CN108134373B - Voltage-regulating compensation transformer excitation inrush current locking method - Google Patents
Voltage-regulating compensation transformer excitation inrush current locking method Download PDFInfo
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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
- H02H7/04—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
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Abstract
A method for locking magnetizing inrush current of a voltage regulating and compensating transformer relates to a method for relay protection of a power system, in particular to a method for locking the magnetizing inrush current of the voltage regulating and compensating transformer in an extra-high voltage power grid. The method comprises the following steps: calculating direct current components, fundamental waves, second harmonic waves, third harmonic waves and waveform asymmetry of phase currents on each side of the transformer and phase difference currents on each longitudinal difference of the transformer, and calculating a floating excitation inrush current comprehensive locking fixed value; according to the calculation result, calculating an inrush current coefficient comprehensive criterion, and comparing the criterion value with an excitation inrush current comprehensive locking fixed value to give a harmonic content mark; calculating by using fundamental wave current, and juxtaposing phase splitting action marks; and identifying whether the transformer is magnetizing inrush current or internal fault according to the calculated phase splitting action mark and the magnetizing inrush current locking mark, and implementing protection on the transformer. The invention can ensure the quick action when the air-drop occurs in the area, and can also ensure the reliable locking through the floating threshold when the internal constant value of the excitation surge current is close.
Description
Technical Field
The invention relates to a relay protection method for a power system, in particular to a method for locking excitation inrush current of a voltage regulation and compensation transformer in an extra-high voltage power grid.
Background
In order to improve the efficiency of the transformer and reduce the size of the transformer, an auto-transformer is generally selected for a high-capacity ultrahigh voltage grade, and the auto-transformer has the advantage of improving the stability of a system in an extra-high voltage power grid. The extra-high voltage autotransformer generally comprises a main transformer and a voltage regulating compensation transformer, and the unique configuration of the autotransformer provides new requirements for excitation inrush current locking differential protection.
In the voltage recovery process after the transformer is put into a power supply in no-load or external faults are removed, the magnetic flux in the iron core of the transformer is increased sharply, the iron core is saturated instantly, and large excitation inrush current with attenuation characteristics occurs. The excitation inrush current flows into a differential circuit through a current transformer on the power supply side, and protection misoperation is caused if no measures for avoiding the excitation inrush current are taken.
For a long time, when implementing transformer differential protection, the contradiction between the maximum unbalanced current of relay protection to the external fault and the sensitivity of the internal fault is solved by adopting a ratio braking method, and the braking characteristic of the ratio braking method is composed of three wire sections. The method for correctly identifying the magnetizing inrush current and the internal fault mainly comprises a second harmonic braking method, a waveform identification method and the like.
The conventional second harmonic inrush braking method is to latch all three-phase rate differential protection at any phase-difference inrush braking, referred to as "or" braking logic. The phase ratio differential protection, namely the split-phase braking mode, is locked when the single-phase differential inrush current is braked, and is called as 'AND' braking logic. If braking is performed by using only the or braking logic, the operation speed of the differential protection may be slow when the differential protection is thrown into a fault transformer. If the AND brake logic braking is used, the differential protection may be mistaken when the transformer is thrown into a fault-free transformer.
With the increase of the working magnetic flux density of the power transformer, the content of the second harmonic in the magnetizing inrush current is reduced, so that the traditional second harmonic braking criterion cannot effectively lock differential protection. In practical engineering application, multiple transformer misoperation events caused by the harmonic braking coefficient setting value have occurred, and if the harmonic braking coefficient setting value is reduced, the sensitivity of the differential protection of the transformer is reduced. Meanwhile, in the application of the extra-high voltage regulating and compensating transformer, the condition of extremely low magnetizing inrush current exists, the content of secondary harmonic is about 5-8%, the traditional magnetizing inrush current criterion cannot effectively lock differential protection, and the possibility of misoperation exists. In addition, the requirements of supplementary notes on Q/GDW 1161-: and canceling the second harmonic locking control word and the constant value. The regulation releases the constraint on the traditional magnetizing inrush current principle and encourages relay protection manufacturers to adopt comprehensive criteria to improve the characteristics of the device.
