How Does That Work?

Why high-voltage power lines ‘hum’ in some weather conditions

It’s a lovely summer evening. Humid, but that’s typical for late summer in Nebraska.

The walking trail curves to run parallel to a high-voltage transmission line when you notice a faint humming noise. When you look up, the noise appears to be coming from the lines.

But there’s no reason to be alarmed. You’re hearing the corona effect, and it is associated with all transmission lines.

What is it?

The discharge of energy that occur when the strength of the electrical field of the conductor is greater than the air strength surrounding it. This discharge also causes energy loss known as corona loss associated with high-voltage power lines.

The intensity of the corona loss discharge is determined by the condition of the air around it. Water increases conductivity. So when air is humid, or when rain, wind and fog are present, the audible humming from the lines can increase. Irregularities on the conductor surface can also increase the activity.

This phenomenon can also affect electrical components within substations. But the public should not be alarmed.

Can it be reduced?

Engineers have a found a way to address the issue. They build and maintain high-voltage power lines in such a way that during dry conditions the lines operate below the voltage that will create the corona effect. This means the line will generate a minimum amount of corona-related noise. But when wet weather occurs, the corona effect can still occur, just not as severe as it would without the precautions.

Besides giving off noise, corona causes power loss on the lines and can cause damage to components over time. Utilities install corona rings to combat the effect. The rings have smooth, round surfaces designed to distribute the electrical charge across a wider area. This then reduces the electrical field and the resulting corona discharges.

OPPD methods

OPPD does just that, installing corona rings on the end of some insulators. This allows for a gradual break between the energized equipment and the insulated equipment, reducing the noise factor.

OPPD also uses specific hardware in the energized zone of a high-voltage line. The hardware limits the amount of sharp edges or points in the hot zone, reducing the likelihood of the corona effect.