A method for reducing the closing inrush current of a power distribution network

Abstract

The application discloses a method for reducing closing excitation magnetic inrush current of a power distribution network, and relates to the technical field of transformer excitation magnetic inrush current suppression. The method comprises the following steps: when a switch of a feeder of the power distribution network is opened, three-phase magnetic fluxes of a load side of the feeder at the moment of opening are calculated; three-phase magnetic fluxes of a power supply side of the feeder at the moment of receiving a closing instruction are calculated; a target initial phase angle of three-phase magnetic fluxes of the power supply side of the feeder is solved when the sum of the three-phase magnetic fluxes of the load side and the three-phase magnetic fluxes of the power supply side is zero; a target initial phase angle of three-phase voltages of the power supply side of the feeder is calculated based on the target initial phase angle of three-phase magnetic fluxes of the power supply side of the feeder; the voltage phase of the power supply side of the feeder is adjusted to the target initial phase angle of three-phase voltages; and the switch is closed after receiving the closing instruction. The application realizes dynamic offset of the excitation magnetic flux of the power supply side and the residual magnetic flux of the load side at the moment of actual closing of the switch, thereby fundamentally reducing the sudden change of the core magnetic flux and effectively reducing the excitation magnetic inrush current of the power distribution network.

Description

Technical Field

[0001] This invention relates to the field of transformer inrush current suppression technology, specifically, to a method for reducing inrush current during power distribution network closing. Background Technology

[0002] With the rapid development of science and technology and the economy in my country, power grid construction has also entered a period of rapid development, and power supply has entered a stage of high reliability. However, with the increase in users, the number and capacity of distribution transformers on single feeders in the distribution network are increasing. When the feeder circuit breaker is closed, the inrush currents generated by the downstream transformers superimposed on each other may produce a large inrush current, which often causes the instantaneous overcurrent protection to malfunction. For instantaneous faults, this may lead to reclosing failure or FA reclosing failure, expanding the power outage area.

[0003] The fundamental reason for the generation of inrush current is the saturation of the transformer core. When the core is in an unsaturated state, the excitation current increases linearly with the increase of magnetic flux, and its value is relatively small. However, when the core is saturated, the magnetic current increases significantly with the increase of magnetic flux, eventually forming an inrush current.

[0004] To address the issue of reducing inrush current, the industry has conducted extensive research, primarily focusing on two directions: Firstly, in material selection, using anti-saturation materials for transformer cores. However, current mainstream core materials still cannot escape saturation, especially when there are many distribution transformers on the feeder line with a large total capacity. Secondly, through research on inrush current identification and prevention of maloperation, some specific application methods have been proposed, such as the second harmonic suppression method, which suppresses protection when the detected second harmonic occupancy rate exceeds a set threshold; the discontinuity angle identification braking method, which identifies inrush current through discontinuity angles to suppress protection; and methods that add time delays to protection to avoid inrush current. Overall, these methods have played a significant role in reducing inrush current and preventing maloperation. However, most of these methods suppress protection tripping after inrush current occurs, which to some extent prolongs the actual fault response time. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of excitation inrush current generation at its root.

[0006] To achieve the above objectives, the present invention provides a method for reducing inrush current during closing in a power distribution network, the method comprising the following steps:

[0007] When the switch on the distribution network feeder trips, record the tripping time. and calculate The three-phase magnetic flux on the load side of the feeder at any given time;

[0008] The moment the closing command is received At time =0, calculate the three-phase magnetic flux of the feeder line at the power supply side at the moment;

[0009] solving the the sum of the three-phase magnetic flux of the feeder line at the load side at the moment and the three-phase magnetic flux of the feeder line at the power supply side at the moment is zero, the target initial phase angle of the three-phase magnetic flux of the feeder line at the power supply side;

[0010] based on the target initial phase angle of the three-phase magnetic flux of the feeder line at the power supply side, the the target initial phase angle of the three-phase voltage of the feeder line at the power supply side at the moment;

[0011] adjusting the voltage phase of the feeder line at the power supply side to the the target initial phase angle of the three-phase voltage of the feeder line at the power supply side at the moment;

[0012] when receiving the closing instruction, closing the switch.

