EP0083718A1

EP0083718A1 - Noise-reduction device for stationary induction apparatus

Info

Publication number: EP0083718A1
Application number: EP82110831A
Authority: EP
Inventors: Yasuro Hori; Minoru Kanoi; Syuya Hagiwara
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1981-12-02
Filing date: 1982-11-23
Publication date: 1983-07-20
Also published as: JPS5895806A; CA1181013A

Abstract

A noice-reduction device for a stationary induction apparatus is disclosed in which sound insulation panels (4) for reducing the noises radiated from the side walls (2) of a tank (1) are mounted on the reinforcing channel (3) protruded outside of the tank (1) of the induction apparatus. Vibration sensors (5) detect the vibrations transmitted from the tank (1) to the sound insulation panels (4) through the reinforcing channels (3). Vibrators (6) apply vibrations of opposite phase to the vibrations detected by the vibration sensors (5). The vibration sensors (5) and vibrators (6) make up vibration cancelling devices.

Description

The present invention relates to a noise-reduction device for reducing the noises generated from the tank of a stationary induction apparatus such as a transformer or reactor.
With the recent expansion of urban areas and the resultant construction of residential housings near to a power station or substation, the demand has increasingly be raised for reducing the noises generated from stationary induction apparatuses such as the transformer. The noises of the stationary induction apparatuses are caused by the magnetostriction of the core which in turn causes electromagnetic vibrations to be transmitted to the tank through such a medium as oil and are radiated into the atmosphere as a noise from the tank. Various measures have so far been taken to prevent such noises.
In one method, the transformer is installed in a sound-proof building of concrete or steel plates to shut off or absorb the noises. This method has various disadvantage including an increased installation space of the stationary induction apparatus, an increased production cost and a lengthened construction period.
A simple noise-reduction method for stationary induction apparatuses overcoming the above-mentioned disadvantages in which the noises are cancelled by a sound of the phase oposite to the noises of the stationary induction apparatus involved has been suggested by Japanese Patent Publication No. 417/58 published on January 28, 1958, which is based on U.S. Patent Application filed on February 9, 1955 by William B. Conorver and Willard F.M. Gray and assigned to General Electric Company. This method, however, is not yet practically used in view of the fact that the noises generated by an induction apparatus, which is complicated in construction, include a multiplicity of frequency components, thereby making it necessary to provide separate loud speakers for different frequency components, with the result that an increased number of loud speakers are required on the one hand and the adjustment of the frequency and sound volume is complicated on the other hand.
A method to improve this disadvantage is disclosed in U.S. Patent Application Serial No. 279,814 filed on July 2, 1981 by Yasuro Hori et al. and entiled "Vibration/Noise Reduction Device for Electrical Apparatus", in which the vibrations generated in an induction apparatus are detected and the frequency components of the vibrations are determined by Fourier transformation, so that additional vibrations are applied in a manner to cancel the vibrations of the respective frequency components by vibrators mounted on the induction apparatus. This system also requires a number of vibrators as in the case of the above-mentioned Japanese Patent Publication. Further, vibrators of larger power is required to cancel the vibrations of the induction apparatus.
_U.S. Patent co-pending Application Serial No. 406,564 filed August 9, 1982 by Syuya Hagiwara and Yasuro Hori and entitled "Method and Apparatus for Reducing Vibrations of Stationary Induction Apparatus" also discloses a system similar to the one disclosed in U.S. Patent Application Serial No. 279,814, in which the phase and amplitude of the vibrations caused by the vibrators are adjusted advantageously. The above-mentioned problems, however, are not solved even by this suggested method.
Other conventional systems include U.S. Patent Application Serial No. 217,772 filed December 18, 1980 and entitled "Static Induction Apparatus" in which a sound- insulating plate is mounted on the framework such as a reinforcing channel on the outside surface of the tank through an elastic member thereby to reduce the noises produced from the tank, and Japanese Patent Publication No. 87306/81 entitled "Static Induction Apparatus" in which a similar sound-insulation panel is provided with a weighty material thereby to reduce the vibrations trans-. mitted from the tank through the reinforcing channel to the sound insulation panel. The former method has the disadvantage that although the noises (primary noises) radiated by way of the outer wall of the tank through the oil from the winding and core are capable of being reduced, it is impossible to reduce the noises (secondary noises) caused by the vibrations of the sound insulation panels in which the vibrations are transmitted from the outer wall of the tank through the reinforcing channel. In the latter method comprising a sound insulation panel and a weighty material combined which is intended to reduce the secondary noises, on the other hand, the noise reduction level is limited by the physical limitations of the strength or dimensions of the elastic member for carrying the sound insulation panels or the size of the weighty material.
An object of the present invention is to provide a noise-reduction device for stationary induction apparatuses, which obviates the disadvantages of the prior art devices and effectively reduces the noises caused by the tank.
- In order to achieve this object, according to the present invention, there is provided a noise-reduction device, in which the primary noises radiated from the outer wall of the tank are prevented by sound insulation panels mounted on the outer wall of the tank through a framework such as reinforcing channels, and vibration cancelling means including vibration sensors and vibrators are mounted on the sound insulation panels, so that the controlling force of a phase opposite to the vibration transmitted from the tank through the reinforcing channel to the sound insulation panels causing the secondary noises is applied thereto, thus making it possible to cancel the vibrations by a smaller number of vibrators with a smaller controlling force than when the controlling force is applied directly to the tank.
The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

