Corona & UV Discharge Inspection Singapore — Daytime UV Camera Survey of HV Lines & Insulators

What Is Corona & UV Discharge Inspection?

Corona and UV discharge inspection is the survey of high-voltage electrical assets — overhead line conductors, insulator strings, bushings, and substation hardware — using a specialised ultraviolet camera that detects and locates corona discharge. Corona is the faint bluish ionisation glow that forms in the air immediately around an energised conductor or fitting whenever the local electric field grows strong enough to break down the surrounding air. Where it appears, and how intensely, tells an engineer a great deal about the health of the hardware beneath it.

The camera at the centre of the survey is a corona, or UV, camera. It exploits the fact that corona emits ultraviolet light. By filtering the scene down to the narrow band of UV that corona produces, the camera isolates the discharge and overlays its signature onto an ordinary visible image, so the operator sees a live picture of the conductor with each discharge point marked exactly where it occurs. Mounted on a drone, that camera can scan an entire span of overhead line, a full insulator string or a bank of substation terminations from a safe standoff distance while the circuit stays in service. This is a full-capability inspection: it does not merely note that something looks wrong, it pinpoints the active discharge and ranks how serious it is.

Because corona only exists while the asset is energised, a UV survey is inherently a live-line technique. It reveals a class of defect that a de-energised visual check or a routine thermal scan simply cannot — the surface discharge that is quietly attacking the hardware right now, under load, in service.

Why Corona Discharge Matters

Corona is never random. It marks a place where the electric field has concentrated, and that concentration almost always has a physical cause: a cracked or punctured insulator, a broken conductor strand, a sharp burr or protrusion on a fitting, a poorly made joint, salt and pollution contamination on an insulator surface, or a design detail that runs too close to the limit for local conditions. Reading the corona pattern is therefore reading the condition of the component itself.

Left in place, sustained corona does real damage. The discharge generates radio-frequency noise that interferes with radio and television reception, and it produces audible hum and hiss that draws complaints near lines and substations. It wastes energy continuously as corona loss. Most damaging of all, corona produces ozone and, in humid air, traces of nitric acid, which chemically attack polymer insulators, silicone sheds and organic coatings — so a component that is discharging is also degrading, and the degradation accelerates the discharge. That feedback loop, if ignored, ends in tracking, erosion and ultimately a flashover across a failed insulator. Singapore's persistent humidity and coastal salt deposition make the pollution-driven forms of this problem especially relevant here, a concern reflected in the insulator pollution guidance of IEC 60815.

Finding corona early breaks that cycle. It converts a hidden, progressive fault into a specific, located component that can be washed, cleaned or replaced at a planned maintenance window rather than after an unplanned outage.

How a UV Corona Camera Works

The key to daylight detection is the solar-blind ultraviolet band. Corona emits UV across a range of wavelengths, but a portion of it falls between roughly 240 and 280 nanometres — a band that the ozone layer absorbs so completely that almost none of it reaches the ground from the sun. To a camera tuned to see only those wavelengths, the daytime world is naturally dark, and the tiny UV flashes of corona stand out sharply against that black background even under a bright tropical sky.

A corona camera couples that solar-blind UV channel with a conventional visible camera and fuses the two. The result is a live image in which each discharge appears as a cluster of marks superimposed on the real conductor or insulator. The instrument counts the individual UV photon events it captures, and that photon count is the basis for grading severity — more counts per minute, at a given gain and distance, means stronger corona. An experienced operator normalises for gain, range and atmospheric conditions so that readings from different assets can be compared consistently.

Carried on a drone, the camera turns this into an aerial survey. The aircraft holds a controlled standoff from the live conductors and works methodically along the asset — scanning conductors and their fittings, each disc of an insulator string, dead-end and tension assemblies, jumper loops, and the terminations and bushings inside a switchyard. Every discharge is located, imaged and logged without a climber going near the hardware and without taking the circuit out of service.

What We Survey

A UV corona survey is directed at the specific hardware where field concentration and surface discharge occur. Each finding is located, imaged, graded by photon count and reported against the asset.

How UV Corona Inspection Complements Other Methods

No single technique sees every high-voltage defect, and a UV corona survey is most powerful understood as one instrument in a coordinated toolkit. What it does uniquely well is image active surface discharge in open air, on hardware you have line of sight to, while the asset is live.

It is distinct from acoustic partial discharge detection, which listens for the ultrasonic and radio-frequency signatures of discharge and is the right tool for enclosed switchgear, cable boxes and other assets where there is no optical path to the discharge. It is also distinct from a purely visual insulator inspection, which records physical condition — cracks, chips, missing sheds — but cannot tell you whether a component is electrically active right now. A UV camera catches the live discharge that a visual or infrared survey can miss entirely.

In practice we fly UV alongside high-zoom visual capture and radiometric thermal imaging so that a single line survey returns three complementary layers at once: thermal for resistive heating at loose or corroded connections, high-zoom visual for physical damage, and UV for active surface discharge. Read together across an overhead line or a transmission tower, these give a far more complete picture of asset health than any one method alone. The approach follows general IEC and utility corona-inspection practice on Singapore's EMA-regulated transmission network.

The advantages of doing this from a drone are decisive:

• Live and non-intrusive — the circuit stays energised and in service, which is essential because corona only exists under voltage.
• Safe standoff — the aircraft holds a controlled distance from the conductors, with no climber near live hardware and no work-at-height exposure.
• Located, graded findings — every discharge is pinpointed on the asset and ranked by photon count, so maintenance is targeted at the worst components.
• Combined survey — UV, thermal and high-zoom visual on the same flight compress what were separate campaigns into one.

Why Choose SG Drone Inspections

We are a specialist industrial and power-asset drone inspection provider in Singapore, focused on returning accurate, decision-ready data on live high-voltage hardware.

Frequently Asked Questions