A ferromagnetic resonance elimination device and method for a medium and low voltage distribution network

Abstract

The present application relates to the field of low-voltage power distribution, in particular to a low-voltage ferromagnetic resonance elimination device and method, which is composed of a power module, a signal acquisition module, a main control module, a resonance elimination module and a man-machine interaction module. The input end of the power module is connected to 220V mains, and the output end of the power module is connected to the signal acquisition module, the main control module and the man-machine interaction module to supply power to the three modules. The input end of the signal acquisition module is connected to the PT open delta to acquire PT zero sequence voltage and zero sequence current. The output end of the signal acquisition module is connected to the input end of the main control module. The main control module determines whether resonance occurs and the resonance type through algorithm and logical operation. One end of the output end of the main control module is connected to the input end of the resonance elimination module to eliminate resonance when resonance occurs. The other output end is connected to the man-machine interaction module to display relevant information of resonance in real time, thereby solving the problems of incomplete elimination of resonance by existing resistance resonance elimination, computer resonance elimination crash and long-time PT short circuit.

Description

Technical Field

[0001] This invention relates to the field of medium and low voltage power distribution, and in particular to a device and method for eliminating ferroresonance in medium and low voltage power distribution networks. Background Technology

[0002] Ferroresonance is a form of self-excited oscillation in power systems. It is a persistent, high-amplitude resonant overvoltage phenomenon caused by the saturation effect of ferromagnetic inductance in transformers, voltage transformers, etc. In neutral-point non-effectively grounded systems, single-phase grounding faults, arcing grounding, and other causes can trigger ferrosonance. Although there have been many research results on ferrosonance both domestically and internationally, and many harmonic suppression measures have been adopted in power grid operation, ferrosonance accidents in low-current grounding systems still occur frequently.

[0003] Existing harmonic suppression technologies commonly fall into two main categories: First, increasing circuit losses to dissipate resonant energy. Common methods include adding arc-suppression coils to the power grid, increasing the neutral point resistance of the PT, and adding open-delta damping resistors. While these methods can have some effect, increasing the neutral point resistance of the PT affects the monitoring of the system's insulation to ground, and damping resistors are often ineffective in eliminating resonance when it occurs. Second, avoiding the conditions for resonance. This can be achieved by changing the system's grounding method during design or by temporarily performing switching operations during operation to disrupt the conditions for ferroresonance; or by not using electromagnetic voltage transformers to avoid the nonlinear excitation characteristics of the iron core. During power grid planning, this can prevent resonance conditions from being reached due to changes in excitation inductance parameters, or by improving the excitation characteristics of the transformer. These methods can prevent resonance during power grid planning, but they are ineffective for existing medium and low voltage distribution networks. Resonance can be induced in various ways, and switching operations alone cannot completely prevent it. For new microcomputer-based harmonic suppression devices, problems such as unreasonable judgment and action logic, and component selection issues lead to frequent system crashes and prolonged short-circuiting of the PT. Summary of the Invention

[0004] Given that existing secondary resistor harmonic elimination and microcomputer harmonic elimination methods cannot completely eliminate resonance, have unreasonable microcomputer judgment and action logic, and have component selection problems, leading to frequent system crashes and prolonged short circuits of the PT, this invention provides a ferroresonant elimination device and method for medium and low voltage distribution networks.

[0005] The technical solution adopted in this invention is as follows:

[0006] A ferroresonance elimination device for medium and low voltage distribution networks includes a power supply module, a signal acquisition module, a main control module, a ferroresonance elimination module, and a human-machine interface module. The input terminal of the signal acquisition module is connected to a PT open delta connection, and the output terminal is connected to the input terminal of the main control module. The output terminal of the main control module is connected to the input terminal of the ferroresonance elimination module and the human-machine interface module, respectively. The output terminal of the ferroresonance elimination module is connected to a PT open delta connection. The input terminal of the power supply module is connected to 220V AC mains power, and the output terminals are connected to the signal acquisition module, the main control module, and the human-machine interface module, respectively.

[0007] A method for eliminating ferroresonance in medium- and low-voltage distribution networks, based on the aforementioned ferroresonance elimination device for medium- and low-voltage distribution networks, includes the following steps:

[0008] Step 1: The signal acquisition module continuously samples the zero-sequence voltage U0 and the zero-sequence current I0 of the PT;

[0009] Step 2: The main control module calculates the amplitude of the half-wave zero-sequence voltage U1 and the signal frequency f1 within the first half-wave cycle based on the continuous sampling of the zero-sequence voltage U0.

[0010] Step 3: The main control module calculates the half-wave zero-sequence voltage amplitude U2 and signal frequency f2 in the second half-wave cycle based on the continuous sampling of the zero-sequence voltage U0.

