The corona effect is an electrical phenomenon that occurs when gas surrounding a charged conductor ionizes. As a result of this effect, transmission efficiency can be reduced, and corrosion may appear in conductors due to ozone formation. Additionally, inductive interference with neighboring communication lines can occur. Internally, the corona effect manifests in transformer windings when the oil loses its dielectric properties, creating an easy path for current from the core to the casing. It serves as an indicator of developing faults, inevitable tripping, or transmission line outages.

Corona effect typically leads to continuous negative consequences, such as the generation of harmful products like nitric acid, ozone, carbon, and ultraviolet radiation due to dirt and dust on power line insulators. If not controlled, it will gradually deteriorate insulation values and metals until a ground fault or short circuit occurs.

Ultrasonic inspection instruments operating at 1 kV or more can detect corona discharges by capturing the high-frequency shortwave signals. However, the corona effect with arc and tracking is only visible in the infrared spectrum. Infrared cameras and corona cameras equipped with special lenses that detect ultraviolet light have become effective tools for detecting the corona effect in its natural state.

It is recommended to inspect electrical panels (480V or higher) with ultrasonic scanning before opening the cabinet. This allows for early detection of corona discharges before serious damage occurs, even before tracking develops. Visual inspections with infrared cameras and corona cameras are also vital to identify potential issues. The corona effect may be present at low amplitudes but can become a more serious problem in the future.

To detect corona, one should be attentive to signs like the smell of ozone upon opening the panel, nitrogen oxide residue (white dust), contamination traces, discoloration near or on conductors, and oxidation or corrosion.

Ultraviolet cameras can detect corona at 1,000 volts (1kV) wherever it exists, making it possible to visualize ultraviolet emissions from external partial discharges (i.e., corona, sparks, and arcs), which indicate equipment or installation degradation and potential failures. This UV inspection technology is based on detecting corona and partial discharges by detecting photons emitted during air ionization, with energy levels in the ultraviolet spectral band.

UV inspection technology is extensively used for predictive maintenance in high-voltage equipment, in conjunction with infrared thermography and ultrasonic devices. The added value of UV inspection lies in its capability to identify corona and arcs, pinpoint fault locations, aid in predicting inevitable crises, visualize both the objects emitting radiation and the emitted radiation itself, and assess the severity of the inspected case.

The UV image displays photons as white spots on a black background. Interpreting fault points becomes easier with a combined visualization of the UV and visible light images. In the example, we can observe a corona effect on an insulator during a substation inspection.

UV inspection is critical to identify vulnerable points in electrical systems' insulation. It can also detect installation issues or poor designs in medium and high-voltage installations. By detecting early-stage component degradation, UV inspections ensure the reliability of power systems and reduce maintenance costs by avoiding unplanned shutdowns.