Transformer substation distance protection method and device

Abstract

The invention discloses a transformer substation distance protection method and device, and the method comprises the following steps: carrying out the parameter fitting based on the collected voltage and current of an instantaneous loop of a power transmission system, and calculating the apparent impedance; comparing the apparent impedance with a preset offset distance characteristic, and judging whether the fault distance is in a protection area or not; adopting zero sequence grounding direction logic, weak feed direction logic and / or increment direction logic to judge a fault direction; if it is detected that the fault is in the protection area and the direction is correct, a predefined protection action is executed, otherwise, the fault continues to be monitored, and if the direction is correct, the positive fault is indicated. According to the method, full-band signal energy is directly utilized through time domain parameter fitting, impedance calculation does not depend on system frequency, the reliability and accuracy of protection are improved, and the measurement precision can be improved under the condition of signal distortion by adopting a time domain wide-spectrum apparent impedance calculation method.

Description

Technical Field

[0001] This invention relates to the field of power system protection technology, and in particular to a method and device for distance protection of substations. Background Technology

[0002] In power systems, distance protection, as an important relay protection method, achieves fault location and isolation by measuring the electrical distance from the fault point to the protection installation location. The core of traditional distance protection methods relies on the accurate extraction and analysis of the power system's fundamental frequency component. Its key logic includes modules such as memory polarization, fault direction determination, and fault loop selection. This is reliable in power grids dominated by traditional synchronous power sources (such as thermal and hydropower) because their fault characteristics conform to the "fundamental frequency dominance" assumption. Although the voltage and current waveforms are disturbed at the moment of the fault, the energy is still mainly concentrated near the fundamental frequency. Narrowband filtering techniques such as cosine filtering or Fourier transform can effectively extract the fundamental frequency phasor, thereby accurately calculating the fault impedance.

[0003] However, with the large-scale grid connection of new energy sources (such as wind power and photovoltaics), the fault characteristics of non-traditional power sources have changed significantly, and the limitations of traditional distance protection methods have become increasingly apparent. Non-traditional power sources connected to the grid via power electronic converters exhibit fundamentally different fault responses compared to traditional synchronous power sources: during a fault, the converter may limit the output current due to control strategies, leading to a reduction in the fault current amplitude; simultaneously, the switching characteristics of power electronic devices cause severe distortion of voltage and current waveforms, significantly increasing harmonics and high-frequency components, and dispersing fault energy across a wider frequency spectrum rather than concentrating it at the fundamental frequency. Therefore, the memory polarization and fault direction determination logic in traditional distance protection methods become ineffective. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method and device for distance protection of substations suitable for new energy access.

[0005] To solve the above-mentioned technical problems, the present invention provides a substation distance protection method, comprising the following steps:

[0006] The apparent impedance is calculated by fitting parameters based on the collected instantaneous circuit voltage and current of the power transmission system.

[0007] The apparent impedance is compared with a preset offset distance characteristic to determine whether the fault distance is within the protection zone;

[0008] The fault direction is determined by zero-sequence grounding direction logic, weak feed direction logic, and / or incremental direction logic.

[0009] If a fault is detected within the protected area and in the correct direction, a predefined protection action is executed; otherwise, the fault monitoring continues. The correct direction refers to a forward fault.

[0010] Furthermore, the step of calculating the apparent impedance by fitting parameters based on the acquired instantaneous circuit voltage and current of the power transmission system includes the following sub-steps:

[0011] Collect the voltage and current of the instantaneous circuit of the power transmission system;

[0012] The objective function is calculated based on the collected voltage and current. The apparent impedance is then calculated by minimizing the objective function, which represents the mean square error between the predicted voltage and the actual measured voltage.

[0013] Furthermore, the objective function includes a first objective function and a second objective function;

[0014] The step of calculating the apparent impedance by minimizing the objective function based on the acquired voltage and current specifically includes:

[0015] When calculating apparent impedance in the continuous time domain, a first objective function is calculated based on the acquired voltage and current, and the apparent impedance is calculated by minimizing the first objective function.

