access point selection, voltage sag evaluation, positioning and the like.
The invention solves the technical problems through the following technical means: a voltage sag acquisition method that takes into account a voltage drop of a transformer impedance, the method comprising:
the method comprises the following steps: acquiring three-phase voltage signals and three-phase current signals in voltage sag event recording data of a high-voltage side of a distribution transformer;
step two: obtaining the amplitude and the phase of three-phase fundamental wave voltage and the amplitude and the phase of three-phase fundamental wave current in the voltage sag event process by utilizing FFT (fast Fourier transform) on the collected three-phase voltage signals and three-phase current signals;
step three: calculating three-sequence components of A-phase fundamental wave voltage and A-phase fundamental wave current according to a symmetric component method;
step four: obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current;
step five: obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer;
step six: and synthesizing the voltage sequence components actually transmitted to the secondary side of the transformer according to a symmetrical component method to obtain the three-phase voltage after the voltage sag passes through the transformer.
The invention considers the transformation ratio (namely coefficient matrix) of the transformer and the voltage sag transmission rule of the transformer under the ideal condition of the equivalent impedance voltage drop correction of the transformer, obtains the three-phase voltage of the voltage sag after passing through the transformer, has higher calculation accuracy, is favorable for obtaining the sag characteristic of a target point according to the existing monitoring point data, and provides data for user access point selection, voltage sag evaluation, positioning and the like.
Further, the third step includes:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α=ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current.
Further, the fourth step includes:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
Further, the fifth step includes:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
still further, the sixth step includes:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix.
The present invention also provides a voltage sag acquisition device considering a voltage sag of a transformer impedance, the device including:
the first acquisition module is used for acquiring three-phase voltage signals and three-phase current signals in the voltage sag event recording data of the high-voltage side of the distribution transformer;
the second acquisition module is used for acquiring the amplitude and the phase of the three-phase fundamental voltage and the amplitude and the phase of the three-phase fundamental current in the voltage sag event process by utilizing FFT (fast Fourier transform) on the acquired three-phase voltage signals and three-phase current signals;
the three-sequence component acquisition module is used for calculating three-sequence components of the A-phase fundamental wave voltage and three-sequence components of the A-phase fundamental wave current according to a symmetric component method;
the equivalent impedance sequence voltage drop obtaining module is used for obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current;
the actual voltage sequence component acquisition module is used for obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer;
and the synthesis module is used for synthesizing the voltage sequence components actually transmitted to the secondary side of the transformer according to a symmetrical component method to obtain the three-phase voltage after the voltage temporarily drops through the transformer.
Further, the three-sequence component obtaining module is further configured to:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α＝ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current.
Further, the equivalent impedance sequence voltage drop obtaining module is further configured to:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
Further, the actual voltage sequence component obtaining module is further configured to:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
still further, the synthesis module is further to:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix.
The invention has the advantages that: the invention considers the transformation ratio (namely coefficient matrix) of the transformer and the voltage sag transmission rule of the transformer under the ideal condition of the equivalent impedance voltage drop correction of the transformer, obtains the three-phase voltage of the voltage sag after passing through the transformer, has higher calculation accuracy, is favorable for obtaining the sag characteristic of a target point according to the existing monitoring point data, and provides data for user access point selection, voltage sag evaluation, positioning and the like.
