Noise reduction system

Abstract

This effectively reduces noise from three-phase transformers while avoiding increased costs. [Solution] The noise reduction system 80 comprises a signal processing device 100 and a speaker 200. The speaker 200 is connected to the output of the signal processing device 100. The signal processing device 100 includes a generation unit 110, an adjustment unit 130, and a drive unit 150. The generation unit 110 generates frequency signals S1, S2a~S2e having a frequency twice that of the fundamental wave of the three-phase AC flowing through the three-phase transformer 35 or twice that of the harmonics of the three-phase AC, according to the output signals SG1, SG2. The adjustment unit 130 generates adjusted signals S1j, S3a~S3e having adjusted phase and amplitude by adjusting the phase and amplitude of the frequency signals S1, S2a~S2e. The drive unit 150 generates a drive signal DS for driving the speaker 200 according to the adjusted signals S1j, S3a~S3e.

Description

Technical Field

[0001] The present disclosure relates to a noise reduction system.

Background Art

[0002] Japanese Patent Application Laid-Open No. 6-61073 (Patent Document 1) discloses a noise reduction device for a power transformer. This device includes a noise detector, a sound wave output device, a high-speed calculation unit, and an output unit. The noise detector detects the noise at each noise generation location of the power transformer and outputs an electrical signal corresponding to the noise at each noise generation location. The high-speed calculation unit quickly calculates the inverse phase signal of the noise at each noise generation location based on the electrical signal. The output unit causes the sound wave output device to output a sound wave having a phase opposite to that of the noise at each noise generation location based on the inverse phase signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a power transformer, a three-phase transformer is widely used. A three-phase transformer is installed in substation equipment and the like and generates noise during operation. Effectively reducing such noise is important from the perspective of quietness in the area outside the equipment where the three-phase transformer is installed. According to the technique of Patent Document 1, a noise detector for detecting the noise from the three-phase transformer is required. However, adding a noise detector may cause an increase in cost due to an increase in the number of components.

[0005] The present disclosure has been made to solve the above problems, and its object is to effectively reduce the noise from the three-phase transformer while avoiding an increase in cost.

Means for Solving the Problems

[0006] The noise reduction system of this disclosure is configured to reduce noise from a three-phase transformer. The noise reduction system comprises a signal processing unit and a speaker. The signal processing unit receives an output signal corresponding to the output of an instrument transformer located on the primary or secondary side of the three-phase transformer. The speaker is connected to the output of the signal processing unit. The signal processing unit includes a generator, an adjustment unit, and a drive unit. The generator unit generates a frequency signal having twice the frequency of the fundamental wave of the three-phase AC flowing through the three-phase transformer or twice the frequency of the harmonics of the three-phase AC according to the output signal. The adjustment unit generates an adjusted signal having the adjusted phase and amplitude by adjusting the phase and amplitude of the frequency signal. The drive unit generates a drive signal for driving the speaker according to the adjusted signal. [Effects of the Invention]

[0007] According to this disclosure, noise from three-phase transformers can be effectively reduced while avoiding increased costs. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram of the power transmission and distribution system in the embodiment. [Figure 2] This is a diagram illustrating the configuration of a noise reduction system according to an embodiment. [Figure 3] This diagram illustrates how noise is reduced by a noise reduction system. [Figure 4] This diagram illustrates the configuration and advantages of a noise reduction system according to Modification 4. [Figure 5] This diagram illustrates the configuration and advantages of a noise reduction system according to Modification 4. [Figure 6] This diagram illustrates the configuration and advantages of a noise reduction system according to Modification 4. [Figure 7] This diagram illustrates the configuration and advantages of a noise reduction system according to Modification 4. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings will be denoted by the same reference numerals and their descriptions will not be repeated. Each embodiment and its modifications may be combined with one another as appropriate.

[0010] Figure 1 is an overall configuration diagram of the power transmission and distribution system in an embodiment. Referring to Figure 1, the power transmission and distribution system 1 comprises an AC power source 10, a transmission line 20, a substation 30, a distribution line 40, and a power receiving facility 50.

[0011] The AC power source 10 is, for example, a three-phase AC power source supplied by a power company and is connected to the transmission line 20. The transmission line 20 includes power lines 25U, 25V, and 25W. Power from the U-phase, V-phase, and W-phase of the transmission line 20 flows through these power lines, respectively.

[0012] Substation equipment 30 is located within area A1 and includes a three-phase transformer 35, an instrument transformer 37, an instrument current transformer 38, a signal processing device 100, and a speaker 200. Area A1 is managed by the operator of substation equipment 30 (in this example, a large-scale power consumer). Area A2 is adjacent to area A1 across boundary BD and is managed by a third party different from the large-scale power consumer (another business, public organization, or general household). Hereinafter, areas located outside boundary BD from the perspective of area A1 will also be referred to as "external areas." For example, area A2 is an example of an external area.

[0013] The three-phase transformer 35 is, for example, an oil-cooled three-phase transformer connected between the transmission line 20 and the distribution line 40. The three-phase transformer 35 steps down the power from the transmission line 20 and supplies the stepped-down power to the distribution line 40. The frequency of the fundamental wave of the three-phase AC flowing through the three-phase transformer 35 (power frequency) is, for example, the commercial frequency of 50Hz or 60Hz.

