The “hum” caused by energized power transformer, under no-load conditions, originates in the core where the laminations tend to vibrate by magnetic forces. The noise is transmitted through the oil to the tank side and thence to the surroundings.
The following are the main factors which produce noise in transformers:
- Magnetostriction (occurrence of dimensional changes both parallel to, and perpendicular to the direction of magnetization).
- The mechanical vibrations caused by the laminations, depending upon the tightness of clamping, size, gauge, associated structural parts, etc.
- The mechanical vibration of trank walls.
- The damping.
The noise emission may be reduced by the following methods/means :
- Prevention of vibration of core-plate by the use of a lower flux density and giving attention to constructional feature (such as clamping bolts, proportions and dimensions of the ‘steps’ in plate width, tightness of clamping and uniformity of plates).
- Using cushions, padding, or oil barriers to sound insulate the transformer from the tank.
- Designing suitable the tank and stiffeners to check tank wall vibration.
- Sound insulating the tank from the ground or surrounding air.
However, the noise problem cannot be solved completely.