Excitation inrush current suppression method

Abstract

To provide an excitation inrush current suppression method that can suppress magnetizing inrush current even when a residual magnetic flux cannot be calculated from voltage information in a case in which a transformer is disconnected in an actual system such as when a device is first installed or when it is not in operation, and that can be applied to widely used three-phase integrated control type circuit breakers.SOLUTION: An excitation inrush current suppression device 30 includes an excitation current calculation unit 1, a magnetic flux generation unit 2, a steady-state magnetic flux calculation unit 3, an effective breaking timing calculation unit 4, an effective residual magnetic flux calculation unit 5, a closing phase angle calculation unit 6, a current phase angle calculation unit 7, and a closing command output unit 8. The excitation inrush current suppression device 30 outputs a closing command to main contacts of a circuit breaker 10 on the basis of information obtained from a detection signal received by a voltage detector 11. This causes the circuit breaker 10 to close.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for suppressing a magnetizing inrush current, which is capable of suppressing a magnetizing inrush current even when a residual magnetic flux cannot be calculated from voltage information when a transformer is disconnected in a real system. [Background technology]

[0002] Transformer inrush current suppression devices are known as devices for eliminating faults caused by magnetizing inrush currents due to transformer re-energization. Patent Document 1 discloses an invention related to a magnetizing inrush current suppression device for a three-phase transformer. This magnetizing inrush current suppression device has a mechanism for controlling a circuit breaker connected between the three-phase transformer and a system power source. It includes a voltage measurement unit, an effective breaking timing calculation unit, an iron core magnetic flux calculation unit, an effective residual magnetic flux calculation unit, a closing phase angle calculation unit, and a closing phase angle control unit. It also includes, as needed, a breaking time calculation unit, an apparent residual magnetic flux calculation unit, a closing operation time calculation unit, an actual closing phase angle calculation unit, and an instantaneous voltage drop calculation unit. This invention is notable for its residual magnetic flux measurement method, and is highly effective in suppressing magnetizing inrush currents using the closing phase angle calculated from the residual magnetic flux.

[0003] This device has the function of calculating the residual magnetic flux when a transformer is disconnected in an actual system, and based on that residual magnetic flux, the three-phase collective circuit breaker controls the closing phase angle to suppress inrush current. However, if the residual magnetic flux cannot be calculated from the voltage information when the transformer is disconnected in an actual system, such as when the device is first installed or when it is not in operation, the optimal closing phase angle cannot be calculated, and therefore the magnetizing inrush current cannot be suppressed.

[0004] An example of a method for reducing residual magnetic flux is disclosed in Patent Document 2. This technology is limited to reducing residual magnetic flux in current transformers (CTs), and there is no mention of magnetizing inrush current. In addition, since the purpose is demagnetization and it is originally specialized for single-phase, it does not perform magnetic flux control in three-phase balance.

[0005] Furthermore, Patent Document 3 describes an electromagnetic induction device that uses an inexpensive demagnetizer that can reduce residual magnetic flux with a low-voltage, small-capacity demagnetization power supply to demagnetize residual magnetic flux, thereby suppressing adverse electrical effects and magnetizing inrush currents. However, this technology is aimed at demagnetization and does not perform magnetic flux control in three-phase balance. Furthermore, because it addresses the need for zero residual magnetic flux, it is limited to a measure that simply reduces the peak value of inrush current without performing input control.

[0006] Furthermore, Patent Document 4 describes an electromagnetic induction device that applies a DC voltage to a single-phase transformer to control the magnetic flux and demagnetize the residual magnetic flux. However, this technology is for single-phase transformers and uses a DC power supply to control the magnetic flux, so it is not possible to control the magnetic flux in a three-phase transformer with three-phase balance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5343118 [Patent Document 2] Japanese Patent Application Publication No. 7-183125 [Patent Document 3] Japanese Patent Application Publication No. 9-223628 [Patent Document 4] Patent No. 5594726 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, the conventional techniques disclosed above disclose a method of demagnetizing residual magnetic flux to reduce the peak value of magnetizing inrush current in order to suppress the magnetizing inrush current. However, this method is only effective in a closing phase angle control system using individual circuit breakers for each phase, and cannot be applied to circuit breakers of the widely used three-phase collective control system.

[0009] Furthermore, when using a method that uses closing phase angle control, control cannot be performed if the residual magnetic flux cannot be calculated, and therefore the magnetizing inrush current cannot be suppressed, particularly immediately after the suppression device is installed (initial energization). This situation is also true when the device is not in operation. Furthermore, when using closing phase angle control using the three-phase integrated control method, a magnetic flux difference will inevitably occur with the initial excitation magnetic flux due to the convergence of the residual magnetic flux, and therefore the magnetizing inrush current cannot be reduced to zero.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a method for suppressing magnetizing inrush current that can suppress magnetizing inrush current even when the residual magnetic flux cannot be calculated from the voltage information when the transformer is disconnected in the actual system, such as when the device is first installed or when the device is not in operation, and that can be applied to widely used three-phase integrated control type circuit breakers. [Means for solving the problem]

[0011] In order to solve the above problems, the magnetizing inrush current suppression method of the present invention is a magnetizing inrush current suppression method that controls a circuit breaker connected between a three-phase transformer and a system power supply, and is characterized in that a magnetic flux generating unit that can pass a magnetizing current is connected to the three-phase transformer that is disconnected from the system power supply, magnetic flux is generated by supplying power to the three-phase transformer from the magnetic flux generating unit, and when the magnetic flux generating unit is disconnected, residual magnetic flux is left in the three-phase transformer, and when the three-phase transformer is connected to the system power supply, the magnetizing inrush current is suppressed by a closing command output unit that controls the closing of the circuit breaker at the timing when the magnetizing inrush current is suppressed.

