Noise (Insulator) In The Transmission Line (220kv)

I presume you mean the connections between the long rod insulator and conductor.

The spark and hissing noise is caused by corona discharges. There should be a grading ring on the line (energized) end of the insulator. If not, it is likely that the corona is emanating from the corners of the relatively small end hardware fitting on the insulator.

Corona and the associated RIV (radio influence voltage) and TVI (television interference) is caused by electrical overstress of the air adjacent the energized electrodes.

Assuming this is a 220 kV AC transmission line, there are three types of corona. A glow discharge occurs at a gradient of approximately 20 kV rms/cm. Glow discharge is a light glow off sharp points that does not generate objectionable RIV/TVI or cause any audible noise. At about 25 kV rms/cm, negative polarity "brush" discharges occur. So named because the appearance is similar to the round ends of a bottle brush. The audible noise associated with brush corona is generally a continuous background type of hissing or frying noise. At a gradient of around 30 kVrms/cm positive polarity plume corona is generated; so named because of its general resemblance to a plume. When viewed in the dark it has a concentrated stem that branches and merges into a violet-colored, tree-like halo. The audible noise associated with plume corona is a rather intense snapping and hissing sound. Plume corona generates significant RIV/TVI.

These observations are based on fair weather conditions. Under wet conditions virtually all energized electrodes will be in corona of one form or another.

The solution to your problem is to install grading or control rings at the energized end of the insulators to electrically grade and shield the high voltage connections.

Woof! You really know your stuff. Your answer reminded me of an article in Scientific American a long, long time ago. They were explaining how to do just what you described, because at that time, transmitted voltages were getting higher.

Impressive!

Got blocked off the mail room immediately after the DNA-marker mention. You too?