CN117595191A - Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset - Google Patents
Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset Download PDFInfo
- Publication number
- CN117595191A CN117595191A CN202311323078.2A CN202311323078A CN117595191A CN 117595191 A CN117595191 A CN 117595191A CN 202311323078 A CN202311323078 A CN 202311323078A CN 117595191 A CN117595191 A CN 117595191A
- Authority
- CN
- China
- Prior art keywords
- current
- differential
- phase
- absolute value
- integral
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 230000005294 ferromagnetic effect Effects 0.000 title claims abstract description 32
- 238000012850 discrimination method Methods 0.000 title claims description 5
- 238000000034 method Methods 0.000 claims abstract description 41
- 238000005070 sampling Methods 0.000 claims description 18
- 238000004364 calculation method Methods 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 7
- 230000001419 dependent effect Effects 0.000 claims description 3
- 238000012886 linear function Methods 0.000 claims description 3
- 230000010354 integration Effects 0.000 claims 1
- 230000000903 blocking effect Effects 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 4
- 230000005284 excitation Effects 0.000 description 4
- 230000006870 function Effects 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 238000004590 computer program Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000003491 array Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 230000007257 malfunction Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000001902 propagating effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000012795 verification Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000004422 calculation algorithm Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000005291 magnetic effect Effects 0.000 description 1
- 239000003550 marker Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
Classifications
-
- 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
- G01R19/10—Measuring sum, difference or ratio
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Protection Of Transformers (AREA)
Abstract
The invention discloses a ferromagnetic saturation and inrush current distinguishing method and device reflecting current waveform concave-convex offset, wherein the method comprises the following steps: obtaining three-phase differential current waveforms according to the three-phase currents at each side of the transformer, and acquiring a variable quantity sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms; calculating the absolute value of a differential flow and a differential flow of the three-phase current variation, the current period integral of the differential flow and the current period integral of the absolute value of the differential flow, the T/3 period integral, the 2T/3 period integral and the maximum number of 2 points of the absolute value of the differential flow; and when the absolute value of the current period integral of the difference flow meets ferromagnetic saturation reflecting the concave-convex offset of the current waveform and a current surge criterion, judging as surge current or CT saturation, and locking differential protection. The invention uses the same criterion to realize the effective identification of the surge and saturation.
Description
Technical Field
The invention belongs to the technical field of relay protection of power systems, and particularly relates to a ferromagnetic saturation and inrush current distinguishing method and device for reflecting concave-convex offset of a current waveform.
Background
In recent years, with the gradual maturity of intelligent substation technology, intelligent substations are operated by a large-scale input power grid, and the phenomenon of transformer protection misoperation occurs, and the reason is mainly expressed in two aspects: (1) The intelligent substation process layer is widely matched with links such as a mutual inductor, a collector and a merging unit to realize a digital sampling loop, and the complicated digital sampling loop is easy to cause abnormal sampling data, so that the transformer is protected from misoperation; (2) The influence of exciting current and restorative current when the fault outside the area is removed during the air drop of the transformer is easy to cause misoperation of transformer protection. Aiming at the problems, the prior device adopts double AD data acquisition and verification, and uses two paths of AD sampling data for logic operation to jointly handle a protection outlet, thereby improving the reliability of a sampling loop; in addition, through analyzing the excitation surge current type of the transformer, differential current second harmonic mutual locking is used, and phase-based comprehensive harmonic open differential protection is adopted when the transformer is in air drop; and during the recovery of the surge current, the differential protection method is opened according to the phase difference current second harmonic wave 'three-out-two'.
For differential protection of transformers, because two or even a plurality of current transformers (Current Transformer, CT) with different voltage levels are involved, the situation that one side CT of the transformer is unsaturated and the other side CT is deeply saturated still can occur when the external fault occurs, the unbalanced current of the differential protection is increased sharply, and the malfunction of the differential protection cannot be avoided only by utilizing the ratio brake characteristic which is widely used currently. Saturation may affect the harmonic content and the magnitude of the break angle in the differential current to different extents, thereby causing malfunction or rejection of the transformer differential protection with the braking characteristics of the magnetizing inrush current. Specifically, CT saturation is easy to increase the content of second harmonic in fault current, and the second harmonic braking principle generates misjudgment; on the other hand, CT saturation may cause the break angle of the exciting surge to become smaller or even disappear, and cause misjudgment of the break angle braking principle and misoperation of differential protection. In the conventional differential protection, the aim of avoiding unbalanced current caused by CT saturation caused by out-of-zone faults is achieved by improving the ratio brake coefficient, but the sensitivity of protection action during in-zone faults is certainly reduced.