[0013] wherein, the principle of the present application is:

[0014] for the power distribution network, the voltage and the magnetic flux added to the primary side of the transformer have the following relationship: (1), wherein, is the steady-state voltage amplitude, is the magnetic flux, is the angular frequency, is the voltage initial phase angle.

[0015] the instantaneous magnetic flux expression can be obtained by solving the differential equation of formula (1): (2), wherein, is the magnetic flux amplitude, , is the decay constant.

[0016] As can be seen from formula (2), when the transformer is put into use, the instantaneous magnetic flux is related to three parts of the steady-state magnetic flux , the transient magnetic bias and the residual magnetism . In order to minimize the instantaneous magnetic flux to reduce the excitation inrush current, the value of should be reduced as much as possible, and in the most ideal case, the value of should be zero.

[0017] wherein, the residual magnetism refers to the magnetic induction intensity of the core material remaining due to the hysteresis effect after the switch is opened, which can be approximately regarded as the three-phase magnetic flux of the feeder line at the load side at the moment . And the transient magnetic bias can be regarded as the three-phase magnetic flux of the power supply side at the moment =0.

[0018] Therefore, the present application first calculates the​ The three-phase magnetic flux on the load side of the feeder at any given time, due to Since the initial phase angles of the three-phase magnetic flux on the feeder load side are known, this value is the actual value; then calculate... The three-phase magnetic flux on the feeder power supply side is listed at this time. Since the initial phase angle of the target three-phase magnetic flux on the feeder power supply side is not yet determined, this step only lists the three-phase magnetic flux. The expression for calculating the three-phase magnetic flux on the power supply side of the feeder at any given time. Then, based on this expression and... The initial phase angle of the target three-phase magnetic flux on the feeder power supply side is calculated when the sum of the three-phase magnetic flux on the load side is zero; finally, the value of the three-phase magnetic flux on the load side is obtained. The target initial phase angle of the three-phase voltage on the feeder power supply side is determined. The phase of the feeder power supply side voltage is adjusted to the target initial phase angle. After the initial phase angle of the target three-phase voltage on the power supply side of the feeder is determined, if the circuit is closed at this time, the magnetic flux will directly enter a steady state and will not saturate. Therefore, a large inrush current will not be generated, which can effectively suppress the generation of inrush current.

[0019] Furthermore, the calculation The three-phase magnetic flux on the load side of the feeder at any given time includes:

[0020] calculate Phase A flux on the load side of the feeder at any time ,in, ;

[0021] calculate Phase B flux on the load side of the feeder at any time ,in, ;

[0022] calculate C-phase flux on the load side of the feeder at any time ,in, ;

[0023] in, The magnitude of the magnetic flux. Angular frequency, , This is the steady-state voltage amplitude. The initial phase angle is the A-phase flux on the load side of the feeder.

[0024] Furthermore, the calculation The three-phase magnetic flux on the power supply side of the time feeder includes:

[0025] calculate Phase A flux on the power supply side of the time feeder ,in, ;

[0026] calculate Phase B flux on the power supply side of the time feeder ,in, ;

[0027] calculate C-phase flux on the power supply side of the time feeder ,in, ;

[0028] in, The initial phase angle is the target phase A magnetic flux on the feeder power supply side.

[0029] Furthermore, the aforementioned The three-phase magnetic flux on the load side of the feeder at that time and the When the sum of the three-phase magnetic flux on the power supply side of the feeder is zero, including:

[0030] + =0、 + =0 and + =0.

[0031] Furthermore, the initial phase angle of the target three-phase magnetic flux calculated based on the power supply side of the feeder is obtained. The initial phase angle of the target three-phase voltage on the power supply side of the feeder at any given time includes:

[0032] calculate Initial phase angle of the target A-phase voltage on the feeder power supply side ,in, ;

[0033] calculate Initial phase angle of the target B-phase voltage on the feeder power supply side ,in, ;

[0034] calculate Initial phase angle of the target C-phase voltage on the feeder power supply side ,in, .

[0035] Furthermore, the closing switch includes:

[0036] The timing of the closing operation is calculated based on the switch closing time. When it reaches At that time, the closing operation is performed.

