CN105021920A - Multiple characteristic identification method of excitation inrush current of main transformer - Google Patents
Multiple characteristic identification method of excitation inrush current of main transformer Download PDFInfo
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Abstract
The invention relates to a multiple characteristic identification method of the excitation inrush current of a main transformer, and belongs to the technical field of relay protection of the power system. The method comprises that characteristics of secondary harmonic, dead angle and CT saturation of the differential current wave are judged; when the excitation inrush current occurs, if the dead angle of the inrush current wage is relatively large and the content of the secondary harmonic is very high, and secondary harmonic can lock, and if the dead angle is relatively small and the content of the secondary harmonic is relatively low, the CT saturation is identified. Via the method, differential protection is not carried out for mistake when no-load of the main transformer is normal, differential protection is carried out rapidly on the transformer with faults, and the reliability of a main transformation protector is improved.
Description
Technical field
The present invention relates to a kind of main transformer excitation surge current multi-feature recognition method, belong to Relay Protection Technology in Power System field.
Background technology
Protective relaying device requires reliably to excise faulty equipment when system jam, ensure the safe and stable operation of system, but the harm that the incorrect operation of protective device (comprising tripping and malfunction) causes also is huge.
In recent years, the phenomenon of transform er differential protection misoperation when scene once occurred that 500kV autotransformer dropped.Record waveform during by dropping main transformer is analyzed, and find that excitation surge current secondary harmonic component is very little, be only about 12%, interval angle is about 90 degree.This situation generally occurs when main transformer has overhauled and put into operation, reason is for after detection main transformer winding D.C. resistance, do not require to carry out demagnetization process to master iron core according to maintenance procedure, master iron core is caused to contain larger remanent magnetism, if drop main transformer near voltage over zero simultaneously, and magnetic flux increase direction is consistent with remanence direction, will cause very large excitation surge current, and waveform is close to sinusoidal wave, secondary harmonic component is very low.
When preventing from dropping main transformer, the way one of differential protection malfunction is that requirement maintainer requires to carry out demagnetization process to master iron core after maintenance in strict accordance with maintenance procedure; Excitation surge current waveform when also adopting new algorithm saturated to the iron core degree of depth by protective device in addition identifies, thus differential protection malfunction when preventing main transformer from dropping.Current magnetizing inrush current discrimination method many employings 2 subharmonic differentiates or waveform recognition criterion; under low remanent magnetism; can correct decision excitation surge current latch-up protection; but in high remanent magnetism situation; 2 subharmonic comparision contents are low; waveform is close to sine wave simultaneously, there is the risk of excitation surge current protection misoperation.
Summary of the invention
The object of this invention is to provide a kind of main transformer excitation surge current multi-feature recognition method, during to solve the air-drop of main transformer height remanent magnetism, cause the problem of main transformer protection error action of device.
The present invention is for solving the problems of the technologies described above and providing a kind of main transformer excitation surge current multi-feature recognition method, and this recognition methods comprises the following steps:
1) gather the electric current of each side of transformer, and synthesize difference current, calculate the current amplitude of each phase difference current, judge whether the difference current amplitude of each phase is greater than criterion and starts threshold;
2) if so, calculate the secondary harmonic component of this phase difference current, judge whether its secondary harmonic component is greater than the highest setting value or is less than minimum setting value, if not, then calculus of differences is carried out to difference current;
3) calculate current waveform interval angle according to differentiated difference current, judge whether interval angle meets the demands, and determine whether that when meeting the demands CT is saturated; if CT is unsaturated; then be defined as excitation surge current, Blocking Differential Protection, otherwise open differential protection.
Described step 3) in interval angle differentiation by differentiate have how many sampled points to meet interval angle discrimination formula to realize, interval angle discrimination formula is:
Δi
K＜0.2min(|i
max|,I
n)
Wherein Δ i
kfor differentiated current sampling data, i
maxfor this cycle difference stream maximal value, I
nfor CT rated current, for every cycle N point sampling, if 13N/72 sampled point meets above formula continuously, be then judged to interval angle and meet.
Described step 3) in CT saturated be realize by judging that whether waveform maximum point identical with the symbol of preceding sample point, if identical, be then judged as that CT is unsaturated, otherwise, think that CT is saturated.
Described step 3) if in difference stream interval angle meet and do not meet the saturated criterion of CT, be judged to excitation surge current and this phase of locking differential protection; Otherwise be judged to non-excitation surge current, open this phase differential protection.