In the prior art, the dominant principle of transformer inrush current blocking is second harmonic blocking. The patent with publication number CN102522726B proposes a method for locking the excitation surge current of a transformer, which judges the excitation surge current according to the difference current harmonic wave and the phase current harmonic wave of each side of the transformer, and identifies the excitation surge current and the internal fault. The patent with publication number CN109884448B proposes a rapid judging method of transformer turn-to-turn faults, when the transformer is in normal operation with load, the influence of load current is removed through the differential motion of fault components, and as the fault components are used, the influence of the load and CT characteristics of the transformer is reduced, the differential motion threshold can be lowered, thus providing the motion sensitivity of the transformer protection device and rapidly cutting off the faults; when the transformer is in air drop, the second harmonic and the waveform break angle criterion are synthesized, when the waveform of the side of the transformer is uninterrupted and the second harmonic content is within a certain range, the fault is indicated, the transformer protection device acts, and the technical defect that the protection action is started at the moment when the inter-turn fault continues to develop until the differential current meets the action condition after the current disappears in the conventional method is overcome. The patent with publication number CN104319734B proposes a large-difference protection method based on the magnetizing inrush current of the converter transformer, and when single-phase grounding faults occur in a valve side area of the converter transformer, the magnetizing inrush current is identified by comprehensively judging the large-difference protection differential current, the Yn/Y converter transformer differential protection differential current and the second harmonic content in the differential current in the Yn/D converter transformer differential protection, so that protection misoperation caused by the large-difference protection differential current and the Yn/Y converter transformer differential protection is effectively avoided.
The patent with publication number CN113267698A proposes a method, a system and a storage medium for judging the saturation of a main transformer CT, and a preset full-cycle differential flow integral function is input according to the amplitude of a second harmonic wave at the high-voltage side of the main transformer, the braking current and the differential flow of sampling points at the current moment of the main transformer, so as to obtain a full-cycle differential flow integral; and carrying out main transformer CT saturation discrimination according to the full-cycle differential flow integral and a preset discrimination rule. The patent with publication number CN115912263a proposes a method and system for identifying a CT saturation fault, wherein two parameters are set, and when the ratio of the original differential current to the original braking current is greater than a first set parameter, serious saturation is considered to occur, and when the ratio is smaller than the first set parameter and greater than a second set parameter, slight saturation is considered to occur. The CT saturation criteria of the two patents cannot be combined with the inrush current criteria, and the same criteria are used, so that both the inrush current and the saturation can be effectively identified.
Disclosure of Invention
In order to solve the defects existing in the prior art, the invention provides a ferromagnetic saturation and inrush current judging method and device for reflecting the concave-convex offset of a current waveform, and the invention can more quickly confirm whether the inrush current and the saturation occur or not by utilizing a certain one-time relation that the ratio of the sum of the absolute value of the T/3 period integral and the 2 point maximum number of the absolute value of the 2T/3 period integral and the difference flow is lower than the absolute value of the current period integral of the difference flow and the T/3 period integral ratio.
The invention adopts the following technical scheme.
A ferromagnetic saturation and inrush current distinguishing method reflecting current waveform concave-convex offset comprises the following steps:
step 1, obtaining three-phase differential current waveforms according to three-phase currents on each side of a transformer, and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
step 2, summing the variable quantities of the three-phase differential currents in the sequence obtained in the step 1 according to the phases to obtain a differential flow of the variable quantities of the three-phase currents, and further obtaining an absolute value of the differential flow;
step 3, calculating the current period integral of the difference stream and the current period integral of the absolute value of the difference stream by taking 23 current and previous time points as the current period;
step 4, taking 8 points with the smallest numerical value in the current period of the absolute value of the difference stream, solving the integral of the absolute value of the difference stream to obtain a T/3 period integral, and subtracting the T/3 period integral from the current period integral of the absolute value of the difference stream to obtain a 2T/3 period integral;
step 5, solving the sum of the maximum value and the secondary maximum value in the current period for the absolute value of the difference stream, and taking the sum as the maximum number of 2 points of the absolute value of the difference stream;
and 6, judging whether the absolute value of the T/3 period integral, the 2T/3 period integral, the sum of the maximum numbers of 2 points of the absolute value of the differential flow and the current period integral of the differential flow meets ferromagnetic saturation and inrush current criteria reflecting the concave-convex offset of the current waveform, and if so, judging that the differential protection is inrush current or CT saturation, and locking the differential protection.
