WO2008093917A1

WO2008093917A1 - Active type noise attenuation device for transformer, active type noise attenuation device for transformer with soundproof part, active type noise attenuation device for transformer with soundproof part and sound absorbing device

Info

Publication number: WO2008093917A1
Application number: PCT/KR2007/002973
Authority: WO
Inventors: Young Dal Kim; Jun Shin Lee; Gyung Duck Ahn
Original assignee: Hanbat National University Industrial-Academic Cooperation Foundation
Priority date: 2007-01-29
Filing date: 2007-06-20
Publication date: 2008-08-07
Also published as: KR100704555B1

Abstract

The present invention relates to a noise attenuation device of an active type for a transformer, and in particular, relates to a noise attenuation device of an active type for a transformer for attenuating noises of the transformer in operation, which is characterized in that it comprises a control speaker 10 for generating a control sound to cancel a main noise having a plurality of frequency components radiated from a noise source 1 of the transformer; an error microphone 20 for detecting a difference between the main noise radiated from the noise source 1 and arrived via a arrival path 43 of the noise source, and the control sound radiated from the control speaker 10 and arrived via a arrival path 43 of the control sound and for outputting an error signal 22 indicating the difference; and a controller 30 for receiving and processing a reference signal 2 extracted from the noise source 1 of the transformer, and the error signal 22, and including a plurality of cancelling algorithms generating control signals 35, 35a, 35b, 35c applied to the speaker 10 for reducing the error signal 22.

Description

Active type noise attenuation device for transformer, active type noise attenuation device for transformer with soundproof part, active type noise attenuation device for transformer with soundproof part and sound absorbing device

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0009098, filed 29. 01, 2007 and, the entire content of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an attenuation device of an active type for a transformer, an attenuation device of an active type for a transformer having a soundproof member, and an attenuation device of an active type for a transformer having a soundproof and a sound absorption device.

2. Description of the Related Art One of the principles of an active sound control is to superimpose the signals of a second sound source that is same to the size of a first sound source, but is inverse to the phase thereof, and noises are reduced by introducing an offset interruption based on this superposition principle. This phenomenon is related to an active attenuation concept of a sound which allows artificial acoustics and noises to be mixed and an offset interruption to be introduced, and it is illustrated in the drawings.

FIG. 17 illustrates a schematic diagram for explaining the principles of an active sound control of a conventional duct. The FIG. 17 explains the concept of a noise control in a duct, and illustrates the state that a noise in the duct progresses as a plane wave from a left direction to a right direction like a sound source A. Here, a microphone M detects a sound in a space, and transmits the noise signal which is converted into an electrical signal to a speaker L via a controller C.

The speaker outputs the control wave that is inverted for the phase of a noise of a sine wave, and the noises and the inverted sound waves are superimposed in the vicinity of the speaker. Thus, an offset interruption is generated, and thereby, a silence zone is created below the speaker.

The conventional active noise control is executed on only one frequency, and thus, it was difficult to apply it to a process for controlling a noise source of a transformer having a plurality of peak frequencies. Further, a research & development for controlling a noise source of a transformer having a plurality of peak frequencies by using an attenuation device of an active type have not been performed in Korea.

According to the present invention, a noise source of a transformer having a plurality of peak frequencies is controlled by a noise attenuation device of an active type for a transformer, and a soundproof member and a sound absorption device the effects of which are not guaranteed because a control using a noise attenuation device of an active type is influenced by very various sensitive factors are reinforced. The present invention is a final product obtained as a result of developing a noise attenuation system for a transformer exhibiting stable performances to absorb and block the sounds within a wide range of frequency.

