AGL-CS-025 — Water Ingress and Transformer Failure
The AGL Knowledge Hub | Engineering Case Study Series. A moisture-related investigation where repeated transformer failures at the same pit location were traced to standing water and inadequate drainage — from pit inspection through insulation testing to environmental correction.
Important: This is an engineering simulation created for training. It is not presented as an actual airport incident. All readings, values, dates and outcomes are illustrative, and no airport, organisation, person or manufacturer is identified or implied.
1Case Study Overview
During the monsoon season, one runway edge light circuit experienced repeated transformer failures at the same field location.
The Constant Current Regulator (CCR) remained healthy, and the primary series circuit showed normal current regulation. However, the transformer associated with one light fitting had been replaced twice within eight months.
Following another period of heavy rainfall, the light became inoperative again.
A detailed investigation identified water ingress into the transformer pit, which had caused moisture contamination of the transformer, progressive insulation deterioration, corrosion of the winding terminations, and eventual transformer failure.
This case demonstrates that repeated transformer replacement will not solve a moisture-related environmental failure unless the source of water ingress is eliminated.
2Learning Objectives
After completing this case study, the learner should be able to:
- Understand moisture-related transformer failure mechanisms.
- Recognize symptoms of water-ingress-related transformer deterioration.
- Investigate transformer pit drainage conditions.
- Differentiate transformer failure from environmental failure.
- Perform insulation and moisture-related transformer testing.
- Assess corrosion damage caused by water ingress.
- Develop long-term preventive maintenance solutions.
3System Background
An AGL isolating transformer is normally installed in a pit adjacent to the runway or taxiway lighting fixture.
The transformer depends on:
- Proper sealing.
- Drainage.
- Environmental protection.
- Moisture control.
- Connector integrity.
Water ingress may occur through:
- Flooded pits.
- Damaged pit covers.
- Poor drainage.
- Defective cable entries.
- Damaged transformer seals.
- Condensation accumulation.
Long-term moisture exposure can affect:
- Winding insulation.
- Core insulation.
- Terminations.
- Connectors.
- Secondary cables.
4Problem Statement
The reported condition was:
- Repeated transformer failures.
- Same pit location affected.
- Recent heavy rainfall.
- Water observed in the pit.
- CCR healthy.
- Adjacent transformers operating normally.
Is the transformer itself defective, or is water ingress causing repeated environmental failure?
5Initial Observations
| CCR status | Healthy |
| Selected current | 6.6 A |
| Affected light | OFF |
| Pit condition | Water accumulation |
| Adjacent transformers | Normal |
| Transformer replacement history | Two failures in eight months |
The repeated failures at the same location strongly suggested an environmental root cause.
6Initial Engineering Hypotheses
The maintenance team considered:
Defective transformer manufacturing.
Incorrect transformer VA rating.
Water ingress into the transformer.
Secondary cable fault.
Poor pit drainage.
7Water-Ingress Failure Mechanism
A typical sequence is:
The process is usually progressive.
8Test Equipment
The investigation used:
- 5 kV insulation resistance tester.
- Winding resistance meter.
- Moisture inspection tools.
- Thermal imaging camera.
- Approved AGL transformer test equipment.
- Pit drainage inspection equipment.
- Circuit drawings.
- Airport-approved PPE.
9Investigation
Step 1: Verify Primary Circuit
Measurements confirmed:
| CCR current | Normal |
| Primary circuit | Healthy |
| Adjacent transformers | Normal |
The primary circuit was healthy.
Step 2: Pit Inspection
Inspection revealed:
- Standing water.
- Blocked drainage.
- Sediment accumulation.
- Water marks above transformer level.
- Corroded pit hardware.
The transformer had been operating in a water-contaminated environment.
Step 3: Transformer Testing
Results:
| Primary continuity | Normal |
| Secondary continuity | Normal |
| Primary-to-earth IR | 6 MΩ |
| Secondary-to-earth IR | 5 MΩ |
The insulation resistance was severely reduced.
Step 4: Connector Inspection
The connector showed:
- Moisture contamination.
- Corrosion.
- Seal deterioration.
- Contact oxidation.
The connector environment supported continued moisture ingress.
Step 5: Internal Transformer Examination
The removed transformer showed:
- Moisture inside the transformer enclosure.
- Corroded winding terminations.
- Insulation discoloration.
- Resin cracking.
- Evidence of long-term water exposure.
The transformer had suffered environmental moisture damage.
10Root Cause
The transformer failures were caused by repeated water ingress into the transformer pit due to inadequate drainage and deteriorated environmental sealing.
