"Preplanning a transformer installation is critical. Make sure you have all of the materials, tools and equipment your crew will need available and in place before the work begins"

Installation and Inspection of Dry Type Transformers       4

Written by Ted "Smitty" Smith  2017
Excerpts Copied from Eaton Reference Material
Keeping Sound from Transformer Vibration to an Acceptable Level

Transformers need to be installed so that the sound produced by their vibration does not travel throughout the building. Here are some things to consider to help reduce transformer noise. You may want to write an RFI and make suggestions if you notice any of these apply to one of your installations, or if after installation, a client is complaining about transformer noise, you may be able to make some suggestions. 

Proper location is the first consideration in a low sound level installation. To keep within or (better) below, prescribed decibel limits:

Rule #1
Keep the transformer as far away as possible from the area in which its noise would be most objectionable.

Rule #2
Avoid mounting the unit in a room corner up near the ceiling. Three sided corners act as megaphones and amplify the sound.

Rule #3
Avoid installation in narrow halls and corridors or in corners of stairwells. The transformer sound reflected from the walls can become additive to the primary sound of the transformer and cause additional decibel buildup.

Rule #4
Where feasible, experimental temporary operation and positioning of a free-standing transformer in a room or area will quickly indicate the best location and orientation of the unit.

Rule #5
Where necessary, cover the walls of the transformer room with acoustical dampening material – fiberglass, acoustical tile, kimsul, and similar absorbent materials – to reduce propagation of transformer noise from the room to any adjacent areas. It should be noted, however, that such material has a major effect on the high harmonics of transformer noise but little, if any, efficacy on the fundamental hum.

How the transformer is mounted is also very important. 

Transformer mounting methods 

Transformer mounting methods play an important role in control and reduction of the audible sound coming from the unit. The prime objective is to “isolate” the noise – that is, prevent its mechanical transmission to the supporting structure and connected raceway system.
This can be accomplished with one, or a combination of the following installation techniques:

Technique #1
Use solid mounting when the transformer can be secured to a heavy, solid mass which cannot vibrate audibly, such as reinforced concrete – floor or wall.

Technique #2

For installation on a structural frame, wall, ceiling or column. use the flexible mounting technique employing special vibration dampeners. There must be no solid metal contact between the transformer and supporting surface, otherwise, the vibration of the pads would be ”short-circuited”.

Technique #3

Use flexible connections between the raceway system and transformer enclosure to prevent transmission of noise vibrations from the enclosure to the raceway system, panels, and other mechanical parts. Flexible metal conduit and nonmetallic tubing are acceptable items for these relatively short “coupling” sections.

Technique #4

Dry-type transformers are provided with vibration dampening pads between core and coil assembly mounting and the case. This mounting is tightly secured with bolts for mechanical strength when shipped. After installation of the unit these mounting bolts must be removed or loosened, depending on the manufacturer's instructions,  for effective vibration dampening and minimizing of noise.

Technique #5

If used, lifting eyebolts may contribute to high sound level and should be removed after installation.

Technique #6

Be sure all screws and bolts on covers and top are tight.