Fig. 1 is a partly cut-away side view showing the general construction of a noise reduction device for a transformer according to an embodiment of the present invention;
Fig. 2 is a partly cut-away perspective view of a noise reduction device on which sound insulation panels and reinforcing channels are mounted;
Fig. 3 is a enlarged sectional view at left hand portion of Fig. 1;
Fig. 4 is a perspective view of the essential parts showing a configuration of a noise reduction device for a transformer according to another embodiment of the present invention; and
Fig. 5 is a central longitudinal sectional view taken parallel to the tank plan view with the noise reduction device of Fig. 4 mounted on the tank through the reinforcing frames.

An embodiment of the present invention will be described below with reference to Figs. 1, 2 and 3.
In these figures, reference numeral 1 designates a transformer tank containing a winding and core 18 and filled with an insulating oil 19. At least a pair of reinforcing channels 3 of U-shaped steel surrounding the tank 1 are securely welded to the side walls 2 of the tank 1 thereby to reinforce the tank 1. A plurarity of sound-insulation panels 4 surrounding the whole periphery of the tank including the main vibration section providing a noise source are mounted in such a manner as to close the part of the side walls 2 between the reinforcing channels 3. At the part of the side walls 2 which is covered by the sound insulation panels 4, as shown by the arrow A in Fig. 3, the primary noises radiated by the vibrations generated from the winding and core 18 and transmitted to the side walls 2 through the insulating oil 19 are blocked by the sound insulation panels 4. The sound insulation panels 4 is preferably made of highly damped plate with resin sandwiched between a pair of steel plates which absorbs vibrations more than an ordinary steel plate.
In this construction, however, although the primary noises caused by the vibrations of the side walls 2 covered by the sound insulation panels 4 are attenuated sufficiently, what is called the secondary noises radiated by the vibrations of the sound insulation panels 4 in which the vibrations are transmitted from the side walls 2 through the reinforcing channels 3 as shown by the arrow B are hardly reduced.
According to the embodiment under consideration, vibration sensors 5 and vibrators 6 are mounted on the sound insulation panels 4, so that detection signals from the vibration sensors 5 are applied to a control signal generator 7, which in turn applies a control signal to the vibrators 6 through an amplifier 8. The vibration transmitted from the reinforcing channels 3 to the sound insulation panels 4 is thus detected by the vibration sensors 5 and a control signal corresponding to the detection signal is generated by the generator 7, which signal, after being amplified by the amplifier 8, is applied to the vibrators 6 to generate vibrations of the phase opposite to the vibrations transmitted to the sound insulation panels 4, thereby cancelling the vibrations of the sound insulation panels 4.
The circuit configuration and the operation of the control signal generator, the amplifier and the vibrators are essentially identical to those of similar devices disclosed in aforesaid U.S. Patent Application Serial No. 279,814, except that according to the present invention, the vibrators are adapted to reduce the vibrations transmitted to the sound insulation panels but not the vibrations of the tank itself and therefore a smaller number of vibrators with a smaller power are used to achieve the object of the invention.
The vibration sensors 4 and the vibrators 5 are mounted on the sound insulation panels 4 in such a manner of construction as shown in Fig. 3. Each of the vibration sensors 5 and the vibrators 6 is held on a mounting plate 9, which is bolted replaceably to the sound insulation panel 4 so that the vibration sensor 5 and the vibrator 6 are situted in the space between the sound insulation panel 4 and the side plate 2 through a hole 10. Lead wires 11, 12 from the vibration sensor 5 and the vibrator 6 are led through a hole 13 into a reinforcing channel 3 and after being wired therein, are connected to the control signal generator 7 and the amplifier 8 together with the lead wires of the other vibration sensors and vibrators.
The advantages of the present invention are described below.