Preferably, the step 1 specifically includes:
step 1.1, collecting three-phase current I of a high-voltage side branch of a transformer H1A 、I H1B 、I H1C Three-phase current I of medium-voltage side branch M1A 、I M1B 、I M1C Three-phase current I of low-voltage side branch L1A 、I L1B 、I L1C ；
Step 1.2, calculating three-phase differential current according to the three-phase current data of each side branch acquired in step 1.1, and forming a three-phase differential current waveform:
I CD_A ＝I H1A +I M1A +I L1A
I CD_B ＝I H1B +I M1B +I L1B
I CD_C ＝I H1C +I M1C +I L1C
wherein I is CD_A 、I CD_B 、I CD_C Differential currents of the A phase, the B phase and the C phase respectively;
step 1.3, according to the three-phase differential current waveform, the variation dI of the three-phase differential current is collected CD_A 、dI CD_B And dI CD_B Sequence.
Preferably, in step 1.1, when three-phase current data of each side branch of the transformer is collected, the sampling rate is greater than 1200Hz, and the sampling rate is not less than 24 sampling points in one sampling period.
Preferably, when the variable quantity sequence of the three-phase differential current of the transformer is collected, regarding the three-phase differential current waveform, the occurrence time of the fault as the time origin, the waveform corresponding to the time period tau before the time origin as the pre-fault waveform, and the waveform after the time origin as the post-fault waveform;
recording waveforms after faults once in each interval time period tau from a time origin;
and subtracting the pre-fault waveforms from the recorded post-fault waveforms to obtain the variable sequence of the three-phase differential current of the transformer.
Preferably, the value of the time period τ is 20ms.
Preferably, in step 3, the formula of the current period integral of the difference stream and the current period integral of the absolute value of the difference stream is:
in the formula, 24' k Representing the current period integral of the difference stream;
24 k a current period integral representing the absolute value of the difference stream;
subscript k represents the current point in time, k being greater than 23;
δi Σi' representing the i' th point difference stream i Σi' Is a variable amount of (a).
Preferably, in step 6, the ferromagnetic saturation and inrush current criteria reflecting the concave-convex offset of the current waveform are:
in the method, in the process of the invention,representing the maximum number of 2 points of the absolute value of the difference stream;
min T/3 representing a T/3 cycle integral;
max 2T/3 representing a 2T/3 cycle integral;
c and b represent the slope and intercept in a linear function with the ratio of the absolute value of the current period integral of the difference stream to the T/3 period integral as a dependent variable.
Preferably, the ferromagnetic saturation reflecting the concave-convex offset of the current waveform and the inrush current criterion are provided with the following using thresholds:
min T/3 ≥0.004I e
wherein min is T/3 Representing a T/3 cycle integral;
I e representing a high voltage rated current;
if the threshold is not met, locking protection is performed.
Preferably, the slope c is 0.016 and the intercept b is a function of time t:
a ferromagnetic saturation and inrush current discriminating apparatus reflecting a current waveform concave-convex offset, comprising:
the acquisition module is used for obtaining three-phase differential current waveforms according to the three-phase currents at each side of the transformer and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
the module value calculation module is used for calculating the absolute value of the differential flow and the differential flow of the three-phase current variation, the current period integral of the differential flow and the current period integral of the absolute value of the differential flow, the T/3 period integral, the 2T/3 period integral and the maximum number of 2 points of the absolute value of the differential flow;
and the locking enabling module is used for judging the current surge or CT saturation when the absolute value of the current period integral of the differential flow meets ferromagnetic saturation reflecting the current waveform concave-convex offset and the surge criterion, and locking differential protection.
Preferably, the different calculation processes in the module value calculation unit respectively use independent registers for calculation.
The invention has the beneficial effects that compared with the prior art:
1. the invention is suitable for distinguishing the inrush current and is also suitable for distinguishing the CT saturation, and only the ratio of the sum of the absolute value 2 points of the absolute value of the difference current and the absolute value 2 points of the integral of the T/3 period is lower than a certain primary relation of the absolute value of the integral of the current period of the difference current and the integral ratio of the T/3 period, the occurrence of the inrush current or the CT saturation can be reflected, so that the blocking protection is realized, and the effective identification of the inrush current and the saturation is realized by using the same criterion;
2. the invention directly uses the discrete point data acquired by the device without using the second harmonic, thereby avoiding Fourier series operation and avoiding instability caused by cross-window calculation when the device operates;
3. when the T/3 period integral is calculated, the method is not used for taking the minimum of 8 continuous points, but is used for converting the minimum of 8 points (which can be discontinuous) in the current period, so that the position of the interruption in the current period can be better reflected, the concave-convex and the bulge of the represented waveform are emphasized, the proportional relation between the T/3 period integral and the 2T/3 period integral is adopted, the concave-convex offset of the current waveform is reflected, the smaller the T/3 period integral is, the more obvious the concave-convex of the waveform is indicated, and the method can be used as a marker post for judging whether the waveform has the inrush current and the saturation.
