A method for calculating parameters under an asymmetric short-circuit fault condition

Abstract

The embodiment of the application discloses a kind of parameter calculation methods under asymmetric short-circuit fault condition. Among them, the method comprises: under symmetric short-circuit fault condition, obtaining the expected current ac component oscillogram of symmetric short-circuit;By expected current ac component oscillogram, the current effective value and the phase angle difference of current voltage of multiple time are measured;Under asymmetric short-circuit fault condition, the voltage phase angle of multiple time is measured;According to current effective value, the phase angle difference of current voltage and voltage phase angle, attenuation coefficient is calculated;According to attenuation coefficient, direct current time constant is calculated;According to current effective value, the phase angle difference of current voltage, voltage phase angle and the direct current time constant determine asymmetric short-circuit current expression, so current expression under asymmetric short-circuit fault condition can be simply and accurately obtained, and the operation amount and error rate are reduced.

Description

Technical Field

[0001] This application relates to the field of short-circuit testing technology for high-voltage AC circuit breakers, and more specifically, to a method for calculating parameters under asymmetrical short-circuit fault conditions. Background Technology

[0002] When a high-voltage AC circuit breaker interrupts an asymmetrical short-circuit fault in a power system, the short-circuit current will not decay to zero quickly due to the large time constant. This results in the presence of a DC component in the short-circuit current, causing the current waveform to become asymmetrical and exhibiting an alternation between large and small half-waves.

[0003] Currently, methods for calculating current under asymmetrical short-circuit fault conditions do not consider the fluctuation of the effective value of the AC component, which can lead to significant errors. Furthermore, the calculation formulas are complex and require a large amount of data, resulting in a complicated and time-consuming calculation process. Therefore, it is essential to derive and calculate a simple and accurate expression for the current under asymmetrical short-circuit fault conditions. Summary of the Invention

[0004] In view of this, this application discloses a method for calculating parameters under asymmetrical short-circuit fault conditions, so as to obtain the current expression under asymmetrical short-circuit fault conditions simply and accurately.

[0005] The technical solutions provided in this application are as follows:

[0006] In a first aspect, embodiments of this application provide a method for calculating parameters under asymmetric short-circuit fault conditions, the method comprising:

[0007] Under symmetrical short-circuit fault conditions, obtain the oscilloscope diagram of the expected AC current component of the symmetrical short circuit;

[0008] The effective value of the current and the phase angle difference between the current and voltage at multiple moments are measured using the oscilloscope of the expected current AC component.

[0009] Under asymmetrical short-circuit fault conditions, the voltage phase angles at multiple moments were measured;

[0010] The attenuation coefficient is calculated based on the effective value of the current, the phase angle difference between the current and the voltage, and the voltage phase angle.

[0011] The DC time constant is calculated based on the attenuation coefficient.

[0012] The expression for the asymmetric short-circuit current is determined based on the effective value of the current, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant.

[0013] In one possible implementation, the effective current value includes the effective value of phase A current, the effective value of phase B current, and the effective value of phase C current; the phase angle difference between current and voltage includes the phase angle difference between phase A current and voltage, the phase angle difference between phase B current and voltage, and the phase angle difference between phase C current and voltage; the voltage phase angle includes the phase angle between phase A voltage, the phase angle between phase B voltage, and the phase angle between phase C voltage.

[0014] The attenuation coefficient of phase A is calculated using the following formula:

[0015]

[0016] Among them, the ΔT The first moment and the second moment represent the time difference between the first moment and the second moment, which are any two moments from the plurality of moments. τ represents the DC time constant of phase A. Aacr This represents the effective value of the phase A current at the first moment. This represents the phase angle of phase A voltage at the first moment. I represents the phase angle of the A-phase current and voltage at the first moment. Aacb This represents the effective value of the phase A current at the second moment. Phase angle of phase A voltage at the second moment. This represents the phase angle of the A-phase current and voltage at the second moment;

[0017] Similarly, the attenuation coefficient of phase B or phase C is derived from the attenuation coefficient of phase A.

[0018] In one possible implementation, the expression for the change of phase A current with time starting from the first moment is:

[0019] For the small half-wave:

[0020] For the majority of the wave:

[0021] Wherein, i A (t) represents the expression for the change of phase A current with time, where p represents the percentage of the DC component.

[0022] Similarly, the expressions for the change of phase B current with time or the change of phase C current with time can be derived from the corresponding expressions for the change of phase A current with time.

[0023] The expressions for the changes in phase A current over time, the expressions for the changes in phase B current over time, and the expressions for the changes in phase C current over time constitute the expression for the asymmetrical short-circuit current.

[0024] In one possible implementation, the first moment is the moment when the current is zero, and the second moment is the moment adjacent to the moment when the current is zero, wherein the moment adjacent to the moment when the current is zero has elapsed a time difference. ΔT Then, at the moment when the current reaches zero.

[0025] In one possible implementation, the method further includes:

[0026] Based on the effective value of the current, the phase angle difference between the current and the voltage, the voltage phase angle, and the DC time constant, determine the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions.

[0027] The per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions is:

[0028] For the small half-wave:

[0029] For the majority of the wave:

[0030] Among them, the p represents the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions in phase A, where p represents the percentage of the DC component. ω represents the angular frequency;

[0031] Similarly, the per-unit expression for the rate of change of current under phase B asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, or the per-unit expression for the rate of change of current under phase C asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, can be derived from the per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions.

[0032] In one possible implementation, the method further includes:

[0033] Obtain the transient recovery voltage and current under symmetrical short-circuit fault conditions at multiple time points;

[0034] Based on the transient recovery voltage and current under the symmetrical short-circuit fault conditions, the loop response parameters are calculated.

[0035] The current under asymmetric short-circuit fault conditions at multiple times can be calculated using the aforementioned asymmetric short-circuit current expression.

