A method for suppressing transformer excitation inrush current based on comprehensive criteria

Abstract

The present invention belongs to the field of magnetizing inrush current suppression and discloses a transformer magnetizing inrush current suppression method based on comprehensive criteria. The method is used in a transformer closing circuit including a power supply side, a main circuit breaker, and a three-phase transformer. The method comprises: installing a phase-controlled closing control device on the transformer closing circuit; recording the voltage of each phase during the closing process of the three-phase transformer using a voltage transformer; calculating the residual magnetism of each phase of the three-phase transformer based on the voltage; calculating the closing angle interval of each phase of the circuit breaker based on the residual magnetism; and closing the main circuit breaker based on the closing angle interval of each phase. The present invention supplements two special cases that exist in the phase-controlled closing strategy based on the voltage integration algorithm. The two cases include: 1. No suitable closing angle interval exists; 2. A suitable closing angle interval exists, but the interval angle is too small, so that closing can be performed more accurately and efficiently.

Description

Technical Field

[0001] The present invention relates to the field of excitation inrush current suppression, and in particular to a transformer excitation inrush current suppression method based on comprehensive criteria. Background Art

[0002] Magnetizing inrush current is a long-standing problem for power transformers. Its essence is that the transformer excitation curve has nonlinear characteristics. When the transformer is operating normally, its total magnetic flux will be less than the transformer's own saturation flux, and the excitation current value is small at this time. When the transformer trips due to a fault and needs to be closed again, due to the residual magnetism in the transformer's internal iron core, the total magnetic flux generated after closing will exceed its own saturation flux, thereby generating a large excitation inrush current. The large excitation inrush current value will cause the transformer differential protection to operate, resulting in unsuccessful closing, aggravating the accident, and also easily damaging the transformer and other power equipment.

[0003] At present, there are two main methods for suppressing transformer excitation inrush current: the first is to connect the switching resistor in series or in parallel. Figure 1 and Figure 2 shown.

[0004] If according to Figure 1 Connect the circuit breaker Qf2 first when the transformer needs to be closed again. After the magnetizing inrush current has decayed, close the circuit breaker Qf1 and open the circuit breaker Qf2.

[0005] If according to Figure 2 Connect the circuit. When the transformer needs to be closed again, it only needs to be closed normally, and the circuit breaker Qf1 can be closed after the excitation inrush current has decayed. The principle of this method is to use the closing resistor to limit the excitation inrush current and increase the decay rate of the excitation inrush current, thereby achieving the purpose of protecting the transformer. Although this method can protect the transformer, it is often necessary to select closing resistors of different resistance values ​​according to different transformers to fully adapt to it. If the resistance value is too small, the differential protection will malfunction. If the resistance value is too large, the efficiency of the transformer will be reduced. In addition, the operation sequence cannot be changed, otherwise the closing resistor will lose its function.

[0006] The second is phase-controlled closing technology, such as Figure 3 As shown, the main method is to control the magnetic flux generated by the three phases by using the different closing sequences of the three-phase circuit breakers to avoid the transformer from generating an excitation inrush current. Usually, the closing voltage angle of a phase circuit breaker is controlled first, and then the remaining two phase circuit breakers are closed.

[0007] The basic principle of this method is to use the residual magnetism of the transformer when the circuit breaker is open as the basis for the next closing. Currently, there are many methods that can estimate the residual magnetism of the transformer when the circuit breaker is open, such as the inrush current back-calculation method and the modeling analysis method.

[0008] Phase-controlled closing technology can effectively control the excitation inrush current of a preset phase, but this method has many problems in controlling the closing time of three-phase circuit breakers. For example, when controlling the closing sequence of three-phase circuit breakers, priority is often given to whether the magnetic flux meets the conditions, while ignoring the time difference of the three-phase circuit breaker closing. The closing time of the three-phase circuit breaker cannot differ too much. Otherwise, the asynchronous closing of the three-phase circuit breaker will also lead to asymmetric three-phase voltages, thereby aggravating the accident. Therefore, this method has shortcomings in suppressing the closing time and the excitation inrush current of the other two phases.

[0009] In summary, the above two methods both unilaterally guarantee the suppression of the excitation inrush current, and neither can reliably suppress the excitation inrush current. Summary of the Invention

[0010] The purpose of the present invention is to disclose a transformer excitation inrush current suppression method based on comprehensive criteria to solve the technical problems raised in the background technology.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] The present invention provides a transformer excitation inrush current suppression method based on comprehensive criteria, which is applied to a transformer closing circuit. The transformer closing circuit includes a power supply side, a main circuit breaker, and a three-phase transformer. There are three main circuit breakers, one end of which is connected to the input end of one phase of the three-phase transformer, and the other end is connected to the power supply side.