[0016] When calculating apparent impedance in the discrete-time domain, a second objective function is calculated based on the acquired voltage and current, and the apparent impedance is calculated by minimizing the second objective function.

[0017] Furthermore, the first objective function is expressed as:

[0018]

[0019] In Equation (I), H1 represents the first objective function, R1 represents the first apparent resistance, L represents the apparent inductance, represents the voltage of the instantaneous circuit, represents the current of the instantaneous circuit, the time interval from T to T0 is the observation period, T0 represents the fault start time, and T represents the latest time, i.e. the current time.

[0020] The second objective function is expressed as:

[0021]

[0022] In equation (ii), H2 represents the second objective function, v AVR(n) i represents the average voltage. AVR(n) i represents the mean value of the current. DER(n) R2 represents the discrete approximation of the reciprocal of the current, X represents the apparent inductive reactance, k represents the index of the currently acquired sample, and N0 represents the length of the data window.

[0023] Furthermore, the fault start time represented by T0 in the first objective function refers to the time when the fault occurs plus a preset delay time.

[0024] Furthermore, the step of calculating the apparent impedance by minimizing the first objective function includes the following sub-steps:

[0025] Find the first apparent resistance and apparent inductance that minimize the first objective function;

[0026] The apparent impedance in the continuous time domain is calculated based on the first apparent resistance and apparent inductance.

[0027] Furthermore, the step of calculating the apparent impedance by minimizing the second objective function includes the following sub-steps:

[0028] Find the second apparent resistance and apparent inductive reactance that minimize the second objective function;

[0029] The apparent impedance in the discrete time domain is calculated based on the second apparent resistance and apparent inductance.

[0030] Furthermore, in the step of determining the fault direction using zero-sequence grounding direction logic, weak feeder direction logic, and / or incremental direction logic, the method of determining the fault direction using zero-sequence grounding direction logic specifically includes:

[0031] Calculate the zero-sequence voltage and zero-sequence current; calculate the phase difference angle between the zero-sequence voltage and the zero-sequence current; if the phase difference angle is within a preset positive angle range, it is determined to be a positive fault; if the phase difference angle is outside the preset positive angle range, it is determined to be a reverse fault.

[0032] The method of determining the fault direction using weak feed direction logic specifically includes:

[0033] Measure the fault circuit current; determine whether the fault circuit current meets the preset weak feed current threshold condition; calculate the apparent impedance representing the reverse fault using the reverse quadrilateral characteristic; if the weak feed current threshold condition is met and the calculated apparent impedance falls within the preset reverse action characteristic region, then it is determined to be a reverse fault.

[0034] Furthermore, in the step of determining the fault direction using zero-sequence grounding direction logic, weak feeder direction logic, and / or incremental direction logic, the method of determining the fault direction using incremental direction logic specifically includes:

[0035] Calculate the incremental voltage of the faulty circuit, where the incremental voltage is the difference between the instantaneous voltage after the fault occurs and the normal voltage memorized before the fault occurs; calculate the simulated incremental replication current based on the inductive characteristics of the faulty circuit; within a preset short time window after the fault occurs, detect the instantaneous polarity relationship between the incremental voltage and the incremental replication current; if the polarities of the incremental voltage and the incremental replication current are opposite, it is determined to be a forward fault; if the polarities of the incremental voltage and the incremental replication current are the same, it is determined to be a reverse fault.

[0036] To solve the above-mentioned technical problems, another technical solution adopted in this paper is to provide a substation distance protection device, comprising:

[0037] The calculation module is used to perform parameter fitting based on the collected voltage and current of the instantaneous circuit of the power transmission system and to calculate the apparent impedance;

[0038] The first judgment module is used to compare the apparent impedance with the preset offset distance characteristics to determine whether the fault distance is within the protection zone;

[0039] The second judgment module is used to determine the fault direction using zero-sequence grounding direction logic, weak feed direction logic and / or incremental direction logic;

[0040] The protection module is used to execute predefined protection actions when a fault is detected within the protection zone and in the correct direction, where the correct direction refers to a forward fault.

