Transformer excitation inrush current suppression method and device based on fixed closing angle
By using a fixed closing angle method, the calculation of the closing angle of the transformer is simplified, the problems of difficulty and inaccuracy of the closing angle calculation in the prior art are solved, and the better effect of suppressing excitation surge current is achieved.
Patent Information
- Application Number
- CN202411706469.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-26
- Publication Date
- 2025-02-25
AI Technical Summary
The existing excitation surge current suppression device is difficult to calculate the closing angle, and relies on accurate residual magnetic calculations, which is easily affected by the selection of the integral interval, resulting in inaccurate closing angle.
The method based on a fixed closing angle is adopted, by obtaining the residual magnetic polarity and pre-induced flux polarity of each phase of the transformer after opening, the closing point in the collection interval is determined to simplify the calculation of the closing angle.
The calculation of the transformer closing angle is achieved, the effect of excitation surge current suppression is improved, the convenience of engineering application is enhanced, and the tolerance for large closing angle errors is allowed.
Smart Images
Figure CN119518613A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method and device for suppressing transformer excitation inrush current based on a fixed closing angle, and is mainly used in the field of suppressing the excitation inrush current generated when the transformer is put into operation without load. Background Art
[0002] The excitation inrush current suppression device is widely used in the occasions of opening and closing no-load transformers. It can effectively suppress the huge inrush current generated when the transformer is closed without load, which has a huge impact on protecting primary equipment, preventing protection malfunction and improving power quality.
[0003] The current inrush current suppression device generally uses the voltage integration method to calculate the residual magnetism, and calculates the opening angle according to the residual magnetism value, so that the closing angle of the transformer next closing is equal to the opening angle, thereby suppressing the excitation inrush current. The existing method usually requires accurate calculation of residual magnetism to obtain a more accurate closing angle, but the accurate calculation of residual magnetism itself is difficult. The accuracy of the voltage integration method depends on the accurate selection of the integration interval. The existing residual magnetism calculation method based on the voltage integration method uses the peak value of the voltage waveform before the opening as the starting point of the integration, and the integration end point is usually a certain set value. If the set value is too large or too small, it may cause the integration end point to be inaccurate, resulting in deviations in the flux calculation, affecting the accuracy of the residual magnetism calculation results, and thus affecting the accuracy of the closing angle. Summary of the invention
[0004] The first object of the present invention is to provide a transformer excitation inrush current suppression method based on a fixed closing angle, which can simplify the calculation difficulty of the transformer closing angle, while having a better excitation inrush current suppression effect and improving the convenience of engineering applications.
[0005] To achieve the above object, the present invention adopts the following technical solution:
[0006] A method for suppressing transformer excitation inrush current based on a fixed closing angle, comprising:
[0007] Obtain the residual magnetic polarity of each phase of the main transformer after opening, and the polarity of the pre-induced magnetic flux of each phase of the transformer when closing;
[0008] Respectively obtain a first interval for making the residual magnetism polarity of phase A of the main transformer and the polarity of the pre-induction magnetic flux of phase A the same, a second interval for making the residual magnetism polarity of phase B of the main transformer and the polarity of the pre-induction magnetic flux of phase B the same, and a third interval for making the residual magnetism polarity of phase C of the main transformer and the polarity of the pre-induction magnetic flux of phase C the same;
[0009] Obtain the union interval of the first interval, the second interval, and the third interval, take any point in the union interval as the closing point, take any phase of the three phases as a reference, and confirm the voltage angle of the closing point, that is, the closing angle of the next closing.