[0012] This makes it possible to suppress magnetizing inrush current even when the residual magnetic flux cannot be calculated from the voltage information when the transformer is disconnected in the actual system, such as when the device is first installed or when it is not in operation, and it can also be applied to circuit breakers with the widely used three-phase integrated control method.

[0013] In the magnetizing inrush current suppression method of the present invention, the magnetic flux generating unit can pass an excitation current equivalent to that when a rated voltage is applied to the three-phase transformer, and can output a voltage and frequency so that the excitation current is equivalent to that when a rated voltage and rated frequency are applied to the three-phase transformer.

[0014] By applying an equivalent voltage and frequency, there is no risk of a large magnetizing inrush current occurring if no countermeasures are taken when applying system power to a three-phase transformer, as occurs during the initial voltage application when the rated voltage and rated frequency are applied. This makes it possible to retain the effective residual magnetic flux in a three-phase balanced state required for control without causing a large magnetizing inrush current to flow in the three-phase transformer. Furthermore, by retaining the effective residual magnetic flux in a three-phase balanced state, the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux becomes small, so that the excitation inrush current can be effectively suppressed with high precision.

[0015] In the magnetizing inrush current suppression method of the present invention, the magnetic flux generating unit outputs and stops a voltage and frequency that makes the excitation current equivalent to that when the rated voltage and rated frequency are applied to the three-phase transformer, thereby determining the reduction rate (k) of the residual magnetic flux when the three-phase transformer is stopped, multiplying the excitation current when the rated voltage and rated frequency are applied to the three-phase transformer by 1 / k, and outputting a voltage and frequency again so that the excitation current becomes 1 / k times that.

[0016] This makes it possible to reduce the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux, thereby making it possible to effectively suppress the magnetizing inrush current with higher accuracy.

[0017] In the method for suppressing magnetizing inrush currents of the present invention, the magnetic flux generating unit includes a first cutoff phase angle control unit that controls the voltage waveform when the power supply output by the magnetic flux generating unit is disconnected from the three-phase transformer, and the cutoff phase angle can be controlled under the condition of two-phase saturation, which is the condition that most effectively suppresses magnetizing inrush currents.

[0018] Compared with the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux in a three-phase saturated state, the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux in a two-phase saturated state is smaller, so the magnetizing inrush current can be effectively suppressed with higher precision.

[0019] In the method for suppressing magnetizing inrush currents of the present invention, the magnetic flux generating unit includes a second cutoff phase angle control unit that controls the voltage waveform when the power supply output by the magnetic flux generating unit is cut off from the three-phase transformer, and by storing the closing phase angle calculated from the effective residual magnetic flux when the cutoff phase angle of the voltage waveform is controlled in a closing phase angle storage unit, any residual magnetic flux can be left remaining, and the closing phase angle can be calculated without having to calculate the residual magnetic flux each time.

[0020] When disconnecting the power output from the magnetic flux generator to the three-phase transformer, the cutoff phase angle is fixed to control the residual magnetic flux to a constant level, and the cutoff timing is output. By storing the closing phase angle calculated from the effective residual magnetic flux when the cutoff phase angle of the voltage waveform is controlled, the closing phase angle can be calculated without having to calculate the residual magnetic flux each time, thereby reducing the amount of hardware and software processing required. [Effects of the Invention]