[0037] Among them, the distribution network switch requires a certain amount of time from the start of closing to the completion of closing. If in The closing operation is performed at any time. Upon completion of the closing, the three-phase magnetic flux on the feeder power supply side will change, causing it to lose its connection with... To prevent the three-phase flux matching on the load side of the feeder from occurring, this invention calculates the timing of the closing operation by taking into account the switch closing time. This ensures that at the moment the switch is actually closed, the three-phase magnetic flux on the feeder power supply side is... The same moment.

[0038] Furthermore, the calculation of the closing operation time based on the switch closing time... ,include:

[0039] Obtain the time taken for the switch to close from the start of closing to the completion of closing. ;

[0040] Will The closing phase offset time is obtained by taking the remainder of the voltage's power frequency period. ;

[0041] Subtract the closing phase offset time from the power frequency period. ,get .

[0042] in, Taking the remainder of the power frequency cycle yields the time required for the switch to close when it exceeds an integer multiple of the power frequency cycle but is less than the power frequency cycle. Subtract the power frequency period from the power frequency period This yielded the time difference needed to complete the full cycle, due to =0, so this time difference is also the actual moment when the closing operation is performed. In this way, when a closing command is received, preparations for closing are made, and when the time is reached... Immediately close the switch, and then... Afterwards, the closing process is completed, thus ensuring that the closing time is consistent with... The time interval between them is an integer multiple of the power frequency cycle, at which time the three-phase magnetic flux on the feeder power supply side and The same moment.

[0043] Furthermore, the initial phase angle of the A-direction magnetic flux on the load side of the feeder... It is 0.

[0044] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0045] The application calculates the residual magnetic state of the load side transformer core at the switching-off moment in real time, calculates the magnetic flux target initial phase angle required at the closing moment of the power supply side, dynamically adjusts the power supply voltage phase to the theoretical matching point, simultaneously compensates the inherent action delay of the switch closing, and finally realizes the dynamic offset of the excitation magnetic flux of the power supply side and the residual magnetic flux of the load side at the actual closing moment of the switch, so as to fundamentally reduce the sudden change of the core magnetic flux and effectively reduce the excitation inrush current of the power distribution network. BRIEF DESCRIPTION OF DRAWINGS

[0046] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and do not limit the application in any way.

[0047] Figure 1 is a flowchart of a method for reducing the closing excitation inrush current of a power distribution network in the application. DETAILED DESCRIPTION

[0048] In order to more clearly understand the above-mentioned purposes, features and advantages of the application, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be noted that the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

[0049] In the following description, many specific details are set forth in order to provide a thorough understanding of the application, however, the application can also be implemented in other ways different from the scope described herein, therefore, the protection scope of the application is not limited by the specific embodiments disclosed below.

[0050] Embodiment one

[0051] Please refer to Figure 1 , the embodiment one of the application provides a method for reducing the closing excitation inrush current of a power distribution network, the method comprises the following steps:

[0052] When the switch of the power distribution network feeder is switched off, the three-phase magnetic flux of the load side at the switching-off moment is recorded, and the three-phase magnetic flux of the load side at the moment is calculated;

[0053] Let the moment when the closing instruction is received =0, the three-phase magnetic flux of the power supply side at the moment is calculated;

[0054] When the sum of the three-phase magnetic flux of the load side at the moment and the three-phase magnetic flux of the power supply side at the moment is zero, the target three-phase magnetic flux initial phase angle of the power supply side is solved;

[0055] The target three-phase magnetic flux initial phase angle of the power supply side is calculated based on the target three-phase magnetic flux initial phase angle of the power supply side The target initial phase angle of the three-phase voltage on the power supply side of the feeder at any given time;

[0056] Adjust the phase of the feeder power supply side voltage to the specified... Initial phase angle of the target three-phase voltage on the power supply side of the feeder at any given time;

[0057] Upon receiving the closing command, the switch is closed.

[0058] In this embodiment, a 10kV distribution network feeder is used as an example, with a system frequency of 50Hz and a steady-state voltage amplitude. =8.16kV, angular frequency =314 rad / s, magnetic flux amplitude =26mWb, the control logic is implemented using protection and control devices, and the closing switch is a VS1 type vacuum circuit breaker with its inherent closing time. =45ms±2ms.

