CN111722002A - Novel voltage sag severity assessment method - Google Patents

Novel voltage sag severity assessment method Download PDF

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CN111722002A
CN111722002A CN202010602868.4A CN202010602868A CN111722002A CN 111722002 A CN111722002 A CN 111722002A CN 202010602868 A CN202010602868 A CN 202010602868A CN 111722002 A CN111722002 A CN 111722002A
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sag
voltage sag
voltage
severity
duration
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CN111722002B (en
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徐琳
刘畅
杨华
魏巍
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Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
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Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
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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
    • G01R19/16576—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 DC or AC voltage with one threshold
    • 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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Abstract

The invention discloses a novel voltage sag severity assessment method, which comprises the following steps: s1: extracting voltage sag characteristic quantities according to the sample data of the single voltage sag characteristic quantities; s2: constructing a voltage sag severity index SSI model for the voltage sag event; s3: and according to the constructed index model, evaluating the severity of the voltage sag to be simulated or to be detected, and guiding industrial use, thereby avoiding the fault risk of the power equipment under the voltage sag. Compared with the existing single event characteristic, the method provided by the invention better reflects the uncertainty of the response of the equipment to the voltage sag; the method fully explains the change of equipment sensitivity by changing parameter setting in an SSI formula, and determines an SSI contour line by setting parameters in the SSI formula; the voltage sag severity index model constructed in the method considers the sensitivity degree of equipment to voltage sag events, and the index can fully and closely relate voltage sag to industrial processes.

Description

Novel voltage sag severity assessment method
Technical Field
The invention relates to the technical field of voltage sag, in particular to a novel voltage sag severity evaluation method.
Background
In the process of recognizing voltage sag in China, the national standard GB/T30137-2013 'Power quality voltage sag and short-term interruption', issued in 12 months in 2013, defines voltage sag (voltagesag) as follows: the square root mean value of the power frequency voltage at a certain point in the power system is suddenly reduced to 0.1p.u. -0.9 p.u., and the power frequency voltage is recovered to be normal after the power frequency voltage is temporarily continued for 10 ms-1 min. Voltage sags cause significant economic losses to many utilities and industries due to frequent interruptions of industrial processes and failures of electronic equipment. Voltage sag is one of the most critical issues in power quality, and sag severity assessment has been a research hotspot in the field of power quality. As a key step in voltage sag compensation measures, it is necessary to accurately assess the severity of the voltage sag.
The severity of the voltage sag is closely related to the response of the device to the voltage sag. Therefore, in order to accurately assess the effects of voltage sags, the sensitivity of equipment and industrial processes to voltage sags must be understood. The sensitivity curve of a specific device is intensively studied, and a plurality of international standards are established, so that guidance on the voltage sag ride-through capability is provided for system design, such as the voltage tolerance curve recommended in IEEE 1346. From the perspective of users and equipment manufacturers, subsequent curves to the CBEMA curve, the information technology industry association (ITIC) curve, were proposed and recommended after extensive research on computer power supplies. The semiconductor industry, through design requirements for minimum voltage sag ride-through capability of its devices, has developed SEMI F47 curves with staircase-like curves.
The prior art evaluates the severity of a voltage sag for a single event signature by calculating the energy change during the voltage sag; the loss energy is used to assess the severity of the voltage sag by calculating the energy that is not delivered to the load by the system during the voltage sag. The severity of the voltage sag is defined in terms of the sustain voltage and the duration of the voltage sag by proposing two indicators representing the amplitude severity index (MSI) and the Duration Severity Index (DSI), respectively, as input parameters for different evaluation methods.
Although many prior art methods provide indicators for evaluating the severity of voltage sag events, most voltage sag severity evaluation indicators do not consider the sensitivity of the device to voltage sag events, and evaluate the severity of voltage sag for a single event signature, and the incorporation of voltage tolerance curves into the sag severity evaluation still requires further investigation.