[0021] According to the present invention, even when the residual magnetic flux cannot be calculated from the voltage information when the transformer is disconnected in the actual system, such as when the device is first installed or when the device is not in operation, it is possible to suppress the magnetizing inrush current, and it is possible to realize a magnetizing inrush current suppression method that can be applied to circuit breakers of the widely used three-phase integrated control system. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a block diagram of an apparatus configuration for realizing a method for suppressing a magnetizing inrush current according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a processing flow of a method for suppressing a magnetizing inrush current according to the first embodiment of the present invention. [Figure 3] FIG. 10 is a diagram illustrating the configuration of an excitation current calculation unit and a magnetic flux generation unit in a second embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing a processing flow of a method for suppressing a magnetizing inrush current according to a second embodiment of the present invention. [Figure 5] This is a graph of the excitation current waveform when a given voltage and frequency are applied and stopped so that the excitation current is equivalent to when the rated voltage and rated frequency are applied to a three-phase transformer. [Figure 6] This is a graph of the voltage waveform when a given voltage and frequency are applied and stopped so that the excitation current is equivalent to when the rated voltage and rated frequency are applied to a three-phase transformer. [Figure 7] This is a graph of the magnetic flux waveform when a given voltage and frequency are applied and stopped so that the excitation current is equivalent to when the rated voltage and rated frequency are applied to a three-phase transformer. [Figure 8] This is a graph of the excitation current when the rated voltage and rated frequency are applied to a three-phase transformer and then stopped. [Figure 9] This is a graph of the voltage waveform when the rated voltage and rated frequency are applied to a three-phase transformer and then stopped. [Figure 10] This is a graph of the magnetic flux waveform when the rated voltage and rated frequency are applied to a three-phase transformer and then stopped. [Figure 11] 1A is a diagram showing the timing at which the initial excitation magnetic flux synchronizes with the effective residual magnetic flux when system power is applied to a three-phase transformer for the effective residual magnetic flux in a three-phase balanced state, and FIG. 1B is a diagram showing the timing at which the initial excitation magnetic flux synchronizes with the effective residual magnetic flux when system power is applied to a three-phase transformer for the effective residual magnetic flux in a three-phase unbalanced state. [Figure 12] FIG. 11 is a diagram illustrating the configuration of an excitation current calculation unit and a magnetic flux generation unit in a third embodiment of the present invention. [Figure 13] FIG. 10 is a diagram showing a processing flow of a method for suppressing a transformer inrush current according to a third embodiment of the present invention. [Figure 14] This figure shows the excitation current waveform when the voltage and frequency are output and stopped, and the reduction ratio (k) is calculated so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied to a three-phase transformer, the excitation current is multiplied by 1 / k, and then the voltage and frequency are applied to the three-phase transformer again and stopped so that the excitation current is 1 / k times that. [Figure 15] This figure shows the voltage waveform when the reduction ratio (k) is calculated when a voltage and frequency that results in an excitation current equivalent to that obtained when the rated voltage and rated frequency are applied to a three-phase transformer and then stopped is output, the excitation current is multiplied by 1 / k, and then the voltage and frequency are applied to the three-phase transformer again and then stopped so that the excitation current becomes 1 / k times that value. [Figure 16] This figure shows the magnetic flux waveform when the voltage and frequency are output and stopped so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied to a three-phase transformer, the reduction ratio (k) is calculated, the excitation current is multiplied by 1 / k, and then the voltage and frequency are applied to the three-phase transformer again so that the excitation current is 1 / k times larger, and then stopped. [Figure 17] This figure shows the timing at which the initial excitation magnetic flux when system power is applied to the three-phase transformer is synchronized with the effective residual magnetic flux when the system power is applied to the three-phase transformer, with respect to the effective residual magnetic flux shown in Figure 16, when the reduction rate (k) when the three-phase transformer is stopped is calculated and the voltage and frequency are applied to the three-phase transformer again so that the excitation current is multiplied by 1 / k and then stopped. [Figure 18] FIG. 10 is a diagram showing the configuration of a magnetic flux generation unit in a fourth embodiment of the present invention. [Figure 19] FIG. 10 is a diagram showing a processing flow of a magnetizing inrush current suppression method according to a fourth embodiment of the present invention. [Figure 20] This figure shows the excitation current waveform when an arbitrary voltage and frequency are applied to a three-phase transformer so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied, and the arbitrary voltage and frequency are stopped under the condition of two-phase saturation, which is the condition that minimizes the excitation inrush current. [Figure 21] This figure shows the voltage waveform when an arbitrary voltage and frequency are applied to a three-phase transformer so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied, and the arbitrary voltage and frequency are stopped under the condition of two-phase saturation, which is the condition that minimizes the excitation inrush current. [Figure 22] This figure shows the magnetic flux waveform when an arbitrary voltage and frequency are applied to a three-phase transformer so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied, and the arbitrary voltage and frequency are stopped under the condition of two-phase saturation, which is the condition that minimizes the excitation inrush current. [Figure 23]23 is a diagram showing the timing at which the initial excitation magnetic flux is synchronized with the effective residual magnetic flux when system power is applied to a three-phase transformer, with respect to the effective residual magnetic flux in FIG. 22. FIG. [Figure 24] FIG. 13 is a diagram illustrating the configuration of a magnetic flux generating unit and a closing phase angle calculating unit in a fifth embodiment of the present invention. [Figure 25] FIG. 10 is a diagram showing a processing flow of a magnetizing inrush current suppression method according to a fifth embodiment of the present invention. [Figure 26] This figure shows the excitation current waveform (Case 1) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is disconnected, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. [Figure 27] This figure shows the voltage waveform (Case 1) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is cut off, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. [Figure 28] This figure shows the magnetic flux waveform (Case 1) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is cut off, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. [Figure 29] This figure shows the excitation current waveform (Case 2) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is disconnected, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. [Figure 30] This figure shows the voltage waveform (Case 2) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is cut off, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. [Figure 31] This figure shows the magnetic flux waveform (Case 2) when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator to the three-phase transformer is cut off, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a method for suppressing a magnetizing inrush current according to the present invention will be described based on an embodiment thereof. 1 shows a block diagram of an apparatus configuration for realizing a method for suppressing a transformer inrush current according to a first embodiment of the present invention. This block diagram shows the basic configuration for realizing the method for suppressing a transformer inrush current according to the present invention, and is also used in the second to fifth embodiments.

[0024] The present invention provides a magnetizing inrush current suppression method for controlling a circuit breaker connected between a three-phase transformer 9 and a system power supply 12. A magnetizing inrush current suppression device 30 for realizing this magnetizing inrush current suppression method includes a magnetizing current calculation unit 1, a magnetic flux generation unit 2, a steady-state magnetic flux calculation unit 3, an effective breaking timing calculation unit 4, an effective residual magnetic flux calculation unit 5, a closing phase angle calculation unit 6, a current phase angle calculation unit 7, and a closing command output unit 8.

[0025] The grid power supply 12 is a system that draws in three-phase power from a power company, or a system that draws in three-phase power from a three-phase power supply system within the facility. The three-phase transformer 9 has the grid power supply 12 side as its primary side and the opposite side as its secondary side. The three-phase transformer 9 converts the three-phase voltage supplied from the grid power supply 12 into a voltage value and outputs it to the secondary side.

[0026] The circuit breaker 10 is provided between the system power supply 12 and the three-phase transformer 9. When the system power supply 12 is charged, the three-phase transformer 9 is powered on by the system power supply 12 by closing the circuit breaker 10. When the circuit breaker 10 is opened, the three-phase transformer 9 is disconnected from the system power supply 12.

[0027] The voltage detector 11 is a measuring device for measuring the voltage on the side of the system power supply 12, and is, for example, a voltage transformer (VT). The voltage detector 11 measures the line voltage and outputs the detected value to the magnetizing inrush current suppression device 30 as a detection signal.

[0028] The magnetizing inrush current suppression device 30 outputs a closing command to the main contacts of the circuit breaker 10 based on information obtained from the detection signal received by the voltage detector 11. This causes the circuit breaker 10 to close.

