CN105866511B - A method of the identification tail currents based on current waveform neighbouring sample point ratio - Google Patents
A method of the identification tail currents based on current waveform neighbouring sample point ratio Download PDFInfo
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Abstract
The invention discloses a kind of methods of the identification tail currents based on analysis current waveform neighbouring sample point ratio size, the current ratio of calculating current waveform neighbouring sample point, if its ratio continuously falls the delay time that the time in set interval is more than setting, judge electric current at this time for tail currents.Since the ratio size of adjacent two sampled point of fault current meets the feature similar with tail currents only at waveform peak in the very little section of (wave crest and trough), this method can in a relatively short period of time make accurate judgment to tail currents.For present microcomputer protecting device, the sampling period is very short, and sampling precision is high and computational accuracy is high, and method using the present invention can accomplish that the time with 1/4 cycle correctly identifies tail currents, substantially increase the recognition speed of tail currents.
Description
Technical field
The method for identifying tail currents based on current waveform neighbouring sample point ratio that the present invention relates to a kind of, belongs to electric power
System automation technical field.
Background technology
When electric system is broken down, fault element protection detects that action outlet tripping after failure, breaker tripping are cut
Except failure, CT primary sides disconnect, and once winding current becomes 0.But for most of CT, CT secondary side winding electricity at this moment
Stream cannot but immediately become 0.It is disconnected when CT primary side currents are in non-zero, the iron core magnetic flux in CT cannot be mutated.It stores at this time
Energy in secondary winding will gradually discharge, and an electric current exponentially decayed will be formed in CT secondary circuits, i.e., so-called
Tail currents.The discharge loop is typical single order RL circuits, and the tail currents being calculated are：I (t)=I0×e-(t/τ),
Wherein：I0Secondary side initial current when being disconnected for CT primary sides, τ are CT secondary side time constants.Even if CT primary sides are in electric current
It is disconnected when being zero, since the presence of exciting current so that there are angular differences for first and second sides CT, secondary side is in the electric current for disconnecting moment
It is not equally 0, still will produce trailing phenomenon, the equivalent model of current transformer is as shown in Figure 1.For " P grades " mutual inductor, two
Secondary time constant is larger, and tail currents decaying is slower, and 0 can just be decayed to by being typically passed through more than ten of cycle, this will extend such as mistake
The time of return of the protection elements such as stream protection, if opened using overcurrent protection actuating signal as failure is opened into accidentally opening the general of failure
Rate will greatly increase, and easily lead to failure protection malfunction.In addition, the presence of tail currents also results in differential protection malfunction.Hangover
Electric current is neither direct current signal, nor the signal of linear change, but the signal exponentially decayed, for Microcomputer Protection
Speech, used sampling filter method all cannot fully filter out the electric current, cause tail currents to the unfavorable of Microcomputer Protection
Influence exists always.Therefore it has to effectively identify tail currents, reduces tail currents to the adverse effect of protection, carry
The correctness and reliability of high protective device action.It is less to the recognition methods of tail currents research at present, it focuses mostly in wave
Tail currents and fault current are distinguished in the identification of shape zero crossing, and still, larger bias current is possible to meeting in fault current
It causes zero crossing of the fault current waveform in 1 cycle to disappear, knows method for distinguishing failure so as to cause using waveform pass zero point.
Invention content
The technical problem to be solved by the present invention is to overcome the deficiencies of existing technologies, provide a kind of adjacent based on current waveform
The method of the identification tail currents of sampled point ratio is quickly known based on the ratio size of neighbouring sample point on analysis current waveform
Other tail currents are latched related defencive function immediately once identifying tail currents, substantially increase the reliable of related protection
Property.
