A method for coordinated suppression of transient overcurrent and ferroresonance of a voltage transformer

Abstract

This invention discloses a method for the coordinated suppression of transient overcurrent and ferroresonance in voltage transformers, relating to the field of relay protection technology. The method includes: collecting electrical quantities of the voltage transformer during circuit breaker operation; associating transient waveforms with the operation time to generate operational sequence data; dividing the continuous half-cycle according to the zero-crossing point of the primary current in the operational sequence data; distinguishing the initial impact section and the continuous oscillation section by combining the inverse-time characteristic of the fuse to obtain the transient overcurrent state; and determining the continuous ferroresonance state based on the synchronous oscillation relationship of electrical quantities within the continuous oscillation section; for the initial impact section corresponding to the transient overcurrent state, using a primary neutral point PTC current-limiting harmonic suppressor to limit the transient current and dissipate transient energy. This invention utilizes the final layer approximation component and the final layer detail component of a fourth-order Dobessi discrete wavelet to characterize low-frequency and mid-frequency changes respectively, avoiding misjudgments caused by cycle phase misalignment and the termination of harmonic suppression before residual oscillations disappear.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology, and in particular to a method for the coordinated suppression of transient overcurrent and ferroresonance in voltage transformers. Background Technology

[0002] Electromagnetic voltage transformers are widely used in medium and high voltage power distribution scenarios for bus voltage measurement, insulation monitoring, and relay protection. When a circuit breaker performs opening or closing operations, a transient electromagnetic process occurs between the bus inductance, capacitance, and excitation branch of the voltage transformer. This can lead to inrush current and transient overvoltage on the primary side of the voltage transformer. Furthermore, after the voltage transformer core enters the nonlinear excitation region, ferroresonance may also occur between the excitation inductance and the capacitance to ground. Existing technologies typically use methods such as connecting a harmonic-suppressing resistor or a PTC current-limiting harmonic suppressor to the neutral point of the primary side of the voltage transformer to limit abnormal current and transient overvoltage. Alternatively, a damping resistor or a microprocessor-based harmonic suppressor can be connected to the open delta winding on the secondary side to suppress power frequency, sub-frequency, and low-frequency resonances in the open delta voltage, thereby reducing the impact of abnormal voltage transformer operation on the primary side fuses and voltage measurements.

[0003] However, the initial high-amplitude transient impact generated by circuit breaker operation differs from the persistent ferroresonance after the initial impact decays in terms of duration, frequency composition, and electrical quantity changes. Existing primary-side harmonic suppression measures mainly limit primary-side overcurrent and transient energy, while secondary-side harmonic suppression measures primarily suppress resonance based on open-delta voltage anomalies. There is usually a lack of temporal correspondence between the two for the same transient process, making it difficult to accurately distinguish between the initial impact segment and the subsequent sustained oscillation segment after circuit breaker operation. When secondary-side harmonic suppression is intervened too early, the initial transient impact is easily confused with the ferroresonance; when secondary-side harmonic suppression is implemented only after a significant sustained anomaly in the open-delta voltage is formed, the ferroresonance that still exists after the primary-side transient impact decays may not be addressed in time. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for the coordinated suppression of transient overcurrent and ferroresonance in voltage transformers to solve the problem of lack of time-sequential coordinated suppression of transient overcurrent and continuous ferroresonance after circuit breaker operation.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for the coordinated suppression of transient overcurrent and ferroresonance in voltage transformers, comprising,

[0008] Collect the electrical quantities of the voltage transformer during the circuit breaker operation, associate them with transient waveforms at the time of operation, and generate runtime sequence data;

[0009] The continuous half-cycle is divided according to the zero-crossing point of the primary current in the runtime sequence data. The first impact section and the continuous oscillation section are distinguished by combining the inverse time characteristic of the fuse to obtain the transient overcurrent state. The continuous ferromagnetic resonance state is determined according to the synchronous oscillation relationship of the electrical quantities in the continuous oscillation section.

[0010] For the first impact section corresponding to the transient overcurrent state, the transient current is limited and the transient energy is dissipated by the primary side neutral point PTC current limiter and harmonic suppressor, generating the primary side suppressed operation data;

[0011] The neutral point current continuous oscillation section in the primary side suppression operation data is extracted using a three-point linear structural element and time-corresponded with the open delta voltage distortion. Combined with the ferromagnetic resonance continuous state control of the secondary side harmonic elimination branch, collaborative suppression operation data is generated.

[0012] By comparing adjacent power frequency cycles in the coordinated suppression operation data and using fourth-order Dobessi discrete wavelets to extract continuous low-frequency and medium-frequency features, the harmonic elimination state of the secondary side harmonic elimination branch is determined, and the voltage transformer protection control results are generated.

[0013] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, wherein: the generation of runtime sequence data specifically includes:

[0014] The three-phase voltage, primary current, primary neutral current and open delta voltage of the bus are collected synchronously, and the opening and closing status and action time of the circuit breaker are recorded to obtain continuous electrical quantities.

[0015] Runtime sequence data is generated by preserving the stable operating waveforms before and after the transient state of continuous electrical quantities at the moment of circuit breaker operation, and maintaining the time relationship between each electrical quantity and the circuit breaker operation according to the sampling time.

[0016] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, wherein: the division of continuous half-cycles specifically includes:

[0017] The current polarity reversal position is determined by the sampling sequence of the primary current in the runtime sequence data, and the zero-crossing point sequence of the primary current is obtained;

[0018] The half-cycle is defined by the adjacent zero-crossing points according to the time sequence of the primary current zero-crossing point sequence, and the primary current, primary neutral point current and open delta voltage of the same period are intercepted according to the start and end times of each half-cycle to obtain the continuous half-cycle electrical quantities.

[0019] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, wherein: the distinction between the initial impact section and the continuous oscillation section by combining the inverse time characteristic of the fuse specifically includes:

[0020] The continuous half-cycle electrical quantities are located according to the circuit breaker's operating time. The maximum absolute value of the primary current in each half-cycle is taken as the half-cycle current amplitude, and compared with the primary current amplitude of the same polarity half-cycle before the transient process occurs.

[0021] When the amplitude of the half-cycle current after the circuit breaker trips is higher than the amplitude of the primary side current of the same polarity half-cycle and the amplitude of the subsequent half-cycle current decreases continuously, the first impact section is determined.

[0022] For the first impact section, the corresponding fusing time is obtained from the inverse time characteristic of the fuse based on the half-cycle current amplitude. The ratio of the duration of each half-cycle to the corresponding fusing time is accumulated in the order of the half-cycle time to obtain the cumulative inverse time occupancy.

[0023] When the cumulative inverse time limit occupancy reaches one, the first impact section is determined as a transient overcurrent state that achieves the fuse breaking effect; when the cumulative inverse time limit occupancy is less than one, the first impact section is determined as a transient overcurrent state that does not achieve the fuse breaking effect.

[0024] Only after the first impact zone has formed and ended, check the primary side current, primary side neutral point current, and open delta voltage. If the three maintain synchronous oscillation in the subsequent continuous power frequency cycle, it is determined to be a continuous state of ferroresonance; otherwise, it is determined to be a non-continuous state of ferroresonance.

[0025] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance co-suppression method of the present invention, the generation of primary-side suppressed operating data specifically includes:

[0026] For the first impact section corresponding to the transient overcurrent state, the transient current of the primary neutral point is made to flow through the PTC current limiting harmonic suppressor. The positive temperature coefficient characteristic of the PTC current limiting harmonic suppressor makes the equivalent resistance increase with its own temperature rise, thereby limiting the transient current of the primary neutral point and dissipating the transient energy. The primary current, the primary neutral point current and the open delta voltage are collected simultaneously to obtain the continuous electrical quantity after the primary side is suppressed.

[0027] The continuous electrical quantities after primary side suppression are arranged according to the continuous half-cycle, and the initial impact attenuation and subsequent changes are retained to generate the operating data after primary side suppression.

[0028] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, wherein: the extraction of primary-side suppressed operating data using three-point linear structure elements specifically includes:

[0029] The neutral point current of the primary side is obtained by extracting the operating data after the primary side suppression from the end position of the first impact section;

[0030] Three consecutive sampling positions of the neutral point current continuous sequence are selected to establish a three-point linear structure element, and the element is moved point by point along the neutral point current continuous sequence to obtain the maximum and minimum current values ​​of each sampling interval, thus obtaining the expansion sequence and corrosion sequence.

[0031] By combining the expansion sequence and corrosion sequence at the same sampling location, the current spikes, high-frequency glitches, current abrupt changes and continuous current oscillations in the initial stage of the PTC current limiter and harmonic suppressor are separated to obtain the morphological filter current sequence.

[0032] By comparing the direction of change of adjacent samples of the morphological filter current sequence and the repetition position within the continuous power frequency cycle, the periodic change segment is obtained. The periodic change segment that spans the continuous power frequency cycle and recurs is determined as the neutral point current continuous oscillation segment. The number of power frequency cycles that continuously cross to form the periodic change repetition relationship is recorded as the continuous determination cycle number.