SUMMARY OF THE INVENTION The object of the present invention is to provide a noise attenuation device of an active type for a transformer for attenuating noised generated by a noise source of a transformer having a plurality of peak frequencies. Another object of the present invention is to provide a noise attenuation device of an active type for a transformer in which a control device is driven by automatically searching a frequency of a control target in connection with a noise attenuation device of an active type for a transformer for attenuating noised generated by a noise source of a transformer having a plurality of peak frequencies. Another object of the present invention is to provide a noise attenuation system of an active type for a transformer having a soundproof member and exhibiting stable performances within a wide range of frequency by reinforcing the high frequency portions the effects of which are not guaranteed because a control using a noise attenuation device of an active type is influenced by very various sensitive factors by a soundproof member. Another object of the present invention is to provide a noise attenuation system of an active type for a transformer having a soundproof member and a sound absorption device in which a low frequency bandpass can be controlled actively, and a middle and high frequency bandpass can be controlled by the soundproof member and the absorption device. Another object of the present invention is to provide a noise attenuation system of an active type for a transformer in which a step for tuning a sound absorption device of a resonance type is easily performed, performances of the absorption device of a resonance type are multiplied, and a soundproof member and a sound absorption device can be easily mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a block diagram of a noise attenuation device of an active type for a transformer according to an embodiment of the present invention. FIG. 2 illustrates a block diagram showing a function to set a lower limit frequency and a upper limit frequency of a bandpass filter according to an embodiment of the present invention.

FIG. 3 illustrates a flowchart showing a step for setting a lower limit frequency and a upper limit frequency of a bandpass filter according to an embodiment of the present invention. FIG. 4 illustrates a diagram showing a noise level for each frequency of a 95 transformer.

FIG. 5 illustrates a diagram showing a transmission path and a shock response in an open space.

FIG. 6 illustrates a diagram showing a transmission path and a shock response in a closed space. 100 FIG. 7 illustrates a diagram of a noise source of a transformer having a plurality of peak frequency components 120Hz, 240Hz, 360Hz, and 480Hz before a noise attenuation device of an active type for a transformer according to an embodiment of the present invention starts to operate.

FIG. 8 illustrates a test result obtained when a noise attenuation device of an 105 active type for a transformer according to an embodiment of the present invention is applied to a noise source of a transformer having a plurality of peak frequency components 120Hz, 240Hz, 360Hz, and 480Hz, and then starts to operate.

FIG. 9 illustrates a diagram of a noise source of a transformer having a single 110 peak frequency component 120Hz before a noise attenuation device of an active type for a transformer according to an embodiment of the present invention starts to operate.

FIG. 10 illustrates a test result obtained when a noise attenuation device of an active type for a transformer according to an embodiment of the present 115 invention is applied to a noise source of a transformer having a single peak frequency component 120Hz and then starts to operate.

FIG. 11 illustrates a diagram of a sound pressure level before a sound absorption device according to an embodiment of the present invention is applied. 120 FIG. 12 illustrates a diagram of a sound pressure level after a sound absorption device according to an embodiment of the present invention is applied.

FIG. 13 illustrates a front diagram of a noise attenuation device of an active type for a transformer including a soundproof member and a sound absorption device according to an embodiment of the present invention which is applied to 125 a transformer.

FIG. 14 illustrates a diagram for explaining a duct unit and a sound absorption device according to an embodiment of the present invention.

FIG. 15 illustrates a block diagram of a noise attenuation device of an active type for a transformer according to an embodiment of the present invention. 130 FIG. 16 illustrates a diagram for explaining a tuning concept of a noise attenuation device of an active type for a transformer according to an embodiment of the present invention.

FIG. 17 illustrates a diagram for explaining the principles of an active sound control of a conventional duct. 135

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In order to accomplish above objects of the present invention, a noise attenuation device of an active type for a transformer according to an embodiment of the present invention is a noise attenuation device of an active 140 type for a transformer for attenuating noises of the transformer in operation, and is characterized in that it includes a control speaker 10 for generating a control sound to cancel a main noise having a plurality of frequency components radiated from a noise source 1 of the transformer; an error microphone 20 for detecting a difference between the main noise radiated from the noise source 1

145 and arrived via a arrival path 43 of the noise source, and the control sound radiated from the control speaker 10 and arrived via a arrival path 43 of the control sound and for outputting an error signal 22 indicating the difference; and a controller 30 for receiving and processing a reference signal 2 extracted from the noise source 1 of the transformer, and the error signal 22, and

150 including a plurality of cancelling algorithms generating control signals 35, 35a,

35b, 35c applied to the speaker 10 for reducing the error signal 22.