[0059] Wherein, the calculation The three-phase magnetic flux on the load side of the feeder at any given time includes:

[0060] calculate Phase A flux on the load side of the feeder at any time ,in, ;

[0061] calculate Phase B flux on the load side of the feeder at any time ,in, ;

[0062] calculate C-phase flux on the load side of the feeder at any time ,in, ;

[0063] in, The magnitude of the magnetic flux. Angular frequency, , This is the steady-state voltage amplitude. The initial phase angle is the A-phase flux on the load side of the feeder.

[0064] In this embodiment, to simplify the calculation, the initial phase angle of the A-direction magnetic flux on the load side of the feeder is assumed. Assume it is 0. Substituting the value at 0.352s, we get:

[0065] = -22.1mWb, =13.5mWb, =8.6mWb.

[0066] The calculation of the target three-phase magnetic flux initial phase angle of the feeder power side based on the target three-phase magnetic flux initial phase angle of the feeder load side includes: The calculation of the A-phase magnetic flux of the feeder power side at the time t includes:

[0067] The calculation of the B-phase magnetic flux of the feeder power side at the time t includes: The calculation of the C-phase magnetic flux of the feeder power side at the time t includes:

[0068] The calculation of the target A-phase voltage initial phase angle of the feeder power side at the time t includes: The calculation of the target B-phase voltage initial phase angle of the feeder power side at the time t includes:

[0069] The calculation of the target C-phase voltage initial phase angle of the feeder power side at the time t includes:

[0070] The calculation of the target three-phase voltage initial phase angle of the feeder power side at the time t based on the target three-phase magnetic flux initial phase angle of the feeder power side includes: The initial phase angle of the target A-phase magnetic flux of the feeder power side.

[0071] The actual time t when the instruction is received is assumed to be the time t0, and the following is substituted into the formula: The time t0 is set to be the 5th second, and the following is substituted into the formula: = 26 mWb, and the following is calculated:

[0072]

[0073] The calculation of the target three-phase magnetic flux initial phase angle of the feeder power side based on the target three-phase magnetic flux initial phase angle of the feeder load side includes: The sum of the three-phase magnetic flux of the feeder load side at the time t and the three-phase magnetic flux of the feeder power side at the time t is zero, and includes:

[0074] = 0, = 0, and = 0, i.e. -22.1 mWb = 0, 13.5 mWb = 0, and 8.6 mWb = 0, and the solution is = ± 35.2°.

[0075] The calculation of the target three-phase voltage initial phase angle of the feeder power side at the time t based on the target three-phase magnetic flux initial phase angle of the feeder power side includes: The calculation of the target A-phase voltage initial phase angle of the feeder power side at the time t based on the target three-phase magnetic flux initial phase angle of the feeder power side includes:

[0076] The calculation of the target B-phase voltage initial phase angle of the feeder power side at the time t based on the target three-phase magnetic flux initial phase angle of the feeder power side includes: The calculation of the target C-phase voltage initial phase angle of the feeder power side at the time t based on the target three-phase magnetic flux initial phase angle of the feeder power side includes: ​​​​​​​​​​​​​​​​

[0077] Computing the target B-phase target voltage initial phase angle of the feeder power side at the moment wherein, ;

[0078] Computing the target C-phase voltage initial phase angle of the feeder power side at the moment wherein, .

[0079] Assuming = 35.2°, we get = -122.5°, = -242.5°, = -2.5°.

[0080] wherein, the closed switch comprises:

[0081] calculating the moment of performing the closing operation based on the closing time of the switch when the moment is reached, the closing operation is performed.

[0082] wherein, the moment of performing the closing operation based on the closing time of the switch comprises:

[0083] obtaining the closing time of the switch from the start of closing to the completion of closing ;

[0084] taking the closing phase offset time modulo the power frequency cycle of the voltage ;

[0085] subtracting the closing phase offset time from the power frequency cycle of the voltage , obtaining .

[0086] wherein, the power frequency cycle = 20ms, and the closing time of the switch is calculated to be = 15ms, that is, after receiving the closing instruction, the closing is started after 15ms, and the actual closing moment of the switch is = + = 60ms (that is, 3 complete cycles), at which time the voltage phase of the power side accurately returns to the target value .