[0033] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance co-suppression method of the present invention, wherein: the generation of co-suppression operating data specifically includes:

[0034] According to the start and end times of the continuous oscillation of the neutral point current, the continuous cycle of the open delta voltage is extracted to determine the oscillation section of the open delta voltage, and the overlapping cycle section of the continuous oscillation section of the neutral point current and the oscillation section of the open delta voltage is obtained.

[0035] The first impact end position, the overlapping cycle section, and the continuous cycle position of the ferromagnetic resonance sustained state are matched in the transient overcurrent state. Only when the overlapping cycle section is located after the first impact end position and within the continuous cycle range of the ferromagnetic resonance sustained state, the overlapping cycle section is determined as the secondary side harmonic elimination access interval; otherwise, the secondary side harmonic elimination branch is kept in the monitoring state.

[0036] According to the secondary side harmonic elimination access interval control, the secondary side harmonic elimination branch acts on the open delta winding, and the primary side current, primary side neutral point current and open delta voltage are collected simultaneously and arranged in continuous cycles to generate coordinated suppression operation data.

[0037] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance co-suppression method of the present invention, wherein: the comparison of adjacent power frequency cycles of the co-suppression operation data specifically includes:

[0038] According to the sequence of zero-crossing points of the primary current, a power frequency cycle is defined by three adjacent zero-crossing points. The number of uniform sampling points is determined according to the ratio of the sampling frequency to the rated power frequency. Normalized sampling positions are set in the two half-cycles of each power frequency cycle according to the same phase interval.

[0039] Based on the actual start and end times of each half-cycle, the primary neutral point current and open delta voltage in the collaborative suppression operation data are linearly interpolated to the normalized sampling position to obtain phase-normalized continuous power frequency cycle data.

[0040] By comparing the current phase-normalized power frequency cycle with the previous phase-normalized power frequency cycle at the same normalized sampling position, the neutral point current and open delta voltage on the primary side are obtained. Data that continues to change for adjacent power frequency cycles are retained to obtain cycle change data.

[0041] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, the step of using fourth-order Dobessi discrete wavelet to extract sustained low-frequency and mid-frequency features specifically includes:

[0042] Multiple consecutive phase-normalized power frequency cycles in the cycle variation data are connected sequentially to form an analysis sequence. The number of decomposition layers is determined based on the phase-normalized sampling frequency and the rated power frequency, so that the upper limit of the frequency band of the final layer approximate component is no higher than half of the rated power frequency, and the upper limit of the frequency band of the previous layer approximate component is higher than half of the rated power frequency.

[0043] The analysis sequence is subjected to layer-by-layer low-pass and high-pass filtering and 2:1 decimation using fourth-order Dobessi discrete wavelets. The final layer approximate components are determined as low-frequency components, and the final layer detail components are determined as mid-frequency components.

[0044] The analysis sequence is moved along the power frequency cycle time sequence with one power frequency cycle as the step size. The low-frequency and mid-frequency components of the primary side neutral point current and open delta voltage in the same decomposition frequency band and the same normalized phase interval are compared. Only the components of the two electrical quantities that appear repeatedly in the continuous analysis sequence are retained to obtain the continuous low-frequency and mid-frequency characteristics after harmonic elimination.

[0045] The same phase normalization and fourth-order Dobessi discrete wavelet decomposition are applied to the stable operating waveform before the transient process to obtain the low-frequency and mid-frequency wavelet features of the stable operation.

[0046] As a preferred embodiment of the voltage transformer transient overcurrent and ferroresonance synergistic suppression method of the present invention, wherein: the generation of voltage transformer protection control results specifically includes:

[0047] Using the effective values ​​of the neutral point current and the open delta voltage of the stable operating power frequency cycle before the transient process occurs as their respective per-unit references, the minimum and maximum energy values ​​of the stable operating low-frequency and medium-frequency wavelet characteristics in the continuous analysis sequence are calculated respectively, so as to obtain the stable operating low-frequency energy range and medium-frequency energy range of the two electrical quantities.

[0048] By analyzing and comparing the energy values ​​corresponding to the continuous low-frequency and mid-frequency characteristics after harmonic elimination with the stable low-frequency and mid-frequency energy ranges of the two electrical quantities, the continuous cycle characteristic change state is obtained.

[0049] When the primary current recovers to the amplitude range of the same polarity half-cycle before the transient, and the low-frequency energy value and medium-frequency energy value of the primary neutral point current and the open delta voltage both enter their respective stable operating energy ranges within a continuous analysis sequence of no less than the number of continuous determination cycles, the secondary harmonic elimination branch is determined to be out of harmonic elimination state.

[0050] When any low-frequency energy value or medium-frequency energy value is still outside the corresponding stable operating energy range, or when two electrical quantities still appear repeatedly in the same decomposed frequency band and the same normalized phase interval, the secondary side harmonic elimination branch is determined to continue the harmonic elimination state, and the newly added power frequency frequency during the harmonic elimination period is continued to the collaborative suppression operation data and then phase normalization, decomposed frequency band extraction and energy range comparison are performed again.

[0051] The current secondary side harmonic elimination ends when exiting the harmonic elimination state, and the secondary side harmonic elimination branch continues to function when entering the harmonic elimination state. The primary side neutral point PTC current-limiting harmonic eliminater is kept grounded, generating the voltage transformer protection control result.

[0052] The beneficial effects of this invention are as follows: using the half-cycle formed by the actual zero-crossing point of the primary current as a unified processing unit, the inverse-time fusing time corresponding to the current amplitude of each half-cycle is converted into an occupancy ratio that can be accumulated over time, so that multiple continuously changing current levels form a unique result of whether the fusing effect has been achieved or not, avoiding inconsistent judgments when comparing a single peak value and the entire duration separately; and only starting the continuous oscillation check after the first impact section has been formed and ended, so that boundary branches without current surges and continuous decays will not enter the processing after the first impact ends, thus maintaining a clear sequential constraint on the transient overcurrent state, the end position of the first impact, and the continuous state of ferromagnetic resonance.

[0053] Furthermore, the secondary-side harmonic cancellation threshold is simultaneously constrained by the end position of the first impact, the overlapping cycle segment of the neutral point current and the open delta voltage, and the continuous state of ferroresonance. This allows for a seamless transition between the transient energy dissipation of the primary side and the elimination of the continuous resonance of the secondary side. During harmonic cancellation, different actual cycles are mapped to the same normalized phase position, eliminating the influence of zero-crossing position and cycle duration variations on point-by-point comparisons. The fourth-order Dobessi discrete wavelet directly uses the final layer approximation component and the final layer detail component to correspond to the low-frequency and mid-frequency components, eliminating reliance on component tracing between different extraction scales. The frequency band changes continuously occurring due to the primary side neutral point current and the open delta voltage, along with the stable operating energy range before the transient state, control the continuation or exit of harmonic cancellation. This establishes a continuous feedback relationship between the phase calibration result, the frequency band result, and the control result, improving the reproducibility of the secondary-side harmonic cancellation exit determination. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 This is a flowchart of a method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers.

[0056] Figure 2 This is a flowchart for determining transient overcurrent state and continuous ferromagnetic resonance state.

[0057] Figure 3 Flowchart for continuous oscillation access and secondary side harmonic elimination branch control.

[0058] Figure 4 A schematic diagram illustrating the changes in the amplitude of abnormal electrical quantities before and after coordinated suppression.

[0059] Figure 5 The wiring diagram of the primary side PTC current limiting harmonic suppressor and the secondary side harmonic suppressor branch in the 35kV verification wiring.

[0060] Figure 6 The diagram shows the voltage and current transient response of the opening and closing operations when no coordinated suppression measures are implemented.

[0061] Figure 7 The transient response diagram of voltage and current during opening and closing operations after the integration of coordinated suppression measures.

[0062] Figure 8 This is a graph showing the instantaneous power and cumulative absorbed energy changes of the suppression device during the opening and closing transients. Detailed Implementation

[0063] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0064] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0065] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0066] Reference Figures 1-8 As one embodiment of the present invention, this embodiment provides a method for synergistic suppression of transient overcurrent and ferroresonance in a voltage transformer, comprising the following steps:

[0067] See Figure 1 , Figure 1 The complete processing path is shown according to the sequential relationship of the processing results in this embodiment: First, the three-phase voltage of the bus, the primary current, the primary neutral point current, the open delta voltage, and the circuit breaker opening and closing status and action time are corresponding to the sampling time to form the running sequence data; then, the continuous half-cycle is divided by the zero-crossing point of the primary current, and the inverse time characteristic of the fuse is used to distinguish the first impact from the subsequent continuous oscillation; the transient current of the first impact is limited by the primary neutral point PTC current limiting harmonic suppressor and transient energy dissipation is performed, and the suppressed continuous electrical quantity continues to be used for the time correspondence of the continuous oscillation of the neutral point current and the distortion of the open delta voltage; after the continuous resonance access is met, the secondary harmonic suppressor branch is controlled, and the cooperative suppression running data is compared with adjacent power frequency cycles and the fourth-order Dobessi discrete wavelet frequency band is verified, and finally the voltage transformer protection control result is formed.

