At the time corona, destructive corona, tracking and arcing were buzz words that many major and local utilities were used to hearing. However, very few had actually heard the sound of corona, destructive corona or tracking with their own ears. Arcing? Yes, who hadn't heard arcing in one form or another before? Also, during this time in the mid to late '90's, there had been some problems with porosity and casting problems with certain polymer insulators.
I can only assume that a couple of airborne ultrasound engineers had got the idea from watching too many football games (audible parabolic dish on sidelines) or from staring at their tv satellite dish (parabolic signal receiver dish) too long, and came up with the idea to use a parabolic dish as an ultrasonic receiver. I know personally, I was amazed that at 70-80 feet away I could hear a 5 psig leak and know within a couple of feet exactly were it was coming from.
Airborne ultrasound is very directional in nature since the sound wave is 1/8-5/16 of an inch long. This same technology when aimed at an electrical power line could easily pinpoint were corona, tracking and arcing was coming from. Some of the parabolic dishes were 18 inches in diameter and others 10-12 inches in diameter. Some with cross hairs for aiming and others had a laser pointer for aiming. Not only were these instruments great for radio/tv interference but great for compressed air audits or looking for steam leaks in the overhead, as well as listening to ballast of lights in the overhead.
One spring morning I arrived at the intersection of what could be known as any utilities operations managers worst nightmare, "that is, a residential intersection were a retired electrical engineer and a ham radio operator resides across the street from one another and on a road with newly installed 13kV power lines with new polymer insulators".
These two men had sent numerous complaint letters to the utilities as well as to the FCC and rightfully so. The ham radio operator had terrible interference with his operations especially when his antennae was pointed in a southwardly direction. The retired electrical engineers concern was the terrible reception he was getting on his television screen (no cable tv).
Picture this, I drive up to an intersection in typical residential USA, I see a row of trucks and men, a caravan! The first two were vans with two crews of radio interference men scanning the area with directional antennae's for the interference. The next truck was a regional supervisor in a pick-up truck. The next truck was the work crew (6 men). The next truck was loaded down with new polymer insulators pulled from the warehouse just in case they needed to replace an insulator. The next truck was a overhead bucket truck with crew and the last truck was another supervisor in a pick-up truck. I had to hand it to them, these men were ready for war on those polymer insulators.
After the introductions were made, the radio/tv interference crew said that the interference was originating somewhere between here and a couple of miles down the road "somewhere". Airborne ultrasound is sound above the human hearing range at 20 kHz and above. The electrical sound of corona, destructive corona, tracking and arcing are all sounds that make a lot of noise. As the air molecules are dispersed into the atmosphere it produces friction, friction produces sound. I immediately began to scan the area while at the same time trying to train the men on the technology and how best to cover an area during a survey.
- Know the area during a survey.
- Is there any other electrical source (transformers, power lines, etc..).
- Always walk around the suspect power pole or tower.
(The molecules dispersing into the atmosphere makes the sound audible to the ultrasonic receiver. These molecules are subject to wind direction. If you walk around the pole or tower you should note the intensity of the sound while downwind vs. upwind)
After several minutes of not finding any notable sound emitting from the 13kV polymer insulators, I continued to talk about how to survey the area. It was while I was talking about knowing about another power source in the area that I noted a 14.4kV service on the intersecting street. This 14.4kV service was within 30 feet of the retired electrical engineers television antennae and directly due south of the ham radio operator's home. After about 10 seconds of scanning the 14.4kV line I could easily hear the problem, it was cut-out switch that was badly corroded and arcing. In fact it was pegging out the needle of the instrument I was using. It was good thing the bucket truck and crew were there. The problem switch was quickly cleaned. The one of the field supervisors visited the retired electrical engineer and found no more interference on his television screen. He later called the ham radio operator who noted all was fine with his reception.
What a day, actually all this took place within about 45 minutes on-site.