Drawings
FIG. 1 is a flow chart of a ferromagnetic saturation and inrush current discrimination method reflecting the concave-convex offset of a current waveform according to the present invention;
FIG. 2 is a graph of the absolute value of the current cycle integral of the difference stream versus the T/3 cycle integral ratio calculated as the ratio of the T/3 cycle integral to the 2T/3 cycle integral plus the 2 point maximum sum of the absolute value of the difference stream at saturation in an embodiment of the present invention;
FIG. 3 is a graph of the absolute value of the current cycle integral of the difference stream versus the T/3 cycle integral ratio calculated as the ratio of the T/3 cycle integral to the 2T/3 cycle integral plus the absolute value of the difference stream plus the 2 point maximum at the time of a surge in an embodiment of the present invention;
FIG. 4 is a graph of the absolute value of the current cycle integral of the difference stream versus the T/3 cycle integral ratio, calculated as the ratio of the T/3 cycle integral to the sum of 2T/3 cycle integral and the 2 point maximum of the difference stream absolute value, at the time of failure in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The embodiments described herein are merely some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art without making any inventive effort, are within the scope of the present invention.
As shown in fig. 1, embodiment 1 of the present invention provides a ferromagnetic saturation and inrush current discriminating method reflecting a concave-convex offset of a current waveform, and in a preferred but non-limiting embodiment of the present invention, the method includes:
step 1, obtaining three-phase differential current waveforms according to three-phase currents on each side of a transformer, and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
further preferably, the step obtains the variation of the three-phase differential current of the transformer by using a recursive algorithm according to the three-phase current of each side of the transformer, and specifically includes:
step 1.1, collecting three-phase current I of a high-voltage side branch of a transformer H1A 、I H1B 、I H1C Three-phase current I of medium-voltage side branch M1A 、I M1B 、I M1C Three-phase current I of low-voltage side branch L1A 、I L1B 、I L1C ；
When three-phase current data of each side branch of the transformer are collected, the sampling rate is more than 1200Hz, and at least 24 sampling points in one period are ensured.
Step 1.2, calculating three-phase differential current according to the three-phase current data of each side branch acquired in step 1.1, and forming a three-phase differential current waveform:
I CD_A ＝I H1A +I M1A +I L1A
I CD_B ＝I H1B +I M1B +I L1B
I CD_C ＝I H1C +I M1C +I L1C
wherein I is CD_A 、I CD_B 、I CD_C Differential currents of the A phase, the B phase and the C phase are respectively obtained.
Step 1.3, obtaining the variation dI of a plurality of three-phase differential currents according to the three-phase differential current waveform CD_A 、dI CD_B 、dI CD_C The method comprises the steps of carrying out a first treatment on the surface of the Wherein dI CD_A 、dI CD_B 、dI CD_C The differential current variation amounts of the phase A, the phase B and the phase C are respectively.
When the variation of the three-phase differential current sampling value of the transformer is collected, regarding the recorded three-phase differential current waveform, taking the fault occurrence time as a time origin, the waveform corresponding to the time period tau before the time origin as a pre-fault waveform, and the waveform after the time origin as a post-fault waveform; preferably, the value of the time period τ is 20ms.
Recording waveforms after faults once in each interval time period tau from a time origin;
and subtracting the pre-fault waveforms from the recorded waveforms after faults respectively to obtain the variation of the three-phase differential current sampling values of the plurality of transformers, namely the variation sequence of the three-phase differential current sampling values of the transformers, wherein the collection times depend on the length of the fault waveforms, and the waveforms after faults are recorded every time interval from the time origin to the end of the waveforms.
In this embodiment, the time period is at least guaranteed to be 40ms, that is, 2 τ, before the fault is recorded, so as to ensure that the available data sample size is rich before the fault occurs.
