Zero-sequence equivalent model analysis method and system for step-down self-coupling phase shifter

Abstract

The invention relates to the technical field of transient analysis of a power system, in particular to a zero-sequence equivalent model analysis method and system for a step-down self-coupling phase shifter, and the method comprises the steps: applying the same zero-sequence voltage condition to a self-coupling branch port of the step-down self-coupling phase shifter, building a zero-sequence current loop model of a self-coupling branch and a phase-shifting branch, and building a zero-sequence equivalent model of the self-coupling branch and a zero-sequence equivalent model of the phase-shifting branch; listing a port current relational expression; solving a current relation between the primary winding and the secondary winding of the phase-shifting transformer based on a magnetomotive force balance principle, and substituting the current relation between the primary winding and the secondary winding into a port current relational expression; deducing an equivalent zero-sequence reactance expression between a self-coupling branch and a phase-shifting branch in the step-down self-coupling phase shifter; establishing a zero-sequence equivalent model of the step-down self-coupling phase shifter based on the equivalent zero-sequence reactance, and calculating and simulating the zero-sequence current of the power grid under the conditions of single-phase grounding, two-phase inter-phase grounding or asymmetric grounding faults by using the equivalent model; and the influence on the zero-sequence current protection sensitivity of the corresponding line after the step-down self-coupling phase shifter is connected is evaluated.

Description

Technical Field

[0001] This invention relates to the field of power system transient analysis technology, and in particular to a zero-sequence equivalent model analysis method and system for step-down autotransformers. Background Technology

[0002] The high proportion of renewable energy power connected to local power grids has further exacerbated the mismatch between power sources and loads, and the problem of power flow restriction between transmission sections in densely loaded areas is becoming increasingly serious. As a power flow control device, phase-shifting transformers have technical advantages such as good economy, small footprint, simple structure, and low operation and maintenance costs. Through effective power control, they can further improve the transmission capacity of the existing power grid and have broad application prospects.

[0003] Based on traditional phase-shifting transformers, step-down autotransformers combine autotransformers with traditional hexagonal single-core phase-shifting transformers. They possess both the function of changing the voltage phase or amplitude on both sides of a line (a traditional phase shifter) and the voltage level transformation function of a traditional autotransformer. However, due to the complex topology of step-down autotransformers, the post-fault transient model is correspondingly more complex, and there is currently no relevant research. To facilitate the smooth implementation of short-circuit current calculations, relay protection configuration adaptability analysis, and setting calculations for power grids with step-down autotransformers, it is urgent to study the zero-sequence equivalent model of step-down autotransformers under asymmetrical grounding faults. This research aims to clarify the zero-sequence current path of power grids with step-down autotransformers under asymmetrical grounding faults, ensuring the safe and stable operation of power systems with step-down autotransformers.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a zero-sequence equivalent model analysis method and system for step-down autotransformers, thereby effectively solving the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a zero-sequence equivalent model analysis method for a step-down autotransformer, comprising the following steps:

[0007] Obtain the structural topology and electrical parameters of the step-down autotransformer;

[0008] Apply the same zero-sequence voltage condition to the autotransformer branch port of the step-down autotransformer, establish the zero-sequence current loop model of the autotransformer branch and the phase-shifting branch, and write the port current relationship according to Kirchhoff's current law.

[0009] Assuming and using an ideal transformer model in the phase-shifting transformer section, the relationship between the primary and secondary winding currents of the phase-shifting transformer is solved based on the principle of magnetomotive force balance. The turns ratio is introduced, and the relationship between the primary and secondary winding currents is substituted into the port current relationship formula.

[0010] The equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in the step-down autotransformer is derived, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactance in series.

[0011] Based on the equivalent zero-sequence reactance, a zero-sequence equivalent model of the step-down autotransformer is established, and the zero-sequence current of the power grid under single-phase grounding, two-phase-to-phase grounding, or asymmetrical grounding fault conditions is calculated and simulated using this equivalent model; and the impact of the step-down autotransformer on the zero-sequence current protection sensitivity of the corresponding line is evaluated.