[0087] Embodiment Two

[0088] ​Based on Example 1, in the prior art, when studying how to reduce inrush current in distribution networks, residual magnetism is usually considered to be constant (e.g., CN 116316430 A). However, in reality, after a transformer is tripped, the residual magnetism in its core slowly decays over time. This decay leads to… When calculating the target magnetic flux at any time, the method used is... The recorded magnetic flux value is higher than the actual residual magnetism value, which eventually leads to a deviation in magnetic flux matching when closing the circuit breaker, making it impossible to completely eliminate inrush current.

[0089] Therefore, in the calculation of this embodiment Before the initial phase angle of the target three-phase magnetic flux on the feeder power supply side, it also includes the... The three-phase magnetic flux values ​​on the load side of the feeder are attenuated and corrected to obtain the corrected three-phase magnetic flux values ​​on the load side. , and .

[0090] Specifically, the above refers to the The three-phase magnetic flux attenuation on the load side of the feeder is corrected, including:

[0091] Calculate separately The three-phase flux density corresponding to the three-phase flux on the load side of the feeder at any given moment, specifically calculated as: Phase A flux density B-phase magnetic flux density and C-phase magnetic flux density ,in, This represents the effective cross-sectional area of ​​the iron core.

[0092] calculate Time and Time interval of time According to the time sequence, with a fixed time step Evenly divide the time interval To obtain a series of moments , , ... ( = , = The value of N can be determined by those skilled in the art based on the actual situation.

[0093] In chronological order, at each moment, resistivity is updated, power loss is calculated, temperature is updated, and magnetic flux density is updated.

[0094] The formula for updating the resistivity is as follows:

[0095] ,in For The core resistivity, The core resistivity at the reference temperature The core resistivity at the reference temperature The temperature coefficient of resistivity, which represents the sensitivity of the core material resistivity to temperature change, , And Can be retrieved from the transformer parameter library; For The actual temperature of the core, Can be obtained by actual measurement.

[0096] The formula for calculating the loss power is:

[0097] Where. For Power loss, For Magnetic flux density, Hysteresis loss coefficient, Eddy current loss coefficient, Hysteresis loss index, , And Can be retrieved from the transformer parameter library, Effective frequency, which can be 50Hz, Eddy current loss, Hysteresis loss.

[0098] The formula for updating the temperature is:

[0099] Where, For The actual temperature of the core, The current ambient temperature, The equivalent heat capacity of the core, The equivalent thermal resistance of the core, And Can be retrieved from the transformer parameter library.

[0100] The formula for updating the magnetic flux density is:

[0101] Where, For Magnetic flux density, Effective volume of the core, which can be obtained by actual measurement, Magnetic permeability of the core, which can be retrieved from the transformer parameter library.

[0102] The above four processes are sequentially cycled between each time, and finally the magnetic flux density at the time , further calculation obtains corrected magnetic flux at the time , , the corrected magnetic flux as input items to calculate the target three-phase magnetic flux initial phase angle of the feeder power side, which can more effectively realize the filtering of the magnetizing inrush current.

[0103] The embodiment establishes the iron core thermal-electric-magnetic dynamic coupling model, and accurately quantifies the decay process of residual magnetism after switching off through the law of conservation of energy, and the specific mechanism is:

[0104] The residual magnetism of the iron core after switching off is converted into heat energy due to eddy current loss and hysteresis loss;

[0105] The heat energy causes the temperature of the iron core to rise, changing the resistivity;

[0106] The resistivity change reacts on the loss power;

[0107] The loss power continuously consumes the magnetic energy, driving the magnetic flux to decay.

[0108] The present application innovatively includes the magnetic permeability , the volume of the iron core into the decay calculation, strictly correlates the magnetic density change and energy dissipation through the differential equation , and introduces the effective frequency , compatible with the non-power frequency state after switching off, solving the defect of ignoring the frequency dependence of the traditional model.

[0109] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to the embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including all changes and modifications falling within the scope of the present application.