[0010] As a preferred implementation, the midpoint of the union interval is used as the closing point. At this time, taking phase A as a reference, the closing angles corresponding to different residual magnetic polarity combinations are:
[0011] Ψ A ≥0;Ψ B <0;Ψ C ≥0, the corresponding closing angle is 120°;
[0012] Ψ A >0;Ψ B ≤0;Ψ C ≤0, the corresponding closing angle is 180°;
[0013] Ψ A ≥0;Ψ B ≥0;Ψ C <0, the corresponding closing angle is 240°;
[0014] Ψ A ≤0;Ψ B >0;Ψ C ≤0, the corresponding closing angle is 300°;
[0015] Ψ A <0;Ψ B ≥0;Ψ C ≥0, the corresponding closing angle is 0°;
[0016] Ψ A ≤0;Ψ B ≤0;Ψ C >0, the corresponding closing angle is 60°;
[0017] Among them, A ,Ψ B ,Ψ C They are the three-phase residual magnetic polarity of A, B and C respectively;
[0018] When phase B or phase C is used as the reference, it corresponds to -120° or +120° based on the above closing angle.
[0019] Considering that there is a time error in the closing of the circuit breaker and an error in the closing angle, selecting the midpoint as the closing point can improve the tolerance to the closing error of the circuit breaker.
[0020] As a preferred implementation, the method for obtaining the residual magnetism polarity of each phase of the main transformer after the switch-off is: using a voltage integration method to calculate the residual magnetism of each phase of the main transformer after the switch-off, and determining the residual magnetism polarity based on the positive and negative residual magnetism.
[0021] As a preferred implementation, the method for calculating the residual magnetism based on the voltage integration method is:
[0022] The transformer external input opening start signal is monitored in real time. When the signal changes from low level to high level, the voltage waveform peak is detected. The collected phase voltage data is integrated with the first voltage waveform peak as the starting point. The integration time is t seconds, and the result of the integration is the residual magnetism of each phase.
[0023] Furthermore, the voltage waveform peak is determined by any of the following positioning rules:
[0024] (1)
[0025] (2)
[0026] In the formula, is the voltage of a phase at the current moment The sampling value of are the sampling values of the same phase voltage at the previous x consecutive moments, x=1, 2, 3, 4; n-2 is the moment of the voltage peak.
[0027] Furthermore, the collected phase voltage data is obtained from a capacitive voltage transformer on the high voltage side of the transformer; or an electromagnetic voltage transformer on the low voltage side.
[0028] Furthermore, the value of t is 2-3s.
[0029] As a preferred implementation, the method for calculating the residual magnetism based on the voltage integration method is:
[0030] Real-time monitoring of the opening start input signal of the transformer external input, and recording the moment when the opening start input signal changes from a low level to a high level as the first moment;
[0031] The moment when the voltage reaches the voltage stabilization point after the switch is opened is recorded as the second moment;
[0032] Take the first n complete cycles of the first moment and calculate the first magnetic flux value by voltage integration, then use the first moment as the lower limit of integration and the second moment as the upper limit of integration to calculate the second magnetic flux value corresponding to the voltage stabilization point;
[0033] The difference between the second magnetic flux value and the first magnetic flux value, i.e., the residual magnetism, is calculated. This voltage integration method does not need to find the voltage peak as the starting point of the integration, but takes the moment when the opening switch is started and turned on (low level to high level) as the starting point, which is simpler to implement; and uses one integration to calculate the magnetic flux existing before the starting point, and uses the difference between the two integrations to calculate the residual magnetism, eliminating the influence of the magnetic flux bias, so that the calculation result is closer to the true value.
[0034] Furthermore, the opening time is determined based on the real-time value of the three-phase voltage. When the real-time values of the three-phase voltage are all less than a preset threshold, the circuit breaker is determined to be open; the preset threshold is the maximum value of the zero drift value of the three-phase voltage sampling value after the opening. Since the effective value of the voltage is calculated based on the real-time value, there is a delay in determining the opening using the effective value of the voltage, but there is no delay problem when using the real-time value, and the calculation amount of the program is reduced.
[0035] Furthermore, the half-wave peak point before the opening of the gate is fitted using the least square method to determine the voltage stabilization point after the opening of the gate.