[0012] Furthermore, applying the same zero-sequence voltage condition at the autotransformer branch port of the step-down autotransformer includes:

[0013] Apply the same zero-sequence voltage to the terminals LA1, LB1, and LC1 of the autotransformer phase shifter. Solve for the zero-sequence voltages at the ports of phase-shifted branches LA2, LB2, and LC2. ;

[0014] The currents in the autotransformer branches LA1, LB1, and LC1 are: , , The currents in the phase-shifting branches LA2, LB2, and LC2 are , , The currents flowing through the primary windings AA', BB', and CC' of the phase-shifting transformer are respectively , , The currents flowing through the secondary windings aa', bb', and cc' of the phase-shifting transformer are respectively , , .

[0015] Furthermore, the step of writing the port current relationship based on Kirchhoff's Current Law includes:

[0016] ;

[0017] ;

[0018] .

[0019] Furthermore, the method for solving the relationship between the primary and secondary winding currents of the phase-shifting transformer based on the magnetomotive force balance principle includes:

[0020] ;

[0021] ;

[0022] In the formula: the number of turns of the primary windings AA', BB', and CC' of the phase-shifting transformer is... The number of turns of the secondary windings aa', bb', and cc' is .

[0023] Furthermore, the introduction of the turns ratio, substituting the relationship between the primary and secondary winding currents into the port current relationship, includes:

[0024] ;

[0025] In the formula: , which is the turns ratio of the phase-shifting transformer, and this value is related to the tap position of the phase-shifting transformer.

[0026] Furthermore, the derivation of the equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in the step-down autotransformer, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactances in series, includes:

[0027] ;

[0028] ;

[0029] In the formula, the leakage reactance of windings AA', BB', and CC' is... The leakage reactance of windings aa', bb', and cc' is ;

[0030] The zero-sequence voltage between the autotransformer branch and the phase-shifting branch of the phase-shifting transformer is considered as an equivalent reactance. The reactance value is .

[0031] Furthermore, the step-down autotransformer's zero-sequence equivalent model based on the equivalent zero-sequence reactance includes:

[0032] Obtain the rated capacity of the step-down autotransformer and the short-circuit impedance of the phase-shifting transformer section and the rated voltage of the primary winding ;

[0033] Obtain real-time tap position information and secondary winding voltage of the phase-shifting transformer section. The equivalent impedance between the autotransformer branch and the phase-shifting branch can be calculated using the derived equivalent impedance formula. ;

[0034] For the autotransformer section of the step-down autotransformer, the leakage reactance of the high-voltage, medium-voltage, and low-voltage windings is calculated based on the short-circuit impedances between the high-voltage-medium-voltage, high-voltage-low-voltage, and medium-voltage-low-voltage windings, respectively. , as well as ;

[0035] A zero-sequence equivalent model of step-down autotransform phase shift is constructed.

[0036] Furthermore, the calculation and simulation of the zero-sequence current of the power grid under single-phase grounding, two-phase-to-phase grounding, or asymmetrical grounding faults using the equivalent model includes:

[0037] Based on the equivalent model, the voltage and current time-domain waveforms of the step-down autotransformer within a given fault time window are simulated, and the zero-sequence equivalent impedance is verified by using Fast Fourier Transform (FFT) or frequency domain analysis to compare the consistency between the simulated and calculated values.

[0038] This invention also includes a zero-sequence equivalent model analysis system for a step-down autotransformer, using the method described above, wherein the system comprises:

[0039] The acquisition unit is used to obtain the structural topology and electrical parameters of the step-down autotransformer.

[0040] The zero-sequence current loop model building unit is used to apply the same zero-sequence voltage condition to the autotransformer branch port of the step-down autotransformer, establish the zero-sequence current loop model of the autotransformer branch and the phase-shifting branch, and write the port current relationship according to Kirchhoff's current law.

[0041] The current relationship calculation unit is used to assume and adopt an ideal transformer model in the phase-shifting transformer section, and solve the current relationship between the primary and secondary windings of the phase-shifting transformer based on the magnetomotive force balance principle. The turns ratio is introduced, and the current relationship between the primary and secondary windings is substituted into the port current relationship formula.

[0042] Equivalent unit, used to derive the equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in a step-down autotransformer, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactance in series;

[0043] The modeling and simulation unit is used to establish a zero-sequence equivalent model of the step-down autotransformer based on the equivalent zero-sequence reactance, and to use the equivalent model to calculate and simulate the zero-sequence current of the power grid under single-phase grounding, two-phase in-phase grounding, or asymmetrical grounding fault conditions; and to evaluate the impact of the step-down autotransformer on the zero-sequence current protection sensitivity of the corresponding line after its connection.