Disclosure of Invention
The invention aims to solve the technical problems that in a method for evaluating the severity of a voltage sag event in the prior art, most indexes do not consider the sensitivity of equipment to the voltage sag event, the severity of the voltage sag is evaluated according to a single event characteristic, the indexes cannot fully and closely relate the voltage sag to an industrial process, and the like. The invention provides a novel voltage sag severity evaluation method for solving the problems, and the voltage tolerance curve is brought into sag severity evaluation for further research; on the basis of a generally accepted and widely applied voltage tolerance curve of equipment, the invention provides a new voltage Sag Severity Index (SSI), which is derived according to the sensitivity of the equipment to voltage sag, the new index can convert sag parameters (sag size and duration) into the severity of the voltage sag, and the SSI is used for evaluating the severity of the voltage sag event, and the evaluation accuracy is high. Compared with the existing single event characteristics, the method is more specific to the uncertainty of the response of the device to the voltage sag; the method of the invention fully explains the change of the equipment sensitivity by changing parameter setting in an SSI formula; the SSI changes continuously in the connection area with different sag severity degrees, and the sensitivity change trend of the equipment considering the voltage tolerance curve is truly reflected.
The invention is realized by the following technical scheme:
a novel voltage sag severity assessment method comprises the following steps:
s1: extracting voltage sag characteristic quantities according to the sample data of the single voltage sag characteristic quantities; the voltage sag characteristic quantity comprises a sag amplitude and a sag duration;
s2: according to the voltage sag characteristic quantity extracted in the step S1, constructing a voltage sag severity index model for the voltage sag event: when the corresponding numerical value of the sag is positioned in the insensitive area, the severity of the voltage sag is 0; when the corresponding value of the sag is in the sensitive area, the formula adopted by the voltage sag severity index model is as follows:
Figure BDA0002559686050000021
in the formula (I), the compound is shown in the specification,
Figure BDA0002559686050000022
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at the Bus (Bus) i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b represents the increase rate of SSI with increasing sag duration; the coefficients a and b make the formed contour line graph more continuous;
s3: and (4) evaluating the voltage sag severity to be simulated or detected according to the voltage sag severity index model established in the step (S2) to guide industrial use, and further avoiding the fault risk of the power equipment under the voltage sag. And combining a voltage tolerance curve of a certain device, if the severity index of the voltage sag of the device is 0, the device is indicated to work in the environment without fault risk. If the severity index of voltage sag of a certain device is not 0, the obtained index value deviates from the standard voltage tolerance curve (as shown in fig. 7) more, which indicates that the device is operated in the environment and is exposed to a great risk of interruption, thereby affecting production and damaging power equipment. At the moment, a clear theoretical basis is provided for the site selection construction of the user.
The working principle is as follows:
based on the prior art that the severity of the voltage sag is evaluated for a single event characteristic, the energy change during the voltage sag is calculated; the loss energy is used to assess the severity of the voltage sag by calculating the energy that is not delivered to the load by the system during the voltage sag. Although many prior art methods provide indicators for evaluating the severity of voltage sag events, most voltage sag severity evaluation indicators do not consider the sensitivity of the device to voltage sag events, and evaluate the severity of voltage sag for a single event signature, and the incorporation of voltage tolerance curves into the sag severity evaluation still requires further investigation.
The invention provides a new voltage Sag Severity Index (SSI) which is derived according to the sensitivity of equipment to voltage sag on the basis of a generally accepted and widely applied equipment voltage tolerance curve, the new index can convert sag parameters (sag amplitude and sag duration) into the voltage sag severity, and the SSI is used for evaluating the severity of the voltage sag event, and the evaluation accuracy is high. According to the method, the voltage sag amplitude and the sag duration are combined to comprehensively represent the fault risk of equipment under the voltage sag, and voltage sag characteristic quantities including the sag amplitude and the sag duration are extracted according to sample data of single voltage sag characteristic quantities; secondly, constructing a voltage sag severity index model for the voltage sag event: when the corresponding numerical value of the sag is positioned in the insensitive area, the severity of the voltage sag is 0; when the corresponding numerical value of the sag is positioned in the sensitive area, the voltage sag severity index model is calculated and analyzed by adopting the index formula provided by the invention; and finally, evaluating the sag severity of the voltage to be detected according to the constructed voltage sag severity index model, and guiding industrial use so as to avoid the fault risk of the power equipment under the voltage sag.