[0041] The substation distance protection method and device of the present invention have at least the following beneficial effects: The present invention directly utilizes the full-band signal energy through time-domain parameter fitting, and the impedance calculation does not depend on the system frequency, thereby improving the reliability and accuracy of protection; at the same time, the observation window is a dynamic window, gradually expanding from the fault initiation time, with a short window for rapid response in the early stage and a long window for noise suppression in the later stage, significantly improving the measurement accuracy in signal distortion scenarios; the direction judgment accuracy is improved through the synergy of multiple logics such as zero-sequence direction logic, weak feed direction logic, and incremental direction logic, ensuring direction reliability; the constant inductance method is adopted, and the protection range remains unchanged when the system frequency fluctuates, avoiding the protection range drift caused by frequency shift in traditional methods; the present invention eliminates the dependence on frequency and polarization voltage, significantly improving the protection accuracy and adaptability in new energy scenarios. Attached Figure Description

[0042] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0043] Figure 1 This is a fault current waveform diagram for a new energy access system.

[0044] Figure 2 This is a fault voltage waveform diagram for a new energy access system.

[0045] Figure 3 This is a flowchart of one embodiment of the substation distance protection method of the present invention.

[0046] Figure 4 for Figure 3 Flowchart of step S100.

[0047] Figure 5 This is a non-directional Mho circle characteristic diagram.

[0048] Figure 6 This is a diagram showing the co-operation of non-directional Mho characteristics and directional logic.

[0049] Figure 7 This is a Mho characteristic map showing forward and reverse offsets.

[0050] Figure 8 This is a structural block diagram of one embodiment of the substation distance protection device of the present invention. Detailed Implementation

[0051] The invention will now be further described with reference to the accompanying drawings.

[0052] Typically, apparent impedance can be calculated using phasor values; dividing the measured voltage phasor by the measured current phasor yields the apparent impedance. However, in typical power system protection, phasors are calculated using cosine or Fourier filters. Therefore, the apparent impedance calculated using phasors is frequency-dependent, typically representing energy around the fundamental power system frequency. See also... Figure 1 and Figure 2 During a fault, the voltage and current supplied by new energy sources may be low and distorted, and the energy of these voltages and currents may be dispersed across the entire spectrum rather than concentrated at the power frequency. Apparent impedance measurements can be improved by using signal energy across a wider spectrum, rather than concentrating it within a narrow band near the power frequency.

[0053] Please see Figure 3 This is a flowchart of an embodiment of the substation distance protection method of the present invention. This embodiment specifically includes the following steps:

[0054] S100, Calculate the apparent impedance.

[0055] Specifically, the apparent impedance is calculated by fitting parameters based on the instantaneous voltage and current of the power transmission system's circuit. In this embodiment, the apparent impedance is calculated using the current and voltage measured at an IED (Intelligent Electronic Device). In a power system, an IED refers to a protection, control, or monitoring device with digital processing capabilities. Its core function is to collect electrical quantities (such as current and voltage) and non-electrical quantities (such as temperature and switch status) in real time, and to realize protection logic execution, control command output, or status monitoring through internal calculations or communication interfaces.

[0056] Please see Figure 4 This step S100 includes the following sub-steps:

[0057] S110, collects voltage and current.

[0058] Specifically, it collects the voltage and current of the instantaneous circuit of the power transmission system.

[0059] S120. Calculate the apparent impedance by minimizing the objective function.

[0060] Specifically, an objective function is calculated based on the acquired voltage and current. The apparent impedance is then calculated by minimizing this objective function, which represents the mean square error between the predicted voltage and the actual measured voltage. The objective function includes a first objective function and a second objective function. Depending on the specific circumstances, the calculation of apparent impedance can be divided into two cases: calculation in the continuous time domain and calculation in the discrete time domain. Calculations can be performed in the continuous time domain for offline analysis or when high accuracy is required; and in the discrete time domain when high real-time performance and sampling rate are demanding.

[0061] The first objective function is expressed as:

[0062]

[0063] Where H1 represents the first objective function, R1 represents the first apparent resistance, L represents the apparent inductance, represents the voltage of the instantaneous loop, represents the current of the instantaneous loop, the time interval from T to T0 is the observation period, T0 represents the start time, and T represents the latest time, i.e., the current time. The start time can be the time when the fault occurred plus a preset delay time to eliminate initial transients that do not reflect the characteristics of the measurement loop.

[0064] The above calculation method allows for the expansion of the measurement window over time, thereby progressively improving accuracy even in the presence of signal distortion and interference. For example, a window starting at T = 5 ms after a fault occurs has a length of 20 ms when T0 = 25 ms (i.e., 25 ms after the fault occurs); a length of 21 ms when T0 = 26 ms, and so on. Distance elements can be intentionally allowed to operate for longer periods to achieve better apparent impedance measurement accuracy. For example, at 40 ms after a fault occurs, the window length used by the relay is 35 ms. Secondly, the above calculation method utilizes signal energy in at least several hundred hertz, which is the spectral range allowed by low-pass filters applied to instantaneous voltage and current. The total energy in this spectrum is higher than the energy carried by phasors in the narrow band near the power system frequency. By processing high-energy signals, measurement accuracy can be improved. Furthermore, this calculation method does not depend on the system frequency or the measured value of the system frequency; therefore, actual changes in the system frequency, frequency measurement lag, or errors will not affect the final result. Furthermore, this is a constant inductance method, which maintains a constant distance from the component range even if the system frequency differs from the nominal value.

[0065] When calculating apparent impedance in the continuous-time domain, a first objective function is calculated based on the acquired voltage and current, and the apparent impedance is calculated by minimizing the first objective function. Specifically, the calculation involves solving for the first apparent resistance and apparent inductance that minimize the first objective function; the apparent impedance in the continuous-time domain is then calculated based on the first apparent resistance and apparent inductance. These are well-established calculation methods and will not be elaborated upon here.

[0066] The first objective function in the continuous-time domain described above can be transformed into a second objective function in the discrete-time domain, which is expressed as:

[0067]

[0068] Where H2 represents the second objective function, R2 represents the second apparent resistance, X represents the apparent inductive reactance, k represents the index of the currently acquired sample, N0 represents the data window length, and v AVR(n) This represents the average voltage. i AVR(n) This represents the average value of the current. i DER(n) This represents a discrete approximation of the reciprocal of the current. f N f represents the nominal system frequency. s This indicates the relay sampling frequency, and n and n-1 both represent the indices for current and voltage sampling.

[0069] When calculating apparent impedance in the discrete-time domain, a second objective function is calculated based on the acquired voltage and current. The apparent impedance is then calculated by minimizing this second objective function. Specifically, the calculation involves solving for the second apparent resistance and apparent inductive reactance that minimize the second objective function. Based on this second apparent resistance and apparent inductive reactance, the apparent impedance in the discrete-time domain is calculated. The second apparent resistance can be expressed by the following formula:

[0070]

[0071] The apparent impedance can be expressed by the following formula:

[0072]

[0073] Among them, A (k) This represents the integral of the system-side current energy. B (k) This represents the integral of the cross-correlation between the system and the new energy current. C (k) This represents the energy integral of the current on the new energy side. D (k) This represents the system-side instantaneous power integral. E (k) This represents the cross-power integral of the new energy current and the system voltage.

[0074] The method of calculating apparent impedance using the second apparent resistance and apparent inductive reactance is existing technology and will not be elaborated here.

[0075] S200, determine whether the fault distance is within the protection zone.

[0076] Specifically, the apparent impedance is compared with a preset offset distance characteristic to determine whether the fault distance is within the protection zone. The calculated apparent impedance is compared with the preset offset distance characteristic; if the impedance point (R,X) is within the characteristic boundary, the fault is determined to be within the protection zone; if the impedance point (R,X) is outside the characteristic boundary, the fault is determined to be outside the protection zone. The specific determination method is a mature existing technology and will not be elaborated here. Please refer to [link to relevant documentation]. Figure 5 and 6 This demonstrates the offset (non-directional) distance characteristics on the apparent impedance plane; please refer to [link to relevant documentation]. Figure 7 The diagram illustrates offset distance characteristics and reverse characteristic curves plotted according to several embodiments of the present invention. Figures 5 to 7 The voltage and current inputs are the voltage and current of the instantaneous circuit, which can be calculated from the instantaneous phase quantities based on the principle of six-circuit distance protection of a three-phase system.

[0077] The time-domain wideband apparent impedance method described in this scheme is particularly suitable for measuring phase-to-phase apparent impedance because the phase-to-phase current supplied by non-traditional sources is very low during phase faults (the system impedance ratio for phase-to-phase faults is very high). It should be understood that this invention is not limited to using time-domain wideband harmonic apparent impedance measurement; phasor-based apparent impedance measurement can also be used, achieving the other advantages described herein. Apparent impedance can be used to determine fault distance using distance-operating characteristics such as MH-operating or quadrilateral-operating characteristics. However, in some cases, using apparent impedance instead of conventional polarization processing may not reliably detect fault direction. For example, for near-distance faults, the measured voltage is very low or zero, which prevents the apparent impedance distance element from detecting the fault direction. Therefore, weak feed-in direction logic, zero-sequence direction logic, and / or incremental direction logic are needed to enhance directivity.

[0078] S300, determine the direction of the fault.

[0079] Specifically, zero-sequence grounding direction logic, weak feed direction logic, and / or incremental direction logic are used to determine the fault direction. For phase-to-ground faults, zero-sequence grounding direction logic is used to determine the fault direction. The specific method includes: calculating the zero-sequence voltage and zero-sequence current; calculating the phase difference angle between the zero-sequence voltage and the zero-sequence current; if the phase difference angle is within a preset positive angle range, it is determined to be a positive fault; if the phase difference angle is outside the preset positive angle range, it is determined to be a reverse fault. The zero-sequence direction logic determines the direction based on the phase difference, avoiding misjudgments caused by voltage drops.

[0080] For phase-to-phase faults, a weak feeder directional logic is used to determine the fault direction. The specific method includes: measuring the fault loop current; determining whether the fault loop current meets a preset weak feeder current threshold condition; calculating the apparent impedance representing a reverse fault using the reverse quadrilateral characteristic; and determining a reverse fault if the weak feeder current threshold condition is met and the calculated apparent impedance falls within a preset reverse action characteristic region. In this embodiment, the weak feeder current threshold condition is: the fault loop current is greater than a lower limit set based on the maximum fault current of the local weak power source, and less than an upper limit set based on the minimum fault current of the remote strong power source. The weak feeder directional logic combines the current threshold and the reverse quadrilateral characteristic to solve the problem of directional inaccuracy for low-amplitude currents.

[0081] For all faults, incremental directional logic can be used to determine the fault direction. The specific method includes: calculating the incremental voltage of the fault circuit, where the incremental voltage is the difference between the instantaneous voltage after the fault occurs and the normal voltage stored before the fault; calculating the simulated incremental replication current based on the inductance characteristics of the fault circuit; detecting the instantaneous polarity relationship between the incremental voltage and the incremental replication current within a preset short-time window after the fault occurs; if the polarities of the incremental voltage and the incremental replication current are opposite, it is determined to be a forward fault; if the polarities of the incremental voltage and the incremental replication current are the same, it is determined to be a reverse fault. In this embodiment, the length of the short-time window is 1 / 4 to 1 / 2 of a power grid frequency cycle. After detecting a valid polarity relationship, a delay circuit is used to maintain the direction determination result for at least 2-3 power grid frequency cycles. The specific calculation methods mentioned above are all existing algorithms and will not be elaborated upon here.

[0082] S400, Start Protection.

