Corona is a serious issue that can occur in switchgear 2000V or greater.
In metal clad switchgear, the most serious result can be a flashover causing enormous damage and personal injury.
Corona results from ionized air or ozone caused by damaged insulation, contamination and faulty design.
The byproducts of corona, nitric acid and carbon, cause a continuous decay of insulation making the situation highly unpredictable.
The ozone is conductive and supports the flashover.
With the correct ultrasound inspection, corona, tracking and arcing can be detected and remedied before serious results occur.
Ultrasound & Corona Detection- What you can’t hear, can hurt you!
Place your cursor over the image to view the damage caused by a corona explosion.
This video below is an example of an arc flashover and is similar to a corona failure.
Imagine the explosion and resultant damage this would cause in an enclosed switchgear panel.
(Click to view arc flashover)
How does ultrasound work?
Arcing, tracking and corona discharge emits ultrasound at the source of the problem. This resulted ultrasound can be located with an ultrasound detection system. This system receives ultrasound waves, which cannot be detected by the human ear, and modulates them so they can be heard.
What type of equipment would benefit from an ultrasound inspection?
Mid and High Voltage: A greater potential for catastrophic failure occurs in equipment of 1000V or greater.
Low Voltage: In equipment below 1000V, arcing is the main concern. Although arcing is usually accompanied by heat, an infrared inspection will not always detect arcing in covered equipment. In these cases, arcing can be heard through air vents and other panel cover openings making the combination of ultrasound and infrared inspections very effective.
What types of problems will an ultrasound inspection detect?
(Click to view sparkling breaker)
(Click to view arcing inside of a bus run)
Arcing: Occurs in all voltages. All forms of arcing, (including tracking), affect the quality of power. In addition, arcing through air or through bulk insulation destroys electrical power equipment.
Corona: Occurs through damaged insulation material when conductors of 1000V or more begin to ionize the air, forming ozone (O3). Ozone will conduct current and can form a direct path to ground, resulting in catastrophic results, especially in enclosed switchgear. Corona also produces nitrogen exides which form nitric acid when combined with moisture. This acid further destroys the insulating material as well as metal components causing possible thermal problems.
Tracking: Often referred to as “Baby arcing,” tracking follows the path of damaged or dirty insulation across component surfaces. Tracking occurs most often in medium to high voltage equipment (1-kV or greater)
Partial Discharge: Occurs inside electrical components such as transformers and insulated buss bars. It is affected by and causes insulation deterioration.
Mechanical Noise: Can be indicative of serious problems in some electrical systems such as transformer coils.
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