[0029] FIG. 2 shows a process flow of the magnetizing inrush current suppression method according to the first embodiment of the present invention.

[0030] (Step 1) The excitation current calculation unit 1 calculates the excitation current when the power is turned on to the three-phase transformer 9, and outputs the information to the magnetic flux generation unit 2.

[0031] (Step 2) The magnetic flux generating unit 2 applies power to the three-phase transformer 9 so as to generate a magnetic flux at the calculated excitation current value based on the information output from the excitation current calculating unit 1.

[0032] (Steps 3 and 4) When the power output from the magnetic flux generating unit 2 is interrupted, the steady-state magnetic flux calculating unit 3 measures data before and after the interruption, and calculates the magnetic flux of the iron core of the three-phase transformer 9 based on the data.

[0033] (Step 5) The effective breaking timing calculation unit 4 calculates the timing at which the magnetic flux calculated by the steady-state magnetic flux calculation unit 3 converges to a constant value as the effective breaking timing (t1).

[0034] (Step 6) The effective residual magnetic flux calculation unit 5 calculates the magnetic flux (Φ(t1)) at the effective shutoff timing (t1) calculated by the effective shutoff timing calculation unit 4 from the magnetic flux (Φ(t)) calculated by the steady-state magnetic flux calculation unit 3 as the effective residual magnetic flux (Φr).

[0035] (Step 7) The closing phase angle calculation unit 6 calculates the closing phase angle (θclose) based on the effective residual magnetic flux (Φr) calculated by the effective residual magnetic flux calculation unit 5 so that the magnetizing inrush current when the circuit breaker 10 is closed is suppressed. By carrying out the above process, it is possible to determine the closing phase angle required for control, and to suppress the magnetizing inrush current at the time of initial voltage application, which has not been solved until now.

[0036] (Steps 8 and 9) The current phase angle calculation unit 7 measures the instantaneous value, polarity, and waveform of the system voltage (V2(t)) on the system power supply 12 side of the circuit breaker 10 using a signal obtained from the voltage detector 11, and when it detects an "in" signal from the circuit breaker 10, it calculates the current phase angle (θ1) of the system voltage (V2(t)) at the detection instant.

[0037] (Steps 10 and 11) The closing command output unit 8 outputs a closing command to the circuit breaker 10 based on the current phase angle (θ1) calculated by the current phase angle calculation unit 7 and the closing phase angle (θclose) calculated by the closing phase angle calculation unit 6, and the closing control of the circuit breaker 10 is completed.

[0038] The above-described device configuration and processing flow make it possible to realize the following processing: connecting the magnetic flux generating unit 2 capable of passing an excitation current to the three-phase transformer 9 that has been disconnected from the system power supply 12; generating magnetic flux by supplying power to the three-phase transformer 9 from the magnetic flux generating unit 2; leaving residual magnetic flux in the three-phase transformer 9 when the magnetic flux generating unit 2 is disconnected; and suppressing the magnetizing inrush current by the closing command output unit 8 that controls the closing of the circuit breaker 10 when the three-phase transformer 9 is connected to the system power supply 12, at the timing when the magnetizing inrush current is suppressed.

[0039] Next, a method for suppressing a magnetizing inrush current according to a second embodiment of the present invention will be described with reference to Figures 3 and 4. In the following embodiments, the characteristic features of each embodiment will be mainly described, and other common features may be omitted since they are the same as those of the first embodiment. The second embodiment of the present invention aims to effectively suppress a magnetizing inrush current with higher accuracy by adding a processing flow to the first embodiment.

[0040] FIG. 3 shows the configuration of an excitation current calculation unit and a magnetic flux generation unit in the second embodiment of the present invention. The excitation current calculation unit 1 includes an excitation current equivalent calculation unit 1a, and the magnetic flux generation unit 2 includes an equivalent voltage / frequency generation unit 2a. As a result, the excitation current calculation unit 1 and the magnetic flux generation unit 2 can output a voltage / frequency that makes the excitation current equivalent to that when the rated voltage / rated frequency is applied to the three-phase transformer 9.

[0041] 4 shows a process flow of a method for suppressing a magnetizing inrush current according to a second embodiment of the present invention. The part enclosed by a dashed line is a characteristic process step according to the second embodiment.

[0042] (Step 1) The excitation current calculation unit 1 calculates the excitation current when the rated voltage and rated frequency are applied to the three-phase transformer 9 , and outputs the information to the magnetic flux generation unit 2 .

[0043] The excitation current I is I =V÷{2πf(L1+Lp)} Equation (1) where V is the rated voltage, L1 is the inductance, and Lp is the leakage inductance. Equation (1) is a calculation formula for finding the excitation current when replacing with an equivalent circuit when the rated voltage (V) and rated frequency (f) are applied to the three-phase transformer 9.

[0044] (Step 2) The magnetic flux generating unit 2 applies an arbitrary voltage and frequency, for example, a low voltage and a low frequency, to the three-phase transformer 9 to generate magnetic flux so that the voltage and frequency are equivalent to the value of the excitation current calculated by equation (1) based on the information output by the excitation current calculating unit 1. Furthermore, "equivalent" here means that the excitation current obtained when a voltage (1.1 kV) and a low frequency (1 Hz) that are 1 / 60th the rated voltage of, for example, 66 kV and 60 Hz is applied to the three-phase transformer 9 will have the same value (equivalent) as the excitation current obtained when a voltage (1.1 kV) and a low frequency (1 Hz) that are 1 / 60th the rated voltage of, for example, 66 kV and 60 Hz is applied to the three-phase transformer 9.