Compared with the existing single event characteristic, the novel voltage sag severity evaluation method provided by the invention better reflects the uncertainty of the response of the equipment to the voltage sag; the method fully explains the change of equipment sensitivity by changing parameter setting in an SSI formula, and determines an SSI contour line by setting parameters in the SSI formula; the SSI changes continuously in the connection area with different sag severity degrees, and the sensitivity change trend of the equipment considering the voltage tolerance curve is truly reflected.
The voltage sag severity index model constructed in the method considers the sensitivity degree of equipment to voltage sag events, and the index can fully and closely relate voltage sag to industrial processes.
Further, the voltage sag tolerance curve employed in the voltage sag severity index model in step S2 is a standard voltage tolerance curve SEMI F47.
Further, the voltage sag event is defined as a triplet (f)Bij，vBij，tBij) Where subscripts j and i denote the jth dip occurring at bus i; f. ofBijIndicating the frequency of sag, vBijRepresenting the sag amplitude, tBijRepresenting the sag duration, the voltage sag amplitude is kept below a threshold, assuming that the voltage sag is rectangular and the sag amplitude is constant; the voltage sag amplitude and the duration are obtained by conventional short circuit simulation;
in the case of a non-rectangular voltage sag, the root mean square sag envelope is decomposed into a series of amplitude and duration pairs sampled from the envelope using a plurality of amplitude duration functions; each pair was evaluated separately and the pair with the highest sag severity was used as the final sag severity.
Further, given that the existing voltage sag event severity indicator does not adequately reflect the sensitivity trend of the device to voltage sag responses, it is difficult to achieve a gradual transition from one severity level to another. Therefore, in step S2, in order to embody the flexibility and ability of the voltage sag severity index, the voltage sag severity index is made to describe a gradual transition from one severity level to another; the formula adopted by the voltage sag severity index model at this time is as follows:
Figure BDA0002559686050000041
in the formula (I), the compound is shown in the specification,
Figure BDA0002559686050000042
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at the Bus (Bus) i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b denotes the increase in the sag duration to adjust the rate of increase of SSI.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the invention provides a new voltage Sag Severity Index (SSI) which is deduced according to the sensitivity of equipment to voltage sag on the basis of a generally accepted and widely applied equipment voltage tolerance curve.
2. Compared with the existing single event characteristics, the method has the advantages that the uncertainty of the response of the equipment to the voltage sag is reflected; the method fully explains the change of equipment sensitivity by changing parameter setting in an SSI formula, and determines an SSI contour line by setting parameters in the SSI formula; the SSI changes continuously in the connection area with different sag severity degrees, and the sensitivity change trend of the equipment considering the voltage tolerance curve is truly reflected.
3. The voltage sag severity index model constructed in the method considers the sensitivity degree of equipment to voltage sag events, and the index can fully and closely relate voltage sag to industrial processes.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a flowchart of a novel voltage sag severity assessment method according to the present invention.
FIG. 2 is a diagram of voltage sag sensitive areas in an embodiment of the present invention.
Fig. 3 is an SSI profile using equation (1) for the method of the present invention.
Fig. 4 is an SSI profile using equation (2) for the method of the present invention.
Fig. 5 shows the SSI contour of formula (1) with different parameters (a is 3 and b is 1/2).
Fig. 6 shows SSI contours for different parameters (a is 3 and b is 1/4) set by formula (1) in the method of the present invention.
Fig. 7 shows the SSI contour line of formula (2) in the case of a-2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in fig. 1, the invention provides a novel voltage sag severity assessment method, which comprises the following steps:
s1: extracting voltage sag characteristic quantities according to the sample data of the single voltage sag characteristic quantities; the voltage sag characteristic quantity comprises a sag amplitude and a sag duration;
s2: according to the voltage sag characteristic quantity extracted in the step S1, constructing a voltage sag severity index model for the voltage sag event: when the corresponding numerical value of the sag is positioned in the insensitive area, the severity of the voltage sag is 0; when the corresponding value of the sag is in the sensitive area, the formula adopted by the voltage sag severity index model is as follows:
Figure BDA0002559686050000061
in the formula (I), the compound is shown in the specification,
Figure BDA0002559686050000062
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at the Bus (Bus) i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b represents the increase rate of SSI with increasing sag duration; the coefficients a and b make the formed contour line graph more continuous;
s3: and (4) evaluating the voltage sag severity to be simulated or detected according to the voltage sag severity index model established in the step (S2) to guide industrial use, and further avoiding the fault risk of the power equipment under the voltage sag.