Drawings
Fig. 1 is a flowchart of a voltage sag acquisition method considering voltage sag of a transformer impedance according to an embodiment of the present invention;
fig. 2 is a schematic diagram of three-sequence components of a phase-a fundamental wave voltage in a voltage sag process of a voltage sag acquisition method considering a voltage drop of a transformer impedance according to an embodiment of the present invention;
fig. 3 is a schematic diagram of three-sequence components of a phase-a fundamental wave current in a voltage sag process of the voltage sag acquisition method considering voltage drop of transformer impedance according to the embodiment of the present invention;
fig. 4 is a schematic diagram of voltage drop of an equivalent impedance sequence of a transformer in a voltage sag process of the voltage sag acquisition method considering voltage drop of impedance of the transformer according to the embodiment of the present invention;
fig. 5 is a schematic diagram of voltage sequence components actually transmitted to the secondary side of the transformer in the voltage sag acquisition method considering the voltage drop of the impedance of the transformer according to the embodiment of the present invention;
fig. 6 is a schematic diagram illustrating an effective value trend of a phase a voltage at high and low voltage sides of a transformer in a voltage sag obtaining method considering voltage drop of impedance of the transformer according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, a voltage sag acquisition method considering a voltage drop of a transformer impedance, the method comprising:
s1: three-phase voltage signals { u ] in voltage sag event recording data of the high-voltage side of the distribution transformer are acquired through the online monitoring deviceA(n)；uB(n)；uC(n) } and three-phase current signals iA(n)；iB(n)；iC(n) }; in this embodiment, the A phase of the high voltage side of the transformer is generated singlyPhase earth fault, type of transformer is class I, wiring mode of transformer is Ynyn, sequence impedance of transformer is [ 35.4935.4928.39 ]]Ω。
S2: for collected three-phase voltage signals { uA(n)；uB(n)；uC(n) } and three-phase current signals iA(n)；iB(n)；iC(n) obtaining the amplitude value (U) of the three-phase fundamental voltage in the voltage sag event process by using Fast Fourier Transform (FFT)A；UB；UCAnd phase PUA；PUB；PUCAnd amplitude of three-phase fundamental current { I }A；IB；ICAnd phase PIA；PIB；PIC}；
S3: calculating three-sequence components of A-phase fundamental wave voltage and A-phase fundamental wave current according to a symmetric component method; the specific process is as follows:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α＝ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current. As shown in fig. 2, the three-sequence components of the a-phase fundamental wave voltage in the voltage sag process refer to positive sequence, negative sequence, and zero sequence, and as shown in fig. 3, the three-sequence components of the a-phase fundamental wave current in the voltage sag process are shown in per unit.
S4: obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current; the specific process is as follows:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
S5: obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer; the specific process is as follows:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
S6: according to a symmetrical component method, voltage sequence components actually transmitted to the secondary side of the transformer are synthesized to obtain three-phase voltage after voltage sag passes through the transformer, and the specific process is as follows:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix. As shown in fig. 6, the trend of the effective value of the phase a voltage on the high-low voltage side of the transformer is shown, and the trend of the effective value of the phase B and phase C voltages is not shown.
Through the technical scheme, the transmission rule of the voltage sag of the transformer under the ideal condition is corrected by considering the transformation ratio (namely the coefficient matrix) of the transformer and the equivalent impedance voltage drop of the transformer, the three-phase voltage of the voltage sag passing through the transformer is obtained, the calculation accuracy is higher, the target point sag characteristic can be obtained according to the existing monitoring point data, and data are provided for user access point selection, voltage sag evaluation, positioning and the like.
Example 2
Based on embodiment 1 of the present invention, embodiment 2 of the present invention further provides a voltage sag acquisition device considering voltage sag of a transformer impedance, where the device includes:
the first acquisition module is used for acquiring three-phase voltage signals and three-phase current signals in the voltage sag event recording data of the high-voltage side of the distribution transformer;
the second acquisition module is used for acquiring the amplitude and the phase of the three-phase fundamental voltage and the amplitude and the phase of the three-phase fundamental current in the voltage sag event process by utilizing FFT (fast Fourier transform) on the acquired three-phase voltage signals and three-phase current signals;
the three-sequence component acquisition module is used for calculating three-sequence components of the A-phase fundamental wave voltage and three-sequence components of the A-phase fundamental wave current according to a symmetric component method;
the equivalent impedance sequence voltage drop obtaining module is used for obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current;
the actual voltage sequence component acquisition module is used for obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer;
and the synthesis module is used for synthesizing the voltage sequence components actually transmitted to the secondary side of the transformer according to a symmetrical component method to obtain the three-phase voltage after the voltage temporarily drops through the transformer.
Specifically, the three-sequence component obtaining module is further configured to:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α＝ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current.