[0068] S1. Collect the electrical quantities of the voltage transformer during the circuit breaker operation, associate them with transient waveforms at the time of operation, and generate runtime sequence data.

[0069] S1.1. During the continuous operation of the voltage transformer, the three-phase voltage of the bus, the primary current of the voltage transformer, the neutral point current of the primary side of the voltage transformer, and the open delta voltage are collected synchronously, and the opening and closing status and operation time of the circuit breaker connected to the bus are recorded.

[0070] The bus three-phase voltage, voltage transformer primary current, voltage transformer primary neutral point current, and open delta voltage are recorded at the same timing reference to ensure that the electrical quantities obtained at the same sampling time are consistent in time. When the circuit breaker's opening and closing states change, the corresponding action time is recorded according to the same timing reference so that the circuit breaker action can be located at the specific sampling position in the continuous electrical quantities to obtain the continuous electrical quantities.

[0071] S1.2. The circuit breaker operation is identified by the circuit breaker's opening and closing status in the continuous electrical quantities. When the circuit breaker changes from the closing state to the opening state, the corresponding opening operation time is determined as the start time of the transient process; when the circuit breaker changes from the opening state to the closing state, the corresponding closing operation time is determined as the start time of the transient process.

[0072] The stable operating waveform is retained from the beginning of the transient process forward along the sampling time of the continuous electrical quantity, and the continuously changing waveform is retained from the beginning of the transient process in the original sampling order to obtain the waveforms before and after the transient process.

[0073] Among them, the stable operating waveform refers to the electrical quantity waveform continuously recorded during the period when the circuit breaker's opening and closing states have not changed, and the continuously changing waveform refers to the electrical quantity waveform continuously recorded from the moment the circuit breaker operates.

[0074] It should be noted that dividing the waveforms before and after the transient state based on the actual moment of action ensures that the transient changes generated by the circuit breaker action and the operating state before action are recorded in the same continuous process, avoiding the discontinuity of the transient process caused by using separate waveform segments.

[0075] S1.3. Arrange the transient waveforms before and after sampling in sequence, keep the three-phase bus voltage, primary current of voltage transformer, primary neutral current of voltage transformer and open delta voltage at the same sampling time at the same time position, and position the circuit breaker opening and closing status and operation time at the corresponding time position.

[0076] The runtime sequence data is arranged continuously according to the sampling time. At each sampling moment, the three-phase voltage of the bus, the primary current of the voltage transformer, the neutral point current of the primary side of the voltage transformer, and the open delta voltage are retained. The sampling position when the circuit breaker opens or closes is also retained at the corresponding action time to generate runtime sequence data.

[0077] S2. Divide the continuous half-cycle according to the zero-crossing point of the primary current in the runtime sequence data, and distinguish the first impact section and the continuous oscillation section by combining the inverse time characteristic of the fuse to obtain the transient overcurrent state. Then, determine the continuous state of ferroresonance based on the synchronous oscillation relationship of the electrical quantities in the continuous oscillation section.

[0078] S2.1. Call the runtime sequence data and check the adjacent sampled values ​​of the primary current of the voltage transformer in sequence according to the sampling time. When the sampled value of the primary current of the voltage transformer is zero, the corresponding sampling time is determined as the zero-crossing point of the primary current of the voltage transformer; when two adjacent sampled values ​​are positive and negative respectively, a linear interpolation is used between the two adjacent sampling times to determine the time when the primary current of the voltage transformer is zero, and the time when the primary current of the voltage transformer is zero is determined as the zero-crossing point of the primary current of the voltage transformer.

[0079] Arrange all the zero-crossing points of the primary current of the voltage transformers in chronological order to obtain the sequence of zero-crossing points of the primary current of the voltage transformers.

[0080] The first linear interpolation is only used to determine the zero-crossing time of the primary current of the voltage transformer between adjacent sampled values ​​with opposite signs. The data involved in the first linear interpolation are all derived from the primary current of the voltage transformer at adjacent sampling times in the runtime sequence data, without changing the amplitude and change order of the original primary current of the voltage transformer.

[0081] S2.2. According to the time sequence of the zero-crossing points of the primary current of the voltage transformer, the waveform between the zero-crossing points of the primary current of two adjacent voltage transformers is determined as a half-cycle, and all half-cycles before and after the circuit breaker operation are arranged in sequence.

[0082] According to the start and end times of each half-cycle, the primary current of the voltage transformer, the neutral point current of the primary voltage transformer, and the open delta voltage within the same time range are extracted from the runtime sequence data. The three electrical quantities are made to use the same half-cycle boundary to obtain continuous half-cycle electrical quantities.

[0083] It should be noted that dividing the continuous half-cycle by the zero-crossing point of the primary current of the voltage transformer ensures that the primary current, neutral point current, and open delta voltage of the voltage transformer before and after the circuit breaker operation are continuously arranged according to the actual electrical cycle. Compared with truncating the waveform according to a fixed data length, this avoids the circuit breaker operation being located within a fixed data segment, which would cause the initial impact and subsequent oscillations to be grouped into the same data segment.

[0084] S2.3. Based on the recorded circuit breaker operating time, locate the half-cycle in the continuous half-cycle electrical quantities where the circuit breaker operating time is located, and compare the primary current amplitude of the voltage transformer sequentially starting from the half-cycle where the circuit breaker operating time is located. The primary current amplitude of the voltage transformer in each half-cycle is taken as the maximum absolute value of the primary current in the corresponding half-cycle, and the comparison reference is taken as the primary current amplitude of the same polarity half-cycle in the stable operating waveform before the transient process occurs.

[0085] When the amplitude of the half-cycle current after the circuit breaker operates is higher than the reference and the amplitude of the subsequent half-cycle current decreases continuously in chronological order, the half-cycle in which the current amplitude begins to be higher than the reference is taken as the starting position of the first impact section, and the half-cycle in which the continuous decrease process ends is taken as the ending position of the first impact section, thus obtaining the first impact section.

[0086] It should be noted that continuous decline refers to a situation where, starting from a half-cycle higher than the benchmark, the current amplitude of at least two consecutive half-cycles is lower than the current amplitude of their respective preceding half-cycles. In other words, at least three consecutive half-cycles must form two adjacent amplitude declines, with no intermediate rises or flattening allowed. After this condition is met for the first time, comparisons continue half-cycles until the current amplitude of the next half-cycle rises or flattens. The half-cycle before the rise or flattening is determined as the half-cycle at the end of the continuous decline process. If sufficient subsequent half-cycle data is not obtained, monitoring continues until sufficient data is acquired before a judgment is made.

[0087] If the amplitude of the half-cycle current after the circuit breaker operates is not higher than the reference, or if it is higher than the reference but does not form a continuous decreasing process, the transient overcurrent state is determined as not having achieved the fusing effect, the first impact section and the first impact end position are not formed, and the monitoring of the subsequent continuous half-cycle electrical quantities is maintained, without entering the continuous oscillation section inspection starting from the first impact end position.

[0088] Once the initial impact zone has been formed, the electrical quantities of the continuous half-cycle are checked only from the end of the initial impact zone. If the primary current of the voltage transformer, the neutral point current of the primary side of the voltage transformer, and the open delta voltage continue to exhibit periodic changes in subsequent continuous half-cycles, the half-cycle in which the periodic change first occurs is taken as the starting point of the continuous oscillation zone; if all three electrical quantities continuously decay with the initial impact and no longer exhibit periodic changes in subsequent half-cycles, a continuous oscillation zone is not formed.

[0089] S2.4. For the first impact section within the first impact zone Record the current amplitude of each half-cycle. The start and end times of the half-cycle are used to determine the duration of the half-cycle by using the difference between the start and end times. ; Find the inverse time characteristic given in the manufacturing documents of the primary side fuse of the voltage transformer. Corresponding circuit breaker time .when When the current coordinates are between adjacent current coordinates with inverse time characteristics, linear interpolation is performed on the fusing time corresponding to the adjacent coordinates within the curvilinear coordinate system used in the manufacturing document to obtain a unique value. .

[0090] The proportion of each half-cycle duration relative to the corresponding melting time is accumulated sequentially along the half-cycle time of the first impact segment. The cumulative occupancy amount in reverse time limit is expressed as:

[0091] ;

[0092] in, Indicates accumulation up to the nth The cumulative occupancy of one and a half cycles in reverse time limit; This indicates the half-cycle sequence number arranged chronologically within the first impact zone; Indicates the sequence number of the half-cycle that participates in the accumulation; Indicates the first The amplitude of the primary current of a voltage transformer during a half-cycle, in amperes; Indicates the first The duration of one and a half cycles, in seconds; Indicating the inverse time-limited property with The corresponding circuit breaker time is in seconds.

