AGL-CS-032 — CCR Output Current Fluctuation
The AGL Knowledge Hub | Engineering Case Study Series. A dynamic-regulation investigation where CCR output current fluctuated continuously due to an intermittent connector and humidity-dependent insulation leakage — from trend recording through impedance monitoring and sectional testing to field-circuit 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 night operation, the maintenance team observed visible brightness fluctuation across a runway edge lighting circuit.
The Constant Current Regulator (CCR) was set to 6.6 A, but the output current continuously fluctuated between 6.2 A and 6.7 A.
The fluctuation occurred even though the selected CCR step remained unchanged.
Several runway edge lights appeared to brighten and dim repeatedly, and the CCR generated intermittent regulation warnings.
A detailed investigation identified an intermittent high-resistance connection combined with unstable insulation leakage in the field circuit, causing continuous impedance variation and corresponding CCR output adjustments.
This case demonstrates that current fluctuation is usually caused by a changing circuit condition rather than a fixed electrical fault.
2Learning Objectives
After completing this case study, the learner should be able to:
- Understand CCR output current regulation behavior.
- Diagnose fluctuating output current.
- Differentiate CCR instability from field-circuit instability.
- Analyze dynamic circuit impedance changes.
- Investigate intermittent high-resistance faults.
- Correlate thermal, insulation, and current fluctuation data.
- Apply waveform and trend analysis in CCR troubleshooting.
3System Background
A CCR continuously monitors:
- Output current.
- Output voltage.
- Feedback current.
- Regulation error.
Normal operation:
Abnormal operation:
4Problem Statement
The reported condition was:
- Selected current: 6.6 A.
- Actual current fluctuating.
- Visible light intensity fluctuation.
- Output voltage varying continuously.
- Intermittent regulation alarms.
- No complete circuit failure.
Is the CCR unstable, or is the field circuit causing dynamic current fluctuation?
5Initial Observations
| CCR status | Operational |
| Selected current | 6.6 A |
| Actual current | 6.2–6.7 A |
| Output voltage | Continuously varying |
| Light intensity | Fluctuating |
| Weather | Humid |
The changing output voltage suggested that the CCR was actively attempting to regulate a changing load condition.
6Initial Engineering Hypotheses
The maintenance team considered:
CCR control-loop instability.
Current feedback sensor fault.
Intermittent field connection.
Insulation leakage fluctuation.
Transformer secondary instability.
7Dynamic Regulation Principle
The CCR attempts to maintain:
If circuit impedance changes continuously:
- Voltage changes continuously.
- Current regulation becomes unstable.
- Light intensity fluctuates.
The key diagnostic question is:
What is changing?
- The CCR?
- The measurement?
- The field circuit?
8Test Equipment
The investigation used:
- CCR monitoring system.
- Digital power analyzer.
- True-RMS multimeter.
- Clamp meter.
- Thermal imaging camera.
- 5 kV insulation resistance tester.
- Data logger.
- Approved AGL circuit test equipment.
- Airport-approved PPE.
9Investigation
Step 1: CCR Internal Verification
The CCR was tested using a controlled test load.
Results:
| Output stability | Stable |
| Current regulation | Stable |
| Voltage regulation | Stable |
The CCR itself was healthy.
Step 2: Output Trend Recording
Data logging showed:
| 00:00 | 6.60 A |
| 00:01 | 6.42 A |
| 00:02 | 6.68 A |
| 00:03 | 6.35 A |
| 00:04 | 6.61 A |
The fluctuation was continuous and irregular.
Step 3: Circuit Impedance Monitoring
Impedance varied between:
22 Ω and 25 Ω
This variation was sufficient to produce observable CCR voltage changes.
Step 4: Sectional Testing
The circuit was divided into sections.
One section showed:
- Intermittent resistance changes.
- Increased instability during cable movement.
- Greater fluctuation under humid conditions.
The fault was localized.
Step 5: Thermal Inspection
Thermal imaging revealed:
- One connector repeatedly heating and cooling.
- Temperature cycling between 48°C and 72°C.
- Resistance changing with temperature.
The connector exhibited thermally unstable contact resistance.
Step 6: Insulation Testing
Insulation resistance showed:
- Significant variation over time.
- Improved values during dry periods.
- Reduced values during humid conditions.
Moisture was influencing circuit behavior.
10Root Cause
The CCR output current fluctuation was caused by an intermittent high-resistance connector combined with humidity-dependent insulation leakage.
The connector resistance changed with:
- Temperature.
- Mechanical contact pressure.
- Moisture conditions.
These variations continuously changed circuit impedance, forcing the CCR to repeatedly adjust output voltage.
The CCR was functioning correctly; the field circuit was dynamically unstable.
11Corrective Action
The maintenance team:
- Isolated the circuit.
- Replaced the defective connector.