[0013] The method comprises:

[0014] The first step is to install a phase-controlled closing control device on the transformer closing circuit. The phase-controlled closing control device includes a parallel closing circuit, a phase-controlled closing module, a voltage integration algorithm module, and a voltage transformer.

[0015] The parallel closing circuit includes branch circuit breakers and closing resistors.

[0016] One end of the branch circuit breaker is connected to the transmission line between the power supply side and the main circuit breaker, and the other end is connected to the closing resistor;

[0017] One end of the closing resistor is connected to the branch circuit breaker, and the other end is connected to the transmission line between the main circuit breaker and the input terminal of one phase of the transformer;

[0018] The circuit formed by the branch circuit breaker and the closing resistor is in parallel with the circuit where the main circuit breaker is located;

[0019] The phase-controlled closing module is connected to the main circuit breaker and the branch circuit breaker respectively;

[0020] The voltage integration algorithm module is connected to the phase-controlled closing module and the voltage transformer respectively;

[0021] The voltage transformer is used to obtain the voltage of each phase of the three-phase transformer;

[0022] In the second step, during the closing process of the three-phase transformer, if the main circuit breaker is disconnected due to the excitation inrush current, the voltage transformer records the voltage of each phase of the three-phase transformer;

[0023] In the third step, the voltage integration algorithm module calculates the residual magnetism of each phase of the three-phase transformer based on the voltage obtained by the voltage transformer;

[0024] In the fourth step, the phase-controlled closing module calculates the closing angle range of each phase of the circuit breaker based on the residual magnetism;

[0025] Step 5: Determine whether the closing angle interval obtained in step 4 is too small or the closing synchronization between phases does not meet the closing time difference requirement. If so, proceed to step 7; if not, proceed to step 8.

[0026] Step 7: Close the branch circuit breaker. After the circuit is stable, close the main circuit breaker and open the branch circuit breaker.

[0027] Step 8: Close the main circuit breaker according to the closing angle range of each phase.

[0028] Preferably, there are three sets of voltage transformers, and each set of voltage transformers is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when it is closed again.

[0029] Preferably, there are two sets of voltage transformers, each set of which is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when closing again.

[0030] After obtaining the voltages of any two phases through two sets of voltage transformers, the voltage data of the third phase is calculated using the symmetry of the three-phase voltages.

[0031] Preferably, obtaining the remanence of each phase of the three-phase transformer includes:

[0032] For any phase of a three-phase transformer, the calculation process of its residual magnetism is as follows:

[0033] R is used to represent the equivalent resistance of transformer copper loss and iron loss, L is used to represent the equivalent excitation inductance, and u is used to represent the equivalent i Denotes the input voltage on the power supply side and α denotes the closing angle, then the following formula 1-1 is obtained:

[0034] u i =U m cos(ωt+α) 1-1

[0035] ω is the cosine voltage angular velocity, U mis the cosine voltage amplitude;

[0036] In the voltage input transformer on the power supply side, current flows through the excitation inductor, generating magnetic flux. The relationship between magnetic flux and voltage is shown in the following equations 1-2 and 1-3:

[0037]

[0038] Φ t＝0 =Φ r 1-3

[0039] Where N represents the number of transformer turns, and i is the current generated in the transformer's power supply circuit. Since NΦ = Li in a three-phase transformer, integrating the voltage according to Equations 1-1 to 1-3 yields the expression for magnetic flux, as shown in Equation 1-4.

[0040]

[0041] According to the above formula, the magnetic flux size at each time point can be calculated. When the gate is open, the residual magnetism Φ of one phase can be calculated by the three-phase voltage. r ;

[0042] Φ is the magnetic flux generated by the excitation inductance, Φ t＝0 is the magnetic flux at the moment when the transformer is closed again after being disconnected from operation, Φ(t) represents the magnetic flux at time t, t0 is the moment when the transformer is closed again, and t is the cumulative operating time after closing.