[0036] Based on the circuit response parameters and the current under the asymmetrical short-circuit fault condition, the current coefficient under the asymmetrical short-circuit fault condition is calculated.

[0037] Based on the circuit response parameters and the current coefficient under the asymmetric short-circuit fault condition, the transient recovery voltage under the asymmetric short-circuit fault condition at multiple times is calculated.

[0038] In one possible implementation, the loop response parameters are calculated according to the following formula:

[0039] Z0 = loop_c(1) / T / I S0

[0040] Z1 = (loop_c(2) / TI) S1 ·Z0) / I S0

[0041] Z2=[loop_c(3) / T-(I S1 ·Z1+I S2 ·Z0)] / I S0

[0042] ...

[0043] Z i =[loop_c(i-1) / T-(I S1 ·Z1+I S2 ·Z0+……I Si ·Z0)] / I S0

[0044] Among them, I S0 I S1 I S2 ...I Si The current coefficient under symmetrical short-circuit fault conditions is represented by T, where T represents the linear fitting step size.

[0045] loop_c(1)=U1

[0046] loop_c(2) = U2 - 2U1

[0047] loop_c(3)=U3-2U2+U1

[0048] ...

[0049] loop_c(i)=U i -2U i-1 +U i-2

[0050] U1 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1, U2 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T2, and U3 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T3. i T representsi The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-1 T represents i-1 The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-2 T represents i-2 The transient recovery voltage under symmetrical short-circuit fault conditions at time i, where i is a positive integer greater than 1;

[0051] The current coefficient under the symmetrical short-circuit fault condition is calculated using the following formula:

[0052] I s0 =I1 / T

[0053] I s1 =(I2-I s0 *T) / T

[0054] I s2 =[I3-(I s0 *2T+I s1 *T)] / T

[0055] ...

[0056] I si =[I i+1 -(I s0 *iT+I s1 *(i-1)T+……I si-1 *T)] / T

[0057] I1 represents the current under the symmetrical short-circuit fault condition at time T1, I2 represents the current under the symmetrical short-circuit fault condition at time T2, and I3 represents the current under the symmetrical short-circuit fault condition at time T3. i+1 T represents i+1 Current under symmetrical short-circuit fault conditions at any given time.

[0058] In one possible implementation, the current coefficient under the asymmetric short-circuit fault condition is calculated according to the following formula:

[0059] I s0_asy =I 1_asy / T

[0060] I s1_asy =(I 2_asy -I s0_asy *T) / T

[0061] I s2_asy =(I 3_asy -I s0_asy *2T-I s1_asy *T) / T

[0062] ...

[0063] I si-1_asy =(I i_asy -I s0_asy *(i-1)T-……I si-3_asy *2T-I si-2_asy *T) / T

[0064] Wherein, the I 1_asy I represents the current under the asymmetrical short-circuit fault condition at time T1. 2_asy I represents the current under the asymmetrical short-circuit fault condition at time T2. i_asy T represents i Current under asymmetrical short-circuit fault conditions at a given time.

[0065] In one possible implementation, the transient recovery voltage under the asymmetric short-circuit fault condition is calculated according to the following formula:

[0066] U 1_asy =U1(I s0_asy ·Z0·T)

[0067] U 2_asy =U 1_asy +loop_t_asy(2)

[0068] ...

[0069] U i_asy =U i-1_asy +loop_t_asy(i)

[0070] in,

[0071] loop_t_asy(2)=I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T

[0072] loop_t_asy(3)=I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T+(I s0_asy ·Z2+I s1_asy ·Z1+I s2_asy ·Z0)T

[0073] ...

[0074] loop_t_asy(i) = I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T+(I s0_asy·Z2+I s1_asy ·Z1+I s2_asy ·Z0)T+……(I s0_asy ·Z i-1 +I s1_asy ·Z i-2 +……I si-1_asy ·Z0)T

[0075] The U 1_asy U1 represents the transient recovery voltage under the asymmetrical short-circuit fault condition at time T1, and I represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1. s0_asy Z0 represents the current coefficient under asymmetrical short-circuit fault conditions, and Z0 represents the loop response parameter; U 2_asy U represents the transient recovery voltage under the asymmetric short-circuit fault condition at time T2; i_asy T represents i The transient recovery voltage under asymmetric short-circuit fault conditions at time U i-1_asy T represents i-1 Transient recovery voltage under asymmetrical short-circuit fault conditions at a given time.

[0076] Based on the above technical solution, this application has the following beneficial effects:

[0077] This application discloses a method for calculating parameters under asymmetrical short-circuit fault conditions. The method includes: under symmetrical short-circuit fault conditions, acquiring an oscilloscope diagram of the expected AC component of the symmetrical short-circuit current; measuring the effective current value and the phase angle difference between the current and voltage at multiple moments using the oscilloscope diagram; under asymmetrical short-circuit fault conditions, measuring the voltage phase angle at multiple moments; calculating an attenuation coefficient based on the effective current value, the phase angle difference between the current and voltage, and the voltage phase angle; calculating a DC time constant based on the attenuation coefficient; and determining an asymmetrical short-circuit current expression based on the effective current value, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant. It is evident that by acquiring the effective value of the AC component under symmetrical short-circuit fault conditions to determine the current expression under asymmetrical short-circuit fault conditions, this method can reduce parameter reading and calculation errors caused by fluctuations in the effective value of the AC component of the short-circuit current, resulting in a more accurate current expression under asymmetrical short-circuit fault conditions. Moreover, by using the effective value of the current, the phase angle difference between the current and voltage, and the voltage phase angle, the current expression under simple asymmetrical short-circuit fault conditions can be easily and conveniently derived, reducing the amount of calculation and the error rate, and making it highly versatile. Attached Figure Description

[0078] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the published drawings without creative effort.