[0014] The three-phase transformer 35 emits noise waves NS because it vibrates mechanically, mainly due to magnetostriction in its iron core. Magnetostriction is caused by the excitation current of the three-phase transformer 35. The frequency components of noise waves NS correspond to the frequency components of the mechanical vibration of the three-phase transformer 35. The frequency components of the mechanical vibration include a frequency component that is twice the frequency of the AC component of the current flowing through the three-phase transformer 35. Specifically, it includes a frequency component that is twice the frequency of the fundamental wave of the three-phase AC, as well as a frequency component that is twice the frequency of the harmonics of the three-phase AC. Therefore, the frequency components of noise waves NS also include the same frequency components as the frequency components of the mechanical vibration described above. The phase of noise waves NS is related to the phase of the mechanical vibration of the three-phase transformer 35 and is somewhat different from the phase of the AC component of the current flowing through the three-phase transformer 35.

[0015] The noise wave NS includes a first noise component caused by magnetostriction in the core of the three-phase transformer 35. The first noise component corresponds to a noise component with a frequency twice that of the fundamental wave of the three-phase AC, and is the main component of the noise wave NS.

[0016] The noise wave NS also includes a second noise component caused by the load current of the three-phase transformer 35. The second noise component includes a noise component with twice the frequency of the fundamental wave of the three-phase AC (a component derived from the fundamental wave) and a noise component with twice the frequency of the harmonics of the three-phase AC (a component derived from harmonics). The component derived from the fundamental wave is the main component of the second noise component and therefore has a very large impact on the noise level. Among the components derived from harmonics, the noise components with twice the frequencies of the 5th, 7th, 11th, and 13th harmonics of the three-phase AC are also main components of the second noise component and have a particularly large impact on the noise level.

[0017] The instrument transformer 37 is provided on the primary side of the three-phase transformer 35. The instrument transformer 37 converts the voltage (high voltage) of the transmission line 20 into a voltage (low voltage) that can be handled by instruments and the like. An instrument (not shown) for measuring the output (specifically, the converted voltage) is attached to the instrument transformer 37. This instrument generates an output signal (specifically, a signal indicating the measurement result of this output) corresponding to the output of the instrument transformer 37. The frequency, phase, and magnitude of this output signal are related to the frequency, phase, and magnitude of the exciting current of the three-phase transformer 35. The instrument transformer 37 is an example of the "instrument transformer" of the present disclosure.

[0018] The instrument current transformer 38 is provided on the secondary side of the three-phase transformer 35. The instrument current transformer 38 converts the current (large current) flowing through the distribution line 40 into a current (small current) that can be handled by instruments and the like. An instrument (not shown) for measuring the output (specifically, the converted current) is attached to the instrument current transformer 38. This instrument generates an output signal (specifically, a signal indicating the measurement result of this output) corresponding to the output of the instrument current transformer 38. This output signal is related to the frequency, phase, and amplitude of the load current of the three-phase transformer 35. The instrument current transformer 38 is an example of the "instrument transformer" of the present disclosure. The signal processing device 100 and the speaker 200 will be described in detail later.

[0019] The noise sensor 60 is provided at a position (in this example, position P1) that contacts the boundary BD within the area A2, and measures the magnitude of the noise at this position. The distance D is the distance from the three-phase transformer 35 to the position P1. Generally, it is desired that the noise generated by the three-phase transformer 35 at the boundary BD between the area A1 and the area A2 be below a predetermined value.

[0020] The distribution line 40 includes power lines 45u, 45v, and 45w. The power of the u-phase, v-phase, and w-phase of the distribution line 40 flows through these power lines, respectively.

[0021] The power receiving equipment 50 includes a load 55. The load 55 is connected to the distribution line 40 and operates by receiving three-phase AC power supplied through the distribution line 40.

[0022] Effectively reducing noise in an external area (e.g., area A2) is important from the standpoint of quietness in that area. A known method for reducing noise involves adding a noise detector near the three-phase transformer 35 and generating sound waves with the opposite phase to the noise wave NS according to the detection results of the noise detector. However, adding such a noise detector can lead to increased costs due to the increased number of components. The noise reduction system according to this embodiment has a configuration for effectively reducing noise while avoiding increased costs. This point will be explained below.

[0023] Figure 2 is a diagram illustrating the configuration of a noise reduction system according to an embodiment. Referring to Figure 2, the noise reduction system 80 comprises a signal processing device 100, a speaker 200, an input device 300, a display device 350, and a noise sensor 60. The signal processing device 100 includes a generation unit 110, an adjustment unit 130, and a drive unit 150.

[0024] The generation unit 110 operates upon receiving an output signal SG1 corresponding to the output of the instrument transformer 37 and an output signal SG2 corresponding to the output of the instrument current transformer 38. Output signals SG1 and SG2 are generated by the aforementioned instruments that measure the outputs of the instrument transformer 37 and the instrument current transformer 38, respectively. If necessary, the aforementioned instruments that measure the outputs of the instrument transformer 37 and the instrument current transformer 38 may be omitted, and the output of the instrument transformer 37 may be used as output signal SG1 and the output of the instrument current transformer 38 as output signal SG2.

[0025] The generation unit 110 includes signal generators 115x, 115a to 115e. Signal generator 115i includes a filter circuit 120i and a frequency multiplier circuit 125i (i = x, a, b, c, d, or e).