[0083] Specifically, if a fault is detected within the protected area and in the correct direction, a predefined protection action is executed; otherwise, fault monitoring continues. "Correct direction" refers to a forward fault. In this embodiment, when a fault is detected within the protected area and in the correct direction, the relevant circuit breaker will trip to isolate the fault and protect the rest of the power system.

[0084] Please see Figure 8 This is a structural block diagram of one embodiment of a substation distance protection device. This embodiment of the substation distance protection device, applicable to new energy access, is used to implement the substation distance protection method for new energy access described in the above embodiment. Specifically, this embodiment of the substation distance protection device for new energy access includes a calculation module 100, a first judgment module 200, a second judgment module 300, and a protection module 400. Wherein:

[0085] The calculation module 100 is used to perform parameter fitting based on the acquired voltage and current of the instantaneous circuit of the power transmission system to calculate the apparent impedance. Specifically, the calculation module 100 is used to acquire the voltage and current of the instantaneous circuit of the power transmission system; calculate an objective function based on the acquired voltage and current; and calculate the apparent impedance by minimizing the objective function. The objective function represents the mean square error between the predicted voltage value and the actual measured voltage.

[0086] The first judgment module 200 is used to compare the apparent impedance with the preset offset distance characteristics to determine whether the fault distance is within the protection zone.

[0087] The second judgment module 300 is used to determine the fault direction using zero-sequence grounding direction logic, weak feedback direction logic, and / or incremental direction logic. The zero-sequence grounding direction logic is mainly used to determine the direction of phase-to-ground faults, the weak feedback direction logic is mainly used to determine the direction of phase-to-phase faults, and the incremental direction logic can be used to determine the direction of all faults.

[0088] The protection module 400 is used to execute a predefined protection action when a fault is detected within the protection zone and in the correct direction, wherein the correct direction refers to a forward fault.

[0089] This invention directly utilizes full-band signal energy through time-domain parameter fitting, and impedance calculation is independent of system frequency, improving the reliability and accuracy of protection. Simultaneously, the observation window is dynamic, gradually expanding from the fault initiation time with a short initial window for rapid response and a long later window to suppress noise, significantly improving measurement accuracy in signal distortion scenarios. The collaborative use of multiple logics, including zero-sequence direction logic, weak-feed direction logic, and incremental direction logic, enhances direction judgment accuracy and ensures direction reliability. Employing a constant inductance method, the protection range remains unchanged despite system frequency fluctuations, avoiding the drift caused by frequency shifts in traditional methods. This invention eliminates dependence on frequency and polarization voltage, significantly improving the accuracy and adaptability of protection in new energy scenarios.

[0090] The above description merely illustrates preferred embodiments of the present invention and is quite specific and detailed; however, it should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for distance protection in a substation, characterized in that, Includes the following steps: The apparent impedance is calculated by fitting parameters based on the collected instantaneous circuit voltage and current of the power transmission system. The apparent impedance is compared with a preset offset distance characteristic to determine whether the fault distance is within the protection zone; The fault direction is determined by zero-sequence grounding direction logic, weak feed direction logic, and / or incremental direction logic. If a fault is detected within the protected area and in the correct direction, a predefined protection action is executed; otherwise, the fault monitoring continues. The correct direction refers to a forward fault.

2. The substation distance protection method as described in claim 1, characterized in that, The step of calculating the apparent impedance by fitting parameters based on the acquired instantaneous circuit voltage and current of the power transmission system includes the following sub-steps: Collect the voltage and current of the instantaneous circuit of the power transmission system; The objective function is calculated based on the acquired voltage and current. The apparent impedance is then calculated by minimizing the objective function, which represents the mean square error between the predicted voltage and the actual measured voltage.

3. The substation distance protection method as described in claim 2, characterized in that: The objective function includes a first objective function and a second objective function; The step of calculating the apparent impedance by minimizing the objective function based on the acquired voltage and current specifically includes: When calculating apparent impedance in the continuous time domain, a first objective function is calculated based on the acquired voltage and current, and the apparent impedance is calculated by minimizing the first objective function. When calculating apparent impedance in the discrete-time domain, a second objective function is calculated based on the acquired voltage and current, and the apparent impedance is calculated by minimizing the second objective function.