[0079] Figure 1 This is a flowchart illustrating a method for calculating parameters under asymmetric short-circuit fault conditions disclosed in an embodiment of this application.

[0080] Figure 2 This is a schematic diagram of an asymmetric short-circuit current and the expected AC component disclosed in an embodiment of this application;

[0081] Figure 3 This is a schematic diagram illustrating the calculation of loop response parameters disclosed in an embodiment of this application. Detailed Implementation

[0082] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0083] The terms “comprising,” “including,” “having,” and variations thereof, used in this specification, all mean “including but not limited to,” unless otherwise specifically emphasized. It should be noted that in the description of embodiments in this application, terms such as “first,” “second,” etc., are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0084] When a high-voltage AC circuit breaker interrupts an asymmetrical short-circuit fault in a power system, the short-circuit current does not decay to zero quickly due to its large time constant. This results in a DC component in the short-circuit current, causing the current waveform to become asymmetrical and exhibiting alternating large and small half-waves. In actual asymmetrical short-circuit fault tests, the closing phase angle and closing asynchrony exhibit a certain degree of randomness. Therefore, existing current calculation methods under asymmetrical short-circuit fault conditions suffer from problems such as complex formulas and poor flexibility. One existing current calculation method under asymmetrical short-circuit fault conditions is as follows: When phases A and B are pre-closed, and phase C is closed after a time interval ΔT, the expression for the three-phase short-circuit current during the closing period is:

[0085] when

[0086] when

[0087] Therefore, when calculating the three-phase current after time ΔT, it is necessary to calculate the following formula: That is, ΔT - The instantaneous values ​​of the three-phase short-circuit currents at time A, B, and C, and the corresponding instantaneous values ​​of the AC components.

[0088]

[0089] From the above expressions (1), (2), and (3), it can be seen that the AC component of the current is set to be constant, requiring a large amount of data to be calculated. When using a generator as the power source in a large-capacity short-circuit test, the effective value of the AC component of the short-circuit current will fluctuate due to the limited energy stored in the unit and the influence of the forced excitation system, resulting in a large error through the current calculation method. Moreover, the formula form and calculation process become more complex when calculating the current parameters of the later-opening phase.

[0090] Therefore, this application discloses a method for calculating parameters under asymmetrical short-circuit fault conditions. The method includes: under symmetrical short-circuit fault conditions, obtaining an oscilloscope diagram of the expected AC component of the symmetrical short-circuit current; measuring the effective current value and the phase angle difference between the current and voltage at multiple moments using the oscilloscope diagram; under asymmetrical short-circuit fault conditions, measuring the voltage phase angle at multiple moments; calculating an attenuation coefficient based on the effective current value, the phase angle difference between the current and voltage, and the voltage phase angle; calculating a DC time constant based on the attenuation coefficient; and determining an asymmetrical short-circuit current expression based on the effective current value, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant. It is evident that by obtaining the effective value of the AC component under symmetrical short-circuit fault conditions to determine the current expression under asymmetrical short-circuit fault conditions, this application reduces the parameter reading and calculation errors caused by fluctuations in the effective value of the AC component of the short-circuit current, resulting in a more accurate current expression under asymmetrical short-circuit fault conditions. Moreover, by using the effective value of the current, the phase angle difference between the current and voltage, and the voltage phase angle, the current expression under simple asymmetrical short-circuit fault conditions can be easily and conveniently derived, reducing the amount of calculation and the error rate, and making it highly versatile.

[0091] The following explains some technical terms:

[0092] Large half-wave / small half-wave: A half-wave in which the duration of the current is greater than / less than half a cycle of the power frequency.

[0093] Asymmetrical short-circuit breaking test (T100a) / Symmetrical short-circuit breaking test (T100s): During a high-voltage, high-capacity short circuit, if the effective value of the AC component of the short-circuit current is equal to the rated short-circuit current value of the circuit breaker, the current cannot change abruptly due to the inductive nature of the circuit. This results in the current initially containing both AC and DC components, equal in magnitude but opposite in direction. During the short circuit, the short-circuit current simultaneously contains both AC and DC components. The AC component exhibits a sinusoidal change, while the DC component decays exponentially according to a time constant (usually above 45ms). When the DC component exceeds the AC component by 20%, the current will no longer be symmetrical, typically exhibiting alternating large and small half-waves, gradually approaching symmetry. The circuit breaker breaking test performed under these conditions is the T100a test method. When the DC component decays to less than 20% of the AC component, the current is symmetrical. The circuit breaker breaking test performed under these conditions is the T100s test method.

[0094] Closing phase angle: The phase of the voltage (relative to ground) when the current starts.

[0095] DC component percentage: The percentage of the peak value of the DC component of the short-circuit current to the peak value of the AC component of the short-circuit current.

[0096] Expected AC component: By adjusting the closing phase angle, the three-phase completely symmetrical short-circuit current (DC component less than 20%) can be obtained, and the effective value of the AC component of the three-phase current at different times can be measured.

[0097] Zero current point: the moment when the current value is zero.

[0098] First-opening phase / Later-opening phase: When a three-pole circuit breaker interrupts a three-phase short-circuit current, the current will first stop flowing in one of the phases. This phase is called the first-opening phase. The current in the other two phases will stop flowing in succession. These two phases are called the later-opening phases.

[0099] See Figure 1 This application discloses a flowchart of a method for calculating parameters under asymmetric short-circuit fault conditions, the method comprising:

[0100] S101. Under symmetrical short-circuit fault conditions, obtain the oscilloscope diagram of the expected AC current component of the symmetrical short circuit.