[0026] Since the excitation current is proportional to the input voltage of the three-phase transformer 35, the filter circuit 120x extracts a value from the output signal SG1 that corresponds to the fundamental wave component of the excitation current of the three-phase transformer 35.

[0027] Filter circuit 120a extracts the fundamental wave component of the load current of the three-phase transformer 35 from the output signal SG2. Each of the filter circuits 120b to 120e extracts the harmonic components of the load current from the output signal SG2. Specifically, filter circuits 120b, 120c, 120d, and 120e extract the 5th harmonic component, the 7th harmonic component, the 11th harmonic component, and the 13th harmonic component, respectively.

[0028] The frequency multiplier circuit 125i is connected to the output of the filter circuit 120i and doubles the frequency of the component extracted by the filter circuit 120i (i = x, a, b, c, d, or e).

[0029] As these filter and frequency multiplier circuits operate, the generation unit 110 generates frequency signals S1, S2a to S2e according to the output signals SG1 and SG2. Each frequency signal has a frequency that is twice the frequency of the fundamental wave of the three-phase AC flowing through the three-phase transformer 35, or twice the frequency of the harmonics of the three-phase AC. For example, the signal generator 115x of the generation unit 110 generates frequency signal S1 according to the output signal SG1. Frequency signal S1 has a frequency that is twice the frequency of the fundamental wave. The signal generators 115a to 115e of the generation unit 110 each generate frequency signals S2a to S2e according to the output signal SG2. Frequency signal S2a has a frequency that is twice the frequency of the fundamental wave. Frequency signals S2b to S2e each have frequencies that are twice the frequencies of the 5th, 7th, 11th, and 13th harmonics, respectively.

[0030] The adjustment unit 130 includes phase and amplitude adjusters 135x, 135a to 135e. The phase and amplitude adjuster 135i includes a phase adjustment circuit 140i and an amplitude adjustment circuit 145i (i = x, a, b, c, d, or e). The signal generator 115k and the phase and amplitude adjuster 135k are also referred to as the "frequency processing unit 148k" (k = a, b, c, d, or e).

[0031] Each phase adjustment circuit 140i is, for example, a CR (capacitor / resistor) circuit or a signal inverting circuit. Alternatively, each phase adjustment circuit 140i may be a circuit using digital signal processing. Each phase adjustment circuit 140i adjusts the phase of the frequency signal input to it and generates a phase-adjusted signal with the adjusted phase. For example, phase adjustment circuit 140x adjusts the phase of frequency signal S1. Phase adjustment circuits 140a to 140e each adjust the phase of frequency signals S2a to S2e. In the above, adjusting the phase may mean either advancing or delaying the phase. Determining the amount of phase adjustment is equivalent to, for example, determining the time constant of a CR circuit. Each phase adjustment circuit 140i does not adjust the frequency and amplitude of the frequency signal input to it. Therefore, the frequency and amplitude of the phase-adjusted signal generated by each phase adjustment circuit 140i are the same as the frequency and amplitude of the frequency signal input to it.

[0032] Each amplitude adjustment circuit 145i is, for example, a variable gain amplifier. Each amplitude adjustment circuit 145i adjusts the amplitude of the phase-adjusted signal input to it and generates a signal with the adjusted amplitude. For example, amplitude adjustment circuit 145x adjusts the amplitude of the phase-adjusted signal generated by phase adjustment circuit 140x and generates an adjusted signal S1j. Amplitude adjustment circuits 145a to 145e each adjust the amplitude of the phase-adjusted signal generated by phase adjustment circuits 140a to 140e. As a result, amplitude adjustment circuits 145a to 145e each generate adjusted signals S3a to S3e. In the above, adjusting the amplitude may mean increasing or decreasing the amplitude. Determining the amount of amplitude adjustment is equivalent to, for example, determining the gain of a variable gain amplifier. Each amplitude adjustment circuit 145i does not adjust the frequency and phase of the phase-adjusted signal input to it. Therefore, the frequency and phase of the signal generated by this amplitude adjustment circuit are the same as the frequency and phase of the phase-adjusted signal. Therefore, the signals generated by each amplitude adjustment circuit 145i have adjusted phase and amplitude.

[0033] As these amplitude adjustment circuits and phase adjustment circuits operate, the adjustment unit 130 adjusts the phase and amplitude of the frequency signals S1, S2a to S2e, thereby generating adjusted signals S1j, S3a to S3e, respectively, which have the adjusted phase and amplitude.

[0034] Preferably, the adjustment amounts in the phase adjustment circuit 140x and the amplitude adjustment circuit 145x are determined at the factory using a test circuit similar to the circuit used for the no-load test of the three-phase transformer 35. The no-load test is a test performed at a factory or the like with the rated voltage applied to the primary side of the three-phase transformer 35 and the secondary side of the three-phase transformer 35 open. The test to adjust the adjustment amounts in the phase adjustment circuit 140x and the amplitude adjustment circuit 145x is performed with the secondary side of the three-phase transformer 35 open, similar to the no-load test, by installing a noise sensor 60 at a distance D equivalent to the actual distance between the three-phase transformer 35 and the interface surface BD at the site, and inputting the maximum value of a predetermined continuous rated voltage to the primary side of the three-phase transformer 35. For example, in this test, the magnitude of the noise caused by the excitation current is determined according to the measurement results of the noise sensor 60 (Figure 1). Then, the adjustment amounts in the phase adjustment circuit 140x and the amplitude adjustment circuit 145x are determined so that the magnitude of the noise is less than the standard. When the background noise is relatively high, the adjustment amounts in the phase adjustment circuit 140x and the amplitude adjustment circuit 145x are determined so that the difference between the noise during the test and the background noise is reduced.