4. The substation distance protection method as described in claim 3, characterized in that, The first objective function is expressed as: In Equation (I), H1 represents the first objective function, R1 represents the first apparent resistance, L represents the apparent inductance, represents the voltage of the instantaneous circuit, represents the current of the instantaneous circuit, the time interval from T to T0 is the observation period, T0 represents the fault start time, and T represents the latest time, i.e. the current time. The second objective function is expressed as: In equation (ii), H2 represents the second objective function, v AVR(n) i represents the average voltage. AVR(n) i represents the mean value of the current. DER(n) R2 represents the discrete approximation of the reciprocal of the current, X represents the apparent inductive reactance, k represents the index of the currently acquired sample, and N0 represents the length of the data window.

5. The substation distance protection method as described in claim 4, characterized in that: The fault start time represented by T0 in the first objective function is the time when the fault occurs plus a preset delay time.

6. The substation distance protection method as described in claim 3, characterized in that, The step of calculating the apparent impedance by minimizing the first objective function includes the following sub-steps: Find the first apparent resistance and apparent inductance that minimize the first objective function; The apparent impedance in the continuous time domain is calculated based on the first apparent resistance and apparent inductance.

7. The substation distance protection method as described in claim 3, characterized in that, The step of calculating the apparent impedance by minimizing the second objective function includes the following sub-steps: Find the second apparent resistance and apparent inductive reactance that minimize the second objective function; The apparent impedance in the discrete time domain is calculated based on the second apparent resistance and apparent inductance.

8. The substation distance protection method as described in claim 1, characterized in that, In the step of determining the fault direction using zero-sequence grounding direction logic, weak feeder direction logic, and / or incremental direction logic, the method of determining the fault direction using zero-sequence grounding direction logic specifically includes: Calculate the zero-sequence voltage and zero-sequence current; calculate the phase difference angle between the zero-sequence voltage and the zero-sequence current; if the phase difference angle is within a preset positive angle range, it is determined to be a positive fault; if the phase difference angle is outside the preset positive angle range, it is determined to be a reverse fault. The method of determining the fault direction using weak feed direction logic specifically includes: Measure the fault circuit current; determine whether the fault circuit current meets the preset weak feed current threshold condition; calculate the apparent impedance representing the reverse fault using the reverse quadrilateral characteristic; if the weak feed current threshold condition is met and the calculated apparent impedance falls within the preset reverse action characteristic region, then it is determined to be a reverse fault.

9. The substation distance protection method as described in claim 1, characterized in that, In the step of determining the fault direction using zero-sequence grounding direction logic, weak feeder direction logic, and / or incremental direction logic, the method of determining the fault direction using incremental direction logic specifically includes: Calculate the incremental voltage of the faulty circuit, where the incremental voltage is the difference between the instantaneous voltage after the fault occurs and the normal voltage memorized before the fault occurs; calculate the simulated incremental replication current based on the inductive characteristics of the faulty circuit; within a preset short time window after the fault occurs, detect the instantaneous polarity relationship between the incremental voltage and the incremental replication current; if the polarities of the incremental voltage and the incremental replication current are opposite, it is determined to be a forward fault; if the polarities of the incremental voltage and the incremental replication current are the same, it is determined to be a reverse fault.

10. A substation distance protection device, characterized in that, include: The calculation module is used to perform parameter fitting based on the collected voltage and current of the instantaneous circuit of the power transmission system and to calculate the apparent impedance; The first judgment module is used to compare the apparent impedance with the preset offset distance characteristics to determine whether the fault distance is within the protection zone; The second judgment module is used to determine the fault direction using zero-sequence grounding direction logic, weak feed direction logic and / or incremental direction logic; The protection module is used to execute predefined protection actions when a fault is detected within the protection zone and in the correct direction, where the correct direction refers to a forward fault.

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