Disclosure of Invention
The invention aims to provide a method for locking the magnetizing inrush current of a voltage regulating and compensating transformer, which can correctly identify the magnetizing inrush current and internal faults, improve the reliability of relay protection on the basis of ensuring the speed and ensure the safe operation of a power system.
The invention aims to realize the purpose, and designs a method for locking the magnetizing inrush current of the voltage regulating and compensating transformer, which comprises the following steps:
A. calculating the direct current component, fundamental wave, second harmonic wave, third harmonic wave and waveform asymmetry of each side phase current of the transformer and the direct current component, fundamental wave, second harmonic wave, third harmonic wave and waveform asymmetry of each phase difference current of the longitudinal difference of the transformer;
the calculation formulas of fundamental wave, second harmonic wave and third harmonic wave are as follows:
real part:
imaginary part:
amplitude value:
in the formula, N: 1 cycle sampling point number of the fundamental wave signal; n: starting a sampling point; m: the mth harmonic corresponds to the fundamental wave, the second harmonic and the third harmonic when m is 1, 2 and 3; i (k): sampling the current for the kth time;
extracting a direct current component in the original sampling current, wherein the direct current component and the direct current component weight calculation formula are as follows:
in the formula I0Is a direct current component, N0Number of sampling points, i, for power frequency waveformkFor instantaneous sampled values of the original current, K0As a weight of the DC component, I1Is the fundamental current amplitude;
the formula for calculating the waveform asymmetry is as follows:
in the formula Ii' is the value at a point in the first half-wave of the derivative,the numerical value of the corresponding point of the second half wave of the derivative, D is the waveform asymmetry;
B. calculating a floating excitation inrush current comprehensive locking constant value;
the floating excitation inrush current comprehensive locking constant value calculation formula is as follows:
wherein: ksetK is a comprehensive locking constant value of the excitation surge current and is more than or equal to 0.05setLess than or equal to 0.15; t is the floating time of the excitation inrush current comprehensive locking fixed value set by a program; t is an air-drop counter and is decreased to 0 from the air-drop moment, and T is more than or equal to 0 and less than or equal to T;
C. calculating an inrush current coefficient comprehensive criterion according to the longitudinal difference differential current and the calculation results of the direct current component, the fundamental wave, the second harmonic, the third harmonic and the waveform asymmetry of each side phase current, and comparing the criterion value with a floating excitation inrush current comprehensive locking fixed value to give a harmonic content mark; if the calculated inrush current coefficient comprehensive criterion is larger than the floating inrush current comprehensive locking fixed value, the calculated inrush current coefficient comprehensive criterion is regarded that the inrush current locks the flag variable of the inrush current to be 1, and if not, the calculated inrush current coefficient comprehensive criterion is set to be 0;
the formula of the excitation inrush current criterion is as follows:
K＝(C0×K0+C2)×K2+C3×K3+Cd×D
wherein, K0Is the weight of the direct current component; k2Second harmonic weights; k3Third harmonic weight; d, waveform asymmetry; c0DC component helps increase the second harmonic coefficient, C0＝0.8；C2Second harmonic coefficient, C2＝1；C3Coefficient of third harmonic, C3＝0.1；CdWave form asymmetry coefficient, Cd＝0.1。
D. Calculating by using fundamental wave current, and juxtaposing phase splitting action marks;
E. identifying whether the phase-splitting action mark is magnetizing inrush current or internal fault according to the calculated phase-splitting action mark and the magnetizing inrush current locking mark, and implementing protection on the transformer; when each phase comparison difference action is judged, firstly judging a phase splitting action mark, if the phase splitting action mark is 1, further judging whether the phase difference current harmonic mark is 1, if the phase difference current harmonic mark is 1, locking the phase protection; if the differential current harmonic mark is 0, judging the current harmonic mark of the differential current relevant side, if the phase current harmonic marks of the relevant sides are all 1, locking the phase differential motion protection, otherwise, acting the phase differential motion protection; in the three-phase differential protection, the longitudinal differential protection operates as long as one phase differential satisfies the operating condition.