Step 2, summing the variable quantities of the three-phase differential currents in the sequence obtained in the step 1 according to the phases to obtain a differential flow of the variable quantities of the three-phase currents, and further obtaining an absolute value of the differential flow;
i.e. step 1 to obtain dI CD_A 、dI CD_B 、dI CD_C After the sequence, step 2 will add all dI in the sequence CD_A Summing to obtain a difference stream of the A-phase current variation, all dI CD_B Summing to obtain a difference stream of B-phase current variation, all dI CD_C Summing to obtain a difference stream of the C-phase current variation, and obtaining absolute values of the difference streams to obtain absolute values of the difference values;
step 3, defining the time origin when the fault occurs, wherein t is 0, along with the change of t, the point corresponding to the moment t is called a current point, a 24-point set formed by the current point and the previous 23 points is used as a current period, and the current period integral of the difference stream and the current period integral of the absolute value of the difference stream are calculated by a recursive method by utilizing the absolute values of the difference stream and the difference stream;
in the formula, 24' k Representing the current period integral of the difference stream, 24 k A current period integral representing the absolute value of the difference stream, the subscript k representing the current point in time; δi Σi' Representing the i' th point difference stream i Σi' Is a difference stream of phase current variation; i' can ensure that all phase current variation difference flows of 23 points before and at the current point are traversed along with the variation of k; it can be understood that the length of i 'is constant as k gradually increases, and the existence of i' can always keep the length of the time window to be 24 points regardless of the change of k;
from the above formula, the current point k needs to be greater than 23. Since the point before the time origin is set to be the 0 th point, the point before the time origin can be understood as a negative number, and the data before the fault is represented, when k is smaller than 23, 24 is calculated k Data before failure is involved. Therefore, k is required to be larger than 23, and i' is 1 at the minimum, which means that data after failure is taken.
This step 3 calculates 24' k And 24 (V) k The concept of the current period is used, which is defined as the 24-point set consisting of the current point and the previous 23 points, and the calculation process must not exceed this range. The current period mentioned in the subsequent step is this concept.
Step 4, simultaneously taking 8 points (discontinuous) with the smallest numerical value in the current period by utilizing the absolute value of the difference stream, solving the integral of the points to obtain a T/3 period integral, and subtracting the T/3 period integral from the current period integral of the absolute value of the difference stream to obtain a 2T/3 period integral;
max 2T/3 ＝24 k -min T/3
in the formula, min T/3 Represents T/3 period integral, max 2T/3 Representing a 2T/3 cycle integral;
in the step 4, when calculating the T/3 period integral, 8 points with the smallest numerical value in the current period in the absolute value of the difference stream need to be selected, and the 8 points can be not continuous, so that the influence on the break angle after CT saturation can be avoided, and the concave-convex and the bulge of the represented waveform are emphasized.
Step 5, the absolute value of the difference stream is used to calculate the sum of the maximum value and the secondary maximum value in the current period, and the sum is used as the maximum number of 2 points of the absolute value of the difference stream;
and 6, judging whether the absolute value of the T/3 period integral, the 2T/3 period integral, the sum of the maximum numbers of 2 points of the absolute value of the differential flow and the current period integral of the differential flow meets ferromagnetic saturation and inrush current criteria reflecting the concave-convex offset of the current waveform, and if so, judging that the differential protection is inrush current or CT saturation, and locking the differential protection.
If the ratio of the sum of the T/3 period integral and the 2 point maximum number of the absolute value of the 2T/3 period integral and the difference flow is lower than a certain primary relation between the absolute value of the current period integral of the difference flow and the T/3 period integral ratio, judging that the current is inrush current or CT is saturated, and locking differential protection, wherein the specific criteria are as follows:
in the method, in the process of the invention,representing the maximum number of points 2 of the absolute value of the differential stream, c and b represent the slope and intercept in a linear function with the ratio of the absolute value of the current period integral of the differential stream to the T/3 period integral as a dependent variable.
Further preferably, in order to ensure that this criterion is applicable to both current blocking and CT saturation discrimination, the slope c is set to 0.016 and the intercept b is set as a function of time t, through verification and function fitting of typical current and multiple sets of CT saturation oscillometric waveforms:
i.e., b=0.0007t+0.03, and 0.0007t+0.03.gtoreq.0.135, b=0.135.
Since in this step 6, min T/3 As denominator, it is guaranteed that it cannot be 0, but in min T/3 When calculating, if the current point is the first 8 points after the fault occurs, the results are all 0, so the criterion needs to set a use threshold, namely min T/3 ≥0.004I e Wherein I e Is a high voltage rated current.
If the threshold is not met, locking protection is performed. If a fault exists, the threshold can be easily reached, and the threshold is used for preventing the current from flowing through the small time, so that the false opening of the opening criterion is caused.