[0011] Step 4: The main control module calculates the amplitude of the half-wave zero-sequence voltage U3 and the signal frequency f3 in the second half-wave cycle based on the continuous sampling of the zero-sequence voltage U0.

[0012] Step 5: The main control module determines whether the system is experiencing three-way resonance, two-way resonance, power frequency resonance, or high-frequency resonance based on the signal frequency f1, signal frequency f2, signal frequency f3, half-wave zero-sequence voltage amplitude U1, half-wave zero-sequence voltage amplitude U2, half-wave zero-sequence voltage amplitude U3, and PT zero-sequence current I0 within two half-wave cycles.

[0013] Step 6: The main control module outputs a control signal value to the harmonic cancellation module according to the resonance type determined in step 5. The harmonic cancellation module closes the solid-state relay to cancel the resonance according to the control signal value. The solid-state relay opens after the closing time is reached.

[0014] Step 7: Repeat steps 1 to 6 until the above situation does not occur within three consecutive half-wave cycles, then the ferroresonance of the medium and low voltage distribution network is eliminated.

[0015] Furthermore, in steps 2, 3, and 4, the half-wave zero-sequence voltage amplitude U is calculated as follows: within the sampling times t1 and t2 of the PT zero-sequence voltage U0 at two consecutive zero-crossing points, the maximum value U of the PT zero-sequence voltage U0 is found. 0max , This refers to the half-wave zero-sequence voltage amplitudes U1, U2, or U3.

[0016] Furthermore, in steps 2, 3, and 4, the signal frequency f is calculated as follows:

[0017]

[0018] In the formula, t0 is the initial sampling time, and t1 is the sampling time of the PT zero-sequence voltage U0 at the first zero-crossing point;

[0019]

[0020] In the formula, t2 is the sampling time of the PT zero-sequence voltage U0 at the second zero-crossing point;

[0021]

[0022] In the formula, t2 is the sampling time of the PT zero-sequence voltage U0 at the second zero-crossing point.

[0023] Furthermore, in step 5:

[0024] If the signal frequencies f1, f2, and f3 within the three half-wave cycles are all within the range of 10-19Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 18V, then the system is determined to have a three-way frequency resonance.

[0025] If the signal frequencies f1, f2, and f3 within the three half-wave cycles are all within the range of 19-30Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 25V, then the system is determined to have a frequency divider resonance.

[0026] If the signal frequencies f1, f2, and f3 within the three half-wave cycles are all within the range of 30-70Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 30V, and the PT zero-sequence current I0 exceeds 0.5A, then the system is determined to have experienced power frequency resonance.

[0027] If the signal frequencies f1, f2, and f3 within the three half-wave cycles are all greater than 70Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 33V, then the system is determined to have high-frequency resonance.

[0028] Furthermore, in step 6, while the main control module outputs a control signal value to the harmonic elimination module according to the resonance type determined in step 5, the main control module also outputs resonance state, zero-sequence voltage, and zero-sequence current information to the human-machine interface.

[0029] Furthermore, in step 6, the solid-state relay closing time is 200-300ms.

[0030] The beneficial effects of this invention are:

[0031] This invention relates to the field of medium and low voltage power distribution, and particularly to a medium and low voltage ferroresonance elimination device and method. The device consists of a power supply module, a signal acquisition module, a main control module, a ferroresonance elimination module, and a human-machine interface module. The power supply module's input is connected to 220V AC mains power, and its output is connected to the signal acquisition module, the main control module, and the human-machine interface module, supplying power to these three modules. The signal acquisition module's input is connected to the open delta connection of the PT (potential transformer) to acquire the PT's zero-sequence voltage and zero-sequence current. The signal acquisition module's output is connected to the main control module's input. The main control module uses algorithms and logic operations to determine whether resonance has occurred and its type. One output of the main control module is connected to the ferroresonance elimination module's input to eliminate resonance when it occurs, and the other output is connected to the human-machine interface module to display resonance-related information in real time. This solves problems such as the inability of existing resistor-based ferroresonance to completely eliminate resonance, microprocessor-based ferroresonance crashing, and prolonged short-circuiting of the PT. Attached Figure Description

[0032] 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.

[0033] in:

[0034] Figure 1 This is a schematic diagram of the overall connection of the present invention. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] 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.

[0038] refer to Figure 1 A ferroresonant elimination device for medium and low voltage distribution networks is disclosed. The ferroresonant elimination device for medium and low voltage distribution networks comprises a power supply module, a signal acquisition module, a main control module, a ferroresonant elimination module, and a human-machine interaction module.