[0045] (Steps 3 and 4) When any voltage and frequency output from the magnetic flux generating unit 2 is interrupted, the steady-state magnetic flux calculating unit 3 measures data before and after the interruption, and calculates the magnetic flux in the three-phase balanced state of the iron core of the three-phase transformer 9 based on that data.

[0046] (Step 5) The effective breaking timing calculation unit 4 calculates the timing at which the magnetic flux calculated by the steady-state magnetic flux calculation unit 3 converges to a constant value as the effective breaking timing (t1).

[0047] (Step 6) The effective residual magnetic flux calculation unit 5 calculates the magnetic flux (Φ(t1)) at the effective shutoff timing (t1) calculated by the effective shutoff timing calculation unit 4 from the magnetic flux (Φ(t)) calculated by the steady-state magnetic flux calculation unit 3 as the effective residual magnetic flux (Φr).

[0048] Figures 5, 6, and 7 are graphs of the excitation current, voltage, and magnetic flux when an arbitrary voltage and frequency are applied and stopped so that the excitation current is equivalent to when the rated voltage and rated frequency are applied to three-phase transformer 9, and Figures 8, 9, and 10 are graphs of the excitation current, voltage, and magnetic flux when the rated voltage and rated frequency are applied and stopped to three-phase transformer 9.

[0049] Figure 11(a) is a diagram showing the timing at which the initial excitation magnetic flux synchronizes with the effective residual magnetic flux when the system power supply 12 is applied to the three-phase transformer 9 for the effective residual magnetic flux in a three-phase balanced state, and Figure 11(b) is a diagram showing the timing at which the initial excitation magnetic flux synchronizes with the effective residual magnetic flux for each phase when the system power supply 12 is applied to the three-phase transformer 9 for the effective residual magnetic flux in a three-phase unbalanced state.

[0050] The excitation current in Figure 5 and the excitation current in Figure 8 show similar values, which indicates that they are equivalent, and that the effective residual magnetic flux in Figure 7 and the effective residual magnetic flux in Figure 10 have similar values.

[0051] (Step 7) The closing phase angle calculation unit 6 calculates the closing phase angle (θclose) based on the effective residual magnetic flux in the three-phase balanced state so as to suppress the magnetizing inrush current when the circuit breaker 10 is closed. Specifically, as shown in Fig. 11(a), the timing at which the initial excitation magnetic flux when the system power supply 12 is applied to the three-phase transformer 9 is synchronized with the effective residual magnetic flux in the three-phase balanced state is calculated as the closing phase angle.

[0052] According to this embodiment, there is no risk of a large magnetizing inrush current occurring if no countermeasures are taken when applying power from the system power supply 12 to the three-phase transformer 9, as occurs during the initial application of a rated voltage and rated frequency. By applying an equivalent voltage and frequency, it is possible to prevent a large magnetizing inrush current from flowing through the three-phase transformer 9 and to retain the effective residual magnetic flux in a three-phase balanced state that is necessary for control.

[0053] In addition, in the first embodiment, as shown in FIG. 11(b), the effective residual magnetic flux in a three-phase unbalanced state is also included, but in FIG. 11(a), the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux is small, so by adopting this embodiment, it is possible to effectively suppress the excitation inrush current with high accuracy.

[0054] The above-described device configuration and processing flow enable the magnetic flux generating unit 2 to pass an excitation current equivalent to that when the rated voltage is applied to the three-phase transformer 9, and to output a voltage and frequency so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied to the three-phase transformer 9.

[0055] Next, a method for suppressing a magnetizing inrush current according to a third embodiment of the present invention will be described with reference to Figures 12 and 13. The third embodiment of the present invention aims to effectively suppress a magnetizing inrush current with higher accuracy by adding a processing flow to the first embodiment.

[0056] 12 shows the configuration of an excitation current calculation unit and a magnetic flux generation unit in the third embodiment of the present invention. The excitation current calculation unit 1 includes a reduction factor (k) calculation unit 1b and an excitation current calculation unit A1c that takes this reduction factor into account. The magnetic flux generation unit 2 includes a voltage / frequency generation unit 2b.

[0057] The excitation current calculation unit 1 and magnetic flux generation unit 2 output and stop a voltage and frequency that results in an excitation current equivalent to that when the rated voltage and rated frequency are applied to the three-phase transformer 9, thereby determining the reduction rate (k) of the residual magnetic flux when the three-phase transformer 9 is stopped, multiplying the excitation current when the rated voltage and rated frequency are applied to the three-phase transformer 9 by 1 / k, and then outputting the voltage and frequency again so that the excitation current becomes 1 / k times that.

[0058] FIG. 13 shows a process flow of a method for suppressing a magnetizing inrush current according to the third embodiment of the present invention. The portions enclosed by dashed lines are characteristic processing steps of the third embodiment.

[0059] (Step 7) The reduction factor (k) calculation unit 1b of the excitation current calculation unit 1 calculates the reduction factor (k) of the effective residual magnetic flux based on the effective residual magnetic flux when an arbitrary voltage and frequency are applied and stopped, so that the excitation current is equivalent to that when the rated voltage and rated frequency are applied to the three-phase transformer 9, as calculated by the effective residual magnetic flux calculation unit 5.

[0060] The reduction ratio k is k=√2×√((φra 2 +φrb 2 +φrc 2 ) / 3)) Equation (2) Here, φra: residual magnetic flux (phase a), φrb: residual magnetic flux (phase b), φrc: residual magnetic flux (phase c).

[0061] (Step 8) Based on the information output from the reduction ratio (k) calculation unit 1b, the excitation current calculation unit A1c of the excitation current calculation unit 1 calculates an excitation current multiplied by 1 / k with respect to the excitation current when the rated voltage and rated frequency are applied to the three-phase transformer 9, and outputs the information to the magnetic flux generation unit 2.