Below, the structure and the operations of a noise attenuation device of an active type for a transformer according to the present invention will be explained in detail with referring to the attached drawings.

155 FIG. 1 illustrates a block diagram of a noise attenuation device of an active type for a transformer according to an embodiment of the present invention.

As illustrated in FIG. 1, the control speaker 10 generates a control signal cancelling a main noise having a plurality of frequency components

160 radiated from the noise source 1 of the transformer.

As illustrated in FIG. 1, the error microphone 20 detects a difference between the main noise radiated from the noise source 1 and arrived via a arrival path 43 of the noise source 1 at a destination point 45 that is a target of a noise attenuation and the control sound radiated from the control speaker 10

165 and arrived via a arrival path 43 of the control sound and then outputs an error signal 22 indicating the difference.

As illustrated in FIG. 1, the controller 30 includes a plurality of cancelling algorithms, and the controller 30 including a plurality of cancelling algorithms receives and processes a reference signal 2 extracted from the noise

170 source 1 of the transformer, and the error signal 22 so that the control signals 35,

35a, 35b, 35c applied to the speaker 10 can be generated for reducing the error signal 22. The cancelling algorithms are arranged in parallel.

As illustrated in FIG. 1, the reference signal 2 passes through at least two filters of bandpass filters 11, 12, 13 arranged in parallel, and a plurality of

175 reference signals 2a, 2b 2c passing through the bandpass filters 11, 12, 13 are received by the controller 30 having at least two algorithms of cancelling algorithms 31 , 32, 33 arranged in parallel, respectively.

Further, the error signal 22 passes through at least two filters of bandpass filters 11', 12', 13' arranged in parallel, and a plurality of error signals

180 22a, 22b 22c passing through the bandpass filters 11', 12', 13' are received by the controller 30 having at least two algorithms of cancelling algorithms 31, 32, 33 arranged in parallel, respectively.

The cancelling algorithms 31, 32, 33 generates control signals 35a, 35b, 35c corresponding to each frequency band for reducing the error signals 22a,

185 22b 22c passing through the bandpass filters 11', 12', 13' by using the reference signals 2a, 2b, 2c passing through the bandpass filters 11, 12, 13, and the error signals 22a, 22b 22c passing through the bandpass filters 11', 12', 13'.

The plurality of control signals 35a, 35b, 35c generated as above is combined as one control signal 35, and is applied to the control speaker 10.

190 The error signal 22 passes through an error signal amplifier 24 before passing through the plurality of bandpass filters 11', 12', 13', and the control signal can pass through a control signal amplifier 41 (for example, a power amplifier) before being applied to the control speaker 10.

The reference signal 2 can be any one selected from a current of the

195 transformer, and an accelerated velocity of vibration of the transformer, and in case of an accelerated velocity of vibration, the reference signal 2 is sensed by an accelerometer, and it is preferable that the reference signal 2 pass through a bandpass filter after passing through the signal amplifier.

FIG. 2 illustrates a block diagram showing a function to set a lower

200 limit frequency and a upper limit frequency of a bandpass filter according to an embodiment of the present invention. FIG. 3 illustrates a flowchart showing a step for setting a lower limit frequency and a upper limit frequency of a bandpass filter according to an embodiment of the present invention.

As illustrated in the drawings, the controller 5 has an automatic setting

205 function for automatically setting a lower limit frequency and a upper limit frequency of the bandpass filters 11, 12, 13 through which the reference signal 12 passes.