Further, a second harmonic weight calculation formula:
in the formula, K2Representing the second harmonic weight, I1Is the amplitude of the fundamental current, I2Is the second harmonic current amplitude;
third harmonic weight calculation formula:
wherein, K3Representing the third harmonic weight, I1Is the amplitude of the fundamental current, I3The third harmonic current amplitude.
Furthermore, the number of the sampling points is 20-48 points.
Further, the amplitude bias weight is a DC component weight K0Multiplying by a second harmonic weight K2。
Further, the air-drop determination threshold is 0.08In, which is the sampling value differential current.
According to the invention, from the physical cause of the excitation inrush current, richer sample current and harmonic components are selected, and the direct current component, the second harmonic, the third harmonic and the waveform asymmetry in each phase current and differential current are calculated and extracted; original second harmonic and waveform identification results are integrated, and third harmonic discrimination is added; the excitation inrush current comprehensive locking fixed value floating in an inverse time limit based on a cosine function is originally introduced, and inverse time limit processing is carried out on the excitation inrush current harmonic locking internal fixed value of the protection device, so that self-adaption of the threshold is realized; when differential current excitation inrush current is judged, relevant side excitation inrush current judgment is added, so that the quick-acting property of air-drop in an area failure can be guaranteed, and reliable locking can be realized when the air-drop is performed on a normal transformer.
Drawings
FIG. 1 is a flow chart of the differential harmonic determination according to the preferred embodiment of the present invention;
FIG. 2 is a flow chart of differential protection according to a preferred embodiment of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples.
As shown in fig. 1, a data acquisition unit (a small current and voltage transformer inside the device) of the device obtains an analog current input quantity of each side of the transformer, converts the analog quantity into a digital quantity through analog/digital conversion, and calculates the data as an instantaneous sampling value by a data processing unit (a vector calculation module) to calculate the amplitudes of a fundamental wave, a second harmonic and a third harmonic of the current of each side. And calculating a direct current component by using a direct current calculation algorithm.
The calculation formulas for calculating fundamental wave, second harmonic wave and third harmonic wave are as follows:
real part:
imaginary part:
amplitude value:
in the formula, N: the number of sampling points of 1 cycle of the fundamental wave signal is 24 in the embodiment; n: starting a sampling point; m: the mth harmonic corresponds to the fundamental wave, the second harmonic and the third harmonic when m is 1, 2 and 3; i (k): the kth current sample.
And the data processing unit converts the current of the middle and low voltage sides of the transformer to the high voltage side, and calculates to obtain each phase difference current of the transformer. And calculating the amplitudes of fundamental wave, second harmonic wave and third harmonic wave in the differential flow by a Fourier algorithm, and calculating the differential flow direct current component by a direct current calculation algorithm.
During the empty charging period, the data processing unit calculates the excitation surge current comprehensive locking fixed value K according to the cosine inverse time-limit characteristic functionsetDuring the empty charge, the threshold floats according to the cosine function characteristic. And during the non-empty charging period, the excitation inrush current comprehensive locking fixed value adopts a fixed value.
The floating excitation inrush current comprehensive locking constant value calculation formula is as follows:
wherein: ksetFor the floating excitation surge current comprehensive locking constant value, K is more than or equal to 0.05setLess than or equal to 0.15; t is the floating time of the excitation inrush current comprehensive locking fixed value set by a program; t is an airdrop counter, from skyThe throwing time is decreased to 0, T is more than or equal to 0 and less than or equal to T.
The data processing unit calculates the second harmonic weight K of the current and the differential current of each side of the transformer2The data processing unit obtains the fundamental wave I of each phase according to the calculation1And second harmonic of each phase I2And calculating the weight of the second harmonic. The calculation formula is as follows:
in the formula, K1Representing the second harmonic weight, I1Is the amplitude of the fundamental current, I2The second harmonic current amplitude.
The data processing unit calculates the third harmonic weight K of the current and the differential current of each side of the transformer3The data processing unit obtains the fundamental wave I of each phase according to the calculation1And third harmonic I of each phase3And calculating the weight of the third harmonic. The calculation formula is as follows:
in the formula, K3Representing the third harmonic weight, I1Is the amplitude of the fundamental current, I3The third harmonic current amplitude.