- Replaced one moisture-damaged cable section.
- Restored connector sealing.
- Verified contact resistance.
- Performed insulation resistance testing.
- Conducted thermal verification.
- Monitored CCR output stability.
- Restored full operation.
- Updated maintenance records.
12Post-Repair Verification
The current fluctuation was completely eliminated.
13Root-Cause Analysis
Current fluctuation observed
Healthy
Fluctuation confirmed
Variable
Localized instability found
Connector resistance unstable
Humidity-related leakage identified
Intermittent connector resistance and insulation instability
Replace connector and damaged cable
14Why This Case Was Important
A fluctuating current is fundamentally different from:
- Low current.
- High current.
- Open circuit.
- Earth fault.
It indicates a changing electrical condition.
Dynamic faults are often more difficult to diagnose because they may disappear during inspection.
15Engineering Lessons
Current fluctuation usually indicates changing circuit impedance.
Current fluctuation usually indicates changing circuit impedance.
A stable CCR with an unstable field circuit will continuously adjust voltage.
A stable CCR with an unstable field circuit will continuously adjust voltage.
Thermal cycling can reveal intermittent connector faults.
Thermal cycling can reveal intermittent connector faults.
Humidity can influence insulation leakage and current stability.
Humidity can influence insulation leakage and current stability.
Data logging is extremely valuable for intermittent CCR problems.
Data logging is extremely valuable for intermittent CCR problems.
16Engineer's Decision Point
You observe: Selected current: 6.6 A. Actual current fluctuating between 6.2 A and 6.7 A. Output voltage continuously changing. Visible light flicker. What should you investigate first?
17Knowledge Check
18Interview Questions
Quick Reference: CCR Output Current Test
A CCR output current test checks that the current the CCR delivers matches the selected brightness step. Use a calibrated meter on the output, and compare the result with the CCR display and the nominal value for that step. A drifting or unstable reading, as in this case, points to a CCR fault or an unstable load in the circuit.
19Frequently Asked Questions
Quick answers about CCR output current fluctuation, based on this case study.
Q1What is AGL-CS-032?
AGL-CS-032 is an engineering training case study on CCR output current fluctuation that made a runway edge lighting circuit brighten and dim repeatedly. It is an engineering simulation created for training, not a report of an actual airport incident.
Q2What were the symptoms?
The CCR was set to 6.6 A, but output current fluctuated between 6.2 A and 6.7 A with the step unchanged. Output voltage varied continuously, lights flickered and intermittent regulation alarms appeared in humid weather.
Q3Is the CCR unstable when its output voltage keeps changing?
Not necessarily. The continuous voltage adjustment showed the CCR was actively regulating a changing load. The CCR was functioning correctly and the field circuit was dynamically unstable.
Q4What was the root cause?
An intermittent high-resistance connector combined with humidity-dependent insulation leakage. Connector resistance varied with temperature, mechanical contact pressure and moisture, continuously changing circuit impedance.
Q5What should you investigate first?
Monitor circuit impedance and inspect connectors for intermittent resistance. Replacing the CCR, increasing the current setting or replacing all transformers is not the right first step.
Q6Which tools helped capture a fluctuating fault?
The team used a CCR monitoring system, digital power analyzer, data logger, true-RMS multimeter, clamp meter, thermal imaging camera and 5 kV insulation resistance tester.
Q7How was the circuit repaired?
The team isolated the circuit, replaced the defective connector and one moisture-damaged cable section, and restored connector sealing. They verified contact resistance, tested insulation resistance, conducted thermal verification and monitored CCR output stability.
Q8How was the repair verified?
Actual current was a stable 6.60 A, output voltage, light intensity and connector temperature were stable and the CCR alarm cleared. The fluctuation was completely eliminated.
Engineering & Expert Notes
Record the Fluctuation Against Conditions
PatternNote time, temperature and weather for each event. The pattern points to the type of defect.
Thermal Cycling Often Reveals the Weak Joint
TechniqueFaults that appear as the circuit warms or cools suggest a marginal contact. Plan inspection at those times.
Humidity Changes Leakage
MoistureInsulation leakage varies with humidity. Compare readings under different conditions.
Replace Unstable Connections, Not Only the Worst One
RepairIf one is unstable, similar connections nearby may be too. Inspect neighbours of the same age.
20Case Study Conclusion
CCR output current fluctuation is usually caused by dynamic changes in field-circuit impedance, commonly produced by intermittent connector resistance, moisture-related insulation leakage, or unstable electrical connections rather than CCR malfunction.
Systematic CCR verification, impedance monitoring, sectional testing, thermal inspection, insulation assessment, and trend analysis can accurately identify the source of current instability and restore reliable constant-current regulation.
In AGL engineering, a fluctuating CCR output is often the electrical signature of a circuit whose resistance is changing from moment to moment.
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