[0044] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0045] The present invention also includes a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described above.

[0046] The beneficial effects of this invention are as follows: Utilizing Kirchhoff's current law and the principle of magnetomotive force balance, and based on the topology of a step-down autotransformer, a zero-sequence equivalent model of the step-down autotransformer is derived. First, the voltage and current relationships between the autotransformer branch and the phase-shifting branch of the phase-shifting transformer in the step-down autotransformer are derived. Further, the zero-sequence equivalent model of the step-down autotransformer is derived: the autotransformer branch and the phase-shifting branch of the phase-shifter can be considered as an equivalent reactance, which is related to the leakage reactance of the phase-shifting transformer winding and the tap position information. This fills the research gap in the field of zero-sequence equivalent models for step-down autotransformers, and is applicable to solving the zero-sequence current under asymmetrical grounding faults such as single-phase grounding and two-phase-to-phase grounding. It lays the foundation for fault calculation and protection adaptability analysis of step-down autotransformers, and has important reference value for ensuring the safe and stable operation of power systems containing step-down autotransformers. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart of the method in Example 1;

[0049] Figure 2 This is a schematic diagram of the system structure in Example 1;

[0050] Figure 3 This is a structural diagram of the step-down autotransformer phase shifter in Example 2;

[0051] Figure 4 This is a voltage vector diagram of the autotransformer branch and the phase-shifting branch of the step-down autotransformer in Example 2;

[0052] Figure 5 This is the zero-sequence current loop diagram of the phase-shifting transformer section of the step-down autotransformer in Example 2;

[0053] Figure 6 This is an equivalent model diagram of the zero-sequence phase-shifting phase transition of the step-down autotransformer in Example 2;

[0054] Figure 7 This is a schematic diagram of the step-down autotransformer connected to the power grid in Example 2;

[0055] Figure 8 This is a schematic diagram of a step-down autotransformer connected to the power grid in Example 2.

[0056] Figure 9 The terminal voltage waveforms of the autotransformer branch and the phase-shifting branch in Example 2;

[0057] Figure 10 The zero-sequence voltage waveforms at the ports of the autotransformer branch and the phase-shifting branch in Example 2;

[0058] Figure 11 The zero-sequence current waveform of the autotransformer branch in Example 2;

[0059] Figure 12 This is a flowchart illustrating the calculation of the zero-sequence impedance of the step-down autotransformer in Example 2.

[0060] Figure 13 This refers to the zero-sequence current on the autotransformer side after connecting the step-down autotransformer in Example 2;

[0061] Figure 14 This refers to the zero-sequence current on the autotransformer side when no step-down autotransformer is connected in Example 2.

[0062] Figure 15 This is a schematic diagram of the structure of the computer device of the present invention. Detailed Implementation

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0064] Example 1:

[0065] like Figure 1 The following is a zero-sequence equivalent model analysis method for a step-down autotransformer, comprising the following steps:

[0066] Obtain the structural topology and electrical parameters of the step-down autotransformer;

[0067] Apply the same zero-sequence voltage condition to the autotransformer branch port of the step-down autotransformer, establish the zero-sequence current loop model of the autotransformer branch and the phase-shifting branch, and write the port current relationship according to Kirchhoff's current law.

[0068] Assuming and using an ideal transformer model in the phase-shifting transformer section, the relationship between the primary and secondary winding currents of the phase-shifting transformer is solved based on the principle of magnetomotive force balance. The turns ratio is introduced, and the relationship between the primary and secondary winding currents is substituted into the port current relationship formula.

[0069] The equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in the step-down autotransformer is derived, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactance in series.

[0070] A zero-sequence equivalent model of a step-down autotransformer is established based on the equivalent zero-sequence reactance. This equivalent model is then used to calculate and simulate the zero-sequence current of the power grid under single-phase grounding, two-phase-to-phase grounding, or asymmetrical grounding fault conditions. The impact of the step-down autotransformer on the zero-sequence current protection sensitivity of the corresponding lines is also evaluated.