In order to solve the above technical problems, the present invention provides a kind of identification hangover based on current waveform neighbouring sample point ratio
The method of electric current, includes the following steps：
1) it is determined for compliance with the ratio P of adjacent two sampled point of tail currents wave character, and fault-tolerant place is done to the P values acquired
Reason, obtains fault-tolerant section；
2) time period threshold of identification tail currents logic is determined；
3) the real effective I of current flow is calculatedrms, when judging IrmsMore than giving constant current threshold IsWhen, it enters step 4)
Tail currents recognition logic；Otherwise, it is identified without tail currents；
4) the current point sampled value I of a certain phase of three-phase current is readk, and judge the upper current sampling data I of the phasek-1
Whether it is 0, if 0, which is done into fault-tolerant processing, ensures that denominator is not zero, and do not judge by accident, be then transferred to step (5)；If
Be not 0, then it is without any processing, it is transferred to step (5)；
5) I is calculatedk/Ik-1Value Qk, and judge whether the value meets and fall in fault-tolerant section (k1× P, k2× P) in；If
The value is fallen in fault-tolerant section and the upper ratio Q a little calculatedk-1It does not fall in section, such as formula (8), start-up study calculates；If
The point is not fallen in section, and such as formula (9), involution delay calculates；If the ratio Q currently calculatedkWith the ratio of upper calculating
Qk-1It all falls in section, such as formula (10), then it is cumulative to carry out the time；
(k1× P ＜ QkANDQk＜ k2×P)AND(Qk-1≤k1×PORQk-1≥k2×P) (8)
Qk≤k1×PORQk≥k2×P (9)
(k1× P ＜ QkANDQk＜ k2×P)AND(k1× P ＜ Qk-1ANDQk-1＜ k2×P) (10)；
Wherein, k1And k2Respectively represent the up-and-down boundary coefficient in fault-tolerant section；
6) judgment step 5) time cumulative whether arrive time period threshold Td；If so, determining that the electric current is tail currents, set
Tail currents distinguishing mark is 1, otherwise by the mark clear 0；
7) current sample values are preserved, such as formula (11)；
Ik-1=Ik(11)；
8) judgement of tail currents is carried out to remaining biphase current according to step 3) to step 7), and according to judging result point
Corresponding tail currents distinguishing mark is not provided.
In aforementioned step 1), the solution procedure of P values is as follows：
The calculation formula of tail currents is as follows：
I (t)=I0×e-(t/τ) (1)
Wherein：I (t) is tail currents, I0Secondary side initial current when being disconnected for CT primary sides, τ are the CT secondary side times
Constant,
By the tail currents represented by formula (1), sliding-model control is carried out, takes the value of -1 point of kth point and kth respectively, and
The ratio for calculating kth point and -1 point of kth, as shown in formula (2)：
Wherein：I(kTs) indicate kth point tail currents, I ((k-1) Ts) indicate -1 tail currents of kth, TsIt is protected for microcomputer
The protection unit sampling period.
In aforementioned step 1), fault-tolerant processing is done to P values, it is (k to obtain fault-tolerant section1× P, k2× P), wherein k1And k2
Respectively represent the up-and-down boundary coefficient in fault-tolerant section, k1Value range is (0,1), k2Value range is (1, ∞).
In aforementioned step 2), according to the fault-tolerant section (k in step 1)1× P, k2× P), estimation fault current waveform and
Tail currents have the sampling number of similitude, if there are N at fault current wave crest1A, there are N at trough2It is a, it takes
Then larger value in the two increases sampled data N the surplus of m points as sampled data N, and convert sampled data to
Time period threshold Td：
Td=(N+m-1) × Ts (5)
Wherein, TsFor the microcomputer protecting device sampling period.
In aforementioned step 4), fault-tolerant processing refers to doing the sampled value to handle plus a minimum Δ, it is ensured that is in
The sampled value of divisor position is not zero, and the fault-tolerant processing will not cause step 5) to be judged by accident, such as formula (7)：
Ik-1=Ik-1+Δ (7)。
In aforementioned step 1), the ratio of adjacent two sampled point is determined, not representing the two sampled points must be continuous, uses
The ratio of discontinuous two sampled points is equally applicable.
The advantageous effect that the present invention is reached：
The method of the present invention is by analyzing two neighboring sampled point ratio size on tail currents waveform and fault current waveform
Changing rule, summarize and form the correct criterion for distinguishing fault current and tail currents, due to adjacent two sampled point of fault current
Ratio size meet the feature similar with tail currents in the very little section of (wave crest and trough) only at waveform peak,
The ratio difference of adjacent two sampled point of supplementary interval internal fault electric current and tail currents is larger, and therefore, this method can be shorter
Time in make accurate judgment to tail currents.In view of existing Microcomputer Protection high sampling rate, high sampling precision and high calculating essence
The features such as spending, the method for the present invention only can reach the correct identification to tail currents with 1/4 cycle time.
Description of the drawings
Fig. 1 is current transformer model；
Fig. 2 is fault current and tail currents oscillogram；
Fig. 3 is the method for the present invention flow chart.
