Influence of Noise on Fault Diagnosis of Transformer based on Vibration Signal

Monitoring transformer vibration signals is a universal application method to realize the diagnosis of internal mechanical faults of transformers. However, the actual transformer operating is interfered by the noise of the surrounding electrical equipment, which reduces the accuracy of the vibration signal identification. This paper simulate the typical noise sources in the actual transformer operating environment, including fan noise and surrounding equipment fault noise, and explore the impact of different noise sources on the transformer vibration signal.

Two-step computational aeroacoustics approach for underhood cooling fan application

Aeroacoustic noise is one of the important characteristics of the fan design. Computational Aeroacoustics (CAA) can provide better design options without relying on physical prototypes and reduce the development time and cost. There are two ways of performing CAA analysis; one-step and two-step approach. In one-step CAA, air flow and acoustic analysis are carried out in a single software. In two-step approach, air flow and acoustic analysis are carried out in separate software. Two-step CAA approach can expedite the calculation process and can be implemented in larger and complex domain problems. For the work presented in this paper, a mockup of an underhood cooling fan was designed. The sound pressure levels were measured for different installation configurations. The sound pressure level for one of the configurations was calculated with two-step approach and compared with test data. The compressible fluid flow field was first computed in a commercially available computational fluid dynamics software. This flow field was imported in a separate software where fan noise sources were computed and further used to predict the sound pressure levels at various microphone locations. The results show an excellent correlation between test and simulation for both tonal and broadband components of the fan noise.

Study on the effect of separation and reattachment flow between blades on fan noise

With the growth of the EV/HV market, the main cause of cabin noise has changed from engine driving sound to air conditioner noise. The blower noise is the largest in the air conditioner noise, and the noise reduction is urgent. Separated and reattached flows between fan blades are considered to be the main sources of blower noise. In the past, we tried to reduce the noise by reducing the separation. This time, the blade shape to further reduce the separation was produced and evaluated. As a result, the noise was greatly reduced, but a new problem was found that there was a flow velocity condition in which the noise increased despite the small separation. Therefore, we visualized the flow between blades by PIV, investigated the state of separated and reattached flow in detail, and investigated the factors related to noise increase and decrease by measuring noise and pressure fluctuation of blade surface simultaneously. As a result, it was found that the noise generation condition in the separation reattachment flow between blades is not only the size of separation but also the distance of separation shear layer from blade surface and the strength of vortex generated in shear layer.

Loudness- and preference-equivalent levels of fan sounds at different absolute levels

In daily life, fans are a common and often unwanted noise source. The sound pressure level in dB(A) is often not sufficient to characterize their unpleasantness and level adjustments would be needed to compensate this shortcoming. In this study, listening experiments were conducted to determine loudness- and preference-equivalent levels of 19 different fan noise stimuli. For this purpose, the level of each stimulus was varied with an adaptive procedure until it was equally loud (loudness task), or equally preferred (preference task) as a common reference noise with a fixed level of 75 dB(A). This study repeats an earlier similar study, with a lower reference level of 60 dB(A) and using a larger set of stimuli. The present results are in broad agreement with the results of the prior study, supporting the stability of the matching procedure. Apparently, level adjustments (penalties) derived from such experiments do not change when stimulus levels are increased by 15 dB. Based on the new results, an existing model developed with a 60 dB(A) reference, can be expanded to also predict preferences for sound sources up to 75 dB(A). Further experiments with a reference level of 45 dB(A) will complement the data to lower levels.

Relationships between prior experience with fan noise and fan noise ratings in laboratory listening tests

In the assessment of noise annoyance and sound quality, judgments made in the laboratory can be influenced by the prior experience that a participant had with the specific type of sound under test. In field tests for noise annoyance, prior experience and individual noise sensitivity are often part of the data collection but they are not always reported for sound quality evaluations in the laboratory. In this paper, data from listening tests dealing with the perception of fan noise was re-analyzed with respect to the individual prior experience participants had with fan noise in their life. The answers to a short questionnaire showed that the prior experience of the participants with fan sounds was quite different. For the investigated 30 fan sounds, five categories of every-day situations could be identified, in which fan sounds had been most commonly heard by the participants. The frequency how often fan sounds had been heard and the overall annoyance by fan sounds in daily life differed considerably between the participants. However, the exploration of the present data did not reveal a strong link between the individual prior experience and the results of the listening tests when averaged across participants with same ratings.

Noise Characteristics of Automobile Cooling Fan Based on Circumferential Mode Analysis

The fan is the main component of the cooling system of an automobile engine. A typical automobile cooling fan consists of a shrouded axial fan, stator vanes, a deflector, and a cover. With recent developments in the automobile industry, the increase in the speed of rotation and blade load of cooling fans has increased the noise generated by them. To reduce it, it is important to analyze the characteristics of this noise. This paper uses an acoustic test to examine the characteristics of flow and noise of automobile cooling fans. The frequency spectrum and far-field radiation of the noise of the fan are first analyzed through far-field measurements, and the influence of the single rotor, tip clearance of the blade, and cover on fan noise is studied. The distribution of the mode spectrum and characteristics of sound propagation of discrete tonal noise are then examined using the circumferential mode test. The influence of the flow structure on fan noise is also studied. The flow characteristics and distribution of the source of noise of the automobile cooling fan are then used to analyze the influence of the structure of the fan on the noise generated by it. The results can help develop designs to reduce the noise of automobile cooling fans.