[0101] In one possible implementation, this embodiment of the application can obtain a three-phase short-circuit current without DC component by closing the switch at a specific phase of the power supply voltage, thus obtaining an oscilloscope diagram of the expected AC component of the symmetrical short-circuit current. The specific method can be as follows: First, close two phases, which can be phase A and phase B, when the phase angle of phase A is a-π / 6. The currents of the first two phases are symmetrical before the third phase short-circuit, and the third phase closes after a quarter cycle, ensuring that all three phase currents are symmetrical and without DC component. It should be noted that historical data, such as single-phase current data or debugging data from a symmetrical breaking test T100s under the same test voltage and current, can also be consulted. There are no specific limitations; the appropriate method can be chosen based on the actual situation.

[0102] Figure 2 This is a schematic diagram of an asymmetrical short-circuit current and its expected AC component disclosed in an embodiment of this application. The horizontal axis represents time, the vertical axis represents the per-unit value of the instantaneous current value relative to the effective current value, and the horizontal line is the curve of the effective current value changing over time. Phase A current AC component i Aac This refers to the short-circuit current waveform of phase A obtained under symmetrical short-circuit fault conditions. It is understandable that, for simplicity, the current waveforms of phases B and C under symmetrical short-circuit fault conditions are not included in the... Figure 2 Draw it out in the middle.

[0103] S102. By using the oscilloscope of the expected current AC component, the effective value of the current and the phase angle difference between the current and voltage at multiple moments are measured.

[0104] The effective current values ​​include the effective values ​​of phase A current, phase B current, and phase C current; the phase angle difference between current and voltage includes the phase angle difference between phase A current and voltage, phase B current and voltage, and phase C current and voltage.

[0105] In this embodiment, the effective value of the current I(t) at time t of each phase and the phase angle difference between the current and voltage at that time are measured and read using an oscilloscope plot of the expected current AC component. For ease of reading, the time difference between the peak values ​​of nearby in-phase current and voltage can be approximated, such as... Figure 2 As shown, the electrical angle converted to the corresponding power frequency is 2πft. The reading accuracy can be adjusted according to actual needs, usually accurate to 5ms. That is, the effective value of the three-phase current is measured and read every 5ms from the start of the short circuit, such as 10ms, 15ms, 20ms, 25ms, 30ms, 35ms, 40ms, 45ms, 50ms, etc., from the start time of the short circuit. There is no specific limit and it can be set according to actual needs.

[0106] S103. Under asymmetrical short-circuit fault conditions, the voltage phase angle at multiple moments is measured.

[0107] The voltage phase angle includes the A-phase voltage phase angle, the B-phase voltage phase angle, and the C-phase voltage phase angle.

[0108] In this embodiment, the three-phase voltage phase of the generator to ground can be measured using a voltage transformer or voltage divider. Alternatively, the voltage phase of a single phase or the voltage phase between two phases can be measured, and the voltage phases of the other phases can be derived through the phase sequence. For example... Figure 2 If the voltage phase angle of phase A at the moment the second vertical line appears is α, then the voltage phase angle of phase B is... C phase is Understandably, there are no restrictions on the specific measurement methods; they can be selected based on actual needs.

[0109] S104. Calculate the attenuation coefficient based on the effective value of the current, the phase angle difference between the current and voltage, and the voltage phase angle.

[0110] It should be noted that at the zero current moment i A Since (t) = 0, the DC component of the current at the first moment can be obtained as:

[0111]

[0112] Among them, i rdc I represents the DC component of the A-phase current at the first moment. Aacr This represents the effective value of the phase A current at the first moment. This represents the phase angle of phase A voltage at the first moment. This represents the phase angle of the A-phase current and voltage at the first moment.

[0113] Similarly, the DC component of the current at the second moment can be calculated as follows:

[0114]

[0115] Among them, i bdc I represents the DC component of phase A current at the second moment. Aacb This represents the effective value of the phase A current at the second moment. Phase angle of phase A voltage at the second moment. This represents the phase angle of the A-phase current and voltage at the second moment.

[0116] Therefore, in this embodiment, the attenuation coefficient of phase A can be calculated according to the following formula:

[0117]

[0118] Where ΔT represents the time difference between the first and second moments, and the first and second moments can be any two moments from multiple moments, and τ represents the DC time constant of phase A.

[0119] Similarly, the attenuation coefficient of phase B or phase C is derived from the attenuation coefficient of phase A.

[0120] In one possible implementation, the first moment in this embodiment can be the moment when the current is zero, corresponding to... Figure 2 The second moment can be the moment adjacent to the current zero point, corresponding to the time indicated by the second vertical line. Figure 2 The moment of the preceding vertical line; the moment of the current zero point after a time difference ΔT between the moments adjacent to the current zero point.

[0121] It should be noted that, for ease of calculation, the embodiments of this application can use the current at the zero point of the current to calculate the current analytical expression, but this should not be construed as a limitation of this application. In fact, the difference between the expected current value and the actual current value at any time, i.e., i... dc =ii ac To calculate the DC component of the current, and simultaneously select two arbitrary times i dc The percentage of the DC component is obtained, and then the analytical expression for the current is derived.

[0122] S105. Calculate the DC time constant based on the attenuation coefficient;

[0123] It should be noted that since the half-wave duration is usually no more than 15ms and the short-circuit time is usually longer than 30ms, the apparent time constant remains unchanged within this time interval.

[0124] S106. Determine the expression for the asymmetric short-circuit current based on the effective value of the current, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant.

[0125] In this embodiment of the application, the expression for the change of phase A current with time starting from the first moment can be:

[0126] For the small half-wave:

[0127] For the majority of the wave:

[0128] Wherein, i A (t) represents the expression for the change of phase A current with time, where p represents the percentage of the DC component.

[0129] Similarly, the expressions for the change of phase B current with time or the change of phase C current with time can be derived from the corresponding expressions for the change of phase A current with time.

[0130] The expressions for the changes in phase A current over time, phase B current over time, and phase C current over time constitute the expression for the asymmetrical short-circuit current.

[0131] It should be noted that, following similar steps, the current expression for extending the majority of the half-wave can also be obtained.

[0132] As can be seen, in the embodiments of this application, the current i = i ac +i dc (where i) ac For the alternating current component, i dc Based on the theory of the DC component of the current, the expression for the asymmetrical short-circuit current is derived and calculated by determining the AC component of the current under symmetrical short-circuit fault conditions. It is applicable to synchronous closing, asynchronous closing, first opening pole and late opening pole. Moreover, the expected symmetrical short-circuit current can be measured by debugging, which reduces the calculation error caused by the fluctuation of the AC component of the short-circuit current and the change of the DC decay time constant, making it more suitable for engineering applications.

[0133] In this embodiment, the expression for the current is determined by identifying the AC component at the zero point of the short-circuit current. Since the AC component of the current is independent of the closing phase angle and closing synchronicity, and is not affected by the DC component, it can be easily obtained from the voltage phase. Therefore, there is no need to consider details such as whether the three-phase closing is synchronous or the three-phase closing phase angle. The expression is simple, highly versatile, and easy to calculate.

[0134] In this embodiment, the effective value of the AC component can be obtained by the expected current, and then the percentage of the DC component can be obtained by the phase of the current zero point. The percentage of the DC component can still be calculated for an asymmetrical current that only flows through one half-wave. This solves the problem that the three-peak method cannot calculate the percentage of the DC component when there are too few current zero points (such as less than 4) or when the AC component fluctuation causes envelope distortion.

[0135] This application discloses a method for calculating parameters under asymmetrical short-circuit fault conditions. Under symmetrical short-circuit fault conditions, an oscilloscope diagram of the expected AC component of the symmetrical short-circuit current is obtained. The effective current value and the phase angle difference between the current and voltage are measured at multiple moments using the oscilloscope diagram. Under asymmetrical short-circuit fault conditions, the voltage phase angle is measured at multiple moments. An attenuation coefficient is calculated based on the effective current value, the phase angle difference between the current and voltage, and the voltage phase angle. A DC time constant is calculated based on the attenuation coefficient. The asymmetrical short-circuit current expression is determined based on the effective current value, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant. It is evident that by obtaining the effective AC component value under symmetrical short-circuit fault conditions to determine the current expression under asymmetrical short-circuit fault conditions, this method reduces parameter reading and calculation errors caused by fluctuations in the effective AC component value of the short-circuit current, resulting in a more accurate current expression under asymmetrical short-circuit fault conditions. Furthermore, by using the effective current value, the phase angle difference between the current and voltage, and the voltage phase angle, a simple current expression under asymmetrical short-circuit fault conditions can be conveniently and easily derived, reducing computational load and error rate, and demonstrating strong versatility.

[0136] Currently, the percentage of the DC component of the current during short-circuit tests is typically read using the three-peak method, as shown in Figure 8 of GB / T1984-2014. This method involves drawing upper and lower envelopes from the current peak values ​​to determine the effective value of the AC component. The percentage of the DC component is calculated using the following formula:

[0137]

[0138] This method is based on the theoretical assumption that the effective value of the AC current component remains essentially constant. However, when the AC current component fluctuates significantly, especially within 0-20ms when the effective current value decays rapidly, the upper envelope crosses, leading to a large reading error in the above method. When the current half-wave number is less than 4, the upper or lower envelope cannot be drawn, rendering the above method unusable. Therefore, this application proposes the following method for calculating the percentage of the DC component and obtaining the per-unit value of the current change rate under asymmetrical short-circuit fault conditions relative to the current change rate under symmetrical short-circuit fault conditions.

[0139] In one possible implementation, the parameter calculation method under asymmetric short-circuit fault conditions provided in the embodiments of this application further includes:

[0140] Based on the effective value of the current, the phase angle difference between the current and the voltage, the voltage phase angle, and the DC time constant, determine the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions.

[0141] The per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions is:

[0142] For the small half-wave:

[0143] For the majority of the wave:

[0144] Among them, the p represents the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions in phase A, where p represents the percentage of the DC component. ω represents the angular frequency;

[0145] Similarly, the per-unit expression for the rate of change of current under phase B asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, or the per-unit expression for the rate of change of current under phase C asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, can be derived from the per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions.

[0146] As can be seen, in the embodiments of this application, the percentage of DC component can be quickly and accurately determined based on the phase angle difference between current and voltage and the voltage phase angle. Based on the effective value of current, the phase angle difference between current and voltage, the voltage phase angle and the DC time constant, the per-unit expression of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions can be quickly and accurately determined, reducing the amount of calculation and the error rate, and making it highly versatile.

[0147] Currently, a two-segment fitting method is used to calculate the transient recovery voltage (TRV) under asymmetric short-circuit fault conditions, resulting in low calculation accuracy and inaccurate TRV values. Therefore, this application proposes the following method for calculating the transient recovery voltage under asymmetric short-circuit fault conditions.

[0148] In one possible implementation, the parameter calculation method under asymmetric short-circuit fault conditions provided in the embodiments of this application further includes:

[0149] S201. Obtain the transient recovery voltage and current under symmetrical short-circuit fault conditions at multiple times;

[0150] It should be noted that, see Figure 3 The current under symmetrical short-circuit fault conditions can be directly calculated using the following formula:

[0151] I1 = sin(ω·T1)

[0152] I² = sin(ω·T²)

[0153] ...

[0154] I i =sin(ω·T) i )

[0155] Among them, I i For voltage recovery T i The symmetrical current injected at time T i The current under symmetrical short-circuit fault conditions at any given time. If equal step size is used, with the step size set to T, then T1 = T, T2 = 2T...T i = i*T. It should be noted that all subsequent formulas are derived using a constant step size T.

[0156] Voltage recovery T i The expected TRV at time T i The transient recovery voltage under symmetrical short-circuit fault conditions at a given time can be measured from the expected TRV envelope. For specific parameters, please refer to [reference needed]. Figure 3 .

[0157] S202. Based on the transient recovery voltage and the current under the symmetrical short-circuit fault conditions, the loop response parameters are calculated.

[0158] It should be noted that the transient recovery voltage after a circuit breaker interrupts the current can be considered as a voltage response to a current injected into the circuit breaker's output terminals, which is equal in magnitude but opposite in direction to the short-circuit current. Furthermore, any type of waveform, viewed at each time step, approximates a superimposed ramp component. See also... Figure 3 This is a schematic diagram of a loop response parameter calculation disclosed in an embodiment of this application. Figure 3 In GB1984-2014, time T1 is the time when the first reference voltage u1 of the four-parameter TRV is reached, and time T2 is the time when the second reference voltage uc of the four-parameter TRV is reached, as specified in GB1984-2014.

[0159] The transient recovery voltage under symmetrical short-circuit fault conditions can be expressed as a function of time as follows:

[0160] U(t)=U s0 +U s1 *ε(tT)+U s2 *ε(t-2T)+U s3 *ε(t-3T)+......

[0161] U s0 U s1 U s2 Us3 Equation represents the voltage coefficient under symmetrical short-circuit fault conditions, i.e., the coefficient of the unit ramp function; ε represents the unit ramp function, t represents time, and T represents the linear fitting step size.

[0162] U s0 =U1 / T

[0163] U s1 =(U2-U s01 *T) / T

[0164] U s2 =[U3-(U s0 *2T+U s1 *T)] / T

[0165] ...

[0166] U1 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1, U2 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T2, and U3 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T3.

[0167] The function of current versus time under symmetrical short-circuit fault conditions can be described as follows:

[0168] I(t)=I s0 +U s1 *ε(tT)+I s2 *ε(t-2T)+I s3 *ε(t-3T)+......

[0169] I s0 I s1 I s2 I s3 Equation represents the current coefficient under symmetrical short-circuit fault conditions, i.e., the coefficient of the unit ramp function; ε represents the unit ramp function, t represents time, and T represents the linear fitting step size.

[0170] I s0 =I1 / T

[0171] I s1 =(I2-I s0 *T) / T

[0172] I s2 =[I3-(I s0 *2T+I s1 *T)] / T

[0173] I s3 =[I4-(I s0 *3T+I s1 *2T+I s2 *T)] / T

[0174] ...

[0175] I1 represents the current under the symmetrical short-circuit fault condition at time T1, I2 represents the current under the symmetrical short-circuit fault condition at time T2, I3 represents the current under the symmetrical short-circuit fault condition at time T3, and I4 represents the current under the symmetrical short-circuit fault condition at time T4.

[0176] Through Lagrange transformation, i.e. TRV sym (s) represents the expression of the transient recovery voltage after linear fitting and Laplace transform, where s represents the Laplace operator.

[0177] Through Lagrange transformation, i.e. I sym (s) represents the expression of the current after linear fitting and Laplace transform, where s represents the Laplace operator.

[0178]

[0179] Where Z(s) represents the response function of the Lagrange domain loop, and Z0, etc., represent the loop response parameters, i.e., the coefficients of the Lagrange expression.

[0180] The TRV can be obtained by performing Laplace transforms on the TRV reference voltage and short-circuit current for symmetrical short-circuit current interruption. sym (s), I sym (s), to obtain the response function Z(s).

[0181] However, according to After calculation, the analytical expression for Z(s) in the time domain cannot be obtained directly through the inverse Laplace transform, making subsequent calculations impossible. Therefore, this application proposes a time-domain-based calculation method to obtain the following formula:

[0182] U1 = I S0 ·Z0·T

[0183] U2=I S0 ·Z0·2T+(I S0 ·Z1+I S1 ·Z0)T

[0184] U3 = I S0 ·Z0·3T+(I S0 ·Z1+I S1 ·Z0)2T+(I S0 ·Z2+I S1 ·Z1+I S2 ·Z0)T

[0185] ...

[0186] It can be further transformed to obtain the functions loop_t(i) and loop_c(i).

[0187] loop_t(2)=U2-U1=I S0 ·Z0·T+(I S0 ·Z1+I S1 ·Z0)T

[0188] loop_t(3)=U3-U2=I S0 ·Z0·T+(I S0 ·Z1+I S1 ·Z0)T+(I S0 ·Z2+I S1 ·Z1+I S2 ·Z0)T

[0189] loop_c(1) = U1 = I S0 ·Z0·T

[0190] loop_c(2)=loop_t(2)-loop_t(1)=(I S0 ·Z1+I S1 ·Z0)T

[0191] loop_c(3)=loop_t(3)-loop_t(2)=(I S0 ·Z2+I S1 ·Z1+I S2 ·Z0)T

[0192] Therefore, the loop response parameters are obtained by calculating using the following formula:

[0193] Z0 = loop_c(1) / T / I S0

[0194] Z1 = (loop_c(2) / TI) S1 ·Z0) / I S0

[0195] Z2=[loop_c(3) / T-(I S1 ·Z1+I S2 ·Z0)] / I S0

[0196] ...

[0197] Z i =[loop_c(i-1) / T-(I S1 ·Z1+I S2 ·Z0+……I Si ·Z0)] / I S0

[0198] Among them, I S0 I S1 I S2 ...I Si The current coefficient under symmetrical short-circuit fault conditions is represented by T, where T represents the linear fitting step size.

[0199] loop_c(1)=U1

[0200] loop_c(2) = U2 - 2U1

[0201] loop_c(3)=U3-2U2+U1

[0202] ...

[0203] loop_c(i)=U i -2U i-1 +U i-2

[0204] U1 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1, U2 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T2, and U3 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T3. i T represents i The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-1 T represents i-1 The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-2 T represents i-2 The transient recovery voltage under symmetrical short-circuit fault conditions at time i, where i is a positive integer greater than 1;

[0205] The current coefficient under the symmetrical short-circuit fault condition is calculated using the following formula:

[0206] I s0 =I1 / T

[0207] I s1 =(I2-I s0 *T) / T

[0208] I s2 =[I3-(I s0 *2T+I s1 *T)] / T

[0209] ...

[0210] I si =[I i+1 -(I s0 *iT+I s1 *(i-1)T+……I si-1*T)] / T

[0211] I1 represents the effective current value at time T1, I2 represents the effective current value at time T2, and I3 represents the effective current value at time T3. i+1 T represents i+1 The effective value of the current at time t.

[0212] S203. The current under asymmetrical short-circuit fault conditions at multiple times is calculated using the aforementioned asymmetrical short-circuit current expression;

[0213] S204. Based on the circuit response parameters and the current under the asymmetrical short-circuit fault condition, calculate the current coefficient under the asymmetrical short-circuit fault condition.

[0214] The current coefficient under the asymmetric short-circuit fault condition is calculated using the following formula:

[0215] I s0_asy =I 1_asy / T

[0216] I s1_asy =(I 2_asy -I s0_asy *T) / T

[0217] I s2_asy =(I 3_asy -I s0_asy *2T-I s1_asy *T) / T

[0218] ...

[0219] I si-1_asy =(I i_asy -I s0_asy *(i-1)T-……I si-3_asy *2T-I si-2_asy *T) / T

[0220] Wherein, the I 1_asy I represents the current under the asymmetrical short-circuit fault condition at time T1. 2_asy I represents the current under the asymmetrical short-circuit fault condition at time T2. i_asy T represents i Current under asymmetrical short-circuit fault conditions at a given time.

[0221] S205. Based on the circuit response parameters and the current coefficient under the asymmetric short-circuit fault condition, calculate the transient recovery voltage under the asymmetric short-circuit fault condition at multiple times.

[0222] The transient recovery voltage under the asymmetric short-circuit fault condition is calculated using the following formula:

[0223] U 1_asy =U1(I s0_asy ·Z0·T)

[0224] U 2_asy =U 1_asy +loop_t_asy(2)

[0225] ...

[0226] U i_asy =U i-1_asy +loop_t_asy(i)

[0227] in,

[0228] loop_t_asy(2)=I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T

[0229] loop_t_asy(3)=I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T+(I s0_asy ·Z2+I s1_asy ·Z1+I s2_asy ·Z0)T

[0230] ...

[0231] loop_t_asy(i) = I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T+(I s0_asy ·Z2+I s1_asy ·Z1+I s2_asy ·Z0)T+……(I s0_asy ·Z i-1 +I s1_asy ·Z i-2 +……I si-1_asy ·Z0)T

[0232] The U 1 asy U1 represents the transient recovery voltage under the asymmetrical short-circuit fault condition at time T1, and I represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1. s0 asy Z0 represents the current coefficient under asymmetrical short-circuit fault conditions, and Z0 represents the loop response parameter; U 2 asy U represents the transient recovery voltage under the asymmetric short-circuit fault condition at time T2; i asy T represents iThe transient recovery voltage under asymmetric short-circuit fault conditions at time U i-1 asy T represents i-1 Transient recovery voltage under asymmetrical short-circuit fault conditions at a given time.

[0233] As can be seen, the transient recovery voltage under asymmetric short-circuit fault conditions is calculated using time-domain analysis in the embodiments of this application. Thus, the current is fitted by multiple slope functions, which improves the calculation efficiency and accuracy.

[0234] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that all or part of the steps in the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network communication device such as a media gateway, etc.) to execute the methods described in various embodiments or some parts of the embodiments of this application.

[0235] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0236] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0237] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0238] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calculating parameters under asymmetric short-circuit fault conditions, characterized in that, The method includes: Under symmetrical short-circuit fault conditions, obtain the oscilloscope diagram of the expected AC current component of the symmetrical short circuit; The effective value of the current and the phase angle difference between the current and voltage at multiple moments are measured using the oscilloscope of the expected current AC component. Under asymmetrical short-circuit fault conditions, the voltage phase angles at multiple moments were measured; The attenuation coefficient is calculated based on the effective value of the current, the phase angle difference between the current and the voltage, and the voltage phase angle. The DC time constant is calculated based on the attenuation coefficient. The expression for the asymmetric short-circuit current is determined based on the effective value of the current, the phase angle difference between the current and voltage, the voltage phase angle, and the DC time constant.

2. The method according to claim 1, characterized in that, The effective current value includes the effective current value of phase A, the effective current value of phase B, and the effective current value of phase C; the phase angle difference between current and voltage includes the phase angle difference between phase A, phase B, and phase C; the voltage phase angle includes the phase angle between phase A, phase B, and phase C. The attenuation coefficient of phase A is calculated using the following formula: Wherein, ΔT represents the time difference between the first and second moments, the first and second moments being any two of the plurality of moments, τ represents the DC time constant of phase A, and I... Aacr This represents the effective value of phase A current at the first moment. This represents the phase angle of phase A voltage at the first moment. The I represents the phase angle of the A-phase current and voltage at the first moment. Aacb This represents the effective value of phase A current at the second moment. The phase angle of phase A voltage at the second moment, the This represents the phase angle of the A-phase current and voltage at the second moment; Similarly, the attenuation coefficient of phase B or phase C is derived from the attenuation coefficient of phase A.

3. The method according to claim 2, characterized in that, The expression for the change of phase A current with time starting from the first moment is: For the small half-wave: For the majority of the wave: Wherein, i A (t) represents the expression for the change of phase A current with time, where p represents the percentage of the DC component. Similarly, the expressions for the change of phase B current with time or the change of phase C current with time can be derived from the corresponding expressions for the change of phase A current with time. The expressions for the changes in phase A current over time, the expressions for the changes in phase B current over time, and the expressions for the changes in phase C current over time constitute the expression for the asymmetrical short-circuit current.