[0043] Preferably, calculating the closing angle interval of each phase of the circuit breaker according to the residual magnetism includes:

[0044] Calculate the sum of transient magnetic flux and steady-state magnetic flux corresponding to each closing angle;

[0045] The saturation flux of the three-phase transformer is used as the threshold to determine the sum of the transient flux and the steady-state flux, and the closing angle range that satisfies the conditions for each phase is obtained, including:

[0046] The saturation flux of the three-phase transformer is used as the threshold, and the sum of the transient flux and the steady-state flux generated when the closing angle range is 0 degrees to 360 degrees is calculated. The angle range in which the sum of the transient flux and the steady-state flux is less than the saturation flux of the transformer from 0 degrees to 360 degrees is obtained, thereby obtaining the closing angle range.

[0047] Preferably, determining whether the closing angle interval obtained in the fourth step is too small includes:

[0048] If the range of the closing angle interval is less than 20 degrees, it means that the closing angle interval obtained in the fourth step is too small.

[0049] Preferably, determining whether the closing synchronization between the phases does not meet the closing time difference requirement includes:

[0050] If the closing time difference between two adjacent main circuit breakers is greater than 1.7ms, it means that the closing synchronization between the phases does not meet the closing time difference requirements.

[0051] Preferably, the circuit stability is determined based on whether the current amplitude of the three-phase transformer has recovered to a range of 90% to 110% of the current amplitude during normal operation.

[0052] Beneficial effects:

[0053] (1) The present invention adopts a voltage integration method module, which can more reliably calculate the residual magnetism remaining inside the transformer after the transformer is opened, providing a reliable closing basis for phase-controlled closing;

[0054] (2) The present invention adopts a series closing resistor as the auxiliary suppression part of the method, and the resistance value of the closing resistor can be selected to be smaller than the method of using only the closing resistor as a method for suppressing the excitation inrush current, which has certain economic efficiency;

[0055] (3) The present invention adopts phase-controlled closing based on voltage integration algorithm as the main method to suppress the excitation inrush current, and uses series closing resistance as an auxiliary method to suppress the excitation inrush current, which can more reliably and comprehensively suppress the generation of the excitation inrush current;

[0056] The present invention supplements two special cases that exist in the phase-controlled closing strategy based on the voltage integration algorithm. The two cases include: 1. There is no suitable closing angle range; 2. There is a suitable closing angle range, but the range angle is too small, which can enable more accurate and effective closing. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0058] Figure 1 Schematic diagram of a circuit for suppressing inrush current by connecting a parallel gate resistor in the prior art.

[0059] Figure 2 This is a schematic diagram of a circuit for inrush current suppression using a series gate resistor in the prior art.

[0060] Figure 3 The figure is a schematic diagram of a circuit for suppressing inrush current by using phase-controlled closing technology in the prior art.

[0061] Figure 4 Schematic diagram of the transformer closing circuit.

[0062] Figure 5 Schematic diagram of the connection method of the phase-controlled closing control device of the present invention.

[0063] Figure 6 Schematic diagram of the equivalent simplified circuit diagram of the power supply side of a single-phase transformer. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0065] The present invention provides a transformer excitation inrush current suppression method based on comprehensive criteria, which is applied to Figure 4 The transformer closing circuit shown is

[0066] Figure 4 Where QfA, QfB, and QfC are main circuit breakers for each phase, and T1, T2, and T3 are transformers for each phase in the three-phase transformer.

[0067] The transformer closing circuit includes the power supply side, the main circuit breaker and the three-phase transformer; there are three main circuit breakers, one end of which is connected to the input end of one phase of the three-phase transformer, and the other end is connected to the power supply side;

[0068] The method comprises:

[0069] The first step is to install a phase-controlled closing control device on the transformer closing circuit. The phase-controlled closing control device includes a parallel closing circuit, a phase-controlled closing module, a voltage integration algorithm module, and a voltage transformer.

[0070] The parallel closing circuit includes branch circuit breakers and closing resistors.

[0071] One end of the branch circuit breaker is connected to the transmission line between the power supply side and the main circuit breaker, and the other end is connected to the closing resistor;

[0072] One end of the closing resistor is connected to the branch circuit breaker, and the other end is connected to the transmission line between the main circuit breaker and the input terminal of one phase of the transformer;

[0073] The circuit formed by the branch circuit breaker and the closing resistor is in parallel with the circuit where the main circuit breaker is located;

[0074] The phase-controlled closing module is connected to the main circuit breaker and the branch circuit breaker respectively;

[0075] The voltage integration algorithm module is connected to the phase-controlled closing module and the voltage transformer respectively;

[0076] The voltage transformer is used to obtain the voltage of each phase of the three-phase transformer;

[0077] Specific connections such as Figure 5 As shown;