FIGS. 2, 3 and 4 are graphs showing the relationship between the ratio of the sum of the T/3 period integral and the 2 point maximum of the absolute value 2 of the 2T/3 period integral and the difference stream and the relationship between the absolute value of the current period integral of the difference stream and the T/3 period integral ratio, when saturation, inrush current and failure occur respectively; as shown in fig. 4, in the event of a slight failure, the left side of the inequality in step 6 is rapidly larger than the right side of the inequality, thereby opening protection.
The embodiment 2 of the invention provides a ferromagnetic saturation and inrush current discriminating device reflecting the concave-convex offset of a current waveform, which comprises: the system comprises an acquisition module, a calculation module and a locking enabling module;
the acquisition module is used for obtaining three-phase differential current waveforms according to the three-phase currents at each side of the transformer and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
the module value calculation module is used for calculating the absolute value of the differential flow and the differential flow of the three-phase current variation, the current period integral of the differential flow and the current period integral of the absolute value of the differential flow, the T/3 period integral, the 2T/3 period integral and the maximum number of 2 points of the absolute value of the differential flow; preferably, the modulus calculation unit comprises 3 independent registers.
And the locking enabling module is used for judging the current surge or CT saturation when the absolute value of the current period integral of the differential flow meets ferromagnetic saturation reflecting the current waveform concave-convex offset and the surge criterion, and locking differential protection.
The invention has the beneficial effects that compared with the prior art:
1. the invention is suitable for distinguishing the inrush current and is also suitable for distinguishing the CT saturation, and only the ratio of the sum of the absolute value 2 points of the absolute value of the difference current and the absolute value 2 points of the integral of the T/3 period is lower than a certain primary relation of the absolute value of the integral of the current period of the difference current and the integral ratio of the T/3 period, the occurrence of the inrush current or the CT saturation can be reflected, so that the blocking protection is realized, and the effective identification of the inrush current and the saturation is realized by using the same criterion;
2. the invention does not use Fourier series, so that instability caused by cross-window calculation can be avoided when the device runs;
3. when the T/3 period integral is calculated, the traditional continuous 8-point minimum interruption concept is abandoned, and the method is converted into the method for selecting the minimum 8 points (which can be discontinuous) in the current period, so that the position of the interruption in the current period can be better reflected, the concave-convex and the convex-convex of the represented waveform are emphasized, and the concave-convex offset of the current waveform is reflected.
The present disclosure may be a system, method, and/or computer program product. The computer program product may include a computer readable storage medium having computer readable program instructions embodied thereon for causing a processor to implement aspects of the present disclosure.
The computer readable storage medium may be a tangible device that can hold and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: portable computer disks, hard disks, random Access Memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static Random Access Memory (SRAM), portable compact disk read-only memory (CD-ROM), digital Versatile Disks (DVD), memory sticks, floppy disks, mechanical coding devices, punch cards or in-groove structures such as punch cards or grooves having instructions stored thereon, and any suitable combination of the foregoing. Computer-readable storage media, as used herein, are not to be construed as transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., optical pulses through fiber optic cables), or electrical signals transmitted through wires.
The computer readable program instructions described herein may be downloaded from a computer readable storage medium to a respective computing/processing device or to an external computer or external storage device over a network, such as the internet, a local area network, a wide area network, and/or a wireless network. The network may include copper transmission cables, fiber optic transmissions, wireless transmissions, routers, firewalls, switches, gateway computers and/or edge servers. The network interface card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium in the respective computing/processing device.
Computer program instructions for performing the operations of the present disclosure can be assembly instructions, instruction Set Architecture (ISA) instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, c++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program instructions may be executed entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computer (for example, through the Internet using an Internet service provider). In some embodiments, aspects of the present disclosure are implemented by personalizing electronic circuitry, such as programmable logic circuitry, field Programmable Gate Arrays (FPGAs), or Programmable Logic Arrays (PLAs), with state information of computer readable program instructions, which can execute the computer readable program instructions.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (11)
1. A ferromagnetic saturation and inrush current distinguishing method reflecting current waveform concave-convex offset is characterized in that:
the method comprises the following steps:
step 1, obtaining three-phase differential current waveforms according to three-phase currents on each side of a transformer, and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
step 2, summing the variable quantities of the three-phase differential currents in the sequence obtained in the step 1 according to the phases to obtain a differential flow of the variable quantities of the three-phase currents, and further obtaining an absolute value of the differential flow;
step 3, calculating the current period integral of the difference stream and the current period integral of the absolute value of the difference stream by taking 23 current and previous time points as the current period;
step 4, taking 8 points with the smallest numerical value in the current period of the absolute value of the difference stream, solving the integral of the absolute value of the difference stream to obtain a T/3 period integral, and subtracting the T/3 period integral from the current period integral of the absolute value of the difference stream to obtain a 2T/3 period integral;
step 5, solving the sum of the maximum value and the secondary maximum value in the current period for the absolute value of the difference stream, and taking the sum as the maximum number of 2 points of the absolute value of the difference stream;
and 6, judging whether the absolute value of the T/3 period integral, the 2T/3 period integral, the sum of the maximum numbers of 2 points of the absolute value of the differential flow and the current period integral of the differential flow meets ferromagnetic saturation and inrush current criteria reflecting the concave-convex offset of the current waveform, and if so, judging that the differential protection is inrush current or CT saturation, and locking the differential protection.
