Left unchecked, discharge in a transformer can lead to an instantaneous short circuit that severely damages components, followed by serious trouble such as equipment downtime and recovery work. This case study shows how a steelworks that had previously suffered a transformer failure used the acoustic camera "AL64" to visualize discharge signs around terminals and bushings early, as part of its routine patrol inspections.
Key Takeaways
- Captures the ultrasound emitted during discharge to visualize hard-to-spot discharge signs around terminals and bushings on screen
- Checks from a distance, non-contact, without carelessly approaching high-voltage parts — improving on-site safety
- Picks up discharge signs at external connections early during daily and patrol inspections, cutting man-hours and helping prevent a recurrence of the instantaneous short circuit
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- Steelworks (name withheld)
- Equipment
- Cast-resin (mold) transformer (600 kVA / primary 6,600 V / secondary 600 V)
- Inspection target
- Primary-side terminals and bushings (externally visible terminal and bushing areas)
- Objective
- Early detection of externally visible discharge signs (daily / patrol inspection)
- Product
- Acoustic camera "AL64 (AlgoLeak)"
What Causes Transformer Discharge? The Short-Circuit Risk Behind Equipment Downtime
The steelworks had previously experienced a transformer failure. On the failed transformer, discharge between the secondary-side conductors and between the bushings was believed to be the cause, and an instantaneous short circuit had severely damaged components.
If the same kind of trouble were to recur, it could have a major impact on equipment downtime and recovery work, so catching the signs of discharge at an early stage became a priority.
The transformer in question is rated at 600 kVA capacity, 6,600 V primary and 600 V secondary. The failed transformer was a cast-resin (mold) type, and the goal of this inspection was not internal discharge diagnosis but rather the early detection of discharge signs around the externally visible terminals and bushings.
The Challenge: Safely Inspecting Discharge Signs Around Terminals & Bushings
Signs of discharge are hard to capture by sight or experience alone, and on live high-voltage equipment the checking work itself carries risk. The steelworks faced the following challenges:
- Discharge is hard to spot visually — discharge around terminals and bushings is difficult to detect from appearance alone.
- Approaching high-voltage parts is dangerous — getting close to live high-voltage parts to check them poses a significant safety risk.
- They wanted to catch it early during patrols — not through special shutdown work, but by picking up discharge signs early within daily and patrol inspections.
The Solution: Visualizing Transformer Discharge (Partial Discharge) with the AL64 Acoustic Camera
The solution we proposed was the acoustic camera "AL64". The AL64 detects the ultrasound generated during discharge and visualizes the sound-source location on the camera screen. This lets workers check abnormal sounds around terminals and bushings from a distance, without carelessly approaching high-voltage parts.
This inspection was limited not to the transformer interior but to the primary-side terminals and bushings — specifically the externally visible terminal and bushing areas. Rather than internal discharge diagnosis, the AL64 is used to catch discharge signs around the external connections — which had been the cause of the past failure — early during daily and patrol inspections.
- Visualizes discharge ultrasound — detects the ultrasound emitted during discharge so that hard-to-spot discharge signs appear as a sound-source position on screen.
- Non-contact checks from a distance — inspection without approaching high-voltage parts, improving on-site safety.
- Easy to build into patrols — no special shutdown work needed; the external connections can be checked within daily and patrol inspections.
| Comparison | Conventional inspection (visual / close-up checks) |
AL64 acoustic camera |
|---|---|---|
| Discharge signs around terminals & bushings | Hard to grasp from appearance alone | Captures the ultrasound of discharge and shows the sound source on screen |
| Safety near high-voltage parts | Must approach live high-voltage parts to check | Checks from a distance, non-contact — improving safety |
| Fit with routine inspection | Checking takes effort and time | Catches signs early within daily and patrol inspections |
The Results: Early Discharge Detection on Patrols — Fewer Man-Hours, Safer Work
With the equipment still energized, the team checked around the primary-side terminals and bushings with the AL64. Because the sound-source location appears on screen, operators could intuitively grasp where discharge was suspected and check the condition of the external connections without approaching the high-voltage parts.
- Early detection of discharge signs — discharge signs around the external connections, the cause of the past failure, can now be caught early during patrols.
- Improved work environment — checking from a distance, non-contact, without carelessly approaching high-voltage parts, raised safety during inspection.
- Fewer inspection man-hours — because the sound source shows on screen, the hands-on searching is reduced and the check fits naturally into daily and patrol inspections.
- Preventive maintenance against a repeat short circuit — catching discharge signs early helps reduce the risk of another instantaneous short circuit damaging components and stopping the equipment.
As a result, by turning a transformer discharge inspection that once relied on sight and experience into something you can see on screen, the team can now check for discharge signs quickly during patrols, without approaching high-voltage parts. Together with the reduction in man-hours and the improved work environment, the AL64 also serves as a safeguard against the cause of the past failure.