[0078] The circuit breakers connected to the phase-controlled closing module with solid lines are main circuit breakers, including QfA, QfB, and QfC; the circuit breakers connected with dotted lines are branch circuit breakers, i.e., auxiliary circuit breakers for the branch where the closing resistor is located, including QfA', QfB', and QfC'; R1 is the closing resistor, and T1, T2, and T3 are the transformers of each phase of the three-phase transformer; the voltage transformer is not in Figure 5 Mark out;

[0079] In the second step, during the closing process of the three-phase transformer, if the main circuit breaker is disconnected due to the excitation inrush current, the voltage transformer records the voltage of each phase of the three-phase transformer;

[0080] In the third step, the voltage integration algorithm module calculates the residual magnetism of each phase of the three-phase transformer based on the voltage obtained by the voltage transformer;

[0081] In the fourth step, the phase-controlled closing module calculates the closing angle range of each phase of the circuit breaker based on the residual magnetism;

[0082] Step 5: Determine whether the closing angle interval obtained in step 4 is too small or the closing synchronization between phases does not meet the closing time difference requirement. If so, proceed to step 7; if not, proceed to step 8.

[0083] Step 7: Close the branch circuit breaker. After the circuit is stable, close the main circuit breaker and open the branch circuit breaker.

[0084] Step 8: Close the main circuit breaker according to the closing angle range of each phase.

[0085] Specifically, when closing the circuit breaker, closing the circuit breaker is performed according to the angle at which the sum of the transient magnetic flux component and the steady-state magnetic flux component is the smallest within the acquired closing angle range.

[0086] Alternatively, the parallel closing circuit may only include a closing resistor. During closing, the main circuit breaker only needs to be closed according to the closing angle range after the circuit stabilizes.

[0087] Preferably, there are three sets of voltage transformers, and each set of voltage transformers is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when it is closed again.

[0088] Preferably, there are two sets of voltage transformers, each set of which is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when closing again.

[0089] After obtaining the voltages of any two phases through two sets of voltage transformers, the voltage data of the third phase is calculated using the symmetry of the three-phase voltages.

[0090] Preferably, obtaining the remanence of each phase of the three-phase transformer includes:

[0091] Since the main cause of the excitation inrush current is the residual magnetic flux of the internal iron core when the transformer is opened, this flux is also called remanence Φ r , and the remanence Φ is calculated r The phase-controlled closing strategy can be combined to control the excitation inrush current generated when closing the circuit again. The role of the three sets of voltage transformers mentioned above is to provide the calculation of residual magnetism Φ r The three-phase voltage data, such as Figure 6 As shown in the figure, this is an equivalent simplified circuit diagram of the power supply side of a single-phase transformer, and the other two phases can also be equivalent;

[0092] For any phase of a three-phase transformer, the calculation process of its residual magnetism is as follows:

[0093] R is used to represent the equivalent resistance of transformer copper loss and iron loss, L is used to represent the equivalent excitation inductance, and u is used to represent the equivalent i Denotes the input voltage on the power supply side and α denotes the closing angle, then the following formula 1-1 is obtained:

[0094] u i =U m cos(ωt+α) 1-1

[0095] ω is the cosine voltage angular velocity, U m is the cosine voltage amplitude;

[0096] In the voltage input transformer on the power supply side, current flows through the excitation inductor, generating magnetic flux. The relationship between magnetic flux and voltage is shown in the following equations 1-2 and 1-3:

[0097]

[0098] Φ t＝0 =Φ r 1-3

[0099] Where N represents the number of transformer turns, and i is the current generated in the transformer's power supply circuit. Since NΦ = Li in a three-phase transformer, integrating the voltage according to Equations 1-1 to 1-3 yields the expression for magnetic flux, as shown in Equation 1-4.

[0100]

[0101] According to the above formula, the magnetic flux size at each time point can be calculated. When the gate is open, the residual magnetism Φ of one phase can be calculated by the three-phase voltage. r ;

[0102] Φ is the magnetic flux generated by the excitation inductance, Φ t＝0 is the magnetic flux at the moment when the transformer is closed again after being disconnected from operation, Φ(t) represents the magnetic flux at time t, t0 is the moment when the transformer is closed again, and t is the cumulative operating time after closing.

[0103] The present invention uses the residual magnetism Φ calculated by the voltage integration algorithm module r As a basis for closing the circuit breakers of each phase to suppress the generation of magnetizing inrush current of each phase;

[0104] From the calculation of the internal magnetic flux of the transformer, it can be seen that when the circuit breaker is closed again, a transient magnetic flux generated by the excitation inductance will be generated. This magnetic flux is related to the voltage amplitude and the closing angle.

