CN110165635B - Transformer circulating current determining method, inrush current compensation method and application thereof - Google Patents
Transformer circulating current determining method, inrush current compensation method and application thereof Download PDFInfo
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- CN110165635B CN110165635B CN201910529255.XA CN201910529255A CN110165635B CN 110165635 B CN110165635 B CN 110165635B CN 201910529255 A CN201910529255 A CN 201910529255A CN 110165635 B CN110165635 B CN 110165635B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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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
- H02H7/0455—Differential protection of transformers taking into account saturation of current transformers
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Abstract
The invention discloses a transformer circulating current determining method, an inrush current compensation method and application thereof, wherein the method comprises the following steps: acquiring three-phase current of an original winding when the transformer is in air-drop in real time; determining the unsaturated phase current value of the transformer at each moment based on the three-phase current; and determining the opposite number of each unsaturated phase current value as a circulating current value to form a circulating current value set. Compensating the three-phase current of the primary winding by adopting the circulating current value set value to obtain the actual three-phase excitation inrush current; and carrying out differential protection based on the actual magnetizing inrush current. Because the unsaturated phase current of the primary winding is the 'offset' current of the primary winding under the influence of the circulating current, the invention determines the opposite number of the current value of the unsaturated phase of the transformer as the circulating current value of the secondary winding, does not need to measure any voltage quantity, does not need specific conditions such as grounding and ungrounded neutral points of the transformer and the like, does not need the balance and symmetry of system voltage, and is simple and convenient, strong in applicability and strong in anti-interference capability. And proved by experiments, the circulation current determined by the method is high in accuracy.
Description
Technical Field
The invention relates to the technical field of relay protection of power systems, in particular to a transformer circulating current determining method, an inrush current circulating current compensating method and application thereof.
Background
The current of the primary winding is compensated by using the circulating current of the triangular secondary winding of the transformer, so that the sensitivity of the differential protection of the transformer can be improved. The current transformer of 500kV or above can obtain the circulation current of the secondary winding by measurement, but the circulation current in the triangular winding of the transformer of 220kV or below voltage class cannot be directly measured.
Currently, many scholars propose a circulation flow calculation method. One of the methods is to assume the three-phase voltage balance of the power system and calculate the secondary side winding circulation of the transformer according to the differential equation of the transformer loop to obtain the proportional relation (i) between the circulation and the zero-mode current at the Y sideD＝ki0) When the current is not saturated, the proportional coefficient is obtained according to the relation that the current of the primary winding and the circulating current of the secondary winding are approximately opposite numbers, and then the circulating current is obtained according to the zero-mode current. However, this type of method is only applicable to the case where the transformer neutral is grounded, and is not effective when the neutral is not grounded. In addition, because the method ignores the imbalance caused by voltage disturbance when the power system operates, the method may fail when the external disturbance occurs, and therefore, the assumption of the three-phase voltage balance of the power system in the method is not tightly attached to the reality, and the adaptability is not strong enough. Another class of methods is applicable where the neutral is not grounded, but such methods require the acquisition (measurement) of the transformer neutral voltage, which is not generally available in the field, and further improvements are needed in both the basic principles and implementation of the methods.
Therefore, a circulation calculating method which is strong in applicability, simple, reliable and practical is not available at present.
Disclosure of Invention
The invention provides a transformer circulating current determining method, an inrush current compensation method and application thereof, which are used for solving the technical problem that circulating current is difficult to determine due to the fact that a transformer with a voltage class of 220kV or below cannot be directly obtained through measurement and the calculation method is poor in practicability in the existing transformer circulating current determining method.
The technical scheme for solving the technical problems is as follows: a transformer secondary winding circulating current determining method comprises the following steps:
step 2, determining the unsaturated phase and the unsaturated phase current value of the transformer at each moment based on the three-phase current;
and 3, determining the opposite number of each unsaturated phase current value as a circulating current value to form a circulating current value set so as to complete the determination of the circulating current of the secondary winding of the transformer.