[0035] The adjustment amounts in the phase adjustment circuits 140a to 140e and the amplitude adjustment circuits 145a to 145e are preferably determined in the factory using a test circuit similar to the short-circuit test (temperature rise test) circuit of the three-phase transformer 35. A short-circuit test is a test performed in a factory or the like with a sinusoidal rated current flowing through the primary side and the secondary side short-circuited. For example, in this test, the magnitude of the noise caused by the fundamental wave current of the three-phase transformer 35 can be determined according to the measurement results of the noise sensor 60. The test to adjust the adjustment amounts in the phase adjustment circuit 140x and the amplitude adjustment circuit 145x is performed with the secondary side of the three-phase transformer 35 short-circuited, similar to the no-load test, by installing the noise sensor 60 at a distance D equivalent to the actual distance between the three-phase transformer 35 and the interface surface BD at the site, and by inputting the maximum value of a predetermined continuous rated current to the primary side of the three-phase transformer 35. For example, in this test, the magnitude of the noise caused by the fundamental wave current can be determined according to the measurement results of the noise sensor 60 (Figure 1). Then, the adjustment amounts in the phase adjustment circuit 140a and the amplitude adjustment circuit 145b are determined so that the magnitude of the noise in question falls below the standard. When the background noise is relatively high, the adjustment amounts in the phase adjustment circuit 140a and the amplitude adjustment circuit 145a are determined so that the difference between the noise during the test and the background noise is reduced.

[0036] The phase and amplitude adjustment amounts in the phase adjustment circuits 140b to 140e and the amplitude adjustment circuits 145b to 145e are determined in the same way as the adjustment amounts in the phase adjustment circuit 140a and the amplitude adjustment circuit 145a. Specifically, the secondary side of the three-phase transformer 35 is short-circuited, and a harmonic current generator is connected to the primary side of the three-phase transformer 35. For each of the assumed maximum harmonic currents of the 5th, 7th, 11th, and 13th order, the magnitude of the noise caused by the harmonic current is determined according to the measurement results of the noise sensor 60, with the harmonic current flowing on the secondary side of the three-phase transformer 35. Then, the adjustment amounts in the phase adjustment circuits 140b to 140e and the amplitude adjustment circuits 145b to 145e are determined so that the magnitude of the noise is below the standard. When the background noise is relatively high, the adjustment amounts in the phase adjustment circuits 140b to 1440e and the amplitude adjustment circuits 145b to 145e are determined so that the difference between the noise during the test and the background noise is reduced.

[0037] When the secondary side of the three-phase transformer 35 is short-circuited, any desired current can be relatively easily passed through the three-phase transformer 35. While it is not easy to pass currents of various magnitudes through the three-phase transformer 35 within the actual power receiving equipment 30, it is reasonable to perform basic adjustments of amplitude and phase during a short-circuit test, and then perform final adjustments within the power receiving equipment 30.

[0038] Furthermore, it is desirable that the frequency processing unit 148k be provided for each phase of the three-phase AC circuit. The drive unit 150 includes a combining circuit 160 and an amplification circuit 180. The combining circuit 160 is, for example, a preamplifier, which generates a combined signal SS by combining the adjusted signals S1j, S3a~S3e. The combined signal SS is a signal obtained by superimposing the adjusted signals S1j, S3a~S3e for each phase of the three-phase AC. That is, the combined signal SS is a signal obtained by superimposing the adjusted signals S1j, S3a~S3e of the U phase, the adjusted signals S1j, S3a~S3e of the V phase, and the adjusted signals S1j, S3a~S3e of the R phase.

[0039] The amplification circuit 180 is, for example, a main amplifier, which generates a drive signal DS by amplifying the combined signal SS. The drive signal DS is a signal for driving the speaker 200. Since the combined signal SS is a signal obtained by superimposing the adjusted signals S1j, S3a to S3e, the drive signal DS includes a component with a frequency twice that of the fundamental wave of the three-phase AC and a component with a frequency twice that of the harmonics of the three-phase AC. The amplification circuit 180 generates the drive signal DS without changing the frequency and phase of the combined signal SS. Therefore, the amplitude and phase of the drive signal DS depend on the amount of amplitude and phase adjustment in the adjustment unit 130. Accordingly, the amplitude and phase of the drive signal DS can be adjusted by determining the amount of adjustment. The information indicating the amount of adjustment is appropriately predetermined in prior evaluation tests using a test circuit similar to the circuit, such as a no-load test or a short-circuit test, as described above, and is stored, for example, in the memory (not shown) of the signal processing device 100. The adjustment unit 130 reads the information from the memory and adjusts the amplitude and phase of the frequency signals S1, S2a to S2e.

[0040] In this way, the drive unit 150 generates the drive signal DS according to the adjusted signals S1j, S3a to S3e.

[0041] The speaker 200 is connected to the output of the signal processing device 100 and is located within the substation 30 near the three-phase transformer 35 (for example, within a predetermined distance from the three-phase transformer 35). The speaker 200 is oriented from the substation 30 toward the boundary BD (towards the external area). The speaker 200 may also be directly attached to the housing of the three-phase transformer 35 (the part at ground potential). In this case, the speaker 200 is attached to the housing of the three-phase transformer 35 by bolting, adhesive, or magnetic attraction.