[0071] Based on Kirchhoff's current law and magnetomotive force balance, and considering the topology of a step-down autotransformer (BRT), a zero-sequence equivalent model of the BRT is derived. First, the voltage and current relationships between the autotransformer branch and the phase-shifting branch of the phase-shifting transformer in the BRT are derived. Then, the zero-sequence equivalent model of the BRT is derived: the autotransformer branch and the phase-shifting branch of the phase-shifter can be considered as an equivalent reactance, which is related to the leakage reactance of the phase-shifting transformer winding and the tap position information. This fills a research gap in the field of zero-sequence equivalent models for BRTs and is applicable to solving zero-sequence currents under asymmetrical grounding faults such as single-phase grounding and two-phase-to-phase grounding. It lays the foundation for fault calculation and protection adaptability analysis of BRTs and has important reference value for ensuring the safe and stable operation of power systems containing BRTs.

[0072] In this embodiment, the same zero-sequence voltage condition is applied to the autotransformer branch port of the step-down autotransformer, including:

[0073] Apply the same zero-sequence voltage to the terminals LA1, LB1, and LC1 of the autotransformer phase shifter. Solve for the zero-sequence voltages at the ports of phase-shifted branches LA2, LB2, and LC2. ;

[0074] The currents in the autotransformer branches LA1, LB1, and LC1 are: , , The currents in the phase-shifting branches LA2, LB2, and LC2 are , , The currents flowing through the primary windings AA', BB', and CC' of the phase-shifting transformer are respectively , , The currents flowing through the secondary windings aa', bb', and cc' of the phase-shifting transformer are respectively , , .

[0075] The port current relationships, based on Kirchhoff's Current Law, include:

[0076] ;

[0077] ;

[0078] .

[0079] Solving the relationship between the primary and secondary winding currents of a phase-shifting transformer based on the principle of magnetomotive force balance includes:

[0080] ;

[0081] ;

[0082] In the formula: the number of turns of the primary windings AA', BB', and CC' of the phase-shifting transformer is... The number of turns of the secondary windings aa', bb', and cc' is .

[0083] As a preferred embodiment of the above, a turns ratio is introduced, and the relationship between the primary and secondary winding currents is substituted into the port current relationship formula, including:

[0084] ;

[0085] In the formula: , which is the turns ratio of the phase-shifting transformer, and this value is related to the tap position of the phase-shifting transformer.

[0086] In this embodiment, the equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in the step-down autotransformer is derived, so that the equivalent reactance between the autotransformer branch and the phase-shifting branch can be regarded as series, including:

[0087] ;

[0088] ;

[0089] In the formula, the leakage reactance of windings AA', BB', and CC' is... The leakage reactance of windings aa', bb', and cc' is ;

[0090] The zero-sequence voltage between the autotransformer branch and the phase-shifting branch of the phase-shifting transformer is considered as an equivalent reactance. The reactance value is .

[0091] Among them, the zero-sequence equivalent model of the step-down autotransformer is established based on the equivalent zero-sequence reactance, including:

[0092] Obtain the rated capacity of the step-down autotransformer and the short-circuit impedance of the phase-shifting transformer section and the rated voltage of the primary winding ;

[0093] Obtain real-time tap position information and secondary winding voltage of the phase-shifting transformer section. The equivalent impedance between the autotransformer branch and the phase-shifting branch can be calculated using the derived equivalent impedance formula. ;

[0094] For the autotransformer section of the step-down autotransformer, the leakage reactance of the high-voltage, medium-voltage, and low-voltage windings is calculated based on the short-circuit impedances between the high-voltage-medium-voltage, high-voltage-low-voltage, and medium-voltage-low-voltage windings, respectively. , as well as ;

[0095] A zero-sequence equivalent model of step-down autotransform phase shift is constructed.

[0096] This equivalent model is used to calculate and simulate the zero-sequence current of the power grid under single-phase grounding, two-phase-to-phase grounding, or asymmetrical grounding fault conditions, including:

[0097] The voltage and current time-domain waveforms of the step-down autotransformer within a given fault time window are simulated based on the equivalent model. The zero-sequence equivalent impedance is verified by Fast Fourier Transform (FFT) or frequency domain analysis to compare the consistency between the simulated and calculated values.

[0098] like Figure 2 As shown, this embodiment also includes a zero-sequence equivalent model analysis system for a step-down autotransformer, using the method described above. The system includes:

[0099] The acquisition unit is used to obtain the structural topology and electrical parameters of the step-down autotransformer.

