Powerline Hum: What Causes It & How to Stop It

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Discussion Overview

The discussion revolves around the causes of the powerline hum, exploring various hypotheses related to its origin, including physical phenomena associated with high voltage power lines and environmental conditions. Participants examine potential mechanisms behind the noise, including corona discharge and electromagnetic effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests the noise may be due to low-level corona discharge from high voltage power lines, particularly in humid conditions.
  • Another proposes that the hum is a 60-cycle sound caused by the physical motion of wires or transformer coverings influenced by changing electromagnetic fields.
  • A later reply elaborates on the idea of phase differences between powerlines acting like a giant electrostatic speaker, although questions the efficiency of this mechanism in producing audible sound.
  • One participant calculates that a 750KV transmission line carrying 30 MW would result in low current, suggesting that the forces involved would be minimal and unlikely to produce significant sound.
  • There is a mention of hiss from corona discharge being modulated at a 120 Hz line rate, indicating a complexity in the sound's frequency characteristics.
  • Another point raised is that proximity to a power substation may result in hearing transformer cores vibrating at 120 Hz, which could contribute to the hum's loudness.

Areas of Agreement / Disagreement

Participants present multiple competing views on the causes of the powerline hum, with no consensus reached on a single explanation. Various hypotheses are discussed, but uncertainty remains regarding the definitive source of the noise.

Contextual Notes

Some claims rely on assumptions about the efficiency of sound production from powerlines and the specific conditions under which the hum is heard. The discussion does not resolve these assumptions or the mathematical implications of the proposed models.

Flying Penguin
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What exactly is the noise?
 
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I believe it's a low-level corona discharge that can happen with HV power lines, but I'm not sure. It's usually worse when the air is real humid, like in foggy conditions, and the conduction of the air is higher. Kind of like the noise from neon signs. It's not magnetostriction, so it seems like it would have to be associated with the corona discharge from the high voltage at 60/50Hz. Anybody else know for sure?
 
The hum is usually a 60-cycle hum, and is probably caused by the physical motion of the wires or metal coverings on transformers, instigated by the changing EM field, exerting a force on the iron/steel. I expect this is acts like a very inefficient speaker.

On powerlines in the air, there is probably a phase difference between powerlines widely spaced or on different circuits causing the air to act like part of a giant electrostatic speaker (in the hearing range).
 
Last edited:
Because they don't know the words.
 
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Nam_Sapper said:
The hum is usually a 60-cycle hum, and is probably caused by the physical motion of the wires or metal coverings on transformers, instigated by the changing EM field, exerting a force on the iron/steel. I expect this is acts like a very inefficient speaker.

On powerlines in the air, there is probably a phase difference between powerlines widely spaced or on different circuits causing the air to act like part of a giant electrostatic speaker (in the hearing range).

I think this would not be efficient enough to be audible. The current
in a high-voltage transmission line is low and conductor spacing is large.
Furthermore, the acoustical radiation efficiency of a wire at 60 or 120 Hz
is quite low.

If a 750KV transmission line carried 30 MW, the current would be around
40 Amps. While this kind of current would make conductors slap the walls
of a conduit, they would be separated by maybe 30 meters in the transmission
system. Forces would be very low.

It's the hiss of corona discharge modulated at the 120 Hz line rate. It's
not 60 Hz because there are two peaks and zero crossings for each
cycle.

Edit: If you are in or near a power substation, then you are likely hearing the
magnetic cores of the transformers as they vibrate at 120 Hz. They are typically quite loud.
 
Last edited:
Thers another penguin on this board??
 
not big enough for 2?
 
faust9 said:
Because they don't know the words.
OMG. brilliant quip. How did I miss it?
 

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