CN109980597B - Overcurrent protection method based on mirror image mutation starting - Google Patents
Overcurrent protection method based on mirror image mutation starting Download PDFInfo
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- 230000035772 mutation Effects 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 title claims abstract description 31
- 238000005070 sampling Methods 0.000 claims description 39
- 230000008859 change Effects 0.000 claims description 10
- 230000035945 sensitivity Effects 0.000 abstract description 4
- 230000007613 environmental effect Effects 0.000 abstract description 2
- 238000004364 calculation method Methods 0.000 description 12
- 238000010586 diagram Methods 0.000 description 6
- 230000002159 abnormal effect Effects 0.000 description 4
- 208000025274 Lightning injury Diseases 0.000 description 2
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- 230000016507 interphase Effects 0.000 description 2
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/006—Calibration or setting of parameters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
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- 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
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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Abstract
The invention discloses an overcurrent protection method based on mirror image mutation starting, which is characterized in that after a mutation is detected, the latest half cycle is compared with the former half cycle point by taking the mirror image value of the latest half cycle and then is subjected to difference value comparison on the basis of the traditional method of judging the mutation only once, so that whether the first detected mutation starting is real and has a fault or mutation mis-starting caused by the interference of external environmental factors is determined. The method can judge the start of the abrupt variable again through the mirror image waveform of the subsequent half cycle after the protection is started for the first time, avoids the protection maloperation caused by the influence of the external environment under the condition of ensuring the protection sensitivity, and improves the reliability of the protection.
Description
Technical Field
The invention relates to the technical field of relay protection of a power system, in particular to an overcurrent protection method based on mirror image mutation starting.
Background
The power distribution network terminal is used as basic equipment of the power distribution automation system, and stable and reliable operation of the power distribution network terminal has decisive influence on whether the whole power distribution network automation system can normally operate and play a role. Reliable operation of the distribution network terminal, in addition to performing the basic "four remote" function, also needs to be able to detect and quickly remove faults. The interphase overcurrent protection realizes protection by utilizing the characteristic that the phase current obviously rises when an interphase short circuit fault occurs in a power system, has the advantages of quick action, simplicity, reliability and easiness in setting management, and becomes a main protection form in a power distribution network. The protection process comprises two steps of starting detection and short circuit judgment. After overcurrent starting is detected, a tripping command is immediately sent to remove the fault when the short-circuit current is judged to exceed a setting value.
However, the power distribution terminal is often installed outdoors, so that the operation environment is severe, the power distribution terminal is more easily influenced by surge signals of external environments such as lightning stroke and the like, the protection misoperation is easily generated, unnecessary power failure accidents are caused, and the power supply reliability is reduced. For the interference, the overcurrent algorithm needs to be further optimized by analyzing the characteristics of sampling, so that the power distribution network terminal is ensured not to malfunction when being interfered, and the reliability and the sensitivity of protection are further ensured.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides an overcurrent protection method based on mirror image mutation starting, which determines whether a fault really occurs or sampling jitter caused by interference is caused by a mirror image mutation method when a stage of judging whether an overcurrent value exceeds a current threshold value is entered after a protection pre-starting stage, thereby solving the false operation of a power distribution network terminal caused by surge signals of external environments such as lightning stroke and the like, ensuring the protection sensitivity and improving the protection reliability.
