What Causes a Power Transformer to Hum?

A Power Transformer to make the noise Hum?

If you've ever stood under a telephone pole with a transformer installed on it, you've heard the unmistakable hum of that electricity unit. Hollywood movies typically emphasize the sound when creating the sense of electricity moving, but what actually makes the transformer give off the specific sound is a bit more scientific in nature. Much of it has to do with the metals used in the construction and function of the transformer.

Cause of the Hum

• In the U.S. electrical transformers the hum that occurs happens at a frequency of 120 Hz. When vibrations reach this level of repetition, the metal used to construct the transformer internal core begins to give off a noise. The vibration, or hum, is a reaction by the transformer metal to the presence of a magnetic field created as electricity passes through. This process is called magnetostriction.

Levels of Hum

• The amount of noise produced by a transformer depends on its size. Industrial-type transformers on the top of telephone poles or power line towers give off a significant amount of noise due to their capacity and the amount of voltage passing through them. Smaller units the size of a hand or less give off a slightly audible sound at the same frequency as their larger cousins.

• The Scientific Process

  • Magnetostriction occurs when the internal iron parts of a transformer passing electricity through conductive parts reverses the electrical path back and forth at least 60 times per second. This activity makes the metal malleable as it begins to deform slightly. The deformation and reformation of the metal creates the noise which measures as a 120 Hz humming sound. The process happens so quickly, the changing shape noise registers to human ears as a humming vibration.

  Dangers

  • Any large electrical unit whether on the ground or up on a pole should be steered clear of. The amount of electricity involved to make one of these large units hum can be in the range of 20,000 to 50,000 volts. It would kill most people instantly if they came in contact with it. No one should ever ignore the warning labels typically plastered all over such equipment.
  • Source From:
  • http://www.ehow.com/info_8035406_causes-power-transformer-hum.html