[0042] Speaker 200 includes a diaphragm, a voice coil, and a magnet (none of which are shown). The diaphragm is, for example, a cone. The voice coil is attached to the diaphragm. When a drive signal DS flows through the voice coil, a Lorentz force is applied to the voice coil due to the electromagnetic interaction between the magnetic field generated by the magnet and the drive signal DS. This causes the voice coil and diaphragm to vibrate. As a result, speaker 200 generates a sound wave SW. The frequency components of the sound wave SW are substantially equal to the frequency components of the drive signal DS. On the other hand, the phase and amplitude of the sound wave SW are different from, but depend on, the phase and amplitude of the drive signal DS.

[0043] The input device 300 receives various user inputs. The display device 350 receives the measurement results from the noise sensor 60 via wired or wireless communication and displays a screen representing these measurement results. These measurement results include a waveform (noise waveform) representing the noise level at position P1 (Figure 1).

[0044] The frequency components of the sound wave SW are substantially equal to the frequency components of the drive signal DS, and the frequency components of the drive signal DS include components having twice the frequency of the frequencies extracted by the filter circuits 120x, 120a to 120e (fundamental and harmonic frequencies). As mentioned above, the frequency components of the noise wave NS from the three-phase transformer 35 include components with twice the frequency of the fundamental wave and components with twice the frequency of the harmonics. Therefore, the sound wave SW includes components with the same frequency as the noise wave NS.

[0045] Figure 3 illustrates how noise is reduced at position P1 by the noise reduction system 80. Figure 2 will be referenced as appropriate in the following explanation.

[0046] Referring to Figure 3(A), as described above, the phase of the drive signal DS can be adjusted by determining the amount of phase adjustment in each phase adjustment circuit 140i, thereby allowing the phase and amplitude of the sound wave SW at the actual interface BD (for example, at position P1) to be adjusted. Therefore, by appropriately determining the amount of phase adjustment in each phase adjustment circuit 140i, the phase of the sound wave SW in the external area can be made out of phase with respect to the phase of the noise wave NS (see Figure 3(B)). In this example, for the sake of ease of understanding, the noise wave NS and sound wave SW are assumed to be sine waves, but in reality, both the noise wave NS and sound wave SW may contain harmonic components.

[0047] In addition, the amplitude of the drive signal DS can be adjusted by determining the amount of amplitude adjustment in each amplitude adjustment circuit 145i. This makes it possible to adjust the magnitude of the sound wave SW, which has an out-of-phase relationship with respect to the phase of the noise wave NS at the actual interface BD (for example, at position P1). As a result, by appropriately determining the amount of amplitude adjustment in each amplitude adjustment circuit 145i, noise can be effectively reduced by the sound wave SW in the external area. Ideally, by adjusting the magnitude of the sound wave SW so that the magnitude of the sound wave SW with an out-of-phase relationship is approximately equal to the magnitude of the noise, the noise wave NS can be canceled out by the sound wave SW in the external area (see Figure 3(C)). The magnitude of the noise depends on the result of superimposing the waveform of the noise wave NS and the waveform of the sound wave SW, and is measured by the noise sensor 60 (Figure 1). In this embodiment, the correlation between the amount of adjustment in the adjustment unit 130 and the magnitude of the noise is quantitatively determined in evaluation tests, etc. Then, the amount of adjustment in the adjustment unit 130 is determined so that the noise in the external area is appropriate (for example, minimum). After on-site adjustments are complete, the noise sensor 60 may be removed, or it may be temporarily installed if further adjustments are necessary.

[0048] Referring again to Figure 2, according to the noise reduction system 80, the drive signal DS is generated by utilizing output signals SG1 and SG2 corresponding to the outputs of the instrument transformer 37 and the instrument current transformer 38. Instrument transformers such as the instrument transformer 37 and the instrument current transformer 38, and instruments that measure the outputs of these transformers and generate signals indicating the measurement results, are almost always provided in general substations such as the substation equipment 30. Therefore, in this embodiment, it is not necessary to separately add equipment such as a noise detector (e.g., a microphone or piezoelectric sensor) near the three-phase transformer 35 and generate sound waves in the opposite phase to the noise wave NS according to the detection results. Thus, noise can be reduced while avoiding the cost increase caused by adding the above equipment. Furthermore, since noise is reduced even if the three-phase transformer 35 does not have special specifications for noise reduction (e.g., an iron core made of expensive materials or a special structure), this also avoids cost increases.

[0049] According to this embodiment, both the first and second noise components of the noise wave NS from the three-phase transformer 35 can be effectively reduced. As mentioned above, the first noise component is a noise component caused by magnetostriction of the iron core of the three-phase transformer 35. The second noise component is a noise component caused by the load current of the three-phase transformer 35.

[0050] For example, by appropriately setting the phase and amplitude adjustment amounts in the phase / amplitude adjuster 135x, the phase and amplitude of the component with a frequency twice that of the fundamental wave of the three-phase AC in the composite signal SS and the drive signal DS can be adjusted. Therefore, the phase and amplitude of the component with that frequency included in the sound wave SW can be adjusted. As a result, the phase can be set to be in opposite phase to the phase of the first noise component, thereby effectively reducing the first noise component in the external area.