4. The method according to claim 2, characterized in that, The first moment is the moment when the current is zero, and the second moment is the moment adjacent to the moment when the current is zero, wherein the time difference between the moments adjacent to the moment when the current is zero is... ΔT Then, at the moment when the current reaches zero.

5. The method according to claim 2, characterized in that, The method further includes: Based on the effective value of the current, the phase angle difference between the current and the voltage, the voltage phase angle, and the DC time constant, determine the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions. The per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions is: For the small half-wave: For the majority of the wave: Among them, the p represents the per-unit value of the rate of change of current under asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions in phase A, where p represents the percentage of the DC component. ω represents the angular frequency; Similarly, the per-unit expression for the rate of change of current under phase B asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, or the per-unit expression for the rate of change of current under phase C asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions, can be derived from the per-unit expression for the rate of change of current under phase A asymmetrical short-circuit fault conditions relative to the rate of change of current under symmetrical short-circuit fault conditions.

6. The method according to claim 1, characterized in that, The method further includes: Obtain the transient recovery voltage and current under symmetrical short-circuit fault conditions at multiple time points; Based on the transient recovery voltage and current under the symmetrical short-circuit fault conditions, the loop response parameters are calculated. The current under asymmetric short-circuit fault conditions at multiple times can be calculated using the aforementioned asymmetric short-circuit current expression. Based on the circuit response parameters and the current under the asymmetrical short-circuit fault condition, the current coefficient under the asymmetrical short-circuit fault condition is calculated. Based on the circuit response parameters and the current coefficient under the asymmetric short-circuit fault condition, the transient recovery voltage under the asymmetric short-circuit fault condition at multiple times is calculated.

7. The method according to claim 1, characterized in that, The loop response parameters are calculated using the following formula: Z0=loop_c(1) / T / I S0 Z1=(loop_c(2) / T-I S1 ·Z0) / I S0 Z2=[loop_c(3) / T-(I S1 ·Z1+I S2 ·Z0)] / I S0 …… Z i =[loop_c(i-1) / T-(I S1 ·Z1+I S2 ·Z0+……I Si ·Z0)] / I S0 Among them, I S0 I S1 I S2 ...I Si The current coefficient under symmetrical short-circuit fault conditions is represented by T, where T represents the linear fitting step size. loop_c(1)=U1 loop_c(2) = U2 - 2U1 loop_c(3)=U3-2U2+U1 …… loop_c(i)=U i -2U i-1 +U i-2 U1 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1, U2 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T2, and U3 represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T3. i T represents i The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-1 T represents i-1 The transient recovery voltage under a symmetrical short-circuit fault condition at time U i-2 T represents i-2 The transient recovery voltage under symmetrical short-circuit fault conditions at time i, where i is a positive integer greater than 1; The current coefficient under the symmetrical short-circuit fault condition is calculated using the following formula: I s0 =I1 / T I s1 =(I2-I s0 *T) / T I s2 =[I3-(I s0 *2T+I s1 *T)] / T …… I si =[I i+1 -(I s0 *iT+I s1 *(i-1)T+……I si-1 *T)] / T I1 represents the current under the symmetrical short-circuit fault condition at time T1, I2 represents the current under the symmetrical short-circuit fault condition at time T2, and I3 represents the current under the symmetrical short-circuit fault condition at time T3. i+1 T represents i+1 Current under symmetrical short-circuit fault conditions at any given time.

8. The method according to claim 7, characterized in that, The current coefficient under the asymmetric short-circuit fault condition is calculated using the following formula: I s0_asy =I 1_asy / T I s1_asy =(I 2_asy -I s0_asy *T) / T I s2_asy =(I 3_asy -I s0_asy *2T-I s1_asy *T) / T …… I si-1_asy =(I i_asy -I s0_asy *(i-1)T-……I si-3_asy *2T-I si-2_asy *T) / T Wherein, the I 1_asy I represents the current under the asymmetrical short-circuit fault condition at time T1. 2_asy I represents the current under the asymmetrical short-circuit fault condition at time T2. i_asy T represents i Current under asymmetrical short-circuit fault conditions at a given time.

9. The method according to claim 8, characterized in that, The transient recovery voltage under the asymmetric short-circuit fault condition is calculated using the following formula: U 1_asy = U1(I s0_asy ·Z0·T) U 2_asy =U 1_asy +loop_t_asy(2) …… U i_asy =U i-1_asy +loop_t_asy(i) in, loop_t_asy(2)=I s0_asy ·Z0·T+(I s0_asy ·Z1+I s1_asy ·Z0)T loop_t_asy(3)=I s0_asy ·Z0·T+(I s0_asy Z1+I s1_asy ·Z0)T+(I s0_asy Z2+I s1_asy Z1+I s2_asy ·Z0)T …… loop_t_asy(i)=I s0_asy ·Z0·T+(I s0_asy Z1+I s1_asy ·Z0)T+(I s0_asy Z2+I s1_asy Z1+I s2_asy ·Z0)T+……(I s0_asy Z i-1 +I s1_asy Z i-2 +……I si-1_asy ·Z0)T The U 1_asy U1 represents the transient recovery voltage under the asymmetrical short-circuit fault condition at time T1, and I represents the transient recovery voltage under the symmetrical short-circuit fault condition at time T1. s0_asy Z0 represents the current coefficient under asymmetrical short-circuit fault conditions, and Z0 represents the loop response parameter; U 2_asy U represents the transient recovery voltage under the asymmetric short-circuit fault condition at time T2; i_asy T represents i The transient recovery voltage under asymmetric short-circuit fault conditions at time U i-1_asy T represents i-1 Transient recovery voltage under asymmetrical short-circuit fault conditions at a given time.

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