As illustrated in FIG. 3, the automatic setting function is realized by a frequency analysis step 101 for obtaining an amplitude level for each frequency

210 of the reference signal 2; a searching and selecting step 103 for searching and selecting N peak frequency components exceeding a constant reference level by using the amplitude level for each frequency acquired in the frequency analysis step; and a setting step 105 for allowing one peak frequency component of N peak frequency components to be passed, and for setting the lower limit

215 frequency and the upper limit frequency of the bandpass filters 11, 12, 13 so that the other N-I peak frequency components can be excluded, and the lower limit frequency and the upper limit frequency of the bandpass filters are characterized in that they are set before the reference signal 2 passes through the bandpass filters 11, 12, 13.

220 A frequency of the control signal 35, 35a, 35b, 35c applied to the control speaker 10 can be at least one frequency selected from a frequency group consisting of 120Hz, 240Hz, 360Hz, and 480Hz, and this is related to the features of a main noise of a transformer which will be explained below.

For controlling the noises of a transformer, an optimum control method

225 should be studied by analyzing the features of the noises, and finding the noise sources, and a frequency bandpass suitable for an active noise control must be verified through frequency analysis of the noises.

For this purpose, a noise signal of a transformer is acquired and a wave shape of a frequency is analyzed, and generally, the noise of a transformer

230 consists of summation of sine waves having a plurality of constant frequencies.

During a process for realizing an algorithm in a real time basis, a second transmission path must be examined in advance by an off-line system. In connection with an error path generated due to an acoustics space between the control speaker 40 and the error microphone 20, there are very tremendous

235 differences between the case that the error path is an open space, and the case that the error path is a closed space.

In case of the open space, there exists a feature that a region of normal sound is expanded, and in case of the closed space, there exists a feature that a mode is created because of a standing wave generated due to reflection by a 240 wall, and a acoustics property is changed at each space position.

In the present invention, a frequency which is a control target is limited for a noise control in an audible frequency bandpass.

It is preferable that a target region is set to a room of a limited size when controlling the noises in the closed space, and at this time, it is preferable

245 that the error microphone 20 is arranged at a position adjacent to the control speaker 10 in order to overcome the difficult problems generated by the created mode.

Features of a noise source of a transformer

250 A noise source of a transformer is generated when a wave shape of a transmission power vibrates a core, a coil and a main body of a transformer. At this time, since the core is vibrated at the frequency corresponding to two times of a frequency of the transmission power, the noise consists of harmonics components of double frequency. For example, since a transmission power

255 of 60Hz is used in Korea, the core vibrates at the frequency of 120Hz, and thus, the noises containing the sine waves such as the harmonics components, that is, 240Hz, 360Hz, and 480Hz are generated, and a frequency spectrum of the noises is illustrated in FIG. 4.

The noises of a transformer consist of harmonics components, and a

260 sound pressure level of all noises is defined as a summation of logarithm of the sound pressure levels of the sine waves. In the drawings, it is apparent that the main components of the noises of a transformer are 120Hz, 240Hz, and 360Hz when comparing the sizes of each frequency. The sizes of sound pressure levels of various components are determined by the structure of a transformer.

265 Other harmonics components of a high frequency are absorbed by an air and a wall, and since the component of 60Hz can not be well recognized, a noise component in which three sine waves of 120Hz, 240Hz, and 360Hz are mixed is selected as a target of an active noise control.

In such a noise having a low frequency below 500Hz, since an active

270 noise control is very suitable, when realizing a real-time system, only a low frequency which passes through a LPF must be used to exclude high frequency components.

An analysis of sound fields of an open space and a close space.

275 FIG. 5 illustrates a diagram showing a transmission path and a shock response in an open space. FIG. 6 illustrates a diagram showing a transmission path and a shock response in a closed space.

The transmission path in an open space where a sine wave can be propagated without stumbling blocks or reflecting objects is relatively simple.

280 When a sine wave generated in a speaker reaches a sensor, the shape of the sine wave is not changed, and is only delayed due to a spatial distance during propagation. As illustrated in FIG. 5, the sine waves radiated to the open space reaches the sensor via a direct transmission path after a constant delay of a

285 sample regardless of frequency. Such a simple sound field can be easily controlled and it becomes also easy to realize a system in which a sensor is arranged in a target region for normal sounds.