The invention has the beneficial effects that: because the unsaturated phase current of the primary winding is generated by the 'offset' current of the primary winding under the influence of the circulating current, the opposite number of the current value of the unsaturated phase of the transformer is determined as the circulating current value of the secondary winding, and the accuracy and the reliability of the conclusion are verified by theory and experiments. Therefore, the method does not need to measure any voltage quantity, does not need specific conditions such as grounding and ungrounded of the neutral point of the transformer, only needs to extract according to three-phase current, and is simple and convenient and strong in applicability. In addition, even if the voltage of the power system is unbalanced due to various factors, the method can still be applied and has strong anti-interference capability. The method is suitable for high-voltage transformers and low-voltage transformers, and has a wide application range.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the step 1 comprises:
and acquiring the three-phase current of the primary winding in real time when the transformer is in air-drop through a current transformer at the wire outlet end of the primary winding.
Further, the step 2 comprises:
and determining a non-maximum and non-minimum current value in the three-phase current corresponding to each moment as the current value of the unsaturated phase of the transformer at the moment, wherein one phase corresponding to the current value is the unsaturated phase of the transformer at the moment.
The invention has the further beneficial effects that: and determining one phase corresponding to the non-maximum and non-minimum current values in the three-phase current at each moment as the current unsaturated phase of the transformer at the moment, and replacing the circulating current value by the opposite number of the current values of the primary windings of the unsaturated phase. In the process of the transformer air-drop, the applied voltage is alternating-current voltage, and the magnitude and the direction of the voltage are constantly changed, so that a certain phase of the original side of the transformer is not always an unsaturated phase, the saturation and the unsaturation alternate in one period, and the current value of the unsaturated phase is the median of three-phase current values at each moment. The relevant theoretical proof and verification are detailed in the detailed description of the embodiment.
The invention also provides a circulating current compensation method of the excitation inrush current of the transformer, which comprises the following steps:
based on the three-phase current obtained by any one of the above methods for determining the transformer secondary winding loop current and the determined set of loop current values, the three-phase current is compensated by the set of loop current values to obtain the actual excitation inrush current of the transformer, thereby completing the loop current compensation of the excitation inrush current of the transformer.
The invention has the beneficial effects that: when the transformer normally operates, the currents on the two sides of the transformer are equal, and no current difference exists. When the transformer is in no-load operation, current exists on one side, no current exists on the outgoing line on the other side, and the current of the three-phase primary winding generates inrush current, so that differential current is generated, and the inrush current is identified by adopting a waveform identification criterion and is braked to prevent misoperation of differential protection. And because the loop current of the secondary winding is offset, the inrush current of the primary current is distorted, and the waveform identification criterion is influenced. At the moment, the inrush current of the three-phase primary winding needs to be compensated, the invention adopts the circulating current value set determined by the circulating current determination method to compensate, the influence of voltage unbalance is not easy to occur, the neutral point needs to be grounded, and the measuring method when the neutral point is not grounded needs to obtain the neutral point voltage which is difficult to measure.
Further, the three-phase current acquired in real time is represented in a time-current curve form, and then the circulating current value set is represented in a time-circulating current value curve form.
The invention has the further beneficial effects that: the three-phase current and circulating current value set is expressed in a curve form, so that the method is visual and convenient to calculate.
Further, when the current value, which is not the maximum and is not the minimum, of the three-phase current values corresponding to each moment in the three-phase currents is determined as the current value of the unsaturated phase of the transformer at the moment and forms a circulating current value set, the circulating current value set is adopted to compensate the three-phase current to obtain the actual magnetizing inrush current of the transformer, and the method specifically comprises the following steps:
forming a new circulation value set by all the circulation values in the circulation value set according to a time sequence;
adding the three-phase current value corresponding to each moment in the three-phase currents to the circulating current value corresponding to the moment in the circulating current value set respectively to obtain compensated three-phase currents;
and obtaining the actual magnetizing inrush current of the transformer based on the compensated three-phase current.
The invention has the further beneficial effects that: the circulation values are arranged according to the time sequence, a time-circulation curve function can be formed, compensation calculation is facilitated, the whole process is simple and efficient, and the reliability of the circulation values obtained by the method is high.
The invention also provides a transformer differential protection method, which comprises the following steps:
differential protection is carried out on the basis of the actual magnetizing inrush current of the transformer obtained by any transformer magnetizing inrush current circulating current compensation method.
The invention has the beneficial effects that: when the transformer normally operates, the currents on the two sides of the transformer are equal, and no current difference exists. When the transformer is in idle-throw, current exists on one side, no current exists on the outgoing line on the other side, the current of the three-phase primary winding generates inrush current and generates differential current, and the inrush current needs to be identified by adopting a waveform identification criterion and braked. And because the loop current of the secondary winding is offset, the inrush current of the primary current is distorted, and the waveform identification criterion is influenced. At the moment, in the working process of the differential protection device, three-phase current during transformer no-load is collected, and the 'inrush current' is determined based on the three-phase current, and the 'inrush current' at the moment influences the correct judgment of the waveform identification criterion due to distortion, so that the phenomenon that the 'inrush current' at the moment is considered as fault current by the differential protection device is possibly caused, and the differential protection device is operated mistakenly. Therefore, in order to prevent the differential protection misoperation, the inrush current compensated by the circulating current compensation method of the transformer inrush current needs to be compensated, the inrush current compensated by the transformer inrush current compensation method can be correctly identified by a differential protection device that a power grid is in a normal state, no misoperation occurs, and the differential protection process is simple and efficient, high in reliability and strong in practicability.
The present invention also provides a storage medium, wherein instructions are stored in the storage medium, and when the instructions are read by a computer, the computer is caused to execute any one of the above-mentioned transformer secondary winding circulating current determining method, any one of the above-mentioned transformer magnetizing inrush current compensation method, and/or any one of the above-mentioned transformer differential protection method.
Drawings
Fig. 1 is a block flow diagram of a method for determining a transformer secondary winding circulating current according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating compensation effects when considering remanence according to an embodiment of the present invention;
fig. 3 is a diagram illustrating the compensation effect when the neutral point of the transformer is grounded according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating the compensation effect when the neutral point of the transformer is not grounded according to an embodiment of the present invention;
FIG. 5 is a graph illustrating the compensation effect of a voltage disturbance with a grounded neutral point according to an embodiment of the present invention;
FIG. 6 is a graph illustrating the compensation effect of a voltage disturbance without a neutral point grounded according to an embodiment of the present invention;
fig. 7 shows compensation effects of the recording current according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example one
A transformer secondary winding circulating current determining method 100, as shown in fig. 1, includes:
110, acquiring three-phase current of an original winding in the process of airdrop of the transformer in real time;
and step 130, determining the opposite number of each unsaturated phase current value as a circulating current value to form a circulating current value set, and finishing the determination of the circulating current of the secondary winding of the transformer.
It should be noted that when describing "circulating current", "current" and "inrush current", it refers to a continuous current for a whole period of time. And the descriptions "circulation value", "current value", and "inrush value" are expressed as values at the present time. Then the "set of circulation values" corresponds to the entire set of circulations.
Since the unsaturated phase current of the primary winding is generated as the 'offset' current of the primary winding under the influence of the circulating current, the opposite number of the current value of the unsaturated phase of the transformer is determined as the circulating current value of the secondary winding. The method of the embodiment does not need to measure any voltage quantity, does not need specific conditions such as grounding and ungrounded of the neutral point of the transformer, only needs to extract according to three-phase current, and is simple and convenient and high in applicability. In addition, even if the voltage of the power system is unbalanced due to various factors, the method can still be applied and has strong anti-interference capability. The method is suitable for high-voltage transformers and low-voltage transformers, and has a wide application range. The accuracy and the reliability of the conclusion are verified by theory and experiment, and the subsequent description is applied to the verification of the correlation theory and the experiment.
Preferably, step 110 includes:
and when the transformer is in air-drop, the three-phase current of the primary winding is acquired in real time through the current transformer at the wire outlet end of the primary winding.
Preferably, step 120 includes:
and determining a non-maximum and non-minimum current value in the three-phase current corresponding to each moment as the current value of the unsaturated phase of the transformer at the moment, wherein one phase corresponding to the current value is the unsaturated phase of the transformer at the moment.
And determining one phase corresponding to the non-maximum and non-minimum current values in the three-phase current at each moment as the current unsaturated phase of the transformer at the moment, and replacing the circulating current value by the opposite number of the current values of the primary windings of the unsaturated phase. In the process of the transformer air-drop, the applied voltage is alternating-current voltage, and the magnitude and the direction of the voltage are constantly changed, so that a certain phase of the original side of the transformer is not always an unsaturated phase, the saturation and the unsaturation alternate in one period, and the current value of the unsaturated phase is the median of three-phase current values at each moment.
The opposite of the unsaturated phase current value, i.e., the circulating current value, can be represented by the following formula:
wherein iDIndicating the circulating current values, A, B and C represent the primary winding three phases, iARepresenting the current of the primary A-phase winding at a time, iBRepresenting the current of the primary B-phase winding at a time, iCRepresenting the current of the primary C-phase winding at one instant.
The above scheme is demonstrated, and the process is as follows:
suppose the A-phase power supply voltage is UsAsin (ω t + α), the closing angle is α, and the A-phase flux linkage is ψAWithout taking into account the influence of the resistance component, according to
Obtaining:
order to
ψmFor the nominal flux linkage amplitude, then:
ψA＝-ψmcos(ωt+α)+ψmcosα+ψrA (2)
formula (2) divided by psimThe saturation coefficient T of the A phase and the B, C phase is obtained after per unitA、TBAnd TC：
TA＝-cos(ωt+α)+cosα+KrA
TB＝-cos(ωt+α-120°)+cos(α-120°)+KrB
TC＝-cos(ωt+α+120°)+cos(α+120°)+KrC (3)
KrA＝-Krcosθ
KrB＝-Krcos(θ+120°)
KrC＝-Krcos(θ+240°) (4)
Wherein KrIs the remanence coefficient, theta is the opening angle of the last opening, KrA、KrBAnd KrCThe percentage of the three-phase remanence in the saturated flux linkage is shown. Obviously, when | TXWhen | < 1, the X-phase flux linkage is less than the saturated flux linkage, and the X-phase iron core is unsaturated (X is a certain phase in A, B, C); when | TXWhen | is greater than 1, the X-phase iron core is saturated. When unsaturated, the following relationship holds:
iX+iD＝iXm≈0 (5)
from the equation (3), it can be found by the mathematical relationship analysis that the remanence (K) is not consideredr＝0)，TA、TBAnd TCAt least one of which satisfies | TXI is less than or equal to 1, that is, there is at least one phase of unsaturation in each time in the whole time period, then according to the formula (5), the circulation current of the secondary winding can be unsaturated by the primary winding in the whole periodAnd the opposite of the phase current, namely:
iD＝-iX (6)
because each moment in the whole time period has at least one phase of unsaturation, the effective time of the circulating current can be replaced by the opposite number of the phase current of the original winding unsaturation in one period is 100 percent.
(1) Only one phase of unsaturation is present at a time, and the unsaturated phase needs to be determined. The method can be obtained according to the numerical analysis of the formula (3) (i.e. adjusting each variable, traversing all possible numerical results, the variables are time, opening angle and closing angle in the formula, the time is carried out according to a period of 0.02s and a step length of 0.0001s, the opening angle and the closing angle are carried out according to 360 degrees and the step length of 1 degree), and when only one phase is unsaturated (if the phase is A, the phase is | T |)A1) and the remaining two phases must satisfy the two saturation coefficients with opposite signs (i.e. T)B·TC< 0), i.e. the sign of the primary winding current value plus the circulating current value of the two saturated phases (i.e. minus the primary winding current value of the unsaturated phase) is opposite. Obviously, two values with opposite signs can be obtained only by subtracting the primary winding current value of the unsaturated phase from a current value larger than the primary winding current value of the unsaturated phase and a current value smaller than the primary winding current value of the unsaturated phase, respectively. Therefore, the phases having the intermediate three-phase primary winding current values are unsaturated phases. Therefore, the median of the current values of the three-phase primary winding is an unsaturated phase current value, and the opposite number of the unsaturated phase current value is defined as a quasi-circulating current value (firstly, it should be noted that for the sake of rigor, the word "quasi" in the "quasi-circulating current" indicates that the circulating current value is not a strictly accurate circulating current, and has a certain deviation from the actual circulating current value, but the circulating current value is enough to be accurately used for compensation and differential protection of magnetizing inrush current, so the "quasi-circulating current" herein is also referred to as "circulating current" in the present application.
(2) If two phases are unsaturated at a certain moment, the unsaturated phase needs to be determined, the current values of the primary windings of the two unsaturated phases are almost overlapped, and the phase with the current value of the primary winding of the three phases in the middle number is necessarily the unsaturated phase. Therefore, the quasi-circulating current is the inverse of the three-phase median, and the equation (7) is also satisfied.
(3) If three phases are unsaturated at a certain moment, no inrush current is generated at the moment, and then the protection device cannot be started.
Through the analysis, when the remanence is not considered, the effective time of replacing the circulation current by the quasi-circulation current in one period accounts for 100 percent.
Taking into account the remanence, depending on the maximum K that the remanence coefficient may reachrAs a result of numerical analysis of formula (3), the effective time for which quasi-circulation can be used instead of circulation in one cycle is 88%, which is 0.7. Further, the smaller the remanence coefficient, the larger the effective time ratio. The active time ratio does not reach 100% because there are times when the three phases are saturated, which occurs when one phase is heavily saturated, just before it enters saturation, and one phase is about to exit saturation. Because the quasi-circulating current is the inverse number of the median of the current values of the three-phase primary windings, and the median is the current value of the primary winding of the phase which just enters saturation or is about to exit saturation at the moment, the quasi-circulating current and the real circulating current have small difference, short duration, small occurrence probability and almost no influence on the method, as shown in fig. 2.
Example two
A method for compensating the circulating current of the magnetizing inrush current of a transformer comprises the following steps:
based on the three-phase current obtained by any method for determining the transformer secondary winding loop current and the determined set of loop current values, the three-phase current is compensated by using the set of loop current values, so as to obtain the actual excitation inrush current of the transformer, and complete the loop current compensation of the excitation inrush current of the transformer.
The related technical solution is the same as the first embodiment, and is not described herein again.
When the transformer normally operates, the currents on the two sides of the transformer are equal, and no current difference exists. When the transformer is in no-load operation, current exists on one side, no current exists on the outgoing line on the other side, and the current of the three-phase primary winding generates inrush current, so that differential current is generated, and the inrush current is identified by adopting a waveform identification criterion and is braked to prevent misoperation of differential protection. And because the loop current of the secondary winding is offset, the inrush current of the primary current is distorted, and the waveform identification criterion is influenced. At the moment, the inrush current of the three-phase primary winding needs to be compensated, the invention adopts the circulating current value set determined by the circulating current determination method to compensate, the influence of voltage unbalance is not easy to occur, the neutral point needs to be grounded, and the measuring method when the neutral point is not grounded needs to obtain the neutral point voltage which is difficult to measure.
Preferably, the three-phase currents acquired in real time are represented in the form of a time-current curve, and then the set of circulating current values is represented in the form of a time-circulating current value curve.
The three-phase current and circulating current value set is expressed in a curve form, so that the method is visual and convenient to calculate.
Preferably, when a non-maximum and non-minimum current value of three-phase current values corresponding to each time in three-phase currents is determined as an unsaturated phase current value of the transformer at the time and a circulating current value set is formed (related technical solutions are the same as embodiment one, and details are not described here), the circulating current value set is used to compensate the three-phase currents, so as to obtain an actual magnetizing inrush current of the transformer, specifically:
all circulation values in the circulation value set form a new circulation value set according to the time sequence;
respectively adding the three-phase current value corresponding to each moment in the three-phase currents to the circulating current value corresponding to the moment in the circulating current value set to obtain the compensated three-phase currents;
and obtaining the actual magnetizing inrush current of the transformer based on the compensated three-phase current.
The circulation values are arranged according to the time sequence, a time-circulation value curve function can be formed, compensation calculation is facilitated, the whole process is simple and efficient, and the circulation value obtained by the method is high in reliability.
Specifically, the three-phase real magnetizing inrush current i is obtained by adding the quasi-loop currents obtained by the original three-phase winding currents to the original three-phase winding currentsAm、iBmAnd iCmThis is represented by the following formula:
The actual excitation inrush current has the inrush waveform characteristic of a typical discontinuous truncated sine wave form.
The reliability and accuracy of the first and second embodiments are verified by simulation and field recording, and the specific verification is as follows:
simulation verification
In order to verify the correctness of the loop current solving method provided by the first embodiment, a transformer simulation system is established by using PSCAD V4.6 software to simulate the actual situation. The simulation was carried out using a high-impedance transformer having a capacity of 240/240/80MVA and a rated voltage transformation ratio of 220/110/10.5kV as a prototype.
Considering the condition of generating the most serious inrush current, setting the three-phase residual magnetism of the transformer simulation model as a switching-off angle theta of 180 degrees, and setting the magnitude per unit value of the residual magnetism (0.70, -0.35, -0.35) when the coefficient of the residual magnetism is Kr of 0.7; the closing angle α of phase a is 0 °.
Fig. 3 and 4 show three-phase primary winding currents (see fig. 3 and 4 (a)), actual circulating currents and quasi-circulating currents (i.e., circulating currents obtained by the method of the present application, which have been waveform-reversed in order to compare with the three-phase primary winding currents) generated by the air-drop transformer in the case of system voltage balance between the grounded state and the ungrounded state, respectively (see fig. 3 and 4 (b)), and magnetizing inrush currents (see fig. 3 and 4 (c)). It can be seen from the figure that the loop and quasi-loop flow fits very well. The primary winding current is affected by the circulating current to generate distortion, and the current with typical magnetizing inrush current characteristics is obtained after the quasi-circulating current obtained by the method of the embodiment is compensated, so that the differential protection action performance is improved.
In summary, when the ground is connected and the ground is not connected, the fitting effect of the circulating current is good, which shows that the method of the present embodiment has strong universality.
Fig. 5 and 6 show the use effect of the method in the case of grounding and non-grounding when the voltage of the power system is disturbed. The quasi-circulating current and circulating current are still high in fitting degree, the compensated primary winding current has the excitation inrush current characteristic of a typical discontinuous truncated sine wave form, and only the size of the whole waveform changes, so that the method is strong in anti-interference performance.
(II) wave recording application
A certain transformer (SSZ11-240MVA/220kV) performs high-voltage side no-load closing charging, and three-phase current recording data is shown in fig. 7 (a). Quasi-toroidal flow obtained by the method proposed in the first embodiment is shown in fig. 7 (b). The primary winding current is compensated to obtain a waveform with a typical magnetizing inrush current characteristic, as shown in (c) of fig. 7. The inrush current after the quasi-toroidal current compensation has more obvious characteristics than the original inrush current of the primary winding, and shows a typical discontinuous truncated sine wave form, which is beneficial to improving the sensitivity of differential protection.
EXAMPLE III
A transformer differential protection method, comprising:
differential protection is performed based on the actual magnetizing inrush current of the transformer obtained by any one of the transformer magnetizing inrush current circulating current compensation methods described in the second embodiment.
The related technical solution is the same as the second embodiment, and is not described herein again.
The differential protection device adopts the real excitation inrush current after the circulation compensation to replace the three-phase inrush current of the original primary winding for the braking criterion operation.
When the transformer normally operates, the currents on the two sides of the transformer are equal, and no current difference exists. When the transformer is in idle-throw, current exists on one side, no current exists on the outgoing line on the other side, the current of the three-phase primary winding generates inrush current and generates differential current, and the inrush current needs to be identified by adopting a waveform identification criterion and braked. And because the loop current of the secondary winding is offset, the inrush current of the primary current is distorted, and the waveform identification criterion is influenced. At the moment, in the working process of the differential protection device, three-phase current during transformer no-load is collected, and the 'inrush current' is determined based on the three-phase current, and the 'inrush current' at the moment influences the correct judgment of the waveform identification criterion due to distortion, so that the phenomenon that the 'inrush current' at the moment is considered as fault current by the differential protection device is possibly caused, and the differential protection device is operated mistakenly. Therefore, in order to prevent the differential protection misoperation, the inrush current compensated by the circulating current compensation method of the transformer inrush current needs to be compensated, the inrush current compensated by the transformer inrush current compensation method can be correctly identified by a differential protection device that a power grid is in a normal state, no misoperation occurs, and the differential protection process is simple and efficient, high in reliability and strong in practicability.
Example four
A storage medium having stored therein instructions that, when read by a computer, cause the computer to execute any one of the above-described transformer secondary winding circulating current determining methods, any one of the above-described transformer magnetizing inrush current compensation methods, and/or a transformer differential protection method.
The related technical solutions are the same as the first to third embodiments, and are not described herein again.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A method for compensating a circulating current of a transformer magnetizing inrush current is characterized by comprising the following steps:
based on a method for determining quasi-loop current of a secondary winding of a transformer, three-phase current is obtained, a quasi-loop current value set is determined, the three-phase current is compensated by the quasi-loop current value set, actual excitation inrush current of the transformer is obtained, and loop current compensation of the excitation inrush current of the transformer is completed;
the method for determining the quasi-circulating current of the secondary winding of the transformer comprises the following steps:
step 1, acquiring three-phase current of an original winding in a transformer air-drop process in real time;
step 2, determining the unsaturated phase and the unsaturated phase current value of the transformer at each moment based on the three-phase current;
step 3, determining the opposite number of each unsaturated phase current value as a quasi-circulating current value to form a quasi-circulating current value set so as to complete the determination of the quasi-circulating current of the secondary winding of the transformer;
the step 2 comprises the following steps:
and determining a non-maximum and non-minimum current value in the three-phase current corresponding to each moment as the current value of the unsaturated phase of the transformer at the moment, wherein one phase corresponding to the current value is the unsaturated phase of the transformer at the moment.
2. A method for compensating a circulating current of a transformer magnetizing inrush current according to claim 1, wherein the step 1 comprises:
and acquiring the three-phase current of the primary winding in real time when the transformer is in air-drop through a current transformer at the wire outlet end of the primary winding.
3. A method for compensating a circulating current of a transformer magnetizing inrush current according to claim 1, wherein the three-phase currents obtained in real time are represented in a time-current curve, and the quasi-circulating current value set is represented in a time-quasi-circulating current value curve.
4. The method for compensating the circulating current of the magnetizing inrush current of the transformer according to claim 1 or 3, wherein the three-phase current is compensated by the quasi-circulating current value set to obtain the actual magnetizing inrush current of the transformer, and specifically comprises:
forming a new circulation value set by all the quasi circulation values in the quasi circulation value set according to a time sequence;
adding the three-phase current value corresponding to each moment in the three-phase currents to the circulating current value corresponding to the moment in the circulating current value set respectively to obtain compensated three-phase currents;
and obtaining the actual magnetizing inrush current of the transformer based on the compensated three-phase current.
5. A method for differential protection of a transformer, comprising:
differential protection is performed based on the actual magnetizing inrush current of the transformer obtained by the method for compensating the circulating current of the magnetizing inrush current of the transformer according to any one of claims 1 to 4.
6. A storage medium, wherein instructions are stored in the storage medium, and when the instructions are read by a computer, the computer is caused to execute a method for compensating a transformer inrush current according to any one of claims 1 to 4 and/or a method for differential protection of a transformer according to claim 5.
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| CN100549709C (en) * | 2007-06-12 | 2009-10-14 | 清华大学 | The computing method and the device of circulation in the Y/ △ transformer triangle winding |
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| CN103683197A (en) * | 2013-11-28 | 2014-03-26 | 国家电网公司 | Method of calculating delta-side three-phase winding primary current of Y/delta transformer |
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| CN103986120B (en) * | 2014-06-04 | 2017-02-01 | 贵州电力试验研究院 | Transformer differential protection system and method based on magnetic flux brake trap combined judgment |
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