What is transformer inspection?
A close, hands-on look at a series isolation transformer and its pit, checking for damage, heat, water and wear before they become a fault. A transformer can look quiet for years and still be failing.
An isolation transformer sits in a pit or base can beside the light and passes the series current to its fitting. Water, heat, rodents, digging and age all act on it out of sight. In a series circuit, a failed transformer can darken its own light, and an open primary can take out the whole loop. Inspection is the cheapest way to find the problem first.
1Make it safe first
Isolate and lock out the circuit and prove it dead, as your site procedure requires, before the pit is opened. Treat the leads as live until then. Work on the airfield only with the right permission and under the site’s safety rules.
2Look closely
Open the pit and note what you find before touching anything: water, silt or debris and the state of the lid. Then check the housing for cracks or damage, heat marks or discolouration, and the nameplate, which should still be readable. Follow the leads and look at their insulation and the connectors. Finally check that the transformer is supported and not hanging by its leads, and that any earth bond (on the base can or metal parts) is in place.
- Prove the circuit dead first
- Photograph defects where they are
- Log against circuit and location
- Lift or pull a transformer by its leads
- Assume a clean look means it is sound
- Leave a damaged transformer in service
3Record and act
Photograph each defect and log it against its circuit and location. Inspection shows what can be seen; testing proves the electrical condition, so a finding often leads to insulation or continuity tests, a repair or a replacement. Close up carefully, refit the lid, and restore the circuit only as your procedure allows.
| Check point | What to look for |
|---|---|
| Pit or base can | Water, silt, debris, damaged lid |
| Housing | Cracks, splits, impact damage, swelling |
| Heat marks | Discolouration, scorching or melted areas |
| Nameplate | Present and readable; matches the position |
| Leads | Damaged insulation, cuts, strain, hard bends |
| Connectors | Corrosion, cracks, loose or part-mated |
| Mounting | Supported and secure, not hanging by the leads |
| Earth bond (where fitted) | In place, tight and undamaged |
| Record | Dated photo, location, circuit and action |
Frequently Asked Questions
Q1Why are isolation transformers inspected?
A transformer sits in a pit or base can for years, where water, heat and damage can build up unseen. In a series circuit a failed transformer can affect its own light or, if the primary opens, the whole loop, so a visual check finds problems early.
Q2Can a transformer be inspected with the circuit live?
No. Inspection is a de-energised, hands-on check. Isolate and lock out the circuit and prove it dead as the maintenance plan and site rules require, and treat the leads as live until then.
Q3What defects should be looked for on a transformer?
Look for a cracked or damaged housing, heat marks or discolouration, damaged lead insulation, wet or corroded connectors, water or silt in the pit, a loose or unsupported transformer, a missing or loose earth bond (where one is fitted) and a nameplate that can no longer be read.
Q4Is inspection the same as transformer testing?
No. Inspection is a visual and hands-on check that finds visible defects. Testing, such as insulation resistance and winding continuity, proves the electrical condition. An inspection finding often leads to a test, and a good-looking transformer can still fail a test.
Q5What happens after a defect is found?
Photograph it, log it against its circuit and location, and raise the repair, test or replacement. Do not leave a visibly damaged transformer in service.
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