FEATURE SAFETY IN ENGINEERING Top techniques for controlling generator noise
Workplace health and safety regulations and industry growth is causing plant operators to take the issue of noise more seriously. Here, Nigel Thompson, sales manager – gas power solutions at Finning UK & Ireland, outlines his top techniques for reducing generator noise
T
he risks from high noise levels for a sustained period of time are well
established. The Health & Safety Executive (HSE) estimates that as many as 170,000 people in the UK suffer from deafness, tinnitus or other ear conditions as a result of exposure to excessive noise at work. Fortunately, noise exposure can be controlled, and technology exists to reduce the hazards. The human ear perceives sound as a
vibration of the eardrum, which results from an incremental variation in air pressure at the ear, or sound pressure, measured in units of Pascal (Pa). The frequency of the sound is the number of pressure variations per second, measured in Hertz (Hz), where the normal audible frequency range is 20-20,000Hz. Sound pressure levels are described
logarithmically in units called decibels (dB). This compresses the large range of typical sound pressures into a smaller, more practical scale that closely parallels the human ear’s ability to judge relative loudness of sounds. Sound levels from 80 to 100dB(A) are
considered ‘very loud’, 100 to 125dB(A) ‘uncomfortable’, and 140dB(A) towards the threshold of pain. An increase of just ten decibels equates to a ten-fold increase in noise to a human ear. When specifying a generator, it is
important to consider the application for which it is being used. While kilowatt output and fuel type are major considerations, noise becomes the next big factor in any decision making. In fact, control and suppression of noise is an essential component of a generator set’s performance.
For operators and decision makers,
there are a number of tactics that can be employed to reduce noise from a generator, such as identifying its main sources (air inlet, outlet, exhaust) and directing them away from noise sensitive areas. Operators should also limit the airflow of speed control fans – higher air flow means more noise. Other techniques to reduce noise include:
VIBRATION ISOLATION A big source of noise from generators is vibrations caused by the machine running that then transfer into the ground and other equipment. Isolation is defined by the level of reduction of vibration passed between the oscillatory system and its surroundings. Typically, 90 per cent isolation and above is required to prevent transmission of vibration, which can cause structure-born noise. Anti-vibration mounts, also known as AV mounts, are a low cost component that possess shock absorption properties. Using combinations of heavy duty rubber, metal, and springs, they act as a vibration dampener to reduce noise and improve the lifespan of machine applications.
LAYOUT The easiest way to reduce the effect noise has on an immediate workforce and surrounding communities is to increase the distance between the operations and the source. If a generator is moved further away, the energy is spread over a greater distance and, as a result, has less acoustic intensity. A general rule is that if distance is doubled, a 6dB(A) noise reduction can be achieved. It is also important to note that the term ‘free field’, which describes where sound freely propagates and spreads uniformly, does not begin until 30-50 feet away from the generator.
THE RIGHT SPECIFICATION Good acoustic design must be considered early on in the planning process to ensure that the most appropriate and cost-effective solution is identified. Most laws are tougher when dealing with prime or continuous power applications because of their extended use of operation. If a particular noise level at the property line must be achieved, then the sound attenuated enclosure manufacturer should be told beforehand
16 DECEMBER / JANUARY 2020 | ELECTRICAL ENGINEERING
what the requirement is and how far the enclosure will be from the property line. In addition, it is important to remember
that insulation must be tailored to reduce frequency, and that there are two major frequency bands, which require different methods of control. Frequencies below 300Hz are considered low frequency, while those above are said to be high. Low frequency noise is best controlled by the use of rigid barriers with substantial mass, while high frequencies can be tackled with sound absorbing insulation, such as rockwool. The human ear is most sensitive to frequencies from 500 and above. By taking all of this into consideration,
decision makers can help ensure that they are installing a generator that is fit for purpose, emitting a noise level that is appropriate for the surrounding site.
Finning UK & Ireland
finning.com
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