[0105] The sum of this flux and the transformer residual magnetism constitutes the transient flux component at closing;

[0106] When the sum of the transient flux component and the steady-state flux component is not greater than the saturation flux of the transformer, no magnetizing inrush current will be generated in each phase.

[0107] Since the voltage phases of the three phases have a corresponding lead-lag relationship, this relationship will cause the transient magnetic flux and steady-state magnetic flux of each phase to be different, so there is a corresponding time difference in the closing of each phase. When the closing time difference between the front and rear phases exceeds 1.7ms, the closing asynchrony is large. Even if the closing angle meets the closing range, the closing failure will be caused by the closing asynchrony. Therefore, the existing phase-controlled closing technology has certain shortcomings.

[0108] Preferably, calculating the closing angle interval of each phase of the circuit breaker according to the residual magnetism includes:

[0109] Calculate the sum of transient magnetic flux and steady-state magnetic flux corresponding to each closing angle;

[0110] The saturation flux of the three-phase transformer is used as the threshold to determine the sum of the transient flux and the steady-state flux, and the closing angle range that satisfies the conditions for each phase is obtained, including:

[0111] The saturation flux of the three-phase transformer is used as the threshold, and the sum of the transient flux and the steady-state flux generated when the closing angle range is 0 degrees to 360 degrees is calculated. The angle range in which the sum of the transient flux and the steady-state flux is less than the saturation flux of the transformer from 0 degrees to 360 degrees is obtained, thereby obtaining the closing angle range.

[0112] Preferably, determining whether the closing angle interval obtained in the fourth step is too small includes:

[0113] If the range of the closing angle interval is less than 20 degrees, it means that the closing angle interval obtained in the fourth step is too small.

[0114] Preferably, determining whether the closing synchronization between the phases does not meet the closing time difference requirement includes:

[0115] If the closing time difference between two adjacent main circuit breakers is greater than 1.7ms, it means that the closing synchronization between the phases does not meet the closing time difference requirements.

[0116] Preferably, the circuit stability is determined based on whether the current amplitude of the three-phase transformer has recovered to a range of 90% to 110% of the current amplitude during normal operation.

[0117] Beneficial effects:

[0118] (1) The present invention adopts a voltage integration method module, which can more reliably calculate the residual magnetism remaining inside the transformer after the transformer is opened, providing a reliable closing basis for phase-controlled closing;

[0119] (2) The present invention adopts a series closing resistor as the auxiliary suppression part of the method, and the resistance value of the closing resistor can be selected to be smaller than the method of using only the closing resistor as a method for suppressing the excitation inrush current, which has certain economic efficiency;

[0120] (3) The present invention adopts phase-controlled closing based on voltage integration algorithm as the main method to suppress the excitation inrush current, and uses series closing resistance as an auxiliary method to suppress the excitation inrush current, which can more reliably and comprehensively suppress the generation of the excitation inrush current;

[0121] The present invention supplements two special cases that exist in the phase-controlled closing strategy based on the voltage integration algorithm. The two cases include: 1. There is no suitable closing angle range; 2. There is a suitable closing angle range, but the range angle is too small, which can enable more accurate and effective closing.