Described step 2) if in secondary harmonic component be greater than the highest setting value, then think this phase excitation surge current this phase of locking differential protection, if secondary harmonic component is less than minimum setting value, then think that this phase current is normally and open this phase differential protection.
Described step 2) in the highest setting value be 30%, minimum setting value is 7.5%.
Described step 2) difference equation that adopts is:
Δi
K＝C(i
K-i
K-2)
Wherein i
kfor current point sampled value, i
k-2for front 2 point sampling values, Δ i
kfor differentiated current sampling data, C is coefficient, relevant with sampling number N, C=N/4 π.
Described step 1) in difference current amplitude be not more than criterion and start threshold, then think that this phase current is normally and open this phase differential protection.
The invention has the beneficial effects as follows: second harmonic, interval angle and CT saturation characteristics that main transformer excitation surge current multi-feature recognition method of the present invention is used for difference current waveform differentiate, when there is excitation surge current, when inrush interval angle is larger, secondary harmonic component can be very high, can by second harmonic locking; When interval angle is smaller, secondary harmonic component is lower; now increase interval angle and the identification of CT saturation characteristics; the present invention adopts above-mentioned multi-feature recognition method to identify excitation surge current; make differential protection not malfunction when main transformer normally drops; quick acting during air-drop failure transformer, improves the reliability of main transformer protection device.
Accompanying drawing explanation
Fig. 1 is autotransformer high-pressure side air-drop current distributing figure.
Fig. 2 is main transformer excitation surge current multi-feature recognition method flow diagram;
Excitation surge current waveform and difference waveform figure thereof when Fig. 3 is the air-drop of main transformer height remanent magnetism;
Fig. 4 is the saturated waveform of troubles inside the sample space CT and difference waveform figure thereof when to be that main transformer is one-sided have a power supply.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described further.
Main transformer excitation surge current multi-feature recognition method is mainly used in the high-voltage relay protective device of intelligent grid; differentiated by the second harmonic to transformer differential current waveform, interval angle, CT saturation characteristics; when preventing sky from filling high remanent magnetism main transformer, excitation surge current second harmonic is too small causes differential protection malfunction, improves the reliability of main transformer protection device.Transform er differential protection electric current gets high voltage side of transformer CT, medium voltage side CT and low-pressure side CT, and the distribution of current during air-drop of high-pressure side as shown in Figure 1.
Main transformer excitation surge current multi-feature recognition method is as an independently functional module, and be integrated in main transformer protection device, this functional module drops into all the time, and its flow process as shown in Figure 2.First differentiate difference current size, if difference stream is greater than differentiation threshold, carry out second harmonic differentiation, otherwise open differential protection; Differentiate whether secondary harmonic component is less than 30%, if do not meet direct Blocking Differential Protection, differentiate whether secondary harmonic component is greater than 7.5 if meet, if do not meet, directly open differential protection, otherwise carry out next step; Difference current waveform is carried out difference processing; differentiate current waveform interval angle; if interval angle is greater than set angle (the present embodiment is 65 degree); waveform maximum point identical with the symbol of its preceding sample point (referring to the 4th point symbol above in the present embodiment) simultaneously; be defined as excitation surge current; Blocking Differential Protection, otherwise open differential protection.The feature of this criterion is saturated with excitation surge current feature for distinguishing CT, although CT is saturated all there is interval angle with excitation surge current, when the two difference is that CT is saturated, secondary current quickly falls near 0, and it is minimum to enter the saturated rear secondary harmonic component of stable state; Excitation surge current is when switching angle is near voltage over zero for large remanent magnetism simultaneously, and its waveform continuous part, close to sinusoidal wave, there will not be the moment reversion of current waveform slope, this with system impedance, Transformer Winding reactance is relevant.
This functional module differentiates differentiated difference current waveform interval angle and CT saturation characteristics, as shown in Figures 3 and 4.Because when transformer drops, excitation surge current waveform has interruption, current changing rate maximum point distance smallest point is far away simultaneously, be greater than 4 sampled point intervals, choosing the 4th sampled point above when judging CT state of saturation is to improve algorithm reliability, because after CT is saturated, electric current can suddenly change, but by every cycle sampling number, CT bis-leakage reactances and sampling filter loop affect the factor in conjunction with difference algorithm itself, cause the not necessarily opposite sign of 1-2 point before difference waveform maximal value, therefore certain surplus is considered, select the 4th sampled point above, algorithm reliability can be improved without when negative effect to algorithm.And CT saturated time, electric current is reduced to 0 fast, and before rate of change maximum point, the 4th slope sign is contrary with slope maximum point symbol, therefore identifies whether as sky fills excitation surge current by these features.