[0036] Furthermore, the three-phase voltage real-time value and the three-phase voltage value used to calculate the voltage integral are derived from the three-phase voltage sampling value on the low-voltage side of the main transformer; the voltage transformer on the low-voltage side is an electromagnetic voltage transformer.
[0037] Furthermore, the value of n is 1-3.
[0038] As a preferred implementation, the main transformer is a three-phase transformer whose power on and off is controlled by a three-phase interlocking circuit breaker.
[0039] A second object of the present invention is to provide a transformer excitation inrush current suppression device based on a fixed closing angle, comprising:
[0040] The AC quantity acquisition module collects the three-phase voltage on the high-voltage side or the low-voltage side of the transformer and outputs it to the CPU module; and
[0041] The CPU module obtains the residual magnetic polarity of each phase of the main transformer after opening, and the polarity of the pre-induced magnetic flux of each phase of the transformer when closing;
[0042] Respectively obtain a first interval for making the residual magnetism polarity of phase A of the main transformer and the polarity of the pre-induction magnetic flux of phase A the same, a second interval for making the residual magnetism polarity of phase B of the main transformer and the polarity of the pre-induction magnetic flux of phase B the same, and a third interval for making the residual magnetism polarity of phase C of the main transformer and the polarity of the pre-induction magnetic flux of phase C the same;
[0043] Obtain the union interval of the first interval, the second interval, and the third interval, take any point in the union interval as the closing point, take any phase of the three phases as a reference, and confirm the voltage angle of the closing point, that is, the closing angle of the next closing.
[0044] As a preferred implementation, the AC quantity acquisition module also acquires the three-phase current on the high-voltage side or the low-voltage side of the transformer and outputs it to the CPU module.
[0045] As a preferred embodiment, the device further comprises an input quantity acquisition module and an output quantity acquisition module;
[0046] The input quantity acquisition module monitors the switch-off start input signal input from the transformer in real time and outputs it to the CPU module;
[0047] The output quantity module receives the opening and closing instructions from the CPU module.
[0048] As a preferred implementation, the device further comprises a display module for providing a visual user interaction interface for user operation and result viewing.
[0049] The present invention has the following beneficial effects:
[0050] The present invention realizes a simplified processing of residual magnetism calculation after the transformer is opened when calculating the closing angle. When integrating the three-phase voltage of the transformer, there is no need to accurately determine the end point of the integration, that is, there is no need to accurately calculate the size of the residual magnetism. The closing angle of the next closing can be determined only according to the polarity of the residual magnetism, thereby suppressing the excitation inrush current of the transformer no-load closing. The method of the present invention has a good inrush current suppression effect and is compatible with different residual magnetism calculation schemes. When the midpoint of the union interval is selected as the closing point, the allowable error of the closing angle is ±30°, the allowable error range is relatively large, and the tolerance to the closing error of the circuit breaker can be improved. BRIEF DESCRIPTION OF THE DRAWINGS
[0051] Figure 1 It is a schematic diagram of the residual magnetism calculation and residual magnetism mode selection program flow of the method shown in Example 1.
[0052] Figure 2 It is a schematic diagram of the principle for determining the fixed closing angle corresponding to residual magnetism mode 3 in Example 1.
[0053] Figure 3 It is a schematic diagram of the main functional modules of the device shown in Example 3. DETAILED DESCRIPTION
[0054] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.
[0055] Example 1
[0056] like Figure 1 As shown, this embodiment specifically describes a method for suppressing transformer excitation inrush current based on a fixed closing angle based on the following steps, including:
[0057] Step 1: collect the three-phase voltage data of the transformer in real time, and monitor the external input opening start input signal. When the signal changes from low level to high level, start to detect the voltage waveform peak. Take the first voltage peak as the starting point and integrate the collected phase voltage data. The integration time is 2 seconds, and the result of the integration is the residual magnetism of each phase.
[0058] Step 2, according to the obtained residual magnetism polarity of each phase, automatically match the residual magnetism mode, and select the corresponding closing angle, which is the angle that can suppress the transformer excitation inrush current when the circuit breaker is closed next time.
