Page 113 - Uninterruptible Power Supplies

Additional Information Relating to the Standby Supply Installation
Additional Information Relating to the Standby Supply Installation 111

TABLE 3.5 Frequency Spectrum for an Unsilenced 2.5 MW Class Gas Turbine
Center frequency Hz 63 125 250 500 1000 2000 4000 8000

Sound power level dBA
Air inlet dB SWL 110 113 116 119 121 124 124 133
Exhaust dB SWL 130 134 135 135 132 130 127 124
Casing dB SWL 98 102 106 110 112 112 112 111

TABLE 3.6 Frequency Spectrum for a Sound Attenuated Packaged 2.5 MW Class
Gas Turbine

Center frequency Hz 63 125 250 500 1000 2000 4000 8000
Sound pressure level dB dBA
Machine acoustic
enclosure 88 85 82 76 74 71 69 64 80
Turbine air inlet 96 90 74 65 65 64 69 76 80
Turbine exhaust 101 90 79 73 70 68 63 64 80
Enclosure ventilation
exhaust 91 86 80 65 61 60 68 78 80
Oil cooler exhaust 81 81 88 69 65 64 60 62 80

package will normally include sound attenuation on all these sources
of noise and typical attenuated sound pressure levels 1 m from the source
are given in Table 3.6.

The Noise Level within the Engine Room
The sound produced from the machine travels to the room boundaries
and is reflected several times from the walls, ceiling, and floor and at
each reflection there is some absorption of sound. The reverberation
time of a room can be calculated and is the time taken for a sound to
fall through 60 dB and depends on the size, the contents, and the mate-
rials used in the construction of the room. The reverberation time will
be different for each frequency band. Knowing the acoustic properties
of the room and the sound power released within it, the resulting sound
pressure level (SPL) within the room can be calculated. The sound
pressure level within an engine room will be high and may exceed 110
dB, it can be reduced by introducing sound absorbent material within
the room or by providing an acoustic hood over the machine.

Acoustic Treatment of Ventilation Openings
If acoustic attenuation is required at ventilation openings, and it
almost certainly will be, it can be achieved by the installation of

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