More specifically, the equivalent impedance sequence voltage drop obtaining module is further configured to:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
More specifically, the actual voltage sequence component obtaining module is further configured to:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
more specifically, the synthesis module is further configured to:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for obtaining a voltage sag that takes into account a voltage drop across an impedance of a transformer, the method comprising:
the method comprises the following steps: acquiring three-phase voltage signals and three-phase current signals in voltage sag event recording data of a high-voltage side of a distribution transformer;
step two: obtaining the amplitude and the phase of three-phase fundamental wave voltage and the amplitude and the phase of three-phase fundamental wave current in the voltage sag event process by utilizing FFT (fast Fourier transform) on the collected three-phase voltage signals and three-phase current signals;
step three: calculating three-sequence components of A-phase fundamental wave voltage and A-phase fundamental wave current according to a symmetric component method;
step four: obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current;
step five: obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer;
step six: and synthesizing the voltage sequence components actually transmitted to the secondary side of the transformer according to a symmetrical component method to obtain the three-phase voltage after the voltage sag passes through the transformer.
2. The method for acquiring voltage sag according to claim 1, wherein the third step comprises:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α＝ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current.
3. The method for acquiring voltage sag according to claim 2, wherein the fourth step comprises:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
4. The method for acquiring voltage sag according to claim 3, wherein the step five comprises:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
5. the method for acquiring voltage sag according to claim 4, wherein the sixth step comprises:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix.
6. A voltage sag acquisition apparatus considering a voltage sag of a transformer impedance, the apparatus comprising:
the first acquisition module is used for acquiring three-phase voltage signals and three-phase current signals in the voltage sag event recording data of the high-voltage side of the distribution transformer;
the second acquisition module is used for acquiring the amplitude and the phase of the three-phase fundamental voltage and the amplitude and the phase of the three-phase fundamental current in the voltage sag event process by utilizing FFT (fast Fourier transform) on the acquired three-phase voltage signals and three-phase current signals;
the three-sequence component acquisition module is used for calculating three-sequence components of the A-phase fundamental wave voltage and three-sequence components of the A-phase fundamental wave current according to a symmetric component method;
the equivalent impedance sequence voltage drop obtaining module is used for obtaining the equivalent impedance sequence voltage drop of the transformer according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current;
the actual voltage sequence component acquisition module is used for obtaining a voltage sequence component actually transmitted to the secondary side of the transformer according to the three-sequence component of the A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer;
and the synthesis module is used for synthesizing the voltage sequence components actually transmitted to the secondary side of the transformer according to a symmetrical component method to obtain the three-phase voltage after the voltage temporarily drops through the transformer.
7. The apparatus according to claim 6, wherein the three-sequence component obtaining module is further configured to:
by the formula
Obtaining three-sequence components of A-phase fundamental wave voltage, wherein K represents a coefficient matrix and
α＝ej120°j is a symbol of a complex number,
which represents the magnitude of the fundamental voltage of the three phases,
represents the amplitude of the a-phase fundamental voltage,
represents the amplitude of the B-phase fundamental voltage,
representing the amplitude of the C-phase fundamental wave voltage;
by the formula
Three-sequence components of the A-phase fundamental wave current are acquired, wherein,
representing the magnitude of the three-phase fundamental current,
represents the amplitude of the a-phase fundamental current,
represents the amplitude of the B-phase fundamental current,
representing the magnitude of the C-phase fundamental current.
8. The apparatus according to claim 7, wherein the equivalent impedance sequence voltage drop obtaining module is further configured to:
according to the equivalent impedance of the transformer sequence and the three-sequence component of the A-phase fundamental wave current, a formula is utilized
9. The apparatus according to claim 8, wherein the actual voltage sequence component obtaining module is further configured to:
according to the three-sequence component of A-phase fundamental wave voltage and the equivalent impedance sequence voltage drop of the transformer, using a formula
10. the apparatus of claim 9, wherein the synthesis module is further configured to:
according to a symmetrical component method, using a formula
Synthesizing voltage sequence components actually transmitted to the secondary side of the transformer to obtain three-phase voltage with voltage sag passing through the transformer, wherein H is the transmission rule of the voltage sag of the transformer under ideal conditions, and K is-1Representing the inverse of the coefficient matrix.
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