In order to achieve the above purpose, the invention adopts the following technical scheme: an overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps:
step 1: the data acquisition device acquires phase current of a protected line; circularly storing the sampling values of the latest two cycles;
step 2: calculating phase current abrupt change quantity by using a point-by-point comparison method of a formula (1) every other half cycle to obtain a difference value Diff;
Diff＝abs(Cur_pos-Pre_pos) (1)
in the formula, Cur _ pos represents a sampling value pointed by the start pointer of the latest cycle sampling point, and Pre _ pos represents a sampling value pointed by the start pointer of the previous cycle sampling point;
and step 3: judging the size of the difference Diff according to the formula (2), if the difference Diff meets the formula (2), adding 1 to the mutation quantity number brkVarCount, and if the difference Diff does not meet the formula, setting the difference to be 0;
Diff>DIFFDZ (2)
in the formula, DIFFDZStarting a fixed value for the amount of mutation;
and 4, step 4: judging the size of the number brkVarCount of the break variable according to the formula (3), and setting an overcurrent protection pre-starting signal as 1 if the formula (3) is met;
brkVarCount>BRKVARCOUNTDZ (3)
in the formula, BRKVARCOUNTDZContinuously starting the number of the mutation quantity to obtain a fixed value;
and 5: after the next half cycle sampling comes, if the 'pre-start' signal is detected to be 1, the latest half cycle sampling value is taken as a mirror image value along the time axis, and is expressed as '-New _ pos', and the phase current break variable is calculated by using the mirror image value through a point-by-point comparison method according to a formula (4):
New_Diff＝abs(-New_pos-Pre_pos) (4)
step 6: determine if the newly computed New _ Diff is greater than DIFFDZIf yes, adding 1 to the new mutation quantity number newBrkVarCount, and if not, setting the new mutation quantity number newBrkVarCount as 0;
and 7: judging whether the new mutation quantity number newBrkVarCount is larger than BRKVARCOUNTDZIf yes, setting an overcurrent starting signal as 1;
and 8: and 7, immediately calculating the effective value of the current phase current of the latest cycle when the step 7 is finished, and recording the fault current value as If；
And step 9: according to the formula (5), whether a start signal exists or not and whether the fault current is greater than an overcurrent fixed value I or not are judgeddzAnd if the fault condition meets the condition (5), the fault condition is a real overcurrent fault, and the data acquisition device sends a relay protection outlet trip command to remove the fault:
(Act＝＝1)&&(If>Idz) (5)。
the overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps: and in the step 1, the minimum sampling frequency of the sampling values of the latest two cycles is 1 kHz.
The overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps: in step 2, the burst variable is detected every half cycle, namely 10 ms.
The overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps: the break variable start-up fixed value DIFFDZThe flexible setting is carried out according to different occasions.
The aforesaid one is based on mirror mutationThe overcurrent protection method of volume start is characterized in that: the number of continuously started sudden change quantity fixed BRKVARCOUNTDZAll are flexibly arranged according to different occasions.
The overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps: and the Fourier algorithm is adopted to calculate the effective value of the current phase current of the latest cycle.
The invention achieves the following beneficial effects: the method can judge the start of the abrupt variable again through the mirror image waveform of the subsequent half cycle after the protection is started for the first time, avoids the protection maloperation caused by the influence of the external environment under the condition of ensuring the protection sensitivity, and improves the reliability of the protection.
Drawings
FIG. 1 is a current recording waveform diagram of a normal phase-to-phase fault;
FIG. 2 is a waveform of current recording with jitter caused by external disturbances;
FIG. 3 is a normal overcurrent fault sampling instant and mirror waveform diagram;
fig. 4 is a waveform diagram of sampling time and mirror image of an abnormal over-current fault.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
FIG. 1 is a waveform diagram of current recording of normal phase-to-phase fault; fig. 2 is a waveform diagram of current recording caused by jitter due to external disturbance, i.e. an abnormal overcurrent fault waveform diagram.