[0059] The object of inrush current suppression is a three-phase transformer, and the circuit breaker that controls the on and off of the transformer is a three-phase linkage circuit breaker; the real-time collected three-phase voltage data can be obtained from the voltage transformer on the high-voltage side or low-voltage side of the transformer; the formula for phase voltage integration is: , where t0 is the moment when the voltage exceeds the peak value, U i (t) is the voltage of each phase; the peak value of the voltage waveform is obtained by selecting one of the following two positioning rules:
[0060] (1)
[0061] (2)
[0062] Where U i (n) is the sampling value of a phase voltage at the current moment, U i (n-1) is the sampling value of the same phase voltage at the previous moment, and so on; n is the current moment, and n-2 is the moment of the voltage peak;
[0063] The corresponding fixed closing angles under different residual magnetism modes are angles based on the A phase voltage; there are 6 residual magnetism modes, and the corresponding fixed closing angles are shown in Table 1:
[0064] Table 1
[0065] Remanence mode Closing angle <![CDATA[Mode 1: Ψ A ≥0; Ψ B <0; Ψ C ≥0]]> 120° <![CDATA[Mode 2: Ψ A > 0; Ψ B ≤ 0; Ψ C ≤ 0]]> 180° <![CDATA[Mode Three: Ψ A ≥0; Ψ B ≥0; Ψ C <0]]> 240° <![CDATA[Mode Four: Ψ A ≤0; Ψ B >0; Ψ C ≤0]]> 300° <![CDATA[Mode Five: Ψ A <0; Ψ B ≥0; Ψ C ≥0]]> 0° <![CDATA[Mode Six: Ψ A ≤0; Ψ B ≤0; Ψ C >0]]> 60°
[0066] In the table, Ψ A ,Ψ B ,Ψ C They are the three-phase residual magnetic polarities of A, B and C respectively.
[0067] Figure 2 For residual magnetism mode three, it is explained how to infer the closing angle through the three-phase residual magnetism polarity. The principles for inferring the closing angle through other residual magnetism modes are similar.
[0068] In the figure, Φa, Φb, and Φc represent the pre-induced magnetic flux of the three phases ABC of the main transformer respectively, and Φra, Φrb, and Φrc represent the residual magnetic flux of the three phases ABC of the main transformer after opening. According to the principle of transformer excitation inrush current suppression, it is only necessary to make the polarity of the pre-induced magnetic flux and the residual magnetic flux the same when closing the circuit breaker to avoid saturation of the transformer core magnetic circuit, thereby suppressing the excitation inrush current. Figure 2 In the figure, the interval of the same polarity between the pre-induced magnetic flux of phase A and the residual magnetic flux is the area between points ① and ②, the interval of the same polarity between the pre-induced magnetic flux of phase B and the residual magnetic flux is the area between points ③ and ④, and the interval of the same polarity between the pre-induced magnetic flux of phase C and the residual magnetic flux is the area between points ⑤ and ⑥. The intersection of these three areas is the area between points ② and ③, which means that when the switch is closed in this area, the core magnetic circuits of the three phases ABC of the transformer will not be saturated, and the inrush current will be suppressed. The point between points ② and ③ is taken as the closing point. The angle of the A-phase magnetic flux at this point is 150°, and the voltage leads the magnetic flux by 90°, so the voltage angle is 240°, which means that when the transformer is in residual magnetic mode 3 after opening, the closing angle of the next closing is 240°.
[0069] Example 2
[0070] This embodiment provides another method for calculating residual magnetism. This method does not require finding the peak value and can calculate the residual magnetism simply and accurately, as follows:
[0071] Step 1: Collect data in real time and cache the three-phase voltage sampling value data on the low-voltage side of the main transformer with a time window of 5s. , , , real-time monitoring of the external input of the opening start signal, when the real-time monitoring of the external input of the opening start signal changes from low level to high level, record the current time as ;
[0072] Step 2: If the three-phase voltage sampling value data collected in real time , , At the same time, if the value is less than the threshold, the circuit breaker is judged to be opened; the threshold is the maximum value of the zero drift value of the three-phase voltage sampling value after opening, which can be determined in advance by experiment.