[0039] The input terminal of the signal acquisition module is connected to the open delta connection of the PT, and the output terminal of the signal acquisition module is connected to the input terminal of the main control module. One end of the output terminal of the main control module is connected to the input terminal of the harmonic suppression module, and the other output terminal is connected to the human-machine interface module. The output terminal of the harmonic suppression module is connected to the open delta connection of the PT. The input terminal of the power supply module is connected to 220V AC mains power, and the output terminal of the power supply module is connected to the signal acquisition module, the main control module, and the human-machine interface module to supply power to the three modules. Preferably, the DC power supply voltage is 5V.

[0040] The function of the signal acquisition module is to acquire the zero-sequence voltage U0 of the open delta of the PT and the zero-sequence current I0 flowing through the PT.

[0041] The main control module's function is to analyze the frequency and amplitude characteristics of the signal based on the zero-sequence voltage U0 and zero-sequence current I0 collected by the signal sampling module, determine whether the resonant voltage setting is exceeded, and if it is, trigger the harmonic cancellation module to perform harmonic cancellation.

[0042] The harmonic suppression module is a high-capacity current-type solid-state relay, preferably with a rated current ≥300A.

[0043] Based on the above-mentioned ferroresonance elimination device for medium and low voltage distribution networks, the following steps can be performed to eliminate ferroresonance in medium and low voltage distribution networks:

[0044] Step 1: The signal acquisition module continuously samples the zero-sequence voltage U0 and the zero-sequence current I0 of the PT.

[0045] Step two: The main control module calculates the half-wave zero-sequence voltage amplitude U1 and signal frequency f1 within the first half-wave cycle based on the continuous sampling of the zero-sequence voltage U0; specifically, within the sampling times t1 and t2 of the PT zero-sequence voltage U0 at two consecutive zero-crossing points, the maximum value U of the PT zero-sequence voltage U0 is found. 0max , The calculated value is the half-wave zero-sequence voltage amplitude U1; the signal frequency f1 is... Continuous sampling, t0 is the initial sampling time.

[0046] Step 3: The main control module calculates the half-wave zero-sequence voltage amplitude U2 and signal frequency f2 within the second half-wave cycle based on the continuous sampling of the zero-sequence voltage U0. Specifically, within the sampling times t2 and t3 of the PT zero-sequence voltage U0 at two consecutive zero-crossing points, the maximum value U of the PT zero-sequence voltage U0 is found. 0max , The calculated value is the half-wave zero-sequence voltage amplitude U2; the signal frequency f2 is... Continuous sampling.

[0047] Step four: The main control module calculates the half-wave zero-sequence voltage amplitude U3 and signal frequency f3 within the second half-wave cycle based on the continuous sampling of the zero-sequence voltage U0; specifically, within the sampling times t3 and t4 of the PT zero-sequence voltage U0 at two consecutive zero-crossing points, the maximum value U of the PT zero-sequence voltage U0 is found. 0max , The calculated value is the half-wave zero-sequence voltage amplitude U3; the signal frequency f3 is... Continuous sampling.

[0048] Step 5: The main control module determines whether the system has experienced a frequency divider resonance, a frequency divider resonance, a power frequency resonance, or a high-frequency resonance based on the signal frequency f1, signal frequency f2, signal frequency f3, half-wave zero-sequence voltage amplitude U1, half-wave zero-sequence voltage amplitude U2, half-wave zero-sequence voltage amplitude U3, and PT zero-sequence current I0 within the three half-wave cycles.

[0049] If the signal frequencies f1, f2, and f3 within two half-wave cycles are all within the range of 10-19Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 18V, then the system is determined to have a frequency divider resonance. If the signal frequencies f1, f2, and f3 within three half-wave cycles are all within the range of 19-30Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 25V, then the system is determined to have a frequency divider resonance. If the signal frequencies f1, f2, and f3 within a wave cycle are all within the range of 30-70Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 30V, and the PT zero-sequence current I0 exceeds 0.5A, then the system is determined to have power frequency resonance. If the signal frequencies f1, f2, and f3 within three half-wave cycles are all greater than 70Hz, and the half-wave zero-sequence voltage amplitudes U1, U2, and U3 all exceed 33V, then the system is determined to have high-frequency resonance.

[0050] Step six: The main control module outputs a control signal value to the harmonic cancellation module via three-way resonant, two-way resonant, power frequency resonant, or high-frequency resonant modes. The harmonic cancellation module closes the solid-state relay to cancel harmonics based on the control signal value. The solid-state relay opens after its closing time is reached. The closing time of the solid-state relay can be set, with a preferred closing time of 200-300ms. Simultaneously, after the main control module determines resonance, it outputs a control signal value to the harmonic cancellation module to close the solid-state relay for harmonic cancellation. At the same time, the main control module outputs information such as resonance status, zero-sequence voltage, and zero-sequence current to the human-machine interface.