And combining a voltage tolerance curve of a certain device, if the severity index of the voltage sag of the device is 0, the device is indicated to work in the environment without fault risk. If the severity index of voltage sag of a certain device is not 0, the obtained index value deviates from the standard voltage tolerance curve (as shown in fig. 7) more, which indicates that the device is operated in the environment and is exposed to a great risk of interruption, thereby affecting production and damaging power equipment. At the moment, a clear theoretical basis is provided for the site selection construction of the user.
In addition, when the formula calculated by the voltage sag severity index model constructed in step S2 does not conform to the design concept of the present invention due to the selection of a few specific points, this type of sample points may be eliminated, and the sample points may be reselected for calculation and the model may be constructed.
The specific implementation is as follows:
as shown in fig. 2, the standard voltage withstand curve SEMI F47 used in fig. 2. Since the arc extinguishing time of the protective relay is less than 1s, and most of the dips are caused by faults and are extinguished by the protective relay, the invention is only considered in [0,1 ]]A dip duration within the range. In fig. 2, the area covered by the voltage withstand curve (i.e., the gray area) represents the sag sensitive area. T isxRepresenting the xth duration range. In fig. 2, there are three ranges of duration along the t-axis from 0.02 to 1 s.
The SSI proposed by the present invention represents the severity of the voltage sag (expressed in sag amplitude and sag duration) in terms of device sensitivity. Voltage sag events are defined as triplets (f)Bij，vBij，tBij) Where subscripts j and i denote the jth dip occurring at bus i; f. ofBijIndicating the frequency of sag, vBijRepresenting the sag amplitude, tBijRepresenting the sag duration, the voltage sag amplitude is kept below a threshold, assuming that the voltage sag is rectangular and the sag amplitude is constant; the voltage sag amplitude and duration are derived from conventional short circuit simulations. In the case of a non-rectangular voltage sag, the root mean square sag envelope is decomposed into a series of amplitude and duration pairs sampled from the envelope using a plurality of amplitude duration functions; each pair was evaluated separately and the pair with the highest sag severity was used as the final sag severity. The severity of the voltage sag is a sag simulation study, and a representative pair of sag characteristic quantities (namely a sag amplitude and a sag duration) are used for representing the voltage sag in the invention.
For a given sag amplitude and sag duration, the voltage sag severity is 0 if the corresponding value is located in the insensitive region, i.e. the region above the voltage tolerance curve; when the corresponding numerical value of the sag is positioned in the sensitive area, the voltage sag severity index model is calculated and analyzed by adopting a formula (1).
In the formula (1), a is 3, b is 1/2; for example, a voltage sag of 0.6p.u. and a duration of 0.6s would be in the third duration range (T) of the duration-amplitude space in FIG. 23) And (4) the following steps. In this case, y is 3, and x ranges from 1 to 2. Vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area. T ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries). The coefficient a is used to control the difference between SSI values estimated from dips in different time duration ranges. The larger the coefficient a, the larger the SSI difference estimated from different duration ranges. The first term of equation (1) adjusts for differences between SSI values estimated from different duration ranges and ensures that for a given amount of sag, the SSI gradually increases as the sag duration increases. In the duration range TyThe coefficient b increases with the sag duration to adjust the rate of increase of SSI. The smaller the coefficient b for a given y (b)<1)，by-1The smaller (b)y-1<1). When ((t)Bij-Tmin(Ty))/(Tmax(Ty)-Tmin(Ty))<1 and by-1<1 time, by-1The smaller, i.e., ((t)Bij-Tmin(Ty))/(Tmax(Ty)-Tmin(Ty) The smaller the index), the greater the rate of increase in SSI at the beginning of the duration range and the smaller the rate of increase in SSI at the end of the duration range. Furthermore, even at fixed parameter b, since b is usedy-1The rate of SSI increase may vary over different durations. When y (y)>1) When increasing, by-1(by-1<1) And decreases. With by-1Is reduced, duration T3Initial SSI increase rate greater than T1And T2Duration T3SSI increase rate at the end of less than T1And T2。
The color profile of SSI evaluated using equation (1) is shown in fig. 3, where the more affected regions are marked with a dark color and the regions that are not disturbed by voltage sags are marked with a light color. In this figure, the standard voltage withstand curve can still be seen blurry. The representation illustrates the variation associated with the sensitivity of the device to voltage sags defined by a single tolerance curve.