2. The method for determining ferromagnetic saturation and inrush current reflecting the concave-convex offset of a current waveform according to claim 1, characterized by:
the step 1 specifically includes:
step 1.1, collecting three-phase current I of a high-voltage side branch of a transformer H1A 、I H1B 、I H1C Three-phase current I of medium-voltage side branch M1A 、I M1B 、I M1C Three-phase current I of low-voltage side branch L1A 、I L1B 、I L1C ；
Step 1.2, calculating three-phase differential current according to the three-phase current data of each side branch acquired in step 1.1, and forming a three-phase differential current waveform:
I CD_A ＝I H1A +I M1A +I L1A
I CD_B ＝I H1B +I M1B +I L1B
I CD_C ＝I H1C +I M1C +I L1C
wherein I is CD_A 、I CD_B 、I CD_C Differential currents of the A phase, the B phase and the C phase respectively;
step 1.3, according to the three-phase differential current waveform, the variation dI of the three-phase differential current is collected CD_A 、dI CD_B And dI CD_B Sequence.
3. The method for determining ferromagnetic saturation and inrush current reflecting the concave-convex offset of a current waveform according to claim 2, characterized by:
in step 1.1, when three-phase current data of each side branch of the transformer is collected, the sampling rate is greater than 1200Hz, and at least 24 sampling points are provided in one sampling period.
4. The ferromagnetic saturation and inrush current discrimination method reflecting the concave-convex offset of a current waveform according to claim 1 or 2, characterized in that:
when the variable quantity sequence of the three-phase differential current of the transformer is acquired, regarding the waveform of the three-phase differential current, taking the occurrence time of a fault as a time origin, wherein the waveform corresponding to a time period tau before the time origin is a waveform before the fault, and the waveform after the time origin is a waveform after the fault;
recording waveforms after faults once in each interval time period tau from a time origin;
and subtracting the pre-fault waveforms from the recorded post-fault waveforms to obtain the variable sequence of the three-phase differential current of the transformer.
5. The method for determining the ferromagnetic saturation and the inrush current reflecting the concave-convex offset of the current waveform according to claim 4, wherein the method comprises the steps of:
the value of the time period τ is 20ms.
6. The method for determining ferromagnetic saturation and inrush current reflecting the concave-convex offset of a current waveform according to claim 1, characterized by:
in step 3, the formula of the current period integral of the difference stream and the current period integral of the absolute value of the difference stream is:
in the formula, 24' k Representing the current period integral of the difference stream;
24 k a current period integral representing the absolute value of the difference stream;
subscript k represents the current point in time, k being greater than 23;
δi Σi' representing the i' th point difference stream i Σi' Is a variable amount of (a).
7. The method for determining ferromagnetic saturation and inrush current reflecting the concave-convex offset of a current waveform according to claim 1, characterized by:
in step 6, the ferromagnetic saturation and inrush current criteria reflecting the concave-convex offset of the current waveform are:
in the method, in the process of the invention,representing the maximum number of 2 points of the absolute value of the difference stream;
min T/3 representation ofT/3 cycle integration;
max 2T/3 representing a 2T/3 cycle integral;
c and b represent the slope and intercept in a linear function with the ratio of the absolute value of the current period integral of the difference stream to the T/3 period integral as a dependent variable.
8. The ferromagnetic saturation and inrush current discrimination method reflecting the concave-convex offset of a current waveform according to claim 1 or 7, characterized by:
the ferromagnetic saturation and inrush current criterion reflecting the concave-convex offset of the current waveform is provided with the following using threshold:
min T/3 ≥0.004I e
wherein min is T/3 Representing a T/3 cycle integral;
I e representing a high voltage rated current;
if the threshold is not met, locking protection is performed.