[0051] Step 7: Repeat steps 1 to 6 until the above situation does not occur within three consecutive half-wave cycles, then the ferroresonance of the medium and low voltage distribution network is eliminated.

[0052] 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 eliminating ferroresonance in medium and low voltage distribution networks, wherein the method is based on a ferroresonance elimination device for medium and low voltage distribution networks, characterized in that: The medium and low voltage distribution network ferroresonance elimination device includes a power supply module, a signal acquisition module, a main control module, a harmonic elimination module, and a human-machine interaction module; The input terminal of the signal acquisition module is connected to the open delta PT, and the output terminal is connected to the input terminal of the main control module. The output of the main control module is connected to the input of the harmonic elimination module and the human-machine interaction module, respectively. The output of the harmonic suppression module is connected to the open delta connection of the PT. The power module input is connected to 220V AC power, and the output is connected to the signal acquisition module, the main control module, and the human-machine interaction module, respectively. The method for eliminating ferroresonance in medium and low voltage distribution networks includes the following steps: Step 1, the signal acquisition module continuously samples the PT zero sequence voltage and zero sequence current ​ Step 2, the main control module determines the zero-sequence voltage. Continuous sampling calculation of the half-wave zero-sequence voltage amplitude within the first half-wave cycle and signal frequency ; Step 3, the main control module determines the zero-sequence voltage. Continuous sampling calculation of the half-wave zero-sequence voltage amplitude during the second half-wave cycle and signal frequency ; Step 4, the main control module determines the zero-sequence voltage. Continuous sampling calculation of the half-wave zero-sequence voltage amplitude within the third half-wave cycle and signal frequency ; Step 5, the main control module determines the signal frequency within the three half-wave cycles. Signal frequency Signal frequency Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude PT zero-sequence current Determine whether the system is experiencing three-way resonance, two-way resonance, power frequency resonance, or high-frequency resonance. Step 6: The main control module outputs a control signal value to the harmonic cancellation module according to the resonance type determined in step 5. The harmonic cancellation module closes the solid-state relay to cancel the resonance according to the control signal value. The solid-state relay opens after the closing time is reached. Step 7: Repeat steps 1 to 6 until the above situation does not occur within three consecutive half-wave cycles, then the ferroresonance of the medium and low voltage distribution network is eliminated.

2. The method for eliminating ferroresonance in medium and low voltage distribution networks according to claim 1, characterized in that: In steps 2, 3, and 4, the half-wave zero-sequence voltage amplitude U is calculated as follows: the zero-sequence voltage at two consecutive zero-crossing points of the PT. Sampling time and Inside, find the zero-sequence voltage of the PT. maximum value , That is, the amplitude of the half-wave zero-sequence voltage. , or .

3. The method for eliminating ferroresonance in medium and low voltage distribution networks according to claim 2, characterized in that: In steps 2, 3, and 4, the signal frequency f is calculated as follows: In the formula is the initial time of adoption, is the PT zero sequence voltage of the first zero crossing point is the sampling time; In the formula PT zero sequence voltage for the second zero crossing sampling time of the In the formula PT zero sequence voltage for the second zero crossing sampling time of the 4. The method for eliminating ferro-resonance in a medium-low voltage distribution network according to claim 3, characterized in that: In step 5; If the signal frequency within three half-wave cycles Signal frequency Signal frequency All are within the 10-19Hz range, and the half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude If all values ​​exceed 18V, it is determined that the system is experiencing a three-way frequency resonance. If the signal frequency within three half-wave cycles Signal frequency Signal frequency All are within the 19-30Hz range, and the half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude If all values ​​exceed 25V, the system is determined to have a frequency divider resonance. If the signal frequency within three half-wave cycles Signal frequency Signal frequency All are within the 30-70Hz range, and the half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude All exceed 30V, PT zero-sequence current If the current exceeds 0.5A, it is determined that the system has experienced power frequency resonance; If the signal frequency within three half-wave cycles Signal frequency Signal frequency All are greater than 70Hz, and the half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude Half-wave zero-sequence voltage amplitude If all values ​​exceed 33V, it is determined that the system has experienced high-frequency resonance.

5. The method for eliminating ferroresonance in medium and low voltage distribution networks according to claim 1, characterized in that: In step 6, the main control module outputs a control signal value to the harmonic elimination module according to the resonance type determined in step 5, while simultaneously outputting resonance state, zero-sequence voltage, and zero-sequence current information to the human-machine interface.

6. The method of ferro-resonance elimination for medium and low voltage electrical distribution networks according to claim 1, characterized in that: In step 6, the solid-state relay closing time is 200-300ms.

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