The moisture caused:
- Insulation deterioration.
- Corrosion.
- Leakage current.
- Thermal degradation.
- Progressive transformer failure.
The replacement transformers failed because the environmental root cause remained uncorrected.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Removed the failed transformer.
- Installed a new approved transformer.
- Replaced damaged connectors.
- Improved pit drainage.
- Cleared drainage blockages.
- Repaired cable-entry sealing.
- Verified pit water removal.
- Performed insulation resistance testing.
- Established monsoon inspection procedures.
12Post-Repair Verification
No further transformer failures occurred after drainage correction.
13Root-Cause Analysis
Repeated transformer failures.
Same pit affected.
Water accumulation found.
Low insulation resistance.
Moisture damage identified.
Water ingress and poor drainage.
Replace transformer and correct environmental conditions.
14Why This Case Was Important
A common maintenance mistake is repeatedly replacing:
- Transformers.
- Connectors.
- Secondary cables.
without investigating:
- Drainage.
- Water accumulation.
- Pit sealing.
- Environmental conditions.
The environment can be the actual failed component.
15Engineering Lessons
Repeated failures at the same location indicate an environmental problem.
Repeated failures at the same location usually indicate an environmental problem.
Pit drainage is a critical reliability factor.
Pit drainage is a critical transformer reliability factor.
Moisture accelerates insulation aging and corrosion.
Moisture accelerates insulation aging and corrosion.
Connector sealing and pit drainage should be inspected together.
Connector sealing and pit drainage should be inspected together.
Root-cause correction is more important than repeated replacement.
Root-cause correction is more important than repeated equipment replacement.
16Engineer's Decision Point
You observe: Third transformer failure at the same pit. Standing water in the pit. CCR operating normally. Adjacent transformers healthy. What should you investigate first?
17Knowledge Check
18Interview Questions
19Frequently Asked Questions
Quick answers about water ingress and transformer failure, based on this case study.
Q1What is AGL-CS-025?
AGL-CS-025 is an engineering training case study on repeated transformer failures at one runway edge light pit, traced to water ingress. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2Why did the same transformer location keep failing?
The transformer at that light had been replaced twice within eight months, while adjacent transformers operated normally. Repeated failures at one location strongly suggested an environmental root cause.
Q3What was the root cause?
Repeated water ingress into the transformer pit due to inadequate drainage and deteriorated environmental sealing. The replacement transformers failed because that environmental cause remained uncorrected.
Q4What did the moisture do to the transformer?
It caused insulation deterioration, corrosion of the winding terminations, leakage current, thermal degradation and progressive transformer failure.
Q5What should you investigate first if a third transformer fails at the same pit with standing water?
Investigate pit drainage, moisture ingress and environmental sealing. Drainage and sealing must be addressed before transformer replacement, so replacing the transformer again is not the right first step.
Q6Which test equipment was used?
The investigation used a 5 kV insulation resistance tester, winding resistance meter, moisture inspection tools, thermal imaging camera, approved AGL transformer test equipment and pit drainage inspection equipment.
Q7How was the problem corrected?
The team isolated the circuit, removed the failed transformer, installed a new approved transformer and replaced damaged connectors. They improved pit drainage, cleared blockages, repaired cable-entry sealing, verified pit water removal, tested insulation resistance and established monsoon inspection procedures.
Q8How was the repair verified?
Pit drainage was functional, insulation resistance was greater than 1000 MΩ and the light was restored. No further transformer failures occurred after the drainage correction.
Engineering & Expert Notes
Record Where Transformers Fail
PatternRepeated failures in one pit identify the environment as the cause. Map them.
Fix Drainage Before Replacing Again
DrainageCheck outlets and gradients. Without drainage improvement replacements will fail the same way.
Upgrade Sealing Where Water Persists
SealingConsider improved seals or a better pit arrangement in chronically wet locations.
Inspect Pits After Heavy Rain
InspectionCheck for standing water and silt after storms. Early action prevents later failures.
20Case Study Conclusion
Water ingress is often an environmental root cause that can repeatedly damage isolating transformers through insulation deterioration, corrosion, and thermal degradation unless drainage and sealing deficiencies are corrected.
Systematic pit inspection, drainage assessment, insulation testing, moisture investigation, and environmental correction can prevent repeated transformer failures and significantly improve the long-term reliability of the AGL field equipment network.
In AGL engineering, replacing the transformer without eliminating the water source usually means replacing the next transformer in the same flooded pit.
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