The concrete steps of main transformer excitation surge current multi-feature recognition method of the present invention are as follows:
1. first gather, calculate the difference current amplitude of A, B, C three-phase current, judge whether each phase difference current amplitude is greater than startup threshold, and the discriminant equation adopted is:
|I
dΦ|＞0.16I
B
Wherein I
d Φfor the amplitude of difference current A, the arbitrary phase current of B, C, I
bfor main transformer reference side electric current, if be not more than startup threshold, then the differential protection of this phase open.
If 2. difference current amplitude is greater than startup threshold, then calculate the secondary harmonic component of this phase difference current, judge whether secondary harmonic component is greater than the highest setting value or is less than minimum setting value, the highest setting value in the present embodiment is 30%, and minimum setting value is 7.5%; When the secondary harmonic component of difference current is greater than 30%, the differential protection of direct this phase of locking, when the secondary harmonic component of difference current is less than 7.5%, directly open differential protection.
If when 3. the secondary harmonic component of difference current is between 7.5% to 30%, difference current waveform is carried out difference, the difference equation adopted is:
Δi
K＝C(i
K-i
K-2)
I in above formula
kfor current point sampled value, i
k-2for front 2 point sampling values, Δ i
kfor differentiated current sampling data, C is coefficient, relevant with sampling number N, C=N/4 π.
4. pair differentiated difference current differentiates interval angle and whether has CT saturation characteristics, and the differentiation of interval angle size has how many sampled points to meet interval angle discrimination formula to realize by differentiating, interval angle discrimination formula is:
i
K＜0.2min(|i
max|,I
n)
In above formula, i
maxfor this cycle difference stream maximal value, I
nfor CT rated current, for every cycle N point sampling, if 13N/72 sampled point meets above formula continuously, be then judged to interval angle and meet; For 80 point samplings, should be continuous 14 sampled points and meet interval angle discrimination formula.
The method of discrimination of non-CT saturation characteristics is: judge this cycle difference stream maximal value i
maxwith the 4th i before it
xsymbol whether consistent, formula is as follows:
i
x·i
max＞0
If above formula meets, being judged to is not that CT is saturated, otherwise, think that CT is saturated.
5. compare the sampled point (in the present embodiment every cycle sample 80 points) in 1 cycle continuously, above condition meets and is then determined as excitation surge current, Blocking Differential Protection; Otherwise open differential protection.
Main transformer excitation surge current multi-feature recognition method carries out phase-splitting differentiation to the second harmonic of difference current waveform, interval angle, CT saturation characteristics, this phase of locking differential protection when certain phase current waveform of difference stream meets barring condition, other phase differential protection of not locking.When difference stream amplitude is less than criterion startup threshold, do not carry out the differentiation of described step 2 to step 5; If secondary harmonic component is less than 7.5% or be greater than 30%, namely do not carry out the differentiation of described step 3 to step 5, to alleviate the amount of calculation of protective device.
Claims (8)
1. a main transformer excitation surge current multi-feature recognition method, is characterized in that, this recognition methods comprises the following steps:
1) gather the electric current of each side of transformer, and synthesize difference current, calculate the current amplitude of each phase difference current, judge whether the difference current amplitude of each phase is greater than criterion and starts threshold;
2) if so, calculate the secondary harmonic component of this phase difference current, judge whether its secondary harmonic component is greater than the highest setting value or is less than minimum setting value, if not, then calculus of differences is carried out to difference current;
3) calculate current waveform interval angle according to differentiated difference current, judge whether interval angle meets the demands, and determine whether that when meeting the demands CT is saturated; if CT is unsaturated; then be defined as excitation surge current, Blocking Differential Protection, otherwise open differential protection.
2. main transformer excitation surge current multi-feature recognition method according to claim 1, is characterized in that, described step 3) in interval angle differentiation by differentiate have how many sampled points to meet interval angle discrimination formula to realize, interval angle discrimination formula is:
Δi
K＜0.2min(|i
max|,I
n)
Wherein Δ i
kfor differentiated current sampling data, i
maxfor this cycle difference stream maximal value, I
nfor CT rated current, for every cycle N point sampling, if 13N/72 sampled point meets above formula continuously, be then judged to interval angle and meet.