[0093] When the value reaches 1 for the first time, the first impact section is defined as the transient overcurrent state that triggers the fuse; when the first impact section ends... If the value is still less than 1, the first impact section is determined to be a transient overcurrent state that has not achieved the fusing effect.

[0094] Each half-cycle participates in the accumulation only once, based on the proportion of its own duration to the corresponding current level's fusing time. Therefore, when the current amplitude changes continuously within the first impact section, it still forms a unique inverse-time cumulative occupancy and a unique result of whether the fusing effect is achieved or not.

[0095] S2.5. Only after the initial impact zone has been formed and ended, the waveform changes of the primary current of the voltage transformer, the neutral point current of the primary side of the voltage transformer, and the open delta voltage are compared sequentially in the continuous oscillation zone by forming a continuous power frequency cycle according to two adjacent half cycles.

[0096] When the initial impact of the primary current of the voltage transformer has decayed, and the three electrical quantities still exhibit periodic changes repeatedly within the same continuous power frequency range, the position of the cycle that maintains the synchronous periodic change is defined as the ferroresonant range, and the ferroresonant state is defined as the continuous state. When the three electrical quantities decay together with the initial impact and subsequent continuous power frequency cycles no longer exhibit periodic changes, the ferroresonant state is defined as the non-continuous state. The continuous oscillation section is used to limit the time range within which the periodic change repeats after the initial impact. The ferroresonant state must also meet the condition that the three electrical quantities maintain synchronous periodic changes within the same continuous power frequency range; it cannot be directly determined by the existence of the continuous oscillation section alone. If this synchronous periodic change condition is not met, the ferroresonant state is defined as the non-continuous state.

[0097] By correlating the transient overcurrent state with the holding time of the corresponding first impact section, and correlating the continuous ferromagnetic resonance state with the holding time of the corresponding continuous cycle position, the transient overcurrent state and the continuous ferromagnetic resonance state are obtained.

[0098] See Figure 2 , Figure 2 The process involves the continuous determination of transient overcurrent and ferroresonant states. During operation, the sequence data first determines the primary current zero-crossing sequence and divides it into continuous half-cycles. The circuit breaker's operating moment is used to locate the half-cycle positions before and after the operation. When a sudden increase in current higher than the pre-operation half-cycle reference occurs after the operation, followed by continuous decay, the first impact segment is formed. The amplitude and duration of each half-cycle current are then correlated with the fuse's inverse-time characteristic half-cycle to obtain the transient overcurrent state. After the first impact, instead of using a single spike as the basis for ferroresonant resonance, the primary current, primary neutral point current, and open delta voltage are continuously checked to ensure they maintain a synchronous periodic change within the continuous power frequency cycle. If the continuous periodic change is satisfied, the ferroresonant state is determined; otherwise, the ferroresonant state is determined to be non-continuous. If a first impact meeting the conditions is not formed, monitoring of subsequent continuous electrical quantities is maintained, and the secondary side harmonic cancellation threshold starting from the end position of the first impact is not triggered.

[0099] S3. For the first impact section corresponding to the transient overcurrent state, the transient current is limited and the transient energy is dissipated by the primary side neutral point PTC current limiter and harmonic suppressor, generating the primary side suppressed operation data.

[0100] S3.1. When it is determined that there is a transient overcurrent caused by the operation of the circuit breaker, the primary current of the voltage transformer, the neutral point current of the primary side of the voltage transformer and the open delta voltage within the same time range are located from the running sequence data according to the start and end times of the first impact section, and the continuous electrical quantities corresponding to the first impact section are determined.

[0101] The neutral point of the primary side of the voltage transformer is grounded through the PTC current limiting and harmonic elimination device. The transient current of the neutral point of the primary side of the voltage transformer corresponding to the first impact section flows through the PTC current limiting and harmonic elimination device, which limits the transient current generated by the circuit breaker operation and allows the transient energy to enter the current limiting and energy dissipation branch of the primary side neutral point.

[0102] S3.2. By utilizing the continuous electrical quantity corresponding to the first impact section to maintain the time position of the transient process, the PTC current limiting harmonic suppressor generates a temperature rise under the action of the transient current at the neutral point of the primary side of the voltage transformer, and uses the positive temperature coefficient characteristic to increase the equivalent resistance, thereby limiting the transient current flowing through the grounded branch of the primary side neutral point, and at the same time converting the transient energy into heat energy dissipation, so that the transient current at the neutral point of the primary side of the voltage transformer in the first impact section undergoes the primary side current limiting energy dissipation process.

[0103] During the primary side energy dissipation process, the primary side current, the primary side neutral point current, and the open delta voltage of the voltage transformer are continuously collected according to the same timing reference used in S1, and the sampling time is kept consistent with the determined first impact section position to obtain the continuous electrical quantities after primary side suppression.

[0104] It should be noted that the PTC current limiting harmonic suppressor is directly located in the neutral point grounding branch of the primary side of the voltage transformer. When the transient current in the first impact section flows through the PTC current limiting harmonic suppressor, the PTC current limiting harmonic suppressor increases its equivalent resistance as its temperature rises, thereby limiting the transient current at the neutral point and dissipating the transient energy. Compared with using only the open delta winding for secondary side harmonic suppression, it is possible to first process the primary side of the first transient impact generated by the circuit breaker operation, and then retain the continuous electrical quantity after the first impact has decayed.

[0105] See Figure 5 In a 35kV verification wiring setup, three 35kV voltage transformers are connected to the busbar. The inductance value of the equivalent branch L3 is taken as 8mH, corresponding to the equivalent electrical parameters of an 8km 35kV cable. When corresponding to the coordinated suppression wiring in this embodiment, the neutral point on the primary side of the voltage transformer is grounded via a PTC current-limiting harmonic suppressor, and the secondary side is connected to the voltage transformer fuse suppression device via an open delta connection. The measurement ratio of the three-phase voltages Ua, Ub, and Uc is 35000:100, the measurement ratio of the open delta voltage is 1:1, and the measurement ratio of the neutral point-to-ground voltage Ud is 1300:1, ensuring that the three-phase voltages, open delta voltage, and neutral point branch electrical quantities can be recorded according to the same transient process.

[0106] Under rated steady-state conditions, the amplitudes of the three-phase secondary voltages of the voltage transformer before and after connecting the coordinated suppression device are 79.21V and 79.47V, respectively. Both waveforms maintain a standard sine wave with a 120° phase difference between the three phases. The three-phase primary currents are both approximately 3.2mA and maintain a symmetrical sine wave. These steady-state waveforms correspond to the stable operating waveforms continuously collected before the circuit breaker operates. Actual transient determination still uses the continuous sampling data before the current transient process occurs as the stable operating benchmark, thus avoiding the substitution of the current operating state with a fixed amplitude.

[0107] S3.3. Divide the continuous electrical quantities after primary side suppression according to the sequence of zero-crossing points of the primary side current of the voltage transformer. Define the half-cycle by the zero-crossing points of the primary side current of two adjacent voltage transformers. Synchronously arrange the primary side current, primary side neutral point current and open delta voltage of the voltage transformer according to the start and end times of each half-cycle.

[0108] The continuous half-cycle of the primary side energy dissipation period is retained from the starting position of the first impact section, and the subsequent continuous changes of the primary side current, the primary side neutral point current, and the open delta voltage of the voltage transformer are retained from the ending position of the first impact section. This ensures that the attenuation process of the first impact and the continuous changes after the end of the first impact maintain the same half-cycle time relationship, generating the operating data after primary side suppression.

[0109] See Figure 6 and Figure 7 During the transient operation of the circuit breaker during opening and closing, without coordinated suppression measures, the peak voltage transient is 123.74V, and the peak primary overcurrent is 0.0147A. After implementing coordinated suppression measures, the three-phase voltage only undergoes transient changes at the moment of closing, with the peak value dropping to 92.72V. The zero-sequence voltage and zero-sequence current are simultaneously suppressed, and the primary current subsequently returns to a stable periodic change. After arranging the above waveforms into the operating sequence data according to the circuit breaker's operating time, the high-amplitude changes after the operation first form the initial impact section. The continuous cycles after the initial impact decay then enter the corresponding judgment of the neutral point current continuous oscillation and the open delta voltage distortion.

[0110] See Figure 8 During the same opening and closing transient, after the opening action occurs, the primary side suppression device continuously limits the neutral point transient current and dissipates oscillation energy; this current limiting energy dissipation change is related to... Figure 6 and Figure 7 The initial impact attenuation process in the data is kept in time correspondence and can be recorded synchronously with the half-cycle position in the operating data after the primary side suppression, so that the transient energy consumption process of the primary side and the subsequent continuous oscillation judgment remain continuous.

[0111] In the single-phase grounding disturbance condition of the same 35kV verification model, without the suppression device, the zero-sequence voltage is approximately 187V and the zero-sequence current is approximately 0.01A. After connecting the cooperative suppression device, the three-phase voltage only experiences a transient change of approximately 83.57V at the moment of the fault, the zero-sequence voltage drops to below 10V, and the zero-sequence current is approximately 0.8mA. Under the action of abnormal current, the PTC current-limiting harmonic suppressor increases its equivalent resistance with its own temperature rise, limiting the transient current of the primary side neutral point and dissipating transient energy. These electrical quantities continue to be retained at the same sampling time, so that the change in the neutral point current after energy dissipation on the primary side can directly correspond to the change in the open delta voltage in subsequent continuous cycles.

[0112] S4. The neutral point current continuous oscillation section in the primary side suppression operation data is extracted using a three-point linear structural element, and time correspondence is performed with the open delta voltage distortion. Combined with the ferromagnetic resonance continuous state control of the secondary side harmonic elimination branch, collaborative suppression operation data is generated.

[0113] S4.1. Call the running data after primary side suppression, determine the interception start point according to the end time of the first impact section, continuously extract the neutral point current of the primary side of the voltage transformer from the interception start point, and retain the sampling time of each current sampling value to obtain a continuous sequence of neutral point current.

[0114] Following the sampling sequence of the neutral point current, a three-point linear structure element is established by selecting the previous sampling position, the current sampling position, and the next sampling position each time. The current sampling position is used as the processing position of the three-point linear structure element, and the three-point linear structure element is moved point by point along the neutral point current continuous sequence.

[0115] For each processing location, the maximum current value among three consecutive sampling locations is selected as the expansion result of the current processing location, and the minimum current value among three consecutive sampling locations is selected as the corrosion result of the current processing location. The expansion results and corrosion results of each processing location are arranged according to the sampling order to obtain the expansion sequence and corrosion sequence.

[0116] S4.2. The expansion and corrosion sequences are processed using expansion and corrosion operations in mathematical morphology. The arithmetic mean of the expansion and corrosion results is obtained at the same sampling position. The arithmetic mean is then arranged according to the original sampling order to obtain the morphological filter current sequence.

[0117] The three-point linear structure element covers three consecutive sampling positions: the previous sampling position, the current sampling position, and the next sampling position. This step defines current changes that only alter the maximum or minimum current value within the coverage area of ​​the current three-point linear structure element and do not repeat at the corresponding position in subsequent continuous power frequency cycles as local current mutations. Spikes and high-frequency glitches generated by circuit breaker operation, as well as local current mutations initially formed by changes in the resistance of the PTC current limiter and harmonic suppressor, are processed within the range of the three consecutive sampling positions and participate in expansion and corrosion calculations. Current changes that cross consecutive sampling positions and repeat in subsequent continuous power frequency cycles are retained as continuous current oscillations.

[0118] The upper boundary of the local current is defined by the expansion result, and the lower boundary of the local current is defined by the corrosion result. Then, the arithmetic mean of the same sampling position is used to form a morphological filter current sequence, thereby distinguishing between local abrupt changes and current oscillations that span consecutive sampling positions.

[0119] It should be noted that the three-point linear structural element directly processes the primary side neutral point current of the voltage transformer after the primary side transient energy has been limited and dissipated by the PTC current limiter and harmonic suppressor. Compared with directly judging the ferroresonance based on the transient current without primary side suppression, it can reduce the impact of the residual spikes and high-frequency glitches from the first impact on the subsequent determination of the continuous oscillation section.

[0120] S4.3. Compare the current values ​​at adjacent sampling positions in the morphological filter current sequence in turn. When the current value at the next sampling position is greater than the current value at the previous sampling position, record it as an upward change; when the current value at the next sampling position is less than the current value at the previous sampling position, record it as a downward change.

[0121] The transition positions between rising and falling changes are checked along the sampling time. The sampling positions where rising changes turn into falling changes and falling changes turn into rising changes are determined as the current change direction transition positions. According to the half-cycle time relationship maintained by S3, the current change direction transition positions are located to the corresponding continuous power frequency cycles.

[0122] By comparing the order of the current change direction transitions within adjacent continuous power frequency cycles, when the continuous power frequency cycles repeatedly exhibit alternating upward and downward changes, the first power frequency cycle in which the periodic change occurs is determined as the starting position of the periodic change segment, and the periodic change segment continues along subsequent continuous power frequency cycles; when subsequent power frequency cycles no longer exhibit alternating changes, the previous power frequency cycle is determined as the ending position of the periodic change segment, thus obtaining the periodic change segment.

[0123] The periodic variation segment spanning continuous power frequency cycles is defined as the neutral point current continuous oscillation segment. The start and end times are retained, and the number of power frequency cycles continuously spanned from the first power frequency cycle with periodic variation to the confirmation that the periodic variation will reappear in subsequent power frequency cycles is recorded as the continuous determination cycle number. The continuous determination cycle number limits the length of time that stable recovery must be maintained in the subsequent harmonic elimination exit judgment.

[0124] S4.4. Based on the start and end times of the continuous oscillation section of the neutral point current, extract the open delta voltage within the same time range from the operating data after the primary side suppression, and compare the open delta voltage with the open delta voltage in the stable operating waveform before the transient process occurs in sequence according to the power frequency cycle.

[0125] When the open delta voltage repeatedly exhibits waveform changes relative to the stable operating waveform within a continuous power frequency cycle, the first power frequency cycle in which the waveform changes continuously occurs is taken as the starting position of the open delta voltage oscillation segment, and the power frequency cycle before the end of the continuous waveform change is taken as the ending position of the open delta voltage oscillation segment, thus obtaining the open delta voltage oscillation segment.

[0126] By comparing the starting and ending positions of the neutral point current continuous oscillation section and the open delta voltage oscillation section, the continuous power frequency cycle that exists simultaneously with the neutral point current continuous oscillation and the open delta voltage periodic distortion is retained to obtain the overlapping cycle section.

[0127] S4.5. Compare the position of the power frequency cycle in the overlapping cycle section with the position of the continuous cycle maintained by the ferromagnetic resonance state cycle by cycle.

[0128] When the overlapping cycle segment is within the continuous cycle range of the continuous state of ferromagnetic resonance, the starting time of the overlapping cycle segment is determined as the starting time of secondary harmonic elimination, and the continuous time range of the overlapping cycle segment is determined as the secondary harmonic elimination time range; when the continuous oscillation segment of the neutral point current and the open delta voltage oscillation segment do not form an overlapping cycle segment, or when the continuous state of ferromagnetic resonance is determined to be non-continuous, the microcomputer harmonic elimination device remains in monitoring mode and does not activate the secondary harmonic elimination branch.

[0129] After the secondary side harmonic elimination time range is determined, the microcomputer harmonic elimination device controls the secondary side harmonic elimination branch to act on the open delta winding. The secondary side harmonic elimination branch consumes the fundamental frequency and low frequency ferroresonant energy that still exist after the primary side transient impact is suppressed.

[0130] It should be noted that the secondary-side harmonic elimination branch is not directly started based solely on the change in the open delta voltage. Instead, it simultaneously utilizes the continuous oscillation section of the neutral point current after the primary-side suppression, the oscillation section of the open delta voltage, and the continuous state of the ferroresonance to limit the harmonic elimination time range on the secondary side. This allows the primary-side neutral point PTC current-limiting harmonic eliminater to limit current and dissipate energy for the first transient impact, while the secondary-side harmonic elimination branch eliminates the ferroresonance that continues to exist after the first transient impact has decayed.

[0131] See Figure 3 , Figure 3 This corresponds to the continuous oscillation access after primary-side suppression and the secondary-side harmonic elimination control process. After primary-side suppression, the operating data is extracted from the end position of the first impact, capturing a continuous sequence of neutral point current. Three-point linear structure elements move point-by-point along the continuous sampling positions to form expansion and corrosion sequences. Morphological filtering retains the periodic changes that repeat across continuous power frequency cycles, resulting in a continuous oscillation segment of the neutral point current. Subsequently, the open delta voltage is extracted within the same time range to form an open delta voltage oscillation segment. The start and end positions of the two oscillation segments are compared to obtain the overlapping cycle segment. The overlapping cycle segment also needs to be matched cycle-by-cycle with the already determined continuous ferromagnetic resonance state. Only when matched is the secondary-side harmonic elimination time range determined, and the microcomputer harmonic elimination device is controlled to act on the open delta winding. If no overlapping cycle segment is formed or the ferromagnetic resonance is not continuous, a monitoring state is maintained. Figure 3 The admission relationship shown uses the primary side neutral point current, open delta voltage and the preceding ferromagnetic resonance continuous state together for the secondary side harmonic elimination start-up, so that the secondary side harmonic elimination branch does not directly operate due to the local abnormality of a single electrical quantity.