[0062] The excitation current I' is I′ = (1 / k) × V / [2πf(L1+ Lp)] Equation (3) where k is the reduction ratio, V is the rated voltage, L1 is the inductance, and Lp is the leakage inductance.

[0063] (Step 9) The voltage / frequency generating unit 2b of the magnetic flux generating unit 2 applies an arbitrary voltage / frequency to the three-phase transformer 9 so as to obtain the calculated excitation current value based on the information output by the excitation current calculating unit A1c, thereby generating magnetic flux.

[0064] (Steps 10 and 11) When any voltage and frequency output from the magnetic flux generating unit 2 is interrupted, the steady-state magnetic flux calculating unit 3 measures data before and after the interruption, and calculates the magnetic flux in the three-phase balanced state of the iron core of the three-phase transformer 9 based on that data.

[0065] (Step 12) The effective breaking timing calculation unit 4 calculates the timing at which the magnetic flux calculated by the steady-state magnetic flux calculation unit 3 converges to a constant value as the effective breaking timing (t1).

[0066] (Step 13) The effective residual magnetic flux calculation unit 5 calculates the magnetic flux (Φ(t1)) at the effective shutoff timing (t1) calculated by the effective shutoff timing calculation unit 4 from the magnetic flux (Φ(t)) calculated by the steady-state magnetic flux calculation unit 3 as the effective residual magnetic flux (Φr).

[0067] Figures 14, 15, and 16 show the excitation current, voltage, and magnetic flux waveforms when the reduction rate (k) is calculated when a voltage and frequency that results in an excitation current equivalent to that obtained when the rated voltage and rated frequency are applied to the three-phase transformer 9 is output and then stopped, the excitation current is multiplied by 1 / k using equation (3), and the voltage and frequency are again applied to the three-phase transformer 9 so that the excitation current is 1 / k times that value and then stopped. Here, the reduction rate is 1 / k, but any arbitrary multiple may be used.

[0068] FIG. 17 is a diagram showing the timing at which the initial excitation magnetic flux when system power supply 12 is applied to three-phase transformer 9 is synchronized with the effective residual magnetic flux shown in FIG. 16 when the reduction rate (k) when three-phase transformer 9 is stopped is calculated and the voltage and frequency are applied to three-phase transformer 9 again so that the excitation current is multiplied by 1 / k and then stopped.

[0069] It can be seen that the excitation current shown in Fig. 14 is greater than the excitation current shown in Fig. 5. It can also be seen that the effective residual magnetic flux (0.6 pu) in Fig. 16 is greater than the effective residual magnetic flux (0.5 pu) in Fig. 7.

[0070] Compared to when the effective residual magnetic flux is controlled in a state equivalent to the rated voltage and rated frequency as in Fig. 11(a), the effective residual magnetic flux in Fig. 17 remains larger than in Fig. 11(a), and the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux becomes smaller. Therefore, by adopting this embodiment, it is possible to effectively suppress the magnetizing inrush current with higher accuracy.

[0071] With the above-described device configuration and processing flow, the magnetic flux generating unit 2 can output and stop a voltage and frequency that will result in an excitation current equivalent to that when the rated voltage and rated frequency are applied to the three-phase transformer 9, calculate the convergence rate (k) of the residual magnetic flux when the three-phase transformer 9 is stopped, multiply the excitation current that would be obtained when the rated voltage and rated frequency are applied to the three-phase transformer 9 by 1 / k, and then output a voltage and frequency again to obtain the 1 / k-fold excitation current.

[0072] Next, a method for suppressing a magnetizing inrush current according to a fourth embodiment of the present invention will be described with reference to Figures 18 and 19. The fourth embodiment of the present invention aims to effectively suppress a magnetizing inrush current with higher accuracy by adding a processing flow to the first embodiment.

[0073] FIG. 18 shows the configuration of a magnetic flux generator according to a fourth embodiment of the present invention. The magnetic flux generating unit 2 includes a cutoff phase angle control unit A2c.

[0074] FIG. 19 shows a process flow of a method for suppressing a magnetizing inrush current according to a fourth embodiment of the present invention. The portion enclosed by the dashed line is a characteristic processing step in the fourth embodiment.

[0075] (Step 3) When disconnecting the power output from the magnetic flux generating unit 2 to the three-phase transformer 9, the cutoff phase angle control unit A2c of the magnetic flux generating unit 2 controls the cutoff phase angle at a timing when the two-phase saturation condition is met.

[0076] (Steps 4 and 5) When any voltage and frequency output from the magnetic flux generating unit 2 is interrupted, the steady-state magnetic flux calculating unit 3 measures data before and after the interruption, and calculates the magnetic flux in the three-phase balanced state of the iron core of the three-phase transformer 9 based on the measurement results.

[0077] (Step 6) The effective breaking timing calculation unit 4 calculates the timing at which the magnetic flux calculated by the steady-state magnetic flux calculation unit 3 converges to a constant value as the effective breaking timing (t1).

[0078] (Step 7) The effective residual magnetic flux calculation unit 5 calculates the magnetic flux (Φ(t1)) at the effective shutoff timing (t1) calculated by the effective shutoff timing calculation unit 4 from the magnetic flux (Φ(t)) calculated by the steady-state magnetic flux calculation unit 3 as the effective residual magnetic flux (Φr).

[0079] 20, 21, and 22 are graphs of the excitation current, voltage, and magnetic flux when an arbitrary voltage and frequency are applied to three-phase transformer 9 so that the excitation current is equivalent to that when rated voltage and rated frequency are applied, and the arbitrary voltage and frequency are stopped under the condition of two-phase saturation, which most effectively suppresses the excitation inrush current. Also, Fig. 23 is a diagram showing the timing at which the initial excitation magnetic flux is synchronized with the effective residual magnetic flux when system power supply 12 is applied to three-phase transformer 9, relative to the effective residual magnetic flux in Fig. 22.

