![]() With the dawn of the electrical age, it was observed that high voltage sparks in air produce acoustic emissions equivalent to the sound of lightning during a thunderstorm although at reduced scale. Similarly, most of the commercial grade lenses in binoculars and cameras are poorly transparent for UV radiation and therefore suppress the discharges that might ordinarily be seen using them. Since this molecule emits light (photons) mainly in the ultraviolet region (with peaks at 298 nm, 347 nm and 358 nm), emissions at such wavelengths are barely visible to the eye whose receptors are sensitive only from 400 nm to 700 nm. During this process, photons are emitted at a wavelength characteristic of the spectroscopic properties of nitrogen. Corona has become the term commonly used to describe all electrical phenomena occurring either in or near the surface of electrical devices that result in UV discharges.Įxcessively high electric fields surrounding energized equipment can ionize nitrogen molecules in the air. Many years later, as sources of high voltage electricity were developed, these same types of phenomena were also observed in test laboratories. Because the rounded head of the mast made this light seem like a crown, it came to be referred to by its Latin equivalent, corona. During stormy weather at sea, sailors noticed reddish and bluish lights at the tops of masts and at the end of yardarms. The term ‘corona’ applied to electrical discharge phenomena has an origin dating back to ancient times. Similarly, being able to see a defect from a distance improves safety and also working conditions for maintenance staff. Having as much data as possible on any problem allows improved decision-making. Generally-speaking, since the causes of hotspots and UV discharges can be quite distinct, different technologies are needed to visualize them and to properly assess their level of severity. Infrared imaging (1997 top, 2015 bottom) has benefited from more portable and more sensitive equipment. However, until the introduction of corona imaging cameras, methods of corona detection, including audible noise, have not been nearly as valuable in pinpointing the source of discharges, even with noise direction finders. Thermal imaging using a range of infrared-based devices (IR) has been utilized for a long time and enabled maintenance staff at power utilities to accurately locate problem areas, commonly referred to as ‘hotspots’. It also reviewed some key elements needed to correctly interpret findings. This edited past contribution to INMR by engineers at Eskom, CSIR and Uvirco Technologies in South Africa, traced the evolution of systems that allow such defects to become visible to maintenance personnel. Ultraviolet (UV) discharges and thermal hotspots are reliable indicators of defects at electrical installations and being able to efficiently visualize these has therefore been a longstanding goal among power utilities.
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