In Fig. 1, N1 and N2 represent first and second umber of turn, I'pAnd Z'pRepresent primary current and resistance of the conversion to secondary side
It is anti-, IsAnd ZsRepresent secondary current and secondary winding impedance, IeAnd ZeRepresent exciting current and excitation impedance, ZdRepresent load resistance
It is anti-.
Specific implementation mode
The invention will be further described below in conjunction with the accompanying drawings.Following embodiment is only used for clearly illustrating the present invention
Technical solution, and not intended to limit the protection scope of the present invention.
As shown in Fig. 2, by the waveform analysis to tail currents and fault current it is found that exponential function is presented in tail currents
The characteristics of variation, and fault current be in varies with sinusoidal function the characteristics of.Pass through two neighboring point after both function discretizations
Further analysis shows that for tail currents, the ratio on waveform between continuous two points is one and is less than 1 but very close to 1
Constant constant, be denoted as P, which is only uniquely determined by CT secondary circuits time constant and sampling period constant, and sampling
Value, sampling period are unrelated；For fault current, the ratio on waveform between continuous two points is not a constant constant,
It is denoted as Qk, it changes with the change of sampling period.By to P and QkAnalysis it is found that with sampling period change, QkIn
Only several values are the sections near P.Therefore by continuous two ratio of sample waveform the characteristics of, analysis was it is found that failure is electric
Waveform is flowed only in the section of very little and tail currents have similitude, in most of section, fault current and tail currents difference
Property is larger, i.e., can correctly distinguish fault current and tail currents by the variation characteristic of continuous 2 ratio of sample waveform.
Based on the above analysis, the correct identification that the invention is realized by the following technical scheme to tail currents：
As shown in figure 3, the present invention is based on the methods of the identification tail currents of current waveform neighbouring sample point ratio, including with
Lower step：
(1) it is determined for compliance with the ratio P of adjacent two sampled point of tail currents wave character, and the P values acquired are done fault-tolerant
Processing.
The solution procedure of P values is as follows：
The calculation formula of tail currents is as follows：
I (t)=I0×e-(t/τ) (1)
Wherein：I (t) is tail currents, I0Secondary side initial current when being disconnected for CT primary sides, τ are the CT secondary side times
Constant.
By the tail currents represented by formula (1), sliding-model control is carried out, takes the value of -1 point of kth point and kth respectively, and
The ratio for calculating kth point and -1 point of kth, as shown in formula (2).
Wherein：I(kTs) indicate kth point tail currents, I ((k-1) Ts) indicate that -1 tail currents of kth, τ are CT secondary sides
Time constant, TsFor the microcomputer protecting device sampling period.
By above formula (2) it is found that τ and TsAll be constant, therefore, ratio P be one and sampled value and sampling sequence number without
The constant of pass.It is commonly used in electromagnetic transformer in electric system, the secondary time constant of " P grades " mutual inductor is several seconds or more,
" TPY grades " mutual inductor time constant also will in hundreds of milliseconds by one or two second, preferable " TPZ grades " mutual inductor of transient characterisitics it is secondary
Time constant also has as many as 60 milliseconds.And present Microcomputer Protection, sampling period TsIt can accomplish hundred Microsecond grades, therefore Ts/ τ connects very much
Nearly 0, it calculatesObtained value P by be one be less than 1 and be in close proximity to 1 positive number.By analyzing formula (3) it is found that just
String function only can at the peak value of waveform (wave crest and trough) the continuous two sampled point ratio of short time occur close with P values
Situation.In view of the influence for bias current of decaying in fault current, at wave crest and trough it is existing with P values close to sampling number meeting
Difference, is located at wave crest that there are N1A, there are N at trough2It is a, when the method for the present invention is implemented, in sampled data N the two
Larger value, such as formula (4).To improve the reliability judged, increase sampled data N the surplus of m points, and converts sampled point to
Time period threshold Td, as shown in formula (5), wherein TsFor the sampling period.
N=max (N1,N2) (4)
Td=(N+m-1) × Ts (5)
T is current cycle, and for 50Hz systems, T values are 0.02s.TsIt is usually to count for Microcomputer Protection for the sampling period
Hundred microseconds.
The sampling precision and computational accuracy for considering Microcomputer Protection do fault-tolerant processing to P values, and fault-tolerant section is (k1× P, k2×
P), that is, the point fallen in the section is regarded as meeting the point of range.Wherein, k1And k2Respectively represent the upper following of fault-tolerant section
Boundary's coefficient.k1Value range is (0,1), k2Value range is (1, ∞).