[0122] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A transformer magnetizing inrush current suppression method based on comprehensive criteria, applied to a transformer closing circuit, which includes a power supply side, a main circuit breaker, and a three-phase transformer; there are three main circuit breakers, one end of which is connected to the input terminal of one phase of the three-phase transformer, and the other end is connected to the power supply side; It is characterized in that The method comprises: The first step is to install a phase-controlled closing control device on the transformer closing circuit. The phase-controlled closing control device includes a parallel closing circuit, a phase-controlled closing module, a voltage integration algorithm module, and a voltage transformer. The parallel closing circuit includes branch circuit breakers and closing resistors. One end of the branch circuit breaker is connected to the transmission line between the power supply side and the main circuit breaker, and the other end is connected to the closing resistor; One end of the closing resistor is connected to the branch circuit breaker, and the other end is connected to the transmission line between the main circuit breaker and the input terminal of one phase of the transformer; The circuit formed by the branch circuit breaker and the closing resistor is in parallel with the circuit where the main circuit breaker is located; The phase-controlled closing module is connected to the main circuit breaker and the branch circuit breaker respectively; The voltage integration algorithm module is connected to the phase-controlled closing module and the voltage transformer respectively; The voltage transformer is used to obtain the voltage of each phase of the three-phase transformer; In the second step, during the closing process of the three-phase transformer, if the main circuit breaker is disconnected due to the excitation inrush current, the voltage transformer records the voltage of each phase of the three-phase transformer; In the third step, the voltage integration algorithm module calculates the residual magnetism of each phase of the three-phase transformer based on the voltage obtained by the voltage transformer; In the fourth step, the phase-controlled closing module calculates the closing angle range of each phase of the circuit breaker based on the residual magnetism, including: Calculate the sum of transient magnetic flux and steady-state magnetic flux corresponding to each closing angle; The saturation flux of the three-phase transformer is used as the threshold to determine the sum of the transient flux and the steady-state flux, and the closing angle range that satisfies the conditions for each phase is obtained, including: The saturation flux of the three-phase transformer is used as the threshold value. The sum of the transient flux and the steady-state flux generated when the closing angle range is 0 degrees to 360 degrees is calculated. The angle range in which the sum of the transient flux and the steady-state flux is less than the saturation flux of the transformer is obtained from 0 degrees to 360 degrees, thereby obtaining the closing angle range. Step 5: Determine whether the closing angle interval obtained in step 4 is too small or the closing synchronization between phases does not meet the closing time difference requirement. If so, proceed to step 7; if not, proceed to step 8. Step 7: Close the branch circuit breaker. After the circuit is stable, close the main circuit breaker and open the branch circuit breaker. Step 8: Close the main circuit breaker according to the closing angle range of each phase.

2. The method for suppressing transformer excitation inrush current based on comprehensive criteria according to claim 1, characterized in that: There are three sets of voltage transformers, and each set of voltage transformers is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when closing again.

3. The transformer excitation inrush current suppression method based on comprehensive criteria according to claim 1 is characterized in that: There are two sets of voltage transformers. Each set of voltage transformers is used to obtain the voltage of one phase of the three-phase transformer before opening and the voltage when closing again. After obtaining the voltages of any two phases through two sets of voltage transformers, the voltage data of the third phase is calculated using the symmetry of the three-phase voltages.

4. The method for suppressing transformer excitation inrush current based on comprehensive criteria according to claim 1, characterized in that: Obtain the residual magnetism of each phase of a three-phase transformer, including: For any phase of a three-phase transformer, the calculation process of its residual magnetism is as follows: R is used to represent the equivalent resistance of transformer copper loss and iron loss, L is used to represent the equivalent excitation inductance, and u is used to represent the equivalent i Denotes the input voltage on the power supply side and α denotes the closing angle, then the following formula 1-1 is obtained: you i =U m cos(ωt+α) 1-1 ω is the cosine voltage angular velocity, U m is the cosine voltage amplitude; In the voltage input transformer on the power supply side, current flows through the excitation inductor, generating magnetic flux. The relationship between magnetic flux and voltage is shown in the following equations 1-2 and 1-3: F t＝0 =Φ r 1-3 Where N represents the number of transformer turns, and i is the current generated in the transformer's power supply circuit. Since NΦ = Li in a three-phase transformer, integrating the voltage according to Equations 1-1 to 1-3 yields the expression for magnetic flux, as shown in Equation 1-4. According to the above formula, the magnetic flux size at each time point can be calculated. When the gate is open, the residual magnetism Φ of one phase can be calculated by the three-phase voltage. r ; Φ is the magnetic flux generated by the excitation inductance, Φ t＝0 is the magnetic flux at the moment the transformer is closed again after being disconnected from operation, Φ(t) represents the magnetic flux at time t, t0 is the moment the transformer is closed again, and t is the cumulative operating time after closing.

5. The transformer excitation inrush current suppression method based on comprehensive criteria according to claim 1, characterized in that: Determine whether the closing angle range obtained in step 4 is too small, including: If the range of the closing angle interval is less than 20 degrees, it means that the closing angle interval obtained in the fourth step is too small.

6. The transformer excitation inrush current suppression method based on comprehensive criteria according to claim 1, characterized in that: Determine whether the closing synchronization between phases does not meet the closing time difference requirements, including: If the closing time difference between two adjacent main circuit breakers is greater than 1.7ms, it means that the closing synchronization between the phases does not meet the closing time difference requirements.

7. The transformer excitation inrush current suppression method based on comprehensive criteria according to claim 1, characterized in that: The criterion for judging the stability of the circuit is that the current amplitude of the three-phase transformer returns to the range of 90% to 110% of the current amplitude during normal operation.

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