Fig. 5 shows the SSI contour of formula (1) with different parameters (a is 3 and b is 1/2). Fig. 6 shows SSI contours for different parameters (a is 3 and b is 1/4) set by formula (1) in the method of the present invention.
The working principle is as follows: the invention provides a new voltage Sag Severity Index (SSI) which is derived according to the sensitivity of equipment to voltage sag on the basis of a generally accepted and widely applied equipment voltage tolerance curve, the new index can convert sag parameters (sag amplitude and sag duration) into the voltage sag severity, and the SSI is used for evaluating the severity of the voltage sag event, and the evaluation accuracy is high. According to the method, the voltage sag amplitude and the sag duration are combined to comprehensively represent the fault risk of equipment under the voltage sag, and voltage sag characteristic quantities including the sag amplitude and the sag duration are extracted according to sample data of single voltage sag characteristic quantities; secondly, constructing a voltage sag severity index model for the voltage sag event: when the corresponding numerical value of the sag is positioned in the insensitive area, the severity of the voltage sag is 0; when the corresponding numerical value of the sag is positioned in the sensitive area, the voltage sag severity index model is calculated and analyzed by adopting the index formula provided by the invention; and finally, evaluating the sag severity of the voltage to be detected according to the constructed voltage sag severity index model, and guiding industrial use so as to avoid the fault risk of the power equipment under the voltage sag.
Compared with the existing single event characteristic, the novel voltage sag severity evaluation method provided by the invention better reflects the uncertainty of the response of the equipment to the voltage sag; the method fully explains the change of equipment sensitivity by changing parameter setting in an SSI formula, and determines an SSI contour line by setting parameters in the SSI formula; the SSI changes continuously in the connection area with different sag severity degrees, and the sensitivity change trend of the equipment considering the voltage tolerance curve is truly reflected.
The voltage sag severity index model constructed in the method considers the sensitivity degree of equipment to voltage sag events, and the index can fully and closely relate voltage sag to industrial processes.
Example 2
As shown in fig. 1 to 7, the present embodiment is different from embodiment 1 in that it is difficult to realize a gradual transition from one severity to another in consideration that the existing voltage sag event severity index does not sufficiently reflect the sensitivity trend of the device to the voltage sag response. In fact, the boundary between device trip and ride-through cannot be defined with an open line due to the many factors that affect the sensitivity of the device to voltage sag. The SSI accurately describes the gradual transition from one severity level to another. In order to embody the flexibility and capability of SSI, in step S2, the formula used by the voltage sag severity index model is as follows:
Figure BDA0002559686050000081
in the formula (I), the compound is shown in the specification,
Figure BDA0002559686050000082
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at the Bus (Bus) i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b denotes the increase in the sag duration to adjust the rate of increase of SSI.
The profile from equation (2) is shown in fig. 4, where the areas that are more affected are marked with a dark color and the areas that are not disturbed by the voltage sag are marked with a light color. As can be seen from fig. 4 in comparison with fig. 3, in this case, the steep slope of the junction region between two adjacent duration ranges becomes soft, and the rate of increase in SSI is relatively stable. In fig. 4, the standard voltage withstand curve can also be seen blurry. In consideration of the flexibility of SSI, the coefficients may be adjusted according to specific situations in practical applications.