[0080] Here, as shown in Figures 11(a) and 23, the scalar difference for each phase between the effective residual flux and the initial excitation flux when the magnitude of the residual flux is 0.5 pu (50%) can be expressed by the following equation. a-phase: |sin(θ)-0.5 × sin(θ)| B phase: |sin(θ-120°)-0.5 × sin(θ-120°)| c phase: |sin(θ-240°)-0.5 × sin(θ-240°)| Formula (4)

[0081] Under the three-phase saturation condition in FIG. 11(a), when θ=270° is substituted into equation (4), the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux is 0.5 pu of the a-phase.

[0082] Under the two-phase saturation condition in FIG. 23, the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux when θ=0° is substituted into equation (4) is 0.433 pu for the b-phase and c-phase.

[0083] Compared with the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux in the three-phase saturation state in FIG. 11(a), the maximum value of the scalar difference between the effective residual magnetic flux and the initial excitation magnetic flux in the two-phase saturation state in FIG. 23 is smaller. Therefore, by adopting this embodiment, it is possible to effectively suppress the magnetizing inrush current with higher accuracy compared to the first to third embodiments.

[0084] With the above-described device configuration and processing flow, the magnetic flux generating unit 2 is provided with a cutoff phase angle control unit A2c that controls the voltage waveform when the power supply output by the magnetic flux generating unit 2 is disconnected from the three-phase transformer 9, and it is possible to realize processing that controls the cutoff phase angle under conditions that result in two-phase saturation, which minimizes the magnetizing inrush current.

[0085] Next, a magnetizing inrush current suppression method according to a fifth embodiment of the present invention will be described with reference to Figures 24 and 25. The fifth embodiment of the present invention aims to reduce the amount of processing required in terms of hardware and software by adding a processing flow to the first embodiment. FIG. 24 shows the configuration of a magnetic flux generating section and a closing phase angle calculating section in a fifth embodiment of the present invention.

[0086] In this embodiment, the magnetic flux generating unit 2 includes a cutoff phase angle control unit B2d that controls the voltage waveform when the power output from the magnetic flux generating unit 2 to the three-phase transformer 9 is cut off, and can leave any residual magnetic flux remaining. The closing phase angle calculating unit 6 includes a closing phase angle storage unit 6a that can calculate the closing phase angle without having to calculate the residual magnetic flux each time.

[0087] FIG. 25 shows a process flow of a method for suppressing a magnetizing inrush current according to a fifth embodiment of the present invention. The portion enclosed by the dashed line is a characteristic processing step in the fifth embodiment.

[0088] (Steps 3 and 4) The cutoff phase angle control unit B2d of the magnetic flux generating unit 2 fixes the cutoff phase angle that controls the residual magnetic flux to be constant when the power output from the magnetic flux generating unit 2 to the three-phase transformer 9 is disconnected, outputs the cutoff timing, and controls the cutoff phase angle of the voltage waveform.

[0089] (Step 5) In the information output from the magnetic flux generating unit 2, the closing phase angle storage process is not yet completed, so the information is output to the steady-state magnetic flux calculating unit 3.

[0090] (Step 6) When any voltage and frequency output from the magnetic flux generating unit 2 is interrupted, the steady-state magnetic flux calculating unit 3 measures data before and after the interruption, and calculates the magnetic flux in the three-phase balanced state of the iron core of the three-phase transformer 9 based on that information.

[0091] (Step 7) The effective breaking timing calculation unit 4 calculates the timing at which the magnetic flux calculated by the steady-state magnetic flux calculation unit 3 converges to a constant value as the effective breaking timing (t1).

[0092] (Step 8) The effective residual magnetic flux calculation unit 5 calculates the magnetic flux (Φ(t1)) at the effective shutoff timing (t1) calculated by the effective shutoff timing calculation unit 4 as the effective residual magnetic flux (Φr) from the magnetic flux (Φ(t)) calculated by the steady-state magnetic flux calculation unit 3.

[0093] (Step 9) Based on the effective residual magnetic flux in the three-phase balanced state calculated in step 8, the closing phase angle calculation unit 6 calculates a closing phase angle (θclose) so that the magnetizing inrush current when the circuit breaker 10 is closed is suppressed.

[0094] (Step 10) The closing phase angle storage unit 6a stores the closing phase angle (θclose) calculated by the closing phase angle calculation unit 6, so that the processes from step 6 to step 9 can be omitted from the next flow.

[0095] Figures 26, 27, 28, 29, 30, and 31 show graphs of the excitation current, voltage, and magnetic flux waveforms for two cases when the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power output from the magnetic flux generator 2 to the three-phase transformer 9, is fixed, the cutoff timing is output, and the cutoff phase angle of the voltage waveform is controlled.

[0096] It can be seen that the effective residual magnetic flux value shown in Fig. 28 and the effective residual magnetic flux value shown in Fig. 31 are approximately the same value. As a result, in the processing flow of Fig. 25, by calculating the effective residual magnetic flux as shown in Fig. 28 in the first step processing and calculating and storing the closing phase angle, in the processing flow from the next time onwards, it is not necessary to calculate the effective residual magnetic flux as shown in Fig. 31 and steps 6 to 10 can be omitted, and from the next time onwards, closing control can be performed using the closing phase angle stored in the first processing flow.