[0132] Under the combined wiring of primary-side energy dissipation and secondary-side continuous harmonic suppression, the same arc grounding transient was recorded three times consecutively. When the primary-side neutral point was directly grounded and the open delta connection was not used to suppress the current, the peak values ​​of phase A, phase B, and phase C currents and the peak value of the neutral point to ground current recorded in the three times were 0.808A, 1.070A, 1.539A, 2.221A; 0.725A, 0.912A, 1.498A, 2.159A; and 0.836A, 0.981A, 1.587A, 2.255A, respectively. The corresponding peak values ​​of the three phase A, phase B, and phase C voltages and the open delta voltage are 167.700V, 0V, 157.497V, 157.584V; 163.880V, 0V, 149.588V, 156.964V; and 166.490V, 0V, 146.615V, 156.126V, respectively.

[0133] When the primary side neutral point is grounded via a PTC current-limiting harmonic suppressor and connected to the secondary side suppression device via an open delta connection, the peak values ​​of the A-phase, B-phase, and C-phase currents and the peak value of the neutral point to ground current recorded three times are 0.491A, 0.704A, 0.814A, 0.740A; 0.387A, 0.794A, 0.787A, 0.829A; 0.525A, 0.718A, 0.842A, 0.788A, respectively. The corresponding peak values ​​of the A-phase, B-phase, and C-phase voltages and the open delta voltage recorded three times are 157.020V, 0V, 150.271V, 154.700V; 155.120V, 0V, 150.364V, 157.895V; 159.190V, 0V, 149.929V, 147.162V, respectively. The maximum values ​​of phase A, phase B, and phase C currents in the three records decreased from 0.836A, 1.070A, and 1.587A to 0.525A, 0.794A, and 0.842A, respectively, while the maximum value of neutral point to ground current decreased from 2.255A to 0.829A.

[0134] Under the combined suppression wiring, the distortion of the three-phase voltage and the open delta voltage is significantly reduced within approximately 3-4 power frequency cycles after the arc grounding disappears, and the continuous oscillation time of the open delta voltage is shortened accordingly. Therefore, whether the continuous oscillation section of the neutral point current and the oscillation section of the open delta voltage after primary-side suppression form overlapping cycle sections is used as the criterion for secondary-side harmonic elimination. The recovery state within continuous cycles controls the exit of secondary-side harmonic elimination, so that the 3-4 cycle recovery process observable in the true waveform corresponds to the actual recording process of continuously determining the number of cycles.

[0135] S4.6. During the operation of the secondary side harmonic elimination branch, the primary side current, the primary side neutral point current, and the open delta voltage of the voltage transformer are synchronously collected according to the same timing reference adopted in S1, and the electrical quantities at each sampling time are arranged in the continuous cycle order maintained in S3.

[0136] From the moment the secondary side harmonic suppression begins, the primary side current, the primary side neutral point current, and the open delta voltage of the voltage transformer are continuously retained, so that the three electrical quantities during the operation of the secondary side harmonic suppression branch maintain the same sampling time and continuous cycle position, thereby generating coordinated suppression operation data.

[0137] See Figure 4 , Figure 4 The variation of abnormal electrical quantity amplitude over time illustrates the aforementioned timing boundaries and the relationship after coordinated suppression. After the circuit breaker operates, the abnormal electrical quantity rises rapidly, corresponding to the first impact section. After the first impact ends, the non-coordinated suppression curve still exhibits oscillations that repeat across consecutive cycles, while the amplitude of the coordinated suppression curve has significantly decreased after the primary side transient energy dissipation. After the neutral point current continuous oscillation section, the open delta voltage oscillation section, and the continuous ferroresonant state satisfy the secondary side harmonic elimination access condition, secondary side harmonic elimination begins, the coordinated suppression curve continues to decay and enters the post-harmonic elimination decay section, while the non-coordinated suppression curve still retains a relatively long oscillation tail. Figure 4 The solid and dashed lines in the diagram are used to represent the relative changes in abnormal electrical quantities after and without coordinated suppression, and are not used as fixed amplitude judgment values. The actual control still determines the continuation or withdrawal of secondary side harmonic suppression according to the determined half-cycle boundary, overlapping cycle section, continuous judgment cycle number and stable operating energy range.

[0138] S5. Compare adjacent power frequency cycles of the coordinated suppression operation data, and use fourth-order Dobessi discrete wavelet to extract continuous low-frequency and medium-frequency features, determine the harmonic elimination state of the secondary side harmonic elimination branch, and generate voltage transformer protection control results.

[0139] S5.1. Call the cooperative suppression operation data, and define a power frequency cycle containing two half cycles (positive and negative) for every three adjacent zero-crossing points according to the sequence of primary current zero-crossing points, and arrange the power frequency cycles in chronological order; adjacent power frequency cycles share the boundary zero-crossing point, without changing the time order of the continuous waveform.

[0140] Let the original sampling frequency be... The rated power frequency is The number of original sampling points for each power frequency cycle is rounded to the nearest even number according to the following formula to obtain the uniform number of sampling points for each phase-normalized power frequency cycle. :

[0141] ;

[0142] in, It is a positive even number and not less than 2. It is set in the first half and second half of each power frequency cycle respectively. Normalized sampling positions with equal phase intervals are used so that the starting zero-crossing point, intermediate zero-crossing point, and ending zero-crossing point of each power frequency cycle correspond to the same electrical cycle position.

[0143] Let the first The three consecutive zero-crossing times of a power frequency cycle are as follows: , and , No. The actual sampling time corresponding to each normalized sampling position is:

[0144] ;

[0145] in, Indicates the power frequency cycle number; Indicates the normalized sampling position number; Indicates the first The first power frequency frequency The actual sampling time corresponding to each normalized sampling position, in seconds; , and These represent three consecutive zero-crossing moments, in seconds; This indicates the number of uniform sampling points.

[0146] according to Linear interpolation is performed on the primary side neutral point current and open delta voltage between the original adjacent sampling times to obtain phase-normalized continuous power frequency cycle data.

[0147] S5.2. Starting from the second phase-normalized power frequency cycle, compare the two electrical quantities at the same normalized sampling position of the current power frequency cycle with those of the previous power frequency cycle point by point. The changes in current frequency and voltage frequency are as follows:

[0148] ;

[0149] in, and They represent the first The phase-normalized chemical frequency frequency of the first cycle The primary neutral point current and open delta voltage at each normalized sampling location; and These represent the corresponding electrical quantities at the same position in the previous phase-normalized chemical frequency cycle; and These represent the changes in current frequency and voltage frequency, respectively.

[0150] The current and voltage frequency changes are arranged according to the normalized sampling positions. When there are consecutive non-zero current or voltage frequency changes in adjacent power frequency cycles, the neutral point current and open delta voltage of the corresponding power frequency cycle are retained to obtain the frequency change data.

[0151] After each power frequency cycle is phase-normalized between actual zero-crossing moments, the same normalized sampling position corresponds to the same electrical phase; even if the actual cycle duration or intermediate zero-crossing position changes, the point-to-point difference between adjacent power frequency cycles will not be mixed with the differences caused by sampling phase misalignment.

[0152] S5.3. Obtain the effective value of the neutral point current on the primary side from the stable operating power frequency before the transient process occurs. and the effective value of open delta voltage Divide the neutral point current on the first side of the frequency variation data by Open delta voltage divided by This forms the per-unit sequences of the two electrical quantities.

[0153] Phase-normalized equivalent sampling frequency Represented as:

[0154] ;

[0155] according to and Determine the number of decomposition levels for a fourth-order Dobessie discrete wavelet. ,make The unique positive integer that satisfies the following expression:

[0156] ;

[0157] ;

[0158] in, This represents the number of positive integer candidate cycles participating in the minimum value comparison; Indicates satisfaction The smallest positive integer, and used as the number of continuous phase-normalized chemical frequency cycles connected to each sliding analysis window; This indicates the length of the fourth-order Dobessie discrete wavelet decomposition filter; This represents the set of positive integers, which consists of all positive integers that increase sequentially from 1 to 3. The candidate frequency in the condition can only take values ​​within this set.

[0159] use Limiting the number of samples ensures that the first After layer decomposition, at least 8 coefficient positions are still retained to meet the effective sample quantity required for low-pass and high-pass convolution and subsequent frequency band energy calculation.

[0160] Connected along the power frequency cycle in time sequence A continuous phase-normalized power frequency wave forms the first sliding analysis window. Subsequently, each time the window moves backward by one power frequency wave, the earliest power frequency wave is removed and the latest power frequency wave is connected, forming a continuous sliding analysis window, so that adjacent sliding analysis windows maintain a continuous cycle time relationship.