In this step, it is analyzed by taking the two sampled point kth points and -1 point of kth of adjacent continuous as an example, calculates kth point
With the ratio of -1 point of kth, but not representing the two sampled points in the methods of the invention must be continuous, and the method for the present invention is also applied for
Using the ratio of discontinuous two sampled points.
(2) time period threshold of identification tail currents logic is determined.
According to the section (k in step (1)1× P, k2× P), estimate that fault current waveform and tail currents have similitude
Sampling number, and according to formula (5) calculate identification tail currents logic time period threshold Td。
(3) the real effective I of current flow is calculatedrms, when judging IrmsMore than giving constant current threshold IsWhen, it enters step
(4) tail currents recognition logic；Otherwise, it is identified without tail currents.
(4) the current point sampled value I of a certain phase of three-phase current is readk, and judge the upper current sampling data I of the phasek-1
Whether it is 0, if 0, which is done into fault-tolerant processing, ensures that denominator is not zero, and do not judge by accident, be then transferred to step (5)；If
Be not 0, then it is without any processing, it is transferred to step (5).
Fault-tolerant processing refers to doing the sampled value to handle plus a minimum Δ, it is ensured that is in the sampled value of divisor position
It is not zero, and the fault-tolerant processing will not cause step (5) to be judged by accident, such as formula (7)：
Ik-1=Ik-1+Δ (7)。
(5) I is calculatedk/Ik-1Value Qk, and judge whether the value meets and fall in section (k1× P, k2× P) in；If the value
Fall the ratio Q above calculated in section and a littlek-1It does not fall in section, such as formula (8), start-up study calculates；If the point is not fallen
In section, such as formula (9), involution delay calculates.If the ratio Q currently calculatedkWith the ratio Q of upper calculatingk-1It all falls within
In section, such as formula (10), then it is cumulative to carry out the time；
(k1× P ＜ QkANDQk＜ k2×P)AND(Qk-1≤k1×PORQk-1≥k2×P) (8)
Qk≤k1×PORQk≥k2×P (9)
(k1× P ＜ QkANDQk＜ k2×P)AND(k1× P ＜ Qk-1ANDQk-1＜ k2×P) (10)。
(6) time of judgment step (5) adds up whether arrive time period threshold Td.If so, determine that the electric current is tail currents,
It is 1 to set tail currents distinguishing mark, otherwise by the mark clear 0.
(7) current sample values are preserved, such as formula (11)；
Ik-1=Ik (11)
(8) judgement of tail currents is carried out to remaining biphase current according to step (3) to step (7), and is tied according to judgement
Fruit provides corresponding tail currents distinguishing mark respectively, to carry out split-phase locking to protection element.
The present invention is based on the ratio size of continuous two sampled points on analysis current waveform, fast and reliable identification hangover electricity
Stream, criterion are simple and reliable.For present microcomputer protecting device, the sampling period is very short, sampling precision height and computational accuracy
Height, coefficient k1And k2Very close to 1, the judgement section in criterion is narrow.Therefore method using the present invention, can accomplish with 1/4
The time of cycle correctly identifies tail currents, improves the recognition speed of tail currents, once identify tail currents, immediately
It is latched relevant defencive function, greatly the reliability and correctness of the action of lifting protection device.
The above is only a preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art
For member, without departing from the technical principles of the invention, several improvement and deformations can also be made, these improvement and deformations
Also it should be regarded as protection scope of the present invention.