[0100] The zero-sequence current loop model building unit is used to apply the same zero-sequence voltage condition to the autotransformer branch port of the step-down autotransformer, establish the zero-sequence current loop model of the autotransformer branch and the phase-shifting branch, and write the port current relationship according to Kirchhoff's current law.

[0101] The current relationship calculation unit is used to assume and adopt an ideal transformer model in the phase-shifting transformer section, and solve the current relationship between the primary and secondary windings of the phase-shifting transformer based on the principle of magnetomotive force balance. The turns ratio is introduced, and the current relationship between the primary and secondary windings is substituted into the port current relationship formula.

[0102] Equivalent unit, used to derive the equivalent zero-sequence reactance expression between the autotransformer branch and the phase-shifting branch in a step-down autotransformer, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactance in series;

[0103] The modeling and simulation unit is used to establish a zero-sequence equivalent model of the step-down autotransformer based on the equivalent zero-sequence reactance, and to use this equivalent model to calculate and simulate the zero-sequence current of the power grid under single-phase grounding, two-phase in-phase grounding, or asymmetrical grounding fault conditions; and to evaluate the impact of the step-down autotransformer on the zero-sequence current protection sensitivity of the corresponding line after its connection.

[0104] Example 2:

[0105] To ensure the safe and stable operation of power systems containing step-down autotransformers, and to provide a theoretical basis for fault analysis and relay protection configuration and setting analysis of power grids with step-down autotransformers, this embodiment proposes a zero-sequence equivalent model analysis method for step-down autotransformers. Step-down autotransformer structure. Figure 3 As shown, based on a traditional autotransformer, a phase-shifting transformer is connected at LA1, LB1, and LC1 on the medium-voltage side. In the figure, AA', BB', and CC' windings are the primary windings (excitation windings) of the phase-shifting transformer, and aa', bb', and cc' windings are the secondary windings of the phase-shifting transformer.

[0106] according to Figure 3 The structure shown has the following voltage phasor diagrams for the autotransformer branches (LA1, LB1, LC1) and phase-shifting branches (LA2, LB2, LC2) of the step-down autotransformer phase shifter: Figure 4 As shown.

[0107] To analyze the zero-sequence equivalent model of the buck autotransformer, the same zero-sequence voltage was applied at the terminals of the autotransformer branches (LA1, LB1, LC1). Solve for the zero-sequence voltage at the ports of the phase-shifting branches (LA2, LB2, LC2). The zero-sequence current loop diagram of the phase-shifting transformer section of the step-down autotransformer is as follows: Figure 5 As shown, the currents in the autotransformer branches LA1, LB1, and LC1 are... , , The currents in the phase-shifting branches LA2, LB2, and LC2 are , , The currents flowing through the primary windings AA', BB', and CC' of the phase-shifting transformer are respectively , , The currents flowing through the secondary windings aa', bb', and cc' of the phase-shifting transformer are respectively , , .

[0108] Depend on Figure 5According to Kirchhoff's current law, the current relationship between the step-down phase-shift autotransformer branch and the phase-shift branch is as follows:

[0109]

[0110]

[0111]

[0112] Assuming the phase-shifting transformer is an ideal transformer, according to the principle of magnetomotive force balance, the current relationship between the primary and secondary windings of the phase-shifting transformer is as follows:

[0113]

[0114] and:

[0115]

[0116] In the formula: the number of turns of the primary windings AA', BB', and CC' of the phase-shifting transformer is... The number of turns of the secondary windings aa', bb', and cc' is .

[0117] The autotransformer branch current can then be transformed into:

[0118]

[0119] In the formula: , which is the turns ratio of the phase-shifting transformer, and this value is related to the tap position of the phase-shifting transformer.

[0120] The leakage reactance of windings AA', BB', and CC' is The leakage reactance of windings aa', bb', and cc' is (Reverted to the original side). According to Figure 5 The zero-sequence voltage relationship at each point in the loop diagram shown is as follows:

[0121]

[0122] but:

[0123]

[0124] As can be seen from the above formula, the zero-sequence voltage between the autotransformer branch and the phase-shifting branch of the phase-shifting transformer can be considered as an equivalent reactance. The reactance value is .

[0125] Therefore, the zero-sequence equivalent model of the step-down autotransformer is as follows: Figure 6 As shown, the left side of the model represents the zero-sequence equivalent circuit of a traditional autotransformer. The leakage reactance parameter of this equivalent circuit can be calculated based on the rated capacity of the step-down autotransformer, the short-circuit impedance between the high-voltage and medium-voltage, medium-voltage and low-voltage, and high-voltage and low-voltage windings. The right side represents the equivalent reactance connected in series between the phase-shifting branch of the phase-shifting transformer and the autotransformer branch. This reactance is related to the winding leakage reactance and tap position of the phase-shifting transformer. The tap position can be obtained in real time, and then the equivalent reactance value can be calculated online.

[0126] After a step-down autotransformer is connected, it alters the voltage and current electrical quantities on both sides. Under asymmetrical fault conditions, this may affect the sensitivity of protection systems such as zero-sequence current protection. Figure 7 The system shown is analyzed using a step-down autotransformer as an example.

[0127] For zero-sequence current protection, when an asymmetrical grounding fault occurs on a 220kV line, the zero-sequence current distribution of the medium-voltage phase-shifting branch and the autotransformer branch will change because the autotransformer branch and the phase-shifting branch of the step-down autotransformer are equivalent to an equivalent impedance. This may lead to a decrease in the sensitivity of the zero-sequence current protection, and the zero-sequence current on each side needs to be recalculated in conjunction with the parameters of the connected step-down autotransformer.

[0128] To verify the zero-sequence equivalent model of the step-down autotransformer, a simulation model of the step-down autotransformer was built. The system topology adopted is as follows: Figure 3 The structure shown, and the system access method are as follows: Figure 8 As shown.

[0129] The parameters of the step-down autotransformer are shown in Table 1. With the phase-shifting transformer section set with 8 taps, the primary winding voltage is 110021.3V, the secondary winding voltage is 9382.5V, the primary winding current is 49.15A, the secondary winding current is 576.4A, the short-circuit impedance is 3.57%, and the no-load phase angle is 8.1°.

[0130] Table 1 Load Loss and Short-Circuit Impedance of Step-Down Autotransformer Phase-Shift Transformer

[0131] Taking a single-phase ground fault occurring at 0.25s on a 220kV line with a step-down autotransformer as an example, the terminal voltage waveforms and zero-sequence voltage waveforms of the medium-voltage autotransformer branch and the medium-voltage phase-shifting branch of the step-down autotransformer are as follows: Figure 9-10 As shown; the current flowing through the autotransformer branch LA1 The waveform is as follows Figure 11 As shown.

[0132] Simulated value of zero-sequence equivalent impedance:

[0133] The zero-sequence voltage of the autotransform branch was extracted by fast Fourier transform. kV; the zero-sequence voltage of the phase-shifting branch is kV; the current in the autotransformer branch LA1 is kA. The zero-sequence equivalent reactance can be calculated using equation (8). =0.1428Ω.

[0134] The zero-sequence equivalent impedance calculation value proposed in this invention is as follows:

[0135] For ease of calculation, the phase shifter impedance is equivalent to that of the primary side, then the rated voltage on the high-voltage side is... Rated capacity Short-circuit impedance Then, from the formula... achievable =1.8006Ω.

[0136] Based on the ratio of the primary and secondary rated voltages, combined with the type Therefore, k = 11.726.

[0137] Then by formula It can be calculated = =0.1415Ω.

[0138] As can be seen from the above simulation analysis, the simulated value of the zero-sequence equivalent impedance is consistent with the calculated value, which verifies the correctness of the zero-sequence equivalent model derived in this invention.

[0139] Therefore, the zero-sequence impedance calculation flowchart proposed in this embodiment is as follows: Figure 12 As shown. When calculating the zero-sequence equivalent model of the buck autotransformer, the rated capacity of the buck autotransformer is collected on the one hand. and the short-circuit impedance of the phase-shifting transformer section and the rated voltage of the primary winding On the one hand, it obtains information such as the tap position of the phase-shifting transformer and the secondary winding voltage. The equivalent impedance between the autotransformer branch and the phase-shifting branch can be calculated using the derived equivalent impedance formula. For the autotransformer portion of the step-down autotransformer, the leakage reactance of the high-voltage, medium-voltage, and low-voltage windings is still calculated based on the short-circuit impedances between the high-voltage-medium-voltage, high-voltage-low-voltage, and medium-voltage-low-voltage windings, respectively. , as well as After calculating these parameters, the zero-sequence equivalent model of the step-down autotransformer phase shift can be obtained.