In the first embodiment, in the method for determining a normal overcurrent fault, it is assumed that the acquired overcurrent fault waveform is shown in fig. 1, and the acquired time is marked and then shown in fig. 3;
in fig. 3, the parameters are explained as follows.
t 0: starting point of fault moment;
t 1: starting point of the first half cycle after the fault;
t 2: starting point of the 2 nd half cycle after the fault;
t 10: starting point of half cycle moment before failure;
t 20: starting point of whole cycle time before failure;
new _ pos: sampling values pointed by a sampling point starting pointer of a second half cycle at a fault moment;
the method for judging normal overcurrent fault comprises the following steps:
collecting the current of a line, and circularly storing the latest two cycle sampling values, namely two cycles between two moments of t20-t0 and t0-t2 in the figure 3;
calculating point-by-point difference values of the sampling point of the half cycle in the period from t0 to t1 and the sampling point of the half cycle in the period from t20 to t10 to obtain a calculation difference point, taking the absolute value of the calculation result, judging that 4 continuous difference points are greater than a specified threshold value, and setting an overcurrent protection pre-starting signal to be 1;
negating the half cycle wave in the period of t1-t2 along the t axis to obtain a mirror image sampling waveform, carrying out point-by-point difference calculation on the sampling point of the half cycle wave in the period of t1-t2 and the sampling point of the half cycle wave in the period of t20-t10 after mirroring to obtain a calculation difference, taking the absolute value of the calculation result, judging that 4 continuous difference points are larger than a specified threshold value, and setting an overcurrent 'starting' signal as 1;
calculating the effective value I of the current of the whole cycle in the period t0-t2 by a Fourier algorithmfAnd comparing the protection current with the overcurrent fixed value, wherein the effective value is greater than the overcurrent fixed value, and the data acquisition device sends a relay protection outlet trip command to remove the fault.
In the second embodiment, the method for determining an abnormal overcurrent fault assumes that the waveform of the collected overcurrent fault is shown in fig. 2, and is shown in fig. 4 after the collection time is marked,
the method for judging the abnormal overcurrent fault comprises the following steps:
collecting the current of a line, and storing the latest two cycle sampling points, namely two cycles between two moments of t20-t0 and t0-t2 in fig. 3;
calculating point-by-point difference values of sampling points of the half cycle wave in the period from t0 to t1 and sampling points of the half cycle wave in the period from t20 to t10 to obtain a calculation difference value, taking an absolute value of a calculation result, judging that 4 continuous difference values are larger than a specified threshold value, and setting an overcurrent protection pre-starting signal to be 1;
and (3) negating the half cycle wave in the period of t1-t2 along the t axis to obtain a mirror image sampling waveform, carrying out point-by-point difference calculation on the sampling point of the half cycle wave in the period of t1-t2 and the sampling point of the half cycle wave in the period of t20-t10 after mirroring to obtain a calculation difference, taking the absolute value of the calculation result, judging that no continuous 4 difference points are greater than a specified threshold value, setting an overcurrent starting signal to be 0, clearing a pre-starting mark to be 0, and entering the next sampling period judgment.
The invention relates to an overcurrent protection method based on mirror image mutation starting, which is characterized in that after a mutation is detected, a difference value is compared point by point between a mirror image value of the latest half cycle and a first half cycle value of the previous cycle after the mutation is detected on the basis of the conventional judgment of the mutation only once, and the difference value is used for determining whether the first detected mutation starting is real and has a fault or mutation misstarting caused by the interference of external environmental factors.
When an unreal fault occurs, the power distribution terminal device sends a protection pre-starting signal, and because of sudden change pre-starting caused by interference, the sudden change disappears in the next half cycle sampling, so that the difference obtained according to the mirror image sudden change starting algorithm cannot meet the condition that a plurality of continuous points cross a threshold value, and the power distribution terminal device cannot send a real protection starting signal, namely, the power distribution terminal protection misoperation caused by external interference is avoided.
When a real fault occurs, the power distribution terminal device sends a protection pre-starting signal, and because of sudden change pre-starting caused by non-interference, the sudden change does not disappear in the next half cycle sampling, so the difference obtained according to the mirror image sudden change starting algorithm still meets the condition that a plurality of continuous points cross a threshold value, the power distribution terminal device sends a real protection starting signal, meanwhile, the magnitude of the current protection current is obtained through Fourier calculation, and if the current protection current is greater than an overcurrent fixed value, a protection tripping command is sent to remove the fault.