[0073] Step 3: According to the cached three-phase voltage sampling value data, obtain The magnetic flux is calculated by integrating the voltage for the three complete cycles before the moment ;Right now: ;
[0074] in, The three-phase voltage sampling value data of the main transformer low-voltage side , , , for The time corresponding to 3 complete cycles before the moment.
[0075] Step 4: Use the least squares method to fit the half-wave peak point before the opening time determined in step 2, determine the voltage stability point after the opening, and record the time corresponding to this point. , using voltage integration, The time is the lower limit of the integral. The moment is the upper limit of integration, and the magnetic flux at the voltage stability point after the gate is opened is obtained. ;
[0076] Step 5: Residual Flux Equal to the value obtained in step 4 And the value obtained in step 3 The difference is .
[0077] Example 3
[0078] The present embodiment provides a transformer excitation inrush current suppression device based on a fixed closing angle, which can collect voltage data on the low-voltage side or high-voltage side of the transformer, automatically calculate the residual magnetism of the transformer after opening by monitoring the external input opening start signal, automatically match the residual magnetism mode according to the polarity of the three-phase residual magnetism, and select the corresponding fixed closing angle.
[0079] like Figure 3 As shown, the device includes an AC quantity acquisition module, a binary input quantity acquisition module, a binary output quantity module, and a CPU module, wherein the AC quantity acquisition module is responsible for acquiring the three-phase voltage on the high-voltage side or the low-voltage side of the transformer and outputting it to the CPU module, and the three-phase voltage data is used to calculate the residual magnetism, and the binary input quantity acquisition module is used to receive the external input of the opening start and closing start signals and the circuit breaker position information, and output them to the CPU module, and the opening start signal is used as the basis for starting the residual magnetism calculation, and the CPU module calculates the residual magnetism based on the opening start signal and the acquired three-phase voltage using the method described in Example 1 or Example 2, and determines the closing angle based on the residual magnetism polarity. The binary output quantity module is used to output the opening and closing signals to the circuit breaker operation circuit, and it receives the opening and closing instructions from the CPU module.
[0080] Preferably, the AC quantity acquisition module also collects the current on the high voltage side or the low voltage side and outputs it to the CPU module for detecting the size of the inrush current. The device is also provided with a display module for providing a human-machine interface for users to set fixed values, view reports, and view AC sampling.
[0081] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A method for suppressing transformer excitation inrush current based on a fixed closing angle, characterized in that: include: Obtain the residual magnetic polarity of each phase of the main transformer after opening, and the polarity of the pre-induced magnetic flux of each phase of the transformer when closing; Respectively obtain a first interval for making the residual magnetism polarity of phase A of the main transformer and the polarity of the pre-induction magnetic flux of phase A the same, a second interval for making the residual magnetism polarity of phase B of the main transformer and the polarity of the pre-induction magnetic flux of phase B the same, and a third interval for making the residual magnetism polarity of phase C of the main transformer and the polarity of the pre-induction magnetic flux of phase C the same; Obtain the union interval of the first interval, the second interval, and the third interval, take any point in the union interval as the closing point, take any phase of the three phases as a reference, and confirm the voltage angle of the closing point, that is, the closing angle of the next closing.