(1) The sound insulation panel 4, which does not participate in the strength of the tank, may be made of a comparatively thin plate and is capable of reducing the vibrations with a small control power as compared with the conventional method in which the control power is applied directly to the outer surface of the tank.
(2) Since the vibrations of the reinforcing channel of comparatively simplified construction provide a source of vibrations of the sound insulation panel, a smaller number of frequency components are contained than the vibrations of the induction apparatus, and therefore a smaller number of vibrators are required than when the vibrations of the induction apparatus are cancelled directly.
(31 The vibration sensors 5 and the vibrators 6 are easily removable from the sound insulation panels 4 and therefore the maintenance and inspection thereof are easy.
(4) The vibration cancelling devices including the vibration sensors 5 and the vibrators 6 are contained in the space surrounded by the tank side walls 2 and the reinforcing channels 3, and therefore the tank dimension is not substantially increased. Further, the vibration cancelling devices, which are enclosed by the sound insulation panels 4 and the mounting plates 9, are not exposed to the elements and have a longer service life.
(5) The lead wires 11 and 12 of the vibration sensor 5 and the vibrator 6 are wired through the channel 3, thus eliminating the need of an exclusive piping for the lead wires.

Another embodiment of the present invention will be described with reference to Figs. 4 and 5. In this embodiment, the sound insulation panel 4 is mounted on the reinforcing channels 3 through a frame 14 and a flexible thin plate 15. The vibration sensor 5 and the vibrator 6 are mounted on the frame 14 through mounting frames 16. The vibration sensor 5 and the vibrator 6 alternatively may be mounted directly on the frame 14 without the mounting frame 16. Numeral 17 designates an inspection cover.
In this construction, the frame 14 and the thin plate 15 function as a weighty member and a spring respectively thereby to reduce the transmission of the vibrations from the reinforcing channel 3. The vibration reduce effect may be increased by reducing the spring constant of the thin plate 15 and increasing the weight of the frame 14. The limitation of the strength and dimensions, however, limit the vibration damping effect.
According to the present embodiment, the vibrators 6 are mounted on the frame 14 through the mounting frame 16 so that the force of the phase opposite to the vibrations applied through the reinforcing channels 3 is applied to the tank 1 thereby to cancel the vibrations thereof, thus cancelling the vibrations of the sound insulation panels 4 and the inspection cover 17 connected with the frame 14.
Each vibrator 6 is mounted on the frame 14 by reason of the fact that the frame 14 has a larger rigidity than the sound insulation panel 4, resulting in a smaller number of natural vibration frequencies in the frequency range to be reduced. Specifically, when cancelling the vibrations of a structure by applying a control force thereto, vibrators as many as number of the natural vibration frequencies are theoretically required. When the vibrators 6 are mounted, not on the sound insulation panel 4, but on the frame 14 which is larger in rigidity, a smaller number of natural vibration frequencies to be reduced are involved, thus making it possible to reduce the vibrations with a smaller number of vibrators 6. The embodiment under consideration, which uses a control signal generator, an amplifier and vibrators similar to those of the first embodiment, has the advantages mentioned below.
(1) As in the first embodiment, only the power sufficient to cancel the vibrations of the sound insulation panels are required and therefore the output power of the vibrators is reduced.
(2) Since the vibrations of the sound insulation panels 4 are controlled by the frame 14 larger in rigidity and smaller in the number of natural vibration frequencies to be reduced, the number of the frequency components of the vibrations to be cancelled is further decreased as compared with the first embodiment, thus reducing the number of vibrators required.
C3) The sound insulation panel 4 is supported from the reinforcing channel 3 by a spring of the thin plate 15, and therefore the vibration system of the sound insulation panel 4 may be considered substantially independently of the reinforcing channel 3, thereby clarifying and making it easy to predict the vibration characteristics of the sound insulation panel 4. This facilitates the vibration control on the one hand and improves the stability of vibration control on the other hand.
(4) By removing the inspection covers 17, the 'maintenance and inspection of the vibration sensors 5 and the vibrators 6 are easily carried out.
(51 In view of the fact that the vibration cancelling devices including the vibration sensors 5, the vibrators 5 and the frame 14 are contained in the space surrounded by the tank side plates 2 and the reinforcing channels 3, the tank dimension is not generally increased. Further, since the vibration cancelling devices are hermetically enclosed by the sound insulation panels 4, the thin plates 15 and the inspection covers 17, the vibration cancelling devices are not exposed to the elements, thus ensuring the long service life thereof.
(6) The fact that the vibrators 6 are mounted through the mounting frames 16 makes it possible to control a plurality of points (four points in the case of Fig. 4) by a single vibrator 6, thus increasing the vibration reducing effect.
It will be understood from the foregoing description that according to the present invention, the primary noises radiated from the surface of the tank are reduced by sound insulation panels mounted on the outer walls of the tank through framework such as reinfocing channels on the one hand, the vibration cancelling devices including vibration sensors and vibrators are mounted on sound insulation panels or weighty members installed on the sound insulation panels thereby to apply the controlling force of opposite phase to the vibrations transmitted to the sound insulation panels through the reinforcing channels from the tank causing the secondary noises on the other hand. As compared with the prior art devices in which the controlling force is applied directly to the tank, the noises generated from the tank are effectively reduced by a small number of vibrators with smaller power.