[0051] Similarly, by appropriately setting the phase and amplitude adjustment amounts in the phase / amplitude adjuster 135a, the phase and amplitude of the component with a frequency twice that of the fundamental wave of the three-phase AC in the composite signal SS and the drive signal DS can be adjusted. Therefore, the phase and amplitude of the component with that frequency included in the sound wave SW can be adjusted. As a result, the phase can be set to be out of phase with the noise component originating from the fundamental wave among the second noise components, thereby effectively reducing that noise component. In addition, by appropriately setting the phase and amplitude adjustment amounts in the phase / amplitude adjusters 135b to 135e, the phase and amplitude of the component with a frequency twice that of the harmonics of the three-phase AC in the composite signal SS and the drive signal DS can be adjusted. Therefore, the phase and amplitude of the component with that frequency included in the sound wave SW can be adjusted. As a result, the phase can be set to be out of phase with the noise component originating from the harmonics among the second noise components, thereby effectively reducing that noise component.

[0052] According to this embodiment, the generation unit 110 generates frequency signals S1 and S2a, as well as frequency signals S2b to S2e having twice the frequencies of the 5th, 7th, 11th, and 13th harmonics, but does not generate frequency signals related to other harmonic frequencies. In other words, the signal processing device 100 does not include frequency processing units (filter circuits, frequency doubling circuits, phase adjustment circuits, and amplitude adjustment circuits) related to harmonics other than those mentioned above, and the frequency processing unit only includes frequency processing units 148a to 148e. The advantages of this will be explained below.

[0053] As mentioned above, among the second noise components, the noise components with frequencies twice the 5th, 7th, 11th, and 13th harmonics of the three-phase AC are the main components of the second noise component. In the three-phase transformer 35, noise components with harmonics that are even multiples of the fundamental wave, and noise components with harmonics that are multiples of three of the fundamental wave can be basically ignored. Therefore, by focusing only on the noise components with frequencies twice the 5th, 7th, 11th, and 13th harmonics and reducing them together with the noise components with frequencies twice the fundamental wave, the noise in the external area can be easily reduced to a predetermined permissible level with the minimum necessary component configuration. In other words, since it is not necessarily required to reduce the noise components with frequencies twice the other harmonics among the second noise components, the number of components can be reduced, and noise can be appropriately reduced with a simple configuration. Generally, distance D and position P1 are the shortest distance between the three-phase transformer 35 and the interface BD, but they may change depending on the angle at which the three-phase transformer 35 faces the interface BD and the arrangement of other equipment within area A1. In such cases, it is desirable to place a noise sensor 60 at point P1 where the noise generated from the three-phase transformer 35 is greatest, and to determine the amount of phase adjustment in each phase adjustment circuit 140i and the amount of amplitude adjustment in the amplitude adjustment circuit 145i. [Example 1] The generation unit 110 may further generate frequency signals having twice the frequency of harmonics other than the 5th, 7th, 11th, and 13th harmonics. In other words, the signal processing device 100 may include a frequency processing unit for the harmonic frequency components of the said order, in addition to the frequency processing units 148a to 148e. In this case, the combining circuit 160 generates a combined signal SS by combining the adjusted signals S1j, S3a to S3e and the adjusted signals generated by the frequency processing unit. [Differentiation 2] The generation unit 110 does not generate all of the frequency signals S2b to S2e having twice the frequencies of the 5th, 7th, 11th, and 13th harmonics, but may generate only one of these frequency signals (i.e., it may generate only frequency signals having twice the frequency of at least one of these harmonics). In this case, the signal processing device 100 includes only one of the frequency processing units 148a to 148e.

[0054] With this configuration, the noise components at twice the frequency of the 5th, 7th, 11th, and 13th harmonics among the second noise components are effectively reduced along with the noise component at twice the frequency of the fundamental wave. As a result, noise can be appropriately reduced in the external area with a simpler configuration. [Difference 3] The adjustment unit 130 may adjust the phase and amplitude according to user input specifying the amount of phase and amplitude adjustment in the adjustment unit 130. This user input is made using the input device 300.

[0055] With this configuration, the user can specify the amount of phase and amplitude adjustment in the adjustment unit 130 while checking the noise measurement results in the external area (noise waveforms before and after phase and amplitude adjustment) displayed on the display device 350. For example, the user can specify these adjustment amounts so that the peak value (maximum value) of the noise waveform falls below an acceptable level.

[0056] The propagation state of noise waves NS and sound waves SW from the substation 30 to the outside area may change depending on the external environment (e.g., temperature) of the substation 30. Therefore, the magnitude of noise in the outside area may also change to some extent depending on the environment. As a result, if the environment changes after the basic settings for the phase and amplitude adjustment amounts in the adjustment unit 130 have been determined, the magnitude of noise in the outside area may change. In this modified example, even in such cases, the user can specify the adjustment amount in the adjustment unit 130 according to the daily environment. This allows the user to perform final fine-tuning of the phase and amplitude of sound waves SW to specify the optimal adjustment amount, even after the basic settings have been determined. Therefore, it is possible to appropriately address changes in the environment and reduce noise in the outside area. [Differentiation Example 4] Figures 4 to 7 illustrate the configuration and advantages of a noise reduction system according to this modified example. Referring to Figure 4, noise reduction system 80A differs from noise reduction system 80 in that it includes signal processing devices 100a, 100b and speakers 200a, 200b. Noise reduction system 80A is the same as noise reduction system 80 in that it includes a three-phase transformer 35, an instrument transformer 37, an instrument current transformer 38, a noise sensor 60, an input device 300, and a display device 350.