But, the closed sound field surrounded by the reflecting walls is very complicated because of a mode in which a sine wave is formed as a

290 three-dimensional type due to reflection. FIG. 6 illustrates a diagram showing a transmission path and a shock response in a closed space. As illustrated in FIG. 6, the sine wave generated in a speaker reaches the sensor via the direct transmission path, and also passes through an indirect path where the sine wave is reflected on a wall and then reaches.

295 A reflected sound generates a second reflection sound, and reaches the sensor after passing through numerous distortions. The shock response is affected by a plurality of reflected sound components as well as a simple delay. One reason which makes it much more difficult to control a sound field of a closed space is ascribed to existence of such a mode, and the sine wave in the

300 closed space forms a standing wave due to reflection on a wall.

In connection with the standing waves each of which has a constant wavelength, superposition and interruption are generated by same components, and a point where a sound pressure is large, and a point where the sound pressure is small are generated. This mode is indicated as a very complicated

305 type and thus, it becomes difficult to make a modelling if it is expanded into a three-dimension.

Therefore, when the noises are generated in the closed space, there exists a difference among the recognized sound pressures. Therefore, it is expected that a large attenuation is performed in a wide region since a larger

310 noise can be extracted by arranging the sensor in a point where a sound pressure is large if possible when controlling the noises.

The error microphone 20 must be arranged in a point where a largest level of the sound pressure levels is indicated in a space through a mode analysis, and if it is judged that the analysis is difficult to execute, the sensor

315 must be arranged on a wall side having a large sound pressure level because of reflection. But, since distribution of such a mode is changed into a totally different type when the roadblocks are provided in a space, and each frequency has a completely different distribution, when numerous frequencies are mixed, it is terribly difficult to spot a point where the positions of a maximum sound

320 pressure level for each frequency are consistent with each other.

Since a position selection of the error microphone 20 becomes difficult due to a complicated mode in a close space, an algorithm of a utterly different type is employed to control the noises. This type is a method which measures an energy of a constant noise, and designates the measured energy as

325 a control target without designating the sound pressure for which a level changes at every measured position as a control target. However, there are drawbacks that it is difficult to measure the energy, and it becomes complicated to realize a system.

In the present study, in order to solve this problem, the error phone 20 330 should be arranged in a position adjacent to a speaker that generates an artificial sound, and a noise source if possible, and it is also to be positioned by measuring a point where a sound pressure level of a noise is large.

Test results of a noise attenuation device of an active type for a transformer

335 FIG. 7 illustrates a diagram of a noise source of a transformer having a plurality of peak frequency components 120Hz, 240Hz, 360Hz, and 480Hz before a noise attenuation device of an active type for a transformer according to an embodiment of the present invention starts to operate. FIG. 8 illustrates a test result obtained when a noise attenuation device of an active

340 type for a transformer according to an embodiment of the present invention is applied to a noise source of a transformer having a plurality of peak frequency components 120Hz, 240Hz, 360Hz, and 480Hz, and then starts to operate.

FIG. 9 illustrates a diagram of a noise source of a transformer having a single peak frequency component 120Hz before a noise attenuation device of an

345 active type for a transformer according to an embodiment of the present invention starts to operate. FIG. 10 illustrates a test result obtained when a noise attenuation device of an active type for a transformer according to an embodiment of the present invention is applied to a noise source of a transformer having a single peak frequency component 120Hz and then starts to

350 operate.

The experiment 1(FIG. 7. and FIG. 8) are the test results obtained by executing an active noise control when the noises of 120Hz, 240Hz, 360Hz, and 480Hz are generated like the noises generated in a transformer. In this case, the total noise generation decibel was 84.6dB, and a total noise is reduced to

355 65dB(that is, 2OdB is attenuated.) in terms of a noise reduction effect, and the total noise is reduced to 47.5dB(that is, 37dB is attenuated.)around the error microphone 20.

Accordingly, the noises are attenuated by 20dB-37dB.

The experiment 2(FIG. 9. and FIG. 10) are the test results obtained by

360 obtained by executing an active noise control when generating a sound of a low frequency, that is, only 120Hz of the noises generated in a transformer which gives extremely much stress to a human being.

In this case, the total noise generation decibel was 81.2dB, and a total noise is reduced to 46.9dB(that is, 34.3dB is attenuated.) in terms of a noise

365 reduction effect, and the total noise is reduced to 44.5dB(that is, 36.7dB is attenuated.)around the error microphone 20.

Accordingly, it was confirmed that the noises are attenuated by 34dB-36dB.

Test results obtained by using a sound absorption device.

370 FIG. 11 illustrates a diagram of a sound pressure level before a sound absorption device according to an embodiment of the present invention is applied. FIG. 12 illustrates a diagram of a sound pressure level after a sound absorption device according to an embodiment of the present invention is applied.

375 As illustrated in FIG. 11 and FIG. 12, you can be aware of the fact that

15dB is attenuated as a noise attenuation result obtained by using a sound absorption device.

FIG. 13 illustrates a front diagram of a noise attenuation device of an active type for a transformer including a soundproof member and a sound

380 absorption device according to an embodiment of the present invention which is applied to a transformer. FIG. 14 illustrates a diagram for explaining a duct unit and a sound absorption device according to an embodiment of the present invention. FIG. 15 illustrates a block diagram of a noise attenuation device of an active type for a transformer according to an embodiment of the present

385 invention.

As illustrated in FIG. 13, the attenuation device of an active type for a transformer can further include a soundproof member 50 surrounding a periphery of the transformer while forming an intake valve 51 and an exhaust valve 53 for cooling the transformer.

390 It is preferable that the error microphone 20 of the attenuation device of an active type for a transformer is positioned in the vicinity of a point selected from the intake valve 51 and the exhaust valve 53. Therefore, it is possible to block a sound radiation effectively by designating the intake valve 51 and/or the exhaust valve 53 as a control target.

395 The attenuation device of an active type for a transformer can further include a soundproof member 50 surrounding a periphery of the transformer while forming an intake valve 51 and an exhaust valve 53 for cooling the transformer, and a duct unit 60, 60' extending to outside from a point selected from the intake valve 51 and the exhaust valve 53.

400 The sound absorption device 70 of a resonance type having a plurality of resonance chambers 71 and a neck 73 are provided in the duct unit 60. It is preferable that the error microphone 20 of the attenuation device of an active type for a transformer is positioned in the vicinity of an end of an external side of the duct unit 60, 60'. Therefore, it is possible to block a sound radiation of

405 a transformer effectively by designating a destination position of a control target as a portion adjacent to an end of an external side of the duct unit 60, 60'. In connection with the adjacent portion, an acoustics must be considered, and if a fact that a frequency of a control target ranges from 120Hz to 300Hz is considered, it means a range between 0-100cm.

410 It is preferable that the duct unit 60 is separated by a separation plate

66, and the resonance chamber 71 of the sound absorption device 70 of a resonance type is arranged as a format of columns corresponding to a number of spaces of the separated duct unit 60.

As a ratio between a horizontal cross-section of the duct unit 60 of a

415 resonator and an area of the neck 73 is getting larger and larger, a noise blocking performance of the sound absorption device 70 of a resonance type increases. Therefore, it is possible to increase a noise reduction performance by reducing the horizontal cross-section of the duct unit 60 by using the separation plate 66 without blocking flow of an air completely.

420 The sound absorption device 70 of a resonance type includes a connection means for connecting the separated neck 73 to an aperture 75 such that the neck 73 can be selectively mounted on the aperture 75. Therefore, it can be formed such that a peak of the main noise source which is formed as a multiple of a basic frequency can be tuned easily.

425 For example, when the sound absorption device 70 of a resonance type having a predetermined specification, for example, two resonators having a resonance frequency of 240Hz, two resonators having a resonance frequency of 360Hz, and two resonators having a resonance frequency of 480Hz is produced and then sold, there may be cases that 240Ha and 360Hz components of a noise

430 frequency characteristics of a transformer are not so superb and the components can be controlled excellently by a noise attenuation device of an active type. In this case, two resonators having a resonance frequency of 240Hz, and two resonators having a resonance frequency of 360Hz occupy spaces meaninglessly and thus can not function normally. Therefore, the technician

435 who installs the two resonators having a resonance frequency of 240Hz, and two resonators having a resonance frequency of 360Hz feels the necessity to replace them with two resonators having a resonance frequency of 480Hz. At this time, if a connection means is provided for connecting the separated neck 73 to an aperture 75 such that a plurality of necks 73 can be selectively

440 mounted on the aperture 75, the technician can replace two resonators having a resonance frequency of 240Hz, and two resonators having a resonance frequency of 360Hz with two resonators having a resonance frequency of 480Hz easily so that the sound absorption device 70 of a resonance type may have a noise characteristics which a tremendous reduction effect is exhibited in

445 a 480Hz bandpass.

Further, when the neck 73 can be selectively mounted on and removed from the aperture 75 by arranging the connection means(for example, by forming the screw threads on an exterior periphery of a lower side of the neck, and forming the screw threads on an interior periphery of the aperture 75), there

450 is a merit that a frequency tuning operation of a resonator can be remarkably easily performed.

FIG. 16 illustrates a diagram for explaining a tuning concept of a noise attenuation device of an active type for a transformer according to an embodiment of the present invention. Theoretically, when a neck of a

455 resonator is positioned at a point where an amplitude of an inherent pressure mode formed inside a duct is largest, it is widely known that a noise reduction(or a sound absorption) characteristics is maximized. For example, if the inherent pressure mode formed inside a duct is identical to the case of FIG. 16, when arranging a resonator having a resonance frequency of 240Hz in

460 L2 region, arranging a resonator having a resonance frequency of 360Hz in L3 region, and arranging a resonator having a resonance frequency of 480Hz in Ll region, the noise reduction characteristics is maximized. When

Claims

WHAT IS CLAIMED IS:

1. A noise attenuation device of an active type for a transformer for attenuating 465 noises of the transformer in operation comprising, a control speaker 10 for generating a control sound to cancel a main noise having a plurality of frequency components radiated from a noise source 1 of the transformer; an error microphone 20 for detecting a difference between the main noise 470 radiated from the noise source 1 and arrived via a arrival path 43 of the noise source, and the control sound radiated from the control speaker 10 and arrived via a arrival path 43 of the control sound and for outputting an error signal 22 indicating the difference; and a controller 30 for receiving and processing a reference signal 2 extracted from 475 the noise source 1 of the transformer, and the error signal 22, and including a plurality of cancelling algorithms generating control signals 35, 35a, 35b, 35c applied to the speaker 10 for reducing the error signal 22.

2. The attenuation device of an active type for a transformer set forth in the claim 1, wherein the reference signal 2 passes through at least two filters of

480 bandpass filters 11, 12, 13 arranged in parallel, and a plurality of reference signals 2a, 2b 2c passing through the bandpass filters 11, 12, 13 are received by the controller 30 having at least two algorithms of cancelling algorithms 31, 32, 33 arranged in parallel, respectively; the error signal 22 passes through at least two filters of bandpass filters 11', 12',

485 13' arranged in parallel, and a plurality of error signals 22a, 22b 22c passing through the bandpass filters 11', 12', 13' are received by the controller 30 having at least two algorithms of cancelling algorithms 31, 32, 33 arranged in parallel, respectively; the cancelling algorithms 31, 32, 33 generates control signals 35a, 35b, 35c

490 corresponding to each frequency band for reducing the error signals 22a, 22b

22c passing through the bandpass filters 11', 12', 13' by using the reference signals 2a, 2b, 2c passing through the bandpass filters 11, 12, 13, and the error signals 22a, 22b 22c passing through the bandpass filters 11', 12', 13'; and the plurality of control signals 35a, 35b, 35c generated as above is combined as

495 one control signal 35, and is applied to the control speaker 10.

3. The attenuation device of an active type for a transformer set forth in the claim 2, wherein the error signal 22 passes through an error signal amplifier 24 before passing through the plurality of bandpass filters 11', 12', 13', and the control signal passes through a control signal amplifier 41 before being applied

500 to the control speaker 10.

4. The attenuation device of an active type for a transformer set forth in the claim 1, wherein the reference signal 2 is any one selected from a current of the transformer, and an accelerated velocity of vibration of the transformer.

5. The attenuation device of an active type for a transformer set forth in the 505 claim 2, wherein the controller 5 has an automatic setting function for automatically setting a lower limit frequency and a upper limit frequency of the bandpass filters 11, 12, 13 through which the reference signal 12 passes, the automatic setting function is realized by a frequency analysis step 101 for obtaining an amplitude level for each frequency of the reference signal 2; a 510 searching and selecting step 103 for searching and selecting N peak frequency components exceeding a constant reference level by using the amplitude level for each frequency acquired in the frequency analysis step; and a setting step 105 for allowing one peak frequency component of N peak frequency components to be passed, and for setting the lower limit frequency and the

515 upper limit frequency of the bandpass filters 11, 12, 13 so that the other N-I peak frequency components can be excluded, and the lower limit frequency and the upper limit frequency of the bandpass filters are set before the reference signal 2 passes through the bandpass filters 11, 12, 13.

520 6. The attenuation device of an active type for a transformer set forth in the claim 1, wherein a frequency of the control signal 35, 35a, 35b, 35c applied to the control speaker 10 is at least one frequency selected from a frequency group consisting of 120Hz, 240Hz, 360Hz, and 480Hz.

7. The attenuation device of an active type for a transformer set forth in any one 525 of the claims 1, 2, 3, and 5, further comprising a soundproof member 50 surrounding a periphery of the transformer while forming an intake valve 51 and an exhaust valve 53 for cooling the transformer; and the error microphone 20 of the attenuation device of an active type for a 530 transformer is positioned in the vicinity of a point selected from the intake valve 51 and the exhaust valve 53.

8. The attenuation device of an active type for a transformer set forth in any one of the claims 1, 2, 3, and 5, further comprising a a soundproof member 50 surrounding a periphery of the transformer while 535 forming an intake valve 51 and an exhaust valve 53 for cooling the transformer, and a duct unit 60, 60' extending to outside from a point selected from the intake valve 51 and the exhaust valve 53; a sound absorption device 70 of a resonance type having a plurality of resonance chambers 71 and a neck 73 are provided in the duct unit 60; and 540 the error microphone 20 of the attenuation device of an active type for a transformer is positioned in the vicinity of an end of an external side of the duct unit 60, 60'.

9. The attenuation device of an active type for a transformer set forth in the claim 8, wherein the duct unit 60 is separated by a separation plate 66, and the

545 resonance chamber 71 of the sound absorption device 70 of a resonance type is arranged as a format of columns corresponding to a number of spaces of the separated duct unit 60.

10. The attenuation device of an active type for a transformer set forth in the claim 9, wherein the sound absorption device 70 of a resonance type includes a

550 connection means for connecting the separated neck 73 to an aperture 75 such that the neck 73 can be selectively mounted on the aperture 75, and thus a peak of the main noise source which is formed as a multiple of a basic frequency can be tuned easily.

11. The attenuation device of an active type for a transformer set forth in the 555 claim 8, wherein a frequency of the control signal 35, 35a, 35b, 35c applied to the control speaker 10 ranges from 120Hz to 240Hz, and a resonance frequency of the sound absorption device 70 of a resonance type is at least one frequency selected from a frequency group consisting of 240Hz, 360Hz, and 480Hz.