9. The method for determining the ferromagnetic saturation and the inrush current reflecting the concave-convex offset of the current waveform according to claim 7, wherein the method comprises the steps of:
slope c is 0.016 and intercept b is a function of time t:
10. a ferromagnetic saturation and inrush current discriminating device reflecting the concave-convex offset of a current waveform, using the method of any of claims 1-9, characterized in that: the device comprises:
the acquisition module is used for obtaining three-phase differential current waveforms according to the three-phase currents at each side of the transformer and acquiring a variation sequence of the three-phase differential currents of the transformer based on the three-phase differential current waveforms;
the module value calculation module is used for calculating the absolute value of the differential flow and the differential flow of the three-phase current variation, the current period integral of the differential flow and the current period integral of the absolute value of the differential flow, the T/3 period integral, the 2T/3 period integral and the maximum number of 2 points of the absolute value of the differential flow;
and the locking enabling module is used for judging the current surge or CT saturation when the absolute value of the current period integral of the differential flow meets ferromagnetic saturation reflecting the current waveform concave-convex offset and the surge criterion, and locking differential protection.
11. The ferromagnetic saturation and inrush current discrimination device of claim 10, wherein the current waveform is reflected in a concave-convex offset, the device comprising:
and different calculation processes in the module value calculation unit respectively adopt independent registers for calculation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311323078.2A CN117595191A (en) | 2023-10-12 | 2023-10-12 | Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202311323078.2A CN117595191A (en) | 2023-10-12 | 2023-10-12 | Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN117595191A true CN117595191A (en) | 2024-02-23 |
Family
ID=89919009
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202311323078.2A Pending CN117595191A (en) | 2023-10-12 | 2023-10-12 | Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN117595191A (en) |
-
2023
- 2023-10-12 CN CN202311323078.2A patent/CN117595191A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Wu et al. | Using mathematical morphology to discriminate between internal fault and inrush current of transformers | |
| CN108183463B (en) | Method for preventing misoperation in ratio differential protection of transformer of intelligent substation | |
| Medeiros et al. | A wavelet-based transformer differential protection: Internal fault detection during inrush conditions | |
| CN107765077B (en) | Magnetizing inrush current identification method and device | |
| CN105140893B (en) | A kind of differential protecting CT saturation recognition methods | |
| CN107765076B (en) | Magnetizing inrush current identification method and device | |
| MS et al. | Detection of three‐phase fault during power swing using zero frequency filtering | |
| EP3560054A1 (en) | A method for detecting inrush and ct saturation and an inteligent electronic device therfor | |
| Zhang et al. | Morphology singular entropy-based phase selector using short data window for transmission lines | |
| Sahebi et al. | Identifying internal fault from magnetizing conditions in power transformer using the cascaded implementation of wavelet transform and empirical mode decomposition | |
| CN107123974B (en) | A kind of open trip method of bus troubles inside the sample space CT saturation based on saturation mechanism | |
| CN109494684B (en) | Transformer excitation inrush current and fault differential current identification method based on babbitt distance algorithm | |
| Shah et al. | New protection scheme for power transformer based on superimposed differential current | |
| CN106026040B (en) | It is a kind of to prevent the abnormal differential protection method for bus several greatly of sampling | |
| CN108963974B (en) | A kind of method and device preventing external area error excision differential protection malfunction | |
| CN113363953A (en) | Method for inhibiting malfunction of fault-removing differential protection by means of hysteresis characteristics | |
| CN117595191A (en) | Ferromagnetic saturation and inrush current discrimination method and device reflecting current waveform concave-convex offset | |
| CN110808575B (en) | Method for preventing power frequency magnetic field interference by bus protection | |
| CN109672154B (en) | Method and device for preventing false operation of non-fault phase saturation differential protection | |
| CN104977488B (en) | A kind of transformer excitation flow recognition method based on difference current gradient angle approximate entropy | |
| CN109119972B (en) | Locking method and device for preventing differential misoperation caused by CT (current transformer) disconnection of balance winding | |
| De Alencar et al. | Transformer inrush currents and internal faults identification in power transformers using wavelet energy gradient | |
| CN106324328B (en) | A kind of transformer excitation flow recognition method based on morphology cascade erosion operation | |
| Suliman et al. | Discrimination Between Inrush and Internal Fault Currents in Protection Based Power Transformer using DWT. | |
| CN110492444B (en) | Transformer substation bus differential protection method and device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |