Principle of operation

Corona discharge activities radiate energy in the form of light. This is mainly ultra-violet light which is invisible to the human eye. A small protion of the energy is however just visible at night and appears as "bluish flames" at sharp edges on high voltage equipment. During the day, the energy radiated by the sun in the UV spectrum, is orders of magnitude larger than that released from corona discharges. The corona discharge energy is thus almost completely absorbed by the solar energy. Consequently, to observe corona during the day is impossible with the naked eye.

The CSIR has overcome this. We have developed a day light corona observation and recording system, which uses three unique technologies. The first one uses an UV optimised detector with the appropriate filters, the second one controls the aperture of the lens, and the last one enhances the pictures obtained.

The CSIR has developed five different CoroCAM cameras, with different features, specifications, applications and users. The CoroCAM produces a corona video image.

What is corona?

St Elmo's fire was probably the first recorded form of corona. During stormy weather at sea, flame like reddish or bluish lights appeared occasionally on the tops of ship masts. Sailors associated it with a form of protection and named it after their patron saint, St Elmo.

During the course of electrostatic investigations in the 17th century, the same light-like phenomenon was first observed in the laboratory. It was also traditionally referred to as corona. The term corona is now commonly used to describe this external electric gas discharge phenomenon.

• Generation of light
• Audible noise
• Radio noise
• Vibration due to electric wind
• A deterioration of materials due to ion bombardment
• Generation of ozone, oxides of nitrogen, and in the presence of moisture, nitric acid
• Dissipation of energy

• Around line conductors
• On spacers and dampers
• Damaged insulators - ceramic or non ceramic
• Polluted insulators
• At the live ends of insulator assemblies and bushings
• At any point of your electrical equipment, where the electrical field strength exceeds 3kV/m

• Spark discharge, occurring between any two metal surfaces bound together electrically
• Micro-spark discharge, occurring in a miniature air gap formed between a conducting and insulating surface
• Surface discharge, occurring across dry bands on the conductive surface of polluted insulators