[0140] The impact of connecting a step-down autotransformer on zero-sequence current protection:

[0141] Taking a single-phase ground fault occurring on the high-voltage side of the step-down autotransformer at 0.25s as an example, the zero-sequence current on the 110kV autotransformer side differs between having and not having the step-down autotransformer connected. The waveforms are as follows: Figure 13 , Figure 14 As shown.

[0142] Depend on Figure 13 and Figure 14 It can be seen that after connecting the step-down autotransformer, the zero-sequence current on the 110kV autotransformer side drops significantly, resulting in a significant decrease in sensitivity. Therefore, it is necessary to consider adjusting the zero-sequence current protection setting value.

[0143] The solution in this embodiment has the following advantages:

[0144] 1) Based on the topology, magnetic coupling relationship and circuit relationship of the step-down autotransformer, the zero-sequence equivalent model of the step-down autotransformer is derived. The key point of this invention is that the autotransformer branch and the phase-shifting branch can be regarded as an equivalent reactance related to the leakage reactance of the phase-shifting transformer winding and the tap position information.

[0145] 2) Study on the zero-sequence equivalent model of step-down autotransformer based on Kirchhoff's current law and magnetic circuit coupling relationship;

[0146] 3) Based on the equivalent model, analyze the impact of step-down autotransformer on the sensitivity of protections such as zero-sequence current protection of the line.

[0147] Please see Figure 15 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the method described above.

[0148] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0149] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0150] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0151] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0152] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0153] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0154] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0155] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0156] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0157] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A zero-sequence equivalent model analysis method for a step-down autotransformer, characterized in that, The method comprises the following steps: obtaining the structural topology and electrical parameters of the step-down autotransformer phase shifter; applying the same zero sequence voltage condition to the autotransformer branch port of the step-down autotransformer phase shifter, establishing a zero sequence current loop model of the autotransformer branch and the phase shifter branch, and writing a port current relationship according to the Kirchhoff's current law; assuming and using an ideal transformer model in the phase shifter transformer part, solving the current relationship of the primary winding and the secondary winding of the phase shifter transformer based on the magnetic motive force balance principle, introducing the transformation ratio, and substituting the current relationship of the primary winding and the secondary winding into the port current relationship; deriving an equivalent zero sequence reactance expression between the autotransformer branch and the phase shifter branch in the step-down autotransformer phase shifter, and making the autotransformer branch and the phase shifter branch be regarded as equivalent reactance in series; establishing a zero sequence equivalent model of the step-down autotransformer phase shifter based on the equivalent zero sequence reactance, and calculating and simulating the zero sequence current of the power grid under the conditions of single-phase grounding, two-phase interphase grounding or asymmetric grounding fault by using the equivalent model; and evaluating the influence of the step-down autotransformer phase shifter on the zero sequence current protection sensitivity of the corresponding line.

2. The method of claim 1, wherein, The step of applying the same zero sequence voltage condition to the autotransformer branch port of the step-down autotransformer phase shifter comprises: The same zero sequence voltage is applied at the ports of the step-down autotransformer phase-shifting autotransformer branches LA1, LB1, LC1 The zero sequence voltage at the ports of the phase-shifting branches LA2, LB2, LC2 is solved ; The currents of the self-coupling branches LA1, LB1 and LC1 are , , The currents of the phase-shifting branches LA2, LB2 and LC2 are , , The currents flowing through the primary winding AA', BB' and CC' of the phase-shifting transformer are respectively , , The currents flowing through the secondary winding aa', bb' and cc' of the phase-shifting transformer are respectively , , .

3. The method of claim 2, wherein, The step of writing a port current relationship according to the Kirchhoff's current law comprises: ； ； 。 4. The method of claim 2, wherein, The step of solving the current relationship of the primary winding and the secondary winding of the phase shifter transformer based on the magnetic motive force balance principle comprises: ； ； In the formula, the number of turns of the primary winding AA', BB', and CC' of the phase-shifting transformer is , and the number of turns of the secondary winding aa', bb', and cc' is .

5. The method of claim 4, wherein, The step of introducing the transformation ratio and substituting the current relationship of the primary winding and the secondary winding into the port current relationship comprises: ； In the formula: is the phase-shift transformer ratio, which is related to the phase-shift transformer tap.