And analyzing a voltage Sag Severity Index (SSI) by combining the sag condition of a certain industrial user. For one embodiment, the voltage sag amplitude and the sag duration are obtained, and the evaluation results are shown in fig. 5, fig. 6, and fig. 7. It can be seen that the contour line marked with zero SSI is identical to the standard voltage tolerance curve. The severity indicator for any point in the sag region above the standard voltage tolerance curve is zero. For dips in the sensitive region (below the voltage tolerance curve), the value of the index evaluated varies according to the size of the dip amplitude and the duration of the dip. The regions of zero SSI and non-zero SSI are divided by the contour lines marked with zero SSI in fig. 5 and 6. In other words, the contour lines marked with zeros help to distinguish between the dip sensitive and insensitive regions defined by the voltage tolerance curve. The contour lines follow the sensitivity curve shape and the severity distribution of the device. In fig. 5, 6, SSI represents an explicit division between different duration ranges, which means to differentiate the severity between different duration ranges. To illustrate the effect of the coefficients on the SSI, fig. 6 gives an outline of the SSI obtained with a smaller setting parameter b. Compared with fig. 5 and 6, the division of the joint region of two adjacent duration ranges is less obvious, and the sensitivity trend of the device to the voltage sag response can be more fully reflected, so that the gradual transition from one sag severity degree to another sag severity degree is realized.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. A novel voltage sag severity assessment method is characterized by comprising the following steps:
s1: extracting voltage sag characteristic quantities according to the sample data of the single voltage sag characteristic quantities; the voltage sag characteristic quantity comprises a sag amplitude and a sag duration;
s2: according to the voltage sag characteristic quantity extracted in the step S1, constructing a voltage sag severity index model for the voltage sag event: when the corresponding numerical value of the sag is positioned in the insensitive area, the severity of the voltage sag is 0; when the corresponding value of the sag is in the sensitive area, the formula adopted by the voltage sag severity index model is as follows:
Figure FDA0002559686040000011
in the formula (I), the compound is shown in the specification,
Figure FDA0002559686040000012
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at bus i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b represents the increase rate of SSI with increasing sag duration;
s3: and (4) evaluating the voltage sag severity to be simulated or detected according to the voltage sag severity index model established in the step (S2) to guide industrial use, and further avoiding the fault risk of the power equipment under the voltage sag.
2. The method according to claim 1, wherein the voltage sag severity index model in step S2 uses a voltage sag tolerance curve that is a standard voltage tolerance curve SEMI F47.
3. A novel voltage sag severity assessment method according to claim 1 or 2, characterized in that said voltage sag events are defined as triplets (f)Bij，vBij，tBij) Where subscripts j and i denote the jth dip occurring at bus i; f. ofBijIndicating the frequency of sag, vBijRepresenting the sag amplitude, tBijRepresenting the sag duration, the voltage sag amplitude is kept below a threshold, assuming that the voltage sag is rectangular and the sag amplitude is constant; the voltage sag amplitude and the duration are obtained by conventional short circuit simulation;
in the case of a non-rectangular voltage sag, the root mean square sag envelope is decomposed into a series of amplitude and duration pairs sampled from the envelope using a plurality of amplitude duration functions; each pair was evaluated separately and the pair with the highest sag severity was used as the final sag severity.
4. The method for evaluating the severity of voltage sag as claimed in claim 1, wherein in step S2, in order to show the flexibility and ability of the severity indicator of voltage sag, the severity indicator of voltage sag describes a gradual transition from one severity level to another; the formula adopted by the voltage sag severity index model at this time is as follows:
Figure FDA0002559686040000021
in the formula (I), the compound is shown in the specification,
Figure FDA0002559686040000022
denotes the voltage sag severity index, subscript BijJ and i in (1) represent the jth dip occurring at bus i; cwRepresents the voltage sag tolerance curve used for the evaluation; y represents a duration range index to which the sag belongs, and x represents a duration range index smaller than y; v. ofBijRepresenting a sag amplitude value; t is tBijRepresents the sag duration; vmax(Tx) And Vmin(Tx) Respectively represent a time range TxMaximum and minimum voltages of the inner sensitive area; t ismax(Tx) And Tmin(Tx) Respectively represent a time range TxMaximum and minimum times (boundaries); the coefficient a represents the difference between SSI values used to control the estimation from voltage sags over different ranges of duration; b denotes the increase in the sag duration to adjust the rate of increase of SSI.
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