Claims (6)
1. a kind of method of the identification tail currents based on current waveform neighbouring sample point ratio, which is characterized in that including following
Step：
1) it is determined for compliance with the ratio P of adjacent two sampled point of tail currents wave character, and fault-tolerant processing is done to the P values acquired,
Obtain fault-tolerant section；
2) time period threshold of identification tail currents logic is determined；
3) the real effective I of current flow is calculatedrms, when judging IrmsMore than giving constant current threshold IsWhen, enter step hangover 4)
Electric current recognition logic；Otherwise, it is identified without tail currents；
4) the current point sampled value I of a certain phase of three-phase current is readk, and judge the upper current sampling data I of the phasek-1Whether be
0, if 0, which is done into fault-tolerant processing, is then transferred to step (5)；If not 0, then it is without any processing, it is transferred to step
(5)；
5) I is calculatedk/Ik-1Value Qk, and judge whether the value meets and fall in fault-tolerant section (k1× P, k2× P) in；If the value is fallen
The ratio Q above calculated in fault-tolerant section and a littlek-1It does not fall in section, such as formula (8), start-up study calculates；If the value is not
It falls in section, such as formula (9), involution delay calculates；If the ratio Q currently calculatedkWith the ratio Q of upper calculatingk-1Fall
In section, such as formula (10), then it is cumulative to carry out the time；
(k1× P ＜ QkANDQk＜ k2×P)AND(Qk-1≤k1×PORQk-1≥k2×P) (8)
Qk≤k1×PORQk≥k2×P (9)
(k1× P ＜ QkANDQk＜ k2×P)AND(k1× P ＜ Qk-1ANDQk-1＜ k2×P) (10)；
Wherein, k1And k2Respectively represent the up-and-down boundary coefficient in fault-tolerant section；
6) judgment step 5) time cumulative whether arrive time period threshold Td；If so, determining that the electric current is tail currents, hangover is set
Electric current distinguishing mark is 1, otherwise by the mark clear 0；
7) current sample values are preserved, such as formula (11)；
Ik-1=Ik(11)；
8) judgement of tail currents is carried out to remaining biphase current according to step 3) to step 7), and is given respectively according to judging result
Go out corresponding tail currents distinguishing mark.
2. a kind of method of identification tail currents based on current waveform neighbouring sample point ratio according to claim 1,
It is characterized in that, in the step 1), the solution procedure of P values is as follows：
The calculation formula of tail currents is as follows：
I (t)=I0×e-(t/τ) (1)
Wherein：I (t) is tail currents, I0Secondary side initial current when being disconnected for CT primary sides, τ are CT secondary side time constants,
By the tail currents represented by formula (1), sliding-model control is carried out, takes the value of -1 point of kth point and kth respectively, and calculate
The ratio of -1 point of kth point and kth, as shown in formula (2)：
Wherein：I(kTs) indicate kth point tail currents, I ((k-1) Ts) indicate -1 tail currents of kth, TsIt is filled for Microcomputer Protection
Set the sampling period.
3. a kind of method of identification tail currents based on current waveform neighbouring sample point ratio according to claim 1,
It is characterized in that, in the step 1), fault-tolerant processing is done to P values, it is (k to obtain fault-tolerant section1× P, k2× P), wherein k1With
k2Respectively represent the up-and-down boundary coefficient in fault-tolerant section, k1Value range is (0,1), k2Value range is (1, ∞).
4. a kind of method of identification tail currents based on current waveform neighbouring sample point ratio according to claim 3,
It is characterized in that, in the step 2), according to the fault-tolerant section (k in step 1)1× P, k2× P), estimation fault current waveform and
Tail currents have the sampling number of similitude, if there are N at fault current wave crest1A, there are N at trough2It is a, it takes
Then larger value in the two increases sampled data N the surplus of m points as sampled data N, and convert sampled data to
Time period threshold Td：
Td=(N+m-1) × Ts (5)
Wherein, TsFor the microcomputer protecting device sampling period.
5. a kind of method of identification tail currents based on current waveform neighbouring sample point ratio according to claim 1,
It is characterized in that, in the step 4), fault-tolerant processing refers to doing the sampled value to handle plus a minimum Δ, it is ensured that is in
The sampled value of divisor position is not zero, and the fault-tolerant processing will not cause step 5) to be judged by accident, such as formula (7)：
Ik-1=Ik-1+Δ (7)。
6. a kind of method of identification tail currents based on current waveform neighbouring sample point ratio according to claim 1,
It is characterized in that, in the step 1), the ratio of adjacent two sampled point is determined, not representing the two sampled points must be continuous, adopts
Ratio with discontinuous two sampled points is equally applicable.
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| CN110119696B (en) * | 2019-04-26 | 2023-07-14 | 三峡大学 | Current transformer tailing current identification method based on waveform characteristic difference |
| CN111797699A (en) * | 2020-06-10 | 2020-10-20 | 积成软件有限公司 | Method for identifying fault-removal CT trailing waveform |
| CN112736845B (en) * | 2020-12-31 | 2023-03-24 | 南京国电南自电网自动化有限公司 | CT trailing current identification method and device based on current phase angle difference calculation and failure protection method |
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