[0057] Each of the signal processing devices 100a and 100b has the same configuration as the signal processing device 100, specifically including a generation unit 110, an adjustment unit 130, and a drive unit 150 (Figure 2). On the other hand, the amount of phase and amplitude adjustment in the adjustment unit 130 of the signal processing device 100a is different from the amount of phase and amplitude adjustment in the adjustment unit 130 of the signal processing device 100b. The amount of adjustment in the signal processing devices 100a and 100b may be predetermined in prior evaluation tests, etc., or may be determined each time using the input device 300.

[0058] The drive unit 150 of the signal processing device 100a generates a drive signal DSa as a drive signal DS for driving the speaker 200a. The drive unit 150 of the signal processing device 100b generates a drive signal DSb as a drive signal DS for driving the speaker 200b. Drive signals DSa and DSb correspond to examples of the "first drive signal" and "second drive signal" in this disclosure, respectively.

[0059] Speakers 200a and 200b each have the same configuration as speaker 200 and generate sound waves SW according to the drive signal DS. Specifically, speaker 200a generates sound wave SW (SWa) according to the drive signal DSa, and speaker 200b generates sound wave SW (SWb) according to the drive signal DSb.

[0060] The phase and amplitude of the drive signal DSa can be adjusted by setting the adjustment amounts for phase and amplitude in the adjustment unit 130 of the signal processing device 100a. This allows the phase and amplitude of the sound wave SWa to be adjusted. Similarly, the phase and amplitude of the drive signal DSb can be adjusted by setting the adjustment amounts for phase and amplitude in the adjustment unit 130 of the signal processing device 100b. This allows the phase and amplitude of the sound wave SWb to be adjusted. Thus, in this modified example 4, the phase and amplitude of the sound wave SWa and the phase and amplitude of the sound wave SWb can be adjusted separately. Note that distance D is the distance between the three-phase transformer 35 and the interface BD (or position P1).

[0061] Referring to Figure 5, the noise wave NS is actually emitted from multiple locations on the three-phase transformer 35. For example, noise wave NS(NSa) is emitted from location sp1 on the three-phase transformer 35, and noise wave NS(NSb) is emitted from location sp2 on the three-phase transformer 35. In reality, noise waves NS are also emitted from locations other than sp1 and sp2, but for ease of understanding, only noise waves NSa and NSb are shown.

[0062] Referring to Figure 6, when the distance D is sufficiently long, the three-phase transformer 35 (substation equipment 30) can be treated as a single sound source, and differences in the location of the noise wave NS can be practically ignored. In this case, the noise level at each location within the external area is not significantly affected by differences in the location of the noise wave NS.

[0063] Referring to Figure 7, when the distance D is relatively short, differences in the origin of noise waves NS can affect the noise level at each location in the external area. For example, the noise level at location P1 is influenced not only by noise wave NSa from location sp1 but also by noise wave NSb from location sp2.

[0064] According to Modification 4, the optimal adjustment amount in the adjustment unit 130 of the signal processing device 100a and the optimal adjustment amount in the adjustment unit 130 of the signal processing device 100b are determined separately. As a result, in the external area, the noise wave NSa from point sp1 can be appropriately canceled by the sound wave SWa, and the noise wave NSb from point sp2 can be appropriately canceled by the sound wave SWb.

[0065] If, as described above, the phase and amplitude of sound wave SWa and the phase and amplitude of sound wave SWb are not adjusted separately (for example, if a single drive signal DS from a single signal processing device 100 is supplied directly to both speakers 200a and 200b), even if the noise wave NSa from point sp1 is properly canceled by sound wave SWa, the noise wave NSb from point sp2 may not be properly canceled by sound wave SWb. As a result, depending on the interference state between noise wave NSb and sound wave SWb, the noise at point P1 may even be amplified. In contrast, this modified example avoids such a situation and can appropriately reduce the noise level even when the distance D is short and differences in the source locations of noise waves NS can affect the noise level.

[0066] In the above description, the noise reduction system 80A is said to consist of two signal processing devices 100 and two speakers 200, but it may also consist of n (n≧3) signal processing devices 100 and n speakers 200 driven by these signal processing devices 100. In this case as well, the optimal adjustment amount in the adjustment unit 130 of each signal processing device 100 is determined separately, and the phase and amplitude of the sound wave SW from the n speakers 200 are also adjusted separately. As a result, noise can be effectively reduced as described above. [Other variations] Referring again to Figure 2, the instrument current transformer 38 may be provided on the primary side of the three-phase transformer 35. In this case as well, the filter circuits 120a to 120e operate upon receiving the output signal SG2. Thus, the instrument current transformer 38 is provided on either the primary or secondary side of the three-phase transformer 35.

[0067] In this embodiment, the amplitude adjustment circuit 145i is connected to the output of the phase adjustment circuit 140i in the adjustment unit 130, but it may also be connected to the input of the phase adjustment circuit 140i. In this case, the amplitude adjustment circuit 145i adjusts the amplitude of the signal according to the frequency signal input to the amplitude adjustment circuit and generates a signal with the adjusted amplitude. The phase adjustment circuit 140i generates the adjusted signals S1j, S3a to S3e by adjusting the phase of the signal thus generated and supplies them to the drive unit 150.

[0068] In this embodiment, the generation unit 110 includes both signal generators 115x and 115a to 115e, but it may also consist of only signal generator 115x or only signal generators 115a to 115e.

[0069] For example, if the generation unit 110 consists only of a signal generator 115x, then the adjustment unit 130 also consists only of a phase / amplitude adjuster 135x. In this case, the combining circuit 160 is not essential, and the phase / amplitude adjuster 135x generates an adjusted signal S1j according to the frequency signal S1 from the signal generator 115x. The adjusted signal S1j is then input directly to the amplification circuit 180, thereby generating the drive signal DS. Even in such a configuration, the aforementioned first noise component can be effectively reduced by appropriately determining the adjustment amount in the phase / amplitude adjuster 135x.

[0070] If the generation unit 110 consists only of signal generators 115a to 115e, then the adjustment unit 130 also consists only of phase and amplitude adjusters 135a to 135e. In this case, the phase and amplitude adjusters 135a to 135e generate adjusted signals S3a to S3e according to the frequency signals S2a to S2e from the signal generators 115a to 115e. These adjusted signals are combined in the combining circuit 160, and the combined signal SS, which is the superposition of these adjusted signals, is input to the amplification circuit 180, thereby generating the drive signal DS. Even in this configuration, the aforementioned second noise component can be effectively reduced by appropriately determining the adjustment amount in the phase and amplitude adjusters 135a to 135e.

[0071] The signal processing device 100 may further include an A / D (Analog-to-Digital) converter and a D / A (Digital-to-Analog) converter (neither of which are shown). In this case, the functions of the generation unit 110, the adjustment unit 130, and the synthesis circuit 160 are implemented on a DSP (Digital Signal Processor). The A / D converter converts the output signals SG1 and SG2 into digital signals. The DSP generates a processed signal (discrete signal) by applying digital signal processing corresponding to the above functions to the digital signals. The D / A converter converts the processed signal into an analog signal corresponding to the synthesis signal SS. The amplification circuit 180 generates a drive signal DS by amplifying the analog signal. The DSP performs digital signal processing so that the phase of the sound wave SW from the speaker 200 is inverse phase with the noise wave NS, and the noise level in the external area is appropriately reduced. In this example as well, the correlation between digital signal processing and the noise level is quantitatively understood in evaluation tests, etc. Then, the content of the digital signal processing is determined so that noise in the external area is minimized.

[0072] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0073] 1 Power transmission and distribution system, 10 AC power supply, 20 power transmission line, 25U, 25V, 25W, 45U, 45V, 45W power line, 30 substation equipment, 35 three-phase transformer, 37 instrument transformer, 38 instrument current transformer, 60 noise sensor, 80, 80A noise reduction system, 100, 100a, 100b signal processing device, 110 generation unit, 130 adjustment unit, 150 drive unit, 200, 200a, 200b speaker, 300 input device, 350 display device.

Claims

1. A noise reduction system for reducing noise from a three-phase transformer, A signal processing device that receives an output signal corresponding to the output of an instrument transformer provided on the primary or secondary side of the three-phase transformer, The system includes a speaker connected to the output of the signal processing device, The signal processing device is A generation unit generates a frequency signal having twice the frequency of the fundamental wave of the three-phase AC flowing through the three-phase transformer or twice the frequency of the harmonics of the three-phase AC, according to the output signal. An adjustment unit that generates an adjusted signal having the adjusted phase and amplitude by adjusting the phase and amplitude of the frequency signal, A noise reduction system including a drive unit that generates a drive signal for driving the speaker according to the adjusted signal.

2. The instrument transformer includes an instrument transformer provided on the primary side of the three-phase transformer. The noise reduction system according to claim 1, wherein the generation unit generates a first signal having twice the frequency of the fundamental wave as the frequency signal, according to a first output signal which is an output signal corresponding to the output of the instrument transformer.

3. The instrument transformer includes an instrument current transformer, The generation unit generates a plurality of second signals, each of which is the frequency signal, according to a second output signal, which is an output signal corresponding to the output of the instrument current transformer. The adjustment unit generates a plurality of third signals, each of which is the adjusted signal, by adjusting the phase and amplitude of the plurality of second signals. The aforementioned drive unit is A synthesis circuit that generates a composite signal by combining the plurality of third signals, the plurality of third signals being superimposed, The noise reduction system according to claim 1 or claim 2, further comprising an amplification circuit that generates the drive signal by amplifying the composite signal.

4. The generation unit generates a plurality of second signals, including a frequency signal having twice the frequency of the fundamental wave and a frequency signal having twice the frequency of the harmonic. The noise reduction system according to claim 3, wherein the harmonics include at least one of the 5th, 7th, 11th, and 13th harmonics of the three-phase AC.

5. The noise reduction system according to claim 1, further comprising an input device for receiving user input specifying the amount of phase and amplitude adjustment in the adjustment unit.

6. The speaker includes a first speaker and a second speaker different from the first speaker. The signal processing device is A first signal processing device that generates a drive signal for driving the first speaker, The noise reduction system according to claim 1, further comprising a second signal processing device for generating a drive signal for driving the second speaker.

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