Chapter 19. Causes and Effects of Transformer Sound Levels

Chapter 19. Causes and Effects of Transformer Sound Levels...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
19 Causes and Effects of Transformer Sound Levels Jeewan L. Puri Transformer Solutions 19.1 Transformer Sound Levels. ............................................. 19 -1 Sound Pressure Level . Perceived Loudness . Sound Power . Sound Intensity Level . Relationship between Sound Intensity and Sound Pressure Level 19.2 Sound-Energy Measurement Techniques. ..................... 19 -4 Sound-Pressure-Level Measurement . Sound-Intensity Measurements 19.3 Sources of Sound in Transformers. ............................... 19 -5 Core Noise . Load Noise . Fan and Pump Sound 19.4 Sound Level and Measurement Standards for Transformers . ............................................................ 19 -6 Transformer Connections during Test . Principal Radiating Surface for Measurements . Prescribed Contour Location for Measurements . Measuring Positions on Prescribed Contour . Sound-Pressure-Level Measurements . Sound-Intensit y Measurements . Calculation of Sound Power Level . Sound-Pressure-Level Calculations at Far Field Receiver Locations 19.5 Factors Affecting Sound Levels in Field Installations. ......................................................... 19 -11 Load Power Factor . Internal Regulation . Load Current and Voltage Harmonics . DC Magnetization . Acoustical Resonance In many cities today there are local ordinances specifying maximum allowable sound levels at commercial and residential property lines. Consequently, the sound energy radiated from transformers has become a factor of increasing importance to the neighboring residential areas. It is therefore appropriate that a good understanding of sound power radiation and its measurement principles be developed for appropriately specifying sound levels in transformers. An understanding of these principles can be helpful in minimizing community complaints regarding the present and future installations of transformers. 19.1 Transformer Sound Levels An understanding of the following basic principles is necessary to evaluate a sound source to quantify the sound energy. ß 2006 by Taylor & Francis Group, LLC.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
19.1.1 Sound Pressure Level The main quantity used to describe a sound is the size or amplitude of the pressure fluctuations at a human ear. The weakest sound a healthy human ear can detect has an amplitude of 20 millionths of a pascal (20 m Pa). A pressure change of 20 m Pa is so small that it causes the eardrum to deflect a distance less than the diameter of a single hydrogen molecule. Amazingly, the ear can tolerate sound pressures more than a million times higher. Thus, if we measured sound in Pa, we would end up with some quite large, unmanageable numbers. To avoid this, another scale is used—the decibel or dB scale. The decibel is not an absolute unit of measurement. It is a ratio between a measured quantity and an agreed reference level. The dB scale is logarithmic and uses the hearing threshold of 20 m Pa as the reference level. This is defined as 0 dB. A sound pressure level L p can therefore be defined as: L p ¼ 10 log (P = P 0 ) 2 (19 : 1) where L p ¼ sound pressure level, dB P 0 ¼ reference level ¼ 20 m Pa One useful aspect of the decibel scale is that it gives a much better approximation of the human perception of relative loudness than the pascal scale.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 14

Chapter 19. Causes and Effects of Transformer Sound Levels...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online