6. The method of claim 5, wherein, The step of deriving an equivalent zero sequence reactance expression between the autotransformer branch and the phase shifter branch in the step-down autotransformer phase shifter, and making the autotransformer branch and the phase shifter branch be regarded as equivalent reactance in series comprises: ； ； In the formula, the leakage reactance of the winding AA', BB', CC' is , and the leakage reactance of the winding aa', bb', cc' is ; The phase-shifting transformer self-coupling branch and the phase-shifting branch zero sequence voltage are regarded as an equivalent reactance , and the reactance value is .

7. The method of claim 1, wherein, The step of establishing a zero sequence equivalent model of the step-down autotransformer phase shifter based on the equivalent zero sequence reactance comprises: Obtaining rated capacity of step-down autotransformer and short-circuit impedance of the phase-shifting transformer part and primary winding rated voltage ; Obtaining real-time gear information of a phase-shifting transformer part and a secondary winding voltage According to the derived equivalent impedance formula, the equivalent impedance value between the autotransformer branch and the phase-shifting branch can be calculated ; For the autotransformer part of the step-down autotransformer phase-shifting device, the leakage inductance of the high-voltage, medium-voltage and low-voltage side windings is calculated according to the short-circuit impedance between the high-voltage-medium-voltage, high-voltage-low-voltage and medium-voltage-low-voltage windings respectively , and ; A zero sequence equivalent model of the step-down autotransformer phase shifter is constructed.

8. The method of claim 1, wherein, The step of calculating and simulating the zero sequence current of the power grid under the conditions of single-phase grounding, two-phase interphase grounding or asymmetric grounding fault by using the equivalent model comprises: Based on the equivalent model, the time-domain waveforms of the voltage and the current of the step-down autotransformer phase shifter in a given fault time window are simulated, and the zero sequence equivalent impedance is verified by using the fast Fourier transform (FFT) or frequency domain analysis, so as to compare the consistency of the simulation value and the calculation value.

9. A zero-sequence equivalent model analysis system for a step-down autotransformer, characterized in that, The system comprises the method according to any one of claims 1 to 8, and further comprises: a collection unit configured to obtain the structural topology and electrical parameters of the step-down autotransformer phase shifter; a zero sequence current loop model construction unit configured to apply the same zero sequence voltage condition to the autotransformer branch port of the step-down autotransformer phase shifter, establish a zero sequence current loop model of the autotransformer branch and the phase shifter branch, and write a port current relationship according to the Kirchhoff's current law; a current relationship calculation unit configured to assume and use an ideal transformer model in the phase shifter transformer part, solve the current relationship of the primary winding and the secondary winding of the phase shifter transformer based on the magnetic motive force balance principle, introduce the transformation ratio, and substitute the current relationship of the primary winding and the secondary winding into the port current relationship; and a zero sequence equivalent model establishment unit configured to derive an equivalent zero sequence reactance expression between the autotransformer branch and the phase shifter branch in the step-down autotransformer phase shifter, make the autotransformer branch and the phase shifter branch be regarded as equivalent reactance in series, establish a zero sequence equivalent model of the step-down autotransformer phase shifter based on the equivalent zero sequence reactance, and calculate and simulate the zero sequence current of the power grid under the conditions of single-phase grounding, two-phase interphase grounding or asymmetric grounding fault by using the equivalent model. An equivalent unit is used to derive an equivalent zero sequence reactance expression between the autotransformer branch and the phase-shifting branch in the voltage reduction autotransformer phase-shifting device, so that the autotransformer branch and the phase-shifting branch can be regarded as equivalent reactance in series; A modeling and simulation unit is used to establish a zero sequence equivalent model of the voltage reduction autotransformer phase-shifting device based on the equivalent zero sequence reactance, and to calculate and simulate the zero sequence current of the power grid under single-phase grounding, two-phase inter-phase grounding or asymmetric grounding fault conditions by using the equivalent model, and to evaluate the influence of the voltage reduction autotransformer phase-shifting device on the sensitivity of the corresponding line zero sequence current protection.

10. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor executes the computer program to implement the method of any one of claims 1-8.

11. A storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to implement the method of any one of claims 1-8. The computer program is executed by the processor to implement the method of any one of claims 1-8.

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