On a recent infrared inspection of a one of our utility client’s substations an interesting problem was discovered on two 69 kV breaker bushings. Some background history on this substation I was told is that corona could be heard constantly emanating from various pieces of equipment. In fact, I had performed an infrared scan of this substation over three year earlier in the summer time and I heard corona at that time. However, not much thought or concern was given to this condition during that first visit since it was thought to be a normal condition given the fact that the substation was located very close to the ocean and humidity was very high (Yes I did drink the “oh it’s just high humidity and that is normal condition” Kool-Aid like many others do). Well on this particular day, humidity was low, very low, in fact it was one of those beautiful low 70 degree days that reminds me and many others of why I live in Florida.
Well getting back to the story, upon entering the substation I was immediately drawn to two bushing that had hot spots located at top of the ceramic skirts where the copper end cap is located. I was also able to confirm using air borne ultrasound that these two location where the worst of where corona was active (but other corona sites did exist on other bushing). Upon further examination of the bushing this is what I saw.
Lesson learned – corona is one of those conditions that eat away on equipment over time. It may seem benign, and in some case it is depending upon where it is located. But in places where rubber based components are, corona is the kiss of death if not eradicated. I have seen numerous conditions of corona and tracking in indoor metal-clad switchgear, in fact we have a paper in the IR Articles and News section of our website that can be downloaded that address the use of infrared and ultrasound technology to address corona problems that as so common in high voltage switchgear. However, this is the first case of corona affecting a piece of outdoor switchgear where the operation and livelihood of the equipment was at risk of failure and loss.
I hope this case study was useful and please do not hesitate to contact for any comments and services regarding the use of infrared and ultrasound for outdoor utility electrical scans.