Because the judgment of the starting result of the mirror image mutation quantity and the calculation of the magnitude of the protection current are completed in the same task period, the judgment of the mirror image mutation starting does not increase the time of a protection outlet, the quick action of the overcurrent protection is ensured, and meanwhile, the reliability of the overcurrent protection is improved because of secondary judgment.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (6)
1. An overcurrent protection method based on mirror image mutation starting is characterized by comprising the following steps:
step 1: the data acquisition device acquires phase current of a protected line; circularly storing the sampling values of the latest two cycles;
step 2: calculating phase current abrupt change quantity by using a point-by-point comparison method of a formula (1) every other half cycle to obtain a difference value Diff;
Diff＝abs(Cur_pos-Pre_pos) (1)
in the formula, Cur _ pos represents a sampling value pointed by the start pointer of the latest cycle sampling point, and Pre _ pos represents a sampling value pointed by the start pointer of the previous cycle sampling point; abs () represents the absolute value;
and step 3: judging the size of the difference Diff according to the formula (2), if the difference Diff meets the formula (2), adding 1 to the mutation quantity number brkVarCount, and if the difference Diff does not meet the formula, setting the difference to be 0;
Diff>DIFFDZ (2)
in the formula, DIFFDZStarting a fixed value for the amount of mutation;
and 4, step 4: judging the size of the number brkVarCount of the break variable according to the formula (3), and setting an overcurrent protection pre-starting signal as 1 if the formula (3) is met;
brkVarCount>BRKVARCOUNTDZ (3)
in the formula, BRKVARCOUNTDZContinuously starting the number of the mutation quantity to obtain a fixed value;
and 5: after the next half cycle sampling comes, when detecting that a 'pre-start' signal is 1, taking a mirror image value of the latest half cycle sampling value along a time axis, and representing the mirror image value as '-New _ pos', and calculating a phase current break variable by using the mirror image value through a point-by-point comparison method according to a formula (4):
New_Diff＝abs(-New_pos-Pre_pos) (4)
step 6: judging whether the newly calculated difference New _ Diff is larger than DIFF or notDZIf yes, adding 1 to the new mutation quantity number newBrkVarCount, and if not, setting the new mutation quantity number newBrkVarCount as 0;
and 7: judging whether the new mutation quantity number newBrkVarCount is larger than BRKVARCOUNTDZIf yes, setting an overcurrent starting signal as 1;
and 8: and 7, immediately calculating the effective value of the current phase current of the latest cycle when the step 7 is finished, and recording the fault current value as If；
And step 9: according to the formula (5), whether a start signal exists or not and whether the fault current is greater than an overcurrent fixed value I or not are judgeddzAnd if the fault condition meets the condition (5), the fault condition is a real overcurrent fault, and the data acquisition device sends a relay protection outlet trip command to remove the fault:
(Act＝＝1)&&(If>Idz) (5)
where Act ═ 1 indicates that there is a "start" signal, IfIs a fault current.
2. The overcurrent protection method based on mirror image mutation starting as set forth in claim 1, wherein: and in the step 1, the minimum sampling frequency of the sampling values of the latest two cycles is 1 kHz.
3. The overcurrent protection method based on mirror image mutation starting as set forth in claim 1, wherein: in step 2, the burst variable is detected every half cycle, namely 10 ms.
4. The overcurrent protection method based on mirror image mutation starting as set forth in claim 1, wherein: the break variable start-up fixed value DIFFDZCan be carried out according to different occasionsAnd (4) setting actively.
5. The overcurrent protection method based on mirror image mutation starting as set forth in claim 1, wherein: the number of continuously started sudden change quantity fixed BRKVARCOUNTDZAll are flexibly arranged according to different occasions.
6. The overcurrent protection method based on mirror image mutation starting as set forth in claim 1, wherein: and the Fourier algorithm is adopted to calculate the effective value of the current phase current of the latest cycle.
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