[0097] In this way, the cutoff phase angle, which is controlled to maintain a constant residual magnetic flux when the power supply output from the magnetic flux generator 2 to the three-phase transformer 9 is cut off, is fixed, the cutoff timing is output, and the closing phase angle calculated from the effective residual magnetic flux when the cutoff phase angle of the voltage waveform is controlled is stored.This makes it possible to calculate the closing phase angle without having to calculate the residual magnetic flux each time, thereby reducing the amount of hardware and software processing required.

[0098] With the above-described device configuration and processing flow, the magnetic flux generating unit 2 is equipped with a cutoff phase angle control unit B2d that controls the voltage waveform when the power supply output by the magnetic flux generating unit 2 is cut off from the three-phase transformer 9, and by storing in the cutoff phase angle storage unit 6a the closing phase angle calculated from the effective residual magnetic flux when the cutoff phase angle of the voltage waveform is controlled, it is possible to realize processing in which any residual magnetic flux remains and the closing phase angle is calculated without calculating the residual magnetic flux each time.

[0099] As explained above, the present invention has a major feature in that it applies a low frequency and a low voltage to a three-phase transformer in a disconnected state, causing an excitation current to flow, stops the application at an appropriate timing, and calculates the residual magnetic flux from the magnetic flux from the timing when the application was stopped using a calculation method specialized for low frequency and low voltage; alternatively, it applies a low frequency and a low voltage to a three-phase transformer in a disconnected state, causing an excitation current to flow, and stops the application at an arbitrary timing to leave an arbitrary residual magnetic flux, and from the found (arbitrarily left) residual magnetic flux, calculates the optimal closing phase angle for the next closing using the method disclosed in Japanese Patent No. 5343118, and controls a three-phase integrated control type circuit breaker to suppress the magnetizing inrush current. Furthermore, by applying a voltage or frequency that is greater than the equivalent, a larger excitation current than expected is passed, and the maximum residual magnetic flux is retained, ignoring the convergence of the residual magnetic flux. This minimizes the magnetic flux difference with the initial excitation magnetic flux at the time of switching on, and has the major feature of more effectively suppressing the excitation inrush current.

[0100] Of the embodiments of the present invention described above, the first embodiment is the basic embodiment, and the other embodiments are configured by adding device configurations and processing flows to this, and for the second to fifth embodiments, each embodiment can be combined as necessary to configure the invention. [Industrial Applicability]

[0101] The present invention can suppress magnetizing inrush current even when the residual magnetic flux cannot be calculated from the voltage information when the transformer is disconnected in the actual system, such as when the device is first installed or when it is not in operation, and can be widely used as a magnetizing inrush current suppression method that can be applied to circuit breakers of the widely used three-phase integrated control system. [Explanation of symbols]

[0102] 1 Excitation current calculation section 1a Excitation current equivalent calculation section 1b Reduction rate (k) calculation part 1c Excitation current calculation section A 2. Magnetic flux generating section 2a Equivalent voltage / frequency generator 2b Voltage and frequency generator 2c Cut-off phase angle control section A 2d Cut-off phase angle control section B 3 Steady-state magnetic flux calculation section 4. Effective shutoff timing calculation section 5 Effective residual magnetic flux calculation section 6 Closing phase angle calculation section 6a Closing phase angle memory section 7 Current phase angle calculation section 8 Closing command output section 9. Three-phase transformer 10 Circuit Breaker 11 Voltage detector 12 Grid power supply 30 Excitation inrush current suppressor

Claims

1. A method for suppressing magnetizing inrush current by controlling a circuit breaker connected between a three-phase transformer and a system power supply, comprising: connecting a magnetic flux generating unit capable of passing a magnetizing current to the three-phase transformer that is disconnected from the system power supply; generating magnetic flux by supplying power to the three-phase transformer from the magnetic flux generating unit; causing residual magnetic flux to remain in the three-phase transformer when the magnetic flux generating unit is disconnected; and suppressing the magnetizing inrush current by a closing command output unit that controls the closing of the circuit breaker at a timing when the magnetizing inrush current is suppressed when the three-phase transformer is connected to the system power supply.

2. 2. The method for suppressing magnetizing inrush currents according to claim 1, wherein the magnetic flux generating unit is capable of passing an excitation current equivalent to that when a rated voltage is applied to the three-phase transformer, and outputs a voltage and a frequency so that the excitation current is equivalent to that when a rated voltage and a rated frequency are applied to the three-phase transformer.

3. 3. The method for suppressing magnetizing inrush current according to claim 1, wherein the magnetic flux generating unit calculates a reduction rate (k) of the residual magnetic flux when the three-phase transformer is stopped by outputting and stopping a voltage and frequency that makes the excitation current equivalent to that when a rated voltage and a rated frequency are applied to the three-phase transformer, multiplies the excitation current when the rated voltage and the rated frequency are applied to the three-phase transformer by 1 / k, and then outputs a voltage and frequency again so as to obtain the 1 / k-fold excitation current.

4. 3. The method for suppressing a magnetizing inrush current according to claim 1, wherein the magnetic flux generating unit includes a first cutoff phase angle control unit that controls a voltage waveform when the power source output by the magnetic flux generating unit is disconnected from the three-phase transformer, and the cutoff phase angle is controlled under conditions that result in two-phase saturation, which is a condition that minimizes the magnetizing inrush current.

5. 3. The method for suppressing inrush currents according to claim 1, wherein the magnetic flux generating unit includes a second cutoff phase angle control unit that controls a voltage waveform when the power source output by the magnetic flux generating unit is cut off from the three-phase transformer, and a closing phase angle storage unit stores a closing phase angle calculated from an effective residual magnetic flux when controlling the cutoff phase angle of the voltage waveform, thereby allowing any residual magnetic flux to remain and calculating the closing phase angle without calculating the residual magnetic flux each time.

Images