3. main transformer excitation surge current multi-feature recognition method according to claim 2, is characterized in that, described step 3) in CT saturated be realize by judging that whether waveform maximum point identical with the symbol of preceding sample point, if identical, then be judged as that CT is unsaturated, otherwise, think that CT is saturated.
4. main transformer excitation surge current multi-feature recognition method according to claim 3, is characterized in that, described step 3) if in difference stream interval angle meet and do not meet the saturated criterion of CT, be judged to excitation surge current and this phase of locking differential protection; Otherwise be judged to non-excitation surge current, open this phase differential protection.
5. main transformer excitation surge current multi-feature recognition method according to claim 1; it is characterized in that; described step 2) if in secondary harmonic component be greater than the highest setting value; then think this phase excitation surge current this phase of locking differential protection; if secondary harmonic component is less than minimum setting value, then think that this phase current normally also opens this phase differential protection.
6. main transformer excitation surge current multi-feature recognition method according to claim 5, is characterized in that, described step 2) in the highest setting value be 30%, minimum setting value is 7.5%.
7. main transformer excitation surge current multi-feature recognition method according to claim 1, is characterized in that, described step 2) difference equation that adopts is:
Δi
K＝C(i
K-i
K-2)
Wherein i
kfor current point sampled value, i
k-2for front 2 point sampling values, Δ i
kfor differentiated current sampling data, C is coefficient, relevant with sampling number N, C=N/4 π.
8. main transformer excitation surge current multi-feature recognition method according to claim 1, is characterized in that, described step 1) in difference current amplitude be not more than criterion and start threshold, then think that this phase current is normally and open this phase differential protection.
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Cited By (6)
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| CN105353258A (en) * | 2015-12-03 | 2016-02-24 | 新疆特变电工自控设备有限公司 | Test method for testing transformer differential protection anti-transformer inrush current |
| CN106207995A (en) * | 2016-08-23 | 2016-12-07 | 许继集团有限公司 | A kind of differential protecting method, device and the saturated recognition methods of CT, device |
| CN108134373A (en) * | 2017-12-28 | 2018-06-08 | 长园深瑞继保自动化有限公司 | Regulating compensation locking magnetizing inrush current of transformer method |
| CN108899871A (en) * | 2018-05-08 | 2018-11-27 | 广东电网有限责任公司 | A kind of recognition methods of excitation surge current, device and computer-readable medium |
| CN110350480A (en) * | 2019-06-10 | 2019-10-18 | 南京国电南自电网自动化有限公司 | A method of by scanning instantaneous excitation inductance value track identification excitation surge current |
| CN116298580A (en) * | 2022-12-09 | 2023-06-23 | 国家电网有限公司 | Transformer inrush current identification method and system based on waveform deviation and interruption characteristics |
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Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105353258A (en) * | 2015-12-03 | 2016-02-24 | 新疆特变电工自控设备有限公司 | Test method for testing transformer differential protection anti-transformer inrush current |
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| CN106207995A (en) * | 2016-08-23 | 2016-12-07 | 许继集团有限公司 | A kind of differential protecting method, device and the saturated recognition methods of CT, device |
| CN108134373A (en) * | 2017-12-28 | 2018-06-08 | 长园深瑞继保自动化有限公司 | Regulating compensation locking magnetizing inrush current of transformer method |
| CN108134373B (en) * | 2017-12-28 | 2019-12-24 | 长园深瑞继保自动化有限公司 | Voltage-regulating compensation transformer excitation inrush current locking method |
| CN108899871A (en) * | 2018-05-08 | 2018-11-27 | 广东电网有限责任公司 | A kind of recognition methods of excitation surge current, device and computer-readable medium |
| CN108899871B (en) * | 2018-05-08 | 2019-11-19 | 广东电网有限责任公司 | A kind of recognition methods of excitation surge current, device and computer-readable medium |
| CN110350480A (en) * | 2019-06-10 | 2019-10-18 | 南京国电南自电网自动化有限公司 | A method of by scanning instantaneous excitation inductance value track identification excitation surge current |
| CN116298580A (en) * | 2022-12-09 | 2023-06-23 | 国家电网有限公司 | Transformer inrush current identification method and system based on waveform deviation and interruption characteristics |
| CN116298580B (en) * | 2022-12-09 | 2024-04-02 | 国家电网有限公司 | Transformer inrush current identification method and system based on waveform deviation and interruption characteristics |
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