2. The method according to claim 1, characterized in that: The midpoint of the union interval is taken as the closing point. At this time, with phase A as the reference, the closing angles corresponding to different residual magnetic polarity combinations are: Ψ A ≥0;Ψ B <0;Ψ C ≥0, the corresponding closing angle is 120°; Ψ A >0;Ψ B ≤0;Ψ C ≤0, the corresponding closing angle is 180°; Ψ A ≥0;Ψ B ≥0;Ψ C <0, the corresponding closing angle is 240°; Ψ A ≤0;Ψ B >0;Ψ C ≤0, the corresponding closing angle is 300°; Ψ A <0;Ψ B ≥0;Ψ C ≥0, the corresponding closing angle is 0°; Ψ A ≤0;Ψ B ≤0;Ψ C >0, the corresponding closing angle is 60°; Among them, A ,Ψ B ,Ψ C They are the three-phase residual magnetic polarity of A, B and C respectively; When phase B or phase C is used as the reference, it corresponds to -120° or +120° based on the above closing angle.
3. The method according to claim 1, characterized in that The method for obtaining the residual magnetism polarity of each phase of the main transformer after the switch-off is: using a voltage integration method to calculate the residual magnetism of each phase of the main transformer after the switch-off, and determining the residual magnetism polarity based on the positive and negative of the residual magnetism.
4. The method according to claim 3, characterized in that: The method for calculating residual magnetism based on the voltage integration method is: The transformer external input opening start signal is monitored in real time. When the signal changes from low level to high level, the voltage waveform peak is detected. The collected phase voltage data is integrated with the first voltage waveform peak as the starting point. The integration time is t seconds, and the result of the integration is the residual magnetism of each phase.
5. The method according to claim 4, characterized in that The voltage waveform peak is determined by any of the following positioning rules: （1） （2） In the formula, is the voltage of a phase at the current moment The sampling value of are the sampling values of the same phase voltage at the previous x consecutive moments, x=1, 2, 3, 4; n-2 is the moment of the voltage peak.
6. The method according to claim 3, characterized in that The method for calculating residual magnetism based on the voltage integration method is: Real-time monitoring of the opening start input signal of the transformer external input, and recording the moment when the opening start input signal changes from a low level to a high level as the first moment; The moment when the voltage reaches the voltage stabilization point after the switch is opened is recorded as the second moment; Take the first n complete cycles of the first moment and calculate the first magnetic flux value by voltage integration, then use the first moment as the lower limit of integration and the second moment as the upper limit of integration to calculate the second magnetic flux value corresponding to the voltage stabilization point; The difference between the second magnetic flux value and the first magnetic flux value, ie, the residual magnetism, is calculated.
7. The method according to claim 6, characterized in that The opening moment is determined based on the real-time values of the three-phase voltages. When the real-time values of the three-phase voltages are all less than a preset threshold, the circuit breaker is determined to be open. The preset threshold is the maximum value of the zero drift value of the three-phase voltage sampling value after opening.
8. A transformer excitation inrush current suppression device based on a fixed closing angle, characterized in that: include: AC quantity acquisition module, which collects the three-phase voltage on the high-voltage side or low-voltage side of the transformer and outputs it to the CPU module; and The CPU module obtains the residual magnetic polarity of each phase of the main transformer after opening, and the polarity of the pre-induced magnetic flux of each phase of the transformer when closing; Respectively obtain a first interval for making the residual magnetism polarity of phase A of the main transformer and the polarity of the pre-induction magnetic flux of phase A the same, a second interval for making the residual magnetism polarity of phase B of the main transformer and the polarity of the pre-induction magnetic flux of phase B the same, and a third interval for making the residual magnetism polarity of phase C of the main transformer and the polarity of the pre-induction magnetic flux of phase C the same; Obtain the union interval of the first interval, the second interval, and the third interval, take any point in the union interval as the closing point, take any phase of the three phases as a reference, and confirm the voltage angle of the closing point, that is, the closing angle of the next closing.
9. The device according to claim 8, characterized in that The AC quantity acquisition module also acquires the three-phase current on the high-voltage side or the low-voltage side of the transformer and outputs it to the CPU module.
10. The device according to claim 8, characterized in that It also includes an input quantity acquisition module and an output quantity module; The input quantity acquisition module monitors the switch-off start input signal input from the transformer in real time and outputs it to the CPU module; The output quantity module receives the opening and closing instructions from the CPU module.