[0161] For each of the two per-unit sequences within a sliding analysis window, a fourth-order Dobesi discrete wavelet is used for stepwise decomposition. Each level uses a fourth-order Dobesi discrete wavelet decomposition low-pass filter and a decomposition high-pass filter to complete convolution and 2:1 decimation. When the beginning and end cannot completely cover the filter length, symmetrical extension is performed according to the mirror image order of the end sample values.

[0162] The first layer uses the per-unit sequence within the sliding analysis window as the sequence to be decomposed, obtaining the first-layer approximate components and the first-layer detail components; the second layer and subsequent layers only use the approximate components of the previous layer as the sequence to be decomposed, until the third layer... The first layer yields the neutral point current and the open delta voltage of the first side, respectively. Layer approximate composition Passing the exam Layer detail components .

[0163] No. Layer approximate composition and the Layer detail components The nominal frequency bands are represented as follows:

[0164] ;

[0165] in, Unique representation of nominal frequency band mapping; Indicates the first Layer approximate composition The nominal frequency band, Indicates the first Layer detail components The nominal frequency band.

[0166] Will Determined to be a low-frequency component, The mid-frequency component is identified as the low-frequency component; the mid-frequency component and the low-frequency component are determined by the same order. Low-pass and high-pass decompositions directly yield the results, without establishing a retention relationship between approximate components at different extraction scales.

[0167] The first of each sliding analysis window Layer approximate composition and the first The layer details are mapped back to the corresponding power frequency and normalized phase interval according to the position of the decomposition coefficients. The component changes of the primary neutral point current and the open delta voltage are compared within the same sliding analysis window, the same decomposition frequency band, and the same normalized phase interval.

[0168] Only when the low-frequency or mid-frequency components of two electrical quantities coexist within the same normalized phase interval and maintain the same frequency band repetition relationship in subsequent continuous sliding analysis windows, the corresponding components and power frequency cycle positions are retained to obtain the continuous low-frequency and mid-frequency characteristics after harmonic elimination; components that appear alone in one electrical quantity or do not cross the continuous sliding analysis window are not used as the basis for the continuous frequency band for further harmonic elimination.

[0169] S5.4. Select the stable operating waveform before the transient process occurs from the waveforms before and after the transient process in the runtime sequence data, extract the neutral point current and open delta voltage on the primary side in the stable operating waveform, and form a stable operating phase normalized power frequency cycle according to the same power frequency cycle division method, unified number of sampling points and half-cycle phase interval as the cooperative suppression operating data.

[0170] Using the same per-unit benchmark and sliding analysis window length Number of decomposition layers The stable operating phase-normalized wavelet cycle is processed by symmetrical extension method, low-pass filtering, high-pass filtering and 2:1 decimation process to obtain stable operating low-frequency and mid-frequency wavelet characteristics.

[0171] The normalized band energy values ​​for the low-frequency and mid-frequency components within each sliding analysis window are calculated separately and expressed as follows:

[0172] ;

[0173] in, For electrical quantity identification, This represents the single-phase neutral point current. This represents a unique open delta voltage; For frequency band identification, Indicates a unique low frequency. Indicates a unique intermediate frequency; Indicates the sliding analysis window number; Indicates frequency band The number of decomposition coefficients within; Indicates the index of the decomposition coefficients; Indicates electrical quantity In the Frequency band of each sliding analysis window Inner Per-unit decomposition coefficient; This represents the mean square energy value for the corresponding frequency band, expressed in squared units (per unit).

[0174] use Normalization can eliminate the influence of inconsistent numbers of coefficients in different decomposition frequency bands on the comparison of energy ranges.

[0175] The minimum, maximum, minimum, and maximum low-frequency energy values ​​of the two electrical quantities within the stable operation sliding analysis window are obtained respectively, forming the stable operation low-frequency energy range and medium-frequency energy range of the primary side neutral point current and open delta voltage. The four corresponding energy values ​​after harmonic elimination are compared with their respective ranges through the sliding analysis window to form the continuous cycle characteristic change state.

[0176] S5.5. Obtain the primary current corresponding to the current sliding analysis window from the collaborative suppression operation data. When the amplitude of the primary current of each half-cycle enters the amplitude range of the same polarity half-cycle in the pre-transient stable operation waveform, and the low-frequency energy value and medium-frequency energy value of the two electrical quantities both enter their respective stable operation energy range within a continuous sliding analysis window of no less than the number of continuous judgment cycles, the secondary side harmonic elimination branch is determined to exit the harmonic elimination state.

[0177] If any low-frequency energy value or medium-frequency energy value is still outside the corresponding stable operating energy range, or if the two electrical quantities still appear repeatedly in the same decomposition frequency band and the same normalized phase interval, the secondary side harmonic elimination branch is determined to continue the harmonic elimination state. During the continued harmonic elimination period, the newly added power frequency cycle is connected to the collaborative suppression operation data, and a new sliding analysis window is formed. The phase normalization, cycle change comparison, fourth-order Dobessi discrete wavelet decomposition, and stable operating energy range comparison are repeated.

[0178] The microprocessor-controlled harmonic elimination device is controlled according to the harmonic elimination state of the secondary side harmonic elimination branch. Exiting the harmonic elimination state corresponds to ending the current secondary side harmonic elimination; continuing the harmonic elimination state corresponds to maintaining the secondary side harmonic elimination branch acting on the open delta winding and processing the newly added power frequency frequency according to the formed feedback relationship until the condition of exiting the harmonic elimination state is met.

[0179] During the period when the secondary side harmonic elimination branch is in the state of exiting harmonic elimination or continuing harmonic elimination, the primary side neutral point PTC current-limiting harmonic elimination device remains grounded. This results in the voltage transformer protection control results of the first impulse inverse time limit cumulative judgment, primary side transient energy consumption, secondary side continuous resonance access, phase normalization frequency band verification, and harmonic elimination exit feedback continuous connection.

[0180] In summary, this invention uses the actual zero-crossing half-cycle as a unified time unit, transforming the current amplitude, duration, and inverse-time fuse time of each half-cycle into a unique result continuously accumulated along the first impact process. Furthermore, it uses the formation and termination of the first impact as a prerequisite for continuous oscillation checking, thus clearly defining the multi-current level processing method and boundary branches for transient overcurrent states. The end position of the first impact, formed by the inverse-time accumulated occupancy, continues to be used to limit the secondary-side harmonic elimination access, preventing the results of previous judgments from becoming ineffective in subsequent control.

[0181] During the secondary harmonic cancellation period, this invention utilizes the actual zero-crossing moment to perform phase normalization on each half-cycle, ensuring that the sequential sampling positions of adjacent power frequency cycles correspond to the same electrical phase. Subsequently, the low-frequency and mid-frequency components are directly obtained from the first low-pass and high-pass decomposition of the Lth layer of the fourth-order Dobesian discrete wavelet, and the common continuity relationship of the two electrical quantities within the same frequency band and the same normalized phase interval eliminates local disturbances of a single signal. The stable operating energy range transforms the above-mentioned common continuity characteristic into conditions for continuing or exiting harmonic cancellation, adding a process of returning the power frequency cycle to phase normalization and frequency band comparison, so that sampling calibration, frequency band extraction, and control feedback are mutually supportive, obtaining a synergistic judgment effect that cannot be obtained by simply adding the independent actions of each processing method.

[0182] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for synergistic suppression of transient overcurrent and ferroresonance in a voltage transformer, characterized in that: include, Collect the electrical quantities of the voltage transformer during the circuit breaker operation, associate them with transient waveforms at the time of operation, and generate runtime sequence data; The continuous half-cycle is divided according to the zero-crossing point of the primary current in the runtime sequence data. The first impact section and the continuous oscillation section are distinguished by combining the inverse time characteristic of the fuse to obtain the transient overcurrent state. The continuous ferromagnetic resonance state is determined according to the synchronous oscillation relationship of the electrical quantities in the continuous oscillation section. For the first impact section corresponding to the transient overcurrent state, the transient current is limited and the transient energy is dissipated by the primary side neutral point PTC current limiter and harmonic suppressor, generating the primary side suppressed operation data; The neutral point current continuous oscillation section in the primary side suppression operation data is extracted using a three-point linear structural element and time-corresponded with the open delta voltage distortion. Combined with the ferromagnetic resonance continuous state control of the secondary side harmonic elimination branch, collaborative suppression operation data is generated. By comparing adjacent power frequency cycles in the coordinated suppression operation data and using fourth-order Dobessi discrete wavelets to extract continuous low-frequency and medium-frequency features, the harmonic elimination state of the secondary side harmonic elimination branch is determined, and the voltage transformer protection control results are generated.

2. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 1, characterized in that: The generation of runtime sequence data specifically includes: The three-phase voltage, primary current, primary neutral current and open delta voltage of the bus are collected synchronously, and the opening and closing status and action time of the circuit breaker are recorded to obtain continuous electrical quantities. Runtime sequence data is generated by preserving the stable operating waveforms before and after the transient state of continuous electrical quantities at the moment of circuit breaker operation, and maintaining the time relationship between each electrical quantity and the circuit breaker operation according to the sampling time.

3. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 2, characterized in that: The division of continuous half-cycles specifically includes: The current polarity reversal position is determined by the sampling sequence of the primary current in the runtime sequence data, and the zero-crossing point sequence of the primary current is obtained; The half-cycle is defined by the adjacent zero-crossing points according to the time sequence of the primary current zero-crossing point sequence, and the primary current, primary neutral point current and open delta voltage of the same period are intercepted according to the start and end times of each half-cycle to obtain the continuous half-cycle electrical quantities.

4. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 3, characterized in that: The method of distinguishing between the initial impact segment and the continuous oscillation segment by combining the inverse time-delay characteristic of the fuse specifically includes: The continuous half-cycle electrical quantities are located according to the circuit breaker's operating time. The maximum absolute value of the primary current in each half-cycle is taken as the half-cycle current amplitude, and compared with the primary current amplitude of the same polarity half-cycle before the transient process occurs. When the amplitude of the half-cycle current after the circuit breaker trips is higher than the amplitude of the primary side current of the same polarity half-cycle and the amplitude of the subsequent half-cycle current decreases continuously, the first impact section is determined. For the first impact section, the corresponding fusing time is obtained from the inverse time characteristic of the fuse based on the half-cycle current amplitude. The ratio of the duration of each half-cycle to the corresponding fusing time is accumulated in the order of the half-cycle time to obtain the cumulative inverse time occupancy. When the cumulative inverse time limit occupancy reaches one, the first impact section is determined as a transient overcurrent state that achieves the fuse breaking effect; when the cumulative inverse time limit occupancy is less than one, the first impact section is determined as a transient overcurrent state that does not achieve the fuse breaking effect. Only after the first impact zone has formed and ended, check the primary side current, primary side neutral point current, and open delta voltage. If the three maintain synchronous oscillation in the subsequent continuous power frequency cycle, it is determined to be a continuous state of ferroresonance; otherwise, it is determined to be a non-continuous state of ferroresonance.

5. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 4, characterized in that: The generated operational data after primary side suppression specifically includes: For the first impact section corresponding to the transient overcurrent state, the transient current of the primary neutral point is made to flow through the PTC current limiting harmonic suppressor. The positive temperature coefficient characteristic of the PTC current limiting harmonic suppressor makes the equivalent resistance increase with its own temperature rise, thereby limiting the transient current of the primary neutral point and dissipating the transient energy. The primary current, the primary neutral point current and the open delta voltage are collected simultaneously to obtain the continuous electrical quantity after the primary side is suppressed. The continuous electrical quantities after primary side suppression are arranged according to the continuous half-cycle, and the initial impact attenuation and subsequent changes are retained to generate the operating data after primary side suppression.

6. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 5, characterized in that: The extraction of the running data after first-order side suppression using a three-point linear structuring element specifically includes: The neutral point current of the primary side is obtained by extracting the operating data after the primary side suppression from the end position of the first impact section; Three consecutive sampling positions of the neutral point current continuous sequence are selected to establish a three-point linear structure element, and the element is moved point by point along the neutral point current continuous sequence to obtain the maximum and minimum current values ​​of each sampling interval, thus obtaining the expansion sequence and corrosion sequence. By combining the expansion sequence and corrosion sequence at the same sampling location, the current spikes, high-frequency glitches, current abrupt changes and continuous current oscillations in the initial stage of the PTC current limiter and harmonic suppressor are separated to obtain the morphological filter current sequence. By comparing the direction of change of adjacent samples of the morphological filter current sequence and the repetition position within the continuous power frequency cycle, the periodic change segment is obtained. The periodic change segment that spans the continuous power frequency cycle and recurs is determined as the neutral point current continuous oscillation segment. The number of power frequency cycles that continuously cross to form the periodic change repetition relationship is recorded as the continuous determination cycle number.

7. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 6, characterized in that: The generated collaborative suppression operation data specifically includes: According to the start and end times of the continuous oscillation of the neutral point current, the continuous cycle of the open delta voltage is extracted to determine the oscillation section of the open delta voltage, and the overlapping cycle section of the continuous oscillation section of the neutral point current and the oscillation section of the open delta voltage is obtained. The first impact end position, the overlapping cycle section, and the continuous cycle position of the ferromagnetic resonance sustained state are matched in the transient overcurrent state. Only when the overlapping cycle section is located after the first impact end position and within the continuous cycle range of the ferromagnetic resonance sustained state, the overlapping cycle section is determined as the secondary side harmonic elimination access interval; otherwise, the secondary side harmonic elimination branch is kept in the monitoring state. According to the secondary side harmonic elimination access interval control, the secondary side harmonic elimination branch acts on the open delta winding, and the primary side current, primary side neutral point current and open delta voltage are collected simultaneously and arranged in continuous cycles to generate coordinated suppression operation data.

8. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 7, characterized in that: The comparison of adjacent power frequency cycles in the collaborative suppression operation data specifically includes: According to the sequence of zero-crossing points of the primary current, a power frequency cycle is defined by three adjacent zero-crossing points. The number of uniform sampling points is determined according to the ratio of the sampling frequency to the rated power frequency. Normalized sampling positions are set in the two half-cycles of each power frequency cycle according to the same phase interval. Based on the actual start and end times of each half-cycle, the primary neutral point current and open delta voltage in the collaborative suppression operation data are linearly interpolated to the normalized sampling position to obtain phase-normalized continuous power frequency cycle data. By comparing the current phase-normalized power frequency cycle with the previous phase-normalized power frequency cycle at the same normalized sampling position, the neutral point current and open delta voltage on the primary side are obtained. Data that continues to change for adjacent power frequency cycles are retained to obtain cycle change data.

9. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 8, characterized in that: The extraction of sustained low-frequency and mid-frequency features using fourth-order Dobessi discrete wavelets specifically includes: Multiple consecutive phase-normalized power frequency cycles in the cycle variation data are connected sequentially to form an analysis sequence. The number of decomposition layers is determined based on the phase-normalized sampling frequency and the rated power frequency, so that the upper limit of the frequency band of the final layer approximate component is no higher than half of the rated power frequency, and the upper limit of the frequency band of the previous layer approximate component is higher than half of the rated power frequency. The analysis sequence is subjected to layer-by-layer low-pass and high-pass filtering and 2:1 decimation using fourth-order Dobessi discrete wavelets. The final layer approximate components are determined as low-frequency components, and the final layer detail components are determined as mid-frequency components. The analysis sequence is moved along the power frequency cycle time sequence with one power frequency cycle as the step size. The low-frequency and mid-frequency components of the primary side neutral point current and open delta voltage in the same decomposition frequency band and the same normalized phase interval are compared. Only the components of the two electrical quantities that appear repeatedly in the continuous analysis sequence are retained to obtain the continuous low-frequency and mid-frequency characteristics after harmonic elimination. The same phase normalization and fourth-order Dobessi discrete wavelet decomposition are applied to the stable operating waveform before the transient process to obtain the low-frequency and mid-frequency wavelet features of the stable operation.

10. The method for synergistic suppression of transient overcurrent and ferroresonance in voltage transformers as described in claim 9, characterized in that: The generated voltage transformer protection control results specifically include: Using the effective values ​​of the neutral point current and the open delta voltage of the stable operating power frequency cycle before the transient process occurs as their respective per-unit references, the minimum and maximum energy values ​​of the stable operating low-frequency and medium-frequency wavelet characteristics in the continuous analysis sequence are calculated respectively, so as to obtain the stable operating low-frequency energy range and medium-frequency energy range of the two electrical quantities. By analyzing and comparing the energy values ​​corresponding to the continuous low-frequency and mid-frequency characteristics after harmonic elimination with the stable low-frequency and mid-frequency energy ranges of the two electrical quantities, the continuous cycle characteristic change state is obtained. When the primary current recovers to the amplitude range of the same polarity half-cycle before the transient, and the low-frequency energy value and medium-frequency energy value of the primary neutral point current and the open delta voltage both enter their respective stable operating energy ranges within a continuous analysis sequence of no less than the number of continuous determination cycles, the secondary harmonic elimination branch is determined to be out of harmonic elimination state. When any low-frequency energy value or medium-frequency energy value is still outside the corresponding stable operating energy range, or when two electrical quantities still appear repeatedly in the same decomposed frequency band and the same normalized phase interval, the secondary side harmonic elimination branch is determined to continue the harmonic elimination state, and the newly added power frequency frequency during the harmonic elimination period is continued to the collaborative suppression operation data and then phase normalization, decomposed frequency band extraction and energy range comparison are performed again. The current secondary side harmonic elimination ends when exiting the harmonic elimination state, and the secondary side harmonic elimination branch continues to function when entering the harmonic elimination state. The primary side neutral point PTC current-limiting harmonic eliminater is kept grounded, generating the voltage transformer protection control result.

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