Claims

1. A noise-reduction device for a stationary induction apparatus comprising a tank (1) filled with the insulating oil (19) and an induction apparatus (18) mounted in said tank, said noise-reduction device comprising:

first means mounted on at least two reinforcing channels (3) arranged substantially parallely to each other in spaced relationship therebetween on side walls (2) of said tank (1) in a manner to surround said tank (1), said first means including sound insulation panels (4) provided to surround the part of said tank side walls (2) between said reinforcing channels (3), thereby reducing the noises generated from said winding and core and radiating outside through said insulating oil (19) and said tank side walls (2); and

second means for cancelling the vibrations of said sound insulation panels, including a plurality of vibration sensors (5) for detecting the vibrations of said sound insulation panels (41, a plurality of vibrators (6) for applying to said sound insulation panels (4) such vibrations as to cancel the frequency components of the vibrations detected by said vibration sensors (6) respectively.

2. A noise reduction device for a stationary induction apparatus according to Claim 1, wherein said sound insulation panels (4) arranged substantially parallelly with said tank side walls (2) form a space with said tank side walls (.2).

3. A noise-reduction device for a stationary induction apparatus according to Claim 2, wherein said vibrators (6) are mounted with said sound insulation panels (4) in the space between said tank side walls C2) and said sound insulation panels (4).

4. A noise-reduction device for a stationary induction apparatus according to Claim 2, wherein each of said vibrators (6) is mounted on a plate member (16) mounted removably on said sound insulation panel (4) in a manner to enclose the opening formed in each of said sound insulation panels (4).

5. A noise-reduction device for a stationary induction apparatus according to Claim 1, comprising a flexible member (15) through which each of said sound insulation panels (4) is mounted on said reinforcing channel (3), and a weighty member (14) on which said vibrator (6) is mounted, said weighty member (14) being located at the junction of each of said sound insulation panels (4) and said flexible member (15).

6. A noise-reduction device for a stationary induction apparatus according to Claim 5, wherein each of said sound insulation panels (4) includes a peep hole (10) for said vibrators (6), said peep hole (10) being closed with a cover (17).