[0110] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for reducing inrush current during closing in a power distribution network, characterized in that, The method includes the following steps: When the switch on the distribution network feeder trips, record the tripping time. and calculate The three-phase magnetic flux on the load side of the feeder at any given time; When the closing command is received At time =0, calculate The three-phase magnetic flux on the power supply side of the feeder at all times; Solve the above The three-phase magnetic flux on the load side of the feeder at that time and the When the sum of the three-phase magnetic flux on the feeder power supply side is zero, the initial phase angle of the target three-phase magnetic flux on the feeder power supply side; The initial phase angle of the target three-phase magnetic flux on the feeder power supply side is calculated to obtain... The target initial phase angle of the three-phase voltage on the power supply side of the feeder at any given time; Adjust the phase of the feeder power supply side voltage to the specified... Initial phase angle of the target three-phase voltage on the power supply side of the feeder at any given time; Upon receiving the closing command, the switch is closed. Before calculating the initial phase angle of the target three-phase magnetic flux on the feeder power supply side, the calculation also includes... The three-phase magnetic flux on the load side of the feeder is attenuated and corrected to obtain... The corrected magnetic flux at time is used as an input to calculate the initial phase angle of the target three-phase magnetic flux on the feeder power supply side; Among them, for the The three-phase magnetic flux attenuation on the load side of the feeder is corrected, including: calculate The three-phase flux density corresponding to the three-phase flux on the load side of the feeder at any given time; calculate Time and Time interval of time According to the time sequence, with a fixed time step Divide the time intervals evenly To obtain a series of moments ,in , ; Following a chronological order, at each moment, resistivity is updated, power loss is calculated, temperature is updated, and magnetic flux density is updated, ultimately yielding... magnetic flux density at time Further calculations yielded Time-corrected magnetic flux : ,in, This represents the effective cross-sectional area of ​​the iron core.

2. The method for reducing inrush current during closing in a distribution network according to claim 1, characterized in that, The calculation The three-phase magnetic flux on the load side of the feeder at any given time includes: calculate Phase A flux on the load side of the feeder at any time ,in, ; calculate Phase B flux on the load side of the feeder at any time ,in, ; calculate C-phase flux on the load side of the feeder at any time ,in, ; in, The magnitude of the magnetic flux. Angular frequency, , This is the steady-state voltage amplitude. The initial phase angle is the A-phase flux on the load side of the feeder.

3. The method for reducing inrush current during closing in a distribution network according to claim 2, characterized in that, The calculation The three-phase magnetic flux on the power supply side of the time feeder includes: calculate Phase A flux on the power supply side of the time feeder ,in, ; calculate Phase B flux on the power supply side of the time feeder ,in, ; calculate C-phase flux on the power supply side of the time feeder ,in, ; in, The initial phase angle is the target phase A magnetic flux on the feeder power supply side.

4. The method for reducing inrush current during closing in a distribution network according to claim 3, characterized in that, The The three-phase magnetic flux on the load side of the feeder at that time and the When the sum of the three-phase magnetic flux on the power supply side of the feeder is zero, including: .

5. The method for reducing inrush current during closing in a distribution network according to claim 3, characterized in that, The initial phase angle of the target three-phase magnetic flux obtained based on the feeder power supply side is calculated. The initial phase angle of the target three-phase voltage on the feeder power supply side includes: calculate Initial phase angle of the target A-phase voltage on the feeder power supply side ,in, ; calculate Initial phase angle of the target B-phase voltage on the feeder power supply side ,in, ; calculate Initial phase angle of the target C-phase voltage on the feeder power supply side ,in, .

6. The method for reducing inrush current during closing in a distribution network according to claim 1, characterized in that, The closing switch includes: The timing of the closing operation is calculated based on the switch closing time. When it reaches At that time, the closing operation is performed.

7. A method for reducing inrush current during closing in a distribution network according to claim 6, characterized in that, The timing for performing the closing operation is calculated based on the switch closing time. ,include: Obtain the time taken for the switch to close from the start of closing to the completion of closing. ; Will The closing phase offset time is obtained by taking the remainder of the voltage's power frequency period. ; Subtract the closing phase offset time from the power frequency period. ,get .

8. The method for reducing inrush current during closing in a distribution network according to claim 1, characterized in that, Initial phase angle of A-direction magnetic flux on the load side of the feeder It is 0.

Images