The data processing unit calculates the direct current component and the direct current component weight of each side current and the differential current. Extracting a direct current component in the original sampling current, wherein the direct current component and the direct current component weight calculation formula are as follows:
in the formula, N0The number of sampling points of the power frequency waveform is 20-48, ikFor instantaneous sampled values of the original current, K0As a weight of the DC component, I1Is the amplitude of the fundamental current。
The harmonic locking criterion is boosted by using richer direct-current components in the excitation surge current, so that the surge current resistance of a certain phase with lower second harmonic content is improved, and the phase differential protection is ensured to be locked reliably during normal empty charging.
The data processing unit calculates the waveform asymmetry. When the fault occurs, a certain phase current is basically a power frequency sine wave, and when the excitation inrush current exists, a large amount of harmonic components exist, so that the waveform is distorted, discontinuous and asymmetric. The formula for identifying this distortion using an algorithm is:
in the formula Ii' is the value at a point in the first half-wave of the derivative,the value of the corresponding point of the second half wave of the derivative is obtained; and D is the waveform asymmetry.
The waveform asymmetry has strong identification capability on all even harmonics in the aspect of information extraction of a certain phase current waveform. It is considered that the smaller D is, the more failure information is included in the waveform, whereas the larger D is, the more magnetizing inrush current information is included in the waveform.
According to the amplitude of each phase difference current, the direct current component, the second harmonic current and the weight of the waveform asymmetry, calculating to obtain a corresponding excitation inrush current coefficient comprehensive criterion:
K＝(C0×K0+C2)×K2+C3×K3+Cd×D
wherein, K0: a direct current component weight; k2: second harmonic weights; k3: third harmonic weight; d: the asymmetry degree of the waveform; c0For increasing the second harmonic coefficient, C, by the DC component0＝0.8；C2Is the second harmonic coefficient, C2＝1；C3Is the coefficient of the third harmonic, C3＝0.1；CdIs a waveform asymmetry coefficient, Cd＝0.1。
Respectively calculating according to the formula to obtain comprehensive criterion K of comprehensive excitation inrush current coefficient of each phaseA、KB、KCAnd comparing the value with a comprehensive locking fixed value of the magnetizing inrush current based on the inverse time-lag characteristic of the cosine function to give a harmonic content mark. And if the calculated inrush current coefficient comprehensive criterion is larger than the current value of the floating inrush current comprehensive locking constant value, setting the magnetizing inrush current locking sign variable to be 1, and otherwise, setting the magnetizing inrush current locking sign variable to be 0. When K isA>KsetSetting the A phase harmonic mark as 1, otherwise, clearing the A phase harmonic mark and setting the A phase harmonic mark as 0; when K isB>KsetSetting a B-phase harmonic mark as 1, otherwise, clearing the B-phase harmonic mark and setting the B-phase harmonic mark as 0; when K isC>KsetOtherwise, the C phase harmonic wave flag is cleared and set to 0.
And calculating by using the fundamental current according to the three-fold line characteristic of the ratio differential, wherein if the fundamental current meets a three-fold line threshold, the phase setting action mark is 1, and if not, the phase setting action mark is 0.
As shown in fig. 2, the apparatus recognizes the inrush current and the internal fault based on the phase splitting operation flag and the harmonic flag of the apparatus, and protects the transformer. When each phase comparison difference action is judged, firstly judging a phase splitting action mark, if the phase splitting action mark is 1, further judging whether the phase difference current harmonic mark is 1, if the phase difference current harmonic mark is 1, locking the phase protection; if the differential current harmonic mark is 0, the related side current harmonic mark is judged, if each side phase current harmonic mark is 1, the phase protection is locked, otherwise, the phase difference acts. In the three-phase differential protection, the longitudinal differential protection is carried out as long as one phase differential meets the action condition.
As shown in fig. 2, firstly, it is determined whether the phase a differential current satisfies an operation threshold, if not, the phase B is determined, if yes, the phase a differential current harmonic identification or the phase a current harmonic identification of each side is determined, if the harmonic identification is 1, the phase a protection is locked, otherwise, the phase a differential operation is performed; judging whether the phase difference B current meets an action threshold, if not, judging the phase C, if so, judging the phase B current harmonic identification or the phase B current harmonic identification on each side, if the harmonic identification is 1, locking the phase B protection, otherwise, moving the phase B; judging whether the phase difference current C meets an action threshold, if not, judging the number of action phases, if so, judging the phase difference current C harmonic identification or the phase C current harmonic identification on each side, if the harmonic identification is 1, locking the phase C protection, otherwise, moving the phase C; and (4) judging whether the number of the entering action phases is more than or equal to 1, if so, setting the differential protection action mark as 1, and otherwise, clearing the differential protection action mark as 0.
The invention ensures that the differential protection can still quickly and sensitively act when the air-drop transformer is in fault, and the normal air-charge differential protection does not act by mistake. In the actual operation process, when an internal fault occurs, the fault phase second harmonic and the waveform symmetry tend to zero, the bias current is small, and the fault phase calculated according to the formula is open in dynamic protection and reliable and correct in action. When the transformer is empty charged in the internal fault, the condition is similar, and the transformer can reliably and correctly act. And in normal empty charging, although the waveform is symmetrical, the contents of second harmonic and third harmonic are high, the weight of direct current component is large, and the magnetizing inrush current locking fixed value based on inverse time-lag cosine function is adopted, and at the moment, the magnetizing inrush current coefficient comprehensive criterion calculated by the formula exceeds the floating magnetizing inrush current comprehensive locking fixed value, so that the corresponding phase is locked, and the device is ensured to be locked reliably.
Example 1: in the process of the voltage regulating compensation transformer empty charging, the content of the second harmonic wave of the voltage regulating compensation transformer is possibly lower than 10 percent, so that the condition of misoperation is easy to occur by adopting a conventional inrush current judging device during the empty charging, at the moment, the excitation inrush current comprehensive locking fixed value floating in an inverse time limit is adopted, the locking value self-adaption characteristic is presented, and the risk of the voltage regulating compensation transformer empty charging misoperation is effectively reduced; in addition, on the basis of judging the second harmonic, the direct-current component, the third harmonic and the waveform asymmetry are additionally judged, the device can be effectively locked, and the protection against misoperation during empty charging is ensured.
Example 2: in the process of the voltage-regulating compensation transformer empty charging, the differential inrush current coefficient comprehensive criterion of the voltage-regulating compensation transformer is possibly lower than the excitation inrush current comprehensive locking fixed value, and at the moment, the harmonic contents of the high side and the low side of the transformer are both larger than the excitation inrush current comprehensive locking fixed value.
The invention can ensure the quick action when the air drop occurs in the area, and can also ensure the reliable locking realized by the floating excitation surge current comprehensive locking constant value when the internal constant value of the excitation surge current is close to the internal constant value.
Claims (5)
1. A method for locking magnetizing inrush current of a voltage regulating and compensating transformer is characterized by comprising the following steps:
A. calculating the direct current component, fundamental wave, second harmonic wave, third harmonic wave and waveform asymmetry of each side phase current of the transformer and the direct current component, fundamental wave, second harmonic wave, third harmonic wave and waveform asymmetry of each phase difference current of the longitudinal difference of the transformer;
the calculation formulas of fundamental wave, second harmonic wave and third harmonic wave are as follows:
real part:
imaginary part:
amplitude value:
in the formula, N: 1 cycle sampling point number of the fundamental wave signal; n: starting a sampling point; m: the mth harmonic corresponds to the fundamental wave, the second harmonic and the third harmonic when m is 1, 2 and 3; i (k): sampling the current for the kth time;
extracting a direct current component in the original sampling current, wherein the direct current component and the direct current component weight calculation formula are as follows:
in the formula I0Is a direct current component, N0Number of sampling points, i, for power frequency waveformkFor instantaneous sampled values of the original current, K0As a weight of the DC component, I1Is the fundamental current amplitude;
the formula for calculating the waveform asymmetry is as follows:
in the formula Ii' is the value at a point in the first half-wave of the derivative,the numerical value of the corresponding point of the second half wave of the derivative, D is the waveform asymmetry;
B. calculating a floating excitation inrush current comprehensive locking constant value;
the floating excitation inrush current comprehensive locking constant value calculation formula is as follows:
wherein: ksetFor the floating excitation surge current comprehensive locking constant value, K is more than or equal to 0.05setLess than or equal to 0.15; t is the floating time of the excitation inrush current comprehensive locking fixed value set by a program; t is an air-drop counter and is decreased to 0 from the air-drop moment, and T is more than or equal to 0 and less than or equal to T;
C. calculating an inrush current coefficient comprehensive criterion according to the longitudinal difference differential current and the calculation results of the direct current component, the fundamental wave, the second harmonic, the third harmonic and the waveform asymmetry of each side phase current, and comparing the criterion with a floating excitation inrush current comprehensive locking fixed value to give a harmonic content mark; if the calculated inrush current coefficient comprehensive criterion is larger than the floating inrush current comprehensive locking fixed value, the calculated inrush current coefficient comprehensive criterion is regarded that the inrush current locks the flag variable of the inrush current to be 1, and if not, the calculated inrush current coefficient comprehensive criterion is set to be 0;
excitation inrush current coefficient comprehensive criterion
K＝(C0×K0+C2)×K2+C3×K3+Cd×D
Wherein, K0Is the weight of the direct current component; k2Is the second harmonic weight; k3Is the third harmonic weight; d is the waveform asymmetry; c0DC component helps increase the second harmonic coefficient, C0＝0.8；C2Second harmonic coefficient, C2＝1；C3Coefficient of third harmonic, C3＝0.1；CdWave form asymmetry coefficient, Cd＝0.1；
D. Calculating by using fundamental wave current, and juxtaposing phase splitting action marks;
E. identifying whether the phase-splitting action mark is magnetizing inrush current or internal fault according to the calculated phase-splitting action mark and the magnetizing inrush current locking mark, and implementing protection on the transformer; when each phase comparison difference action is judged, firstly judging a phase splitting action mark, if the phase splitting action mark is 1, further judging whether the phase difference current harmonic mark is 1, if the phase difference current harmonic mark is 1, locking the phase protection; if the differential current harmonic mark is 0, judging the current harmonic mark of the differential current relevant side, if the phase current harmonic marks of the relevant sides are all 1, locking the phase differential motion protection, otherwise, acting the phase differential motion protection; in the three-phase differential protection, the longitudinal differential protection operates as long as one phase differential satisfies the operating condition.
2. The inrush current blocking method for a voltage regulating and compensating transformer as claimed in claim 1, wherein the second harmonic weight calculation formula is:
in the formula, K2Representing the second harmonic weight, I1Is the amplitude of the fundamental current, I2Is the second harmonic current amplitude;
third harmonic weight calculation formula:
wherein, K3Representing the third harmonic weight, I1Is the amplitude of the fundamental current, I3The third harmonic current amplitude.
3. The inrush current blocking method for the voltage regulating compensation transformer of claim 1, wherein: the number of the sampling points is 20-48 points.
4. The inrush current blocking method for the voltage regulating compensation transformer of claim 1, wherein: the weight of the amplitude bias is a DC component weight K0Multiplying by a second harmonic weight K2。
5. The inrush current blocking method for the voltage regulating compensation transformer of claim 1, wherein: the air drop judgment threshold is 0.08In, and In is the sampling value differential current.
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| CN109871832A (en) * | 2019-03-18 | 2019-06-11 | 国家电网有限公司 | Excitation inrush current identification method and system based on amplitude correlation |
| CN112444745B (en) * | 2019-09-03 | 2024-09-20 | 南京南瑞继保工程技术有限公司 | A method and device for judging phase regulator demagnetization failure caused by pulse loss |
| CN110568248B (en) * | 2019-09-23 | 2021-09-07 | 谢广宇 | Excitation inrush current identification method based on differential flow fundamental component phase |
| CN111273108B (en) * | 2020-03-17 | 2022-06-21 | 深圳供电局有限公司 | Method for judging transformer empty charge tripping reason |
| CN117200138B (en) * | 2023-09-07 | 2024-10-11 | 三一重能股份有限公司 | Relay protection method and device of transformer, wind generating set and storage medium |
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| CN108134373A (en) | 2018-06-08 |
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